ABSTRACT
Wildfire activity is increasing globally. The resulting smoke plumes can travel hundreds to thousands of kilometers, reflecting or scattering sunlight and depositing particles within ecosystems. Several key physical, chemical, and biological processes in lakes are controlled by factors affected by smoke. The spatial and temporal scales of lake exposure to smoke are extensive and under-recognized. We introduce the concept of the lake smoke-day, or the number of days any given lake is exposed to smoke in any given fire season, and quantify the total lake smoke-day exposure in North America from 2019 to 2021. Because smoke can be transported at continental to intercontinental scales, even regions that may not typically experience direct burning of landscapes by wildfire are at risk of smoke exposure. We found that 99.3% of North America was covered by smoke, affecting a total of 1,333,687 lakes ≥10 ha. An incredible 98.9% of lakes experienced at least 10 smoke-days a year, with 89.6% of lakes receiving over 30 lake smoke-days, and lakes in some regions experiencing up to 4 months of cumulative smoke-days. Herein we review the mechanisms through which smoke and ash can affect lakes by altering the amount and spectral composition of incoming solar radiation and depositing carbon, nutrients, or toxic compounds that could alter chemical conditions and impact biota. We develop a conceptual framework that synthesizes known and theoretical impacts of smoke on lakes to guide future research. Finally, we identify emerging research priorities that can help us better understand how lakes will be affected by smoke as wildfire activity increases due to climate change and other anthropogenic activities.
Subject(s)
Ecosystem , Lakes , Smoke , Wildfires , Smoke/analysis , North America , Environmental MonitoringABSTRACT
Submerged macrophytes are integral to the functioning of shallow lakes through their interaction with microorganisms. However, we have a limited understanding of how microbial communities in shallow lakes respond when macrophytes are restored after being historically extirpated. Here, we explored the interactions between prokaryotic communities and carbon utilization in two lakes where submerged macrophytes were restored. We found restoration reduced total carbon in sediment by 8.9 %-27.9 % and total organic carbon by 16.7 %-36.9 % relative to control treatment, but had no effects on carbon content in the overlying water. Sediment microbial communities were more sensitive to restoration than planktonic microbes and showed enhanced utilization of simple carbon substrates, such as Tween 40, after restoration. The increase in carbon utilization was attributed to declines in the relative abundance of some genera, such as Saccharicenans and Desertimonas, which were found weakly associated with the utilization of different carbon substrates. These genera likely competed with microbes with high carbon utilization in restored areas, such as Lubomirskia. Our findings highlight how restoring submerged macrophytes can enhance microbial carbon utilization and provide guidance to improve the carbon sequestration capacity of restored shallow lakes.
Subject(s)
Carbon , Lakes , Microbiota , Lakes/microbiology , Carbon/metabolism , Water Microbiology , Carbon Sequestration , Geologic Sediments/microbiology , Bacteria/metabolism , Environmental Restoration and Remediation/methodsABSTRACT
Dissolved organic matter may offer a way to track and restore the health of fresh waters.
Subject(s)
Dissolved Organic Matter , Environmental Monitoring , Fresh Water , Water Pollutants , Fresh Water/analysis , Fresh Water/chemistry , Water Pollutants/analysis , Water Pollutants/chemistry , Water Pollutants/toxicity , Environmental Health , Dissolved Organic Matter/analysis , Dissolved Organic Matter/chemistry , Dissolved Organic Matter/toxicity , Mass Spectrometry/methodsABSTRACT
Dissolved organic matter (DOM) is one of the most important fluxes in the global carbon cycle but its response to light exposure remains unclear at a molecular-level. The chemical response of DOM to light should vary with its molecular composition and environmental conditions while some basic hypotheses are still unclear, such as the balance between photobleaching and photo-humification and the question of oxidative properties. Here we exposed aquatic DOM from diverse freshwaters impacted by different levels of anthropogenic activity and algal exudates to environmentally-realistic light conditions. We found that photobleaching occurred in DOM with relatively high initial humic content producing low H/C molecules, whereas DOM with low initial humic content was humified. DOM pools with relatively high initial saturation and low aromaticity were prone to transform towards more unsaturated molecular formulae and high H/C molecules with a distinct decrease of bioavailability. Photo-transformation was mainly influenced by reactive intermediates, with reactive oxygen species (ROS) playing a dominant role in humification when the initial humus content of DOM was high. In contrast, for algal DOM with high protein content, it was likely that the autoxidation of excited state DOM was more important than indirect oxidation involving ROS. Our results reveal how photo-transformation patterns depend on the initial composition of DOM and provide new insights into the role of photochemical processes in biogeochemical cycling of DOM.
ABSTRACT
Soils are losing increasing amounts of carbon annually to freshwaters as dissolved organic matter (DOM), which, if degraded, can offset their carbon sink capacity. However, the processes underlying DOM degradation across environments are poorly understood. Here we show DOM changes similarly along soil-aquatic gradients irrespective of environmental differences. Using ultrahigh-resolution mass spectrometry, we track DOM along soil depths and hillslope positions in forest catchments and relate its composition to soil microbiomes and physico-chemical conditions. Along depths and hillslopes, we find carbohydrate-like and unsaturated hydrocarbon-like compounds increase in abundance-weighted mass, and the expression of genes essential for degrading plant-derived carbohydrates explains >50% of the variation in abundance of these compounds. These results suggest that microbes transform plant-derived compounds, leaving DOM to become increasingly dominated by the same (i.e., universal), difficult-to-degrade compounds as degradation proceeds. By synthesising data from the land-to-ocean continuum, we suggest these processes generalise across ecosystems and spatiotemporal scales. Such general degradation patterns can help predict DOM composition and reactivity along environmental gradients to inform management of soil-to-stream carbon losses.
Subject(s)
Dissolved Organic Matter , Microbiota , Organic Chemicals/analysis , Soil/chemistry , CarbonABSTRACT
The diversity of intrinsic traits of different organic matter molecules makes it challenging to predict how they, and therefore the global carbon cycle, will respond to climate change. Here we develop an indicator of compositional-level environmental response for dissolved organic matter to quantify the aggregated response of individual molecules that positively and negatively associate with warming. We apply the indicator to assess the thermal response of sediment dissolved organic matter in 480 aquatic microcosms along nutrient gradients on three Eurasian mountainsides. Organic molecules consistently respond to temperature change within and across contrasting climate zones. At a compositional level, dissolved organic matter in warmer sites has a stronger thermal response and shows functional reorganization towards molecules with lower thermodynamic favorability for microbial decomposition. The thermal response is more sensitive to warming at higher nutrients, with increased sensitivity of up to 22% for each additional 1 mg L-1 of nitrogen loading. The utility of the thermal response indicator is further confirmed by laboratory experiments and reveals its positive links to greenhouse gas emissions.
ABSTRACT
Humanity has drastically altered the biophysical systems that sustain life on Earth. We summarize progress and chart future directions in the emerging field of global change ecology, which studies interactions between organisms and their changing environment.
Subject(s)
Ecology , Planets , Earth, PlanetABSTRACT
Dissolved organic matter (DOM) is widely studied in environmental and biogeochemical sciences, but is susceptible to chemical and biological degradation during sample transport and storage. Samples taken in remote regions, aboard ships, or in large numbers need to be preserved for later analysis without changing DOM composition. Here we compare high-resolution mass spectra of solid phase extractable DOM before and after freezing at -20 °C. We found that freezing increases compositional dissimilarity in DOM by between 0 to 18.2% (median = 2.7% across 7 sites) when comparing replicates that were frozen versus unfrozen, i.e., processed immediately after sampling, as compared with differences between unfrozen replicates. The effects of freezing primarily consisted of a poorer detection limit, but were smaller than other sample preparation and analysis steps, such as solid phase extraction and variable ionisation efficiency. Freezing samples for either 21 or 95 days led to similar and only slight changes in DOM composition, albeit with more variation for the latter. Therefore, we conclude that sample freezing on these time scales should not impede scientific study of aquatic DOM and can be used where it makes logistical sense, such as for large spatial surveys or study of archived samples.
ABSTRACT
Microbes play an important role in aquatic carbon cycling but we have a limited understanding of their functional responses to changes in temperature across large geographic areas. Here, we explored how microbial communities utilized different carbon substrates and the underlying ecological mechanisms along a space-for-time substitution temperature gradient of future climate change. The gradient included 47 lakes from five major lake regions in China spanning a difference of nearly 15°C in mean annual temperatures (MAT). Our results indicated that lakes from warmer regions generally had lower values of variables related to carbon concentrations and greater carbon utilization than those from colder regions. The greater utilization of carbon substrates under higher temperatures could be attributed to changes in bacterial community composition, with a greater abundance of Cyanobacteria and Actinobacteriota and less Proteobacteria in warmer lake regions. We also found that the core species in microbial networks changed with increasing temperature, from Hydrogenophaga and Rhodobacteraceae, which inhibited the utilization of amino acids and carbohydrates, to the CL500-29-marine-group, which promoted the utilization of all almost carbon substrates. Overall, our findings suggest that temperature can mediate aquatic carbon utilization by changing the interactions between bacteria and individual carbon substrates, and the discovery of core species that affect carbon utilization provides insight into potential carbon sequestration within inland water bodies under future climate warming.
Subject(s)
Cyanobacteria , Lakes , Lakes/microbiology , Temperature , Cyanobacteria/metabolism , Cold Temperature , Carbon/metabolismABSTRACT
Methylmercury (MeHg) uptake by phytoplankton represents a key step in determining the exposure risks of aquatic organisms and human beings to this potent neurotoxin. Phytoplankton uptake is believed to be negatively related to dissolved organic matter (DOM) concentration in water. However, microorganisms can rapidly change DOM concentration and composition and subsequent impact on MeHg uptake by phytoplankton has rarely been tested. Here, we explored the influences of microbial degradation on the concentrations and molecular compositions of DOM derived from three common algal sources and tested their subsequent impacts on MeHg uptake by the widespread phytoplankton species Microcystis elabens. Our results indicated that dissolved organic carbon was degraded by 64.3â74.1% within 28 days of incubating water with microbial consortia from a natural mesoeutrophic river. Protein-like components in DOM were more readily degraded, while the numbers of molecular formula for peptides-like compounds had increased after 28 days' incubation, probably due to the production and release of bacterial metabolites. Microbial degradation made DOM more humic-like which was consistent with the positive correlations between changes in proportions of Peaks A and C and bacterial abundance in bacterial community structures as illustrated by 16S rRNA gene sequencing. Despite rapid losses of the bulk DOM during the incubation, we found that DOM degraded after 28 days still reduced the MeHg uptake by Microcystis elabens by 32.7â52.7% relative to a control without microbial decomposers. Our findings emphasize that microbial degradation of DOM would not necessarily enhance the MeHg uptakes by phytoplankton and may become more powerful in inhibiting MeHg uptakes by phytoplankton. The potential roles of microbes in degrading DOM and changing the uptakes of MeHg at the base of food webs should now be incorporated into future risk assessments of aquatic Hg cycling.
Subject(s)
Dissolved Organic Matter , Methylmercury Compounds , Humans , Methylmercury Compounds/chemistry , Methylmercury Compounds/metabolism , Phytoplankton , RNA, Ribosomal, 16S , Water , Water Pollutants, Chemical/chemistry , Water Pollutants, Chemical/metabolismABSTRACT
Climate warming increases tree mortality which will require sufficient reproduction to ensure population viability. However, the response of tree reproduction to climate change remains poorly understood. Warming can reduce synchrony and interannual variability of seed production ("masting breakdown") which can increase seed predation and decrease pollination efficiency in trees. Here, using 40 years of observations of individual seed production in European beech (Fagus sylvatica), we showed that masting breakdown results in declining viable seed production over time, in contrast to the positive trend apparent in raw seed count data. Furthermore, tree size modulates the consequences of masting breakdown on viable seed production. While seed predation increased over time mainly in small trees, pollination efficiency disproportionately decreased in larger individuals. Consequently, fecundity declined over time across all size classes, but the overall effect was greatest in large trees. Our study showed that a fundamental biological relationship-correlation between tree size and viable seed production-has been reversed as the climate has warmed. That reversal has diverse consequences for forest dynamics; including for stand- and biogeographical-level dynamics of forest regeneration. The tree size effects suggest management options to increase forest resilience under changing climates.
Subject(s)
Fagus , Trees , Humans , Trees/physiology , Pollination , Fagus/physiology , Reproduction , Forests , SeedsABSTRACT
Dissolved organic matter (DOM) is the most reactive pool of organic carbon in soil and one of the most important components of the global carbon cycle. Phototrophic biofilms growing at the soil-water interface in periodically flooding-drying soils like paddy fields consume and produce DOM during their growth and decomposition. However, the effects of phototrophic biofilms on DOM remain poorly understood in these settings. Here, we found that phototrophic biofilms transformed DOM similarly despite differences in soil types and initial DOM compositions, with stronger effects on DOM molecular composition than soil organic carbon and nutrient contents. Specifically, growth of phototrophic biofilms, especially those genera belonging to Proteobacteria and Cyanobacteria, increased the abundance of labile DOM compounds and richness of molecular formulae, while biofilm decomposition decreased the relative abundance of labile components. After a growth and decomposition cycle, phototrophic biofilms universally drove the accumulation of persistent DOM compounds in soil. Our results revealed how phototrophic biofilms shape the richness and changes in soil DOM at the molecular level and provide a reference for using phototrophic biofilms to increase DOM bioactivity and soil fertility in agricultural settings.
Subject(s)
Dissolved Organic Matter , Soil , Carbon , Agriculture , BiofilmsABSTRACT
We urgently need solutions to make our use of the planet's resources more sustainable and protect nature. A new collection of articles outlines a vision for a better tomorrow that draws on new advances in the development of green technologies.
Subject(s)
Planets , TechnologyABSTRACT
Northern lakes disproportionately influence the global carbon cycle, and may do so more in the future depending on how their microbial communities respond to climate warming. Microbial communities can change because of the direct effects of climate warming on their metabolism and the indirect effects of climate warming on groundwater connectivity from thawing of surrounding permafrost, especially at lower landscape positions. Here we used shotgun metagenomics to compare the taxonomic and functional gene composition of sediment microbes in 19 peatland lakes across a 1600-km permafrost transect in boreal western Canada. We found microbes responded differently to the loss of regional permafrost cover than to increases in local groundwater connectivity. These results suggest that both the direct and indirect effects of climate warming, which were respectively associated with loss of permafrost and subsequent changes in groundwater connectivity interact to change microbial composition and function. Archaeal methanogens and genes involved in all major methanogenesis pathways were more abundant in warmer regions with less permafrost, but higher groundwater connectivity partly offset these effects. Bacterial community composition and methanotrophy genes did not vary with regional permafrost cover, and the latter changed similarly to methanogenesis with groundwater connectivity. Finally, we found an increase in sugar utilization genes in regions with less permafrost, which may further fuel methanogenesis. These results provide the microbial mechanism for observed increases in methane emissions associated with loss of permafrost cover in this region and suggest that future emissions will primarily be controlled by archaeal methanogens over methanotrophic bacteria as northern lakes warm. Our study more generally suggests that future predictions of aquatic carbon cycling will be improved by considering how climate warming exerts both direct effects associated with regional-scale permafrost thaw and indirect effects associated with local hydrology.
Subject(s)
Lakes , Permafrost , Climate , Permafrost/microbiology , Carbon Cycle , Archaea/metabolism , Carbon/metabolismABSTRACT
There are vast but uncharacterized microbial taxa and chemical metabolites (that is, dark matter) across the Earth's ecosystems. A lack of knowledge about dark matter hinders a complete understanding of microbial ecology and biogeochemical cycles. Here, we examine sediment bacteria and dissolved organic matter (DOM) in 300 microcosms along experimental global change gradients in subtropical and subarctic climate zones of China and Norway, respectively. We develop an indicator to quantify the importance of dark matter by comparing co-occurrence network patterns with and without dark matter in bacterial or DOM assemblages. In both climate zones, dark matter constitutes approximately 30-56% of bacterial taxa and DOM metabolites and changes connectivity within bacterial and DOM assemblages by between -15.5 and +61.8%. Dark matter is generally more important for changing network connectivity within DOM assemblages than those of microbes, especially in the subtropical zone. However, the importance of dark matter along global change gradients is strongly correlated between bacteria and DOM and consistently increased toward higher primary productivity because of increasing temperatures and nutrient enrichment. Our findings highlight the importance of microbial and chemical dark matter for changing biogeochemical interactions under global change.
Subject(s)
Dissolved Organic Matter , Ecosystem , Bacteria/metabolism , Climate , ChinaABSTRACT
Global change is altering the vast amount of carbon cycled by microbes between land and freshwater, but how viruses mediate this process is poorly understood. Here, we show that viruses direct carbon cycling in lake sediments, and these impacts intensify with future changes in water clarity and terrestrial organic matter (tOM) inputs. Using experimental tOM gradients within sediments of a clear and a dark boreal lake, we identified 156 viral operational taxonomic units (vOTUs), of which 21% strongly increased with abundances of key bacteria and archaea, identified via metagenome-assembled genomes (MAGs). MAGs included the most abundant prokaryotes, which were themselves associated with dissolved organic matter (DOM) composition and greenhouse gas (GHG) concentrations. Increased abundances of virus-like particles were separately associated with reduced bacterial metabolism and with shifts in DOM toward amino sugars, likely released by cell lysis rather than higher molecular mass compounds accumulating from reduced tOM degradation. An additional 9.6% of vOTUs harbored auxiliary metabolic genes associated with DOM and GHGs. Taken together, these different effects on host dynamics and metabolism can explain why abundances of vOTUs rather than MAGs were better overall predictors of carbon cycling. Future increases in tOM quantity, but not quality, will change viral composition and function with consequences for DOM pools. Given their importance, viruses must now be explicitly considered in efforts to understand and predict the freshwater carbon cycle and its future under global environmental change.
Subject(s)
Greenhouse Gases , Viruses , Amino Sugars/metabolism , Bacteria/genetics , Bacteria/metabolism , Carbon/metabolism , Carbon Cycle , Greenhouse Gases/metabolism , Lakes/microbiology , Viruses/genetics , Viruses/metabolism , Water/metabolismABSTRACT
Plastic debris widely pollutes freshwaters. Abiotic and biotic degradation of plastics releases carbon-based substrates that are available for heterotrophic growth, but little is known about how these novel organic compounds influence microbial metabolism. Here we found leachate from plastic shopping bags was chemically distinct and more bioavailable than natural organic matter from 29 Scandinavian lakes. Consequently, plastic leachate increased bacterial biomass acquisition by 2.29-times when added at an environmentally-relevant concentration to lake surface waters. These results were not solely attributable to the amount of dissolved organic carbon provided by the leachate. Bacterial growth was 1.72-times more efficient with plastic leachate because the added carbon was more accessible than natural organic matter. These effects varied with both the availability of alternate, especially labile, carbon sources and bacterial diversity. Together, our results suggest that plastic pollution may stimulate aquatic food webs and highlight where pollution mitigation strategies could be most effective.
Subject(s)
Lakes , Plastics , Bacteria/metabolism , Carbon/metabolism , Environmental Pollution/analysis , Heterotrophic Processes , Plastics/chemistryABSTRACT
Microbes regulate the composition and turnover of organic matter. Here we developed a framework called Energy-Diversity-Trait integrative Analysis to quantify how dissolved organic matter and microbes interact along global change drivers of temperature and nutrient enrichment. Negative and positive interactions suggest decomposition and production processes of organic matter, respectively. We applied this framework to manipulative field experiments on mountainsides in subarctic and subtropical climates. In both climates, negative interactions of bipartite networks were more specialized than positive interactions, showing fewer interactions between chemical molecules and bacterial taxa. Nutrient enrichment promoted specialization of positive interactions, but decreased specialization of negative interactions, indicating that organic matter was more vulnerable to decomposition by a greater range of bacteria, particularly at warmer temperatures in the subtropical climate. These two global change drivers influenced specialization of negative interactions most strongly via molecular traits, while molecular traits and bacterial diversity similarly affected specialization of positive interactions.
Subject(s)
Climate , Dissolved Organic Matter , Bacteria/genetics , TemperatureABSTRACT
Dissolved organic matter (DOM) is a large and complex mixture of molecules that fuels microbial metabolism and regulates biogeochemical cycles. Individual DOM molecules have unique functional traits, but how their assemblages vary deterministically under global change remains poorly understood. Here, we examine DOM and associated bacteria in 300 aquatic microcosms deployed on mountainsides that span contrasting temperatures and nutrient gradients. Based on molecular trait dimensions of reactivity and activity, we partition the DOM composition into labile-active, recalcitrant-active, recalcitrant-inactive, and labile-inactive fractions and quantify the relative influences of deterministic and stochastic processes governing the assembly of each. At both subtropical and subarctic study sites, the assembly of labile or recalcitrant molecules in active fractions is primarily governed by deterministic processes, while stochastic processes are more important for the assembly of molecules within inactive fractions. Surprisingly, the importance of deterministic selection increases with global change gradients for recalcitrant molecules in both active and inactive fractions, and this trend is paralleled by changes in the deterministic assembly of microbial communities and environmental filtering, respectively. Together, our results highlight the shift in focus from potential reactivity to realized activity and indicate that active and inactive fractions of DOM assemblages are structured by contrasting processes, and their recalcitrant components are consistently sensitive to global change. Our study partitions the DOM molecular composition across functional traits and links DOM with microbes via a shared ecological framework of assembly processes. This integrated approach opens new avenues to understand the assembly and turnover of organic carbon in a changing world.
Subject(s)
Dissolved Organic Matter , Microbiota , Bacteria/metabolism , Carbon/metabolismABSTRACT
Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long-lived plants requires direct observation over many years and such datasets have rarely been made publicly available. Here we introduce MASTREE+, a data set that collates reproductive time-series data from across the globe and makes these data freely available to the community. MASTREE+ includes 73,828 georeferenced observations of annual reproduction (e.g. seed and fruit counts) in perennial plant populations worldwide. These observations consist of 5971 population-level time-series from 974 species in 66 countries. The mean and median time-series length is 12.4 and 10 years respectively, and the data set includes 1122 series that extend over at least two decades (≥20 years of observations). For a subset of well-studied species, MASTREE+ includes extensive replication of time-series across geographical and climatic gradients. Here we describe the open-access data set, available as a.csv file, and we introduce an associated web-based app for data exploration. MASTREE+ will provide the basis for improved understanding of the response of long-lived plant reproduction to environmental change. Additionally, MASTREE+ will enable investigation of the ecology and evolution of reproductive strategies in perennial plants, and the role of plant reproduction as a driver of ecosystem dynamics.
Aún existen importantes vacíos en la comprensión de la respuesta reproductiva de las plantas al cambio medioambiental, en parte, porque su monitoreo en especies de plantas longevas requiere una observación directa durante muchos años, y estos conjuntos de datos rara vez han estado disponibles. Aquí presentamos a MASTREE +, una base de datos que recopila series de tiempo de la reproducción de las plantas de todo el planeta, poniendo a disposición estos datos de libre acceso para la comunidad científica. MASTREE + incluye 73.828 puntos de observación de la reproducción anual georreferenciados (ej. conteos de semillas y frutos) en poblaciones de plantas perennes en todo el mundo. Estas observaciones consisten en 5971 series temporales a nivel de población provenientes de 974 especies en 66 países. La mediana de la duración de las series de tiempo es de 10 años (media = 12.4 años) y el conjunto de datos incluye 1.122 series de al menos dos décadas (≥20 años de observaciones). Para un subconjunto de especies bien estudiadas, MASTREE +incluye un amplio conjunto de series temporales replicadas en gradientes geográficos y climáticos. Describimos el conjunto de datos de acceso abierto disponible como un archivo.csv y presentamos una aplicación web asociada para la exploración de datos. MASTREE+ proporcionará la base para mejorar la comprensión sobre la respuesta reproductiva de plantas longevas al cambio medioambiental. Además, MASTREE+ facilitará los avances en la investigación de la ecología y la evolución de las estrategias reproductivas en plantas perennes y el papel de la reproducción vegetal como determinante de la dinámica de ecosistemas.