Changes in soil abiotic and biotic properties can be powerful drivers of feedback between plants and soil microbial communities. However, the specific mechanisms by which seasonal changes in environmental factors shape soil microbial communities are not well understood. Here, we collected soil samples from three sites along an elevational gradient (200–1200 m) in subtropical forests with unvarying canopy vegetation. We used an elevation gradient with similar annual precipitation but a clear temperature gradient, and phospholipid fatty acids (PLFAs) were measured to determine the seasonal variations in the composition of soil microbial communities in response to rising temperatures. Our results showed that the abundance of Gram-negative bacteria and total PLFAs were the lowest at low elevations in winter, and the ratio of Gram-positive to Gram-negative bacteria decreased with increasing elevation. However, the biomass of other microbial groups was the highest at medium elevations in summer, with the exception of actinomycetes species and fungi. Regardless of seasonal changes, soil fungal biomass tended to increase with increasing elevation. Moreover, in summer, microbial carbon use efficiency (CUE) increased with increasing elevation, whereas an opposite trend was observed in winter. Redundancy analysis and structural equation modeling showed that the dissolved organic carbon in soil was the main factor affecting the microbial communities along the elevation gradient in winter, whereas in summer, the microbial community structure was driven by shifting nitrogen availability, with both being associated with changing microbial CUE. As such, this study demonstrates distinct seasonal changes in the soil microbial community composition across an elevation gradient that are driven by carbon and nitrogen resource availability and shifts in microbial CUE. Furthermore, our results suggest that the interaction of underground plant roots and microbes drives changes in resource availability, thereby resulting in seasonal variation in soil microbial community composition across an elevation gradient.

As a consequence of changing global rainfall patterns, frequent extreme droughts will significantly affect plant growth and ecosystem functions. Fine roots and arbuscular mycorrhizal fungi (AMF) both facilitate Chinese fir nutrient uptake. However, how the growth of fine roots and AMF is regulated for the Chinese fir under drought conditions is unclear. This study used a precipitation reduction treatment (−50% throughfall) to study the seasonal effects of drought on a subtropical Chinese fir plantation. The effects measured included the fine root production, root diameter, specific root length, specific surface area, root tissue density, mycorrhizal hyphal density, spore number, mycorrhizal infection rate and total glomalin. Drought had no significant effect on Chinese fir fine root production but decreased the diameter and tissue density of primary and secondary roots while increasing the specific surface area of secondary roots. Additionally, drought significantly decreased the arbuscular mycorrhizal infection rate and significantly increased hyphal density. The results showed that drought caused the decrease in root diameter, which decreased the surface area available for AMF infection and led to the increase in mycorrhizal hyphal density. Redundancy analyses showed that soil-dissolved organic carbon and nitrogen were the key factors affecting AMF. Our results show that drought could enhance the cooperative strategy of nutrient and moisture absorption by roots and mycorrhizae of the Chinese fir, improving the resistance of Chinese fir growth to drought.

Abiotic processes of nitrogen (N) are suggested to contribute to nitrous oxide (N₂O) production; however, the important role of these processes in N₂O emissions is invariably ignored. This review synthesized the main abiotic processes of hydroxylamine and nitrite and associated biogeochemical controls in estuarine and coastal ecosystems. Abiotic processes of hydroxylamine and nitrite are availably detected in estuarine and coastal environments. The abiotic processes of hydroxylamine contribute more to N₂O production than the abiotic processes of nitrite in estuarine and coastal environments, suggesting that hydroxylamine plays an important role in N₂O production. The isotopic fractionation effects of N can occur during the abiotic processes of hydroxylamine and nitrite and are enriched with the increasing rates of N reactions. In addition, abiotic processes of hydroxylamine and nitrite are highly dependent on pH, oxygen, Fe²⁺, Fe³⁺, and Mn⁴⁺ and are also triggered by the increasing substrate contents. These results suggest that abiotic processes of hydroxylamine and nitrite have been greatly concerned for the estuarine and coastal environments, whereas the dynamics of these processes are still sparse for projecting N fates and dynamics in response to environmental factors changes. This review highlights the importance of abiotic processes of N and associated environmental implications and presents the future trend of N cycling in estuarine and coastal environments.

We conducted a short-term laboratory soil warming incubation experiment, sampling both warmed and un-warmed soils from a subtropical plantation in southeastern China, incubating them at 20 °C, 30 °C, and 40 °C. Our aim was to study the SOC mineralization response to increasing temperatures. Our findings revealed that the temperature sensitivity (Q₁₀) of SOC mineralization to short-term experimental warming varied between the warmed soil and the un-warmed soil. The Q₁₀ of the un-warmed soil escalated with the temperature treatment (20–30 °C: 1.31, 30–40 °C: 1.63). Conversely, the Q₁₀ of the warmed soil decreased (20–30 °C: 1.57, 30–40 °C: 1.41). Increasing temperature treatments decreased soil substrate availability (dissolved organic C) in both un-warmed and warmed soil. The C-degrading enzyme in un-warmed soil and warmed soil had different trends at different temperatures. In addition, warming decreased soil microbial biomass, resulting in a decrease in the total amount of phospholipid fatty acids (PLFAs) and a decrease in the abundance of fungi and Gram-negative bacteria (GN) in both un-warmed and warmed soil. The ratio of fungal to bacterial biomass (F:B) in un-warming soil was significantly higher than that in warmed soil. A drop in the microbial quotient (qMBC) coupled with a rise in the metabolic quotient (qCO₂) indicated that warming amplified microbial respiration over microbial growth. The differential Q₁₀ of SOC mineralization in un-warmed and warmed soil, in response to temperature across varying soil, can primarily be attributed to shifts in soil dissolved organic C (DOC), alterations in C-degrading enzyme activities, and modifications in microbial communities (F:B).