长芒草不同季节碳氮磷生态化学计量特征

内稳性理论和生长速率理论是生态化学计量学存在的前提和基础。为探讨高等植物不同发育阶段碳(C)、氮(N)、磷(P)元素含量及其计量比的内稳性特征以及与生长速率的关系，研究了黄土高原天然草地建群种植物长芒草（Stipa bungeana）地上组织C、N、P含量季节动态及其化学计量比的变化，探讨家畜采食对植物体内元素内稳性的影响。结果表明，围封样地（1）长芒草3-7月地上生物量逐步增加，且最大生长速率出现在3-5月；3-5月植物体C∶N、C∶P、N∶P显著提高,不符合生长速率理论。（2）长芒草C含量3-5月显著升高，5-9月差异不显著，而N和P含量3月含量最高，5-9月逐渐降低；3-9月，长芒草的C∶N与C∶P表现出逐渐增加的趋势，而N∶P表现出先增大后减小的趋势，不同生育时期长芒草C含量和N∶P的变异系数较小，分别为3.65%和6.60%，表现出较强的内稳性，而N、P含量及C∶N、C∶P的变异系数均大于30%。放牧样地，（1）长芒草叶片N、P含量均高于围封样地，C∶N和C∶P小于围封草地，且5、7月N∶P高于围封草地。（2）长芒草C含量和N∶P变异也较小，但N∶P变异明显大于围封草地，为21.30%。表明放牧影响长芒草C、N、P计量特征，且C、N∶P具有较强的内稳性。

Seasonal dynamics of carbon,nitrogen and phosphorus stoichiometry in Stipa bungeana

Less is known about whether the "Homeostasis Theory" and "Growth Rate Hypothesis" work in higher plants.Our objective was to study the seasonal dynamics of carbon(C)、nitrogen(N) and phosphorus(P) contents and test the "Growth Rate Hypothesis" in wild higher plants.Additionally,we tried to explore the influence of grazing on plants’ homeostasis traits.This study was conducted at Semi-Arid Climate and Environment Obwervatory of Lanzhou University in Loess Plateau(35°57′ N,104°09′ E).We collected the aboveground biomass of Stipa bungeana in the grazed and exclosure treatments in different seasons and quantified the C,N and P contents in the leaf tissue.The specific growth rates of plant S.bungeana were calculated and seasonal dynamics of C∶N,C∶P and N∶P ratios were described.In the exclosure(1) the aboveground biomass of S.bungeana accumulated gradually,and the maximum specific growth rate occurred during the period from March to May.Meanwhile,during this period,plant grew with higher C∶N,C∶P,N∶P ratios.Combined,these results did not support the "Growth Rate Hypothesis";(2) the C content in S.bungeana increased significantly from March to May,but there were no differences among the C contents from May to September.The maximum values of N and P contents occurred in March,but the N and P contents decreased gradually from May to September.From March to September,the C∶N and C∶P ratios increased gradually,but N∶P ratio increased firstly and then decreased.Finally,there were small variations in C content and N∶P ratios(3.65% and 6.60%,respectively) during these four seasons,which showed strong homeostasis in both above parameters.However,there were huge variations in N、P contents and C∶N、C∶P ratios,and all of these values were bigger than 30%.In the grazed treatment(1) the dynamics of C and N contents in S.bungeana were similar to those in the exclosure,but the P content in September was bigger than that in July.Additionally,grazing resulted in higher N and P contents compared to those in the exclosure,and lower C∶N and C∶P ratios in the grazed site.While,N∶P ratios were bigger in grazed site than those in the excosure in both May and July.(2) there were also small variations in C content and N∶P ratios during these four seasons in the grazed treatment,but the variation of N∶P ratios(21.30%) is markedly bigger than that in the exclosure(6.60%).