若尔盖沙化草甸群落特征和土壤特性的耦合关系

Coupling relationship between community and soil characteristics in Zoige desertified meadow

若尔盖高寒草甸部分地区呈现严重沙化态势,了解植物和土壤之间如何相互作用对揭示沙化过程具有重要意义.选取潜在、轻度、中度和重度4种沙化草甸为研究对象,探究不同沙化程度下高寒草甸的植被特征和土壤理化性质变化规律及二者间的耦合关系.结果表明:(1)随沙化程度加剧,高寒草甸植物群落盖度、高度、地下生物量、总生物量以及地下与地上生物量之比逐步下降,而植物群落α多样性指数和地上生物量呈先增加后降低的趋势,在轻度沙化程度下最大(丰富度为15,Shannon-Wiene指数为2.38,地上生物量为468.94 g/m^(2)).(2)潜在沙化和重度沙化草甸中禾本科生物量最高(1574.66 g/m^(2),400.47 g/m^(2)),轻度沙化草甸中莎草科生物量最高(1863.65 g/m^(2)),中度沙化草甸中杂类草生物量最高(496.02 g/m^(2)),显示出草甸沙化不同阶段植物群落组成和结构的变化.(3)草甸沙化导致土壤容重和pH显著增加,而土壤中的水分和养分含量显著下降.(4)群落盖度、高度和群落总生物量与土壤含水量、全碳、全氮、阳离子交换量、硝态氮和铵态氮呈显著正相关,与土壤容重呈显著负相关;禾本科生物量与土壤含水量、总有机碳、全碳、全氮和阳离子交换量呈显著正相关,与土壤容重呈显著负相关;莎草科生物量与土壤全碳、全氮、硝态氮和铵态氮呈显著正相关,与土壤pH呈显著负相关;杂类草生物量与土壤pH呈显著正相关.可见,土壤铵态氮和总有机碳是高寒草甸沙化过程中决定其土壤肥力以及植被群落结构和组成的主要因素;结果可为草甸沙化治理中物种功能群配置以及促进自然恢复过程提供理论依据.

A few areas of the Zoige alpine meadow in southwestern China have recently exhibited severe desertification.The interaction between plants and soil is significant in revealing the desertification process.Four types of alpine meadows,classified as potential,light,medium,and heavy desertification(PD,LD,MD,and HD,respectively),were selected to explore the changes in vegetation characteristics and soil physical and chemical properties under different desertification levels and the correlation between them.Results showed that(1)plant community coverage,height,underground biomass,total biomass,and underground/aboveground biomass ratio of the alpine meadow gradually decreased as desertification increased.In contrast,the α diversity index and aboveground biomass increased and then decreased with increasing desertification,reaching their maximum values under LD(richness 15,Shannon-Wiene index 2.38,and aboveground biomass 468.94 g/m^(2)).(2)The grass biomass was the highest in the PD and HD meadows(1574.66 and 400.47 g/m^(2),respectively),the sedge biomass was the highest in the LD meadow(1863.65 g/m^(2)),and the forb biomass was the highest in the MD meadow(496.02 g/m^(2)),indicating distinct community composition and structural changes along the different stages of meadow desertification.(3)Meadow desertification significantly increased soil bulk density and pH;however,it decreased soil moisture and nutrient content.(4)Community coverage,height,and total biomass were positively correlated with soil water content,total carbon,total nitrogen,cation exchange capacity,nitrate,and ammonium nitrogen;however,they were negatively correlated with soil bulk density.A significant positive correlation was observed between grass biomass and soil moisture content,total organic carbon,total carbon,total nitrogen,and cation exchange capacity;however,a significant negative correlation was observed with soil bulk density.The biomass of the sedge family was significantly correlated with soil total carbon,total nitrogen,nitrate,and ammonium nitrogen and negatively correlated with soil pH values.A significant positive correlation was observed between grass biomass and soil pH.Therefore,soil ammonium nitrogen and TOC were the main factors determining soil fertility,vegetation community structure,and alpine meadow composition during grassland desertification.The results of this study provide a theoretical basis for the allocation of species work groups and the promotion of natural restoration processes in meadow desertification management.