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The physicochemical environment within aggregates controls the distribution of carbon and microbial communities in soils. Agricultural management, such as tillage, can disrupt aggregates and the microscale habitat provided to microorganisms, thus altering microbial community dynamics. Categorizing microbial communities into life history strategies with shared functional traits—as has been done to understand plant community structure for decades—can illuminate how the soil physicochemical environment constrains the membership and activity of microbial communities. We conducted an aggregate scale survey of microbial community composition and function through the lens of the yield–acquisition–stress (Y–A–S) tolerator life history framework. Soils collected from a 7-year tillage experiment were separated into 4 aggregate size classes and enzyme activity, multiple-substrate-induced respiration, and carbon use efficiency were measured to reveal trade-offs in microbial resource allocation. Microbial community structure was interrogated with bacterial and fungal marker gene sequencing, and metagenomic features such as community weighted genome size and traits conferring stress tolerance were predicted using PICRUSt2. Consistent with our hypothesis, aggregates of different size classes harbored distinct microbial communities manifesting distinct life history strategies. Large macroaggregate communities >2 mm were classified as acquisition strategists based on increased enzyme activity relative to other aggregate size classes. Small and medium microaggregate (0.25–2 mm) communities did not show a strong tendency toward any particular life history strategy. Genes conferring stress tolerance were significantly enriched in microaggregates

Dried and incinerated sewage sludge (SS) have the potential to be used as phosphorus (P) fertilisers. Arbuscular mycorrhizal fungi (AMF) contribute to plant P uptake; however, their role in P uptake from SS has yet to be fully explored. A compartmented pot system with an isotope pool dilution approach was used to investigate wheat ( Triticum aestivum L.) P uptake from soluble P, dried SS and incinerated SS, via roots and/or AMF hyphae. Wheat was sown into an inner compartment containing a 33 P label with/without AMF ( Rhizophagus irregularis ) inoculum. An outer soil compartment contained the P source. Compartments were separated by mesh of different sizes to allow root and/or AMF hyphal access. Plants obtained P from dried SS via AMF but there was limited evidence that plants obtained P from incinerated SS via AMF. Phosphorus uptake was significantly greater when both roots and hyphae could access dried SS than when only roots could access dried SS. We discuss the results in terms of availability of P to roots and hyphae. We conclude that AMF play an important role in wheat P acquisition from dried SS and therefore can assist in the recycling of P in waste.

As phosphorus (P) fertilisers become increasingly expensive there is a need to find innovative ways to supply crops with P. Organic amendments (OA) can contain high concentrations of total P, although the P is present in various forms. We aimed to determine the forms of P and carbon (C) in a range of OA and the effect of these OA on soil microbial biomass, P release, arbuscular mycorrhizal (AM) colonisation, and plant P uptake. Four OA were investigated: two chicken litters (CHK-STR and CHK-SD, one with straw bedding and one with sawdust bedding), a pig litter (PIG-STR) and a municipal waste compost (COMP). An incubation experiment and a plant growth experiment were conducted in which OA and INORG-P were supplied at 15 mg P kg −1 soil and a zero P control was included. All OA had high P concentrations and did not result in an increase in the soil microbial biomass C. There were few temporal changes in available P throughout the incubation experiment suggesting that solubilisation and/or mineralisation of P occurred at a similar rate as conversion of P to unusable forms. Of the OA, PIG-STR had the largest proportion of orthophosphate P and bicarbonate extractable P, and it provided the most P to plants. While CHK-STR had a higher proportion of orthophosphate P and bicarbonate extractable P than CHK-SD, both CHK-STR and CHK-SD provided plants with similar amounts of P. This could be because CHK-SD had a higher proportion of phytate, which can be rapidly mineralised to orthophosphate, and/or because plants in the CHK-SD had higher rates of arbuscular mycorrhizal (AM) colonisation compared with CHK-STR. This study provides new insights into plant and microbial responses to OA which could help in the development of sustainable food production systems.

Reforestation of pastures in riparian zones has the potential to decrease nutrient runoff into waterways, provide both terrestrial and aquatic habitat, and help mitigate climate change by sequestering carbon (C). Soil microbes can play an important role in the soil C cycle, but are rarely investigated in studies on C sequestration. We surveyed a chronosequence (0-23years) of mixed-species plantings in riparian zones to investigate belowground (chemical and biological) responses to reforestation. For each planting, an adjacent pasture was surveyed to account for differences in soil type and land-use history among plantings. Two remnant woodlands were included in the survey as indicators of future potential of plantings. Both remnant woodlands had significantly higher soil organic C (SOC) content compared with their adjacent pastures. However, there was no clear trend in SOC content among plantings with time since reforestation. The substantial variability in SOC sequestration among plantings was possibly driven by differences in soil moisture among plantings and the inherent variability of SOC content among reference pastures adjacent to plantings. Soil microbial phospholipid fatty acids (PLFA, an indicator of microbial biomass) and activities of decomposition enzymes (β-glucosidase and polyphenol oxidase) did not show a clear trend with increasing planting age. Despite this, there were positive correlations between total SOC concentration and microbial indicators (total PLFA, fungal PLFA, bacterial PLFA and activities of decomposition enzymes) across all sites. The soil microbial community compositions (explored using PLFA markers) of older plantings were similar to those of remnant woodlands. There was a positive correlation between the soil carbon:nitrogen (C:N) and fungal:bacterial (F:B) ratios. These data indicate that in order to maximise SOC sequestration, we need to take into account not only C inputs, but the microbial processes that regulate SOC cycling as well.

Inland waters are the largest natural source of methane (CH4) to the atmosphere, yet the contribution from small streams to this flux is not clearly defined. To fully understand CH4 emissions from streams and rivers, we must consider the relative importance of CH4 emission pathways, the prominence of microbially-mediated production and oxidation of CH4, and the isotopic signature of emitted CH4. Here, we construct a complete CH4 emission budgets for four lowland headwater streams by quantifying diffusive CH4 emissions and comparing them to previously published rates of ebullitive emissions. We also examine the isotopic composition of CH4 along with the sediment microbial community to investigate production and oxidation across the streams. We find that all four streams are supersaturated with respect to CH4 with diffusive emissions accounting for approximately 78–100% of total CH4 emissions. Isotopic and microbial data suggest CH4 oxidation is prevalent across the streams, depleting approximately half of the dissolved CH4 pool before emission. We propose a conceptual model of CH4 production, oxidation, and emission from small streams, where the dominance of diffusive emissions is greater compared to other aquatic ecosystems, and the impact of CH4 oxidation is observable in the emitted isotopic values. As a result, we suggest the CH4 emitted from small streams is isotopically heavy compared to lentic ecosystems. Our results further demonstrate streams are important components of the global CH4 cycle yet may be characterized by a unique pattern of cycling and emission that differentiate them from other aquatic ecosystems.