草原化荒漠草本植物对人工施加磷素的响应

荒漠地区因土壤水分和养分含量较低而限制了植被的生长，且磷素对于植物的生长具有重要的作用。利用人工施加磷素的控制实验研究了不同磷肥处理对荒漠区草本植物物种丰富度、多度、盖度、生物量、植物株高等群落学特征的影响。实验表明：物种丰富度和多度在施肥量分别为12.5，25和50 g?m-2的梯度下，施肥当年和第二年相较于对照均有所降低，且施肥梯度越高，降低越明显；植被盖度和地上部生物量则在两年的实验中表现出相似的规律，在不同的施肥梯度下均有所提高，高肥处理对其促进作用更大，且在降水充足的07年高于降水较少的08年，说明水肥耦合更有助于群落生产力的提高；优势种株高则对磷素的响应存在种间差异，年际间的差异也较大，这或许与荒漠植物本身特有的生物学特性有关。

Response of herbaceous vegetation to phosphorus fertilizer in steppe desert

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 different water-nutrient regimes. It is inferred that P addition is able to decrease species diversity and improve plant productivity of the desert herbaceous vegetation community in a moist year, whereas low annual precipitation inhibits the residual effect of P fertilizer in the subsequent drier year, which resulted in no significant effect on species diversity and population productivity. Generally, our results indicate that water is the most important abiotic factor for the growth of the desert herbaceous vegetation, and that water and nutrient are colimiting factors in the desert ecosystem.