天山高寒草原植物叶片氮磷化学计量特征对氮沉降的响应

人类活动和气候变化导致的大气氮沉降急剧升高，将会影响高寒草原植物养分循环。为了研究氮沉降对高寒草原植物养分含量及生态化学计量学特征的影响。依托2009年在新疆天山巴音布鲁克高寒草原设置的长期氮沉降研究平台，于2017年7月和10月采集溚草（Koeleria cristata）、二裂委陵菜（Potentilla bifurca）和天山赖草（Leymus tianschanicus）3种植物的成熟叶和老叶，分析3种植物叶片N、P元素生态化学计量对不同施氮水平的响应规律。结果表明：① 3种植物养分浓度及其化学计量比在成熟叶和老叶之间存在较大差异，成熟叶和老叶的N、P含量分别为12.78 mg·g^-1、0.88 mg·g^-1和6.88 mg·g^-1、0.46 mg·g-1mg·g^-1。3种植物成熟叶和老叶的N元素含量均为：二裂委陵菜>天山赖草>溚草,P元素含量同N元素含量趋势一致；② 氮添加增加了成熟叶和老叶N浓度，分别达12%和48%；成熟叶与老叶P浓度对氮添加的响应规律不一致，成熟叶P浓度对氮添加的响应与物种有关，而老叶P浓度呈一致的下降趋势；氮添加对成熟叶和老叶N∶P的比值影响亦不同，其中相对于成熟叶，老叶的N∶P呈显著增加趋势。③ 植物叶片的N元素、P元素和N∶P比三者之间的相关分析表明:N元素和N∶P之间呈显著正相关关系(P<0.05),在生长旺盛期和枯黄期，溚草和天山赖草的N与P元素之间没有发现显著相关性(P>0.05)，而二裂委陵菜呈现一定的差异性，在生长旺盛期二裂委陵菜叶片N与P元素呈显著的正相关、枯黄期呈显著的负相关(P<0.05)。表明长期氮的添加显著影响了3种植物叶片的养分含量和生态化学计量，不同物种间存在一定差异，未来氮沉降升高将会影响天山山地草原的植物养分循环。

Response of Stoichiometric Characteristics of Nitrogenand Phosphorus in Plant Leaves in an Alpine Grasslands toNitrogen Deposition in the Tianshan Mountains

Atmospheric nitrogen (N) deposition is rapidlyincreased due to the increase of human activities and climate change, whichenhances the N availability and affects the nutrient cycling of plants inalpine grasslands. However, there is still much debate about how the change ofnutrient availability affects P content in plants, therefore, the effects of Naddition on N and P contents and N∶P stoichiometry in mature andsenesced leaves at plant organ level in the Bayinbuluk alpine grasslands in thenorthwest Tianshanin Mountains in China were examined based on a 10-year fieldexperiment. The nitrogen and phosphorus contents in mature and senesced leavesof Potentilla bifurca, Leymus tianschanicus and Koeleria cristata were measured, and thevalues of foliar stoichiometry under N addition treatments at levels of 0,3,9 g·m^-2·a^-1) wereestimated. Results showed that there were the significant differences of thevalues of nutrient concentration and foliar stoichiometry between the matureand senesced leaves. The N contents in mature and senesced leaves were 12.78 mg·g^-1 and 6.88 mg·g^-1,andthe P contents were 0.88 mg·g^-1 and 0.46 mg·g^-1, respectively. N and P concentrations in mature andsenesced leaves were in an order of P.bifurca > L.tiansecalinus > K.cristata. After the N treatments for10 years, the N contents in mature and senesced leaves were increased by 12%and 48% respectively. It was found that there was a divergent response of Pcontent in leaves, the effect of N addition on foliar P content was differentfrom different plant species, and the P content in senesced leaves wasdecreased by N addition. N∶P in senesced leaves wasincreased significantly but not in mature leaves. In addition, the correlationsbetween N and P elements and plant stoichiometry in mature and senesced leaveswere different. There was a positive correlation between foliar N and Pcontents of P.bifurca in matureleaves (P<0.05), but a negativecorrelation in senesced leaves. Our finds revealed that nitrogen additionaffected significantly the nutrient content and stoichiometry in leaves of thethree species, but there was a significant difference among species. Theincrease of N deposition would affect the nutrient cycling of plants ingrasslands in the Tianshan Mountains.