Interruption after Short-Term Nitrogen Additions Improves Ecological Stability of Larix olgensis Forest Soil by Affecting Bacterial Communities

Abstract

Atmospheric nitrogen deposition can alter soil microbial communities and further impact the structure and function of forest ecosystems. However, most studies are focused on positive or negative effects after nitrogen addition, and few studies pay attention to its interruption. In order to investigate whether interruption after different levels of short-term N additions still benefit soil health, we conducted a 2-year interruption after a 4-year short-term nitrogen addition (10 and 20 kg N·hm^-2·yr^-1) experiment; then, we compared soil microbial diversity and structure and analyzed soil physicochemical properties and their correlations before and after the interruption in Larix olgensis forest soil in northeast China. The results showed that soil ecological stabilization of Larix olgensis forest further improved after the interruption compared to pre-interruption. The TN, C:P, N:P, and C:N:P ratios increased significantly regardless of the previous nitrogen addition concentration, and soil nutrient cycling was further promoted. The relative abundance of the original beneficial microbial taxa Gemmatimonas, Sphingomonas, and Pseudolabrys increased; new beneficial bacteria Ellin6067, Massilia, Solirubrobacter, and Bradyrhizobium appeared, and the species of beneficial soil microorganisms were further improved. The results of this study elucidated the dynamics of the bacterial community before and after the interruption of short-term nitrogen addition and could provide data support and a reference basis for forest ecosystem restoration strategies and management under the background of global nitrogen deposition.

Keywords: bacterial community; bacterial diversity; interruption; nitrogen addition; soil ecological health.

Figure 1

Effect of interruption after short-term N additions on soil environmental factors. CK: 0 kg N hm⁻²·yr⁻¹, LN: 10 kg N hm⁻²·yr⁻¹, HN: 20 kg N hm⁻²·yr⁻¹; (a): soil pH, (b): SWC, (c): TC content, (d): TN content, (e): TP content, (f): C:N value, (g): C:P value, (h): N:P value, (i): C:N:P value. Different lowercase letters indicate differences between high and low N additions in the same year (p < 0.05), Different capital letters indicate differences between 2021 and 2023 at the same N addition (p < 0.05).

Figure 2

Venn plots of interruption after short-term N additions on soil bacteria. CK: 0 kg N hm⁻²·yr⁻¹, LN: 10 kg N hm⁻²·yr⁻¹, HN: 20 kg N hm⁻²·yr⁻¹, (a): August 2021, (b): August 2023, Yellow: control treatment, Red: low-nitrogen treatment, Blue: high-nitrogen treatment.

Figure 3

Effect of interruption after short-term N additions on bacterial diversity indices. CK: 0 kg N hm⁻²·yr⁻¹, LN: 10 kg N hm⁻²·yr⁻¹, HN: 20 kg N hm⁻²·yr⁻¹; (a): Chao1 index, (b): Shannon index, (c): Simpson index. Different lowercase letters indicate differences between high and low N additions in the same year (p < 0.05), Different capital letters indicate differences between 2021 and 2023 at the same N addition (p < 0.05).

Figure 4

Comparison of short-term nitrogen additions and interruption on the abundance of bacterial. (a,b) Bacteria phylum level; (c,d) Bacteria genus level. Note: “Others” indicates the sum of the relative abundance of all gates except the top 20. CK: 0 kg N hm⁻²·yr⁻¹, LN: 10 kg N hm⁻²·yr⁻¹, HN: 20 kg N hm⁻²·yr⁻¹.

Figure 5

Correlation heat map of soil environmental factors and soil microbial community structure. * indicates significant correlation at the 0.05 level, ** indicates high correlation at the 0.01 level.

Figure 6

Redundancy analysis (RDA) of diverse environmental influences associated with dominant taxa of soil bacteria under interruption after short-term nitrogen additions.