Mixing of pine and arbuscular mycorrhizal tree species changed soil organic carbon storage by affecting soil microbial characteristics.

Pure and mixed pine forests are found all over the world. The mycorrhizal type affects soil microbial activity and carbon sequestration capacity in pure forests. However, the effects of mycorrhizal type on microbial characteristics and carbon sequestration capacity in pine mixed forests remain untested. Further, making it difficult to predict carbon storage of the conversion from pure pine forests to mixed forests at larger scales. Herein, a meta-analysis showed that the contents of soil microbial biomass, mineral-associated organic carbon, and soil organic carbon in pine mixed forests with introduced arbuscular mycorrhizal tree species (PMAM) increased by 26.41 %, 58.55 %, and 27.41 %, respectively, compared to pure pine forests, whereas those of pine mixed forests without arbuscular mycorrhizal tree species (PMEcM) remained unchanged. Furthermore, the effect size of microbial biomass, mineral-associated organic carbon and organic carbon contents in subsoil of PMAM are 56.48 %, 78.49 % and 43.05 %, respectively, which are higher than those in topsoil. The improvement of carbon sinks throughout the PMAM soil profile is positively correlated with increases in microbial biomass and mineral-associated organic carbon in subsoil, according to regression analysis and structural equation modelling. In summary, these results highlight that the positive effects of introducing arbuscular mycorrhizal tree species rather than ectomycorrhizal tree species into pure pine forests on soil microbial biomass and carbon sequestration. The positive link between microbial biomass, mineral-associated organic carbon, and soil organic carbon suggests an underlying mechanism for how soil microorganisms store carbon in pine mixed forests. Nevertheless, our findings also imply that the soil carbon pool of PMAM may be vulnerable under climate change. Based on the above findings, we propose that incorporating mycorrhizal type of tree species and soil thickness into mixed forests management and biodiversity conservation.

[Effects of ant colonization on spatiotemporal variation of organic carbon mineralization in Xishuangbanna tropical forest soils]. / 蚂蚁筑巢对西双版纳热带森林土壤碳矿化动态的影响.

Ants as ecosystem engineers can increase the input of soil organic matter, change soil physicochemical properties, and stimulate microbial activities through their colonization, thus affecting the spatiotemporal dynamics of soil organic carbon mineralization. We explored the spatiotemporal characteristics of carbon mineralization rates in ant nests and the adjacent soils in Syzygium oblatum community of Xishuangbanna, Yunnan. We analyzed the association of the variation in carbon mineralization rates with soil physicochemical properties. We found that ant colonization had a significant effect on soil organic carbon mineralization. The mean carbon mineralization rate was 19.2% higher in nest soils than that in the surrounding soils. The monthly carbon mineralization rate in nest soils and the reference soils was ranked as June ＞ September ＞ March ＞ December. The highest increase of carbon mineralization rate in ant nests was observed in 10-15 cm soil layer, while that in the reference soils was in 0-5 cm soil depth. Ant colonization had a significant effect on soil physicochemical properties. Compared with reference soils, soil temperature, soil water, soil organic carbon,soil microbial carbon, total nitrogen, hydrolytic nitrogen, nitrate, and ammonium increased by 7.6%, 5.4%, 9.9%, 14.8%, 13.4%, 9.9%, 24.1%, 6.6% and 19.4%, respectively. In contrast, soil bulk density and soil pH were decreased by 1.4% and 2.5%, respectively. Results from correlation coefficients and principal component analysis (PCA) showed that soil organic carbon and soil microbial carbon were the key factors controlling the mineralization of soil organic carbon, followed by total nitrogen, hydrolyzed nitrogen, ammonium, nitrate, temperature, and soil moisture. We conclude that ant colonization mainly alter the substrate components (i.e., soil organic carbon and microbial biomass carbon) of soil organic carbon mineralization and thus affect its spatio-temporal dynamics in Xishuangbanna tropical forests.