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Natural wetlands are intrinsically heterogeneous and typically composed of a mosaic of ecosystem patches with different vegetation types. Hydrological and biogeochemical processes in wetlands vary strongly among these ecosystem patches. To date, most remote sensing classification approaches for wetland vegetation either rely on coarse images that cannot capture the spatial variability of wetland vegetation or rely on very-high-resolution multi-spectral images that are detailed but very sporadic in time (less than once per year). This study aimed to use NDVI time series, generated from NASA’s HLS dataset, to classify vegetation patches. We demonstrate our approach at a temperate, coastal lake, estuarine marsh. To classify vegetation patches, a standard time series library of the four land-cover patch types was built from referencing specific locations that were identified as “pure” pixels. These were identified using a single-time high-resolution image. We calculated the distance between the HLS-NDVI time series at each pixel and the “pure”-pixel standards for each land-cover type. The resulting true-positive classified rate was >73% for all patch types other than water lily. The classification accuracy was higher in pixels of a more uniform composition. A set of vegetation maps was created for the years 2016 to 2020 at our research site to identify the vegetation changes at the site as it is affected by rapid water elevation increases in Lake Erie. Our results reveal how changes in water elevation have changed the patch distribution in significant ways, leading to the local extinction of cattail by 2019 and a continuous increase in the area cover of water lily patches.

Present-day forests use water more efficiently, probably owing to the effect of increased atmospheric carbon dioxide on leaf stomata, which partially close to maintain a near-constant level of carbon dioxide inside the leaves despite increasing atmospheric levels. Large increase in forest water-use efficiency Theory suggests that rising atmospheric CO 2 concentrations should increase the efficiency with which plants use water, but the actual magnitude of this effect in natural forest ecosystems remains unknown. An analysis of long-term measurements of carbon and water fluxes from forest research sites across the Northern Hemisphere has identified an unexpectedly large increase in water-use efficiency during the past two decades, coinciding with an increase of atmospheric CO 2 from 350 to 400 parts per million. This trend is often accompanied by concurrent increases in rates of photosynthetic uptake and carbon sequestration. The authors suggest partial closure of stomata — to maintain constant CO 2 concentrations in the plant leaves — as the most likely explanation for the observed trend in water-use efficiency. The results are inconsistent with current theory and terrestrial biosphere models. Terrestrial plants remove CO 2 from the atmosphere through photosynthesis, a process that is accompanied by the loss of water vapour from leaves 1 . The ratio of water loss to carbon gain, or water-use efficiency, is a key characteristic of ecosystem function that is central to the global cycles of water, energy and carbon 2 . Here we analyse direct, long-term measurements of whole-ecosystem carbon and water exchange 3 . We find a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades. We systematically assess various competing hypotheses to explain this trend, and find that the observed increase is most consistent with a strong CO 2 fertilization effect. The results suggest a partial closure of stomata 1 —small pores on the leaf surface that regulate gas exchange—to maintain a near-constant concentration of CO 2 inside the leaf even under continually increasing atmospheric CO 2 levels. The observed increase in forest water-use efficiency is larger than that predicted by existing theory and 13 terrestrial biosphere models. The increase is associated with trends of increasing ecosystem-level photosynthesis and net carbon uptake, and decreasing evapotranspiration. Our findings suggest a shift in the carbon- and water-based economics of terrestrial vegetation, which may require a reassessment of the role of stomatal control in regulating interactions between forests and climate change, and a re-evaluation of coupled vegetation–climate models.

During periods of hydrologic stress, vegetation productivity is limited by soil moisture supply and atmospheric water demand. This study shows that atmospheric demand has a greater effect in many biomes, with implications for climate change impacts. Soil moisture supply and atmospheric demand for water independently limit—and profoundly affect—vegetation productivity and water use during periods of hydrologic stress 1 , 2 , 3 , 4 . Disentangling the impact of these two drivers on ecosystem carbon and water cycling is difficult because they are often correlated, and experimental tools for manipulating atmospheric demand in the field are lacking. Consequently, the role of atmospheric demand is often not adequately factored into experiments or represented in models 5 , 6 , 7 . Here we show that atmospheric demand limits surface conductance and evapotranspiration to a greater extent than soil moisture in many biomes, including mesic forests that are of particular importance to the terrestrial carbon sink 8 , 9 . Further, using projections from ten general circulation models, we show that climate change will increase the importance of atmospheric constraints to carbon and water fluxes in all ecosystems. Consequently, atmospheric demand will become increasingly important for vegetation function, accounting for >70% of growing season limitation to surface conductance in mesic temperate forests. Our results suggest that failure to consider the limiting role of atmospheric demand in experimental designs, simulation models and land management strategies will lead to incorrect projections of ecosystem responses to future climate conditions.

Drought and pluvial extremes are defined as deviations from typical climatology; however, background climatology can shift over time in a non‐stationary climate, impacting interpretations of extremes. This study evaluated trends in meteorological drought and pluvial extremes by merging tree‐ring reconstructions, observations, and climate‐model simulations spanning 850–2100 CE across North America to determine whether modern and projected future precipitation lies outside the range of natural climate variability. Our results found widespread and spatially consistent exacerbation of drought and pluvial extremes, especially summer drought and winter pluvials, with drying in the west and south, wetting trends in the northeast, and intensification of both extremes across the east and north. Our study suggests that climate change has already shifted precipitation climatology beyond pre‐Industrial climatology and is projected to further intensify ongoing shifts. Plain Language Summary Managing water resources has become challenging due to the effect of human‐caused climate change on precipitation. This study examines trends in droughts and pluvials from the distant past (850 CE) to the projected future (2100 CE) to determine whether precipitation extremes in the modern, Industrial era and future are beyond what is typical of natural climate variability in North America. Trends were generated by merging information from tree rings, observations, and climate models using a novel statistical approach. Results indicate the widespread intensification of both drought and pluvials–especially summer drought and winter pluvials during the modern and future periods. Spatially, southern and western regions of North America are becoming drier, while the northeast is getting wetter, and central areas of North America show a wider range between drought and pluvial years. Our study suggests that anthropogenic climate change has already modified drought and pluvial extremes beyond natural, pre‐Industrial conditions and these ongoing trends are projected to intensify through the future. Key Points This study models seasonal drought and pluvial trends, merging reconstructions, observations, and projections from 850 to 2100 CE Results show widespread exacerbation of both extremes with overall drying (wetting) in southern (northeastern) North America Modern drought and pluvial distributions are outside pre‐Industrial (1850) conditions, and exhibiting substantial shifts in some regions

Seed size and dormancy are reproductive traits that interact as adaptations to environmental conditions. Here, we explore the evolution of these traits in environments that differ in overall mean favorability and in the extent of temporal predictability. Our model simulates a population of annual plants living in a range of environments that differ in aridity, namely mean annual precipitation and inter-annual variation of this mean precipitation. The optimal fitness curve is investigated assuming density dependence, three alternative hypothetical relationships between seed mass and seed survival in the soil (negative, positive, and independent of mass), and three alternative relationships between survival in soil and precipitation (strong and intermediate negative relationships, and no relationship). Our results show that seed size and dormancy are not two substitutable evolutionary traits; that specific combinations of these two traits are selected in environments that differ in favorability and temporal predictability; that a certain degree of seed dormancy is advantageous not only in temporally unpredictable environments but also in temporally predictable environments with high competition; and that more than one combination of seed size and dormancy (defined in terms of germination fraction) can be optimal, even in spatially homogeneous environments, potentially allowing selection for more variation in these traits within and among species.

Methane flux from freshwater mineral-soil (FWMS) wetlands and its variability among sites is largely modulated by plant-mediated transport. However, plant-mediated transport processes are rarely resolved in land surface models and are poorly parametrized for plants commonly found in FWMS wetlands. Here, relationships between methane flux and CO₂ uptake, as well as plant conductance of methane were evaluated for three plant species and two characteristic functional types: emergent (narrow-leaved cattail) and floating-leaved (American lotus and water lily). We found significant but contrasting correlations between methane flux and CO₂ uptake in cattails (r² = 0.51, slope = −0.16, during morning) and water lily (r² = 0.32, slope = 0.064, after midday). This relationship was not significant in American lotus, showing that stomata regulation of methane fluxes is species-specific and not generalizable across the floating-leaved plant functional type. Conductance of methane per leaf area showed distinct seasonal dynamics across species. Conductance was similar among the floating-leaved species (6.2 × 10−3 m d−1 in lotus and 7.2 × 10−3 m d−1 in water lily) and higher than conductance in the emergent species (2.7 × 10−3 m d−1). Our results provide direct observations of plant conductance rates and identify the vegetation parameters (leaf area, stomatal conductance) that modify them. Our results further suggest that models of methane emissions from FWMS should parameterize plant-mediated transport in different plant functional types, scaled by leaf area and with variable seasonal phenological dynamics, and consider possible species-specific mechanisms that control methane transport through plants.

The current paradigm, widely incorporated in soil biogeochemical models, is that microbial methanogenesis can only occur in anoxic habitats. In contrast, here we show clear geochemical and biological evidence for methane production in well-oxygenated soils of a freshwater wetland. A comparison of oxic to anoxic soils reveal up to ten times greater methane production and nine times more methanogenesis activity in oxygenated soils. Metagenomic and metatranscriptomic sequencing recover the first near-complete genomes for a novel methanogen species, and show acetoclastic production from this organism was the dominant methanogenesis pathway in oxygenated soils. This organism, Candidatus Methanothrix paradoxum, is prevalent across methane emitting ecosystems, suggesting a global significance. Moreover, in this wetland, we estimate that up to 80% of methane fluxes could be attributed to methanogenesis in oxygenated soils. Together, our findings challenge a widely held assumption about methanogenesis, with significant ramifications for global methane estimates and Earth system modeling. Methane production is traditionally not found in oxygenated soils, a paradigm incorporated in global greenhouse gas modelling efforts. Here the authors show geochemical and biological evidence of active methanogenesis in bulk-oxic wetland soils, attributing up to 80% of the total methane budget for the site.

The timing of life-history events has a strong impact on ecosystems. Now, analysis of the phenology of temperate forests in the eastern US indicates that in the case of an earlier spring and a later autumn, carbon uptake (photosynthesis) increases considerably more than carbon release (respiration). The timing of phenological events exerts a strong control over ecosystem function and leads to multiple feedbacks to the climate system 1 . Phenology is inherently sensitive to temperature (although the exact sensitivity is disputed 2 ) and recent warming is reported to have led to earlier spring, later autumn 3 , 4 and increased vegetation activity 5 , 6 . Such greening could be expected to enhance ecosystem carbon uptake 7 , 8 , although reports also suggest decreased uptake for boreal forests 4 , 9 . Here we assess changes in phenology of temperate forests over the eastern US during the past two decades, and quantify the resulting changes in forest carbon storage. We combine long-term ground observations of phenology, satellite indices, and ecosystem-scale carbon dioxide flux measurements, along with 18 terrestrial biosphere models. We observe a strong trend of earlier spring and later autumn. In contrast to previous suggestions 4 , 9 we show that carbon uptake through photosynthesis increased considerably more than carbon release through respiration for both an earlier spring and later autumn. The terrestrial biosphere models tested misrepresent the temperature sensitivity of phenology, and thus the effect on carbon uptake. Our analysis of the temperature–phenology–carbon coupling suggests a current and possible future enhancement of forest carbon uptake due to changes in phenology. This constitutes a negative feedback to climate change, and is serving to slow the rate of warming.

Here we used soil metagenomics and metatranscriptomics to uncover novel members within the genus Methylobacter . We denote these closely related genomes as members of the lineage OWC Methylobacter . Despite the incredibly high microbial diversity in soils, here we present findings that unexpectedly showed that methane cycling was primarily mediated by a single genus for both methane production (“ Candidatus Methanothrix paradoxum”) and methane consumption (OWC Methylobacter ). Metatranscriptomic analyses revealed that decreased methanotrophic activity rather than increased methanogenic activity possibly contributed to the greater methane emissions that we had previously observed in summer months, findings important for biogeochemical methane models. Although members of this Methylococcales order have been cultivated for decades, multi-omic approaches continue to illuminate the methanotroph phylogenetic and metabolic diversity harbored in terrestrial and marine ecosystems. Microbial carbon degradation and methanogenesis in wetland soils generate a large proportion of atmospheric methane, a highly potent greenhouse gas. Despite their potential to mitigate greenhouse gas emissions, knowledge about methane-consuming methanotrophs is often limited to lower-resolution single-gene surveys that fail to capture the taxonomic and metabolic diversity of these microorganisms in soils. Here our objective was to use genome-enabled approaches to investigate methanotroph membership, distribution, and in situ activity across spatial and seasonal gradients in a freshwater wetland near Lake Erie. 16S rRNA gene analyses demonstrated that members of the methanotrophic Methylococcales were dominant, with the dominance largely driven by the relative abundance of four taxa, and enriched in oxic surface soils. Three methanotroph genomes from assembled soil metagenomes were assigned to the genus Methylobacter and represented the most abundant methanotrophs across the wetland. Paired metatranscriptomes confirmed that these Old Woman Creek (OWC) Methylobacter members accounted for nearly all the aerobic methanotrophic activity across two seasons. In addition to having the capacity to couple methane oxidation to aerobic respiration, these new genomes encoded denitrification potential that may sustain energy generation in soils with lower dissolved oxygen concentrations. We further show that Methylobacter members that were closely related to the OWC members were present in many other high-methane-emitting freshwater and soil sites, suggesting that this lineage could participate in methane consumption in analogous ecosystems. This work contributes to the growing body of research suggesting that Methylobacter may represent critical mediators of methane fluxes in freshwater saturated sediments and soils worldwide. IMPORTANCE Here we used soil metagenomics and metatranscriptomics to uncover novel members within the genus Methylobacter . We denote these closely related genomes as members of the lineage OWC Methylobacter . Despite the incredibly high microbial diversity in soils, here we present findings that unexpectedly showed that methane cycling was primarily mediated by a single genus for both methane production (“ Candidatus Methanothrix paradoxum”) and methane consumption (OWC Methylobacter ). Metatranscriptomic analyses revealed that decreased methanotrophic activity rather than increased methanogenic activity possibly contributed to the greater methane emissions that we had previously observed in summer months, findings important for biogeochemical methane models. Although members of this Methylococcales order have been cultivated for decades, multi-omic approaches continue to illuminate the methanotroph phylogenetic and metabolic diversity harbored in terrestrial and marine ecosystems.

The even-aged northern hardwood forests of the Upper Great Lakes Region are undergoing an ecological transition during which structural and biotic complexity is increasing. Early-successional aspen ( Populus spp.) and birch ( Betula papyrifera ) are senescing at an accelerating rate and are being replaced by middle-successional species including northern red oak ( Quercus rubra ), red maple ( Acer rubrum ), and white pine ( Pinus strobus ). Canopy structural complexity may increase due to forest age, canopy disturbances, and changing species diversity. More structurally complex canopies may enhance carbon (C) sequestration in old forests. We hypothesize that these biotic and structural alterations will result in increased structural complexity of the maturing canopy with implications for forest C uptake. At the University of Michigan Biological Station (UMBS), we combined a decade of observations of net primary productivity (NPP), leaf area index (LAI), site index, canopy tree-species diversity, and stand age with canopy structure measurements made with portable canopy lidar (PCL) in 30 forested plots. We then evaluated the relative impact of stand characteristics on productivity through succession using data collected over a nine-year period. We found that effects of canopy structural complexity on wood NPP (NPP W ) were similar in magnitude to the effects of total leaf area and site quality. Furthermore, our results suggest that the effect of stand age on NPP W is mediated primarily through its effect on canopy structural complexity. Stand-level diversity of canopy-tree species was not significantly related to either canopy structure or NPP W . We conclude that increasing canopy structural complexity provides a mechanism for the potential maintenance of productivity in aging forests.