Predicting how human activity will influence the response of alpine grasslands to future warming has many uncertainties.In this study, a field experiment with controlled warming and clipping was conducted in an alpine meadow at three elevations（4313 m, 4513 m and 4693 m） in Northern Tibet to test the hypothesis that clipping would alter warming effect on biomass production.Open top chambers（OTCs） were used to increase temperature since July,2008 and the OTCs increased air temperature by approximately 0.9o C ~ 1.8o C during the growing in2012.Clipping was conducted three times one year during growing season and the aboveground parts of all live plants were clipped to approximately 0.01 m in height using scissors since 2009.Gross primary production（GPP） was calculated from the Moderate-Resolution Imaging Spectroradiometer GPP algorithm and aboveground plant production was estimated using the surface-measured normalized difference vegetation index in 2012.Warming decreased the GPP, aboveground biomass（AGB） and aboveground net primary production（ANPP） at all three elevations when clipping was not applied.In contrast, warming increased AGB at all three elevations, GPP at the two lower elevations and ANPP at the two higher elevations when clipping was applied.These findings show that clipping reduced the negative effect of warming on GPP, AGB and ANPP, suggesting that clipping may reduce the effect of climate warming on GPP, AGB and ANPP in alpine meadows on the Tibetan Plateau, and therefore, may be a viable strategy for mitigating the effects of climate change on grazing and animal husbandry on the Tibetan Plateau.
FU GangSUN WeiYU Cheng-QunZHANG Xian-ZhouSHEN Zhen-XiLI Yun-LongYANG Peng-WanZHOU Nan
Highland barley is an important staple food in the Tibet,and the Tibetan Plateau is experiencing obvious climatic warming.However,few studies have examined the warming effects on highland barley growth and biomass allocation under conditions of controlled experimental warming.This limits our ability to predict how highland barley will change as the climate changes in the future.An experiment of field warming at two magnitudes was performed in a highland barley system of the Tibet beginning in late May,2014.Infrared heaters were used to increase soil temperature.At the end of the warming experiment（September 14,2014）,plant growth parameters（plant height,basal diameter,shoot length and leaf number）,biomass accumulation parameters（total biomass,root biomass,stem biomass,leaf biomass and spike biomass）,and carbon and nitrogen concentration parameters（carbon concentration,nitrogen concentration,the ratio of carbon to nitrogen concentration in root,stem,leaf and spike）were sampled.The low-and high-level experimental warming significantly increased soil perimental warming did not significantly change.The low-and high-level experimental warming did not significantly affect plant growth parameters,biomass accumulation parameters,and carbon and nitrogen concentration parameters.There were also no significant differences of plant growth parameters,biomass accumulation parameters,and carbon and nitrogen concentration parameters between the low-and high-level experimental warming.Our findings suggest that the response of highland barley growth,total and component biomass accumulation,and carbon and nitrogen concentration to warming did not linearly change with warming magnitude in the Tibet.
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1.00m。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1.00m的开顶式气室分别显著增加了0.60和0.20kPa的2013年7-9月份平均的饱和水汽压差。开口直径0.60m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1.00m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1.00m的开顶式气室分别显著减少了约12.9%(即0.06g C/MJ)和3.1%(即0.01g 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。
