Herbivore assemblages affect soil microbial communities by altering root biomass and available nutrients in an alpine meadow

Abstract

Three different herbivore grazing assemblages, namely, yak grazing (YG), Tibetan sheep grazing (SG) and yak and Tibetan sheep co-grazing (MG), are practiced in alpine meadows on the Qinghai-Tibetan Plateau (QTP), but the effects of the different herbivore assemblages on soil microbes are relatively unknown. The microbial community plays an important role in the functional stability of alpine grassland ecosystems. Therefore, it is important to understand how the microbial community structure of grassland ecosystems changes under different herbivore grazing assemblages to ensure their sustainable development. To fill this gap, a field study was carried out to investigate the effects of YG, SG, and MG on plant communities, soil physico-chemical properties and microbial communities under moderate grazing intensity in alpine meadows. Grazing increased the β-diversity of the bacteria community and decreased the β-diversity of the fungal community. The herbivore assemblage affected the microbial community diversity, but not the plant community diversity. Total phosphorus, soil bulk density, root biomass, and plant α-diversity were correlated with both the bacterial and fungal community composition, available phosphorus and soil moisture were correlated only with the bacterial community composition, while available potassium and above-ground net primary production (ANPP) were correlated only with the fungal community composition. Soil available nitrogen, soil available phosphorus and soil bulk density were highest in SG, while ANPP was highest in MG. It was concluded that MG can improve ANPP and stabilize the soil microbial community, suggesting that MG is an effective method for sustainable use and conservation of alpine meadows on the QTP.

Keywords: Qinghai-Tibetan Plateau; herbivore assemblage; plant community; soil microbial community; β-diversity of soil microbes.

Figure 1

Non-metric multidimensional scaling (NMDS) ordination of all sampling units indicating the relative differences in bacterial (A) and fungal (B) community compositions. YG, Yak grazing; SG, Tibetan Sheep grazing; MG, Yak and Tibetan sheep mixed grazing; NG, No grazing.

Figure 2

Relative abundances of bacterial phyla under different herbivore assemblages (A); relative abundances of fungal families under different herbivore assemblages (B); dominant bacterial phyla (C); dominant fungal families (D). Significance level: P< 0.05. YG, Yak grazing; SG, Tibetan Sheep grazing; MG, Yak and Tibetan sheep mixed grazing; NG, No grazing.

Figure 3

Indicator bacteria with LDA scores of 3 or greater in bacterial communities under different herbivore assemblages (A); indicator fungi with LDA scores of 3 or greater in fungal communities under different herbivore assemblages (B). YG, Yak grazing; SG, Tibetan Sheep grazing; MG, Yak and Tibetan sheep mixed grazing; NG, No grazing.

Figure 4

Canonical correspondence analysis using pooled data of bacterial (A) and fungal (B) communities and abiotic and biotic variables (arrows). The values of Axis 1 and 2 are percentages that the corresponding axis can explain. TC, soil total carbon; TN, soil total nitrogen; C/N, carbon/nitrogen; TP, soil total phosphorus; ${\text{NO}}_3^{-}$ -N, soil nitrate; ${\text{NH}}_4^{+}$ -N, soil ammonium; AP, soil available phosphorus; AK, soil available potassium; SBD, soil bulk density; ANPP, above-ground net primary productivity. YG, Yak grazing; SG, Tibetan Sheep grazing; MG, Yak and Tibetan sheep mixed grazing; NG, No grazing.

Figure 5

Piecewise structural equation model (SEM) describing the effects of grazing on soil bacteria (A) and fungi (B) β diversity. TP, soil total phosphorus; ${\text{NH}}_4^{+}$ -N, soil ammonium; AK, soil available potassium.