Effects Of Precipitation Change On Plant Belowground Biomass And Its Underlying Mechanisms

The precipitation pattern has significantly changed over the past decades in terrestrial ecosystem,which will have a profound impact on ecosystem structure and function in the context of global climate change.As a major component of ecosystem productivity,plant belowground biomass plays an important role in global carbon cycling.Previous research on the relationship between biomass and precipitation mainly focuses on the aboveground part of the plants,while belowground biomass is relatively less considered.This may make it difficult to predict the dynamic changes of terrestrial ecosystem vegetation under global change.To accurately assess and predict the changes of belowground biomass in terrestrial ecosystem under the future precipitation pattern,it is urgent to explore the influence of precipitation on belowground biomass and its underlying mechanism by using multiple methodsIn this study,we assessed the sensitivity of plant belowground biomass to precipitation change and its main drivers at the global scale by using both meta-analysis and sampling survey.Furthermore,we explored the distribution of belowground biomass in the subtropical forest,and quantified the effects of climatic conditions,soil factors,and root traits on the spatial distribution pattern of fine roots.The main findings were as follows(1)By using a meta-analysis with altered precipitation experiments,we examined the responses and sensitivity of the belowground biomass to simulated precipitation change.Our results showed that the sensitivity of belowground biomass to both increased and decreased precipitation were positive.In grasslands,the sensitivity of belowground biomass to increased and decreased precipitation were 5.63 and 2.69 times higher than those in forests,respectively.The responses of belowground biomass to precipitation change were influenced by climatic variables and experimental factors Specifically,the sensitivity of belowground biomass to precipitation decreased with the increases in average annual temperature.These results indicated that the short-term responses of grassland belowground biomass to precipitation change were more obvious than those in forests(2)Based on the biomass dataset from long-term site observations,the effects of precipitation change on plant belowground biomass along different precipitation gradients were examined and compared with those on the aboveground biomass.Our results showed that both above-and belowground biomass increased with increasing precipitation,and the sensitivity of belowground biomass to precipitation changes was higher than that of aboveground biomass.The sensitivity of belowground biomass was correlated with the average annual temperature(R2=0.46,P<0.05),while that of aboveground biomass was affected by the annual precipitation(R2=0.70,P<0.05).In different ecosystems,the responses of grassland belowground biomass to precipitation changes were higher than that of forest ecosystems.The sensitivity of grassland belowground biomass to precipitation changes was mainly affected by total biomass rather than biomass allocation(3)Based on field sampling and survey in subtropical forest ecosystems,we explored the spatial distribution of belowground biomass along the precipitation gradient,and mainly focused on the responses of fine root biomass to precipitation change from the viewpoint of regulation of precipitation on root traits.The results showed that precipitation significantly affected the fine root biomass of 0-10 cm and 20-30 cm soil layers.For every 1-mm increase in precipitation,fine root biomass increased by 25.88 g m-2 and 4.07 g m-2 in 0-10 cm and 10-20 cm soils,respectively Among the morphological root traits,the specific root length was negatively correlated with fine root biomass.Fine root biomass was determined by specific root length,annual precipitation,and fine root length as indicated by the correlation analysis Overall,the relative contributions of climate,soil,and root traits to belowground biomass were 52.8%,31.6%and 15.7%,respectively,which had a comprehensive effect on belowground biomass.These results emphasized the important regulation of root morphology on biomass,suggesting that precipitation may affect belowground biomass by changing plant traits at the regional scaleIn conclusion,we revealed how the belowground biomass responded to altered precipitation and its underlying mechanisms.These findings were of pivotal to understand the variation characteristics of productivity along the precipitation gradient,providing a theoretical basis for the ecosystem's responses to precipitation changes and for estimating the impacts of future climate change on the carbon cycle in different ecosystems.