土壤pH值变化对3种草原类型土壤碳氮磷生态化学计量特征的影响

酸碱性是土壤的重要化学性质，土壤pH值的升高和降低会影响土壤养分的分布及转化情况，进而影响群落组成及生态系统的功能。全球变化和人类活动降低了草原生态系统的土壤pH值，而不同草原类型的土壤碳氮磷生态化学计量特征对土壤pH值变化的响应尚不清楚。本研究以内蒙古自治区土壤酸碱性不同的荒漠草原、典型草原和草甸草原3种草原类型作为研究对象，通过酸碱添加试验改变土壤pH值，研究土壤碳氮磷生态化学计量特征的相应变化。结果表明：1）荒漠草原和典型草原0~10 cm土层的土壤pH值显著高于草甸草原，3种草原类型10~30 cm土层的土壤pH值无显著差异；荒漠草原土壤有机碳、全氮和全磷以及土壤碳氮比、氮磷比和碳磷比均低于典型草原和草甸草原，除土壤全磷外均存在显著差异；典型草原的土壤全氮在10~30 cm土层显著高于草甸草原；草甸草原0~10 cm土层的碳氮比显著高于典型草原。2）对于0~10 cm土层而言，酸添加显著增加了荒漠草原的土壤有机碳、碳氮比和碳磷比；碱添加显著降低了荒漠草原的土壤有机碳和氮磷比以及典型草原的土壤全氮和全磷，升高了荒漠草原的土壤碳磷比。对于10~30 cm而言，碱添加升高了荒漠草原的土壤碳氮比，降低了典型草原的全氮和氮磷比以及草甸草原的碳磷比。3）荒漠草原0~10 cm土层的土壤有机碳、全氮、碳磷比和氮磷比均与土壤pH值具有显著负相关关系；典型草原和草甸草原的土壤碳氮磷生态化学计量特征与土壤pH值不存在显著相关关系。以上结果说明，不同草原受土壤pH值改变的影响表现为荒漠草原>典型草原>草甸草原，且表层土壤相比下层土壤受到的影响更为明显。酸碱添加对不同草原类型土壤碳氮磷化学计量特征的影响揭示了生态系统对土壤pH值改变的短期响应。因此，在全球气候变化和人为活动引起的土壤pH值发生变化的背景下，草原生态系统在土壤退化后的恢复重建中应合理调节土壤pH值，以保证土壤养分元素的平衡及循环过程。

Effects of soil pH on soil carbon,nitrogen,and phosphorus ecological stoichiometry in three types of steppe

Soil acidity or alkalinity is one of the most important physico-chemical features of the soil,and affects the ecological stoichiometry of soil carbon,nitrogen,and phosphorus through its impact on physical,chemical and biological processes of an ecosystem.Accordingly,the soil pH in grassland ecosystems has changed as a result of climate change and human activities for decades or even centuries.Existing studies have generally focused on the changes in soil nutrients in response to grazing,fertilization,and altered temperature or precipitation.It remains unclear how ecological stoichiometry of soil carbon,nitrogen and phosphorus in various categories of steppe responds to changing soil pH.In this study,three types of steppe(i.e.desert,typical and meadow steppe)with a range of pH values were selected and their soil acidity or alkalinity was altered through manipulative experiments by adding sulphuric acid or sodium hydroxide.We found that:1)The soil pH values of the 0-10 cm layer in both desert and typical steppes were significantly higher than in meadow steppe.However,the soil pH values of the 10-30 cm layer in all three types of steppe were not significantly different.The values of soil organic carbon,total nitrogen and phosphorus,as well as the ratios of soil carbon to nitrogen,nitrogen to phosphorus and carbon to phosphorus in desert steppe were lower than in typical and meadow steppes.The soil total nitrogen in typical steppe was significantly higher than that in meadow steppe for the 10-30 cm layer.The ratio of carbon to nitrogen in the 0-10 cm layer in meadow steppe was significantly higher than in typical steppe.2)For the 0-10 cm layer,the addition of acid significantly increased the soil organic carbon,the ratios of carbon to nitrogen and carbon to phosphorus in desert steppe.Soil organic carbon and the ratio of nitrogen to phosphorus in desert steppe,and soil total nitrogen and phosphorus in typical steppe were also significantly reduced by the addition of alkali.In contrast,the addition of alkali enhanced the ratio of soil carbon to phosphorus in desert steppe.For the 10-30 cm layer,the addition of alkali increased the ratio of soil carbon to nitrogen in desert steppe,but it decreased total nitrogen and the ratio of nitrogen to phosphorus in typical steppe.The ratio of carbon to phosphorus also declined in meadow steppe after adding alkali.3)Soil organic carbon,total nitrogen,and the ratios of carbon to phosphorus and nitrogen to phosphorus at the 0-10 cm soil layer in desert steppe were negatively correlated with soil pH values.The correlations between soil pH and ecological stoichiometry of soil carbon,nitrogen and phosphorus did not differ significantly in typical steppe or in meadow steppe.These results indicate that the ecological stoichiometric characteristics of soil carbon,nitrogen and phosphorus in the three studied steppe types were affected by changing soil pH in the order:desert steppe>typical steppe>meadow steppe.The surface soil was more sensitive to the change in acidity or alkalinity than the subsoil.The similarities and differences of the results between variance and correlation analyses reflected the different effects of soil pH on the three types of steppe in short and long-term adaptation to a changing acidic or alkaline environment.Therefore,in the context of changes in soil pH caused by climate change and anthropogenic activities,grassland ecosystems are likely to adjust their soil pH during the restoration and reconstruction of soil degradation,in order to ensure a nutrient balance and cycling.