Characteristics of Poplar Plantation Light Use Efficiency
湖南岳阳杨树人工林光能利用率动态特征分析

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.