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Abstract: We used natural abundance 13C:12C (δ 13C) and 8 yr of labeling with 13C-depleted CO2 in a Pinus taeda Free Air CO2 Enrichment (FACE) experiment to investigate carbon sources of saprotrophic fungi, ectomycorrhizal fungi, and fungi of uncertain life history. Sporocarp δ 13C identified Sistotrema confluens as ectomycorrhizal, as suspected previously from morphological characteristics. Saprotrophic δ 13C declined by 2 ‰–13 ‰ between ambient to elevated CO2 treatments and corresponded to different carbon sources, including surface litter (Rhodocollybia, Mycena), pine cones (Baeospora), wood (Gymnopilus, Pholiota), and soil (Ramariopsis). Ectomycorrhizal fungi, foliage, and surficial litter declined 12 ‰ in δ 13C between ambient and elevated treatments, confirming that these fungi depend on recent photosynthate. The δ 13C of ectomycorrhizal genera correlated between treatments with a slope (4.3 ± 1.2) greater than the expected value of one. This suggested that Inocybe and Cortinarius incorporated some pre-treatment, soil-derived carbon (presumably from amino acids) whereas Lactarius and Russula only incorporated current-year photosynthate or recent, litter-derived carbon. Combining natural abundance and tracer 13C measurements proved a powerful technique to examine carbon sources of different fungi. [Copyright &y& Elsevier]

Abstract: The relationships of mycorrhizal fungal respiration and productivity to climate and atmospheric chemistry remain under characterized. We quantified mycorrhizal sporocarp and hyphal respiration, as well as growing season net hyphal production, under ambient and elevated carbon dioxide (CO2) and ozone (O3) in relation to natural temperature and moisture variation. Hyphal respiration did not respond significantly to elevated CO2 and O3. Sporocarp respiration was affected by temperature and moisture content while hyphal respiratory response to temperature was undetected over the narrower range of soil temperatures captured. Hyphal respiration comprised 31 % of soil respiration, and the ratio of hyphal respiration to soil respiration declined with elevated CO2. Hyphal biomass was reduced under all treatments though not statistically significant. Given the large fraction of soil respiration represented by mycorrhizal fungi and its sensitivity to climate, a small change in fungal respiration could strongly affect carbon budgets and cycling under climate change. [Copyright &y& Elsevier]

Agricultural management decisions on factors such as tillage, fertilization, and cropping system determine the fate of much of the world's soils, and soil microbes both mediate and respond to these changes. However, relationships between management practices and soil microbial properties are poorly understood, especially in semiarid regions. To address this knowledge gap, we reviewed research papers published between 2000 and 2020 that analyzed soil microorganisms in semiarid wheat fields. We aimed to determine if and how soil microbial properties reliably respond to management, and how these properties indicate long-term changes in soil health, carbon (C) sequestration, and crop yield. We found that reducing tillage increases microbial activity as much as 50% in upper soil layers and stratifies both bacteria and fungi by depth. Higher cropping intensity (reduced fallow) increases C storage, microbial activity, and biomass, and particularly fungal biomass, which can be three times greater under continuous wheat than wheat-fallow. Chemical and organic fertilizers both increase bacterial biomass, though only organic inputs provide lasting benefits by promoting C storage and increasing fungal as well as bacterial biomass. We found microbial properties to be sensitive indicators of long-term changes in soil health and productivity, and formed recommendations on appropriate sampling, analysis, and interpretation of microbial data depending on the system studied. [ABSTRACT FROM AUTHOR]