Response of Functional Traits of Key Species in Meadow Steppe to Long-Term Grazing and Grazing Exclusion

The response of plant functional traits to environmental changes and external disturbances reflects the phenotypic plasticity, survival strategies and adaptability of plants. The study on the changes of functional traits of grassland plants under long-term grazing and the recovery response after stopping grazing can provide a theoretical basis for grassland restoration management.

In this study, the changes of leaf functional traits (leaf dry mass, leaf total water content, leaf area, specific leaf area, leaf nitrogen content, leaf phosphorus content, leaf C/N raito, leaf N/P ratio) of six key species (Leymus chinensis,Carex pediformis,Cleistogenes squarrosa,Astragalus adsurgens,Artemisia tanacetifolia L.,Pulsatilla turczaninovii) in Hulunbuir meadow steppe under different grazing intensities during growing season were studied. The immediate recovery response of leaf functional traits of key species in meadow steppe after stopping grazing during growing season was discussed.

(1) The relative biomass and importance values of the six key species decreased with the increase of grazing intensity, and the values of light and heavy grazing intensity after stopping grazing were greater than that after continuing grazing. (2)The leaf dry mass and leaf C/N ratio of six key species decreased with the increase of grazing intensity; the leaf total water content, specific leaf area and leaf nitrogen content increased with the increase of grazing intensity; the leaf area of all species except Artemisia tanacetifolia L. decreased with the increase of grazing intensity; the leaf phosphorus content increased with the increase of grazing intensity except Cleistogenes squarrosa; with the increase of grazing intensity, the leaf N/P ratio of Leymus chinensis,Carex pediformis,Cleistogenes squarrosa,Pulsatilla turczaninovii showed an increasing trend, while that of Astragalus adsurgens,Artemisia tanacetifolia L. decreased. (3) After stopping grazing, the resilience of heavy grazing was higher than that of light grazing, and the functional traits of 6 key species recovered better as a whole, leaf dry mass, leaf total water content, leaf area, specific leaf area and leaf N/P ratio showed positive response, leaf phosphorus content showed negative response, leaf nitrogen content and leaf C/N ratio showed different positive and negative responses among six key species, the negative response of leaf nitrogen content was less than positive response, and the positive response of leaf C/N was more than negative response. (4) The leaf morphological traits of grasses and the nutrient characteristics of miscellaneous grasses were more sensitive to recovery after stopping grazing, and the responses of leaf dry mass, leaf area and leaf phosphorus content to the interaction between grazing intensity and species were more significant. After stopping grazing, leaf dry mass of leaves increased with the increase of leaf area, leaf nitrogen content and leaf N/P of the six key species.

Long-term grazing led to individual miniaturization of grassland plants. After stopping grazing, the positive response of plant functional traits is more than negative response, and the grassland vegetation function shows an obvious recovery response, which increases the productivity of the grassland. Above-ground biomass of the meadow grassland increases.