Responses of two contrasting saline‐alkaline grassland communities to nitrogen addition during early secondary succession

Abstract

Question (1) How do secondary successional dynamics differ in high and low saline‐alkaline grassland communities in semi‐arid lands; and (2) does nitrogen (N) enrichment promote plant secondary succession towards a perennial community under saline‐alkaline stress? Location Saline‐alkaline grassland in northeast China. Methods We selected two early successional communities differing in soil saline‐alkaline stress and floristic composition: one ‘high‐stress community’ co‐dominated by the annual grass Chloris virgata and the annual forbs Artemisia scoparia and Kochia sieversiana, and one ‘low‐stress community’ dominated by the annual forb K. sieversiana. A complete randomized design experiment with five N addition levels was conducted in triplicate for four consecutive years (2008–2011). The vegetation variables (above‐ground biomass of individual species, functional group, community level, community species richness) and soil characteristics (pH, electrical conductivity as a proxy for salinity) were investigated every year. Detrended correspondence analysis (DCA) was used to evaluate the successional trajectories. Results DCA revealed clear differences in species composition and successional trajectories between the two communities. There were few changes in the species composition of the high‐stress community, with annual species dominating all the plots over the 4 yr. However, most of the low‐stress communities developed from the annual‐dominated stage to the perennial‐dominated stage. N addition had no effect on the relative biomass of the perennial functional group in the two communities. Thus, N addition did not obviously promote plant succession towards a perennial community, even under low saline‐alkaline stress. Species richness did not respond to N addition in the high‐stress community, whereas species richness declined across the N addition gradient in the low‐stress community. Conclusion Our results provided direct empirical evidence that high saline‐alkaline stress limits plant community succession, and low saline‐alkaline stress communities exhibit a succession direction from the annual‐dominated stage to the perennial‐dominated stage. Interestingly, replicates within the same treatment under low‐stress conditions did not develop towards a similar community composition, indicating the importance of environment heterogeneity at a small spatial scale. N addition did not promote the expected perennial plant succession; however, N enrichment reduced plant diversity and enhanced above‐ground biomass, suggesting that artificial N addition (e.g. N deposition) may have an important effect in our system.

Overall supply level, not the relative supply of nitrogen and phosphorus, affects the plant community composition of a supratidal wetland in the Yellow River Delta

“…A possible reason could be that those pot-culture studies were conducted using sand as the substrate which contains no nutrition, therefore the N:P ratio in the substrate could be accurately controlled as same as the nutrient solution supplied. However, there always exist background interference of nutritional status under field condition (Bai et al, 2015). Though supply ratio did affect the soil N:P ratio significantly in our study, variations of soil N:P ratio are far slighter than the Table 4 Repeated measures analysis of variance for Species Richness and Shannon Index using Supply Level, Supply Ratio, Year, and all interactions as fixed-effects.…”

Fine-scale characteristics of the boundaries between annual patches and perennial patches in a meadow steppe

“…With succession proceeding, the patch size and the species richness increase, and the adjacent patches would meet and merge together to form larger but fewer patches. At the final stages, one or two perennial grasses such as L. chinensis should be dominant in these large patches (several hundred square meters) (Bai et al, 2015). Han et al (1996) found that the variation of species number with increasing area of patch shows a humped relationship.…”

Response of soil microbial community structure to increased precipitation and nitrogen addition in a semiarid meadow steppe

“…First, an initial path model is constructed (Figure S1, Supporting Information). Predicted causal relations between variables were based on prior knowledge of the effects of additional N and water on the performance of plant communities (Bai et al ., ) and the correlation analysis. Then the effect of the relative strength of each independent variable on the dependent variable is estimated.…”