冠层光能利用率的叶绿素荧光光谱探测

Estimating light-use efficiency by the separated Solar-induced chlorophyll fluorescence from canopy spectral data

设计了玉米生长期日变化试验,同步获取玉米冠层光谱和通量观测数据,探究从植被发射荧光光谱角度实现植被光能利用率可靠反演的可能性。运用涡度相关法获取群体生态系统净生产力(NEP),通过呼吸作用拟合得到冠层总初级生产力(GPP);在此基础上结合吸收光合有效辐射(APAR)获取冠层光能利用率(LUE);同时,利用叶绿素荧光光谱分离算法,提取了光合作用叶绿素荧光绝对强度和相对强度。结论表明,植被发射荧光光谱与光合有效辐射(PAR)显著正相关,760nm波段荧光与PAR的复相关系数R2在0.99以上;叶绿素荧光绝对强度与NEP和GPP显著正相关,荧光和NEP对环境日变化具有类似的响应特征;688nm和760nm植被发射的叶绿素荧光相对强度与LUEGPP存在可靠负相关关系,即叶绿素荧光强度越大,光能利用率越低。同时,通过比较几种植被指数与各种光合参量的相关性表明,叶绿素荧光能够更好的跟踪植被光合状态的变化,更适宜于植被光能利用率的探测。

Light-use efficiency （LUE） is a critical parameter in many primary production models for estimating ecosystem carbon exchange. The application of these models on regional and global scale is restricted because of the difficulty of retrieving LUE from airborne and satellite remote sensing images. Vegetation chlorophyll fluorescence is a direct indicator of plant physiology. In this paper, a diurnal experiment was carried on maize on July 5, 2008. The canopy radiance spectra and tower-based flux data were acquired synchronously to test the possibility of retrieving LUE by the solar-induced vegetation ChlF signals. The canopy net primary production （NEP） values were calculated using eddy covariance measurement by a CSAT3-Li7500 Flux system, and the gross primary production （GPP） was also calculated by adding the simulated day time respiration. Two kinds of LUE based on GPP （LUEGPP） and NEP （LUENEP） were defined by dividing the absorbed photosynthetic active radiation （APAR）. The ChlF signals at 760nm and 688nm were also separated from the reflected radiance spectra based on Fraunhofer line depth algorithm in the two oxygen absorption bands. The ChlF signals were strongly correlated with photosynthetic active radiation （PAR）, especially the ChlF at 760nm （R20.99）. Both NEP and GPP had a significant correlation with ChlF. Furthermore, LUEGPP was negatively correlated with the ChlF’s relative intensity at 688nm and 760nm, with a correlation coefficient R2 of 0.6331 and 0.7861 respectively. Moreover, the LUE models based on the solar-induced vegetation ChlF signals were compared to some popular vegetation Indices （VIs） from the canopy reflected spectra. Canopy LUEGPP was proved able to be estimated from the remotely sensed ChlF signals.