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Viruses are extremely abundant in soils and have various important ecological implications therein. The quantification and identification of soil viruses a

Microplastics provide a new ecological niche for microorganisms, and the accumulation levels of microplastics (MPs) in terrestrial ecosystems are higher th

Cellulose decomposition is a key process in soil carbon (C) cycling due to the high abundance of cellulose in plant biomass. Microbial functional groups that sequester C from cellulose, and the accumulation of cellulose C in soil aggregates, remains debated. We hypothesized that cellulose derived 13C would be more efficiently converted into soil organic C by microorganisms, and retained in soil subjected to long-term application of compost. In this study, soil sampled from a long-term (27 years) field experiment with application of compost (Compost), NPK fertilizers (NPK) and without fertilizers (control), was incubated with 13C-cellulose for 120 days. The cellulose 13C content, microbial community structure (lipid biomarkers) and microbial 13C use efficiency (CUE) were measured. The incorporation of 13C into large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm), and silt + clay fraction (<53 μm) was analyzed to elucidate cellulose 13C sequestration process in aggregates. In contrast to our initial hypothesis, 13C remaining in soil after 120 days of incubation was maximal in unfertilized soil (25%) and minimal in Compost soil (17%). Compost soil had higher abundance of fungi and especially fast-growing bacteria (Gram-negative (G–) bacteria) than NPK and control soils. This accelerated decomposition and lowered CUE of 13C, therefore reducing the amount of 13C remaining in the Compost soil. In contrast, in the other soils, the lower fungal abundance reduced cellulose decomposition, which in turn contributed to growth of Gram-positive (G+) bacteria characterized by larger CUE than G– bacteria. This increased the ratio of G+/G– bacteria, resulting in larger CUE and more 13C remaining in NPK and control soils. Cellulose-derived 13C content decreased in small macroaggregates and microaggregates for all three soils, and in silt + clay fraction for the Compost soil; meanwhile, cellulose-derived 13C content increased in the silt + clay fraction for NPK and control soils from day 14 onwards. The ratios of 13C content in small macroaggregates and microaggregates to that in silt + clay fraction were higher in NPK and unfertilized soils than in Compost soil during the incubation. This indicated that less 13C was redistributed from large aggregates to silt + clay fraction in Compost soil. Overall, cellulose was more rapidly decomposed and incorporated into aggregates in organic C-rich soil, but their transformation efficiency into soil organic C was lower than in organic C-poor soil.

Tropical forests, where the soils are nitrogen (N) rich but phosphorus (P) poor, have a disproportionate influence on global carbon (C) and N cycling. While N deposition substantially alters soil C and N retention in tropical forests, whether P input can alleviate these N-induced effects by regulating soil microbial functions remains unclear. We investigated soil microbial taxonomy and functional traits in response to 10-year independent and interactive effects of N and P additions in a primary and a secondary tropical forest in Hainan Island. In the primary forest, N addition boosted oligotrophic bacteria and phosphatase and enriched genes responsible for C-, P-mineralization, nitrification and denitrification, suggesting aggravated P limitation while N excess. This might stimulate P excavation via organic matter mineralization, and enhance N losses, thereby increasing soil CO2 and N2O emissions by 86% and 110%, respectively. Phosphorus and NP additions elevated C-mining enzymes activity mainly due to intensified C limitation, causing 82% increase in CO2 emission. In secondary forest, P and NP additions reduced phosphatase activity, enriched fungal copiotrophs and increased microbial biomass, suggesting removal of nutrient deficiencies and stimulation of fungal growth. Meanwhile, soil CO2 emission decreased by 25% and N2O emission declined by 52–82% due to alleviated P acquisition from organic matter decomposition and increased microbial C and N immobilization. Overall, N addition accelerates most microbial processes for C and N release in tropical forests. Long-term P addition increases C and N retention via reducing soil CO2 and N2O emissions in the secondary but not primary forest because of strong C limitation to microbial N immobilization. Further, the seasonal and annual variations in CO2 and N2O emissions should be considered in future studies to test the generalization of these findings and predict and model dynamics in greenhouse gas emissions and C and N cycling.

Plant-microbial interactions alter C and N balance in the rhizosphere and affect the microbial carbon use efficiency (CUE)–the fundamental characteristic of microbial metabolism. Estimation of CUE in microbial hotspots with high dynamics of activity and changes of microbial physiological state from dormancy to activity is a challenge in soil microbiology. We analyzed respiratory activity, microbial DNA content and CUE by manipulation the C and nutrients availability in the soil under Beta vulgaris. All measurements were done in root-free and rhizosphere soil under steady-state conditions and during microbial growth induced by addition of glucose. Microorganisms in the rhizosphere and root-free soil differed in their CUE dynamics due to varying time delays between respiration burst and DNA increase. Constant CUE in an exponentially-growing microbial community in rhizosphere demonstrated the balanced growth. In contrast, the CUE in the root-free soil increased more than three times at the end of exponential growth and was 1.5 times higher than in the rhizosphere. Plants alter the dynamics of microbial CUE by balancing the catabolic and anabolic processes, which were decoupled in the root-free soil. The effects of N and C availability on CUE in rhizosphere and root-free soil are discussed.

Increased root exudation under elevated atmospheric CO 2 and the contrasting environments in soil macro- and microaggregates could affect microbial growth strategies. We investigated the effect of elevated CO 2 on the contribution of fast- ( r -strategists) and slow-growing ( K -strategists) microorganisms in soil macro- and microaggregates. We fractionated the bulk soil from the ambient and elevated (for 5 years) CO 2 treatments of FACE-Hohenheim (Stuttgart) into large macro- (>2 mm), small macro- (0.25–2.00 mm), and microaggregates (<0.25 mm) using ‘optimal moist’ sieving. Microbial biomass (C mic ), the maximum specific growth rate (μ), growing microbial biomass (GMB) and lag-period ( tlag ) were estimated by the kinetics of CO 2 emission from bulk soil and aggregates amended with glucose and nutrients. Although C org and C mic were unaffected by elevated CO 2 , μ values were significantly higher under elevated than ambient CO 2 for bulk soil, small macroaggregates, and microaggregates. Substrate-induced respiratory response increased with decreasing aggregate size under both CO 2 treatments. Based on changes in μ, GMB and lag period, we conclude that elevated atmospheric CO 2 stimulated the r- selected microorganisms, especially in soil microaggregates. Such an increase in r -selected microorganisms indicates acceleration of available C mineralization in soil, which may counterbalance the additional C input by roots in soils in a future elevated atmospheric CO 2 environment.

Niche partitioning by time, space and chemical forms has been suggested as an important mechanism to maintain species coexistence. Climate warming is assum

Trees and their associated arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi drive carbon (C) and nitrogen (N) cycling patterns. However, the mechanisms underpinning this relationship and the degree to which mycorrhiza mediate the effects of forest tree composition on soil N cycling outside of the temperate zone remain unclear. Here, we conducted field surveys to establish a natural gradient with increasing ECM tree dominance in subtropical forests, and explored the effects of tree mycorrhizal associations on soil N cycling. Across this mycorrhizal gradient, we quantified soil available N, microbial biomass N, net N transformation rates, as well as N-acquiring enzyme activities, litterfall biomass and quality, and soil pH during the one-year growing season. We found that with increasing ECM tree dominance, the dissolved organic N and nitrate N decreased, while the microbial biomass N increased linearly. Soils dominated by AM trees had 1.8–2.3 times larger mineral N contents, net N mineralization rate, and net nitrification rate than ECM-dominated stands, suggesting a rapid N cycling in AM-dominated stands. ECM trees and their associated fungi reduce the net N mineralization rate in topsoil mainly by producing recalcitrant litterfall (i.e., higher C:N) and by secreting β-N-acetylglucosaminidase to deplete N directly from soil organic matter, which together increased N limitation for free-living decomposers. The low pH and high C:N ratio in ECM-dominated soils inhibit the proliferation of ammonia-oxidizers and thus decrease the net nitrification rate. Our results demonstrate that the increasing ECM tree dominance increase soil N-acquiring enzyme activity and C:N ratio but decrease pH value, all of them critically mediating soil N availability. Consequently, by altering the relative abundances of tree mycorrhizal associations shifts in forest composition under global changes and plantation establishment can be expected to result in altered soil N cycling.

Organic carbon (C) released from living roots forms a major resource for microorganisms controlling energy, C pathways and, hence, food web structure and dynamics. However, knowledge on quantitative C fluxes into food web compartments is scarce. Nematodes, with functional groups at each trophic level, served as a model community for assessing root C fluxes into the micro-food web. Maize, grown on soil cores from an arable field, was pulse-labeled with 14CO2 followed by sampling 2, 5, 10 and 16days after labeling. Nematode population density, community structure, trophic groups and their 14C activities were analyzed. Overall, 55 genera of 22 families were detected. Plant-feeders, which had the highest density, showed the fastest and highest incorporation of root C. Bacterial-feeders incorporated more root-derived 14C than fungal-feeders. This was consistent with a bacterial- to fungal-feeder-ratio of 0.63 and a moderate to low Channel Index (average 38), a nematode faunal index that assigns the magnitude of carbon flow via the bacterial or fungal channel, both indicating a major energy flux in the bacterial decomposition pathway. Predators and omnivores showed low incorporation of root-derived C, pointing to a basal food web structure with short food chains and low energy transfer to higher trophic levels. Combining 14C tracing with taxonomic identification of nematodes allowed quantification of root C fluxes into food web compartments. The incorporation of root C into nematodes was small (~0.1% of that in microbial biomass), yet forms an important part of belowground C channeling as it links microbial and faunal food web.

Abstract The ability of roots to extract water and nutrients from soil depends on the biophysical properties of the rhizosphere, which are strongly influenced by mucilage secretion. The aim of this study was to introduce the concept of rhizoligands to engineer the biophysical properties of the rhizosphere. A rhizoligand is defined as an additive that increases the wettability of the rhizosphere and links the mucilage network to main intimate contact with the root surface. We hypothesize that rhizoligands: i) facilitate the rewetting of the rhizosphere during repeated drying and wetting cycles; ii) enhance rhizosheath formation; iii) increase enzyme activities in the rhizosphere; and iv) increase plant biomass. A commercial surfactant was selected as the prototype rhizoligand to test the effect on the rhizosphere biophysical properties of white lupin grown in quartz sand and subjected to six drying-rewetting cycles. Half of the plants were irrigated with water and the other half with the rhizoligand solution. When plants were 50 days old, we measured: i) soil water content; ii) rhizosheath mass; iii) activity of selected enzymes; iv) carbon content in the rhizosphere; and v) plant biomass. Rhizoligand increased rewetting rate of the rhizosphere after drying and subsequent rewetting, resulting in a greater soil water content. Rhizosheath formation was improved in plants irrigated with rhizoligand and sand particles attached to the roots increased by 1.64 times compared to plants irrigated with water. Activity of the enzymes chitinase, sulfatase, and β-glucosidase were 4, 7.9, and 1.5 times greater in the rhizosphere of plants irrigated with rhizoligand than in the rhizosphere of plants irrigated with water. Plant biomass was 1.2 fold greater in samples irrigated with rhizoligand solution than in samples irrigated with water. We conclude that application of rhizoligand improves plant performance by influencing the water dynamics in the rhizosphere and the plant, increasing the mechanical stability of the rhizosheaths and increasing the enzyme activities in the rhizosphere. Such effects are probably triggered by the interaction between mucilage and the applied rhizoligand, which reduces mucilage swelling (possibly by cross-linking mucilage polymers) and thus by increasing its viscosity keeps the mucilage close to the root surface. We propose the rhizoligand concept as a strategy to engineer the rhizosphere properties and to improve plant tolerance to water shortage.

Understanding the balance between the priming effect and the retention of added organic carbon (C) in soil is important in evaluating the role of specific practices for terrestrial C sequestration. However, knowledge about the effects of biochar addition on soil net C accumulation following various C input patterns remains limited. We incubated soil with aged and fresh biochar, and added 14C-labeled glucose at three frequencies over 120 days: single, repeated, and continuous additions. Regardless of glucose addition, the presence of aged or fresh biochar reduced the accumulative CO2 emissions, by 23% on average, relative to the soil without biochar addition. Compared with the soil without biochar addition, glucose mineralization significantly increased by 1.4–2.0% in the soils with aged biochar, but decreased by 0.1–1.9% in the soils with fresh biochar. Relative to repeated and continuous glucose additions, the single addition may slightly overestimate priming effects, especially during the early incubation period. At the end of incubation, repeated and continuous additions showed a higher net C accumulation than the single addition. Regardless of the glucose addition frequency, net C accumulation was lower in soils with aged or fresh biochar than in the control. In summary, biochar amendment has an interactive effect with glucose addition frequency and thus affects the direction and magnitude of priming. Despite the direct contribution of biochar to C sequestration in soil, the low net C accumulation from glucose in the biochar-amended soil highlights the necessity of C balance accounting.