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Summary: Tree stems from wetland, floodplain and upland forests can produce and emit methane (CH4). Tree CH4 stem emissions have high spatial and temporal variability, but there is no consensus on the biophysical mechanisms that drive stem CH4 production and emissions. Here, we summarize up to 30 opportunities and challenges for stem CH4 emissions research, which, when addressed, will improve estimates of the magnitudes, patterns and drivers of CH4 emissions and trace their potential origin. We identified the need: (1) for both long‐term, high‐frequency measurements of stem CH4 emissions to understand the fine‐scale processes, alongside rapid large‐scale measurements designed to understand the variability across individuals, species and ecosystems; (2) to identify microorganisms and biogeochemical pathways associated with CH4 production; and (3) to develop a mechanistic model including passive and active transport of CH4 from the soil–tree–atmosphere continuum. Addressing these challenges will help to constrain the magnitudes and patterns of CH4 emissions, and allow for the integration of pathways and mechanisms of CH4 production and emissions into process‐based models. These advances will facilitate the upscaling of stem CH4 emissions to the ecosystem level and quantify the role of stem CH4 emissions for the local to global CH4 budget. [ABSTRACT FROM AUTHOR]

Summary: While recent reports demonstrate that the direct emission of methane from living tree trunks may be a significant terrestrial emission source, there has been debate whether tree emissions are due to transport from soils or produced in the wood environment itself. Reports of methanogens from wood of trees were prominent in the literature 40 years ago but have not been revisited with molecular ecology approaches.We examined communities associated with Populus deltoides using rRNA gene sequence analyses and how these vary with tree and wood properties.Our data indicate that wood environments are dominated by anaerobic microbiomes. Methanogens are prominent in heartwood (mean 34% relative abundance) compared to sapwood environments (13%), and dominant operational taxonomic units (OTUs) were classified as the Methanobacterium sp. Members of the Firmicutes phylum comprised 39% of total sequences and were in 42% greater abundance in sapwood over heartwood niches. Tree diameter was the strongest predictor of methanogen abundance, but wood moisture content and pH were also significant predictors of taxon abundance and overall community composition.Unlike microbiomes of the soil, rhizosphere and phyllosphere, wood associated communities are shaped by unique environmental conditions and may be prominent and overlooked sources of methane emissions in temperate forest systems. [ABSTRACT FROM AUTHOR]

I.II.III.IV.V.References Summary: Interactions between trees and microorganisms are tremendously complex and the multispecies networks resulting from these associations have consequences for plant growth and productivity. However, a more holistic view is needed to better understand trees as ecosystems and superorganisms, where many interacting species contribute to the overall stability of the system. While much progress has been made on microbial communities associated with individual tree niches and the molecular interactions between model symbiotic partners, there is still a lack of knowledge of the multi‐component interactions necessary for holistic ecosystem‐level understanding. We review recent studies in Populus to emphasize the importance of such holistic efforts across the leaf, stem and rooting zones, and discuss prospects for future research in these important ecosystems. [ABSTRACT FROM AUTHOR]

Previous work in the Colorado alpine ecosystem has shown that amino acids are a potentially important N source for the sedge, Kobresia myosuroides. This plant is the only known sedge to harbour associations with ectomycorrhizal fungi. The aim of the present work was to test the hypothesis that these ectomycorrhizas transfer N from amino acids in the soil solution to the host plant, and thereby have an important role in the N nutrition of this species. We used a two-chamber system (rhizoboxes) in which K. myosuroides plants were separated from a soil chamber by nylon mesh that allowed fungal hyphae, but not plant roots, to cross it. Injections of [15N, 2-13C]glycine were made into the soil chamber. The hyphal crossings on half of the rhizoboxes were regularly disrupted to control for leakage of label across the barrier. Plants in the intact rhizoboxes showed significantly higher 15N enrichment than those in controls, and mycorrhizal root tips were significantly more enriched than bulk roots. The mycorrhizas transferred an average of 1.3% of the added 15N label to plants, a figure comparable to those obtained in previous studies in which plant roots were directly exposed to label. We conclude that fungal associations have an important role in the N nutrition of K. myosuroides by transferring N from amino acids to their hosts. [ABSTRACT FROM AUTHOR]