Investigation of the biocontrol mechanism of a novel Pseudomonas species against phytopathogenic Fusarium graminearum revealed by multi-omics integration analysis.

Phytopathogenic Fusarium graminearum poses significant threats to crop health and soil quality. Although our laboratory-cultivated Pseudomonas sp. P13 exhibited potential biocontrol capacities, its effectiveness against F. graminearum and underlying antifungal mechanisms are still unclear. In light of this, our study investigated a significant inhibitory effect of P13 on F. graminearum T1, both in vitro and in a soil environment. Conducting genomic, metabolomic, and transcriptomic analyses of P13, we sought to identify evidence supporting its antagonistic effects on T1. The results revealed the potential of P13, a novel Pseudomonas species, to produce active antifungal components, including phenazine-1-carboxylate (PCA), hydrogen cyanide (HCN), and siderophores [pyoverdine (Pvd) and histicorrugatin (Hcs)], as well as the dynamic adaptive changes in the metabolic pathways of P13 related to these active ingredients. During the logarithmic growth stage, T1-exposed P13 strategically upregulated PCA and HCN biosynthesis, along with transient inhibition of the tricarboxylic acid (TCA) cycle. However, with growth stabilization, upregulation of PCA and HCN synthesis ceased, whereas the TCA cycle was enhanced, increasing siderophores secretion (Pvd and Hcs), suggesting that this mechanism might have caused continuous inhibition of T1. These findings improved our comprehension of the biocontrol mechanisms of P13 and provided the foundation for potential application of Pseudomonas strains in the biocontrol of phytopathogenic F. graminearum. IMPORTANCE: Pseudomonas spp. produces various antifungal substances, making it an effective natural biocontrol agent against pathogenic fungi. However, the inhibitory effects and the associated antagonistic mechanisms of Pseudomonas spp. against Fusarium spp. are unclear. Multi-omics integration analyses of the in vitro antifungal effects of novel Pseudomonas species, P13, against F. graminearum T1 revealed the ability of P13 to produce antifungal components (PCA, HCN, Pvd, and Hcs), strategically upregulate PCA and HCN biosynthesis during logarithmic growth phase, and enhance the TCA cycle during stationary growth phase. These findings improved our understanding of the biocontrol mechanisms of P13 and its potential application against pathogenic fungi.

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.

Thermal adaptation of microbial respiration persists throughout long-term soil carbon decomposition.

Soil microbial respiration is expected to show adaptations to changing temperatures, greatly weakening the magnitude of feedback over time, as shown in labile carbon substrates. However, whether such thermal adaptation persists during long-term soil carbon decomposition as carbon substrates decrease in decomposability remains unknown. Here, we conducted a 6-year incubation experiment in natural and arable soils with distinct properties under three temperatures (10, 20 and 30°C). Mass-specific microbial respiration was consistently lower under higher long-term incubation temperatures, suggesting the occurrence and persistence of microbial thermal adaptation in long-term soil carbon decomposition. Furthermore, changes in microbial community composition and function largely explained the persistence of microbial respiratory thermal adaptation. If such thermal adaptation generally occurs in large low-decomposability carbon pools, warming-induced soil carbon losses may be lower than previously predicted and thus may not contribute as much as expected to greenhouse warming.

Convergence of carbon sink magnitude and water table depth in global wetlands.

Wetlands are strategic areas for carbon uptake, but accurate assessments of their sequestration ability are limited by the uncertainty and variability in their carbon balances. Based on 2385 observations of annual net ecosystem production from global wetlands, we show that the mean net carbon sinks of inland wetlands, peatlands and coastal wetlands are 0.57, 0.29 and 1.88 tons of carbon per hectare per year, respectively, with a mean value of 0.57 tons of carbon per hectare per year weighted by the distribution area of different wetland types. Carbon sinks are mainly in Asia and North America. Within and across wetland types, we find that water table depth (WTD) exerts greater control than climate- and ecosystem-related variables, and an increase in WTD results in a stronger carbon sink. Our results highlight an urgent need to sustain wetland hydrology under global change; otherwise, wetlands are at high risk of becoming carbon sources to the atmosphere.

Opposing seasonal temperature dependencies of CO2 and CH4 emissions from wetlands.

Wetlands are critically important to global climate change because of their role in modulating the release of atmospheric greenhouse gases (GHGs) carbon dioxide (CO2 ) and methane (CH4 ). Temperature plays a crucial role in wetland GHG emissions, while the general pattern for seasonal temperature dependencies of wetland CO2 and CH4 emissions is poorly understood. Here we show opposite seasonal temperature dependencies of CO2 and CH4 emissions by using 36,663 daily observations of simultaneous measurements of ecosystem-scale CO2 and CH4 emissions in 42 widely distributed wetlands from the FLUXNET-CH4 database. Specifically, the temperature dependence of CO2 emissions decreased with increasing monthly mean temperature, but the opposite was true for that of CH4 emissions. Neglecting seasonal temperature dependencies may overestimate wetland CO2 and CH4 emissions compared to the use of a year-based static and consistent temperature dependence parameter when only considering temperature effects. Our findings highlight the importance of incorporating the remarkable seasonality in temperature dependence into process-based biogeochemical models to predict feedbacks of wetland GHG emissions to climate warming.

Spatiotemporal variability of fire effects on soil carbon and nitrogen: A global meta-analysis.

A consensus about the fire-related soil carbon (C) and nitrogen (N) impacts that determine soil health and ecosystem services at the global scale remains elusive. Here, we conducted a global meta-analysis of 3173 observations with 1444, 1334, 228, and 167 observations for soil C, N, pyrogenic C (PyC), and the percent of PyC to total organic C (PyC/TOC) from 296 field studies. Results showed that fire significantly decreased soil C (-15.2%) and N (-14.6%) but increased soil PyC (40.6%) and PyC/TOC (30.3%). Stronger negative fire impacts on soil C and N were found in tropical and temperate climates than in Mediterranean and subtropical climates; stronger effects were found in forest ecosystems than in non-forest ecosystems. Wildfire and high-severity fire led to greater soil C and N losses than prescribed and low-severity fires, respectively, while they promoted greater increases in soil PyC and PyC/TOC than prescribed and low-severity fires, respectively. However, soil C and N recovered to control levels approximately 10 years after fire, which is a shorter period than previously determined. These results suggest that fire-induced PyC production should be accounted for in the C budget under global change. These results will improve our knowledge of the spatiotemporal variability of fire effects on soil C and N storage and have implications for fire management and ecosystem recovery.

Temperature adaptation of soil microbial respiration in alpine, boreal and tropical soils: An application of the square root (Ratkowsky) model.

Warming is expected to stimulate soil microbial respiration triggering a positive soil carbon-climate feedback loop while a consensus remains elusive regarding the magnitude of this feedback. This is partly due to our limited understanding of the temperature-adaptive response of soil microbial respiration, especially over broad climatic scales. We used the square root (Ratkowsky) model to calculate the minimum temperature for soil microbial respiration (Tmin , which describes the temperature adaptation of soil microbial respiration) of 298 soil samples from alpine grasslands on the Tibetan Plateau and forest ecosystems across China with a mean annual temperature (MAT) range from -6°C to +25°C. The instantaneous soil microbial respiration was determined between 4°C and 28°C. The square root model could well fit the temperature effect on soil microbial respiration for each individual soil, with R2 higher than 0.98 for all soils. Tmin ranged from -8.1°C to -0.1°C and increased linearly with increasing MAT (R2  = 0.68). MAT dominantly regulated Tmin variation when accounting simultaneously for multiple other drivers (mean annual precipitation, soil pH and carbon quality); an independent experiment showed that carbon availability had no significant effect on Tmin . Using the relationship between Tmin and MAT, soil microbial respiration after an increased MAT could be estimated, resulting in a relative increase in respiration with decreasing MAT. Thus, soil microbial respiration responses are adapted to long-term temperature differences in MAT. We suggest that Tmin  = -5 + 0.2 × MAT, that is, every 1°C rise in MAT is estimated to increase Tmin of respiration by approximately 0.2°C, could be used as a first approximation to incorporate temperature adaptation of soil microbial respiration in model predictions. Our results can be used to predict future changes in the response of soil microbial respiration to temperature over different levels of warming and across broad geographic scales with different MAT.

Rising Temperature May Trigger Deep Soil Carbon Loss Across Forest Ecosystems.

Significantly more carbon (C) is stored in deep soil than in shallow horizons, yet how the decomposition of deep soil organic C (SOC) will respond to rising temperature remains unexplored on large scales, leading to considerable uncertainties to predictions of the magnitude and direction of C-cycle feedbacks to climate change. Herein, short-term temperature sensitivity of SOC decomposition (expressed as Q 10) from six depths within the top 1 m soil from 90 upland forest sites (540 soil samples) across China is reported. Results show that Q 10 significantly increases with soil depth, suggesting that deep SOC is more vulnerable to loss with rising temperature in comparison to shallow SOC. Climate is the primary regulator of shallow soil Q 10 but its relative influence declines with depth; in contrast, soil C quality has a minor influence on Q 10 in shallow soil but increases its influence with depth. When considering the depth-dependent Q 10 variations, results further show that using the thermal response of shallow soil layer for the whole soil profile, as is usually done in model predictions, would significantly underestimate soil C-climate feedbacks. The results highlight that Earth system models need to consider multilayer soil C dynamics and their controls to improve prediction accuracy.

Biogeographic variation in temperature sensitivity of decomposition in forest soils.

Determining soil carbon (C) responses to rising temperature is critical for projections of the feedbacks between terrestrial ecosystems, C cycle, and climate change. However, the direction and magnitude of this feedback remain highly uncertain due largely to our limited understanding of the spatial heterogeneity of soil C decomposition and its temperature sensitivity. Here we quantified C decomposition and its response to temperature change with an incubation study of soils from 203 sites across tropical to boreal forests in China spanning a wide range of latitudes (18°16' to 51°37'N) and longitudes (81°01' to 129°28'E). Mean annual temperature (MAT) and mean annual precipitation primarily explained the biogeographic variation in the decomposition rate and temperature sensitivity of soils: soil C decomposition rate decreased from warm and wet forests to cold and dry forests, while Q10-MAT (standardized to the MAT of each site) values displayed the opposite pattern. In contrast, biological factors (i.e. plant productivity and soil bacterial diversity) and soil factors (e.g. clay, pH, and C availability of microbial biomass C and dissolved organic C) played relatively small roles in the biogeographic patterns. Moreover, no significant relationship was found between Q10-MAT and soil C quality, challenging the current C quality-temperature hypothesis. Using a single, fixed Q10-MAT value (the mean across all forests), as is usually done in model predictions, would bias the estimated soil CO2 emissions at a temperature increase of 3.0°C. This would lead to overestimation of emissions in warm biomes, underestimation in cold biomes, and likely significant overestimation of overall C release from soil to the atmosphere. Our results highlight that climate-related biogeographic variation in soil C responses to temperature needs to be included in next-generation C cycle models to improve predictions of C-climate feedbacks.

The temperature sensitivity of soil organic carbon decomposition is greater in subsoil than in topsoil during laboratory incubation.

The turnover of soil organic carbon (SOC) in cropland plays an important role in terrestrial carbon cycling, but little is known about the temperature sensitivity (Q 10) of SOC decomposition below the topsoil layer of arable soil. Here, samples of topsoil (0-20 cm) and subsoil (20-40 cm) layers were obtained from paddy fields and upland croplands in two regions of China. Using a sequential temperature changing method, soil respiration rates were calculated at different temperatures (8 °C to 28 °C) and fitted to an exponential equation to estimate Q 10 values. The average SOC decomposition rate was 59% to 282% higher in the topsoil than in the subsoil layer because of higher labile carbon levels in the topsoil. However, Q 10 values in the topsoil layer (5.29 ± 1.47) were significantly lower than those in the subsoil layer (7.52 ± 1.84). The pattern of Q 10 values between the topsoil and subsoil was significantly negative to labile carbon content, which is consistent with the carbon quality-temperature hypothesis. These results suggest that the high temperature sensitivity of SOC decomposition in the subsoil layer needs to be considered in soil C models to better predict the responses of agricultural SOC pools to global warming.