湖南岳阳杨树人工林光能利用率动态特征分析

Characteristics of Poplar Plantation Light Use Efficiency

植物光能利用率（Light Use Efficiency,LUE）作为表征植被利用光能合成生物化学能效率的重要指标,直接影响到生态系统生产力。本文使用2006年4月-10月湖南岳阳站通量观测资料,探讨杨树人工林不同时间尺度的光能利用率动态特征。结果表明：①杨树人工林生态系统典型晴天LUE_（30min）存在明显的＂V＂形日变化,其值介于（13.18~45.28）mmol/mol,最低值都出现在中午前后;②5日累计光能利用率（LUE_5）季节动态呈双峰型变化,峰值分别出现在5月初（42.57mmol/mol）和7月中旬（57.50mmol/mol）;③月尺度光能利用率（LUEmon）分别为24.79、27.85、20.95、42.27、32.60、24.91和10.47mmol/mol,最大值出现在7月份,且LUE_（mon）最大值较LUE5和LUE_（30min）低,最小值较LUE5和LUE_（30min）高。这些结果将为提高生态系统资源的利用提供重要的定量化依据。

Light use efficiency（LUE） directly determines ecosystem gross productivity, is a key factor indicating the efficiency at which vegetation translates light energy into biochemical energy through photosynthesis, and a vital parameter for production efficiency models. Progress in carbon sequestration under photosynthesis by improvements in the LUE of ecosystems requires an appreciation of the dynamic characteristics of LUE. Here, we used half-hourly eddy-covariance measurements of carbon dioxide （CO2 ） to analyze the dynamic characteristics of LUE of a poplar plantation in Yueyang, Hunan from April-October 2006. The climate is subtropical moist monsoon, the species of plants belonged to Euramerican poplar and their growing seasons ranged from the last third of March to November. We examined the characteristics of LUE by analyzing data from different temporal scales （30 min, 5 days, months）. We found that LUE30min showed significant diurnal variation and on typical sunny days varied from 13.18~45.28 mmol/mol and followed a V shaped curve. The minimum value appeared around noon, revealing that LUE30min has a remarkable negative relevance to light. Different months showed different ranges of depression, and the minimums in June, July and August were higher than for other months. The change in LUE5days during the growing season appeared as dual peaks and the maximum LUE5days （42.57 mmol/mol and 57.50 mmol/mol） occurred in early May and mid-July. Variation in LUE5days was consistent with accumulated photosynthetic active radiation（PARa ） and accumulated gross ecosystem productivity （GEPa ）, which also followed dual peak curves （maximum of PARmax ： 44.52 mol/（m2·d） and 42.13 mol/（m2·d）; maximum GEPa ： 14.56 gC/（m2·d） and 14.47 gC/（m2·d））. LUEmonths from April to October were 24.79, 27.85, 20.95, 42.27, 32.60, 24.91 and 10.47mmol/mol, respectively. The maximum was in July, indicating that LUE varied during the growing season. LUEmonth variation was also consistent with PAR and GEP. LUE responses varied at different scales： LUE had a negative relationship with PAR at the scale of hour, and LUE was positively related with PAR at the scales of day and month. Maximum LUEmonth was lower than LUE5days and LUE30min ; and minimum LUEmonth was higher than LUE5days and LUE30min .