春季休牧对三江源区高寒草甸“植物-土壤-微生物”碳氮磷化学计量特征的影响机理

The deterioration of alpine meadow has great impact on ecosystem services at the alpine region of Qinghai-Tibetan Plateau. Although there were many reasons for alpine meadow degradation, the most direct is overgrazing at the Three-River Source Region. Scientific development of grazing system and rational use of forage resources are the key issues to solve the degradation of alpine meadow. Spring is a critical period for the nutrients accumulation and seeding growth of pasture. Previous studies showed that height, coverage, and above-ground biomass of pasture in spring rest-grazing increased comparing to the grazing. Spring rest-grazing can fundamentally solve the problems of seasonal overgrazing for the grassland and forage-lack for the livestock. Most previous studies of spring rest-grazing focus on aboveground vegetation and soil characteristics. In contrast, the impact of spring rest-grazing on the soil microbe and the regulatory mechanism has been less explored. Then the most studies happened in the temperate typical steppe at inner Mongolia, but less in alpine meadow at the Three-River Source Region. Therefore, it is very important to systematically research the effects of spring rest-grazing on the “plant-soil-microbe” in the alpine meadow, especially in these areas of optimizing the grazing system, revealing the causes of grassland degradation and enhance the ecosystem function. Based on the principle of ecological stoichiometry, our project would investigate the carbon, nitrogen, and phosphorus ratio characteristics of plant, soil, microbe under different times of spring rest-grazing to analyze the effect of spring rest-grazing on the C\N\P coupling relationship in the alpine meadow. In addition, we would determine the soil extracellular enzymes (β-glucosidase, β-glucosaminidase, Acid Phosphomonesterase), microbial community (PLFAs, fungi and bacteria) and diversity (high-throughput sequencing) in trying to reveal the mechanism of microbial regulation in the process of spring rest-grazing. The implementation of this project can provide a scientific basis for formulating the suitable period of spring rest-grazing and sustainable development of alpine meadow husbandry.

过度放牧是三江源区高寒草甸退化的直接原因。科学制定放牧制度，合理利用牧草资源是解决退化草地恢复的关键问题。研究表明，春季作为关键忌牧期，是牧草贮藏营养物质和生长的关键时期，能从根本上解决草地季节性过牧和家畜季节性缺草的问题。以往研究较多集中在春季休牧对植被和土壤的影响，较少关注土壤微生物对休牧的响应及调控机理，且高寒草甸春季休牧的研究处于初级阶段。因此，系统地研究春季休牧对三江源区高寒草甸“植物-土壤-微生物”的影响，对优化放牧制度、揭示生态系统退化原因，提升生态系统功能至关重要。本项目基于生态化学计量学原理，拟通过监测不同春季休牧期植物、土壤、微生物碳氮磷化学计量学特征，研究春季休牧对高寒草甸碳氮磷耦合关系的影响，并通过监测土壤胞外酶、微生物群落及多样性试图揭示微生物对春季休牧过程中的调控机理。本项目的实施可为制定高寒草甸适宜春季休牧期和草地畜牧业的可持续发展提供科学理论依据。

春季作为青藏高原关键忌牧期，是牧草贮藏营养物质和生长的关键时期，能从根本上解决草地季节性过牧和家畜季节性缺草的问题。以往研究较多集中在春季休牧对植被和土壤的影响，较少关注土壤微生物对休牧的响应及调控机理。本项目对三江源区典型高寒草甸进行了不同春季休牧期试验，即CK（放牧）、休牧20d、休牧30d、休牧40d和休牧50d。通过监测不同春季休牧期植物-土壤-微生物碳氮磷化学计量学特征，系统地研究了春季休牧对高寒草甸碳氮磷耦合关系的影响，通过土壤胞外酶、微生物群落及多样性探究微生物的调控机理。结果表明：植物C:N、N:P、C:P、土壤C:N和MBC：MBN在不同春季休牧期差异显著，植物C:N与土壤C:N、MBN:MBP显著相关；植物N:P和MBN:MBP显著相关。三种胞外酶中酸性磷酸单酯酶（AP）活性最高，尤其是CK和休牧40d处理下。β-氨基葡糖苷酶（NAG）在休牧20d和40d活性较高，休牧50d活性最低。β-葡糖苷酶（BG）活性随着休牧天数增加而增加，但休牧50d则活性最低。总磷脂脂肪酸（total PLFA）在休牧50d最高，土壤中放线菌(Actinomyces)、丛枝菌根真菌（AMF）和革兰氏阴性菌（G-）与total PLFA有相同的趋势。BG:AP解释了微生物群落结构变异的31.1%，且达到显著水平（P=0.014）；土壤温度解释了19.7%（P=0.018）、土壤C:P解释了9.7%（P=0.034）、土壤湿度解释了5.45%（P=0.004）。细菌多样性指数在不同春季休牧期下差异显著，且CK的细菌多样性较高；而真菌多样性在不同春季休牧期下指数差异不显著，但CK真菌多样性也较高。从功能预测结果来看，休牧30d以上处理下腐生营养型真菌较多，休牧40d处理下参与硝化和反硝化作用的细菌功能群增加。因此我们提出在牧草返青开始可进行休牧，直到家畜转场到夏季牧场，为期40-50天时间。但考虑到在休牧期间需对家畜进行舍饲圈养、补喂精饲料，我们建议在春季进行相对短的休牧时间（40d），可兼顾高寒草地的生态效益和经济效益。本项目研究结果对优化放牧制度和提升生态系统功能至关重要，可为制定高寒草甸适宜春季休牧期和草地畜牧业的可持续发展提供科学理论依据。