放牧对青藏高原东部两种典型高寒草地类型凋落物分解的影响

为认识放牧对青藏高原东部中生性的高寒草甸草地和半湿生的沼泽草地凋落物分解的影响,在这两种草地上分别设置了围栏和放牧样地,研究了其各自的混合凋落物样品和4个优势物种(发草Deschampsiacaespitos、鹅绒委陵菜Potentilla anserine、木里苔草Carexmuliensis、藏嵩草Kobresiatibetica)凋落物的分解和养分释放动态,这4个优势物种也大致代表了当地沼泽草地生态系统在放牧和气候变暖驱动下逆行演替不同阶段的优势物种类群。结果表明,各优势物种凋落物的分解速率有显著差异;放牧在总体上促进了凋落物的分解,但不同物种的响应有所不同;放牧对凋落物C的释放影响不显著或有抑制作用,但对N、P的释放具有一定促进作用。对各优势物种凋落物分解和养分释放模式的分析表明,群落逆行演替过程中,凋落物分解和C释放加速,可能促进沼泽湿地退化的正反馈效应。草甸草地的退化标志物种鹅绒委陵菜具有较高的凋落物质量和分解速度,反映了中生条件下植物应对牲畜啃食采用"逃避"而非"抵抗"策略的趋向。

Effects of grazing on litter decomposition in two alpine meadow on the eastern Qinghai-Tibet Plateau

Litter decomposition is an important component of nutrient cycling and carbon decomposition in grassland ecosystems,and livestock grazing has been a major human intervention to these process.The effects of grazing on litter decomposition vary with climate environment conditions and grassland vegetation types.Alpine mesophytic meadow and alpine semi-hydric marsh meadow are the two rangeland ecosystems commonly seen on the eastern Qinghai-Tibet Plateau,which differentiate themselves by not only the physic/bio environments but also the plant species composition and therefore the litter qualities.In order to understand grazing effects on the litter decomposition of these two meadows,grazed and fenced plots were set respectively on the both meadows.The rates of decomposition and nutrient release were measured for the three littler samples(mesophytic meadow mixed litter,Deschampsia caespitos litter,and Potentilla anserine litter) in the alpine mesophytic meadow plots,and three litter samples(semi-hydric marsh mixed litter,Carex muliensis litter、Kobresia tibetica litter) in the semi-hyddric marsh meadow plots.The four species generally also represented the dominant species showing respectively in the reverse succession series driven by grazing and climate warming.It was found that there were significant differences in litter decompositions for the dominant species.In alpine mesophytic meadow,Potentilla anserine decomposed faster than Deschampsia caespitos,while in alpine semi-hydric meadowKobresia tibetica decomposed more quickly.Grazing accelerated the litter decomposition in general,but the responses varied with the species.On the other hand,Deschamp siacaespitos and Carex muliensis have lower decomposition rates in the grazed plots.Grazing has little effect on organic carbon decomposition and the release of C,but positively affected on the release of N and P from the litters.The patterns of litter decomposition and nutrient release of the dominant species suggested that there might exist a positive feedback effect in the alpine marsh meadow degradation due to the accelerating decomposition rate and C release along the reverse succession series.In addition,Potentilla anserine,a typical dominant species of in degraded meadow,was found to have higher litter quality and faster decomposition rate than the other species,reflecting that in the mesophytic community,the plant adopted ’evasion strategy’ rather than ’resistance strategy’ in response to heavy grazing.