Ecostoichiometry Reveals the Separation of Microbial Adaptation Strategies in a Bamboo Forest in an Urban Wetland under Simulated Nitrogen Deposition

Abstract

The effect of nitrogen (N) deposition on N limitation, phosphorus (P) limitation and the related soil and microbial stoichiometries remains unclear. A simulated nitrogen deposition (SND) experiment (control, ambient, medium and high) and molecular techniques (high-throughput sequencing of 16S and ITS) were conducted to examine the variations in abiotic and biotic properties and to describe the responses of microbial (bacteria and fungi) adaptation strategies in a moso bamboo (Phyllostachys edulis J. Houzeau) forest following SND. Soil water content (SWC) was positively correlated with the microbial community composition. Observed increases in total N and nitrate N contents and decreased ammonia N suggested that SND influenced nitrification. Chao1 and F:B showed that bacteria were more sensitive to SND than fungi. PCoA and linear discriminant analysis (LDA), coupled with effect size measurements (LefSe), confirmed that microbial community composition, including the subgroups (below class level), responded to SND by employing different adaptation strategies. Soil C:N indicated that the soil of the moso bamboo forest was under N limitation prior to SND. The increase in total P (TP), available P (AP) and microbial biomass P (MBP) suggested the acceleration of soil P cycling. Microbial biomass C (MBC) and microbial biomass N (MBN) were not affected by SND, which led to a significant shift in MBC:MBP and MBN:MBP, suggesting that P utilization per unit of C or N was promoted. There was a negative gradient correlation between the fungal community composition and MBC:MBP, while bacteria were positively correlated with MBN:MBP. The results illustrated that the response of fungi to MBC was more sensitive than that of bacteria in the process of accelerated P cycling, while bacteria were sensitive to MBN. Prior to P limitation, SND eliminated the soil N limitation and stimulated soil microorganisms to absorb more P, resulting in an increase in MBP, but did not alter MBC or MBN. This study contributes to our understanding of the adaptation strategies of fungi and bacteria and their responses to soil and microbial stoichiometries.

Decomposition and Carbon and Nitrogen Releases of Twig and Leaf Litter Were Inhibited by Increased Level of Nitrogen Deposition in a Subtropical Evergreen Broad-Leaved Forest in Southwest China

“…N addition treatments, thus, would probably reduce the fungi-to-bacteria ratio [55,56]. Furthermore, fungi have been reported to be more effective than bacteria in degrading active organic matter to support high metabolic rates [55,57]. The present study's findings of a lower litter C/N ratio as a consequence of N treatments provided strong evidence that N treatments can reduce the fungi-to-bacteria ratio, thus preventing lignin and cellulose degradation [58].…”

“…Firstly, lowering the C/N ratio led to an elevation in the number of bacteria in the microbial community waiting for such opportunities, which may benefit the accumulation of microbial necromass by increasing microbial C use efficiency. N addition treatments, thus, would probably reduce the fungi-to-bacteria ratio [55,56]. Furthermore, fungi have been reported to be more effective than bacteria in degrading active organic matter to support high metabolic rates [55,57].…”

Phosphorus Reduces Negative Effects of Nitrogen Addition on Soil Microbial Communities and Functions

“…The investment of host plants in mycorrhizal fungi may be decreased for optimal economic strategy, thus hyphae growth and production of mycorrhizal fungi were reduced correspondingly [ 74 , 75 ]. Therefore, increased N deposition and P addition partly weakened the symbiotic relationship between arbuscular mycorrhizal fungi and host plants [ 76 ]. It should be noted that the informations on functional groups of FAPROTAX and FUNGuild databases are established mostly based on the current literature [ 48 , 49 ], and they include limited culturable microbes with defined functions comparing to large and complex soil microbiome; therefore, further researches on functional genes, such as metagenomics sequencing [ 77 ] or functional genes’ quantification (Geochip) [ 78 ], would be helpful for better understanding the response of soil microbial activity to N and P addition in temperate forests of China.…”