Investigating the Patterns and Controls of Ecosystem Light Use Efficiency with the Data from the Global Farmland Fluxdata Network

Ecosystem light use efficiency (ELUE) is generally defined as the ratio of gross primarily productivity (GPP) to photosynthetically active radiation (PAR), which is an important ecological indictor used in dry matter prediction. Herein, investigating the dynamics of ELUE and its controlling factors is of great significance for simulating ecosystem photosynthetic production. Using 35 site-years eddy covariance fluxes and meteorological data collected at 11 cropland sites globally, we investigated the dynamics of ELUE and its controlling factors in four agroecosystems with paddy rice, soybean, summer maize and winter wheat. A U diurnal pattern of hourly ELUE was found in all the fields, and daily ELUE varied with crop growth. The ELUE for the growing season of summer maize was highest with 0.92 & PLUSMN; 0.06 g C MJ(-1), followed by soybean (0.80 & PLUSMN; 0.16 g C MJ(-1)), paddy rice (0.77 & PLUSMN; 0.24 g C MJ(-1)) and winter wheat (0.72 & PLUSMN; 0.06 g C MJ(-1)). Correlation analysis showed that ELUE positively correlated with air temperature (T-a), normalized difference vegetation index (NDVI), evaporative fraction (EF) and canopy conductance (g(c), except for paddy rice sites), while it negatively correlated with the vapor water deficit (VPD). Besides, ELUE decreased in the days after a precipitation event during the active growing seasons. The path analysis revealed that the controlling variables considered in this study can account for 73.7%, 85.3%, 75.3% and 65.5% of the total ELUE variation in the rice, soybean, maize and winter wheat fields, respectively. NDVI is the most confident estimators for ELUE in the four ecosystems. Water availability plays a secondary role controlling ELUE, and the vegetation productivity is more constrained by water availability than T-a in summer maize, soybean and winter wheat. The results can help us better understand the interactive influences of environmental and biophysical factors on ELUE.

Automated summary

The study investigated the dynamics of ELUE and its controlling factors in different agroecosystems. The results showed significant differences in ELUE among different crops, which were closely related to meteorological factors and water availability, providing important implications for future ecosystem simulations.