【摘要】 准确监测中国南亚热带常绿林生态系统光合作用动态变化对全球陆地生态系统碳吸收估计及其对气候变化的响应至关重要。涡动协方差技术一直被认为是评估生态系统碳通量最直接的方法,虽然具有较高的时间分辨率,但在空间上有其自身的局限性。近10年,光谱观测和卫星遥感技术在植被生产力监测方面的应用大大提高了对碳通量的时空评估能力。本研究基于长时间序列光谱观测数据,提取叶绿素荧光指数(FRI)和光化学植被指数(PRI),进而评价两个生理遥感指数跟踪亚热带常绿林光合作用季节动态变化的能力。结果表明,传统NDVI指数受光照条件影响较大(R~2=0.88,p<0.001),并呈现出饱和现象,而FRI和PRI指数则能较好地跟踪植物光和功能季节性变化,且在季节尺度上两者受光照条件的影响相对较弱(FRI指数R~2=0.13;PRI指数R~2=0.51);相比PRI指数与光能利用效率(LUE)在午间具有较强的相关性,FRI指数与GPP的相关性则在早上优于午间时段;而这两种相关关系均在植被衰退季优于植被生长季。另外,通过考虑光合有效辐射因子,基于FRI指数监测GPP的能力得到显著提高,R 2从0.22提高到0.69,呈显著正相关关系(p<0.001);同时,在植被衰退季也呈现出更强的相关性(R~2=0.79,p<0.001)。研究成果表明,FRI和PRI两个生理遥感指数能够准确地监测亚热带常绿林光合作用季节动态变化,建议把其引入碳循环模型中以改进区域碳收支估计。更多还原

【Abstract】 The accurate measurement of the dynamics of photosynthesis in China’s subtropical evergreen forest ecosystems is an important contribution to carbon(C) sink estimates in global terrestrial ecosystems and their responses to climate change. Eddy covariance has historically been the only direct method to assess C flux of whole ecosystems with high temporal resolution, but it suffers from limited spatial resolution. During the last decade, continuous global monitoring of plant primary productivity from spectroradiometer sensors on flux towers and satellites has extended the temporal and spatial coverage of C flux observations. In this study, we evaluated the performance of two physiological remote sensing indices, fluorescence reflectance index(FRI) and photochemical reflectance index(PRI), to measure the seasonal variations of photosynthesis in a subtropical evergreen forest ecosystem using continuous canopy spectral and flux measurements in the Dinghushan Nature Reserve in southern China.The more commonly used NDVI has been shown to be saturated and mainly affected by illumination(R~2=0.88, p <0.001), but FRI and PRI could better track the seasonal dynamics of plant photosynthetic functioning by comparison and are less affected by illumination(R~2=0.13 and R~2=0.51, respectively) at the seasonal scale. FRI correlated better with daily gross primary production(GPP) in the morning hours than in the afternoon hours, in contrast to PRI which correlated better with light-use efficiency(LUE) in the afternoon hours. Both FRI and PRI could show greater correlations with GPP and LUE respectively in the senescence season than in the recovery-growth season. When incident PAR was taken into account, the relationship between GPP and FRI was improved and the correlation coefficient increased from 0.22 to 0.69(p < 0.001). The strength of the correlation increased significantly in the senescence season(R~2=0.79, p < 0.001). Our results demonstrate the application of FRI and PRI as physiological indices for the accurate measurement of the seasonal dynamics of plant community photosynthesis in a subtropical evergreen forest, and suggest these indices may be applied to carbon cycle models to improve the estimation of regional carbon budgets.更多还原