Response of herbaceous vegetation to phosphorus fertilizer in steppe desert
草原化荒漠草本植物对人工施加磷素的响应

In desert ecosystems, low soil moisture and high soil alkalinity decrease phosphorus (P) bioavailability, which results in a scarcity of soil P. Low soil P availability limits plant growth, development and reproduction, and consequently P is one of the most important limiting factors for vegetation growth and restoration in desert ecosystems. Furthermore, productivity of most plant communities increases following nutrient addition, while species diversity shows different responses to nutrient addition. Nevertheless, little attention has been directed towards identification and quantification of P pools in water-limited desert ecosystems, and results of P fertilization experiments in non-arid regions are not applicable to arid regions receiving <200 mm annual precipitation. The aim of this study was to understand the effects of artificial P addition on the vegetation structure of herbage synusia and to offer a solid basis for long-term restoration and scientific management of desert ecosystems. We selected the herbaceous vegetation in steppe desert on the southeastern margin of the temperate Tengger Desert, northern China, as a case study and collected data through field surveys after artificial addition of P fertilizer in spring. Phosphorus fertilizer was added in the first year, in which the annual precipitation was 271 mm (1.4 times the average annual precipitation). In the second year, no P was applied and the annual precipitation was 127 mm. The species, number of individuals, height and coverage were recorded monthly. Using these data, we analyzed the response in species richness, abundance, coverage, biomass and the height of frequent species of the desert herbaceous vegetation community to artificially amended P under ambient precipitation. Species richness and abundance decreased gradually with increasing level of P fertilization in the first year, and both variables did not change significantly in response to 12.5 and 25 g/m2 fertilization (P > 0.05), but decreased significantly with 50 g/m2 fertilization treatment, compared with the control (P < 0.05). Coverage and aboveground biomass increased gradually with the increase in P fertilization level in the same year, and in the 50 g/m2 fertilization treatment the coverage and aboveground biomass increased by 47.59% and 360.49%, respectively, compared with the control (P < 0.05). In the second year, species richness, abundance, coverage and aboveground biomass all showed no significant difference in the different fertilization treatments compared with the control (P > 0.05). The plant community composition changed markedly following P addition, with species number decreasing from 12 to 6 in the first year and to 5 in the second year. Addition of P decreased root biomass of the herbaceous plants. Artemisia capillaris Thunb., Cleistogenes songorica (Roshev.) Ohwi, Allium polyrhizum Turcz. ex Regel and Tragus berteronianus Schult. showed different responses in plant height to P addition under