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树木水分利用效率特征存在地域及树种差异,北京山区作为华北土石山区典型森林生态系统,其主要树种侧柏水分利用效率(WUE)长期变化的研究未见报道.本研究通过测定侧柏树轮稳定碳同位素值(δ~(13)C),计算年均水分利用效率(WUE_i),分析其长期变化趋势及对环境条件变化的响应,并结合树轮宽度,探究侧柏WUE_i与净固碳量的关系.结果表明:1918—2013年期间,北京山区年均气温呈逐渐升高趋势,年降水量波动较大.在此期间,侧柏树轮δ~(13)C逐渐减小,WUE_i呈逐渐增大趋势.侧柏WUE_i对气温变化的响应最为敏感,呈显著正相关关系,且WUE_i对气温升高的响应敏感性大于气温降低.侧柏WUE_i与年降水量的相关性不明显,该地区降水量不是影响侧柏WUE_i的主要因素.侧柏去趋势树轮宽度值呈现先上升后下降趋势,近20年下降趋势明显.结合WUE_i与环境因子的相关性分析,认为气温升高导致气孔导度(g_s)降低,蒸腾量减少,同时增加了呼吸损耗,结果导致WUE_i升高,但侧柏净固碳量减少,生长减缓.
The characteristics of water use efficiency of trees exist in different regions and different tree species. However, the long-term changes of water use efficiency (WUE) of arborvitae, a major tree species in Beijing mountainous area as a typical forest ecosystem in northern China, have not been reported.In this study, (Δ ~ (13) C), the average annual water use efficiency (WUE_i) was calculated, and its long-term trend and its response to environmental conditions were analyzed. Based on the tree-ring width, the relationship between WUE_i and net carbon sequestration The results showed that the annual mean temperature in the mountainous area of Beijing increased gradually during the period of 1918-2013, and the annual precipitation fluctuated greatly during the period from 1918 to 2013. During this period, the δ ~ (13) C of the arborvitae tree shrub gradually decreased and WUE_i gradually increased The trend of WUE_i is the most sensitive to the change of temperature, and there is a significant positive correlation between WUE_i and the temperature, and the sensitivity of WUE_i to temperature increase is greater than the decrease of temperature.The correlation between WUE_i and annual precipitation is not obvious, Is not the main factor that affected the WUE_i of Platycladus orientalis .There is a tendency that the width of the trend tree rings of Platycladus orientalis first increases and then decreases, and the declining trend is obvious in the past 20 years.Combined with the correlation analysis of WUE_i and environmental factors, Hole conductance (G_S) decreases, reducing transpiration, while breathing loss increases, resulting in WUE_i increased, but the net orientalis solid carbon reduction, slowing growth.