Trade-off Strategy of Three Dominant Species in Grazing Exclusion of Desert Steppe,china

Background and AimsGrazing exclusion is a powerful measure to restore the ecological environment in desert steppe. Studying the changing trend of functional traits and trade-off strategy about dominant species what is of great significance to understand the effect of grazing exclusion on species succession. Methods We studied that the change of leaf and root functional traits of three dominant species (Lespedeza potaninii, Agropyron mongolicum and Stipa breviflora) under different term of grazing exclusion. ResultsWe found that the leaf area and leaf nitrogen content, leaf dry matter content, total root length, specific root length and specific root surface of Lespedeza potaninii in grazing were higher than grazing exclusion. The highest specific leaf area, specific root length of Agropyron mongolicum and Stipa breviflora were observed in short-term grazing exclusion. Leaf tissue density and root tissue density significantly decreased in short-term grazing exclusion. Economic spectrum exist, Lespedeza potaninii have more conservation strategy in short-term grazing exclusion compared with grazing. Agropyron mongolicum and Stipa breviflora have more acquisition strategy in grazing exclusion. Average diameters have great effected on above-ground biomass.ConclusionThe result showed that grazing exclusion change leaf and root functional traits of three dominant species, different species have different trade-off strategy.

Nitrogen Uptake by Two Plants in Response to Plant Competition as Regulated by Neighbor Density

Plant species may acquire different forms of nitrogen (N) to reduce competition for the same resource, but how plants respond to neighbors with different densities in their N uptake is still poorly understood. We investigated the effects of competition regime on the uptake of different N forms by two hygrophytes, Carex thunbergii and Polygonum criopolitanum, by conducting a hydroponic test of excised roots and an in situ experiment in a subtropical wetland ecosystem. The two species were grown either in monocultures or mixtures with various neighbor densities. Root functional traits and N uptake rates of different N forms were measured. Our results showed that N uptake was mainly determined by N form, rather than species identity. Both species were able to use organic N sources, but they took up relatively more N supplied as NO3- than as NH4+ or glycine, irrespective of competition treatments. Both species preferred NO3- when grown in monoculture, but in the presence of competitors, the preference of fast-growing C. thunbergii persisted while P. criopolitanum acquired more NH4+ and glycine, with stronger responses being observed at the highest neighbor density. The hydroponic test suggested that these divergences in N acquisition between two species might be partially explained by different root functional traits. To be specific, N uptake rates were significantly positively correlated with root N concentration and specific root length, but negatively correlated with root dry matter content. Our results implicated that C. thunbergii has a competitive advantage with relatively more stable N acquisition strategy despite a lower N recovery than P. criopolitanum, whereas P. criopolitanum could avoid competition with C. thunbergii via a better access to organic N sources, partly mediated by competition regimes.