Terrestrial Production Research Articles

Ecological resilience in water-land transition zones: A case study of the Dongting Lake region, China

Water-land transition zones (WLTZs) are quintessential, complex human-land systems where aquatic and terrestrial environments intermingle, playing a pivotal role in bolstering global ecological resilience (ER). Human terrestrial production activities have encroached upon ecologically sensitive aquatic areas, weakening the inherent ER patterns in WLTZs. To address these issues, we developed an ER assessment process chain across the disturbance-carrying-recovery (D-C-R) dimensions. Applied it to the Dongting Lake region, this model diagnosed the spatiotemporal variations in ER from 2000 to 2020 and revealed the stress mechanisms of various driving factors. The results indicate: (1) The ER spatial pattern in the Dongting Lake region featured a radiating enhancement structure originating from a low-value core in the central plain’s lake network area, displaying distinct water-land gradient variations. Areas with declining ER levels were mainly distributed around the main body of the lake, water system runoff areas, and near governmental centers. (2) The spatiotemporal differentiation effects of ER manifested as an east–west axial development trend, tending toward polarization. The spatiotemporal aggregation effect appeared as L-L clustering and cold spots in the north, gradually expanding toward the peripheral forest areas. (3) Factors related to land use were the dominant drivers of spatiotemporal changes in ER. Simultaneously, the nonlinear interaction intensity among these driving factors showed a significant annual increase. This research framework can be extended to assess ER in similar regions, potentially offering policy recommendations for the ecological protection and sustainable management of WLTZs.

Early Nuclear Fusion Cross-Section Advances 1934–1952 and Comparison to Today’s ENDF Data

We describe the advancing knowledge of fusion cross sections from 1934 through the development of the first thermonuclear tests fielded by Los Alamos (the singular entity denoted Los Alamos Laboratory/Los Alamos Scientific Laboratory/Los Alamos National Laboratory at different times is designated “Los Alamos” in this paper) in the Pacific in 1951–1952; this technical history has not been previously documented. We compare these nuclear reaction cross sections to the current state of their knowledge as codified in the Evaluated Nuclear Data File (ENDF) databases, focusing on the Big Five reactions: 3H ( d , n ) 4 He, 3He ( d , p ) 4 He, 2H ( d , n ) 3 He, 2H ( d , p ) 3 H, and 3H ( t , 2 n ) 4 He. At Oppenheimer’s July 1942 University of California, Berkeley, “galaxy of luminaries” conference, Konopinski suggested that the cross section for 3H ( d , n ) 4 He “DT” could be large, and although Teller described this as an “inspired guess,” we provide evidence instead suggesting that Konopinski knew of a 1938 measurement by Ruhlig that secondary DT reactions were “exceedingly probable.” Bethe’s direction that the DT cross section should be measured at Purdue University (Purdue) in 1943 led to the remarkable and unexpected finding that the DT cross section exceeds deuteron-deuteron (DD) by a factor of 100. This was a game-changing result, making Teller’s dream, i.e., the terrestrial production of fusion energy, feasible. Eyewitness accounts are transcribed from the earliest discoveries of the large magnitude of the resonant DT cross section. A description is given of the Manhattan Project’s early 1942–1944 DD measurements at the University of Chicago, the 1943 DT measurements at Purdue, and the subsequent 1945–1946 DD and DT measurements at Los Alamos. The Los Alamos experiments, led by Bretscher, were the first to extend to very low incident ion center-of-mass energies in the 6- to 50-keV range needed in applications and the first to identify, characterize, and document the 3/2+ “Bretscher state” responsible for the resonance-enhanced DT cross section. The early measurements were based on thick-target experiments that required a knowledge of hydrogen-isotope stopping powers, much of which was informed by 1930s German studies. We end with the high-accuracy APSST (named for Arnold, Phillips, Sawyer, Stovall, and Tuck) measurements at Los Alamos, 1951–1952. The very first 1942–1946 measurements were accurate to about 50% or somewhat better, but by the early 1950s, the cross sections were determined much more accurately, to within a few percent of our best values today, which come from R-matrix Energy Dependent Analysis (EDA) code analyses of the data, most notably the very accurate 1980s–1990 Los Alamos DT and DD fusion data from Jarmie and Brown. We show that Fermi, in his 1945 Los Alamos lectures, anticipated the S-factor (for the DT cross section), which is a concept widely used later in nuclear astrophysics. To this long abstract, we add a final tidbit: Marshall Holloway, a coauthor on the first-ever 1943 DT cross-section measurement at Purdue, went on to lead the engineering and fabrication of the first H-bomb test, Ivy Mike.

Nitrogen, phosphorus, and potassium co‐limitation in terrestrial ecosystems: A global meta‐analysis

Societal Impact StatementNitrogen, phosphorus, and potassium are essential elements for plant growth and are the primary nutrients in commercial fertilizers. However, the extent to which these nutrients individually limit plant growth is still unclear, as is the influence of their interactions. Using a meta‐analysis approach, plant growth was found to be co‐limited by nitrogen, phosphorus, and potassium. Furthermore, these findings demonstrate that multiple nutrient additions are primarily additive, with the exception of synergistic effects observed with NP additions on plant growth. These findings are important as they provide a timely and valuable reference for assessing the ecosystem‐scale consequences of increasing nutrient deposition caused by human activities.Summary Numerous field studies and a few meta‐analyses have confirmed that terrestrial primary production is individually or jointly limited by nitrogen (N) and phosphorus (P). Meanwhile, a recent synthesis emphasized that potassium (K) limitation in terrestrial ecosystems is more widespread than previously thought. However, it remains unclear whether N, P, and K co‐limit terrestrial production and how their interactions influence plant growth. Therefore, we conducted a globally comprehensive synthesis of a total 2877 observations to explore the individual and interactive effects of N, P, and K additions on plant growth. We found that N, P, K, NP, NK, PK, and NPK additions significantly increased aboveground biomass production (AGP) by 30.8%, 15.3%, 12.3%, 68.4%, 36.5%, 21.1%, and 78.7%, respectively. The combined addition of multiple nutrients resulted in a larger increase in AGP than a single addition of nutrients. These findings suggested that terrestrial production is widely co‐limited by N, P, and K. However, no significant responses of belowground biomass production (BGP) to nutrient additions were observed. Except for synergistic interactions between N and P additions, the responses of AGP to other pairs of nutrient additions were predominantly additive. This meta‐analysis highlights the importance of multiple‐nutrient limitation in regulating terrestrial primary production while pointing out that non‐additive effects (including synergistic and antagonistic) of multiple‐nutrient additions on terrestrial production are relatively rare.

Can seaweeds feed the world? Modelling world offshore seaweed production potential

Pressure on the terrestrial ecosystems is large and big concerns exist regarding whether a growing world population can be fed from the land. Little is known about if and how much these concerns could be alleviated by harvesting more from the oceans. We modelled the biophysical production potential of seaweeds, and their current and possible future contribution to world food supply. We estimate seaweeds currently provide up to 0.13% of global food energy supply. Seaweed production is increasing more rapidly than terrestrial production. At current rates of increase we estimate seaweed energy contribution of 0.25% in 2050. Production potential of seaweeds could contribute up to 2 to 14% of global food supply if farming 1% of the modelled suitable space within the Exclusive Economic Zone. We show this large potential contribution to world food supply will only be achieved with unprecedented increases in seaweed production, while offshore seaweed cultivation is still in its infancy. The study shows large uncertainties that warrant further research. Modelling shows vast areas of world oceans are unsuitable because of being too far out of shore, having too low nutrient concentrations or having too high waves. Only 2–9% of world oceans and 6–25% of the Exclusive Economic Zone (EEZ) was shown to be suitable for seaweed production. Identifying suitable sites for offshore seaweed cultivation is therefore important. Site suitability maps reported for the 3 model species can be useful for private companies and policy makers expanding seaweed in new high potential production areas around the world.

Effects of the 2018 European heatwave and drought on coastal biogeochemistry in the German Bight

In 2018, Europe experienced an unprecedented heatwave and drought, especially in central and northern Europe, which caused decreased terrestrial production and affected ecosystem health. In this study, the effects of this event on the marine environment are investigate, with a focus on the biogeochemical response in the German Bight of the North Sea. Using time series data from FerryBoxes, research cruises, monitoring programs and remote sensing we compare conditions in 2018 to climatological values. We find that (1) the heatwave caused rapid warming of surface waters, (2) the drought reduced river discharge and nutrient loads to the coast, and (3) these combined effects altered coastal biogeochemistry and productivity. During 2018, both water discharge and nutrient loads from rivers discharging into the German Bight were below the seasonally variable 10th percentile from March onward. Throughout the study domain, water temperature was near or below that threshold in March 2018, but higher than in other years during May 2018, representing not only a heat wave, but also the fastest spring warming on record. This extreme warming period saw concurrent high peaks in chlorophyll a, dissolved oxygen and pH, consistent with the development of a strong spring bloom. It appears that productivity was above 75th percentile of the 21-year record in most of the nearshore region, while offshore it was widely below the 25th percentile in 2018. The drought-related low discharge limited nutrient supply from the rivers, but likely increased water residence time nearshore, where a surge in primary production with efficient nutrient utilization during the spring depleted nutrients available for transport offshore. There, the heatwave-related rapid warming of surface water resulted in the establishment of a stable thermal water column stratification, hindering vertical nutrient supply to the surface layer during the summer.

Aquatic biomass is a major source to particulate organic matter export in large Arctic rivers

Arctic rivers provide an integrated signature of the changing landscape and transmit signals of change to the ocean. Here, we use a decade of particulate organic matter (POM) compositional data to deconvolute multiple allochthonous and autochthonous pan-Arctic and watershed-specific sources. Constraints from carbon-to-nitrogen ratios (C:N), δ13C, and Δ14C signatures reveal a large, hitherto overlooked contribution from aquatic biomass. Separation in Δ14C age is enhanced by splitting soil sources into shallow and deep pools (mean ± SD: -228 ± 211 vs. -492 ± 173‰) rather than traditional active layer and permafrost pools (-300 ± 236 vs. -441 ± 215‰) that do not represent permafrost-free Arctic regions. We estimate that 39 to 60% (5 to 95% credible interval) of the annual pan-Arctic POM flux (averaging 4,391 Gg/y particulate organic carbon from 2012 to 2019) comes from aquatic biomass. The remainder is sourced from yedoma, deep soils, shallow soils, petrogenic inputs, and fresh terrestrial production. Climate change-induced warming and increasing CO2 concentrations may enhance both soil destabilization and Arctic river aquatic biomass production, increasing fluxes of POM to the ocean. Younger, autochthonous, and older soil-derived POM likely have different destinies (preferential microbial uptake and processing vs. significant sediment burial, respectively). A small (~7%) increase in aquatic biomass POM flux with warming would be equivalent to a ~30% increase in deep soil POM flux. There is a clear need to better quantify how the balance of endmember fluxes may shift with different ramifications for different endmembers and how this will impact the Arctic system.

Progress of studies on satellite-based terrestrial vegetation production models in China

Vegetation production is an important variable in terrestrial ecosystems, playing crucial roles in sustaining carbon balance, reducing atmospheric CO2 concentration, and mitigating global climate change. Satellite-based models, which benefit from spatially and temporally continuous remote sensing observations of vegetation growth conditions, are widely used for quantifying regional and global vegetation production. Satellite-based vegetation production models were initially simple statistical models, but later, process-based light use efficiency models were developed. The latest models are based on the relationship between solar-induced chlorophyll fluorescence and vegetation production. An increasing number of satellite-based studies are being conducted by Chinese scientists, who are developing and implementing plant production models, particularly by self-developing a number of light consumption efficiency models and establishing a long-term worldwide dataset of vegetation production. Furthermore, Chinese scientists have investigated the spatial and temporal patterns of vegetation using diverse models, significantly improving our understanding of terrestrial functions and structures. However, current models and estimation techniques need further improvement, and Chinese scientists had the opportunity to improve model capability and our understanding of vegetation production patterns and their regulating elements.

On the Feasibility of Fusion Energy

The conditions needed for fusion to occur are known. But terrestrial controlled fusion energy production remains, nevertheless, extremely difficult and potentially impracticable.

Characterisation of dissolved organic matter from temperate wetlands: field dynamics and photoreactivity changes driven by natural inputs and diagenesis along the hydroperiod

ABSTRACT Wetlands store large amounts of C in biomass, sediments and water. A major C fraction is in the dissolved organic matter (DOM) with multiple regulatory functions. Patagonian wetlands undergo changes in the water cycle due to climate warming and lower precipitation, causing shorter hydroperiods and reduced landscape connectivity with effects on C budgets. This study focuses on the optical characterisation of the DOM of an ephemeral wetland of North Patagonia. Along the hydroperiod the DOM showed optical signatures indicating terrestrial inputs, degradation and internal production. Dissolved organic carbon (DOC) concentration ranged between ∼4 and ∼9 mg L−1. The DOM pool displayed high molecular weight/size and aromatic fingerprints. Humic components C1 (microbial and/or vegetation derived) and C2 (soil/sediment) prevailed in the DOM, whereas the non-humic component C3 (from aquatic processes) increased from early spring. Experimental exposure to PAR + UVR produced slight changes in DOC and reduction in DOM molecular weight/size. The components showed distinctive photoreactivity/lability: C1 > C3 > C2. Along the hydroperiod the relative contribution of the humic vs. non-humic components (C1 and C3) determined the reactivity/lability of the DOM. In Fantasma pond, the DOM pool fluctuates in response to hydrology and degradation processes, and the alternance between dry and flooded periods determines C dynamics.

Integrating Aquatic and Terrestrial Carbon Fluxes to Assess the Net Landscape Carbon Balance of a Highly Erodible Semiarid Catchment

AbstractThe magnitude of the carbon (C) sink due to terrestrial primary production may be overestimated if the C losses through fluvial networks are not properly accounted for. In this study, we hypothesize that terrestrial‐aquatic C transfers represent a major loss of the terrestrial C sink in semiarid catchments. To test the hypothesis, we assessed the net landscape carbon balance (NLCB) of a highly erodible catchment on the semiarid Chinese Loess Plateau by compiling terrestrial net ecosystem productivity (NEP) estimates and aquatic fluxes of downstream C export, emission of CO2 and CH4, and C burial. Our results showed that, despite the severe erosion and strong C mobilization, this catchment was a net C sink (NLCB = 48.3–54.8 Mg C km−2 year−1). Downstream C export at catchment outlet and evasion of CO2 and CH4 only offset terrestrial NEP by 7.7%–8.5% due largely to low flow discharge and small water surface area of the stream network. Furthermore, C burial in reservoirs played a considerable role, reducing an additional 7.5%–8.3% of the NEP. Altogether, approximately 84% of the net terrestrial C production was stored within the catchment. Our study reveals that semiarid catchments with widespread erosion and low terrestrial production remain a net C sink, although the magnitude is lower than those found in other climate zones. Our study further advocates the need to integrate terrestrial‐aquatic C transfer into a comprehensive net C balance accounting at the landscape scale. Ignoring the aquatic C loss will cause biased estimates of the overall C sink strength.

Seafood in Food Security: A Call for Bridging the Terrestrial-Aquatic Divide

The contribution of seafood to global food security is being increasingly highlighted in policy. However, the extent to which such claims are supported in the current food security literature is unclear. This review assesses the extent to which seafood is represented in the recent food security literature, both individually and from a food systems perspective, in combination with terrestrially-based production systems. The results demonstrate that seafood remains under-researched compared to the role of terrestrial animal and plant production in food security. Furthermore, seafood and terrestrial production remain siloed, with very few papers addressing the combined contribution or relations between terrestrial and aquatic systems. We conclude that far more attention is needed to the specific and relative role of seafood in global food security and call for the integration of seafood in a wider interdisciplinary approach to global food system research.

Does feeding type matter? Contribution of organic matter sources to benthic invertebrates on the Arctic Chukchi Sea shelf

Benthic communities play an important role in the nutrient cycling of settling organic matter and provide an energy link to higher trophic levels. These benthic communities are highly dependent on the food sources provided through sinking organic material, with pelagic-benthic coupling particularly strong on Arctic shelf systems. Arctic shelves, however, are experiencing shifts in the timing of sea ice breakup that can have severe implications on the amount and composition of organic matter from different primary production sources supplied to the benthos. The role of benthic invertebrates in processing organic matter is typically classified by feeding types. The goal of this study was to evaluate if benthic invertebrate feeding types are a useful concept for understanding how organic matter from various biosynthetic sources is used by benthic invertebrates across the Arctic Chukchi Sea. We employed essential amino acid (EAA) specific stable isotope fingerprinting to identify proportional contributions of three EAA sources (from bacterial, phytoplankton, and terrestrial production) as a proxy of carbon sources to the diets of benthic consumers. When grouped by feeding types, the proportional contributions of the three EAA sources were similar among suspension, deposit feeders and predators/scavengers. Different genera within the same feeding type, however, showed significant differences among the EAA sources, indicating that EAA use is genus-specific rather than feeding type-specific. We discuss characteristics other than feeding mode among genera that could account for different EAA use, including mobility, selectivity of available EAA in sediments, and other trophic aspects such as assimilation efficiency. These characteristics provide useful additional considerations when grouping organisms by feeding types. High proportions of terrestrial EAA were found in the majority of benthic genera across all feeding types and characteristics in this study, reflecting the high proportions of this organic matter source in sediments and confirming that this source is being used by benthic consumers in the Arctic. EAA contributions to various benthic genera across the Chukchi Sea shelf had only weak correlations with environmental variables. While the distinctly different uses of different EAA sources by benthic-feeding genera but not by feeding types may represent high trophic plasticity in Arctic benthic invertebrates, expected climate change-driven shifts in the supply of EAA sources to the Chukchi Sea shelf benthos may still have implications for the composition of benthic communities and energy flow through the benthic food web, including energy pathways that support current top predators.

Consumption of fishery products in Turkey's coastal regions

PurposeDemand for fishery products rich in protein, vitamins, minerals and omega fatty acids has been increasing daily to meet the world population's increasing nutritional request, estimated to be 7.6 billion. Despite aquatic products' positive effects on human health, their consumption in Turkey has decreased over time and is currently lower than most countries with 6.3 kg per capita. The reason why fish consumption in Turkey is less than in other countries is the more preference for terrestrial production. Therefore, it was aimed to determine the consumption habits of consumers in Turkey's coastal region.Design/methodology/approachThis study was carried out between Feb–March 2018 to determine the consumption habits of aquatic products; 28 areas in the coastal regions of Turkey random were selected, 650 volunteer consumers were randomly selected to answer a set of 25 questions. The survey results were evaluated by Chi-square analysis.FindingsFrom the survey results, 81.4% of the respondents prefer to consume fish from the natural environment. Additionally, from the consumers, there was no statistical difference between natural (81.4%) and aquaculture (85.4%) fish taste (p = 0.05). It was found that 63% of the participants consumed fish meat once a week, with an average per capita consumption of 17.50 ± 2.34 and 10.50 ± 1.66 kg for fish and other seafood consumption, respectively. As a result, it was estimated that fish products were consumed at the desired level in the provinces examined. Accordingly, individuals need to be more conscious and encouraged to increase the consumption of seafood.Research limitations/implicationsBecause Turkey's seafood consumption is still held in coastal regions in this article are the limitations of this article results. In the future, the difference between inland and coastal regions for fish consumption needs to be explored further.Practical implicationsThe article says exports of fish / fisheries products have gradually decreased due to the global COVID-19 crisis, but producers / markets will have to target the domestic market more and sales with TL will come to the fore. As a result, it was estimated that fish products were consumed at the desired level in the studied provinces. Accordingly, it has been revealed that individuals should be more conscious and encouraged to increase their consumption of seafood.Social implicationsThrough this research, the consumption of fisheries consumption preferences of individuals in Turkey's coastal regions uncovered.Originality/valueOn the other hand, since Turkey's aquaculture and fisheries sector attaches great importance to foreign sales (exports), domestic consumption amounts are low, and the issue of increasing this is an issue that has remained in the background for the producer. However, during the COVID-19 pandemic period, it was well understood that the closing of the customs gates partially and/or completely and the export figures becoming scanty will cause the end of 2020 and 2021 to be more troublesome in this sense. Therefore, producers/markets will have to target the domestic market more, and sales with TL (Turkish Lira) will come to the fore, various campaigns and price reductions will be made during some special hours during the day in order to increase sales in domestic market.

Yak excreta-induced changes in soil microbial communities increased the denitrification rate of marsh soil under warming conditions

Microbial denitrification is a major contributor to the terrestrial production of greenhouse nitrous oxide (N2O). The responses of soil denitrifiers to yak excreta addition in marsh soil under a warming background have not been well evaluated. We investigated the soil physicochemical properties, denitrification rate (DR), enzymes and community of denitrifier genes (nirS and nirK) of marsh soil with different yak excreta additions (dung addition, D; urine addition, U) on the Southeast Qinghai-Tibetan Plateau under three different temperatures (13 °C, 19 °C and 25 °C). Excreta addition significantly increased the DR of marsh soil under different temperatures (P < 0.05). However, as temperature increased, yak excreta addition had no obvious effect on nitrate reductase (NAR) and nitrite reductase (NIR). Excreta addition reduced the diversity of the denitrifier community. nirK was more sensitive to excreta addition and temperature than nirS. For nirK, the proportions of Phyllobacteriaceae and Bradyrhizobiaceae were greater than those of other species and were mainly observed in the control (CK) and U, and Rhizobiaceae was mainly distributed in D. The proportion of Rhizobiaceae increased with increasing temperature, but the proportion of Hyphomicrobiaceae decreased. Unclassified Proteobacteria and unclassified bacteria were the dominant species for nirS. Oxalobacteraceae and Rhodocyclaceae were much more sensitive to temperature changes than other denitrifiers. The nirK community was mainly affected by NO2–N and TOC, but NO2–N and AP had a significant effect on nirS. AP, NO2–N and moisture could affect DR directly or indirectly by affecting the diversity of the denitrifier community and soil enzymes. Our findings suggest that yak excreta addition could profoundly promote DR by regulating the diversity of the denitrifier community of marsh ecosystems under warming conditions.

Net landscape carbon balance of a tropical savanna: Relative importance of fire and aquatic export in offsetting terrestrial production

The magnitude of the terrestrial carbon (C) sink may be overestimated globally due to the difficulty of accounting for all C losses across heterogeneous landscapes. More complete assessments of net landscape C balances (NLCB) are needed that integrate both emissions by fire and transfer to aquatic systems, two key loss pathways of terrestrial C. These pathways can be particularly significant in the wet-dry tropics, where fire plays a fundamental part in ecosystems and where intense rainfall and seasonal flooding can result in considerable aquatic C export (ΣFaq ). Here, we determined the NLCB of a lowland catchment (~140km2 ) in tropical Australia over 2years by evaluating net terrestrial productivity (NEP), fire-related C emissions and ΣFaq (comprising both downstream transport and gaseous evasion) for the two main landscape components, that is, savanna woodland and seasonal wetlands. We found that the catchment was a large C sink (NLCB 334MgCkm-2 year-1 ), and that savanna and wetland areas contributed 84% and 16% to this sink, respectively. Annually, fire emissions (-56MgCkm-2 year-1 ) and ΣFaq (-28MgCkm-2 year-1 ) reduced NEP by 13% and 7%, respectively. Savanna burning shifted the catchment to a net C source for several months during the dry season, while ΣFaq significantly offset NEP during the wet season, with a disproportionate contribution by single major monsoonal events-up to 39% of annual ΣFaq was exported in one event. We hypothesize that wetter and hotter conditions in the wet-dry tropics in the future will increase ΣFaq and fire emissions, potentially further reducing the current C sink in the region. More long-term studies are needed to upscale this first NLCB estimate to less productive, yet hydrologically dynamic regions of the wet-dry tropics where our result indicating a significant C sink may not hold.

The Ratio between Primary Production Values of Lake and Terrestrial Ecosystems.

At low latitudes (i.e., in the equatorial zone), the primary production of lake ecosystems is comparable with the plant production in their water catchment areas. In contrast, at high latitudes, the primary production of lake ecosystems is less than the primary terrestrial production approximately by two orders of magnitude. This paper addresses the reason behind the different reactions of the terrestrial and lake ecosystems to external factors determined by the geographical zone. Computational experiments show that in accordance with van't Hoff's rule, at high latitudes featuring low temperatures and higher humidity, the plant matter decomposition rates in lake basins are lower in comparison with low latitudes. The lower decomposition rates slow down the release and outflow into the water of nutrients essential for the organic matter production by aquatic autotrophs.

ORCHIDEE MICT-LEAK (r5459), a global model for the production, transport, and transformation of dissolved organic carbon from Arctic permafrost regions – Part 2: Model evaluation over the Lena River basin

Abstract. In this second part of a two-part study, we performed a simulation of the carbon and water budget of the Lena catchment with the land surface model ORCHIDEE MICT-LEAK, enabled to simulate dissolved organic carbon (DOC) production in soils and its transport and fate in high-latitude inland waters. The model results are evaluated for their ability to reproduce the fluxes of DOC and carbon dioxide (CO2) along the soil–inland-water continuum and the exchange of CO2 with the atmosphere, including the evasion outgassing of CO2 from inland waters. We present simulation results over the years 1901–2007 and show that the model is able to broadly reproduce observed state variables and their emergent properties across a range of interacting physical and biogeochemical processes. These include (1) net primary production (NPP), respiration and riverine hydrologic amplitude, seasonality, and inter-annual variation; (2) DOC concentrations, bulk annual flow, and their volumetric attribution at the sub-catchment level; (3) high headwater versus downstream CO2 evasion, an emergent phenomenon consistent with observations over a spectrum of high-latitude observational studies. These quantities obey emergent relationships with environmental variables like air temperature and topographic slope that have been described in the literature. This gives us confidence in reporting the following additional findings: of the ∼34 Tg C yr−1 left over as input to soil matter after NPP is diminished by heterotrophic respiration, 7 Tg C yr−1 is leached and transported into the aquatic system. Of this, over half (3.6 Tg C yr−1) is evaded from the inland water surface back into the atmosphere and the remainder (3.4 Tg C yr−1) flushed out into the Arctic Ocean, mirroring empirically derived studies. These riverine DOC exports represent ∼1.5 % of NPP. DOC exported from the floodplains is dominantly sourced from recent more “labile” terrestrial production in contrast to DOC leached from the rest of the watershed with runoff and drainage, which is mostly sourced from recalcitrant soil and litter. All else equal, both historical climate change (a spring–summer warming of 1.8 ∘C over the catchment) and rising atmospheric CO2 (+85.6 ppm) are diagnosed from factorial simulations to contribute similar significant increases in DOC transport via primary production, although this similarity may not hold in the future.

Phosphine as a Biosignature Gas in Exoplanet Atmospheres.

A long-term goal of exoplanet studies is the identification and detection of biosignature gases. Beyond the most discussed biosignature gas O2, only a handful of gases have been considered in detail. In this study, we evaluate phosphine (PH3). On Earth, PH3 is associated with anaerobic ecosystems, and as such, it is a potential biosignature gas in anoxic exoplanets. We simulate the atmospheres of habitable terrestrial planets with CO2- and H2-dominated atmospheres and find that PH3 can accumulate to detectable concentrations on planets with surface production fluxes of 1010 to 1014 cm-2 s-1 (corresponding to surface concentrations of 10s of ppb to 100s of ppm), depending on atmospheric composition and ultraviolet (UV) irradiation. While high, the surface flux values are comparable to the global terrestrial production rate of methane or CH4 (1011 cm-2 s-1) and below the maximum local terrestrial PH3 production rate (1014 cm-2 s-1). As with other gases, PH3 can more readily accumulate on low-UV planets, for example, planets orbiting quiet M dwarfs or with a photochemically generated UV shield. PH3 has three strong spectral features such that in any atmosphere scenario one of the three will be unique compared with other dominant spectroscopic molecules. Phosphine's weakness as a biosignature gas is its high reactivity, requiring high outgassing rates for detectability. We calculate that tens of hours of JWST (James Webb Space Telescope) time are required for a potential detection of PH3. Yet, because PH3 is spectrally active in the same wavelength regions as other atmospherically important molecules (such as H2O and CH4), searches for PH3 can be carried out at no additional observational cost to searches for other molecular species relevant to characterizing exoplanet habitability. Phosphine is a promising biosignature gas, as it has no known abiotic false positives on terrestrial planets from any source that could generate the high fluxes required for detection.

Iron oxides affect denitrifying bacterial communities with the nirS and nirK genes and potential N2O emission rates from paddy soil

Microbial denitrification in agricultural soil is a major contributor to the terrestrial production of the greenhouse gas nitrous oxide (N2O). Iron oxides play influential roles in both biochemical and chemical pathways that produce N2O; however, their role in the denitrifying bacterial community is not clear. In this study, a laboratory soil-slurry pot experiment was carried out to determine the impacts of ferric iron (Fe(III)) reduction on the abundance and community structure of denitrifiers and on N2O generation. Three treatments were included: paddy soil from which iron oxides were removed (control), non-treated paddy soil, and paddy soil supplemented with ferrihydrite (86.3 μmol Fe(III) g−1). N2 and N2O concentrations in the headspace were measured using a robotized sampling and analysis system. The gene copy numbers of nirK, nirS, and the 16S rRNA gene were quantified by qPCR and amplification products were sequenced on the Illumina MiSeq platform. The results showed that ferrihydrite supplementation accelerated N2O fluxes in the initial days, and at later stages, N2 production. Ferrihydrite increased the total bacterial abundance and strongly increased nirS and nirK gene abundances. The abundance of nirS gene correlated with the soil nitrate content, and nirK abundance correlated with the ferrous iron concentration in the soil. Fe(III) oxides were identified as one of the environmental parameters impacting the abundance and diversity of nirK-type denitrifiers. Paracoccus and Rhodopseudomonas were dominant species of nirK-type denitrifiers in the ferrihydrite-supplemented samples, which indicated the both iron-dependent species were involved in the denitrification process.

Environmental history of the northwestern Québec Treeline

Latitudinal treeline in northwestern Québec, Canada, is a broad band of forest-tundra between 56 and 58°N. Three new pollen records from the forest-tundra zone were combined with ten previously-published records to form a transect of paleoecological data across this treeline. The area was deglaciated ∼6–7 ka, with only a brief period of shrub tundra vegetation in the oldest sediments of all sites. Noticeable values of Populus, Juniperus and Larix pollen percentages were found during this time in the southernmost sites, suggesting they comprised part of the initial plant migration. Maximum Picea pollen percentages were found between 2 and 4 ka across the boreal forest and forest-tundra, with values remaining constant in the boreal forest and decreasing in the forest-tundra in the past 3 ka. Across the entire area, pollen influx decreased in the past 4 ka, and non-arboreal pollen increased in the forest-tundra, suggesting an opening of the forest and decrease in terrestrial production. Charcoal influx also declined, indicating a reduction in fire activity in the past 2–4 ka. Although the treeline has remained in the same average location in the region over the past 6 ka, the strength of the temperature gradient across the frontal zone changed over the course of the Holocene.