Effects of Soil Resources on Species Composition, Plant Diversity, and Plant Biomass in an Alpine Meadow, Qinghai-Tibetan Plateau

Abstract

We investigated the effects of soil resources on species composition, plant diversity, and plant biomass in four alpine Kobresia meadow communities. Species diversity was lower in the Kobresia tibetica swamp meadow community than in the other three communities, but this community was characterized by the highest aboveground and belowground biomass and soil nutrients. Aboveground biomass was positively correlated with soil organic matter and soil total nitrogen in all four alpine meadow communities. The proportion of light fraction organic carbon (LFOC) was positively correlated with soil total organic carbon in all types of grassland. In alpine meadows, belowground biomass mostly occurred at 0-10 cm soil, as did soil nutrients. Community differences in plant species composition were reflected in biomass distribution. The highest total biomass (13,759 ± 497 g/m2) including above- and belowground biomass appeared in the sedge-dominated Kobresia tibetica swamp meadow community. Intermediate biomass (3,235 ± 142 g/m2, 2,645 ± 16 g/m2) was found in the Kobresia pygmaea swamp meadow and Potentilla fruticosa shrubs meadow community, dominated by forbs, sedges, and woody plants. The lowest biomass (2,433 ± 162 g/m2) was observed in the Kobresia humilis meadow, mainly dominated by forbs and grasses. The results indicated that fertility of the vegetation caused a decrease in plant species, increase in plant biomass, and also changes in species composition. Species traits (such as ability to respond to higher nutrient levels) as well as competitive interaction may determine ecosystem function (e.g., productivity). Plants with higher competitive ability would then have access to a greater proportion of available resources, leading to increased total resource uptake by roots, lower nutrient losses from the ecosystems, and increased aboveground and belowground biomass. The distribution of aboveground and belowground biomass is largely influenced by the plant species and growth forms within spatial gradients in soil moisture and edaphic conditions.