Effect of different grazing intensities on bacterial community composition and diversity in rhizosphere and non-rhizosphere soils in desert steppe of China

Abstract

Degradation and desertification are extremely significant environmental problems in arid and semi-arid grassland ecosystems. Long-term overgrazing is the most fundamental cause of grassland degradation. We investigated relationships between grazing intensity and bacterial communities in non-rhizospheric and rhizospheric soils in desert steppe, including 0-10, 10-20 and 20-30 cm depth soils, as well as Stipa breviflora Griseb., Cleistogenes songorica (Roshev.) Ohwi, Artemisia frigida Willd. and plant community rhizospheric soils. This involved simulating grazing intensities in a long-term localization experiment, using a randomized block design. The effects of grazing on non-rhizospheric soil bacterial abundance were reflected in the 0-10 cm layer, increasing under light grazing and decreasing rapidly under moderate and heavy grazing, mainly related to Bacillus. Bacterial abundance in dominant plant rhizosphere responded differently. In A. frigida Willd. Rhizosphere, it decreased with increasing grazing intensity (a trend repeated in mixed rhizosphere). Bacterial abundance in S. breviflora and C. songorica rhizosphere increased under light and decreased under moderate and heavy grazing. Thus, changes in the dominant plant rhizospheric bacterial community did not significantly affect bacterial abundance in mixed rhizosphere. Changes in the rhizospheric bacterial abundance mainly resulted from levels of the dominant species, Streptomyces and Arthrobacter. There were significantly different results for bacterial community structure. Specifically, grazing had a nonsignificant and significant impact on bacterial community structures in non-rhizospheric (F PERMANOVA = 1.38, p = 0.199) and rhizospheric (FPERMANOVA = 2.03, p = 0.012) soil, respectively, varying significantly among plants (FPERMANOVA = 1.9, p = 0.022). In conclusion, bacterial communities in rhizosphere were mainly affected by plant species and were more sensitive to changing grazing intensity than in non-rhizospheric soil.

Time-course of soil microbial communities in different tillage and crop rotation systems

“…However, the bacterial populations showed the same concentration in the 0-5 and 5-15 cm strata, while fungal populations were significantly equal between 5-15, and 15-30 cm. This pattern coincides with studies in which microbial biomass often decreases with soil depth (Hartmann et al, 2009;Zhang et al, 2019). Eilers et al (2012), when analyzing soil microbial communities at different depths, found significant differences between profiles separated by 10 cm, and the same was observed in the present study.…”

Characterization of soil microbes associated with a grazing‐tolerant grass species, Stipa breviflora, in the Inner Mongolian desert steppe

“…These results are consistent with previous findings that grazing has a significant impact on the rhizosphere bacterial community structure, but has no effect on bulk soil bacterial community structure in S . breviflora desert steppe (Zhang et al., 2019). Evidence suggests that effects of grazing on soil microbes have been attributed to increased release of root exudates that are rapidly used by rhizosphere microbes and increase available N in plant shoots; this process may result in a positive feedback to the plant of improved nutrient recycling and uptake (Bardgett et al., 1998).…”

Effects of grazing intensity on diversity and composition of rhizosphere and non‐rhizosphere microbial communities in a desert grassland

“…An intriguing result from our experiment was that the rhizosphere bacterial diversity was more sensitive to grazing intensity than that in non‐rhizosphere (Zhang et al, 2019 ). As indicated in Figure 2a , the rhizosphere bacterial richness declined dramatically under heavy grazing intensity, while that in non‐rhizosphere remained unchanged (Zhang et al, 2019 ). Such differing responses also held for other diversity indices, including Shannon diversity, ACE, Chao1, and phylogenetic diversity (Figure A2 ).…”

“…These inconsistent results suggest that the impacts of grazing on microbial communities are likely to be mediated by grazing intensity and grazing history. Moreover, a previous study indicated that grazing could alter the composition of microbial communities in rhizosphere soil rather than in non‐rhizosphere soil (Zhang et al, 2019 ), highlighting the contrasting responses of microbial communities between rhizosphere and non‐rhizosphere soils. In fact, soil microbial communities can differ greatly in diversity and composition between the two zones because host plants usually exert a select effect on microbial taxa in their rhizosphere soil (Hartmann et al, 2009 ; Nan et al, 2020 ).…”

“…Overgrazing not only reduces vegetation cover, decreases plant production, and alters vegetation composition (Wei et al, 2013 ) but also has profound impacts on the diversity and composition of soil microbial communities (Hu et al, 2017 ; Lamb et al, 2011 ; Wang, Ding, et al, 2021 ; Zhang et al, 2020 ). Some studies in desert steppe ecosystems showed that grazing could significantly reduce the diversity of microbial communities in bulk soil and in rhizosphere soil (Wang, Ding, et al, 2021 ; Zhang et al, 2019 ). In contrast, another study in the same ecosystem showed that grazing had little effect on bacterial diversity and fungal diversity in rhizosphere soil, nor in bulk soil (Chen et al, 2020 ).…”