Roots are the most critical underground organs of plants. This study investigates the dynamic effects of grazing disturbance on the root functional traits of meadow steppe communities, aiming to clarify the mechanisms by which grazing affects the structure and function of grassland community roots. It provides insights into the regulatory mechanisms and survival strategies of grassland plants under grazing disturbance.

The root functional traits including total root length, number of root tips, number of root forks, root average diameter, root surface area, and total root volume were measured using minirhizotron technology under six grazing intensity treatments: no grazing (G0), light grazing (G1), light moderate grazing (G2), moderate grazing (G3), heavy grazing (G4), and extreme grazing (G5). Each grazing intensity treatment was replicated with nine minirhizotron tubes.

(1) Both below-ground biomass and root-soil ratio exhibited significant decreasing trends with increasing soil depth (P < 0.05). The maximum below-ground biomass and root-soil ratio were observed in the 0-10 cm soil layer under G4 grazing treatment, but there were no significant differences in below-ground biomass among grazing treatments. (2) The root morphological characteristics of meadow steppe communities vary significantly with the progression of the growing season and are affected by grazing intensity, with total root length and number of root forks showing an increasing trend over the growing season, whereas both root average diameter and total root volume reached their maxima in July before subsequent declines. Under varying grazing intensity gradients, root traits exhibit distinct patterns: moderate grazing (G1-G3) promotes root growth in the early growing season, whereas heavy or extreme grazing increases total root length and number of root forks in the late growing season but still reduces root average diameter and total root volume. (3) Specific root length (SRL) and specific root area (SRA) showed an increasing trend as the growing season progressed, peaking in September, while root tissue density (RTD) fluctuated. From June to July, SRL and SRA were highest under G3 grazing intensity, while from August to September, SRL increased with grazing intensity, and SRA decreased. RTD was generally higher under G3-G5 intensities compared to G0-G2. (4) Over time, plant height and coverage increased seasonally and peaked in September, while root-shoot ratio (R:S) decreased. With increasing grazing intensity, both height and coverage significantly decreased significantly in each month, while R:S significantly increased. (5) SRL and SRA were significantly correlated with plant community characteristics, and total root length and RTD were strongly correlated with R:S. However, average root diameter and number of root tips showed no significant correlation with soil factors or plant community characteristics.

The response of root morphological traits to grazing intensity exhibited dynamic differences, reflecting trade-offs in resource acquisition and structural strength at different periods. The functional composition of plant communities was strongly correlated with root traits, warranting further research. This study provides valuable insights into the response mechanisms and adaptability of meadow steppe plant roots to grazing intensity and seasonal dynamics.

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.