Effects of Increasing the Nitrogen-Phosphorus Ratio on the Structure and Function of the Soil Microbial Community in the Yellow River Delta

Abstract

Nitrogen (N) deposition from human activities leads to an imbalance in the N and phosphorus (P) ratios of natural ecosystems, which has a series of negative impacts on ecosystems. In this study, we used 16s rRNA sequencing technology to investigate the effect of the N-P supply ratio on the bulk soil (BS) and rhizosphere soil (RS) bacterial community of halophytes in coastal wetlands through manipulated field experiments. The response of soil bacterial communities to changing N and P ratios was influenced by plants. The N:P ratio increased the α-diversity of the RS bacterial community and changed the structure of the BS bacterial community. P addition may increase the threshold, causing decreased α-diversity of the bacterial community. The co-occurrence network of the RS community is more complex, but it is more fragile than that of BS. The co-occurrence network in BS has more modules and fewer network hubs. The increased N:P ratio can increase chemoheterotrophy and denitrification processes in the RS bacterial community, while the N:P ratio can decrease the N-fixing processes and increase the nitration processes. The response of the BS and the RS bacterial community to the N:P ratio differed, as influenced by soil organic carbon (SOC) content in terms of diversity, community composition, mutualistic networks, and functional composition. This study demonstrates that the effect of the N:P ratio on soil bacterial community is different for plant roots and emphasizes the role of plant roots in shaping soil bacterial community during environmental change.

Keywords: Yellow River Delta; bacterial community diversity; nitrogen and phosphorus input ratio; rhizosphere and bulk soil; salt marshes.

Figure 1

Location of the YRD and experimental site.

Figure 2

The Shannon and Chao1 indexes of bacterial communities in the RS and BS under different N:P ratio treatments. Different lowercase and uppercase letters indicate that the difference between N:P ratio treatments is significant at 0.05 level in the RS and BS, respectively. CK indicates the addition of distilled water.

Figure 3

PCoA of bacterial communities in the rhizosphere soil and bulk soil. CK indicates the addition of distilled water.

Figure 4

The dominant phylum of bacterial communities in the RS and BS communities. Different lowercase letters indicate that the difference is significant. CK indicates the addition of distilled water.

Figure 5

The dominant genera in the RS and BS communities. Different lowercase letters indicate that the difference is significant in the same soil. CK indicates the addition of distilled water.

Figure 6

(A,B) Co-occurrence network of the RS and BS bacterial communities (12 samples). (C,D) Correlation between network modules and soil environmental factors in RS and BS. (E,F) Zi-Pi analysis of RS and BS. *, ** and *** indicate that the correlation coefficients are significant at the 0.05, 0.01, and 0.001 levels, respectively.

Figure 7

Faprotax functional analysis of the BS (A) and RS (B) bacterial communities. Different lowercase letters indicate that the difference is significant at a 0.05 level. CK indicates the addition of distilled water.

Figure 8

The pathway of N cycle of the BS (top) and RS (bottom) bacterial communities. CK indicates the addition of distilled water.

Figure 9

The correlation analysis between the physical and chemical properties and the bacterial community.

Figure 10

RDA analysis and multiple regression analysis. (A) RDA analysis for BS bacterial phlya. (B) RDA analysis for RS bacterial phlya. (C) Effect of the environmental factors on soil bacterial community Shannon diversity in BS and RS from multiple regression models. CK indicates the addition of distilled water.