Abstract
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 ± 0.06 g C MJ−1, followed by soybean (0.80 ± 0.16 g C MJ−1), paddy rice (0.77 ± 0.24 g C MJ−1) and winter wheat (0.72 ± 0.06 g C MJ−1). Correlation analysis showed that ELUE positively correlated with air temperature (Ta), normalized difference vegetation index (NDVI), evaporative fraction (EF) and canopy conductance (gc, 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 Ta in summer maize, soybean and winter wheat. The results can help us better understand the interactive influences of environmental and biophysical factors on ELUE.
Highlights
Previous studies suggested that soil moisture, air temperature, vapor pressure deficit and crop management practice have significant influence on ecosystem light use efficiency (ELUE) variability through regulating stomatal aperture and the related photosynthetic reaction [12,13], while some others concluded that vegetation indices (i.e., normalized difference vegetation index (NDVI) or LAI) are the dominant control factors on the process of carbon exchange by affecting the fraction of radiation absorbed by photosynthesis [14,15]
A synergistic relationship was found between gross primary production (GPP) and photosynthetically active radiation (PAR), of which the trends were opposite to ELUE
Non-photochemical quenching (NPQ) of chlorophyll fluorescence is thought to be an indicator of an essential regulation and photoprotection mechanism against high-light stress in photosynthetic organisms [47]
Summary
ELUE is the combined effects of environmental controls, e.g., incoming solar radiation, air temperature, soil and atmosphere dry-wet conditions [7,8], physiological factors (canopy conductance and foliar age) [9], vegetation index [10,11], etc. Previous studies suggested that soil moisture, air temperature, vapor pressure deficit and crop management practice have significant influence on ELUE variability through regulating stomatal aperture and the related photosynthetic reaction [12,13], while some others concluded that vegetation indices (i.e., NDVI or LAI) are the dominant control factors on the process of carbon exchange by affecting the fraction of radiation absorbed by photosynthesis [14,15]
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