不同放牧方式对荒漠草原土壤碳氮储量及固持的影响

研究放牧对草地碳氮储量及固持的影响对草地科学管理具有重要意义。以宁夏荒漠草原为对象，研究了封育、自由放牧和暖季轮牧下0～40 cm土壤有机碳和全氮储量及碳氮固持特征。结果表明：1)经过5年放牧，土壤碳氮含量暖季轮牧最高，分别为5.66±0.32 g·kg-1和0.32±0.01 g·kg^-1，自由放牧最低。随土层的加深，有机碳含量在暖季轮牧处理中增加，封育和自由放牧变化不显著；氮含量3种处理垂直变化均不显著。自由放牧碳氮比最高，达到26.98±1.05，暖季轮牧最低。0～40 cm土壤碳氮储量表现为暖季轮牧>封育>自由放牧。2)以封育为对照，碳氮固持量和固持速率呈暖季轮牧>封育>自由放牧。3)Pearson相关性分析表明，土壤碳氮储量、固持与地上生物量呈显著相关性(P<0.05)；与物种多样性呈极显著正相关(P<0.01,P<0.001)。研究认为，从土壤碳氮储量及固持考虑，暖季轮牧的草地利用方式更有利于研究区荒漠草原碳汇能力提升和草地持续发展。

Effects of different grazing patterns on soil carbon and nitrogen storage and sequestration in desert steppee

It is important for scientific grassland management to know the effects of grazing on carbon and nitrogen storage and sequestration. Soil organic carbon and total nitrogen storage and carbon and nitrogen sequestration in the 0-40 cm soil horizon were studied in a Ningxia desert steppe under treatments of enclosure to prevent grazing， free grazing and warm season rotational grazing. It was found that： 1） After 5 years of grazing， the soil carbon and nitrogen contents were the highest （5.66±0.32 g·kg^-1 and 0.32±0.01 g·kg^-1， respectively） in warm season rotational grazing， and the lowest in free grazing. The organic carbon content increased with soil depth in warm season rotational grazing， but the differences between warm season rotational grazing and enclosure to prevent grazing and free grazing were not significant. The vertical variation of nitrogen content did not differ significantly among the three treatments. The C∶N ratio under free grazing was the highest （26.98±1.05）， while warm season rotation grazing was the lowest. Soil carbon and nitrogen storage for the 0-40 cm soil horizon ranked warm season rotation grazing>enclosure to prevent grazing>free grazing. 2） The carbon and nitrogen sequestration and sequestration rates ranked warm season rotation grazing>enclosure to prevent grazing>free grazing. 3） Pearson correlation analysis showed that soil carbon and nitrogen storage and retention were significantly correlated with aboveground biomass （P<0.05）. It is positively correlated with species diversity （P<0.01， P<0.001）. It was concluded that， from a perspective of soil carbon and nitrogen storage and retention， warm season rotational grazing is more conducive to the improvement of carbon sink capacity and sustainable development of desert steppe in the study area.