Soil microbes make up a significant portion of the genetic diversity and play a critical role in belowground carbon (C) cycling in terrestrial ecosystems. Soil microbial diversity and organic C are often tightly coupled in C cycling processes; however, this coupling can be weakened or broken by rapid global change. A global meta-analysis was performed with 1148 paired comparisons extracted from 229 articles published between January 1998 and December 2021 to determine how nitrogen (N) fertilization affects the relationship between soil C content and microbial diversity in terrestrial ecosystems. We found that N fertilization decreased soil bacterial (−11%) and fungal diversity (−17%), but increased soil organic C (SOC) (+19%), microbial biomass C (MBC) (+17%), and dissolved organic C (DOC) (+25%) across different ecosystems. Organic N (urea) fertilization had a greater effect on SOC, MBC, DOC, and bacterial and fungal diversity than inorganic N fertilization. Most importantly, soil microbial diversity decreased with increasing SOC, MBC, and DOC, and the absolute values of the correlation coefficients decreased with increasing N fertilization rate and duration, suggesting that N fertilization weakened the linkage between soil C and microbial diversity. The weakened linkage might negatively impact essential ecosystem services under high rates of N fertilization; this understanding is important for mitigating the negative impact of global N enrichment on soil C cycling.

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Carbon (C):nitrogen (N):phosphorus (P) stoichiometry in plants, soils, and microbial biomass influences productivity and nutrient cycling in terrestrial ecosystems. Anthropogenic inputs of P to ecosystems are increasing; however, our understanding of the impacts of P addition on terrestrial ecosystem C:N:P ratios remains elusive. By conducting a meta‐analysis with 1413 paired observations from 121 publications, we showed that P addition significantly decreased plant, soil, and microbial biomass N:P and C:P ratios, but had negligible effects on C:N ratios. The reductions in N:P and C:P ratios became more evident as the P application rates and experimental duration increased. The P addition effects on terrestrial ecosystem C:N:P stoichiometry did not vary with ecosystem types or climates. Moreover, the responses of N:P and C:P ratios in soil and microbial biomass were associated with the responses of soil pH and fungi:bacteria ratios. Additionally, P additions increased net primary productivity, microbial biomass, soil respiration, N mineralization, and N nitrification, but decreased ammonium and nitrate contents. Decreases in plant N:P and C:P ratios were both negatively correlated to net primary productivity and soil respiration, but positively correlated to ammonium and nitrate contents; microbial biomass, soil respiration, ammonium contents, and nitrate contents all increased with declining soil N:P and C:P ratios. Our findings highlight that P additions could imbalance C:N:P stoichiometry and potentially impact the terrestrial ecosystem functions.

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Nitrogen (N) and phosphorus (P) deposition have increased rapidly during the past decades, which likely changes soil N and P availability. These soil resource variations will further affect N, P concentration and N:P ratio in different ecosystem pools (i.e., soil, leaf, litter, root, and microbe). Various pools may show different stoichiometric responses to nutrient enrichment, with a further influence on ecosystem nutrient cycling. However, few studies have been conducted to fully examine the stoichiometric responses of different pools and their nutrient relationships in a given ecosystem. Here we established a 2‐year experiment of N (10 g m−2 year−1), P (10 g m−2 year−1), and combined N + P addition in a temperate forest of Changbai Mountain. We found significantly different N:P stoichiometric responses among various ecosystem components under P addition, with the leaves showing a higher response than litter and root while microbe behaving the lowest response. The responses of N:P ratio to N + P addition were similar with those under P addition in all pools. In most cases, N addition did not significantly affect N:P ratio. These results indicate that N:P ratio response was mainly determined by changes in P rather than N concentration in this temperate forest ecosystem. Moreover, we found tighter N:P stoichiometric correlations than elements among diverse ecosystem components under nutrient addition. Overall, our research reveals different responses and tight links of element stoichiometric variations among various ecosystem components in face of nutrient enrichment. It calls our attention to considering stoichiometric changes in the whole ecosystem beyond individual plant organ or microbial component.

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