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The carbon use efficiency (CUE) of soil microorganisms is a critical parameter for the first step of organic carbon (C) transformation by and incorporation into microbial biomass and shapes C cycling in terrestrial ecosystems. As C and nitrogen (N) cycles interact closely and N availability affects microbial metabolism, N addition to soil may shift the microbial CUE. We conducted a meta-analysis (100 data pairs) to generalize information about the microbial CUE response to N addition in soil based on the two most common CUE estimation approaches: (i)

Litter decomposition is a vital link between material circulation and energy flow in forest ecosystems and is intensely affected by global change factors, such as increased nitrogen (N) deposition and altered precipitation regimes. As essential nutrients, calcium (Ca), magnesium (Mg), and manganese (Mn) play crucial roles in plant energy metabolism, photosynthesis, and membrane transport of plants, and the major source of these nutrients is litter decomposition. However, the dynamics of Ca, Mg, and Mn during decomposition have been largely ignored. Thus, to better understand Ca, Mg, and Mn dynamics during leaf litter decomposition in the scenario of increasing N deposition and decreasing precipitation, we carried out a two-year field litterbag experiment in a natural evergreen broad-leaved forest in the central area of the rainy area of Western China. Two levels of N deposition (ambient N deposition and 150 kg·N·ha−1·y−1) and precipitation reduction (no throughfall reduction and 10% throughfall reduction) were set, i.e., control (Ctr: without nitrogen deposition or throughfall reduction), N deposition (N, 150 kg·N·ha−1·y−1), throughfall reduction (T, 10% throughfall reduction), and N deposition and throughfall reduction (NT, 150 kg·N·ha−1·y−1 and 10% throughfall reduction). We found that leaf litter Ca concentration increased in the early decomposition stage and then decreased, while Mg and Mn concentrations generally decreased during the whole period of decomposition. The amount of Ca showed an accumulation pattern, while Mg and Mn generally showed a release pattern. N deposition and throughfall reduction affected the Ca, Mg, and Mn dynamics, varying with different decomposition stages, i.e., N deposition significantly affected the concentration and amount of Ca, regardless of the decomposition stages, while throughfall reduction significantly affected the Ca concentration in the whole and early decomposition stages. N deposition significantly affected the concentration and amount of Mg in the whole and early decomposition stages, while throughfall reduction had no significant effects. Throughfall reduction significantly affected the concentration and amount of Mn in the whole and late decomposition stages, while N deposition had no significant effects. Ca concentration generally showed a significant positive linear relationship with mass loss in the early decomposition stage, Mg concentration showed a significant positive linear relationship with mass loss in the Ctr and N treatments in the early and late decomposition stages, Mn generally showed a significant negative linear relationship with mass loss, regardless of the decomposition stage. Overall, the results suggest that Ca accumulation is more likely affected by N deposition, while Mg and Mn releases are more likely affected by N deposition combined with throughfall reduction, particularly in the early decomposition stage.

Nitrogen (N) and phosphorus (P) control biogeochemical cycling in terrestrial ecosystems. However, N and P addition effects on litter decomposition, especially biological pathways in subtropical forests, remain unclear. Here, a two-year field litterbag experiment was employed in a subtropical forest in southwestern China to examine N and P addition effects on litter biological decomposition with nine treatments: low and high N- and P-only addition (LN, HN, LP, and HP), NP coaddition (LNLP, LNHP, HNLP, and HNHP), and a control (CK). The results showed that the decomposition coefficient (k) was higher in NP coaddition treatments (P0.05), and lower in N- and P-only addition treatments than in CK (P0.05). The highest k was observed with LNLP (P0.05). The N- and P-only addition treatments decreased the losses of litter mass, lignin, cellulose, and condensed tannins, litter microbial biomass carbon (MBC), litter cellulase, and soil pH (P0.05). The NP coaddition treatments increased the losses of litter mass, lignin, and cellulose, MBC concentration, litter invertase, urease, cellulase, and catalase activities, soil arthropod diversity (S) in litterbags, and soil pH (P0.05). Litter acid phosphatase activity and N:P ratio were lower in N-only addition treatments but higher in P-only addition and NP coaddition treatments than in CK (P0.05). Structural equation model showed that litter MBC, S, cellulase, acid phosphatase, and polyphenol oxidase contributed to the loss of litter mass (P0.05). The litter N:P ratio was negatively logarithmically correlated with mass loss (P0.01). In conclusion, the negative effect of N addition on litter decomposition was reversed when P was added by increasing decomposed litter soil arthropod diversity, MBC concentration, and invertase and cellulase activities. Finally, the results highlighted the important role of the N:P ratio in litter decomposition.

The increase in the nitrogen/phosphorus (N/P) ratio with rising N deposition is changing the biodiversity and function of terrestrial ecosystems at an unprecedented speed. However, the specific effects of P addition and its interaction with N on soil arthropods during litter decomposition in forests are unclear. A two-year experiment was carried out in western China to examine the effects of N and P addition on soil arthropods during litter decomposition. We applied a factorial design in a litterbag experiment combining two levels of low and high N and P alone addition (LN, HN, LP, and HP) and their coaddition (LNLP, LNHP, HNLP, and HNHP), including a no-addition control treatment (CK). The results show that soil pH, litter microbial biomass carbon (MBC), soil arthropod group number (G), individual number (I), diversity index (S), and richness index (M) were lower in the LN and HN treatments than in CK. Compared with CK, the LP and HP treatments reduced I but did not alter G, S, and M. The MBC, soil pH, and G, I, S, and M were higher and the cellulose and lignin concentrations and soil arthropod dominance index values were lower in the LNLP, LNHP, HNLP, and HNHP treatments than in CK. The positive effects of the LNLP, LNHP, HNLP, and HNHP treatments on the soil arthropods were related to the increased MBC and soil pH and decreased cellulose and lignin concentrations and litter N/P ratio. The litter N/P ratio was inversely related to the soil arthropod diversity. In conclusion, the negative effect of N addition on soil arthropod diversity during litter decomposition was reversed when P was added by shifting the MBC, cellulose and lignin concentrations, soil pH, and litter N/P ratio. Thus, increased P availability under rising N deposition scenarios may enhance soil arthropod diversity in this forest.

Acid deposition from the emission of nitrogen (N) and sulfur (S) has become an important factor affecting the soil nutrient balance and biogeochemical cycling in terrestrial ecosystems. The average levels of N and S deposition in the rainy area of southwestern China from 2008 to 2010 were 9.5 g N m−2 y−1 and 19.3 g S m−2 y−1, respectively. External additions of N and S fertilizers combined with high levels of acid deposition may affect the soil ecological stoichiometry in the region’s widely distributed subtropical evergreen broad-leaved forest. Therefore, we investigated the responses of the soil stoichiometric ratios and enzyme activities to added N (+N), added S (+S), added N and S (+NS), and a control (Ctr) in the 0–20 cm layer in an evergreen broad-leaved forest in the rainy area of southwestern China from April 2013 to April 2015. The results showed that the soil total N (TN) concentration and N/P ratio were higher and the soil organic C (SOC) concentration and C/N ratio were lower in the fertilization treatments than the Ctr, although N and S additions did not significantly alter the soil total P (TP) concentration. The +N, +S, and +NS treatments increased the soil acid phosphatase activity and reduced the soil invertase, cellulase, catalase, and polyphenol oxidase activities. The +N and +NS treatments increased the soil urease activity and reduced soil peroxidase activity. The +S treatment reduced the soil urease activity and did not alter soil peroxidase activity. N and S additions had synergistic decreasing effects on the SOC concentration, C/N ratio, and soil cellulose and catalase activities. Moreover, structural equation models identified that N and S additions regulated the SOC, TN, and TP concentrations via shifting the activities of soil enzymes and the pathways differed between N addition and S addition. In conclusion, N and S additions decreased the SOC concentration, C/N ratio, and most soil C-cycle enzyme activities and increased the TN concentration, N/P ratio, and soil acid phosphatase activity. All these results indicated that external N and S additions combined with acid deposition increased soil N concentrations and exacerbated soil C and P limitations in this forest.