本研究以西藏自治区班戈县的典型高寒草原为研究对象,设置田间小区控制试验,于2013-2015年施加不同数量氮磷肥(N:0、7.5、15.0 g N·m^-2,P:0、7.5、15.0、30.0 g P2O5·m^-2),调查各处理不同类群植物生物量、分析土壤理化性质,进而评价氮磷养分添加对高寒草原草地质量和土壤环境质量的影响。试验结果表明:1)氮磷配施优于氮磷肥单施,不同氮磷配施处理均能提高草地质量指数(IGQ),以N1P1(7.5 g N·m^-2,7.5 g P2O5·m^-2)施肥处理的草地质量指数最大(90.27),相较对照增加了67.16%(P<0.05)。2)选择土壤有机质(OM),全氮(TN)、全磷(TP)、有效氮(AN)、有效磷(AP)和pH作为土壤环境质量评价指标,应用主成分分析法对不同土层(0~10 cm、10~20 cm、20~30 cm)12个施肥处理的土壤理化性质进行分析。结果表明,短期施肥主要影响土壤0~10 cm土层环境质量的变化;增施氮肥土壤pH呈下降趋势;高磷添加处理(30.0 g P2O5·m^-2)增加了土壤全磷、有效磷含量,但植物吸收效率下降。3)结合草地质量指数和土壤理化性质变化进行草地质量综合评价,结果表明氮磷肥配施好于单施,且N1P1(7.5 g N·m^-2,7.5 g P2O5·m^-2)处理相对得分最高,为本试验条件下的适宜施肥量。
Warming increases competition among plant species in alpine communities by ameliorating harsh environmental conditions,such as low temperatures. Grazing, as the main human activity, may mitigate the effect of warming, as previously reported.However, it is critical to refine the effects of warming on biotic interactions among species, for example, by taking the competitive ability of species into consideration. Based on a 10-year warming and grazing experiment in a Tibetan alpine meadow, we evaluated interspecific biotic interactions of dominant and subordinate species, using the approach of interspecific spatial associations. Warming significantly increased competition between subordinate and dominant species as well as among subordinate species, but not among dominant species. Moreover, facilitation of dominant-subordinate species also increased under warming. Simulated rotational grazing had similar effects to warming, with increasing interspecific competition. Our results show that, when studying the effects of warming on biotic interactions among species, it is necessary to characterize different species pairs relative to their competitive ability, and that simulated rotational grazing does not mitigate the effects of warming in the long term. Our results also provide evidence that the spatial pattern of species is a critical mechanism in species coexistence.
