Abstract
BackgroundThe impacts of increasing nitrogen (N) deposition and overgrazing on terrestrial ecosystems have been continuously hot issues. Grazing exclusion, aimed at restoration of grassland ecosystem function and service, has been extensively applied, and considered a rapid and effective vegetation restoration method. However, the synthetic effects of exclosure and N deposition on plant and community characteristics have rarely been studied. Here, a 4-year field experiment of N addition and exclusion treatment had been conducted in the desert steppe dominated by Alhagi sparsifolia and Lycium ruthenicum in northwest of China, and the responses of soil characteristics, plant nutrition and plant community to the treatments had been analyzed.ResultsThe grazing exclusion significantly increased total N concentration in the surface soil (0-20 cm), and increased plant height, coverage (P < 0.05) and aboveground biomass. Specifically, A. sparsifolia recovered faster both in individual and community levels than L. ruthenicum did after exclusion. There was no difference in response to N addition gradients between the two plants.ConclusionsOur findings suggest that it is exclusion rather than N addition that has greater impacts on soil properties and plant community in desert steppe. Present N deposition level has no effect on plant community of desert steppe based on short-term experimental treatments.
Highlights
The impacts of increasing nitrogen (N) deposition and overgrazing on terrestrial ecosystems have been continuously hot issues
Present N deposition level has no effect on plant community of desert steppe based on short-term experimental treatments
Leaf element concentrations and nutrient resorption efficiency Compared with free grazing, the exclusion treatment decreased Pgreen of A. sparsifolia (P < 0.05) (Fig. 2 d), but showed no significant effect on Ngreen of both plants (Fig. 2 a)
Summary
The impacts of increasing nitrogen (N) deposition and overgrazing on terrestrial ecosystems have been continuously hot issues. A 4-year field experiment of N addition and exclusion treatment had been conducted in the desert steppe dominated by Alhagi sparsifolia and Lycium ruthenicum in northwest of China, and the responses of soil characteristics, plant nutrition and plant community to the treatments had been analyzed. Nutrient resorption patterns can be altered by soil nutrient availability, the divergent results have been found based on either inter- or intra-species studies [5, 16, 20]. Given the increasing N deposition scenarios, studies demonstrated that N addition resulted in higher availability of soil inorganic N [21], increased the leaf N and phosphorous (P) concentrations [22, 23], and decreased the nutrient resorption efficiency [20, 24]. The diverse results indicate that more manipulate experiments are needed for better understanding the regulating mechanisms of N enrichment on ecosystem productivity and predicting plant community composition in a nutritionally restricted ecosystem such as desert steppe
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