藏北高原高寒草甸光能利用效率对短期模拟增温的响应

光能利用效率(light use efficiency,LUE)是一个非常重要的生理生态指标。定量化不同时空尺度上的LUE对研究全球碳循环和气候变化有重要的指示作用。为了评估LUE对气候变暖的短期响应,2013年6月底在藏北高原一个高寒草甸布设了模拟增温实验,采用开顶式气室提高环境温度。通过控制开顶式气室的开口大小实现两个幅度的增温,开口直径分别为0.60和1.00 m。基于MODIS算法,利用观测的日最小空气温度和白天的平均饱和水汽压差模拟了2013年7-9月的各个处理的LUE。结果表明,开口直径0.60和1.00 m的开顶式气室分别显著增加了0.60和0.20 kPa的2013年7-9月份平均的饱和水汽压差。开口直径0.60 m的开顶式气室显著增加了0.66℃的2013年7-9月份平均的日最低空气温度,而开口直径1.00 m的开顶式气室则非显著增加了0.25℃的2013年7-9月份的日最低空气温度。 开口直径0.60和1.00 m的开顶式气室分别显著减少了约12.9%(即0.06 g C/MJ)和3.1%(即0.01 g C/MJ)的2013年7-9月份平均的LUE。因此,气候变暖将可能会减少藏北高原高寒草甸的光能利用效率,且可能会随着增温幅度的增大LUE的减少幅度增大。

Initial response of light use efficiency to experimental warming in an alpine meadow in the Northern Tibetan Plateau

Light use efficiency (LUE)is an important eco-physiological variable and the quantification of LUE at a variety of spatial and temporal scales would be advantageous for global carbon cycle and climatic change re-search.In order to assess the initial response of LUE to climatic warming,a field experiment was conducted in an alpine meadow in Northern Tibet beginning late June,2013.Open-top chambers (OTC)with two different warming magnitudes (top diameter 0.60 and 1.00 m,labeled as OTC2 and OTC1,respectively)were used toincrease temperatures.Daily LUE was estimated by using daily minimum air temperature and daytime mean vapor pressure deficit,based on a Moderate-Resolution Imaging Spectroradiometer (MODIS)algorithm,be-tween July and September in 2013.Compared to the control,OTC2 and OTC1 significantly increased average vapor pressure deficit by 0.60 and 0.20 kPa,respectively.Compared to the control,OTC2 significantly in-creased average daily minimum air temperature by 0.66℃,whereas OTC1 did not produce a significant increase (0.25℃).OTC2 and OTC1 significantly reduced LUE by 12.9% (i.e.0.06 g C/MJ)and 3.1% (i.e.0.01 g C/MJ),respectively.Our findings suggested that climatic warming will probably decrease LUE in alpine meadow ecosystems and that the negative effect of experimental warming on LUE may increase with the magni-tude of warming on the Northern Tibetan Plateau.