围栏封育对黄河源区斑块化退化高寒草甸碳交换及其组分的影响

为明确围栏封育对斑块化退化高寒草甸净生态系统碳交换(NEE)不同组分的影响，本研究选取青藏高原黄河源区斑块化退化高寒草甸进行围封试验，设置4个围封年限(1、2、5、11 a)和1个正常放牧对照，研究NEE及组分对不同围封年限的响应。结果表明，围封5 a退化高寒草甸总初级生产力(GPP)和生态系统呼吸(ER)显著大于正常放牧、围封1 a、2 a和11 a,围封2 a和5 a退化高寒草甸NEE显著小于正常放牧、围封1 a和11 a样地(P<0.01),其他NEE组分对不同围封年限的响应情况不一致。植被自养呼吸(Ra)、根系呼吸(Rr)和土壤异养呼吸(Rh)占ER的比例在不同围封年限间差异显著(P<0.01)。此外，土壤温度与NEE呈二次曲线的关系，与ER以及除Rh以外的其他呼吸组分呈指数关系，土壤含水量与NEE、GPP、ER、土壤呼吸(Rs)、Ra、Rr呈线性关系(P<0.05)。全氮、全磷、生物量和NEE及组分存在显著的相关关系。说明围封5 a能显著提高退化草地的土壤养分和固碳功能，并能维持草地生产力，无需进行长期围封。

Effects of enclosure on carbon exchange and its components in patchily degraded alpine meadow in the source region of the Yellow River

To clarify the effects of enclosure on the carbon exchange of patchily degraded alpine meadow ecosystems, this study selected the degraded alpine meadow in the source area of the Yellow River on the Qinghai-Tibet Plateau for enclosure experiments. Four enclosure durations (1, 2, 5, and 11 a) and a normal grazing control were set up to investigate the response of net ecosystem carbon exchange (NEE) and its components to different enclosure durations. The results showed that after 5 a enclosure, the gross primary productivity (GPP) and ecosystem respiration (ER) of the degraded alpine meadow were significantly higher than those of the normally grazed meadow, 1, 2, and 11 a enclosure, while the NEE of the degraded alpine meadow after 2 and 5 a enclosure was significantly lower than that of normalized grazed meadow, 1, and 11 a enclosure (P<0.01). The response of other NEE components to different enclosure durations was inconsistent. The proportions of autotrophic respiration (Ra), root respiration (Rr), and heterotrophic respiration (Rh) in ER differed significantly among different enclosure durations (P<0.01). In addition, soil temperature had a quadratic relationship with NEE and exponential relationships with ER and other respiration components except Rh. Soil water content had linear relationships with NEE, GPP, ER, soil respiration (Rs), Ra, and Rr (P<0.05). Total nitrogen, total phosphorus, biomass, NEE, and its components showed significant correlations amont them. The results indicate that 5 a enclosure can significantly improve soil nutrient content and the carbon sequestration function in the degraded meadows, and maintaining their original productivity, without the need for long-term enclosure.