Mechanism underlying temperature sensitivity of soil organic carbon decomposition: A review.

Temperature sensitivity (Q10) of soil organic carbon (SOC) decomposition is an important index to estimate the dynamics of soil C budget. However, the spatial variation of Q10 and its influencing factors remain largely uncertain. In this study, we reviewed the effects of climate environment, spatial geographic pattern, soil physicochemical property, vegetation type, microbial community composition and function, and global climate change on Q10 to summarize the general rule of each factor influencing Q10 and compare the relative contribution of each factor to Q10 in different ecosystems. The results showed that Q10 decreases with the increases of temperature and precipitation, but increases with the rise of latitude and altitude. The Q10 value is higher in grassland than that in forest, and also in coniferous forest and deciduous forest than that in evergreen broad-leaved forest. Carbon quality is negatively correlated with Q10, but the C quality hypothesis is not always valid with exogenous substrate input. For example, the increment of substrate availability may significantly increase Q10 in low-quality soils. Q10 decreases with the enhanced proportion of r-strategy microorganisms (Proteobacteria and Ascomycetes), but increases with the enhanced proportion of K-strategy microorganisms (Acidobacteria and Basidiomycetes). Q10 increases with elevated CO2 concentration, but declines with atmospheric nitrogen deposition. In natural ecosystems, Q10 is mainly regulated by temperature and C quality. Temperature is the main factor regulating Q10 in the topsoil while C quality is the main factor in deep soil. Our review provided a theoretical support to improve the coupled climate-C cycle model and achieved the C neutral strategy under global warming.

[Effects of nitrogen deposition and management intensity on stoichiometry of leaf litter in Moso bamboo forest.] / 氮沉降和经营强度对毛竹林凋落叶生态化学计量特征的影响.

In this study, a field experiment was conducted to estimate the effects of simulated nitrogen (N) deposition (low-N: 30 kg N·hm-2·a-1, moderate-N: 60 kg N·hm-2·a-1, high-N: 90 kg N·hm-2·a-1) on ecological stoichiometry of leaf litter in Moso bamboo forest under conventional management (CM) and intensive management (IM) practices. The results showed that compared with CM, IM significantly increased C, N and P concentrations of leaf litter by 9.3%, 32.4% and 22.7%, respectively, but significantly decreased C:N, C:P and N:P ratios by 17.4%, 54.3% and 44.6%, respectively. In CM Moso bamboo plots, low- and moderate-N deposition significantly increased C, N and P concentrations of leaf litter but decreased C:N, C:P and N:P, high-N deposition significantly increased C, N concentrations, C:P and N:P, but decreased P concentration. In IM Moso bamboo plots, low-N deposition significantly increased P concentration but decreased C concentrations, C:P and N:P, moderate-N deposition significantly increased N and P concentrations but decreased C concentration, C:N, C:P and N:P, high-N deposition significantly increased C:N, C:P and N:P but decreased P concentration. The interaction of management intensity and N deposition significantly influenced stoichiometry of leaf litter, except for C:N. The P concentration of leaf litter was significantly correlated with P concentration in soils.

[Effects of simulated nitrogen deposition and management type on soil enzyme activities in Moso bamboo forest.] / æ¨¡æ‹Ÿæ°®æ²‰é™åŠç»è¥æ–¹å¼å¯¹æ¯›ç«¹æž—åœŸå£¤é ¶æ´»æ€§çš„å½±å“.

In this study, a field experiment was conducted using simulated N deposition method in conventionally managed (CM) and intensively managed (IM) Moso bamboo forests to test the responses of five soil enzymes (including ß-fructofuranosidase, cellulase, nitrate reductase, hydrogen peroxidase and urease) to simulated N deposition of four treatment levels of 0, 30, 60 and 90 kg N·hm-2·a-1. The results showed that compared with CM, IM significantly increased soil ß-fructofuranosidase, cellulase, urease activities by 55.5%, 112.9% and 28.6%, respectively, but significantly decreased nitrate reductase activity by 31.5%, and had no significant effect on hydrogen peroxidase activity. Nitrogen deposition significantly decreased soil ß-fructofuranosidase (20.0%-49.4% and 36.2%-45.1%), cellulase (20.5%-46.3% and 18.3%-49.0%), nitrate reductase (67.9%-85.2% and 15.2%-34.2%) activities in both CM and IM plots, respectively, and also urease activity (23.1%-47.6%) in IM, but enhanced the urease activity (8.1%-50.6%) in CM, and had no significant effects on hydrogen peroxidase activity. The combination of N deposition and management types significantly impacted the four soil enzyme activities except for hydrogen peroxidase.

[Effect of UV-B radiation on the chemical composition and subsequent decomposition of Cyclobalanopsis glauca leaf litter].

A experiment on leaf litter decomposition was carried out to evaluate the effects of UV-B radiation on the chemical composition and subsequent decomposition of leaf litter in humid subtropical forest systems. The leaf litter was derived from Cyclobalanopsis glauca seedlings exposed to elevated and ambient ultraviolet B (UV-B) radiation treatments during growth for one year. The results showed that UV-B treatment significantly increased the original N, K and P content of leaf litter by 154.9%, 29.8% and 9.7%, respectively, and decreased the ratios of C: N, lignin: N and C: P of leaf litter by 60.5%, 61.7% and 8.5%, respectively (P < 0.05), but had no significant effect on C and lignin content. The decomposition of leaf litter derived from seedlings exposed to elevated UV-B treatment during growth was faster, but did not show significant difference from that of ambient UV-B treatment. Exposure to elevated UV-B radiation during growth did not significantly influence the K release, but promoted the P release and retarded the N accumulation during leaf litter decomposition. Our result will contribute to the better understanding of the role of UV-B radiation in moist subtropical forest ecosystem.

[Effect of UV-B radiation on release of nitrogen and phosphorus from leaf litter in subtropical region in China].

The release of nitrogen and phosphorus from leaf litter of six representative species, Cunninghamia lanceolata, Pinus massoniana, Schima superba, Cinnamanun camphora, Cyclobalanopsis glauca and Castanopsis eyeri, was investigated with litterbag method under ambient and reduced UV-B radiation (22.1% below ambient) treatments in subtropical region. The results showed that, the N dynamics exhibited three patterns: immobilization, mineralization-immobilization and mineralization-immobilization-mineralization. P dynamics also exhibited three different patterns: mineralization, immobilization-mineralization-immobilization and no large change. Compared with ambient treatment, the reduced treatment significantly delayed the N release from C. eyeri and P release from both C. glanca and C. eyeri (P<0.05), but significantly stimulated P release from C. camphora (P<0.05). The initial N contents and C: N ratios can not account for the N dynamics during leaf litter decomposition. The C: P ratios can partly explain the P dynamics during decomposition. The more works need to be done to better understand the role of UV-B radiation in the forest ecosystem in humid subtropical China under global environment change.

[Effects of UV-B radiation on the decomposition of Cunninghamia lanceolata leaf litter].

A litterbag experiment was conducted to study the decomposition of Cunninghamia lanceolata leaf litter under ambient and reduced UV-B radiation (22.1% below ambient). Comparing with ambient treatment, the reduced treatment decreased the decomposition rate of C. lanceolata leaf litter by 69.6% (P<0.001), making the relative contents of nitrogen (N), phosphorus (P), and lignin in the litter increased by 150%, 83.3%, and 13.8%, respectively, and the release of potassium (K) and carbon (C) slowed down. In the process of litter decomposition, photo-degradation of lignin didn't play crucial role. The results suggested that UV-B radiation could accelerate the decomposition rate of C. lanceolata leaf litter, promote the release of N, P, K, and C from it, and increase the nutrients turnover rate in litter layer as well as the carbon flux on the ground, giving potential effects on the function of C. lanceolata forest as a carbon source or sink in humid subtropical China.

[Characteristics of soil seed banks in logging gaps of forests at different succession stages in Changbai Mountains].

An investigation was made on the soil seed banks in the logging gaps of Populus davidiana--Betula platyphylla secondary forest, secondary broad-leaved forest, and broad-leaved Korean pine mixed forest at their different succession stages in Changbai Mountains. Among the test forests, secondary broad-leaved forest had the highest individual density (652 ind x m(-2)) in its soil seed bank. With the succession of forest community, the diversity and uniformity of soil seed bank increased, but the dominance decreased. The seed density of climax species such as Pinus koraiensis, Abies nephrolepis, and Acer mono increased, whereas that of Maackia amurensis and Fraxinus mandshurica decreased. Moreover, the similarity in species composition between soil seed bank and the seedlings within logging gaps became higher. The individual density and similarity between soil seed bank and the seedlings in non-logging gaps were similar to those in logging gaps. All of these indicated that soil seed bank provided rich seed resources for forest recovery and succession, and the influence of soil seed bank on seedlings regeneration increased with the succession.

[Litter decomposition of dominant plant species in successional stages in mid-subtropical zone].

The litters of seven tree species representing the dominant plant species in three main successional stages in subtropical China, i.e., Pinus massoniana in early successional forests, Schima superba and Cinnamanun camphora in transitional forests, and Castanopsis eyeri, Cyclobalanopsis gracilis, Cyclobalanopsis glauca, and Michelia chapensis in late successional forests, were collected, and their decomposition rates were measured with litterbags. The results showed that M. chapensls and C. gracilis had the highest litter decomposition rate (k = 1.12 and 0.89, respectively), followed by C. camphora and S. superba (k = 0.61 and 0.55, respectively), and P. massoniana (k = 0.51), indicating that there was a trend of litter decomposition rate being increased with succession stage. Litter decomposition rate had significant correlations with the litter' s initial P, N, and lignin contents, lignin/N ratio (P < 0.01), and C/N ratio (P < 0.05), suggesting that the initial P, N, and lignin contents and lignin/N ratio of leaf litter could be the good indictors of litter decomposition rate.