叶重比及株高质量比解释亚高寒草甸禾本科对氮素添加的积极响应

Using leaf mass fractions and height/mass ratios to explain the positive response of Gramineae to nitrogen addition on a sub-alpine meadow

草地生态系统的氮素添加往往增强禾本科的优势度,而该过程的作用机制却鲜有报道。本文以青藏高原亚高寒草甸为研究对象,通过分析不同功能群植物对氮素添加的响应及形态特征差异,探讨禾本科植物对氮素添加的适应机制。结果显示,对照群落代表物种的叶重比、株高质量比与植株高度显著相关(P<0.05),其中禾本科植物的叶重比和株高质量比分别为77.86%和34.32cm·g–1,显著高于杂类草的66.12%和7.20cm·g–1(P<0.05)。氮素添加15g·m–2时显著提高群落生物量(P<0.001)、植株高度(P<0.01)、盖度(P<0.01)以及叶绿素含量(P<0.05),各功能群中仅禾本科和莎草科(即禾草类)生物量比例显著上升(均为P<0.001)、仅禾本科的盖度显著上升(P<0.01);添加氮素与否,禾本科植物的平均植株高度均高于其他功能群植物(P<0.001)。因此,禾本科植物较高的叶重比和株高质量比,提高了其地上资源的竞争能力,使其能够对氮素添加作出快速而有效的响应。

Nitrogen addition tends to increase the dominance of Gramineae in grassland ecosystems. However, the underlying mechanism is rarely reported. We analyzed the morphological characteristics and responses of functional groups to nitrogen addition to explore the adaptation mechanism of Gramineae to nitrogen addition on a sub-alpine meadow on the Qinghai-Tibet plateau. Results showed that the leaf mass fraction (LMF) and height/mass ratio (HMR) were significantly correlated with the plant height for a representative species (P < 0.05). The LMF and HMR of Gramineae were 77.86% and 34.32 cm·g–1, respectively, which is significantly higher (P < 0.05) than those of forbs (66.12% and 7.20 cm·g–1, respectively). Nitrogen addition (15 g·m–2) significantly increased the aboveground biomass (P < 0.001), plant height (P < 0.01), coverage (P < 0.01) and, chlorophyll content (P < 0.05) of the community, for which only the biomass proportions of only Gramineae and sedge increased significantly (both P < 0.001), and coverage of only Gramineae increased significantly (P < 0.01). Plant height of Gramineae was always higher than that of the other functional groups whether nitrogen was added or not (P < 0.001, respectively). Therefore, a high LMF and HMR of Gramineae enhances their competition potential for aboveground resources, and enables them to respond quickly and effectively to nitrogen addition.