Effects of Caragana microphylla plantations on organic carbon sequestration in total and labile soil organic carbon fractions in the Horqin Sandy Land, northern China

Afforestation is conducive to soil carbon（C） sequestration in semi-arid regions. However, little is known about the effects of afforestation on sequestrations of total and labile soil organic carbon（SOC） fractions in semi-arid sandy lands. In the present study, we examined the effects of Caragana microphylla Lam. plantations with different ages（12-and 25-year-old） on sequestrations of total SOC as well as labile SOC fractions such as light fraction organic carbon（LFOC） and microbial biomass carbon（MBC）. The analyzed samples were taken from soil depths of 0–5 and 5–15 cm under two shrub-related scenarios： under shrubs and between shrubs with moving sand dunes as control sites in the Horqin Sandy Land of northern China. The results showed that the concentrations and storages of total SOC at soil depths of 0–5 and 5–15 cm were higher in 12-and 25-year-old C. microphylla plantations than in moving sand dunes（i.e., control sites）, with the highest value observed under shrubs in 25-year-old C. microphylla plantations. Furthermore, the concentrations and storages of LFOC and MBC showed similar patterns with those of total SOC at the same soil depth. The 12-year-old C. microphylla plantations had higher percentages of LFOC concentration to SOC concentration and MBC concentration to SOC concentration than the 25-year-old C. microphylla plantations and moving sand dunes at both soil depths. A significant positive correlation existed among SOC, LFOC, and MBC, implying that restoring the total and labile SOC fractions is possible by afforestation with C. microphylla shrubs in the Horqin Sandy Land. At soil depth of 0–15 cm, the accumulation rate of total SOC under shrubs was higher in young C. microphylla plantations（18.53 g C/（m^2·a）; 0–12 years） than in old C. microphylla plantations（16.24 g C/（m^2·a）; 12–25 years）, and the accumulation rates of LFOC and MBC under shrubs and between shrubs were also higher in young C. microphylla plantations than in old C. microphylla plantations. It can be concluded that the establishment of C. microphylla in the Horqin Sandy Land may be a good mitigation strategy for SOC sequestration in the surface soils.

Effects of continuous nitrogen addition on microbial properties and soil organic matter in a Larix gmelinii plantation in China

Continuous increases in anthropogenic nitrogen（N） deposition are likely to change soil microbial properties, and ultimately to affect soil carbon（C） storage.Temperate plantation forests play key roles in C sequestration, yet mechanisms underlying the influences of N deposition on soil organic matter accumulation are poorly understood. This study assessed the effect of N addition on soil microbial properties and soil organic matter distribution in a larch（Larix gmelinii） plantation. In a 9-year experiment in the plantation, N was applied at100 kg N ha-1 a-1 to study the effects on soil C and N mineralization, microbial biomass, enzyme activity, and C and N in soil organic matter density fractions, and organic matter chemistry. The results showed that N addition had no influence on C and N contents in whole soil. However,soil C in different fractions responded to N addition differently. Soil C in light fractions did not change with N addition, while soil C in heavy fractions increased significantly. These results suggested that more soil C in heavy fractions was stabilized in the N-treated soils. However,microbial biomass C and N and phenol oxidase activity decreased in the N-treated soils and thus soil C increased in heavy fractions. Although N addition reduced microbial biomass and phenol oxidase activity, it had little effect on soil C mineralization, hydrolytic enzyme activities, d13 C value in soil and C–H stretch, carboxylates and amides, and C–O stretch in soil organic matter chemistry measured by Fourier transform infrared spectra. We conclude that N addition（1） altered microbial biomass and activity without affecting soil C in light fractions and（2） resulted in an increase in soil C in heavy fractions and that this increase was controlled by phenol oxidase activity and soil N availability.

Early positive effects of tree species richness on soil organic carbon accumulation in a large-scale forest biodiversity experiment

Aims tree species richness has been reported to have positive effects on aboveground biomass and productivity,but little is known about its effects on soil organic carbon(SOC)accumulation.Methods to close this gap,we made use of a large biodiversity-ecosystem functioning experiment in subtropical china(BEF-china)and tested whether tree species richness enhanced SOC accumulation.In 2010 and 2015,vertically layered soil samples were taken to a depth of 30 cm from 57 plots ranging in tree species richness from one to eight species.Least squares-based linear models and analysis of variance were used to investigate tree diversity effects.Structural equation modeling was used to explore hypothesized indirect relationships between tree species richness,leaf-litter biomass,leaf-litter carbon content,fine-root biomass and SOC accumulation.Important Findings Overall,SOC content decreased by 5.7 and 1.1 g C kg^(-1) in the top 0-5 and 5-10 cm soil depth,respectively,but increased by 1.0 and 1.5 g C kg^(-1) in the deeper 10-20 and 20-30 cm soil depth,respect-ively.converting SOC content to SOC stocks using measures of soil bulk density showed that tree species richness did enhance SOC accumulation in the different soil depths.these effects could only to some extent be explained by leaf-litter biomass and not by fine-root biomass.Our findings suggest that carbon storage in new forests in china could be increased by planting more diverse stands,with the potential to contribute to mitigation of climate warming.

Fine root litter quality regulates soil carbon storage efficiency in subtropical forest soils

●High-quality and low-quality root litter had contrasting patterns of mass loss.●Greater litter-derived C was incorporated into soils under high-quality root litter.●Root litter decay rate or litter-derived C were related to soil microbial diversity.●Root litter quality had little effect on soil physicochemical properties.●High root litter quality was the main driver of enhanced soil C storage efficiency.Decomposing root litter is a major contributor to soil carbon(C)storage in forest soils.During decomposition,the quality of root litter could play a critical role in soil C storage.However,it is unclear whether root litter quality influences soil C storage efficiency.We conducted a two-year greenhouse decomposition experiment using 13C-labeled fine root litter of two tree species to investigate how root litter quality,represented by C to nitrogen(C/N)ratios,regulates decomposition and C storage efficiency in subtropical forest soils in China.‘High-quality’root litter(C/N ratio=26)decayed faster during the first year(0−410 days),whereas‘low-quality’root litter(C/N ratio=46)decomposed faster toward the end of the two-year period(598−767 days).However,over the two years of the study,mass loss from high-quality root litter(29.14±1.42%)was lower than‘low-quality’root litter(33.01±0.54%).Nonetheless,root litter C storage efficiency(i.e.,the ratio of new root litter-derived soil C to total mineralized root litter C)was significantly greater for high-quality root litter,with twice as much litter-derived C stored in soils compared to low-quality root litter at the end of the experiment.Root litter quality likely influenced soil C storage via changes in microbial diversity,as the decomposition of high-quality litter declined with increasing bacterial diversity,whereas the amount of litter-derived soil C from low-quality litter increased with fungal diversity.Our results thus reveal that root litter quality mediates decomposition and C storage in subtropical forest soils in China and future work should consider the links between root litter quality and soil microbial diversity.