Key microorganisms mediate soil carbon-climate feedbacks in forest ecosystems

Bioclimatic zonation and spatial-scale dependence of lacustrine microbial assemblages

Bioclimatic zonation is critical for understanding how climate shapes biodiversity and biogeographic patterns. However, existing studies have primarily focused on macroorganisms, leaving microbial communities largely underexplored. This study seeks to address this gap through extensive sampling of bacterial communities from 931 sediment samples across 199 lakes in China. Based on the obtained data, we identified five distinct lacustrine microbial bioclimatic zones, each showing significant differences in multiple facets of bacterial diversity (i.e., alpha, beta, and gamma diversity) and clear bioclimatic zone-dependent microbial biogeographic patterns. Notably, the alpha and beta diversity of the bacterial communities showed opposing patterns across bioclimatic zones. Dominant environmental variables-specifically mean annual temperature, elevation, lake hydrological variables, and sediment pH-exerted contrasting effects on the alpha and beta diversity and played critical roles in shaping microbial community distribution at different spatial scales. At continental scales, predominant geographic and climatic variables dictated the patterns of bioclimatic zonation of lacustrine microbial communities. At regional scales, hydrological variables influenced the dispersal capacity of lake microbes, whereas sediment physicochemical variables were the most important selection factors shaping local microbial communities. Furthermore, our findings indicated that bioclimatic boundaries substantially enhanced the contribution of variable selection on bacterial community assembly and led to marked changes in distance-decay relationships in community dissimilarities. Overall, this study established a continental bioclimatic framework for lacustrine microbial communities, clarifying how environmental variables control microbial distributions across spatial scales, providing new insights into microbial biogeography, and advancing our knowledge about biodiversity under future climate change scenarios.

Diversified crop rotations improve soil microbial communities and functions in a six-year field experiment

Diversified crop rotations can help mitigate the negative impacts of increased agricultural intensity on the sustainability of agroecosystems. However, the impact of crop rotation diversity on the complexity of soil microbial association networks and ecological functions is still not well understood. In this study, a 6-year field experiment was conducted to evaluate how six different crop rotations change the composition and network complexity of soil microbial communities, as well as their related ecological functions. Microbial traits were measured in six crop rotations with different crop diversity index (CDI) during 2016-2022, including winter wheat-summer maize (CDI 1, WM) as the control, sweet potato→winter wheat-summer maize (CDI 1.5, SpWM), peanut→winter wheat-summer maize (CDI 1.5, PWM), soybean→winter wheat-summer maize (CDI 1.5, SWM), spring maize→winter wheat-summer maize (CDI 1.5, SmWM), and ryegrass-sweet sorghum→winter wheat-summer maize (CDI 2, RSWM). The study findings indicated that diversified crop rotations significantly increased ASV richness of both bacterial and fungal communities after 6-year treatments, and the β-diversity profiles of bacterial and fungal communities significantly distinguished at the year of 2022 from 2016. The relative abundance of Acidobacteria and Chloroflexi was significantly enriched in SpWM rotation at 2022, while Basidiomycota significantly declined in five diversified rotations compared to WM. Diversified crop rotations at 2022 increased the complexity and density of bacterial and fungal networks than 2016. SpWM and PWM rotations had the highest functional groups involved in chemoheterotrophy and saprotroph, respectively. Structural equation modelling (SEM) also revealed that diversified crop rotations increased soil nutrients through improving the composition of bacterial communities and the augmented intricacy of the interconnections within both bacterial and fungal communities. This research underscores the importance of preserving the diversity and ecological functions of soil microorganisms in the nutrient-recycling processes for efficient agricultural practices.

Aridity-Driven Change in Microbial Carbon Use Efficiency and Its Linkage to Soil Carbon Storage

Global warming is generally predicted to increase aridity in drylands, while the effects of aridity changes on microbial carbon use efficiency (CUE) and its linkage to soil organic carbon (SOC) storage remain unresolved, limiting the accuracy of soil carbon dynamic predictions under changing climates. Here, by employing large-scale soil sampling from 50 sites along an ~6000 km aridity gradient in northern China, we report a significant decreasing trend in microbial CUE (ranging from approximately 0.07 to 0.59 across the aridity gradient) with increasing aridity. The negative effect of aridity on microbial CUE was further verified by an independent moisture manipulation experiment, which revealed that CUE was lower under lower moisture levels than under higher moisture levels. Aridity-induced increases in physicochemical protection or decreases in microbial diversity primarily mediated the decrease in CUE with increasing aridity. Moreover, we found a highly positive microbial CUE-SOC relationship, and incorporating CUE improved the explanatory power of SOC variations along the aridity gradient. Our findings provide empirical evidence for aridity-induced reductions in microbial CUE over a broad geographic scale and highlight that increasing aridity may be a crucial mechanism underlying SOC loss by suppressing the ability of soil microorganisms to sequester carbon.

Response of soil microbial community structure to temperature and nitrogen fertilizer in three different provenances of Pennisetum alopecuroides

Soil microorganisms are key indicators of soil health, and it is crucial to investigate the structure and interactions of soil microbial communities among three different provenances of Pennisetum alopecuroides under varying nitrogen fertilizer and temperature levels in Northwest China. This study aims to provide theoretical support for the sustainable use of artificial grassland in this region. Employing a two-factor pot-control experiment with three nitrogen fertilizer treatments and three temperature treatments, a total of all treatments was utilized to examine the composition and abundance of soil microbial communities associated with Pennisetum alopecuroides using high-throughput sequencing, PCR technology, and molecular ecological network analysis. The results revealed that Proteobacteria was the dominant bacterial phylum while Ascomycota was the dominant fungal phylum in the soil samples from three provenances of Pennisetum. Specifically, Proteobacteria exhibited higher abundance in the N3T2 treatment compared to other treatments under N3T2 (25-30°C, 3 g/pot) treatment conditions in Shaanxi and Gansu provinces; similarly, Proteobacteria was more abundant in the N1T2 (25-30°C, 1 g/pot) treatment in Inner Mongolia under N1T2. Moreover, Ascomycota displayed higher abundance than other treatments in both Inner Mongolia and Gansu provinces. Additionally, Pennisetum Ascomycota demonstrated greater prevalence under (25-30°C, 3 g/pot) treatment compared to other treatments; furthermore, Shaanxi's Pennisetum Ascomycota exhibited increased prevalence under N3T1 (18-23°C, 3 g/pot) treatment compared to other treatments. The richness and diversity of soil microbial communities were significantly influenced by nitrogen fertilizer and temperature changes, leading to notable alterations in their structure. Molecular ecological network analyses revealed strong collaborative relationships among microbial species in Shaanxi Pennisetum and Inner Mongolia Pennisetum under high nitrogen and high temperature treatments, while competitive relationships were observed among microbial species in Gansu Pennisetum under similar conditions. Redundancy analysis indicated that soil pH, total potassium, and total phosphorus were the primary environmental factors influencing microorganisms. In summary, this study offers a theoretical foundation for assessing the sustainable utilization of Pennisetum artificial grasslands in Northwest China by investigating the shifts in soil microbial communities and the driving factors under varying nitrogen fertilizer and temperature levels.

Direct Evidence for Microbial Regulation of the Temperature Sensitivity of Soil Carbon Decomposition

Soil physicochemical protection, substrates, and microorganisms are thought to modulate the temperature sensitivity of soil carbon decomposition (Q10), but their regulatory roles have yet to be distinguished because of the confounding effects of concurrent changes of them. Here, we sought to differentiate these effects through microorganism reciprocal transplant and aggregate disruption experiments using soils collected from seven sites along a 5000-km latitudinal transect encompassing a wide range of climatic conditions and from a 4-year laboratory incubation experiment. We found direct microbial regulation of Q10, with a higher Q10 being associated with greater fungal:bacterial ratios. However, no significant direct effects of physicochemical protection and substrate were observed on the variation in Q10 along the latitudinal transect or among different incubation time points. These findings highlight that we should move forward from physicochemical protection and substrate to microbial mechanisms regulating soil carbon decomposition temperature sensitivity to understand and better predict soil carbon-climate feedback.

Nutrient Addition Enhances the Temperature Sensitivity of Soil Carbon Decomposition Across Forest Ecosystems

Atmospheric nitrogen (N) and phosphorus (P) depositions have been shown to alter nutrient availability in terrestrial ecosystems and thus largely influence soil carbon cycling processes. However, the general pattern of nutrient-induced changes in the temperature response of soil carbon decomposition is unknown. Yet, understanding this pattern is crucial in terms of its effect on soil carbon-climate feedback. Here, we report that N and P additions significantly increase the temperature sensitivity of soil organic carbon decomposition (Q10) by sampling soils from 36 sites across China's forests. We found that N, P, and their co-addition (NP) significantly increased the Q10 by 11.3%, 11.5%, and 23.9%, respectively. The enhancement effect of nutrient addition on Q10 was more evident in soils from warm regions than in those from cold regions. Moreover, we found that nutrient-induced changes in substrate availability and initial substrate and nutrient availability mainly regulated nutrient addition effects. Our findings highlight that N and P deposition enhances the temperature response of soil carbon decomposition, suggesting that N and P deposition should be incorporated into Earth system models to improve the projections of soil carbon feedback to climate change.

Enhanced home-field advantage in deep soil organic carbon decomposition: Insights from soil transplantation in subtropical forests

Climate change affects microbial community physiological strategies and thus regulates global soil organic carbon (SOC) decomposition. However, SOC decomposition by microorganisms, depending on home-field advantage (HFA, indicating a faster decomposition rate in 'Home' than 'Away' conditions) or environmental advantage (EA, indicating a faster decomposition rate in warmer-wetter environments than in colder-drier environments) remains unknown. Here, a soil transplantation experiment was conducted between warmer-wetter and colder-drier evergreen broadleaved forests in subtropical China. Specifically, soil samples were collected along a 60 cm soil profile, including 0-15, 15-30, 30-45, and 45-60 cm layers after one year of transplantation. SOC fractions, soil chemical properties, and microbial communities were evaluated to assess where there was an HFA of EA in SOC decomposition, along with an exploration of internal linkages. Significant HFAs were observed, particularly in the deep soils (30-60 cm) (P < 0.05), despite the lack of a significant EA along a soil profile, which was attributed to environmental changes affecting soil fungal communities and constraining SOC decomposition in 'Away' conditions. The soils transplanted from warmer-wetter to colder-drier environments changed the proportions of Mortiereltomycota or Basidiomycota fungal taxa in deep soils. Furthermore, the shift from colder-drier to warmer-wetter environments decreased fungal α-diversity and the proportion of fungal necromass carbon, ultimately inhibiting SOC decomposition in 'Away' conditions. However, neither HFAs nor EAs were significantly present in the topsoil (0-30 cm), possibly due to the broader adaptability of bacterial communities in these layers. These results suggest that the HFA of SOC decomposition in deep soils may mostly depend on the plasticity of fungal communities. Moreover, these results highlight the key roles of microbial communities in the SOC decomposition of subtropical forests, especially in deep soils that are easily ignored.

Drought may exacerbate dryland soil inorganic carbon loss under warming climate conditions

Low moisture conditions result in substantially more soil inorganic carbon (SIC) than soil organic carbon (SOC) in drylands. However, whether and how changes in moisture affect the temperature response of SIC in drylands are poorly understood. Here, we report that the temperature sensitivity of SIC dissolution increases but that of SOC decomposition decreases with increasing natural aridity from 30 dryland sites along a 4,500 km aridity gradient in northern China. To directly test the effects of moisture changes alone, a soil moisture control experiment also revealed opposite moisture effects on the temperature sensitivities of SIC and SOC. Moreover, we found that the temperature sensitivity of SIC was primarily regulated by pH and base cations, whereas that of SOC was mainly regulated by physicochemical protection along the aridity gradient. Given the overall increases in aridity in a warming world, our findings highlight that drought may exacerbate dryland soil carbon loss from SIC under warming.

Temperature fluctuation promotes the thermal adaptation of soil microbial respiration

The magnitude of the feedback between soil microbial respiration and increased mean temperature may decrease (a process called thermal adaptation) or increase over time, and accurately representing this feedback in models improves predictions of soil carbon loss rates. However, climate change entails changes not only in mean temperature but also in temperature fluctuation, and how this fluctuation regulates the thermal response of microbial respiration has never been systematically evaluated. By analysing subtropical forest soils from a 2,000 km transect across China, we showed that although a positive relationship between soil microbial biomass-specific respiration and temperature was observed under increased constant incubation temperature, an increasing temperature fluctuation had a stronger negative effect. Our results further indicated that changes in bacterial community composition and reduced activities of carbon degradation enzymes promoted the effect of temperature fluctuation. This adaptive response of soil microbial respiration suggests that climate warming may have a lesser exacerbating effect on atmospheric CO2 concentrations than predicted.

Urbanization Reduces Phyllosphere Microbial Network Complexity and Species Richness of Camphor Trees

Studies on microbial communities associated with foliage in natural ecosystems have grown in number in recent years yet have rarely focused on urban ecosystems. With urbanization, phyllosphere microorganisms in the urban environment have come under pressures from increasing human activities. To explore the effects of urbanization on the phyllosphere microbial communities of urban ecosystems, we investigated the phyllosphere microbial structure and the diversity of camphor trees in eight parks along a suburban-to-urban gradient. The results showed that the number of ASVs (amplicon sequence variants), unique on the phyllosphere microbial communities of three different urbanization gradients, was 4.54 to 17.99 times higher than that of the shared ASVs. Specific microbial biomarkers were also found for leaf samples from each urbanization gradient. Moreover, significant differences (R² = 0.133, p = 0.005) were observed in the phyllosphere microbial structure among the three urbanization gradients. Alpha diversity and co-occurrence patterns of bacterial communities showed that urbanization can strongly reduce the complexity and species richness of the phyllosphere microbial network of camphor trees. Correlation analysis with environmental factors showed that leaf total carbon (C), nitrogen (N), and sulfur (S), as well as leaf C/N, soil pH, and artificial light intensity at night (ALIAN) were the important drivers in determining the divergence of phyllosphere microbial communities across the urbanization gradient. Together, we found that urbanization can affect the composition of the phyllosphere bacterial community of camphor trees, and that the interplay between human activities and plant microbial communities may contribute to shaping the urban microbiome.