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2 Polish Journal of Ecology

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Seasonal Changes of Soil Nitrogen Mineralization Along Restoration Gradient of Sandy Grassland, Northern China

Lv Peng, Zuo Xiaoan, Sun Shanshan, Zhang Jing, Zhao Shenglong, Hu Ya

Polish Journal of Ecology

2020

Vol. 68, nr 4

283--295

Soil nitrogen mineralization strongly affects N availability, thus impacting the primary productivity in ecosystems. The seasonal environmental changes affect soil mineralization in restored sandy grasslands such as a studied mobile dune (MD), a semi-fixed dune (SFD), a fixed dune (FD) and a grassland (G). During the growing season, we examined the association of soil N mineralization rate with vegetation characteristics, soil properties and climatic factors through the multivariate stepwise regression model. The vegetation cover, species diversity, above- and belowground biomass, soil carbon, nitrogen, soil water content (SWC), pH, electrical conductivity, very fine sand, clay and silt fractions increased during sandy grassland restoration. The NH4+-N concentration in MD and SFD was higher than that in FD and G, while NO3--N and inorganic N concentration showed a reverse trend. The NH4+N, NO3--N and inorganic N concentrations in MD, SFD and FD reached to the highest values in June, while in G they were highest in May. The net mineralization and nitrification rates increased with sandy grassland restoration; both of these rates were much greater in June than in other months at all sites. Regression analysis showed that the NO3--N concentration, SWC, pH of the soil and precipitation could explain 75% of the total variation in net nitrification rate, and the NO3--N concentration and precipitation could explain 59% of the total variation in the net mineralization rate. These results illustrate that the sandy grassland restoration can enhance the soil N availability, with soil N mineralization mainly determined by the changes of the NO3--N concentration and precipitation.

Plant Functional Trait Response to Habitat Change and Grazing in a Semiarid Grassland : Unravelling Species Turnover and Intraspecific Variation Effects

Zhang Jing, Zuo Xiaoan, Lv Peng, Zhao Shenglong, Zhao Xueyong

Polish Journal of Ecology

2019

Vol. 67, nr 1

62--74

Plant community assembly is determined by species turnover and intraspecific trait variations (ITV) controlled by environment changes. However, little is known about how species turnover and ITV affect the responses of plant community to habitat changes and grazing disturbance in semiarid grasslands. Here, we measured five functional plant traits in four typical grassland habitats under fencing and grazing disturbance in a semiarid grassland, Northern China, including plant height, specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC) and leaf carbon: nitrogen ratio (C:N). We also calculated the community weighted means (CWM) and non-weighted means (CM) of all traits and examined the relative roles of species turnover and ITV in affecting the responses of community traits to habitat changes and grazing disturbance. Our results showed that the CWM and CM values of five functional traits differed with grassland habitat changes. As compared to other grasslands, the Stipa steppe had the higher plant height, the sandy grassland had the higher SLA and lower LDMC, and the meadow had the lower LNC and higher C:N. Grazing decreased plant height across grassland habitats, as well as decreased SLA and increased LDMC in meadow. The responses of all community-level traits to habitat changes were driven by species turnover, while the responses of phenotypic traits (height, SLA and LDMC) to grazing were determined by both species turnover and ITV. So, we argue that ITV should be considered when understanding plant community assembly under grazing disturbance regime in semiarid grasslands.