Interannual variation of the Bowen ratio in a subtropical coniferous plantation in southeast China, 2003-2012.

Yakun Tang,Xiaomin Sun,Huimin Wang,Xuefa Wen,Gil Bohrer

doi:10.1371/journal.pone.0088267

Abstract

The interannual variation of the Bowen ratio, through its effect on the warming extent of available energy to the ecosystem land surface air, heavily influences the ecosystem microclimate and affects the hydrological cycle at both regional and global scales. Although the precipitation amount in southeast China is not expected to change greatly as a result of climate change, the precipitation frequency may be altered in the future. We explored the interannual variation of the Bowen ratio and its affecting mechanisms based on eddy covariance measurements in a subtropical plantation in southeast China during 2003–2012. The results indicated that the annual mean Bowen ratio was 0.35±0.06, with a range of 0.29–0.45. The Bowen ratio during the dry season (July-October) positively correlated with the annual Bowen ratio (R2 = 0.85, p<0.001). The effective precipitation frequency during the dry season, through its positive effect on shallow soil water content, indirectly and negatively affected the annual Bowen ratio. Between 2003 and 2012, the annual Bowen ratio exhibited a marginally significant decreasing trend (p = 0.061), meanwhile the effective precipitation frequency and shallow soil water content during the dry season increased significantly (p<0.001). The annual Bowen ratio may decrease further if the effective precipitation frequency and shallow soil water content during the dry season follow similar trends in the future. The warming effect of available energy to the surface air of our studied plantation may decline with the decreasing annual Bowen ratio.

Highlights

The consumption of available energy as sensible heat flux warms the land surface air [1]
The air temperature exhibited a single peak, with the maximum and minimum values occurring in summer (June-August) and winter (DecemberFebruary), respectively
The results indicated that the effective precipitation frequency during the dry season did not directly affect the annual Bowen ratio (R2 = 0.29, p = 0.111) (Fig. 7B)

Summary

Introduction

The consumption of available energy as sensible heat flux warms the land surface air [1]. The Bowen ratio, which is the ratio of the sensible heat flux to latent heat flux, through its effect on the warming extent of available energy to the ecosystem land surface air, heavily influences the ecosystem microclimate and the hydrological cycle at both regional and global scales [3,4,5]. Keenan et al [10] demonstrated that the Bowen ratio shows a global increasing trend due to the adjustment of leaf stomata in response to increasing atmospheric CO2, based on the energy fluxes of 21 forest sites ranging from 7 to 18 years. There is a lack of consensus between these models and the observations because these models do not fully considering the interactive relationships between the atmosphere-biosphere energy fluxes and vegetation in response to climate change, especially for forests [8,14]

Objectives

Methods

Results

Discussion

Conclusion