Nitrogen deposition and management practices increase soil microbial biomass carbon but decrease diversity in Moso bamboo plantations

Abstract

Because microbial communities play a key role in carbon (C) and nitrogen (N) cycling, changes in the soil microbial community may directly affect ecosystem functioning. However, the effects of N deposition and management practices on soil microbes are still poorly understood. We studied the effects of these two factors on soil microbial biomass carbon (MBC) and community composition in Moso bamboo plantations using high-throughput sequencing of the 16S rRNA gene. Plantations under conventional (CM) or intensive management (IM) were subjected to one of four N treatments for 30 months. IM and N addition, both separately and in combination, significantly increased soil MBC while decreasing bacterial diversity. However, increases in soil MBC were inhibited when N addition exceeded 60 kg N∙ha−1∙yr−1. IM increased the relative abundances of Actinobacteria and Crenarchaeota but decreased that of Acidobacteria. N addition increased the relative abundances of Acidobacteria, Crenarchaeota, and Actinobacteria but decreased that of Proteobacteria. Soil bacterial diversity was significantly related to soil pH, C/N ratio, and nitrogen and available phosphorus content. Management practices exerted a greater influence over regulation of the soil MBC and microbial diversity compared to that of N deposition in Moso bamboo plantations.

Effects of Nitrogen Deposition on Soil Dissolved Organic Carbon and Nitrogen in Moso Bamboo Plantations Strongly Depend on Management Practices

“…Our previous study [21] at this site demonstrated that differences in microbial community structure were primarily due to a combination of N deposition and management practices (57.73%), with management practices alone accounting for 36.26% of the variation and N addition accounting for 21.47%, indicating that the combination of two factors has a stronger impact on DOM than each factor singly, which also supported our present result. In summer, the positive effects of high temperature partially offset the negative effects of N deposition and IM alone on DOC and DON, thus contributing to the low combination of these two factors (Table 2).…”

“…Yang et al [31] proved that the growth of plant roots and soil microorganisms (represented by MBC) was enhanced by fertilization, increasing the amount of organic compounds (i.e., DOM) released by plant roots and soil microorganisms. Our previous study on this site showed that IM significantly increased soil MBC [21], indicating an increase in DOC consumption, which might greatly contribute to lower DOC concentrations in the IM plots than in the CM plots. Changed nutrient dynamics caused by management practices can also affect DOM concentrations between the native forests and plantations [27].…”

“…The effect mentioned above contributes to a decline in soil DOC and DON. Notably, N deposition can intensify soil acidification and decrease soil pH [21], which can potentially change the acidity of soil solutions [41][42][43][44]. This, in turn, may lead to the decline in DOC and DON in the CM plots.…”

“…Moso bamboo plantations are mainly distributed in subtropical China, which is suffering severe N deposition of 30-37 kg N ha −1 year −1 [19]. Our previous study [21] found that IM and N deposition significantly increased soil MBC but decreased bacterial diversity, and the combination of management practices and N deposition had greater effects on soil microbial biomass and diversity than either practice system or N deposition independently, which may impact soil DOC and DON. However, the mechanism of DOM response to these complicated factors and subsequent C and N cycles in Moso bamboo plantations remains unknown.…”

“…Typically, conventional management (CM) requires the regular harvest of bamboo stems and shoots, without any of the IM practices mentioned [19]. Thus, IM can affect soil organic carbon (SOC) [20], soil microbial biomass [21], and enzyme activities [22], which may affect the soil DOM. Moso bamboo plantations are mainly distributed in subtropical China, which is suffering severe N deposition of 30-37 kg N ha −1 year −1 [19].…”