The impacts of several global change drivers on tropical root traits and dynamics

Tropical ecosystems are threatened by escalating anthropogenic activities that worsen global change, potentially disrupting the carbon (C) equilibrium in tropical forests and affecting global climate regulation. While considerable research has explored the impact of global change on aboveground tropical vegetation, our comprehension of belowground components, particularly roots that mediate plant-soil interactions, such as nutrient and water uptake, remains limited. We conducted an analysis of existing research on how tropical roots respond to key global change drivers, including warming, drought, flooding, cyclones, nitrogen (N) deposition, elevated (e) CO2, and fires. Drawing from tree species- and community-level outcomes from experimental studies, we compiled 266 root trait observations from 96 studies conducted across 24 tropical countries. From the existing knowledge, we noted in this review that tropical root systems tend to increase in biomass in response to warming and eCO2, but community-level experiments were rare for warming and non-existent for eCO2. Drought increased root:shoot ratio without changing root biomass, indicating a reduction in aboveground biomass. While N deposition may not greatly impact most tropical forests in the short term due to strong phosphorus limitation, mycorrhizal colonization and root phosphatase exudation were predominantly down- and up-regulated, respectively. Cyclones, fires, and flooding resulted in decreased root biomass, which, under elevated CO2 and warming, could lead to greater carbon losses from tropical soils. Cyclones and fires increased root production, potentially in response to plant community shifts and nutrient input, while flooding altered compounds related to plant regulatory metabolism due to low oxygen conditions. We also emphasize the importance of in situ studies, comparing adapted versus non-adapted species to these disturbances and the need for methodological consistency among experiments. Our findings underscore the necessity for further research to enhance our understanding of tropical root responses to global changes. The responses of root traits and dynamics to several global change drivers would affect the functioning of the whole forest and, consequently, carbon cycling and stocks above and belowground.