Rhizosphere microbes in forests are key elements of the carbon sequestration of terrestrial ecosystems. To date, little is known about how the diversity and species interactions of the active rhizomicrobial community change during soil carbon sequestration and what interactions drive these changes. In this study, we used a combination of DNA and stable isotope method to explore correlations between the composition of microbial communities, N transformation, and the sequestration de novo of carbon in soils around Pinus tabuliformis and Quercus variabilis roots in North China. Rhizosphere soils from degraded lands, primary stage land (tree roots had colonized in degraded soil for 1 year), and nature forest were sampled for analyses. The results showed that microbial communities and newly sequestered soil organic carbon (SOC) contents changed with different tree species, environments, and successive stages. The fungal unweighted and weighted UniFrac distances could better show the different microbial species structures and differences in successive stages. Newly sequestered SOC was positively correlated with the bacterial order Rhizobiales (in P. tabuliformis forests), the fungal order Russulales (in Q. variabilis forests), and δ¹⁵N. Consequently, the bacterial order Rhizobiales acted as an important taxa for P. tabuliformis root-driven carbon sequestration, and the fungal order Russulales acted as an important taxa for Q. variabilis root-driven carbon sequestration. The two plant species allocated root exudates to different portion of their root systems, which in turn altered microbial community composition and function. The δ¹⁵N of soil organic matter could be an important indicator to estimate root-driven carbon sequestration.

Understanding the response of soil respiration to changes in temperature and moisture is critical to accurately assess the impact of afforestation on regional carbon balance. In order to investigate the response of soil respiration to soil temperature and moisture, we partitioned soil respiration into three components (heterotrophic respiration, root respiration, and rhizomicrobial respiration) using ¹³C natural abundance during the growing season in a Robinia pseudoacacia plantation in northern China. Root respiration and soil microbial respiration had a significantly positive relationship with soil temperature. Heterotrophic respiration was positively correlated with soil moisture, while rhizomicrobial respiration significantly decreased with a reduction in soil moisture. Our findings suggest that the responses of plant roots and soil microorganisms to soil temperature and moisture were different. According to the prediction of the rootmicrobial model developed in this study, average soil respiration will increase by 12 mg C m^-2 h^-1 when soil temperature increases by 2ºC in the plantation. By modelling the relationship of a root-microbial system during the growing season in a plantation in northern China, the temperature and moisture sensitivities of soil respiration can be characterized.

Fungal-biogeography studies have shown global patterns of biotic interactions on microbial biogeography. However, the mechanisms underlying these patterns remain relatively unexplored. To determine the dominant factors affecting forest soil fungal diversity in China, soil and leaves from 33 mountain forest reserves were sampled, and their properties were measured. We tested three hypotheses and established the most realistic one for China. The results showed that the soil fungal diversity (Shannon index) varied unimodally with latitude. The relative abundance of ectomycorrhizae was significantly positively correlated with the leaf nitrogen/phosphorus. The effects of soil available phosphorus and pH on fungal diversity depended on the ectomycorrhizal fungi, and the fungal diversity shifted by 93% due to available phosphorus, potassium, and pH. Therefore, we concluded that latitudinal changes in temperature and the variations in interactions between different fungal guilds (ectomycorrhizal, saprotrophic, and plant pathogenic fungi) did not have a major influence. Forest soil fungal diversity was affected by soil pH, available phosphorus, and potassium, which are driven by the phosphorus limitation of trees.

Plant leaf functional traits can reflect the adaptive strategies of plants to environmental changes. Exploring the patterns and causes of geographic variation in leaf functional traits is pivotal for improving ecological theory at the macroscopic scale. In order to explore the geographical variation and the dominant factors of leaf functional traits in the forest ecosystems of China, we measured 15 environmental factors on 16 leaf functional traits in 33 forest reserves in China. The results showed leaf area (LA), carbon-to-nitrogen ratio (C/N), carbon-to-phosphorus ratio (C/P), nitrogen-to-phosphorus ratio (N/P), phosphorus mass per area (Pa) and nitrogen isotope abundance (δ¹⁵N)) were correlated with latitude significantly. LA, Pa and δ¹⁵N were also correlated with longitude significantly. The leaf functional traits in southern China were predominantly affected by climatic factors, whereas those in northern China were mainly influenced by soil factors. Mean annual temperature (MAT), mean annual precipitation (MAP) and mean annual humidity (MAH) were shown to be the important climate factors, whereas available calcium (ACa), available potassium (AK), and available magnesium (AMg) were shown to be the important climate factors that affect the leaf functional traits of the forests in China. Our study fills the gap in the study of drivers and large-scale geographical variability of leaf functional traits, and our results elucidate the operational mechanisms of forest–soil–climate systems. We provide reliable support for modeling global forest dynamics.

Rhizosphere microbes in forests are key elements for carbon accumulation in terrestrial ecosystems. To date, little is known on the rhizomicrobial community changes occurring during soil carbon accumulation. Using high-throughput DNA sequencing, we identified the phyla composing the rhizomicrobial communities of Pinus tabuliformis Carr. and Quercus variabilis Blume forests in North China and their abundance. These results were correlated with the soil organic carbon (SOC) accumulation driven by tree roots. Rhizomicrobial community composition and abundance and SOC accumulation varied with tree species, but root presence benefited SOC accumulation significantly. Different phyla played different roles in root-driven carbon accumulation during the succession of a recovery forest ecosystem, but Proteobacteria and Basidiomycota were keystones for root-driven carbon accumulation.