环青海湖地区天然草地和退耕恢复草地植物群落生物量对氮、磷添加的响应

Responses of plant community biomass to nitrogen and phosphorus additions in natural and restored grasslands around Qinghai Lake Basin

植物群落生物量反映了植被的初级生产能力,是陆地生态系统碳(C)输入的最主要来源,往往受到自然界中氮(N)、磷(P)元素供应的限制。该试验以青藏高原环青海湖地区的高寒草原为研究对象,探讨了天然草地和退耕恢复草地植被群落生物量对N(10 g·m^(–2))、P(5 g·m^(–2))养分添加的响应。N、P添加显著增加了天然草地禾草的生物量,进而促使地上总生物量显著提高。退耕恢复草地禾草和杂类草的生物量对N添加均有一致的正响应,从而促使地上总生物量显著增加174%,群落地上和地下总生物量显著增加34%;而P添加对恢复草地生物量各项参数均无显著影响。回归分析显示:天然草地植物群落地上生物量随土壤中NO_3–-N含量的增加而增加(p<0.05),退耕恢复草地植被地上、地下和总生物量均与土壤NO_3–-N含量显著正相关(p<0.01),说明环湖地区高寒草原植物生长主要受N供应的限制,P的限制作用随土地利用方式的转变和群落演替阶段的不同而变化;相比天然草地,恢复草地在现阶段植被初级生产力受N的限制作用更强烈,土壤中可利用N含量是限制其植被自然恢复和重建的关键因子。

Aims Plant biomass reflects the primary productivity of community vegetation, and is the main resource of car- bon input in the terrestrial ecosystem. It is usually limited by nitrogen （N） and phosphorus （P） availability in the soil. Alpine grassland around Qinghai Lake Basin has experienced extensive land-use changes due to the cultiva- tion of native grassland and vegetation recovery on cropped land. In this experiment, two grassland types were chosen, natural alpine grassland （NG） and its adjacent restored grassland （RG）, to determine the responses of plant community biomass to N and P additions with different land-use. Methods NHaNO3 and Ca（H2PO4）2·H2Owere added in a completely randomized block design, with medium levels of 10 g·m^-2 and 5 g·m^-2. Soil NO3--N and available P contents, and the plant community biomass were measured in the two grasslands. Two-way ANOVA was used to determine the effects of nutrient additions on all measured indicators, and regression analysis was used to analyze the correlations between plant biomass and soil NO3--N and available P contents. Important findings Results showed： （1） N and P additions both increased grass biomass in the NG~ and signifi- cantly elevated the total aboveground biomass, with the promoting effect of N addition higher than that of P addi- tion; N addition significantly increased both grass and forb biomass in the RC and markedly promoted the total aboveground biomass, while P addition had no effects on the functional groups and total aboveground biomass （p 〉 0.05）. （2） N and P additions both had no effects on the belowground and total biomass in the N whereas N addition significantly increased the total biomass by 34% in the RC1 which suggested that the effect of Nlimitation on the vegetation primary productivity was stronger in the RG at present stage. （3） The aboveground biomass in the NG increased with soil NO3--N content （p 〈 0.05）, and the above- and below-ground as well as the total biomass were all positively correlated with soil NO3--N content in the RG （p 〈 0.01）. These results indicated that the plant growth in alpine grassland around Qinghai Lake Basin was prone to N limitation, and the effect of P limitation changed with land-use. Soil available N might be the key limiting factor for vegetation restoration and reconstruction in the RG. The ＂Grain for Green＂ project （the land-use policy） and atmospheric N deposition are benefiting both plant growth and C accumulation in the alpine grassland ecosystem around Qinghai Lake Basin.