[Show abstract][Hide abstract] ABSTRACT: To assess the recovery trajectory and self-maintenance of restored ecosystems, a successional gradient (1, 3, 5, 15, and 30years
after abandonment) was established in a sub-alpine meadow of the eastern Tibetan Plateau in China. Plant communities and soil
carbon and nitrogen properties were investigated and analyzed. Regression analyses were used to assess the models (linear
or quadratic) relating measures of species richness, soil carbon and nitrogen properties to fallow time. We found that species
richness (S) increased over the first 20years but decreased thereafter, and aboveground biomass showed a linear increase
along the fallow time gradient. The richness of different functional groups (forb, grass and legume) changed little along
the fallow time gradient, but their corresponding above ground biomass showed the U-shaped, humped or linear pattern. Soil
microbial carbon (MBC) and nitrogen (MBN) in the upper 20cm showed a U-shaped pattern along the fallow time gradient. However,
soil organic carbon (Corg) and total nitrogen (TN) in the soil at depth greater than 20cm showed significant patterns of linear decline along the
fallow time gradient. The threshold models of species richness reflected best the recovery over the 15year fallow period.
These results indicated that fallow time had a greater influence on development of the plant community than soil processes
in abandoned fields in sub-alpine meadow ecosystem. These results also suggested that although the succession process did
not significantly increase soil C, an increase in microbial biomass at the latter stage of succession could promote the decomposability
of plant litter. Therefore, abandoned fields in sub-alpine meadow ecosystem may have a high resilience and strong rehabilitating
capability under natural recovery condition.
[Show abstract][Hide abstract] ABSTRACT: One of the most important areas in ecology is to elucidate the factors that drive succession in ecosystems. The purpose of our study was to assess the effects of legume species (Medicago sativa, Melilotus suaveolens and Astragalus adsurgens) introduction to abandoned arable land on vegetation development in the Loess Plateau, China. Results from our study showed that addition of legume species strongly affected the composition of recently abandoned-field vegetation. Legume species were effective at reducing the number and dominance of natural colonizers (mainly weeds from the seed bank). The introduction of legume species into newly abandoned fields maintained high total cover and above-ground biomass and could improve soil organic carbon and total nitrogen. However, the effects of the treatments were species-specific. Melilotus suaveolens turned out to be severely suppressive to natural colonizers (weed species). Also, Melilotus suaveolens-adding maintained the highest cover and above-ground biomass and was helpful to improve later succession species, e.g. Stipa breviflora and Astragalus polycladus, to invade and establish. Medicago sativa-adding was superior in enhancing the soil organic carbon and total nitrogen. The present results suggested that addition of legume species with greater cover and biomass strongly suppressed the dominance of the weedy species in early succession and the course of old-field succession may be accelerated by introduction of legume species at least temporarily. However, the experimental period was too short to assess to what extent succession may be affected in the longer term.