Freezing-induced loss of carbon uptake in a subtropical coniferous plantation in southern China

Abstract

In January 2008, a freeze in southern China, unprecedented in 50 years, severely affected local subtropical coniferous plantations. We investigated the freezing-induced loss of carbon uptake in a subtropical coniferous plantation at Qianyanzhou site in southern China. We used data from eddy covariance observations, field surveys and remote sensing. Field surveys revealed that the trees (especially slash pine, Pinus elliottii) at forest edges and valley banks were susceptible to the freezing weather, and about 6% of trees were severely damaged by glaze ice. The vegetation index showed a phenological lag of about 10 days in 2008 due to the freezing weather. Photosynthesis in 2008 was more sensitive to the freezing weather than was ecosystem respiration, and this fact led to significantly less annual carbon uptake. This uptake loss (∼66 g C m–2, 17% of annual uptake) was due to the physical damage caused by glaze ice and physiological injuries caused by low temperatures. With gradual ecosystem recovery over time, the quarterly ratios of ecosystem respiration to photosynthesis in 2008 returned gradually to normal levels. Because of the seasonal variation of footprint biases with monsoon transition, the flux observations possibly overestimated both carbon uptake loss in early 2008 and ecosystem recovery in the following months to some extent.