International Journal of Molecular Ecology and Conservation 2025, Vol.15, No.6 http://ecoevopublisher.com/index.php/ijmec © 2024 EcoEvoPublisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved.
International Journal of Molecular Ecology and Conservation 2025, Vol.15, No.6 http://ecoevopublisher.com/index.php/ijmec © 2024 EcoEvoPublisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved. EcoEvoPublisher is an international Open Access publisher specializing in molecular ecology and conservation research registered at the publishing platform that is operated by Sophia Publishing Group (SPG), founded in British Columbia of Canada. Publisher EcoEvo Publisher Editedby Editorial Team of International Journal of Molecular Ecology and Conservation Email: edit@ijmec.ecoevopublisher.com Website: http://ecoevopublisher.com/index.php/ijmec Address: 11388 Stevenston Hwy, PO Box 96016, Richmond, V7A 5J5, British Columbia Canada International Journal of Molecular Ecology and Conservation (ISSN 1927-663X) is an open access, peer reviewed journal published online by EcoEvoPublisher. The journal is considering all the latest and outstanding research articles, letters and reviews in all aspects of molecular ecology and conservation, containing the contents of the ranges from the applied to the theoretical in molecular ecology and nature conservation, the policy and management with comprehensive and applicable information; the ecological bases for the conservation of ecosystems, species, genetic diversity, the restoration of ecosystems and habitats; as well as the expands the field of ecology and conservation work. All the articles published in International Journal of Molecular Ecology and Conservation are Open Access, and are distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. EcoEvoPublisher uses CrossCheck service to identify academic plagiarism through the world’s leading plagiarism prevention tool, iParadigms, and to protect the original authors’ copyrights.
International Journal of Molecular Ecology and Conservation (online), 2025, Vol. 15, No.6 ISSN 1927-663X https://ecoevopublisher.com/index.php/ijmec © 2024 EcoEvoPublisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved. Latest Content Thermal Stress and Coral Resilience: Mechanisms of Bleaching and Adaptation Wenzhong Huang International Journal of Molecular Ecology and Conservation, 2025, Vol. 15, No. 6, 260-266 Nutrient Cycling and Decomposition Processes in Grassland Ecosystems JiongFu International Journal of Molecular Ecology and Conservation, 2025, Vol. 15, No. 6, 267-276 White Blanket: The Ecological Importance of Snowpack Jing He , Jun Li International Journal of Molecular Ecology and Conservation, 2025, Vol. 15, No. 6, 277-285 Genomic Evolutionary Uniqueness of Pineapple: CAM Photosynthesis, Chromosomal Rearrangement, and Gene Duplication Clusters Zhen Li, Zhonggang Li International Journal of Molecular Ecology and Conservation, 2025, Vol. 15, No. 6, 286-293 Breeding Challenges and Improvement Strategies in Yellow Pitaya: Enhancing Cultivation Efficiency and Disease Resistance Yeping Han, Haimei Wang International Journal of Molecular Ecology and Conservation, 2025, Vol. 15, No. 6, 294-302
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 260-266 http://ecoevopublisher.com/index.php/ijmec 260 Research Insight Open Access Thermal Stress and Coral Resilience: Mechanisms of Bleaching and Adaptation Wenzhong Huang Biomass Research Center, Hainan Institute of Tropical Agricultural Resouces, Sanya, 572025, Hainan, China Corresponding email: wenzhong.huang@@hitar.org International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5 doi: 10.5376/ijmec.2025.15.0026 Received: 09 Sep., 2025 Accepted: 21 Oct., 2025 Published: 07 Nov., 2025 Copyright © 2025 Huang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Huang W.Z., 2025, Thermal stress and coral resilience: mechanisms of bleaching and adaptation, International Journal of Molecular Ecology and Conservation, 15(6): 260-266 (doi: 10.5376/ijmec.2025.15.0026) Abstract This study reviews the mechanism by which heat stress affects corals and explores how reactive oxygen species (ROS) generation, symbiotic rupture, and metabolic imbalance cause physiological damage and bleaching. Meanwhile, different albinism patterns and the regulation of their degrees by environmental and interspecific factors were analyzed. Then, focus on the mechanisms of coral resilience: including physiological recovery (such as heat shock proteins, metabolic regulation), ecological recovery (such as recolonization, community renewal), and the potential mechanisms of recovery failure. The evolutionary and ecological mechanisms of coral adaptation to heat stress were further discussed, including the screening of symbiotic algae, host genetic responses and ecological strategies. This study also combines the background of global change and proposes intervention strategies based on ecological engineering and management policies to enhance the recovery and resilience of coral systems. Studies have shown that the responses of corals to bleaching and heat stress are the result of the coordinated effects of multiple levels and mechanisms. Future conservation strategies should take into account both natural recovery potential and human intervention, and utilize molecular and ecological tools to monitor and guide the adaptation process. This research not only helps to deepen the understanding of the vulnerability of the coral-symbiotic algal system, but also provides an important theoretical basis for understanding the dynamic mechanism of coral recovery and adaptation under heat stress conditions. Keywords Coral; Heat stress; Albinism; Resilience; Symbiotic algae 1 Introduction Coral reef ecosystems are among the most productive and diverse ecosystems in the ocean, providing habitats for approximately a quarter of Marine species and supporting ecological services such as fisheries, tourism, and coastal protection through their complex structures and functions (Hoegh-Guldberg et al., 2017; Keshavmurthy et al., 2019). However, corals are particularly sensitive to environmental stress, especially the rise in sea water temperature. They are highly sensitive to both local (such as pollution, overfishing, and habitat destruction) and global (such as climate change and ocean acidification) stress factors. Their structural stability and biodiversity can be easily damaged by heat stress. It led to a rapid decline in coral coverage and ecosystem health (Putnam et al., 2017). In recent years, the frequency, intensity and duration of Marine heatwaves have all increased significantly, which is closely related to global warming. Abnormal sea surface temperatures caused by heat waves are an important trigger for coral bleaching. Coral bleaching refers to the breakdown of the relationship between corals and their symbiotic algae (such as Symbiodiniaceae), resulting in the expulsion of symbiotic algae or a decrease in their density, thereby losing pigment and basic metabolic support (Eakin et al., 2019). Frequent and extreme thermal events have made coral bleaching no longer an occasional event but a common phenomenon, posing a significant ecological threat to global coral reefs. Resilience refers to the ability of corals to restore their healthy state, species composition and functional structure after heat stress. Understanding the mechanism of coral resilience is crucial for ecological conservation (Mcleod et al., 2020; Bang et al., 2021; Shaver et al., 2022). On the one hand, it helps identify coral populations with high survival potential under future environmental pressures; On the other hand, it provides the basis for restoration and intervention for scientists and managers, such as strategies like ecological restoration, symbiotic algae intervention, and anthropogenic selection (Mcleod et al., 2019).
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 260-266 http://ecoevopublisher.com/index.php/ijmec 261 This study will introduce the mechanism of heat stress and coral resilience, explore the impact mechanism of heat stress on corals, analyze the bleaching patterns and influencing factors, and expound the resilience mechanism of corals. Meanwhile, discuss the evolution and ecological mechanisms of coral adaptation to heat stress; In light of global changes, propose management and intervention strategies. This study aims to provide a theoretical basis for coral protection and point out the direction for future research. 2 The Mechanism of the Impact of Heat Stress on Corals 2.1 Direct effects of seawater temperature rise The increase in seawater temperature is the main cause of coral heat stress. When the temperature exceeds a certain limit, the balance between corals and their symbiotic algae will be disrupted. High temperatures will accelerate the respiration and metabolism of algae, and at the same time affect their photosynthetic capacity. Some mathematical models, such as bioenergy models, indicate that an increase in temperature will accelerate metabolism. However, high temperatures can also damage the photosynthetic organs and metabolic processes of algae, thereby reducing the amount of carbon that algae transfer to corals. Over time, this imbalance can damage the relationship between corals and algae and trigger coral stress (Figure 1) (Pfab et al., 2024). Figure 1 The model describes the effect of temperature on a coral host and its algae symbiont (Adopted from pfab et al., 2024) Image caption: Increased temperature is assumed to accelerate metabolic processes and damage the photosynthetic machinery of the symbiont (Adopted from pfab et al., 2024) 2.2 ROS (reactive oxygen species) generation and cell damage mechanism Reactive oxygen species (ROS) play a key role in the process of heat stress. Heat stress can cause symbiotic algae and hosts to produce excessive ROS, including superoxide anion (O₂⁻), hydrogen peroxide (H₂O₂), etc. (Doering et al., 2023). When these ROS exceed the processing capacity of the clearance system (such as superoxide dismutase and catalase), they can cause oxidative damage to cells, membrane damage and signal imbalance. Especially H₂O₂, the relationship between its dynamic changes and albinism is more complex at high temporal resolution. Some studies have pointed out that its concentration fluctuations are not necessarily the direct cause of albinism (Schlotheuber et al., 2024). 2.3 Symbiotic relationship breakdown and albinism process With the imbalance of ROS generation and metabolism, the coral-symbiotic algal system may enter a stage of breakdown. Heat stress can disrupt the photosynthesis of symbiotic algae, reducing their efficiency in transferring carbon to the host. Meanwhile, ROS signaling may induce the host to expel the symbiotic algae (Brown et al., 2024). To reduce internal environmental pressure, corals will decrease the density of symbiotic algae by shedding, expelling or digesting them, which leads to the forced interruption of symbiotic relationships. As the number of symbiotic algae significantly decreases, the transparency of coral tissue increases, presenting a white appearance, which is known as bleaching. After that, the sharp decline in energy supply will further expose corals to the risk of death in the face of food scarcity, disease attacks or continuous high temperatures.
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 260-266 http://ecoevopublisher.com/index.php/ijmec 262 3 Coral Bleaching Patterns and Influencing Factors Under Heat Stress Conditions 3.1 Types and degrees of albinism Coral bleaching shows significant heterogeneity. Some corals are only slightly bleached, some have completely lost their symbiotic algae, and others die directly. Long-term studies have shown that individuals of the same coral species may exhibit different bleaching and recovery trajectories during repeated heat waves. For instance, some initially sensitive individuals showed adaptability after several heat waves - their bleaching decreased in subsequent heat waves (Brown et al., 2023). Some corals can still sustain their lives temporarily even if they lose most of their symbiotic algae. However, when the degree of albinism develops beyond the critical threshold, the energy gap becomes difficult to make up for and may eventually lead to large-scale deaths. 3.2 Influence of environmental factors Environmental conditions strongly affect how easily corals bleach. Heat-stress tools, such as NOAA’s Degree Heating Weeks (DHW), are often used to estimate bleaching risk. However, the usual DHW value cannot fully explain why different regions do not respond the same way (Whitaker and DeCarlo, 2024). Some studies show that places with large temperature swings or strong water mixing are not always safer. Bleaching can still happen in coral areas where the temperature changes a lot (Brown et al., 2022). Local factors also matter. Water flow, nutrients, and the amount of sediment can change how much light corals absorb, how much energy they need, and how much stress their cells face. For example, slow water flow can make heat stress even worse. In contrast, moderate water movement can help corals lose heat faster and spread out waste products, which may reduce stress. 3.3 Differences in coral species Different coral species show very different levels of heat tolerance. This variation comes from several factors, such as the coral’s own genes, the type of symbiotic algae they host, and the conditions they experienced in the past. For example, a transcriptome study showed that a type of Acropora coral from Ningaloo Island changed its gene activity very quickly when exposed to sudden heat stress at 33°C. Genes related to heat-shock proteins, ion transport, and immunity became adjusted during the stress period. The heat tolerance of the symbiotic algae (for example, different groups within Symbiodiniaceae) also affects how fast and how strongly bleaching happens. Even the same coral species can show different bleaching thresholds in different regions, since long-term exposure to different environments can shape their ability to handle heat. 4 The resilience Mechanism of Corals 4.1 Physiological recovery pathways The restoration of coral functions and symbiotic relationships requires a series of physiological regulations. First, heat shock proteins (HSPs) are expressed, which help fold damage proteins and buffer heat stress damage. Secondly, corals may reduce energy consumption and accelerate recovery by regulating their metabolic rate. Long-term studies (Kaneohe Bay, Hawaii) have shown that some corals significantly improve their heat tolerance through "acclimatization" after heatwaves (Brown et al., 2023). 4.2 Ecological restoration mechanism In addition to individual physiological recovery, ecological restoration is also of vital importance. This includes larval settlement, community structure reconstruction, etc. Young corals (larvae) have unique adaptive strategies to heat stress: at high temperatures, they reduce basal metabolism and increase nitrogen absorption to maintain a stable relationship with symbiotic algae, thereby avoiding bleaching (Huffmyer et al., 2024). In addition, supplementary populations can be enhanced through ecological engineering-based methods (such as designing basement structures that are more conducive to the settlement of young corals). 4.3 Mechanism of failed recovery Recovery failure often occurs under conditions where the frequency of heat waves intensifies and the recovery time is insufficient. Long-term monitoring shows that although some coral species survive after heatwaves, their
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 260-266 http://ecoevopublisher.com/index.php/ijmec 263 growth rate, regenerative capacity or symbiotic density is difficult to return to the original level (Brown et al., 2023). In addition, the continuous deterioration of the environment (such as deteriorating water quality and nutritional imbalance) will also reduce the success rate of recovery. Habitat complexity and community structure also affect the settlement and growth of coral larvae, thereby determining the long-term recovery potential of the entire population. 5 The Evolutionary and Ecological Mechanisms of Coral Adaptation to Heat Stress 5.1 Adaptation and screening of symbiotic algae Symbiotic algae (Symbiodiniaceae) are an important component of coral heat tolerance. Different algae (such as Clade D, Clade C) show significant differences in heat tolerance. Corals can improve their heat tolerance by combining with more heat-tolerant symbiotic algae (such as certain symbiotic algal branches like Durusdinium trenchii and Cladocopium C15) (Cunning and Baker, 2020; Al-hammady et al., 2022). Long-term heat stress may lead to the screening of heat-tolerant symbiotic algae in coral populations (adaptive bleaching hypothesis). Furthermore, under the background of heat stress, the structure of symbiotic algal communities may be reassembled to enhance the heat tolerance of the overall host-algal system. Heat stress can disrupt the nutrient exchange between corals and algae, leading to coral bleaching (Figure 2) (Radecker et al., 2021; Marangon et al., 2025). Important heat-tolerant genes are involved in functions such as cellular stress response, membrane stability and metabolic reprogramming, and their expression characteristics can directly affect the tolerance threshold of corals to heat waves. Figure 2 Proportion of dividing algal symbiont cells on day 10 of heat stress (Adopted from Rädecker et al., 2021) Image caption: NanoSIMS images for 12C14N− were used to quantify the abundance of (A) regular and (B) dividing algal symbiont cells in the coral tissue sections (Adopted from Rädecker et al., 2021) 5.2 Adaptation mechanisms of coral hosts There are mainly two ways for corals to respond to heat stress: genetic alteration and plasticity. Selective breeding can help corals better withstand heat waves. Studies have shown that this method is highly effective (Moghaddam et al., 2021). Heat resistance is partly hereditary. It is estimated that genetic factors account for approximately 20% to 30% of this ability. Chemical markers on DNA are also very important. This is particularly important for young coral larvae. These markers will affect their future growth and health (Bisanti et al., 2025). Corals living in areas with drastic or frequent temperature changes usually have stronger adaptability. They can regulate metabolism and immune responses more precisely. This helps them tolerate higher temperatures. 5.3 Ecological adaptation strategies Corals use a variety of strategies to survive in the environment. They can adjust the breeding time. They may instead coexist with different types of symbiotic algae or migrate to cooler and more shady microhabitats. Some coral reefs experience significant daily temperature variations. These places can serve as "adaptive hotspots". Corals in these areas are usually better able to withstand heat waves (Banaszak et al., 2023).
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 260-266 http://ecoevopublisher.com/index.php/ijmec 264 Coral hosts may establish stable relationships with new symbiotic algae by adjusting immune responses and nutrient exchange mechanisms. This "symbiotic level" adaptation model expands the range of coral adaptation to environmental changes and also provides potential advantages for their long-term survival. There are also coral-related bacteria that change in response to high temperatures, and certain microbial communities can enhance the host's recovery ability and recovery speed. 6 Coral Restoration and Management Strategies in the Context of Global Change 6.1 Potential and limitations of natural recovery Although some coral species have shown astonishing recovery potential (Brown et al., 2023). However, frequent and intense heat waves make natural recovery even more difficult. In addition, the time required for recovery (re-colonization and growth) is often longer than the heatwave interval, compressing the recovery window. For instance, by establishing Marine protected areas, reducing overfishing, controlling land-based pollution and enhancing water cleanliness, the quality of coral habitats can be improved and the hindrance of non-climatic pressures on their recovery and growth can be alleviated. At the same time, maintaining a rich community of herbivorous fish helps control the excessive expansion of algae and creates more favorable conditions for the settlement of coral larvae. 6.2 Intervention strategies based on ecological engineering Ecological engineering offers several ways to support coral resilience. Common methods include assisted breeding, symbiotic algae transplantation, and improving artificial substrates. Experiments show that selective breeding can raise the heat tolerance of individual corals. Helping young corals settle on better substrates, especially those with small surface structures, also makes recolonization easier. Artificial reefs, larval release, and simple planting techniques provide practical options for restoring damaged reef areas. But these actions often need careful control during the process, and their long-term influence on ecosystem stability must be checked before large-scale use. 6.3 Environmental management and policy measures At the policy level, management plans need to make good use of monitoring and early-warning systems, such as NOAA’s coral heat-stress observations. Protecting and restoring habitats with strong daily temperature changes is also important, since these places often serve as natural shelters during heat waves. Mitigating climate change by lowering greenhouse-gas emissions remains the most basic step. By using sea-surface temperature data, heat-wave prediction models, and remote-sensing tools, managers can estimate heat-stress risks in advance. This allows stricter measures during high-risk periods, for example temporary limits on diving or fishing. In addition, stronger community involvement and better coordination between management policies can help raise the efficiency and long-term success of conservation work. 7 Concluding Remarks Heat stress is now widely seen as the main factor driving coral bleaching. Current studies show that when seawater keeps warming, the balance between corals and their symbiotic algae is quickly disturbed. This leads to a chain of reactions, such as the build-up of reactive oxygen species, cell damage, and the loss of symbiotic algae. These changes form the basic process that triggers bleaching events. As Marine heatwaves become more frequent and last longer, bleaching is no longer an occasional event but a larger system-level threat to coral reefs. Understanding how heat stress works helps explain why corals are so sensitive to bleaching, and it also offers scientific support for later recovery and management work. The resilience of corals depends on a variety of factors, including physiological regulation, the reconstruction of symbiotic relationships, and changes in ecological processes. Physiologically, corals respond to heat damage by increasing antioxidants, adjusting energy utilization and repairing cells. After bleaching, reshaping the symbiotic system helps corals rebuild their energy supply and may enhance their tolerance to future heatwaves. At the ecological level, support from communities, the restoration of interspecies interactions, and the improvement of local habitats all contribute to the recovery of corals. However, if environmental stress is too high or heat waves occur too frequently, these mechanisms may not be sufficient to cope. Some species or communities may
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 260-266 http://ecoevopublisher.com/index.php/ijmec 265 experience long-term decline and even disappear in certain areas. Therefore, it is crucial to understand the reasons why coral restoration sometimes fails. As heat stress intensifies, the adaptive evolution of corals is crucial for their long-term survival. Studies have shown that the differences in heat tolerance among various algal strains, the genetic characteristics of coral hosts, epigenetic regulation, and changes in ecological strategies all affect the survival potential of corals. These adaptation processes usually take time. Despite this, signs of natural selection, changes in population genetics, and cases of "rapid adaptation" have already been observed in some coral groups. This indicates that corals still have some room for evolution. Even so, it remains unclear whether this evolutionary potential is sufficient to cope with future climate warming. Under global change, the future of coral reefs will rely on both natural recovery and human intervention. Ecological engineering methods - including coral nurseries, cultivation of heat-tolerant strains, and local cooling or shading - can help protect areas under high risk. At the same time, reducing local stressors, improving Marine protected-area planning, and setting more forward-looking management policies form the basic support needed to raise overall resilience. In the long term, coral reefs may only keep their ecological roles and biodiversity through combined global emission reduction and strong regional ecological management. Acknowledgments The author sincerely appreciates the valuable opinions and suggestions provided by the two anonymous reviewers, whose meticulous review helped us improve the quality of this article. Conflict of Interest Disclosure The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Al-Hammady M.A., Silva T.F., Hussein H.N., Saxena G., Modolo L.V., Belasy M.B., and Farag M.A., 2022, How do algae endosymbionts mediate for their coral host fitness under heat stress? A comprehensive mechanistic overview, Algal Research, 67: 102850. https://doi.org/10.1016/j.algal.2022.102850 Bang A., Kuo C., Wen C., Cherh K., Ho M., Cheng N., Chen Y., and Chen C., 2021, Quantifying coral reef resilience to climate change and human development: An evaluation of multiple empirical frameworks, Frontiers in Marine Science, 7: 610306. https://doi.org/10.3389/fmars.2020.610306 Banaszak A., Speelman P., Parger M., and Schoepf V., 2023, Divergent recovery trajectories of intertidal and subtidal coral communities highlight habitat-specific recovery dynamics following bleaching in an extreme macrotidal reef environment, PeerJ, 11. https://doi.org/10.7717/peerj.15987 Bisanti L., La Corte C., Dara M., Bertini F., Rizzuto G., Valenti R., Naselli F., Parrinello D., Parisi M., Tomasello A., Caradonna F., Chemello R., and Cammarata M., 2025, Stress memory and epigenome variations: Insights into the thermal tolerance potential of Cladocora caespitosa, Frontiers in Marine Science, 12: 1579913. https://doi.org/10.3389/fmars.2025.1579913 Brown K., Eyal G., Dove S., and Barott K., 2022, Fine-scale heterogeneity reveals disproportionate thermal stress and coral mortality in thermally variable reef habitats during a marine heatwave, Coral Reefs, 42: 131-142. https://doi.org/10.1007/s00338-022-02328-6 Brown K.T., Lenz E.A., Glass B.H., Kruse E., McClintock R., Drury C., Nelson C.E., Putnam H.M., Barott K.L., and 2023, Divergent bleaching and recovery trajectories in reef-building corals following a decade of successive marine heatwaves, Proceedings of the National Academy of Sciences, 120(52): e2312104120. https://doi.org/10.1073/pnas.2312104120 Cunning R., and Baker A., 2020, Thermotolerant coral symbionts modulate heat stress‐responsive genes in their hosts, Molecular Ecology, 29(15): 2940-2950. https://doi.org/10.1111/mec.15526 Doering T., Maire J., Chan W.Y., Perez-Gonzalez A., Meyers L., Sakamoto R., Buthgamuwa I., Blackall L.L., and van Oppen M.J.H., 2023, Comparing the role of ROS and RNS in the thermal stress response of two cnidarian models, Antioxidants, 12(5): 1057. https://doi.org/10.3390/antiox12051057 Eakin C., Sweatman H., and Brainard R., 2019, The 2014-2017 global-scale coral bleaching event: Insights and impacts, Coral Reefs, 38: 539-545. https://doi.org/10.1007/s00338-019-01844-2 Hoegh‐Guldberg O., Poloczanska E., Skirving W., and Dove S., 2017, Coral reef ecosystems under climate change and ocean acidification, Frontiers in Marine Science, 4: 252954. https://doi.org/10.3389/fmars.2017.00158
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International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 267-276 http://ecoevopublisher.com/index.php/ijmec 267 Research Insight Open Access Nutrient Cycling and Decomposition Processes in Grassland Ecosystems JiongFu Hainan Provincial Key Laboratory for Crop Molecular Breeding, Sanya, 572025, Hainan, China Corresponding email: jiong.fu@hitar.org International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5 doi: 10.5376/ijmec.2025.15.0027 Received: 12 Sep., 2025 Accepted: 24 Oct., 2025 Published: 11 Nov., 2025 Copyright © 2025 Fu, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Fu J., 2025, Nutrient cycling and decomposition processes in grassland ecosystems, International Journal of Molecular Ecology and Conservation, 15(6): 267-276 (doi: 10.5376/ijmec.2025.15.0027) Abstract This study analyzed the cycling mechanisms of major nutrients in grasslands, the decomposition processes of litter and soil organic matter, the ecological functions of microorganisms and soil animals, as well as the regulatory effects of climate change and human interference on nutrient cycling. Research has found that grassland ecosystems, with their unique vegetation structure, climatic conditions and soil environment, play a significant role in the global biogeochemical cycle. As one of the largest types of terrestrial ecosystems in terms of area, grasslands undertake key functions such as carbon storage, soil conservation, energy flow and food supply, while the nutrient cycle and decomposition process constitute the core mechanism for their stable operation. In the grassland, plants, microorganisms and soil animals achieve the redistribution of key nutrients such as nitrogen, phosphorus and carbon through multi-scale and multi-pathway interactions. Meanwhile, the decomposition of litter, rhizosphere processes and the physical and chemical environment of the soil jointly regulate the speed and direction of nutrient release, thereby maintaining grassland productivity and system resilience. This research is of great significance for understanding the sustainable state of grassland ecosystems, predicting future functional changes and formulating management strategies, providing a theoretical basis for grassland protection and ecological management. Keywords Grassland ecosystem; Nutritional cycle; Decomposition of fallen leaves; Microbial processes; Soil animals 1 Introduction Grassland ecosystems are one of the core components of global terrestrial ecosystems, distributed across vast areas such as the Eurasian steppe, the American savanna, and the African savanna. This type of ecosystem usually features moderate precipitation, high evaporation, open soil structure, and strong seasonality in plant growth, making its nutrient cycling mode more open and sensitive than that of forests and wetlands. The primary production of grasslands mainly relies on perennial grasses and legumes. Its productivity level is not only closely related to climatic factors, but also highly dependent on the cycling efficiency of nutrient elements among plants - litter - soil. In the grassland ecosystem, nutrient cycling mainly includes the carbon cycle, nitrogen cycle, phosphorus cycle and the migration and transformation of trace elements (Bai and Cotrufo, 2022). The redistribution process of these elements is jointly driven by plant absorption, litter return, microbial decomposition, soil-animal disturbance and gas exchange, etc. Among them, the decomposition of litter and the mineralization of soil organic matter are regarded as the key links of grassland nutrient regeneration, and are an important basis for maintaining grassland soil fertility and promoting plant renewal (Liu et al., 2023). Compared with forests, grasslands rely more on the circulation pathways of underground parts (root biomass, root secretions, rhizosphere microorganisms). This "underground dominant" circulation model enables grasslands to have a certain degree of resilience when dealing with disturbances such as drought and grazing. In recent years, global changes have had a profound impact on the nutrient cycling and decomposition process of grasslands. The increase in temperature alters the metabolic rate and enzyme activity of microorganisms. The sharp fluctuations in precipitation patterns lead to periodic stress of soil moisture. Nitrogen deposition and anthropogenic grazing have altered the structure of plant communities and the nutrient status of soil. Especially in the context of the increasing frequency of drought, the decomposition process of the grassland system may show a significant slowdown, thereby causing a series of changes such as the accumulation of litter and the weakening of
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 267-276 http://ecoevopublisher.com/index.php/ijmec 268 soil organic matter input (Yang et al., 2019). Furthermore, the role of grassland ecosystems in carbon storage and greenhouse gas emissions has also been intensified by global change, making the study of their nutrient cycles have more prominent Earth system significance. This study will conduct a comprehensive discussion from four aspects: the cycling pathways of nutrient elements, the decomposition mechanisms of litter and soil organic matter, the functions of microorganisms and soil animals, and the impact of global change, with the aim of revealing the functional maintenance mechanisms of grassland ecosystems in dynamic environments. A systematic review of the grassland nutrient cycle model, decompression functions, and multi-scale regulatory mechanisms from the perspective of ecological processes not only helps to deepen the understanding of the operation mode of grassland ecosystems but also provides scientific references for grassland restoration, degradation control, and sustainable utilization. 2 Basic Characteristics of Grassland Ecosystems 2.1 Climatic conditions and vegetation types Grasslands are widely distributed, ranging from temperate grasslands, tropical savannas to alpine meadows. There are significant differences in climatic conditions, but the general characteristics are: the annual precipitation is at a medium level and the seasonal distribution is obvious. The evapotranspiration is often similar to or slightly higher than that of precipitation, resulting in water becoming an important limiting factor determining productivity (Zheng et al., 2023). The seasonal combination of temperature and precipitation determines the length of the growing season and the production intensity of the grassland. In temperate grasslands, summer is the main growing season, while in plateau and high-latitude grasslands, the growing period is short and the growth intensity is limited by low temperatures. The vegetation types are mainly grasses of the Poaceae family, mostly perennial herbs, accompanied by legumes, compositae, and a small number of shrubs or semi-shrubs. There are differences in species composition, root distribution and biomass allocation among different types of grasslands: the aboveground biomass of moist grasslands is higher, while the root system is shallower. The underground root system in arid grasslands takes up a larger proportion, with deep and resilient roots to enhance water acquisition capacity. The functional differences of forage communities (such as nitrogen-fixing plants, drought-tolerant species, and fast-decomposing species) directly affect the litter quality and nutrient cycling patterns (Zheng et al., 2023). 2.2 Soil characteristics and moisture conditions Grassland soil is usually formed on sedimentary or aeolian materials, featuring good mineral content and high air permeability. However, the distribution and stability of soil organic matter are significantly influenced by climate, vegetation and management intensity. Typical grassland soil is rich in humus and root residues in the surface layer, and there is a relatively high aggregate structure beneath the surface layer, which plays an important role in water retention and organic carbon protection. Moisture status is the core constraint of grassland ecological function: the seasonal variation of soil moisture controls microbial activity, enzymatic reactions and root metabolism. Arid grasslands often exhibit a distinct alternation of dry and wet conditions: after a rainfall event, the soil responds rapidly, and the activities of microorganisms and root systems briefly increase, followed by a re-entry into a state of drought suppression. Soil texture (such as sandy soil or loam) and topography (aspect, slope) can affect infiltration, runoff and evapotranspiration, thereby determining local water availability and nutrient cycling efficiency (Zheng et al., 2023). 2.3 Main functional groups Herbaceous plants: As primary producers, they not only fix carbon through photosynthesis but also input carbon and nutrients into the soil through root secretions, root turnover, and fallen ground debris. Different functional groups (grasses, legumes, etc.) have different nutrient configurations and litter masses, thereby affecting the subsequent decomposition rate and nutrient release.
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 267-276 http://ecoevopublisher.com/index.php/ijmec 269 Soil animals: including earthworms, arthropods (such as jump worms, beetle larvae), nematodes and micro-arthropods (such as mites). They change substrate accessibility and microenvironment through fragmentation of litter, soil stirring, excrement release and food web interaction, promoting microbial degradation and nutrient recycling (Zheng et al., 2023). Microbial communities: Bacteria, fungi, actinomycetes and archaea form the biological basis for decomposition and mineralization. Fungi play a significant role in the decomposition of complex aromatic and lignin substances, while bacteria mainly deal with easily decomposable carbon sources. The structure and function of microbial communities are determined by soil moisture, temperature, pH and substrate supply, and are highly sensitive to disturbances such as dry-wet cycles and nitrogen deposition. Rhizosphere microorganisms and mycorrhizal fungi: Rhizosphere microorganisms enhance plants' adaptability to environmental stress by promoting nutrient absorption, altering root physiology, and defending against pathogens. Mycorrhizal fungi play a particularly crucial role in phosphorus absorption and the mitigation of drought stress. These functional groups form a complex interdependent network through the exchange of matter and energy, jointly supporting the productivity and stability of the grassland. 2.4 Ecosystem structure and energy flow characteristics The ecological structure of the grassland shows the characteristics of "strong underground and dynamic above-ground" : although the above-ground biomass fluctuates significantly within the seasons, the underground root system and soil organic matter constitute a long-term stable energy and material reservoir. Energy flow begins with photosynthetic capture, is transferred by herbivores to higher trophic levels, and is largely returned to the soil system through litter and manure input. Unlike forests, there is a high aboveground ratio variation in the energy distribution of grasslands: in drought years, more energy is stored in the form of root systems for use in adverse times. Energy flow is characterized by significant seasonality and impulsivity: the growing season is the peak of energy input, and rainfall pulses can activate photosynthesis and microbial mineralization in a short period of time, generating a strong "short-term pulse-long-term balance" feature. Disturbances (such as grazing or burning) play a dual role in energy flow: they rapidly release energy by consuming aboveground biomass and reshape the direction of matter flow, while also causing the system to experience phased high productivity or degradation - the long-term effects depend on the frequency and intensity of the disturbances. 3 The Nutrient Element Cycling Mechanism of the Grassland Ecosystem 3.1 Carbon cycle: dual control of vegetation-soil systems The carbon cycle of the grassland ecosystem is composed of processes such as plant photosynthesis, litter return, soil organic matter accumulation and mineralization, and carbon gas exchange (Bicharanloo et al., 2022). The carbon storage of grasslands is mainly concentrated in the underground part, and the proportion of root biomass and soil organic carbon in the total carbon pool can exceed 70%. This underground dominant carbon allocation model enables grasslands to have a certain recovery capacity under disturbances such as drought, fire and grazing. On the one hand, plants fix atmospheric CO₂ as organic matter through photosynthesis and input it into the soil in the form of root secretions, root renewal and ground litter. On the other hand, the decomposition of these organic substances by microorganisms can release CO₂ and dissolved organic carbon, thereby driving soil respiration. The annual net ecosystem carbon exchange capacity of grasslands is usually significantly affected by precipitation changes. Carbon absorption increases in humid years, while in dry years, the phenomenon of "carbon sourization" may occur. In addition, fire, changes in grazing intensity and soil erosion can alter the vegetation structure and the stability of the soil carbon pool, thereby affecting the long-term carbon balance. 3.2 Nitrogen cycle: the dominant role of microbial processes Nitrogen is a key element that limits the primary productivity of grasslands. The nitrogen cycle in grasslands mainly includes processes such as nitrogen fixation, mineralization, nitrification, denitrification, nitrogen
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 267-276 http://ecoevopublisher.com/index.php/ijmec 270 deposition and nitrogen leaching. Among them, biological nitrogen fixation and soil nitrogen mineralization are the most important ways to provide inorganic nitrogen for plants. Common leguminous plants in grasslands form a symbiotic system with nitrogen-fixing microorganisms, which can significantly increase soil nitrogen input. With the increase of global nitrogen deposition, some grassland areas have begun to witness a transformation of plant communities from leguminous plants to highly productive graminogenic plants, leading to a reorganization of community structure and nutrient requirements. Furthermore, changes in soil temperature and humidity strongly affect the rates of mineralization and nitrification. In semi-arid grasslands with frequent alternations of dry and wet conditions, short-term moist pulses can rapidly stimulate nitrogen mineralization, forming the "nitrogen burst" phenomenon (Bicharanloo et al., 2022; Bilotto et al., 2022). There is a strong coupling relationship between the nitrogen cycle and the carbon cycle: the alleviation of nitrogen limitation can enhance the efficiency of photosynthesis, accelerate carbon input, and thereby affect the kinetics of soil organic matter formation and decomposition. 3.3 Phosphorus cycling: a restrictive process dominated by soil properties Unlike carbon and nitrogen, phosphorus in grassland ecosystems mainly comes from the weathering of parent material, with less external input. Therefore, it is a highly limiting nutrient in many grasslands. Phosphorus in soil mostly exists in inorganic adsorbed form and organic combined form, and it needs to be converted into usable forms through chemical weathering, microbial decomposition or enzymatic action in the rhizosphere. Disturbances such as drought, wind erosion and fire can alter the soil particle structure and mineral composition, thereby affecting the availability of phosphorus. For instance, frequent burning may lead to enhanced organic phosphorus mineralization in the soil, while long-term grazing may alter the spatial distribution of phosphorus through trampling and manure input. With the change of soil pH, the degree of combination of phosphorus with iron and aluminum oxides or calcium varies, thereby changing its availability. This is also one of the important reasons for the productivity differences among different types of grasslands. 3.4 Multi-scale coupling mechanism of element cycling Grassland nutrient cycling is not an isolated process of a single element, but a multi-element coupling network driven by the interaction among plants, microorganisms and soil. Recent studies have shown that the carbon, nitrogen and phosphorus cycles are closely related, and any change in the input or conversion rate of any one element may trigger a chain reaction. For instance, the increase in nitrogen deposition can alter the utilization efficiency of carbon substrates by microorganisms, thereby affecting the carbon stability of the soil. An increase in carbon input may raise the demand for phosphorus by microorganisms, leading to an intensification of phosphorus limitation. These interactive influences make the grassland nutrient cycle highly dynamic and complex (Figure 1)(Bilotto et al., 2022). Figure 1 Modelled Phosphorus (P), carbon (C) and nitrogen (N) processes and cycling depicted by nutrient transfer dynamics in hill-country pastoral landscapes to a 300 mm depth (Adopted from Bilotto et al., 2022) Image caption: TSP total soil phosphorus, SOC soil organic carbon, TSN total soil nitrogen (Adopted from Bilotto et al., 2022)
International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 267-276 http://ecoevopublisher.com/index.php/ijmec 271 4 Driving Factors of Grassland Decomposition Process 4.1 Quantity and quality of fallen debris Litter, as the main substrate in the decomposition process, its quantity and quality directly affect the rate of nutrient release. The larger the quantity, the stronger the micro-environmental protection received during the initial decomposition, and the better the water retention capacity. When the quantity decreases, the exposure of fallen leaves is high, and the increase in light and wind erosion makes the early decomposition slower. In terms of the quality of litter, the chemical composition of herbaceous plants varies significantly. Gramineous plants: The litter usually has a high fiber content, a large C/N ratio, and a relatively slow decomposition rate. Leguminous plants: They have a high nitrogen content and a low lignin content, and their decomposition rate is relatively fast. Semi-shrub plants: They have a high degree of lignification, a large residual proportion, and significant limitations in later decomposition. The composition changes of grassland plant communities will thus lead to the overall migration of litter mass. Grazing, burning and fertilization often indirectly affect the litter cycling pattern by changing species dominance. 4.2 Soil Microbial community: the core of decomposition and nutrient transformation Microorganisms are the core drivers of grassland decomposition and nutrient cycling. Fungi, bacteria and actinomycetes respectively undertake different decomposition functions. Fungi are good at decomposing refractory substances such as lignin and are the main force in the later stage of decomposition. Bacteria prefer easily decomposable substrates, such as cellulose and soluble organic matter. Actinomycetes have a strong metabolic capacity in dry and high-temperature environments. However, the activity of grassland microorganisms is significantly restricted by moisture, and the alternating dry and wet conditions lead to frequent fluctuations in their activity. After rainfall, microorganisms rapidly resume growth, triggering "pulse-like" carbon-nitrogen mineralization, a phenomenon that is widespread in temperate and semi-arid grasslands. Human activities that change the way land is used can also cause a reorganization of the microbial community structure. For example, long-term application of nitrogen fertilizer may lead to an increase in the proportion of bacteria and a relative decrease in fungi, thereby affecting the carbon turnover rate. 4.3 The participation of soil animals Soil animals change the physical structure of litter through activities such as gnawing, crushing, digging holes and excreting, increasing the contact area with microorganisms and thus accelerating decomposition. Its main functions are reflected in: large soil animals (such as earthworms) promoting the formation of aggregates and enhancing soil aeration and water infiltration. Medium-sized animals (jumping insects, mites), break up litter and regulate the distribution of microorganisms on the surface of the litter. Micro-animals (nematodes, protozoa) prey on microorganisms to form "micro-food webs", accelerating the recycling of nitrogen and carbon. The relative composition of soil animals varies significantly among different types of grasslands. The animal diversity in arid grasslands is low, resulting in the decomposition process being more dependent on microbial drive. The functions of moist grassland animals are relatively complete, and the decomposition pathways are more diverse (Dipman and Meyer, 2019). 4.4 Climatic factors: The limiting effects of temperature and precipitation Temperature and moisture are the most important environmental factors for the decomposition of grasslands. Temperature affects metabolic rate, while moisture determines microbial activity and substrate accessibility. In arid grasslands, rainfall events often have sudden "activation effects", which can increase soil respiration and nitrogen mineralization by 2 to 5 times in the short term. Long-term climate change also has a profound impact on the decomposition process: warming up and increasing the rate of surface decomposition, but it may cause instability in the deep soil carbon pool. Intensified drought reduces microbial activity and hinders the degradation of litter. The temporal distribution of precipitation changes, affecting the frequency of the dry-wet cycle and thereby altering the intensity of pulse-type decomposition (Hou et al., 2022).
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