Abstract
BackgroundAlthough community structure and species richness are known to respond to nitrogen fertilization dramatically, little is known about the mechanisms underlying specific species replacement and richness loss. In an experiment in semiarid temperate steppe of China, manipulative N addition with five treatments was conducted to evaluate the effect of N addition on the community structure and species richness.Methodology/Principal FindingsSpecies richness and biomass of community in each plot were investigated in a randomly selected quadrat. Root element, available and total phosphorus (AP, TP) in rhizospheric soil, and soil moisture, pH, AP, TP and inorganic N in the soil were measured. The relationship between species richness and the measured factors was analyzed using bivariate correlations and stepwise multiple linear regressions. The two dominant species, a shrub Artemisia frigida and a grass Stipa krylovii, responded differently to N addition such that the former was gradually replaced by the latter. S. krylovii and A. frigida had highly-branched fibrous and un-branched tap root systems, respectively. S. krylovii had higher height than A. frigida in both control and N added plots. These differences may contribute to the observed species replacement. In addition, the analysis on root element and AP contents in rhizospheric soil suggests that different calcium acquisition strategies, and phosphorus and sodium responses of the two species may account for the replacement. Species richness was significantly reduced along the five N addition levels. Our results revealed a significant relationship between species richness and soil pH, litter amount, soil moisture, AP concentration and inorganic N concentration.Conclusions/SignificanceOur results indicate that litter accumulation and soil acidification accounted for 52.3% and 43.3% of the variation in species richness, respectively. These findings would advance our knowledge on the changes in species richness in semiarid temperate steppe of northern China under N deposition scenario.
Highlights
Nitrogen (N) is recognized as a primary factor limiting plant growth in many terrestrial ecosystems, and N fertilization has been widely used to stimulate plant growth and improve productivity [1,2]
Soil pH was significantly reduced by 9%, 12% and 18% in N8, N16 and N32 plots compared with the control, respectively (Table 1)
N addition had no effect on soil available phosphorus (AP) and total phosphorus (TP) concentrations (Table 1)
Summary
Nitrogen (N) is recognized as a primary factor limiting plant growth in many terrestrial ecosystems, and N fertilization has been widely used to stimulate plant growth and improve productivity [1,2]. Annual N input into terrestrial ecosystem has been increased from 34 Tg N yr21(1860s) to 100 Tg N yr (1990s) through the use of N fertilizer, N-fixation of legume plants, fuel combustion and other anthropogenic activities [3]. It is predicted that annual N input will reach to 200 Tg N yr by the year of 2050 [3] This increase in N input has great impacts on ecosystem N cycling [4,5], ecosystem structures and other functions [6,7,8,9]. There are many reports demonstrating that N addition alters the community structure and composition in different terrestrial ecosystems. In an experiment in semiarid temperate steppe of China, manipulative N addition with five treatments was conducted to evaluate the effect of N addition on the community structure and species richness
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