Ecosystem light use efficiency (LUE) is a critical parameter in estimating CO₂ uptake by vegetation from climatological and satellite data. However, there are no studies on light use efficiency and its controlling factors at the ecosystem scale. 

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) used eddy covariance (EC) to explore spatiotemporal variations and controls of LUE in four contrasting forest ecosystems (savanna, tropical rainforest, subtropical evergreen forest, and subalpine coniferous forest) in Yunnan.　 

The researchers used data of 27 site-years to measure the light use efficiency (i.e. ratio of gross primary productivity to total incident photosynthetically active radiation). They found that light use efficiency showed considerable spatiotemporal variability. 

Evergreen broad-leaved forest ecosystem showed higher LUE than subalpine coniferous/savanna ecosystems. The savanna ecosystem had the lowest LUE. Ecosystems with similar/same forest type showed nearly the same LUE despite considerable spatiotemporal variability in LUE. 

They further found that the leaf area index played a key positive role in forest photosynthesis. The vapor pressure deficit and leaf area index largely determined the variability in LUE. 

Moreover, warming might decrease LUE in the savanna ecosystem and may increase LUE in the other three ecosystems. 

"This study improves our understanding of the influence of biophysical factors on LUE and demonstrates how LUE changes with variations in temperature, soil moisture and leaf area index, thereby improving estimations of large‐scale carbon exchange/cycling", said Prof. ZHNAG Yiping, principal investigator of the study. 

The study entitled "Patterns and controls of light use efficiency in four contrasting forest ecosystems in Yunnan, Southwest China" has been published online in Journal of Geophysical Research: Biogeosciences.