Impacts of diffuse radiation on light use efficiency across terrestrial ecosystems based on Eddy covariance observation in China.

Kun Huang,Peili Shi,Yanfen Wang,Junhui Zhang,Huimin Wang,Liang Zhao,Lei Zhou,Shaoqiang Wang,Junhua Yan,Dafeng Hui

doi:10.1371/journal.pone.0110988

Abstract

Ecosystem light use efficiency (LUE) is a key factor of production models for gross primary production (GPP) predictions. Previous studies revealed that ecosystem LUE could be significantly enhanced by an increase on diffuse radiation. Under large spatial heterogeneity and increasing annual diffuse radiation in China, eddy covariance flux data at 6 sites across different ecosystems from 2003 to 2007 were used to investigate the impacts of diffuse radiation indicated by the cloudiness index (CI) on ecosystem LUE in grassland and forest ecosystems. Our results showed that the ecosystem LUE at the six sites was significantly correlated with the cloudiness variation (0.24≤R2≤0.85), especially at the Changbaishan temperate forest ecosystem (R2 = 0.85). Meanwhile, the CI values appeared more frequently between 0.8 and 1.0 in two subtropical forest ecosystems (Qianyanzhou and Dinghushan) and were much larger than those in temperate ecosystems. Besides, cloudiness thresholds which were favorable for enhancing ecosystem carbon sequestration existed at the three forest sites, respectively. Our research confirmed that the ecosystem LUE at the six sites in China was positively responsive to the diffuse radiation, and the cloudiness index could be used as an environmental regulator for LUE modeling in regional GPP prediction.

Highlights

Terrestrial ecosystems play an increasingly important role in global carbon cycle under climate change [1]
Seasonal variation of cloudiness index and light use efficiency across ecosystems Figure 2 showed the seasonal variations of the cloudiness index and light use efficiency of the six sites from 2003 to 2006
The cloudiness index (CI) values peaked during the mid-growing season (Figure 2a, d, e and f), while the CI values of the subtropical ecosystems failed to show substantial variations with the seasonal changes

Summary

Introduction

Terrestrial ecosystems play an increasingly important role in global carbon cycle under climate change [1]. The fact that GPP represents the critical flux component driving the terrestrial ecosystem carbon cycle implies that subtle fluctuations in GPP have substantial implications for future climate warming scenarios [3,4]. With the quantification terrestrial ecosystem GPP for regions, continents, or the globe, we can gain insight into the feedbacks between the terrestrial biosphere and the atmosphere under global change and climate policy-making facilitation [5,6]. GPP predictions at regional scale to global scale are a major challenge due to the spatial heterogeneity [7,8]. With the great carbon sequestration potential of the terrestrial ecosystem of China in global carbon budget [9], large uncertainties exist in terrestrial ecosystem GPP simulation in China

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Results