Publications

Although diversified crop rotations raise drought tolerance and system productivity, the underlying mechanisms within the crop–soil system that confer this resilience remain incomplete.The drought tolerance mechanisms of maize grown under a 20–year field experiment encompassing low, medium, and high crop diversity rotations was evaluated by combining soil zymography and high–throughput sequencing.Crop diversification increased maize biomass by 56–87% and mitigated the drought stress by 14.1-58.8%. It also reinforced root diameter stability7–2.5 times and drought tolerance 2.2–2.7 times, which linked to drought tolerance of rhizosphere microbiota. The complexity of the rhizosphere bacterial network increased with crop diversification, and the keystone taxa like biofilm–producing Pseudomonas demonstrated bolstered drought tolerance. These microbiota help stabilize niches and habitats under drought, thereby raising rhizosphere’s stress tolerance and the ecosystem's provisioning and regulatory functions. Enzyme activities and hotspot areas decreased in soils with crop diversification, but has minimal changes with drought systems, suggesting that enzymes may not directly control plant drought tolerance.Crop diversification enrich drought–tolerance soil microbial species that maintain rhizosphere microenvironment stability and facilitate root proliferation, underscoring the significance of optimizing crop–microbe interactions to bolster resilience against soil drought.

Nitrogen (N) is an essential element for plants and microorganisms. In most terrestrial ecosystems, N is a major nutrient limiting plant growth, leading to strong competition for N between roots and rhizosphere microorganisms. Given the importance of N, investigations of plant-microbial competition for N over time and space are a prerequisite for better understanding of net primary production, nutrient cycling and root-microbial interactions. Here we proposed an in situ approach using stable isotopes (15N and 13C) to quantify plant-microbial N and C flows. The approach is based on 15N and 13C partition between plants and microorganisms and allows to investigate the chemical (N forms), spatial (labeling depths) and temporal (seasons) parameters for better understanding ecological functions of belowground systems. In this method, quadrats are selected and labeled with 15N tracers (organic N forms also labeled with 13C), i.e., introducing 15N labeled NH4 + or NO3 −, or 15N and 13C dual labeled amino acids allows to quantifying uptake preferences by plants and/or microorganisms. Detailed calculations of the amount of 15N and 13C label are presented. Such approach is necessary for comparisons between studies, and to advance our knowledge of rhizosphere interactions in terrestrial ecosystems.

No abstract is provided for this article.

Increased belowground carbon (C) transfer by plant roots at elevated CO 2 may change properties of the microbial community in the rhizosphere. Previous investigations that focused on total soil organic C or total microbial C showed contrasting results: small increase, small decrease or no changes. We evaluated the effect of 5 years of elevated CO 2 (550 ppm) on four extracellular enzymes: β-glucosidase, chitinase, phosphatase, and sulfatase. We expected microorganisms to be differently localized in aggregates of various sizes and, therefore analyzed microbial biomass (C mic by SIR) and enzyme activities in three aggregate-size classes: large macro- (> 2 mm), small macro- (0.25-2 mm), and microaggregates (< 0.25 mm). To estimate the potential enzyme production, we activated microorganisms by substrate (glucose and nutrients) amendment. Although C total and C mic as well as the activities of β-glucosidase, phosphatase, and sulfatase were unaffected in bulk soil and in aggregate-size classes by elevated CO 2 , significant changes were observed in potential enzyme production after substrate amendment. After adding glucose, enzyme activities under elevated CO 2 were 1.2-1.9-fold higher than under ambient CO 2 . This indicates the increased activity of microorganisms, which leads to accelerated C turnover in soil under elevated CO 2 . Significantly higher chitinase activity in bulk soil and in large macroaggregates under elevated CO 2 revealed an increased contribution of fungi to turnover processes. At the same time, less chitinase activity in microaggregates underlined microaggregate stability and the difficulties for fungal hyphae penetrating them. We conclude that quantitative and qualitative changes of C input by plants into the soil at elevated CO 2 affect microbial community functioning, but not its total content. Future studies should therefore focus more on the changes of functions and activities, but less on the pools.

Plant residues in soil create temporal and spatial hotspots of extremely high microbial activities leading to very intensive greenhouse gas (GHG) fluxes that challenge our mechanistic understanding and predictive power. Using a series of well-controlled soil microcosm experiments, we examine how abiotic processes (e.g., iron reduction-oxidation cycling) at residue/soil interfaces contribute to hotspot dynamics. We quantify for the first time the contributions of microbially-initiated Fenton reactions, which produce strongly oxidizing hydroxyl radicals (HO ), to organic matter solubilization and mineralization in hotspots 0–3 mm from the litter surface. The concentrations of ferrous iron (Fe2+), hydrogen peroxide (H2O2) and HO were 2.1–3.0, 3.0–9.0 and 2.6–2.8 times higher, respectively, at the straw-soil interface than in the bulk soil. Thus, iron minerals, especially in concert with microorganisms, produce a burst of hydroxyl radicals that explain extremely high GHG fluxes from soil hotspots. Our findings highlight how Fe minerals and microorganisms synergistically influence global carbon cycling. These synergistic effects should be accounted for mechanistic understanding of processes in soil hotspots.

Aims Although plant–microbial interactions are essential in sustaining terrestrial ecosystem functions, root–microbial interactions remain poorly understood. Therefore, effects of fine root species richness, composition and biomass, and functional traits on soil microbial community richness and composition were assessed in subtropical secondary forests. Methods Fine root identity (DNA meta bar coding) was linked with microbial species (high-throughput Illumina sequencing) to reveal root effects on richness and composition of bacterial and fungal communities. Results The results showed that bacterial and fungal richness was principally determined by functional dispersion of specific root length (FDis_SRL) and community weighted means of root diameter (CWM_diam), and their richness increased with these two root parameters. Microbial community composition was mainly regulated by FDis_SRL, and the abundance of eutrophic bacteria (r-strategists, e.g., Proteobacteria and Actinobacteria ), saprotrophs and pathogens increased with FDis_SRL. These two root parameters still directly affect microbial community richness and composition even after accounting for soil and aboveground plant properties and also indirectly by increasing pH, total nitrogen, TP, and AP and decreasing C:N ratio. Furthermore, the richness and composition of fungi were more affected by fine root traits than bacteria, whereas bacteria were more strongly influenced by soil properties. Conclusions Overall, soil microbial community richness and composition in subtropical secondary forests were primarily determined by fine root functional traits, especially FDis_SRL and CWM_diam. These results will improve our understanding of the important role of root–microbial interactions in terrestrial biogeochemical processes.

Belowground plant transfer of carbon (C) and nitrogen (N) can benefit soil ecosystems, increasing soil C gains and plant N availability, while improving soil pore structure. We explored such transfers among three plant species of North American prairie, where C and N were transferred from a grass (Panicum virgatum L., switchgrass (Sgrass)) to either a legume (Lespedeza capitata Michx., bush clover (Bclover)), a forb (Rudbeckia hirta L., black-eyed Susan (BSforb)), or a mixture of the two. The plants were grown either with/out direct root contact, thus allowing assessment of the relative contributions of fungal- and root-based transfer pathways. The Sgrass was labeled with 13C and 15N, and C and N transfers were assessed by measuring isotope enrichment of roots and aboveground biomass of neighboring plants. Soil inputs of plant-derived C and N were assessed by isotope analyses of the rhizosphere soil. X-ray computed tomography was used for pore structure analyses. Carbon transfer was much higher in the presence of direct/close root contact between source and recipient plants, yet N transfers appeared to be mainly fungal driven. While C and N were readily transferred from Sgrass to other Sgrass and Bclover neighbors, transfers to BSforb were negligible. However, in a three species system, the presence of the legume enhanced C and N transfers to BSforb, suggesting non-additive influences of diverse plant community composition. The more plant-derived C and N was found in the rhizosphere of recipient plants, the greater C and N transfers through roots. Greater C and N transfers were associated with increases in 8–30 μm diameter pores and decreases in >150 μm pores. Summarily, diverse plant communities, especially those with legumes, increase C and N transfers, which then benefit soil C inputs and its protection via changes in pore structure.