氮添加对内蒙古退化草地植物群落多样性和生物量的影响

Effects of nitrogen addition on the plant diversity and biomass of degraded grasslands of Nei Mongol, China

人为干扰及气候变化导致内蒙古草地发生了大面积退化,氮添加是促进退化草地生产力恢复的一项重要措施。该文基于2011年建立的氮肥添加实验平台,以3个不同退化程度(中度退化、重度退化、极度退化)草地群落为研究对象,设置对照、10、20、30、40和50 g·m^(-2)·a^(-1) 6种氮添加处理,分析氮添加对退化草地恢复过程中群落多样性和生物量的影响。结果表明:(1)氮添加降低了中度、重度退化草地恢复进程中物种丰富度和多样性,对极度退化草地恢复进程中物种丰富度和多样性无明显影响。(2)氮添加促进了3个不同退化程度草地恢复进程中群落地上生物量的增加。(3)氮添加显著增加了群落中禾草的地上生物量及其在群落地上生物量中所占的比例,降低了杂类草在群落地上生物量中的比例,但对杂类草地上生物量无显著影响。研究表明在利用施肥措施治理退化草地的过程中,需要充分考虑草地退化程度以及由氮添加引起的群落多样性和生产力的改变对草地生态系统功能的影响。

Aims Anthropogenic disturbances and climate change have resulted in large scale degradation of grasslands across the landscapes in Nei Mongol. Fertilization, especially with nitrogen（N） addition, has been proposed and applied as an important management practice to promote primary production for these degraded grasslands. In this study, we examined the changes in plant diversity and biomass at three levels of degradations with N addition. Methods Nitrogen addition experiment was installed in 2011. Six levels of N addition（0, 10, 20, 30, 40, and 50 g·m^-2·a^-1） were conducted at grasslands with three levels of degradations. Nitrogen was added at the beginning of each month from May to August each year. We investigated the changes in plant species richness and aboveground biomass by species in August, 2016. The total biomass of the community, as well as the biomass of each plant functional group（grasses and forbs） was calculated based on species composition. Important findings We found that：（1） N addition decreased species richness and diversity at communities under moderate and severe degradations, but insignificant under extreme degradation.（2） N addition increased the aboveground biomass at communities under three levels of degradations.（3） N addition increased the aboveground biomass of the grasses and its proportion to the total biomass, but not on the total biomass of the forbs although it also decreased the proportion of aboveground biomass. These results indicate that the impacts of N addition on ecosystem function depended on plant function type. In addition, the fertilization effects should are examined at community level and by the degree of the degradation.