Response of plant community functional traits in different grasslands to enclosure and grazing in Horqin Sandy Land

Abstract: Functional traits as a link between plants and environment, express plants' physiological, phenological and morphological adaptive strategy when plants face environment changes. In recent years, some trait-based means show that plant functional traits are some of the most reliable predictors of ecosystem, increasingly used to assess and predict the ecosystem feature and succession. Grazing is one of the most common utilization methods for pasture, affecting the semiarid and arid grassland ecosystems in various ways. It not only alters individual plant growth and population dynamics, but also changes soil properties, ultimately changing the vegetation composition and structure. The influence of grazing on plant communities is much greater than that of individual plant. At the community level, herbivores have extensive range of food intake, and different plant species have different response to nibbling, and therefore, it is more reasonable to explore the influence of grazing at the community level. Based on the changes of 18 dominant species in 4 different types of grassland under grazing and enclosure in Horqin sandy land, in this study, we compared the plant community functional traits in the meadow, Stipa steppe, scattered tree grassland and sandy grassland. We measured the 6 functional traits related to the process of plant growth and photosynthesis in different types of grassland under the condition of enclosure and grazing, and these traits included the plant height, specific leaf area (SLA), leaf dry matter content (LDMC), leaf area (LA), leaf nitrogen content (LNN) and leaf carbon isotopes (δ13C). The results showed that: 1) Long term grazing increased the species richness and dominance of annuals and C4 species, as well as decreased the relative biomass of perennials; 2) The SLA and δ13C in sandy grassland were higher than the other 3 types of grassland, while LDMC showed a reversed trend; 3) Grazing decreased the plant height and LA and increased the δ13C, while the other functional traits in different grasslands did not differ due to grazing; 4) Correlation relationship analysis showed that SLA was significantly and negatively correlated with LDMC in different types of grassland under both grazing and enclosure, suggesting that long term grazing did not change the negative associations of SLA and LDMC; however, long term grazing resulted in the significant and negative correlations between plant height, SLA and δ13C, as well as a significant and positive correlation between SLA and δ13C. In Horqin sandy land, long term grazing increased the proportion of annuals and C4 species, and these species had the lower plant height and LA and the higher water use efficiency, which illustrates that the grassland community adapts to the long term grazing through the change in species competition structure and function strategy trade off. Therefore, to improve the functional traits of plant community by reducing grazing pressure is helpful and meaningful to the vegetation restoration and sustainable management in the degraded grasslands.