Molecular Soil Biology 2024, Vol.15, No.4, 172-182 http://bioscipublisher.com/index.php/msb 178 7.3 Root-mediated changes in soil moisture Root structures significantly influence overall soil moisture retention during drought. Trees with extensive and deep root systems can enhance soil moisture retention by accessing and utilizing water from deeper soil layers, which helps in maintaining soil moisture levels during dry periods (Christina et al., 2017). Moreover, the presence of roots can improve soil structure and water holding capacity, as roots create channels that facilitate water infiltration and reduce surface runoff. The interaction between roots and soil microbes also plays a role in improving soil moisture retention, as symbiotic relationships can enhance root growth and soil structure, leading to better water retention (Shoaib et al., 2022). In ecosystems with varying rooting depths, species-specific differences in root architecture can lead to distinct soil moisture dynamics, with deep-rooted species maintaining more stable soil moisture levels compared to shallow-rooted species (Bucci et al., 2009). 8 Influence of Root Structure on Carbon Sequestration 8.1 Relationship between root growth and carbon storage Deep-rooted species play a crucial role in sequestering carbon and mitigating climate change. These species can access deeper soil layers, which allows them to store carbon more effectively and for longer periods. Deep roots enhance bedrock weathering (Figure 3), which regulates the long-term carbon cycle by connecting deep soil/groundwater to the atmosphere and influencing the hydrologic cycle and climate (Fan et al., 2017). Additionally, deep-rooted trees can improve water and nutrient acquisition, indirectly stimulating photosynthetic CO2 capture and promoting belowground carbon sequestration (Bach and Gojon, 2023). The presence of deep roots in various ecosystems underscores their importance in enhancing ecosystem resilience to environmental stress, such as drought, and in contributing to long-term carbon storage (Pierret et al., 2016). Figure 3 Schematic of soil water profiles along a drainage gradient, wetted from above by rain infiltration and from below by groundwater capillary rise, with a dry gap that diminishes downslope. Along this gradient, plant rooting depths vary systematically (see text). SI Appendix, Fig. S3 gives examples of published root images at different drainage positions (Adopted from Fan et al., 2017) 8.2 Carbon allocation in drought-stressed trees Drought significantly affects carbon allocation in trees, particularly in their root systems. During drought conditions, trees often adjust their root biomass and undergo anatomical and physiological changes to tolerate stress (Brunner et al., 2015). These adjustments can lead to a reduction in carbon sequestration, as observed in studies where drought diminished carbon sequestration by up to 67% despite an increase in water-use efficiency (Martínez-Sancho et al., 2022). Drought also decreases the total non-structural carbohydrates (NSC) in roots, which are essential for energy storage and metabolic processes (Li et al., 2018). This reduction in NSC can impact the overall carbon balance of forest ecosystems, highlighting the need for more research on the belowground responses of trees to drought (Brunner et al., 2015). 8.3 Soil organic carbon and root-sourced contributions Tree root systems contribute significantly to building and maintaining soil organic carbon (SOC) levels. Roots are the primary source of carbon input into soils, and their growth and development are crucial for belowground carbon sequestration (Bach and Gojon, 2023). Mycorrhizal fungi associated with tree roots also play a vital role in
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