The Responses to Long-Term Water Addition of Soil Bacterial, Archaeal, and Fungal Communities in A Desert Ecosystem

Abstract

The response of microbial communities to continual and prolonged water exposure provides useful insight when facing global climate changes that cause increased and uneven precipitation and extreme rainfall events. In this study, we investigated an in situ manipulative experiment with four levels of water exposure (ambient precipitation +0%, +25%, +50%, and +100% of local annual mean precipitation) in a desert ecosystem of China. After 9 years of water addition, Illumina sequencing was used to analyze taxonomic compositions of the soil bacterial, archaeal, and fungal communities. The results showed significant increases in microbial biomass carbon (MBC) at higher amended precipitation levels, with the highest values reported at 100% precipitation. Furthermore, an increase in the bacterial species richness was observed along the water addition gradient. In addition, the relative abundance of several bacterial phyla, such as Proteobacteria, significantly increased, whereas that of some drought-tolerant taxa, including Actinobacteria, Firmicutes, and Bacteroidetes, decreased. In addition, the phyla Planctomycetes and Nitrospirae, associated with nitrification, positively responded to increased precipitation. Archaeal diversity significantly reduced under 100% treatment, with changes in the relative abundance of Thaumarchaeota and Euryarchaeota being the main contributors to shifts in the archaeal community. The fungal community composition was stable in response to water addition. Results from the Mantel test and structural equation models suggested that bacterial and archaeal communities reacted contrastingly to water addition. Bacterial community composition was directly affected by changing soil moisture and temperature, while archaeal community composition was indirectly affected by changing nitrogen availability. These findings highlight the importance of soil moisture and nitrogen in driving microbial responses to long-term precipitation changes in the desert ecosystem.

Keywords: Illumina sequencing; desert; global climate change; microbial community; water addition.

Figure 1

Alpha-diversity of bacterial (a–c), archaeal (d–f), and fungal (g–i) taxonomic communities in different water addition treatments. Boxes represent values from the lower 1/4 quantile to the upper 1/4 quantile. The tops and bottoms of boxes represent the upper 95% CI and the lower 95% CI, respectively. Outliers are drawn as black solid circles above or below boxes. Lowercase letters depict significant differences across treatments. C = ambient precipitation; W25 = ambient precipitation +25% of local annual mean precipitation; W50 = ambient precipitation + 50% of local annual mean precipitation; W100 = ambient precipitation +100% of local annual mean precipitation.

Figure 2

PCoA plots of Bray–Curtis dissimilarities highlighting that bacterial (a), archaeal (b), and fungal (c) communities were significantly different in composition depending on water addition treatments. Circles represent samples from each treatment. C = ambient precipitation; W25 = ambient precipitation +25% of local annual mean precipitation; W50 = ambient precipitation +50% of local annual mean precipitation; W100 = ambient precipitation +100% of local annual mean precipitation.

Figure 3

Relative abundances of microbial phyla in bacterial (a), archaeal (b), and fungal (c) communities. C = ambient precipitation; W25 = ambient precipitation +25% of local annual mean precipitation; W50 = ambient precipitation +50% of local annual mean precipitation; W100 = ambient precipitation +100% of local annual mean precipitation.

Figure 4

Mantel’s correlations between the environmental factors and bacterial, archaeal, and fungal taxonomic communities in different water addition treatments (The widths of lines represent the magnitudes of Mantel’s r statistics and the colors indicate the significance of test; the sizes of colored blocks denote the significance of Pearson correlation between two environmental factors, and the absolute values of the Pearson correlation coefficient were labelled along the colored bar on the right).

Figure 5

Structural equation modeling showing the relationships between plant/soil properties and the bacterial (a) and archaeal (b) community compositions. Solid arrows indicate positive effects, and the dashed arrow indicates a negative correlation. The standardized path coefficients are adjacent to the arrows and indicate the effect size of the relationship. Arrow widths are proportional to the strength of each relationship. Percentages beside the response variables refer to the proportion of variance explained by the model (R²). Results of model fitting: (a) bacteria: χ² = 0.449, df = 2, p = 0.799; CFI = 1.000; AIC = 36.449; RMSEA = 0.000, p = 0.806; (b) archaea: χ² = 1.833, df = 4, p = 0.766; CFI = 1.000; AIC = 35.834; RMSEA = 0.000, p = 0.779. TN, soil total nitrogen; TC, soil total carbon; Temperature, soil temperature at the depth of 20 cm; Moisture, soil moisture at the depth of 20 cm. * p < 0.05, ** p < 0.01, and *** p < 0.001.