沙质草地植物功能性状对放牧、增水、氮添加及其耦合效应的响应机制

Abstract

人类活动和气候变化对陆地生态系统结构和功能的影响日益明显。在中国半干旱草原区，植物功能性状对这些变化的响应机制仍不是很清楚。以科尔沁沙质草地植物群落功能性状（CWM_trait）、一年生和多年生植物平均功能性状为研究对象，开展非生长季放牧、增水、氮添加及其耦合效应的模拟控制试验，于2016年8月中旬在沙质草地开展了植物功能性状的调查及测定，主要包括植物高度、比叶面积（specific leaf area，SLA）、叶片干物质含量（leaf dry matter content，LDMC）、叶片氮含量（leaf nitrogen content，LNC）和叶片碳同位素（leaf carbon isotopes，δ¹³C）。结果表明：氮添加显著提高了CWM_height和CWM_LNC（P<0.05），降低了CWM_LDMC（P<0.05），同时放牧和增水的耦合效应对CWM_SLA具有显著影响（P<0.05）；放牧显著降低了一年生植物的平均高度（P<0.05），氮添加显著提高了一年生植物的平均高度、LNC和δ¹³C （P<0.05）；氮添加显著提高了多年生植物的平均SLA、LNC和δ¹³C （P<0.05），同时放牧和增水的耦合效应对多年生植物的平均SLA和LDMC具有显著影响（P<0.05）。主成分分析表明，放牧促进了植物群落和多年生植物SLA与LDMC、LNC和δ¹³C之间的负相关关系，增水促进了植物群落和多年生植物高度与SLA之间的正相关关系以及LDMC、LNC和δ¹³C之间的正相关关系，说明多年生植物在调控沙质草地植物群落响应外界干扰时具有较强的主导性作用。非生长季放牧、生长季禁牧有利于沙质草地的可持续发展和管理，增水能够减缓放牧压力对于草地植物的影响，氮添加有利于植物同化δ¹³C，并提高植物叶片的水分利用效率。;The impacts of human activities and climate change on the structure and function of terrestrial ecosystems have become increasingly obvious. In the semi-arid grasslands of China, the response mechanism of plant functional traits to these changes is still not clear. In this study, the functional traits of plant communities (CWMtrait)in Horqin sandy grassland and the average functional traits of annuals and perennials were used as the research objects. The simulation control experiment of grazing, water increase, nitrogen addition and their coupling effects in the non-growing season was carried out in August 2016. The survey and determination of plant functional traits were carried out on sandy grassland in mid-month, including plant height (height), specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC) and leaf carbon isotopes (δ¹³C). The results showed that nitrogen addition significantly increased CWM_height and CWM_LNC (P<0.05), and decreased CWM_LDMC (P<0.05). At the same time, the coupling effect of grazing and water increase had a significant impact on CWM_SLA (P<0.05). Grazing significantly reduced the average height of annuals (P<0.05), nitrogen addition significantly increased the average height, the LNC and δ¹³C of annuals (P<0.05). Nitrogen addition significantly increased the average SLA, LNC and δ¹³C of perennials (P<0.05). At the same time, the coupling effect of grazing and water increase had a significant impact on the average SLA and LDMC of perennials (P<0.05). Showed that grazing promoted the negative correlation between SLA and LDMC, LNC and δ¹³C of plant community and perennials, and water increase promoted the positive correlation between height and SLA of plant community and perennials, as well as the positive correlation between LDMC, LNC, SLA between δ¹³C of plant community and perennials. The results showed that perennials had a strong leading role in regulating sandy grassland plant community in response to external disturbances. Grazing in the non-growing season and grazing prohibition in the growing season can be used for sustainable development and management of sandy grassland. Increased water can reduce the impact of grazing pressure on grassland plants. Nitrogen addition is beneficial to plant assimilation of δ¹³C and improves the water use efficiency of plant leaves.