Van Gaalen K Eric, Flanagan Lawrence B, Peddle Derek R
Department of Biological Sciences, University of Lethbridge, 4401 University Drive West, Lethbridge, AB, Canada T1K 3M4.
Oecologia. 2007 Aug;153(1):19-28. doi: 10.1007/s00442-007-0718-y. Epub 2007 Apr 4.
Moss samples from the Fluxnet-Canada western peatland flux station in the Boreal Region of Alberta were measured in the laboratory to obtain the net photosynthesis rate and chlorophyll fluorescence of the moss under controlled environmental conditions, including the regulation of moss water content, simultaneously with measurements of moss spectral reflectance. One objective was to test whether the photochemical reflectance index (PRI) detected changes in moss photosynthetic light-use efficiency that were consistent with short-term (minutes to hours) changes in xanthophyll cycle pigments and associated changes in non-photochemical quenching (NPQ), as recorded by chlorophyll fluorescence. The rate of net photosynthesis was strongly inhibited by water content at values exceeding approximately 9 (fresh weight/dry weight) and declined as the water content fell below values of approximately 8. Chlorophyll fluorescence measurements of maximum photosystem II efficiency generally remained high until the water content was reduced from the maximum of about 20 to values of approximately 10-11, and then declined with further reductions in moss water content. A significant linear decline in NPQ was observed as moss water content was reduced from maximum to low water content values. There was a strong negative correlation between changes in NPQ and PRI. These data suggest that PRI measurements are a good proxy for short-term shifts in photosynthetic activity in Sphagnum moss. A second objective was to test how accurately the water band index (WBI, ratio of reflectance at 900 and 970 nm) recorded changes in moss water content during controlled laboratory studies. Strong linear relationships occurred between changes in moss water content and the WBI, although the slopes of the linear relationships were significantly different among sample replicates. Therefore, WBI appeared to be a useful tool to determine sample-specific water content without destructive measurements.
对来自艾伯塔省北方地区弗拉克斯奈特-加拿大西部泥炭地通量站的苔藓样本在实验室进行了测量，以获取在可控环境条件下苔藓的净光合速率和叶绿素荧光，包括对苔藓含水量的调节，同时测量苔藓的光谱反射率。一个目的是测试光化学反射指数（PRI）是否能检测到苔藓光合光利用效率的变化，这些变化与叶黄素循环色素的短期（数分钟至数小时）变化以及叶绿素荧光记录的非光化学猝灭（NPQ）的相关变化一致。当含水量超过约9（鲜重/干重）时，净光合速率受到强烈抑制，并随着含水量降至约8以下而下降。最大光系统II效率的叶绿素荧光测量值通常在含水量从约20的最大值降至约10 - 11之前保持较高，然后随着苔藓含水量的进一步降低而下降。随着苔藓含水量从最大值降至低含水量值，观察到NPQ有显著的线性下降。NPQ的变化与PRI之间存在很强的负相关。这些数据表明，PRI测量是泥炭藓光合活性短期变化的良好指标。第二个目的是测试在可控实验室研究中，水波段指数（WBI，900和970纳米处反射率的比值）记录苔藓含水量变化的准确程度。苔藓含水量变化与WBI之间存在很强的线性关系，尽管不同样本重复之间线性关系的斜率存在显著差异。因此，WBI似乎是一种无需进行破坏性测量即可确定样本特定含水量的有用工具。
