[Seasonal changes of ammonia-oxidizing bacterial communities during tropical forest restoration]. / 热带森林恢复过程中氨氧化细菌群落的季节变化.

In this study, we used a high-throughput sequencing technology to survey the dry-wet seasonal change characteristics of soil ammonia-oxidizing bacteria (AOB) communities in the three restoration stages [i.e., Mallotus paniculatus community (early stage), Millettia leptobotrya community (middle stage), and Syzygium oblatum community (later stage)] of Xishuangbanna tropical forest ecosystems. We analyzed the effects of soil physicochemical characteristics on AOB community composition and diversity during tropical forest restoration. The results showed that tropical forest restoration significantly affected the relative abundance of dominant AOB phyla and their dry-wet seasonal variation. The maximum relative abundance of Proteobacteria (71.3%) was found in the early recovery stage, while that of Actinobacteria was found in the late recovery stage (1.0%). The abundances of Proteobacteria and Actinobacteria had the maximum ranges of dry-wet seasonal variation in the early and late stages, respectively. The abundance of dominant AOB genera and its dry-wet seasonal variation varied across tropical forest restoration stages. The maximum average relative abundance of Nitrosospira and Nitrosomonas in the late recovery stage was 66.2% and 1.5%, respectively. In contrast, the abundance of Nitrosovibrio reached its maximum (25.6%) in the early recovery stage. The maximum dry-wet seasonal variation in relative abundance of Nitrosospira and Nitrosomonas occurred in the early recovery stage, while that of Nitrosovibrio occurred in the middle recovery stage. The Chao1, Shannon, and Simpson diversity indices of AOB communities increased along the restoration stages, which were significantly higher in the wet season than in the dry season. The results of canonical correspondence analysis showed that soil easily oxidized carbon was the main factor controlling AOB community diversity and Actinobacteria abundance. Soil bulk density and temperature were the main factors affecting Proteobacteria abundance. Soil pH, microbial biomass carbon, water content, ammonium nitrogen, bulk density, and temperature were the main factors controlling the abundances of Nitrosospira, Nitrosomonas, and Nitrosovibrio. Therefore, tropical forest restoration can regulate the change of relative abundance of dominant AOB taxa via mediating the changes of soil temperature, bulk density, and readily oxidized carbon, leading to an increase in soil AOB community diversity.

[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.

[Effects of ant nesting on soil microbial biomass carbon and quotient in tropical forest of Xishuangbanna.] / 蚂蚁筑巢对西双版纳热带森林土壤微生物生物量碳及熵的影响.

Ant nesting can modify soil physicochemical conditions in the tropical forest, exerting a crucial effect on spatiotemporal variation in soil microbial biomass carbon and quotient. In this study, the chloroform fumigation method was used to measure the spatiotemporal dynamics of microbial biomass carbon and quotient in ant nests and the reference soils in Syzygium oblatum community of tropical Xishuangbanna. The results were as following: 1) Microbial biomass carbon and quotient were significantly higher in ant nests (1.95 g·kg-1, 6.8%) than in the reference soils (1.76 g·kg-1, 5.1%). The microbial biomass carbon in ant nests and the reference soils showed a signifi-cantly unimodal temporal variation, whereas the temporal dynamics of microbial biomass quotient presented a distribution pattern of "V" type. 2) The microbial biomass carbon and quotient showed significant vertical changes in ant nests and the reference soils. The microbial biomass carbon decreased, and microbial biomass quotient increased significantly along the soil layers. The vertical variations in microbial biomass carbon and quotient were more significant in ant nests than in refe-rence soils. 3) Ant nesting significantly changed the spatiotemporal distributions of soil water and temperature in ant nests, which in turn affected spatiotemporal dynamics of soil microbial biomass carbon and quotient. Soil water content could explain 66%-83% and 54%-69% of the variation of soil microbial biomass carbon and quotient, respectively. Soil temperature could explain 71%-86% and 67%-76% of the variation of soil microbial biomass carbon and quotient in ant nests and the reference soils, respectively. 4) Changes in soil physicochemical properties induced by ant nesting had significant effect on the soil microbial biomass carbon and quotient. There were positive correlations of soil microbial biomass carbon to soil organic carbon, soil temperature, total nitrogen and soil water content, and to bulk density, nitrate nitrogen and hydrolyzed nitrogen; whereas a negative correlation of them was observed with soil pH. Soil pH was positively and other soil physicochemical properties were negatively correlated with microbial biomass quotient. Total organic carbon, total nitrogen and soil temperature had greater contribution to microbial biomass carbon, while total organic carbon and total nitrogen had the least negative effect on microbial biomass quotient. Therefore, ant nesting could modify microhabitats (e.g., soil water and soil temperature) and soil physicochemical properties (e.g., total organic carbon and total nitrogen), thereby regulating the spatiotemporal variation in soil microbial biomass carbon and quotient in tropical forests.

[Effects of ant nesting on the spatiotemporal dynamics of soil easily oxidized organic carbon in Xishuangbanna tropical forests, China]. / 蚂蚁筑巢对西双版纳热带森林土壤易氧化有机碳时空动态的影响.

Ant nesting can form microhabitat and soil nutrient condition in their nests that is diffe-rent from the surrounding environment, thus having a crucial effect on the variation of soil easily oxidized organic carbon (EOC). In this study, the Mallotus paniculatus communities in Menglun Tropical Botanical Garden of Xishuangbanna, Chinese Academy of Sciences was taken as the research object. We compared the spatiotemporal distribution of soil EOC in ant nests and the refe-rence soils, and analyzed the relationship of the variation in soil EOC to the changes in soil physicochemical properties. The results showed that soil EOC in ant nests and the reference soils had a unimodal change trend with months. The order was ranked as June>September>March>December. The soil EOC decreased with the soil layers. The EOC was higher in 0-5 cm nest soils than in the refe-rence soils, while it was not significantly different in the 5-10 cm and 10-15 cm soil layers. Ant nesting increased soil temperature, soil organic carbon, soil easily oxidized organic carbon, soil microbial biomass carbon, total nitrogen, soil nitrate nitrogen and hydrolysis nitrogen, but reduced the soil water content and bulk density. The impacts of ant nesting on soil ammonium and pH was not significant. The soil organic carbon and microbial biomass carbon had crucial roles in regulating the spatiotemporal variation in EOC in ant nests and the reference soils, whereas the effects of soil temperature, soil water content, total nitrogen and nitrate nitrogen ranked the second. The ant nesting had a crucial effect on the spatiotemporal variations in easily oxidized organic carbon, mainly through changing the microhabitat (e.g., soil temperature and moisture) and soil nutrients (e.g., soil organic carbon and microbial biomass carbon) in Xishuangbanna tropical forests.