控雨对荒漠草原植物、微生物和土壤C、N、P化学计量特征的影响

以宁夏荒漠草原为研究对象,于2014—2015年设置了降雨量变化(减雨50%、减雨30%、自然降雨、增雨30%和增雨50%)的野外模拟试验,测定了植物、微生物和土壤C、N、P含量,同时调查了植物群落组成和土壤含水量等指标,研究了各组分C、N、P化学计量特征对连续两年降雨量变化的响应,分析了土壤C∶N∶P和含水量分别与植物生长、养分利用以及微生物量积累的相关性。结果表明,控雨改变了植物叶片C∶N∶P,且其影响程度随物种不同而异:减雨50%提高了牛枝子(Lespedeza potanimill)绿叶N和P以及猪毛蒿(Artemisia scoparia)绿叶P摄取能力,增雨(30%和50%)降低了猪毛蒿绿叶N摄取能力。增雨提高了猪毛蒿绿叶C∶N,增雨30%提高了苦豆子(Sophora alopecuroides)绿叶C∶N。增雨降低了猪毛蒿绿叶N∶P,增雨30%降低了白草(Pennisetum centrasiaticum)绿叶N∶P。相比之下,控雨条件下枯叶C∶N∶P的变化幅度较小;随降雨量增加微生物量C、N以及C∶N逐渐增加,但增雨50%使微生物量C和C∶N降低;控雨对土壤C∶N∶P的影响较小,但增雨提高了土壤水分有效性,因此促进了植物和微生物生长;试验期内,相对稳定的土壤C∶N∶P不能很好地指示植物和微生物生长发育的养分受限状况;干旱时提高叶片养分摄取、湿润时增强叶片养分回收,可能解释了牛枝子对降雨量变化的弹性适应能力。

Effects of precipitation levels on the C: N: P stoichiometry in plants, microbes, and soils in a desert steppe in China

Changes in precipitation are affecting the dynamics of C, N, and P in ecosystems, which are coupled within plants, microbes, and soils. Therefore, studying the responses of C:N:P stoichiometry in plants, microbes, and soils to changing precipitation levels are significant for elucidating how biogeochemical cycling responds to global climate change. Based on a two-year simulated experiment of precipitation change in a desert steppe in the Ningxia region, which was conducted from May 2014 to August 2015 and included five treatments (50% reduction in precipitation, 30% reduction in precipitation, natural precipitation, 30% increase in precipitation, and 50% increase in precipitation), we measured the levels of C, N, and P in plants, microbes, and soils, and explored the C:N:P stoichiometry in these three components of plant-soil systems. Meanwhile, plant communities were investigated and soil water contents, pH levels, and temperatures were monitored. Through the correlation analyses between soil indices and plant and microbe indices, the indications of soil C:N:P stoichiometry for the growth and nutrient conservation of plants (uptake and resorption) and the growth of microbes were estimated, respectively. The results showed that 1) two years of precipitation treatments altered the C:N:P stoichiometry in green leaves of plants and the influences were different among species. Generally, a 50% reduction in precipitation increased the N and P uptakes in green leaves of Lespedeza potanimill and P uptake in green leaves of Artemisia scoparia, whereas both 30% and 50% increases in precipitation decreased the N uptake in green leaves of A. scoparia. Both 30% and 50% increases in precipitation increased the C:N in green leaves of A. scoparia, whereas only a 30% increase in precipitation increased the C:N in green leaves of Sophora alopecuroides. Both 30% and 50% increases in precipitation reduced the N:P in green leaves of A. scoparia, whereas only a 30% increase of precipitation decreased the N:P in green leaves of Pennisetum centrasiaticum. In contrast, two years of precipitation treatments had lesser effects on the C:N:P stoichiometry in senescing leaves of the studied species. 2) Reduced precipitation decreased microbial biomass C, N, and C:N, whereas increased precipitation stimulated an increased microbial biomass accumulation. However, a 50% increase in precipitation inhibited the C accumulation of microbes and thus reduced the C:N. 3) Two years of precipitation treatments had little effect on the soil C:N:P stoichiometry (except soil organic C and C:N). Increased precipitation improved the soil water availability, and thus stimulated the growth of plants and microbes. 4) During 2014-2015, a relatively stable soil C:N:P stoichiometry could not indicate the nutrient limitations for plant growth and microbe reproduction. The self-adjusted nutrient conservation strategy, specifically in increased leaf nutrient uptake when supplied with low precipitation, and enhanced leaf nutrient resorption when supplied with high precipitation, probably explains the high adaptation ability of L. potaninii in response to precipitation change.