藏北高寒草地牧草营养品质对放牧的响应机制

Responses of forage nutrient quality to grazing in the alpine grassland of Northern Tibet

基于藏北高原的3个围栏与自由放牧试验样地,探讨了高寒草地牧草营养品质对放牧的响应机制。结果表明:在一个高寒草原化草甸冷季牧场,冷季放牧分别减少了24.29%和18.98%的杂草酸性洗涤纤维和中性洗涤纤维含量,并增加了41.05%的杂草粗灰分含量,从而增加了杂草营养品质;而没有改变群落和优势牧草营养品质。在一个高寒草原化草甸暖季牧场,暖季放牧分别减少了31.82%和27.45%的群落酸性洗涤纤维和中性洗涤纤维含量,并分别增加了137.35%和24.73%的群落粗灰分和粗脂肪含量,从而增加了群落营养品质;暖季放牧分别减少了22.04%和22.50%的优势牧草酸性洗涤纤维和中性洗涤纤维含量,并增加了202.19%的优势牧草粗灰分含量,从而增加了优势牧草营养品质;而没有改变杂草营养品质。在一个高寒草甸暖季牧场,暖季放牧分别减少了37.18%和25.10%的杂草酸性洗涤纤维和中性洗涤纤维含量,从而增加了杂草营养品质;增加了26.55%的优势牧草粗蛋白含量,从而趋于增加了优势牧草营养品质;而对群落营养品质无影响。植物群落营养品质与植物群落α和β多样性相关,优势牧草营养品质主要与土壤变量相关,杂草营养品质与土壤变量和杂草α多样性有关。因此,藏北高寒草地牧草营养品质对放牧的响应因草地类型和放牧季节的不同而不同,高寒草地应该采取分类放牧管理。

In this study,we determined the responses of herbage nutrient quality to grazing in alpine grasslands in different seasons and different grassland types.Three fenced and free-grazing grassland sites in the alpine grassland in the Northern Tibetan Plateau were selected for this study.We found that winter grazing increased the nutritional quality of forbs by decreasing the acid detergent fiber content by 24.29%and the neutral detergent fiber content by 18.98%,and by increasing the crude ash content by 41.05%.However,winter grazing did not affect the nutritional quality of the plant community and high-quality forage in the alpine steppe meadow.Summer grazing increased the nutrient quality of the plant community by decreasing the acid detergent fiber content by 31.82%and the neutral detergent fiber content by 27.45%,and by increasing the crude ash content by 137.35%and the crude fat content by 24.73%in an alpine steppe meadow.Summer grazing increased the nutrient quality of high-quality forage by decreasing the acid detergent fiber by 22.04%and the neutral detergent fiber content by 22.50%,and by increasing the crude ash content by 202.19%.However,summer grazing did not change the nutrient quality of forbs in the alpine steppe meadow.Summer grazing increased the nutritional quality of forbs through decreasing the acid detergent fiber content by 37.18%and the neutral detergent fiber content by 25.10%,and tended to increase the nutritional quality of high-quality forage through increasing the crude protein content by 26.55%,but had no effect on the nutritional quality of plant community in an alpine meadow.The nutritional quality of the plant community was related to itsαandβdiversity.The nutritional quality of high-quality forage was mainly related to soil variables,and the nutritional quality of forbs was related to itsαdiversity and soil variables.Therefore,in alpine grasslands of Northern Tibet,the responses of forage nutrient quality to grazing differ depending on plant types and grazing seasons.Alpine grassland should be managed by different grazing patterns.