Variation of relative monthly CPC deficits and relative monthly air temperature (Ta) deficits
Figure 2. Variation of relative monthly CPC deficits and relative monthly air temperature (Ta) deficits. CPC deficits monthly dynamics (black line) and Ta deficits monthly dynamics (blue line). Ta deficits were calculated by corresponding half-hourly meteorological data with the perfect-deficit approach. The relative deficits were the values of CPC and Ta deficits normalized by the total area of their perfect curve integrated over each month, respectively.
Increasing occurrences of climate extreme events urge us to study their impacts on terrestrial carbon sequestration. Ecosystem potential productivity deficits could characterize such impacts and display the ecosystem vulnerability and resilience to the extremes in climate change, whereas few studies have analyzed the yearly dynamics of forest potential productivity deficits. Based on a perfect-deficit approach, we used in situ eddy covariance flux data and meteorological observation data at Qianyanzhou station from 2003 to 2010 to explore the relationship between potential productivity and climate extremes, such as droughts in 2003 and 2007, ice rain in 2005, and an ice storm in 2008. We found (1) the monthly canopy photosynthetic capacity (CPC) deficits could be mainly explained by air temperature (Ta) deficits (R2 = 0.45, p < 0.000 01); (2) a significant correlation was noted between seasonal CPC deficits and co-current Ta deficits (R2 = 0.45, p < 0.000 01), especially in winter (R2 = 0.79, p = 0.003); (3) drought in summer exerted a negatively lagged effect on potential productivity (R2 = 0.59, p = 0.02), but at a short time scale; and (4) annual CPC deficits captured the impacts of climate extremes on the forest ecosystem potential productivity, and the two largest potential productivity deficits occurred in 2003 (relative CPC deficits = 0.34) and in 2005 (relative CPC deficits = 0.35), respectively. With the perfect-deficit approach, the forest ecosystem vulnerability to extremes was analyzed in a novel way.