Abstract
Climatic variables not only directly affect the interannual variability (IAV) in net ecosystem exchange of CO2 (NEE) but also indirectly drive it by changing the physiological parameters. Identifying these direct and indirect paths can reveal the underlying mechanisms of carbon (C) dynamics. In this study, we applied a path analysis using flux data from 65 sites to quantify the direct and indirect climatic effects on IAV in NEE and to evaluate the potential relationships among the climatic variables and physiological parameters that represent physiology and phenology of ecosystems. We found that the maximum photosynthetic rate was the most important factor for the IAV in gross primary productivity (GPP), which was mainly induced by the variation in vapour pressure deficit. For ecosystem respiration (RE), the most important drivers were GPP and the reference respiratory rate. The biome type regulated the direct and indirect paths, with distinctive differences between forests and non-forests, evergreen needleleaf forests and deciduous broadleaf forests, and between grasslands and croplands. Different paths were also found among wet, moist and dry ecosystems. However, the climatic variables can only partly explain the IAV in physiological parameters, suggesting that the latter may also result from other biotic and disturbance factors. In addition, the climatic variables related to NEE were not necessarily the same as those related to GPP and RE, indicating the emerging difficulty encountered when studying the IAV in NEE. Overall, our results highlight the contribution of certain physiological parameters to the IAV in C fluxes and the importance of biome type and multi-year water conditions, which should receive more attention in future experimental and modelling research.
Highlights
During the past century, increased human activities have caused large changes in the global climate system, such as an increase in mean air temperature, a decrease in diurnal temperature range, a redistribution of precipitation and intensification of extreme climate events (IPCC, 2013)
We found that the maximum photosynthetic rate was the most important factor for the interannual variability (IAV) in gross primary productivity (GPP), which was mainly induced by the variation in vapour pressure deficit
In all the biomes being studied, the maximum photosynthetic rate (Am) was the most important factor for the IAV in C fluxes (the standardised path coefficient (r) as an analogy of the correlation coefficient fell between (0.32 and (0.68 for net ecosystem exchange of CO2 (NEE) and 0.72Á0.85 for GPP), which was mainly induced by the variation in vapour pressure deficit (VPD) (Figs. 1 and 2)
Summary
During the past century, increased human activities have caused large changes in the global climate system, such as an increase in mean air temperature, a decrease in diurnal temperature range, a redistribution of precipitation and intensification of extreme climate events (IPCC, 2013). The difficulty in predicting the IAV in NEE might result partially from the failure of models to represent the temporal evolution of ecophysiological (e.g. physiological and phenological) factors, which outweigh the climatic factors in most eddy-flux sites at the interannual scale (Shao et al, 2015). Empirical and semi-empirical research suggests that the ecophysiological properties of ecosystems should be taken into consideration for better simulation of the IAV in C fluxes (Kuzyakov and Gavrichkova, 2010; Migliavacca et al, 2011; Xia et al, 2015), the results from modelling studies indicate that it is still troublesome to predict the temporal changes in the biotic factors or ecophysiological properties of ecosystems (Richardson et al, 2012).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
