Artemisia smithii patches form fertile islands and lead to heterogeneity of soil bacteria and fungi within and around the patches in alpine meadows of the Qinghai-Tibetan Plateau

Abstract

Herbivore-avoided plant patches are one of the initial characteristics of natural grassland degradation. These vegetation patches can intensify the spatial heterogeneity of soil nutrients within these grasslands. However, the effects of non-edible plant patches patches on the spatial heterogeneity of microorganisms have not been sufficiently studied in alpine meadows of the Qinghai-Tibetan Plateau, especially patches formed by herbaceous plants. To answer this question, soil nutrients, plant assembly, and microbial communities were measured inside, around, and outside of Artemisia smithii patches. These were 0 m (within the patch), 0-1 m (one meter from the edge of the patch), 1-2 m (two meters from the edge of the patch), 2-3 m (three meters from the edge of the patch), and >30 m (non-patch grassland more than thirty meters from the edge of the patch). Our results showed that A. smithii patches accumulated more aboveground biomass (AGB) within the patches (0 m), and formed fertile islands with the soil around the patches. Additionally, A. smithii patches increased soil bacterial diversity within (0 m) and around (0-1 m) the patches by primarily enriching copiotrophic bacteria (Actinobacteria), while the diversity of fungal communities increased mainly in the 0-1 m area but not within the patches. Bacterial community diversity was driven by pH, urease, nitrate nitrogen (NO₃ ^--N), and microbial biomass carbon (MBC). The contents of soil water (SWC), soil organic matter (SOM), urease, NO₃ ^--N, and MBC were the main factors influencing the diversity of the fungal community. This study elucidates the vegetation, nutrients, and microbial heterogeneity and their interrelationships, which are observed in fertile islands of herbivore-avoided plant patches in alpine meadows, and provides further insights into the spatial pattern of nutrients in patchy degraded grasslands.

Keywords: Artemisia smithii; alpine meadows; fertile islands; herbivore-avoided plant patches; heterogeneous distribution; soil microorganism.

Figure 1

Observed phases of Artemisia smithii expansion in the Qinghai Tibetan Plateau.

Figure 2

The location of the study area and the sampling sites.

Figure 3

The relative abundance of the dominant bacterial (A, B) and fungal (C, D) communities at the phylum and genus level inside and outside the patches of Artemisia smithii.

Figure 4

The characteristics of soil bacterial and fungal diversity and richness indices inside and outside the patches of Artemisia smithii. (A–D) were Shannon, Simpson, Chao1, and ACE indexes of bacterial communities, respectively; (E–H) were Shannon, Simpson, Chao1, and ACE indexes of fungal communities, respectively. (*, p<0.05; **, p<0.01; ***, p<0.001).

Figure 5

Non-metric multidimensional scaling (NMDS) of bacterial (A) and fungal (B) communities based on the Bray-Curtis distances and flower plot of bacteria (C) and fungi (D) inside and outside the patches of Artemisia smithii.

Figure 6

Results of linear discriminant analysis (LDA) effect size (LEfSe). Bacterial (A) and fungal (B) taxon nodes that significantly enriched in each treatment were shown in color, and branch areas were shaded according to the highest ranked variety for that taxon. Only taxa with LDA score > 4.0 were shown.

Figure 7

The redundancy analysis (RDA) of the bacterial (A, B) and fungal (C, D) communities at the phylum and genus level with environmental factors inside and outside the patches of Artemisia smithii. SWC, soil water content; TN, total nitrogen; TP, total phosphorus; SOM, soil organic matter; AN, alkali-hydrolyzable nitrogen; AP, available phosphorus; NO₃ ⁻-N, nitrate nitrogen; NH₄ ⁺-N, Ammonia nitrogen; MBC, microbial biomass carbon; MBN, microbial biomass nitrogen; MBP, microbial biomass phosphorus.

Figure 8

Mantel test for the correlation between community composition and environmental variables for bacteria and fungi based on α-diversity. Pairwise comparisons of environmental factors with a color gradient denoting Spearmen’s correlation coefficient. Edge width corresponds to the Mantel’s r statistic for the corresponding distance correlations, and edge color denotes the statistical significance. The solid and dotted lines indicate positive and negative effects between the variables, respectively. SWC, soil water content; TN, total nitrogen; TP, total phosphorus; SOM, soil organic matter; AN, alkali-hydrolyzable nitrogen; AP, available phosphorus; NO₃ ⁻-N, nitrate nitrogen; NH₄ ⁺-N, Ammonia nitrogen; MBC, microbial biomass carbon; MBN, microbial biomass nitrogen; MBP, microbial biomass phosphorus.

Figure 9

The dynamic changes in soil microbial networks. The co-occurrence network was investigated under different treatments for soil bacterial community (A), fungal community (B). The top 100 microorganisms with relative abundance ranking at the genus level were selected for correlation analysis (Spearman correlation coefficient p>0.5, p<0.05). Each node in the network has a different color based on its phylum, and node size was weighted according to the degree. Red links represent positive correlations between nodes, and green links represent significant correlations between nodes.