Serrano Lydia, Peñuelas Josep
Departament d'Enginyeria Agroalimentària i Biotecnologia, Universitat Politècnica de Catalunya, Barcelona, Spain.
Tree Physiol. 2005 Jan;25(1):67-74. doi: 10.1093/treephys/25.1.67.
Annual changes in structural attributes and seasonal dynamics in water content, photosynthetic rate and light-use efficiency (LUE) were assessed by spectral transmittance for 4 years (1999-2003) in six stands of a Mediterranean holm oak forest. Green biomass, total biomass and leaf area index (LAI) were determined. In 1999, seasonal dynamics of net carbon dioxide (CO2) exchange and water content were measured. We recorded photosynthetically active radiation (PAR) transmittance and hyperspectral transmittance in the 400-1100 nm region and derived reflectance-based vegetation indices. Transmittance over the PAR region derived from either ceptometer or spectroradiometer measurements (PART and TPAR, respectively) was related to green and total biomass. Both PART and TPAR were also related to LAI (r=0.79 and r=0.70, respectively, P <0.001) and were appropriate for comparison among stands, whereas subtle changes in LAI within a stand were better assessed by the transmittance amplitude in the red edge region (TRE) (within a stand, r=0.77-0.99, P <0.001). Spectral transmittance-based indices successfully captured physiological processes that occurred on temporal (seasonal) and spatial scales. The transmittance-based water index (TWI) was related to both foliage and canopy water content (r=0.69, P <0.001). Estimates of foliage and canopy water content improved in dense (closed) stands (r=0.84 and r=0.87, respectively, P <0.001) compared with low-density stands. Under non-drought conditions, transmittance-based photochemical reflectance index (TPRI) was related to LUE (r=0.58, P <0.05) and net CO2 exchange (r=0.72, P <0.01), and the combined TPAR x TPRI index greatly improved these relationships (r=0.93 and r=0.84, respectively, P <0.01), indicating that both structural and physiological adjustments modified CO2 fixation capacity in these forest stands. Our novel approach to the study of transmitted radiation provides a tool for estimating structural and functional variables such as LAI, LUE and water content, which are key determinants of terrestrial productivity.
通过光谱透射率评估了地中海圣栎林6个林分在4年（1999 - 2003年）间结构属性的年度变化以及水分含量、光合速率和光能利用效率（LUE）的季节动态。测定了绿色生物量、总生物量和叶面积指数（LAI）。1999年，测量了净二氧化碳（CO₂）交换和水分含量的季节动态。我们记录了光合有效辐射（PAR）透射率和400 - 1100 nm区域的高光谱透射率，并推导了基于反射率的植被指数。由采光仪或光谱辐射仪测量得出的PAR区域的透射率（分别为PART和TPAR）与绿色生物量和总生物量相关。PART和TPAR也都与LAI相关（r分别为0.79和0.70，P <0.001），适用于林分间的比较，而林分内LAI的细微变化通过红边区域的透射率幅度（TRE）能得到更好的评估（在林分内，r = 0.77 - 0.99，P <0.001）。基于光谱透射率的指数成功捕捉了在时间（季节）和空间尺度上发生的生理过程。基于透射率的水分指数（TWI）与叶片和冠层水分含量均相关（r = 0.69，P <0.001）。与低密度林分相比，在密集（封闭）林分中，叶片和冠层水分含量的估计值有所改善（r分别为0.84和0.87，P <0.001）。在非干旱条件下，基于透射率的光化学反射指数（TPRI）与LUE相关（r = 0.58，P <0.05）和净CO₂交换相关（r = 0.72，P <0.01），并且组合的TPAR×TPRI指数极大地改善了这些关系（r分别为0.93和0.84，P <0.01），表明结构和生理调整都改变了这些林分中的CO₂固定能力。我们研究透射辐射的新方法为估算诸如LAI、LUE和水分含量等结构和功能变量提供了一种工具，这些变量是陆地生产力的关键决定因素。
