International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5, 229-239 http://ecoevopublisher.com/index.php/ijmec 23 5 5.2 The cycle of matter and energy Epiphytic plants play an important role in the material and energy cycles of forest ecosystems. Epiphytes profoundly affect the forest water cycle by intercepting rainfall and conserving water (Hembre et al., 2021). Epiphytes play the role of "accumulators and converters" in the forest canopy during the nutrient cycle. Epiphytes intercept nutrients and fallen tree debris from atmospheric deposition and temporarily store them in the canopy (Victoriano-Romero et al., 2020). The process by which epiphytic plants participate in the carbon cycle. Epiphytes fix CO₂ through photosynthesis and store carbon in the forest canopy in the form of their own biomass. In addition, epiphytes change the path of energy flow. Many epiphytic plants' leaves, flowers and fruits are fed by predators such as insects and birds. This is a food chain independent of the ground vegetation, which transports the energy of the primary producers in the forest canopy to a group of specialized consumers. 5.3 Potential contribution to forest carbon sink function Forests, as global carbon sinks, play a key role in mitigating climate change. Although epiphytes have a relatively small biomass compared to trees, they also make certain contributions to forest carbon storage and the carbon cycle. Epiphytic plants net accumulate carbon through their growth. Although individual epiphytes are light in weight, the total carbon content per unit area of forest land in high-density epiphytic communities cannot be ignored. The presence of epiphytes may enhance the net carbon fixation efficiency of the host tree. The reason lies in that epiphytes improve the canopy microclimate, thereby alleviating the adverse effects of extreme heat and drought on the photosynthesis of the host (Amici et al., 2020). The canopy soil and organic matter pads composed of epiphytes are also part of the carbon stock and may reduce the rate of carbon leakage to the outside. From another perspective, epiphytes promote soil carbon accumulation. When they fall to the ground, they provide high C/N litter rich in lignin and polysaccharides, which is difficult to decompose and can increase the soil organic carbon pool (Furtado and Menini Neto, 2021). Meanwhile, certain epiphytic plants such as lichens can fix exogenous carbon (through photosynthesis by symbiotic algae) and eventually convert it into soil humus, which increases the carbon input to the ecosystem from the source. Furthermore, in the context of global climate change, the feedback effect of epiphytic plants on the carbon cycle deserves attention. 6 Threats and Protection Strategies Faced by Epiphytes 6.1 The impact of deforestation, climate change and air pollution on epiphytes Although epiphytes play a crucial role in ecosystems, they are highly sensitive to environmental changes and human disturbances. Habitat loss, climate change and pollution load caused by human activities all exert multiple pressures on epiphytes. Many epiphytic plants are endemic species of small populations and have poor adaptability to environmental changes. Once the habitat is destroyed or the climate exceeds its tolerance range, it may die out rapidly. For instance, epiphytic orchids and ferns with narrow distribution tend to become extinct first with deforestation (Kromer et al., 2025). The loss of large trees led to the direct extinction of many plant populations that were originally epiphytic to them, and the young trees in the secondary forest failed to carry the same epiphytic species again, indicating that the aftereffects of the destruction of stand structure are serious (Cruz et al., 2022). Climate warming may force epiphytes to migrate to higher altitudes, but it is a problem whether the distribution of suitable host trees can keep up. Many epiphytes may fall into the predicament of "nowhere to go" (Suissa et al., 2021). Air pollution mainly affects the epiphytic layer of moss and lichen, and its decline will cause negative feedback on the water and nutrient cycle of the forest canopy (because moss and lichen are the main force in intercepting water and nutrients) (Phoenix and Khafsha, 2023). In summary, when the forest environment deteriorates, epiphytes are usually regarded as "ecologically sensitive indicators" : their decline often occurs earlier than large-scale changes in trees and is an early warning signal of impaired ecological health (Mitchell et al., 2021)
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