Root Functional Trait and Soil Microbial Coordination: Implications for Soil Respiration in Riparian Agroecosystems

Differential responses of plant and microbial respiration to extreme precipitation and drought during spring and summer in the Eurasian meadow steppe

Increasing extreme precipitation and drought events along changes in their seasonal patterns due to climate change are expected to have profound consequences for carbon cycling. However, how these climate extremes impact ecosystem respiration (Reco) and whether these impacts differ between seasons remain unclear. Here, we reveal the responses of Reco and its components to extreme precipitation and drought in spring and summer by conducting a five-year manipulative experiment in a temperate meadow steppe. Based on a 5-year average, the seasonal mean values (±SE) of Reco, Rh, Rroot, Rabg and Rplant significantly increased (p < 0.01) under both extreme precipitation treatments: wet spring (WSP) and wet summer (WSU), and significantly decreased (p < 0.01) under both extreme drought treatments: dry spring (DSP) and dry summer (DSU), except in Rabg under DSU, which remained comparable to the control. The sensitivity of Reco, Rh, Rroot and Rplant to extreme precipitation was significantly higher in spring than in summer. On average, Rplant was the primary contributor of Reco, accounting for 37.18% and 38.31% of the total across all its components under WSP and WSU, respectively during the growing season over the five study years. Moreover, linear models revealed Rplant explained 87% of the variance in Reco. Our findings indicate that future changes in precipitation events, particularly extreme precipitation may lead to increased carbon release from ecosystems, largely driven by enhanced plant respiration rather than microbial respiration. However, due to this study focused solely on respiration and did not measure photosynthesis, the findings represent only the carbon release processes and do not account for potential carbon uptake by plants during the same conditions. These emergent identified contribution to ecosystem respiration provide valuable insights for improving model benchmarks to better predict ecosystem respiration responses to extreme climate in specified season.

An integrated fast-slow plant and nematode economics spectrum predicts soil organic carbon dynamics during natural restoration

Aboveground and belowground attributes of terrestrial ecosystems interact to shape carbon (C) cycling. However, plants and soil organisms are usually studied separately, leading to a knowledge gap regarding their coordinated contributions to ecosystem C cycling. We explored whether integrated consideration of plant and nematode traits better explained soil organic C (SOC) dynamics than plant or nematode traits considered separately. Our study system was a space-for-time natural restoration chronosequence following agricultural abandonment in a subtropical region, with pioneer, early, mid and climax stages. We identified an integrated fast-slow trait spectrum encompassing plants and nematodes, demonstrating coordinated shifts from fast strategies in the pioneer stage to slow strategies in the climax stage, corresponding to enhanced SOC dynamics. Joint consideration of plant and nematode traits explained more variation in SOC than by either group alone. Structural equation modeling revealed that the integrated fast-slow trait spectrum influenced SOC through its regulation of microbial traits, including microbial C use efficiency and microbial biomass. Our findings confirm the pivotal role of plant-nematode trait coordination in modulating ecosystem C cycling and highlight the value of incorporating belowground traits into biogeochemical cycling under global change scenarios.

Impacts of plant root traits and microbial functional attributes on soil respiration components in the desert-oasis ecotone

Dividing soil respiration (Rs) into autotrophic respiration (Ra) and heterotrophic respiration (Rh) represents a pivotal step in deciphering how Rs responds to environmental perturbations. Nevertheless, in arid ecosystems beset by environmental stress, the partitioning of Rs and the underlying mechanisms through which microbial and root traits govern the distinct components remain poorly understood. This study was strategically designed to investigate Rs and its components (Ra and Rh), soil properties, and root traits within the desert-oasis ecotone (encompassing the river bank, transitional zone, and desert margin) of northwest China. Employing metagenomics, we quantitatively characterized microbial taxonomic attributes (i.e., taxonomic composition) and functional attributes (specifically, functional genes implicated in microbial carbon metabolism). Field measurements during the growing season of 2019 unveiled a pronounced decline in soil respiration rates along the environmental gradient from the river bank to the desert margin. The mean soil respiration rate was recorded as 1.82 ± 0.41 μmol m-2 s-1 at the river bank, 0.49 ± 0.15 μmol m-2 s-1 in the transitional zone, and a meager 0.45 ± 0.12 μmol m-2 s-1 in the desert margin. Concomitantly, the Ra and Rh components exhibited a similar trend throughout the study period, with Rh emerging as the dominant driver of Rs. Utilizing random forest modeling, we unearthed significant associations between microbial taxonomic and functional features and Rs components. Notably, both Ra and Rh displayed robust positive correlations with the abundance of phosphatidylinositol glycan A, a key player in microbial carbon metabolism. Partial least squares path modeling further elucidated that soil properties and microbial functions exerted direct and positive influences on both Ra and Rh, whereas taxonomic features failed to register a significant impact. When considering the combined effects of biotic and abiotic factors, microbial functional attributes emerged as the linchpin in dictating Rs composition. Collectively, these findings suggest that a trait-based approach holds great promise in more effectively revealing the response mechanisms of Rs composition to environmental changes, thereby offering novel vistas for future investigations into carbon cycling in terrestrial soils.

Phosphate solubilization potential of PSB: an advance approach to enhance phosphorous availability for phytostimulation

Rhizosphere engineering approach is considered a quantum leap in plant sciences. The current study focused on investigating rhizobacterial efficiency to mobilize bioavailable phosphate from insoluble-phosphate source. Four efficient phosphate-solubilizing bacterial isolates, i.e., Pseudomonas songnenensis (GR3), Stutzerimonas stutzeri (HH2), Bacillus bingmayongensis (KH3), and Achromobacter aegrifaciens (MH1) were selected for the current study. Interactions between various physiological parameters and phosphate solubilization efficiency of isolates revealed that glucose significantly facilitated phosphorus solubilization at 37 ℃, with media having pH 7 and 0.5% phosphorous. Additionally, positive correlation among P-solubilization potential, acids produced, and pH was observed. Plant microbe-interaction analysis was performed to evaluate the efficiency of these bacterial isolates on various morpho-physiological responses of Zea mays L. For this purpose, various concentrations of tricalcium phosphate (TCP) (0, 10, 20, 30, 40, and 50 mM) were applied to plants in the presence and absence of bacterial isolates. The results showed that lower phosphate levels (10 and 20 mM) trigger shoot development and improve plant weight and leaf formation whereas higher phosphate concentrations (30 mM and above) stimulated the development of longer root system. The bacterial isolates, KH3 and HH2, were observed as efficient phosphate-solubilizing bacteria (PSB) that positively stimulated various plant growth and biochemical attributes over untreated plants. At lower phosphate levels, substantial increase of 92, 65, and 200% in shoot length, fresh weight, and number of leaves was recorded with bacterial isolate HH2, whereas, at 30 mM TCP, increase of 165% was observed in root length of plants treated with bacterial isolate KH3 compared to control. Similarly, at lower phosphate levels, increment of 57.3, 76.7, and 217% in phosphate, protein, and auxin content was recorded in plants treated with bacterial isolate HH2, and increase of 188.8% in total soluble carbohydrates was observed in plants treated with bacterial isolate KH3 as compared to control. Contrarily, increment in total chlorophyll content was most substantial (207%) by the bacterial isolate KH3 when provided with 30 mM TCP. Hence, the current study reviled that the use of these phosphates (KH3 and HH2)-solubilizing PGPR, as an efficient phytostimulator used for crop production in the replacement of chemical fertilizers, is carcinogenic and deteriorating our eco-system.

Effects of riparian pioneer plants on soil aggregate stability: Roles of root traits and rhizosphere microorganisms

Pioneer plants are vital in stabilizing soil structure while restoring reservoir drawdown areas. However, uncertainties persist regarding the mechanism of pioneer plants to soil stability in these delicate ecosystems. This study aims to unravel the plant-soil feedback mechanisms from the roles of root traits and rhizosphere microorganisms. We conducted a mesocosm experiment focusing on four common pioneer plants from the drawdown area of Three Gorges Reservoir, China. Using the wet sieving methodology, trait-based approach and high-throughput sequencing technology, we explored soil aggregate stability parameters, plant root traits and rhizosphere microbial communities in experimental plant groups. The interacting effect of pioneer plant species richness, root traits, and rhizosphere microbial communities on soil aggregate stability was quantified by statistical and machine-learning models. Our results demonstrate that diverse pioneer plant communities significantly enhance soil aggregate stability. Notably, specific species, such as Cynodon dactylon (L.) Pers. and Xanthium strumarium L., exert a remarkably strong influence on soil stability due to their distinctive root traits. Root length density (RLD) and root specific surface area (RSA) were identified as crucial root traits mediating the impact of plant diversity on soil aggregate stability. Additionally, our study highlights the link between increased rhizosphere fungal richness, accompanied by plant species richness, and enhanced soil aggregate stability, likely attributable to elevated RLD and RSA. These insights deepen our understanding of the role of pioneer vegetation in soil structure and stability, providing valuable implications for ecological restoration and management practices in reservoir drawdown areas.

CO2-assimilation, sequestration, and storage by urban woody species growing in parks and along streets in two climatic zones

Using two cities, Rimini (Italy, Cfa climate) and Krakow (Poland, Cfb), as living laboratories, this research aimed at measuring in situ the capacity of 15 woody species to assimilate, sequester, and store CO2. About 1712 trees of the selected species were identified in parks or along streets of the two cities, and their age, DBH, height, and crown radius were measured. The volume of trunk and branches was measured using a terrestrial LiDAR. The true Leaf Area Index was calculated by correcting transmittance measurements conducted using a plant-canopy-analyser for leaf angle distribution, woody area index, and clumping. Dendrometric traits were fitted using age or DBH as independent variable to obtain site- and species-specific allometric equations. Instantaneous and daily net CO2-assimilation per unit leaf area was measured using an infra-red gas-analyser on full-sun and shaded leaves and upscaled to the unit crown-projection area and to the whole tree using both a big-leaf and a multilayer approach. Results showed that species differed for net CO2-assimilation per unit leaf area, leaf area index, and for the contribution of shaded leaves to overall canopy carbon gain, which yielded significant differences among species in net CO2-assimilation per unit crown-projection-area (AcpaML(d)). AcpaML(d) was underestimated by 6-30 % when calculated using the big-leaf, compared to the multilayer model. While maximizing AcpaML(d) can maximize CO2-assimilation for a given canopy cover, species which matched high AcpaML(d) and massive canopy spread, such as mature Platanus x acerifolia and Quercus robur, provided higher CO2-assimilation (Atree) at the individual tree scale. Land use (park or street), did not consistently affect CO2-assimilation per unit leaf or crown-projection area, although Atree can decline in response to specific management practices (e.g. heavy pruning). CO2-storage and sequestration, in general, showed a similar pattern as Atree, although the ratio between CO2-sequestration and CO2-assimilation decreased at increasing DBH.

Functionality of methane cycling microbiome during methane flux hot moments from riparian buffer systems

Riparian buffer systems (RBS) are a common agroforestry practice that involves maintaining a forested boundary adjacent to water bodies to protect the aquatic ecosystems in agricultural landscapes. While RBS have potential for carbon sequestration, they also can be sources of methane emissions. Our study site at Washington Creek in Southern Ontario, includes a rehabilitated tree buffer (RH), a grassed buffer (GRB), an undisturbed deciduous forest (UNF), an undisturbed coniferous forest (CF), and an adjacent agricultural field (AGR). The objective of this study was to assess the diversity and activity of CH₄ cycling microbial communities in soils sampled during hot moments of methane fluxes (July 04 and August 15). We used qPCR and high-throughput amplicon sequencing from both DNA and cDNA to target methanogen and methanotroph communities. Methanogens, including the archaeal genera Methanosaeta, Methanosarcina, Methanomassiliicoccus, and Methanoreggula, were abundant in all RBSs, but they were significantly more active in UNF soils, where CH₄ emissions were highest. Methylocystis was the most prevalent taxon among methanotrophs in all the riparian sites, except for AGR soils where the methanotrophs community was composed primarily of members of rice paddy clusters (RPCs and RPC-1) and upland soil clusters (TUSC and USCα). The main factors influencing the composition and assembly of methane-cycling microbiomes were soil carbon and moisture content. We concluded that the differences in CH₄ fluxes observed between RBSs were primarily caused by differences in the presence and activity of methanogens, which were influenced by total soil carbon and water content. Overall, this study emphasizes the importance of understanding the microbial drivers of CH₄ fluxes in RBSs in order to maximize RBS environmental benefits.

The role of plant functional traits and diversity in soil carbon dynamics within riparian agroforests

Restoration of agricultural riparian buffers with trees (agroforestry) provides an elegant solution to enhance carbon storage while also augmenting local biodiversity. Yet the scope and role of riparian plant community diversity in key soil dynamics remain unresolved. Operationalizing riparian age (young [<10 yr] and mature [>30 yr] since establishment] and forest stand type (coniferous and deciduous dominant) to capture the potential extent of plant diversity, we measured plant functional trait diversity and community weighted mean trait values, microbial composition, abiotic soil conditions, and rates of soil CO₂ efflux (mg CO₂ -C m^-2 h^-1 ). We used piecewise structural equation modeling (SEM) to further refine the role of biotic indices (leaf, root, and microbial characteristics), and abiotic factors (soil physio-chemical metrics) on soil C cycling processes in riparian systems. We found significantly lower rates of CO₂ efflux (F = 8.47; p < .01) over one growing season and higher total soil C (F = 3.46; p = .03) in mature buffers compared with young buffers. Using SEM, we describe influences on soil C content (marginal r²  = 61) and soil CO₂ efflux (marginal r²  = 53). Within young buffers, soil C content was significantly predicted by fungal/bacterial ratio and root length density, whereas in mature buffers, tree leaf characteristics were associated with soil C content. Soil CO₂ efflux was predicted by soil moisture, soil carbon content, and herbaceous root characteristics. Evidently, leaf and root functional traits in combination with broad soil parameters significantly describe soil C dynamics in the field; however, significant pathways are not the same throughout the life cycle of a riparian agroforest.

Benefits of phosphate solubilizing bacteria on belowground crop performance for improved crop acquisition of phosphorus

Although research on plant growth promoting bacteria began in the 1950s, basic and applied research on bacteria improving use of phosphorus (P) continues to be a priority among many agricultural research institutions. Ultimately, identifying agriculturally beneficial microbes, notably P solubilizing bacteria (PSB), that enhance the efficient use of P supports more sustainable cropping systems and the judicious use of mineral nutrients. In parallel, there is more attention on improving crop root P acquisition of existing soil P pools as well as by increasing the proportion of fertilizer P that is taken up by crops. Today, new lines of research are emerging to investigate the co-optimization of PSB-fertilizer-crop root processes for improved P efficiency and agricultural performance. In this review, we compile and summarize available findings on the beneficial effects of PSB on crop production with a focus on crop P acquisition via root system responses at the structural, functional and transcriptional levels. We discuss the current state of knowledge on the mechanisms of PSB-mediated P availability, both soil- and root-associated, as well as crop uptake via P solubilization, mineralization and mobilization, mainly through the production of organic acids and P-hydrolyzing enzymes, and effects on phytohormone signaling for crop root developement. The systematic changes caused by PSB on crop roots are discussed and contextualized within promising functional trait-based frameworks. We also detail agronomic profitability of P (mineral and organic) and PSB co-application, in amended soils and inoculated crops, establishing the connection between the influence of PSB on agroecosystem production and the impact of P fertilization on microbial diversity and crop functional traits for P acquisition.