Primary Production Research Articles

High-quality genome of a novel Thermosynechococcaceae species from Namibia and characterization of its protein expression patterns at elevated temperatures.

Thermophilic cyanobacteria thrive in extreme environments, making their thermoresistant enzymes valuable for industrial applications. Common habitats include hot springs, which act as evolutionary accelerators for speciation due to geographical isolation. The family Thermosynechococcaceae comprises thermophilic cyanobacteria known for their ability to thrive in high-temperature environments. These bacteria are notable for their photosynthetic capabilities, significantly contributing to primary production in extreme habitats. Members of Thermosynechococcaceae exhibit unique adaptations that allow them to perform photosynthesis efficiently at elevated temperatures, making them subjects of interest for studies on microbial ecology, evolution, and potential biotechnological applications. In this study, the genome of a thermophilic cyanobacterium, isolated from a hot spring near Okahandja in Namibia, was sequenced using a PacBio Sequel IIe long-read platform. Cultivations were performed at elevated temperatures of 40, 50, and 55°C, followed by proteome analyses based on the annotated genome. Phylogenetic investigations, informed by the 16S rRNA gene and aligned nucleotide identity (ANI), suggest that the novel cyanobacterium is a member of the family Thermosynechococcaceae. Furthermore, the new species was assigned to a separate branch, potentially representing a novel genus. Whole-genome alignments supported this finding, revealing few conserved regions and multiple genetic rearrangement events. Additionally, 129 proteins were identified as differentially expressed in a temperature-dependent manner. The results of this study broaden our understanding of cyanobacterial adaptation to extreme environments, providing a novel high-quality genome of Thermosynechococcaceae cyanobacterium sp. Okahandja and several promising candidate proteins for expression and characterization studies.

Mapping intertidal microphytobenthic biomass with very high-resolution remote sensing imagery in an estuarine system

Microphytobenthos (MPB) contributes significantly to estuarine primary production, so that quantifying its biomass is crucial for assessing their ecosystem functioning. Conventional sampling methods are labour-intensive, logistically challenging, and cannot provide a comprehensive spatial distribution map of MPB biomass. Satellite imagery has offered a feasible alternative for mapping large areas at various temporal and spatial resolutions. However, no imaging device with a spatial resolution consistent with the few square centimetres sampled in-situ has been used in the field. This makes it challenging to accurately relate field biomass measurements with remotely sensed radiometric observations. In this study, two similar multispectral sensors were mounted on an unmanned aerial vehicle (UAV) at different altitudes, as well as on a custom-built device specifically designed to acquire images at ∼1 m altitude, in order to collect very-high spatial resolution reflectance data of MPB biofilms at the Guadalquivir Estuary (Spain) mudflats. In addition, a hyperspectral spectroradiometer acquiring in-situ field reflectance was used for validation. Simultaneously, MPB samples were collected using a 2 mm depth contact corer method, which were analysed through high-performance liquid chromatography (HPLC) to measure the concentrations of major MPB pigments. To assess the relationship between the MPB pigments and different reflectance-based spectral indices, generalised linear mixed effects models (GLMMs) were used, achieving a significant positive relationship between chlorophylls and all spectral indices tested. These models were used to map microphytobenthic biomass, yielding a mean biomass in the range of 30–50 mg Chl-a m−2 in the Guadalquivir estuary during late winter. This study demonstrates the potential of low-altitude/high spatial resolution radiometric imaging as an efficient, rapid, and non-destructive addition to in-situ measurements of MPB biomass, providing exciting perspectives for the monitoring of estuarine systems on a millimetric scale of variability.

Soil carbon and nitrogen cycling at the atmosphere-soil interface: Quantifying the responses of biocrust-soil interactions to global change.

In drylands, where water scarcity limits vascular plant growth, much of the primary production occurs at the soil surface. This is where complex macro- and microbial communities, in an intricate bond with soil particles, form biological soil crusts (biocrusts). Despite their critical role in regulating C and N cycling in dryland ecosystems, there is limited understanding of the fate of biologically fixed C and N from biocrusts into the mineral soil, or how climate change will affect C and N fluxes between the atmosphere, biocrusts, and subsurface soils. To address these gaps, we subjected biocrust-soil systems to experimental warming and drought under controlled laboratory conditions, monitored CO2 fluxes, and applied dual isotopic labeling pulses (13CO2 and 15N2). This allowed detailed quantification of elemental pathways into specific organic matter (OM) pools and microbial biomass via density fractionation and phospholipid fatty acid analyses. While biocrusts modulated CO2 fluxes regardless of the temperature regime, drought severely limited their photosynthetic C uptake to the extent that the systems no longer sustained net C uptake. Furthermore, the effect of biocrusts extended into the underlying 1 cm of mineral soil, where C and N accumulated as mineral-associated OM (MAOM<63μm). This was strongly associated with increased relative dominance of fungi, suggesting that fungal hyphae facilitate the downward C and N translocation and subsequent MAOM formation. Most strikingly, however, these pathways were disrupted in systems exposed to warming, where no effects of biocrusts on the elemental composition of the underlying soil nor on MAOM were determined. This was further associated with reduced net biological N fixation under combined warming and drought, highlighting how changing climatic conditions diminish some of the most fundamental ecosystem functions of biocrusts, with detrimental repercussions for C and N cycling and the persistence of soil organic matter pools in dryland ecosystems.

An exceptional phytoplankton bloom in the southeast Madagascar Sea driven by African dust deposition

Abstract Rising surface temperatures are projected to cause more frequent and intense droughts in the world's drylands. This can lead to land degradation, mobilization of soil particles, and an increase in dust aerosol emissions from arid and semi-arid regions. Dust aerosols are a key source of bio-essential nutrients, can be transported in the atmosphere over large distances, and ultimately deposited onto the ocean's surface, alleviating nutrient limitation and increasing oceanic primary productivity. Currently, the linkages between desertification, dust emissions and ocean fertilization remain poorly understood. Here, we show that dust emitted from Southern Africa was transported and deposited into the nutrient-limited surface waters southeast of Madagascar, which stimulated the strongest phytoplankton bloom of the last two decades during a period of the year when blooms are not expected. The conditions required for triggering blooms of this magnitude are anomalous, but current trends in air temperatures, aridity, and dust emissions in Southern Africa suggest that such events could become more probable in the future. Together with the recent findings on ocean fertilization by drought-induced megafires in Australia, our results point toward a potential link between global warming, drought, aerosol emissions, and ocean blooms.

Process‐Based Modeling of Ecosystem‐Level Monoterpene From a Japanese Larch (Larix kaempferi) Forest

AbstractGlobally, the emission of biogenic volatile organic compounds (BVOC) by plants represents the dominant source of volatile organic compounds emitted to the atmosphere. Monoterpenes, as the major BVOC group, can contribute to forming secondary organic aerosols and influence cloud properties. In this study, we developed a process‐based monoterpene module in the Vegetation Integrative SImulator for Trace gases (VISIT) model by considering the production, storage, and emission of monoterpene as three main processes. We further evaluated the modeled monoterpene emissions against the ecosystem‐level observation data at a half‐hour scale at a Japanese larch (Larix kaempferi) forest site on Mt. Fuji, Japan. The VISIT model performed with relatively higher accuracy with a Willmott's index of agreement at 0.61, a mean bias error (MBE) at 0.29, and a root mean squared error (RMSE) at 0.43, comparable to that of Model of Emissions of Gases and Aerosols from Nature model with a Willmott's index of agreement at 0.63, a MBE at 0.40, and a RMSE at 0.54. In a long‐term simulation under high CO2 emission scenarios, the ratio between monoterpene emission and gross primary production exhibited a stronger correlation with CO2 concentration than temperature. Our study provides a process‐based modeling approach for more accurately simulating monoterpene emissions from Japanese larch.

Sedimentary geochemistry in P-limited freshwater drained marshes (Charente-Maritime, France): original drivers for phosphorus mobilization

Phosphorus bioavailability is a major issue in aquatic environments, where it generally limits primary production. In this work, the analysis of the pore water and the solid phase of the sediment was carried out over a 9-month monitoring period between February 2020 and April 2021 in two drained marshes (Marans and Genouillé, France) distinct by their uses and management tools. Soluble reactive phosphorus (SRP) enrichment in the sediment was intimately controlled by iron oxide dissolution. The latter seemed highly controlled by seasonal nitrate inputs (winter and early spring) that favoured denitrification as a major benthic mineralization process promoting iron curtain development and stability. Following benthic mitigation of nitrate other anaerobic metabolisms developed such as iron dissolutive reduction promoting P recycling and planktic bioavailability. Surprisingly, sulphur cycle seemed to affect P dynamics, especially in the absence of nitrate. The absence of NO3- triggered high sulphate reduction rates in the two first centimeters depth, reaching -8.9E-03 ± 0.5E-03 and -5.0E-03 ± 0.2E-03 nmol cm-3 s-1 in August and July at Marans and Genouillé respectively. These values placed this process at higher rates than the denitrification (maximum in May at Marans with -5.0E-03 ± 1.1E-03 nmol cm-3 s-1) and reduced iron production (maximum in July at Genouillé with 0.5E-03 ± 0.1E-03 nmol cm-3 s-1). The rapidity with which process changes occur (monthly scale) testified to the dynamism of these systems. The similarity in geochemical patterns regarding NO3- pressure at both sites underlines the importance of diffuse pollution in coastal systems for nitrogen mitigation and phosphorus trapping. The results obtained in this study could lead to the development of a generalized diagenetic operating model for temperate systems with high agricultural pressure. This would enable to target management efforts to both optimize the purification function and limit eutrophication risks in these systems.

Hydrogen peroxide mediated thermo-catalytic conversion of carbon dioxide to C1-C2 products over Cu (0)

The global challenge concerning CO2 conversion to valuable products is anticipated to execute an essential task towards net zero carbon emissions. Thermal CO2 reduction is advantageous in terms of higher conversion rates, selectivity, and already-established industrial thermal instruments for scalability. However, the method is energy-intensive, a hindrance to sustainably practical adoption. Herein, we present a comprehensive study of H2O2-mediated thermal CO2 conversion in the presence of dendritic zerovalent copper (d-ZCu) in a batch-type reactor, yielding C1 and C2 carbon products, with acetic acid (AcOH) as the major product (achieving an optimized yield of approximately 0.98 M and a selectivity of around 97 % at near ambient conditions of 25–150 °C and 1–15 bar), along with trace amounts of methanol and ethanol, and carbon monoxide (CO) as a gaseous product. The reaction parameters, including temperature, time, pressure, and concentrations, were optimized to gain better insight into the reaction. To further explore the feasibility of the process, experiments were conducted in a continuous flow-packed bed reactor using similar parameters as those in the batch reactor, where CO was identified as the primary product of CO2 reduction. For advanced real-life applicability, the as-emitted exhaust gases from diesel and petrol engines, as sources of anthropogenic CO2, were utilized to establish the practical applicability of the proposed method.

Picophytoplankton prevail year-round in the Elbe estuary.

Picophytoplankton are important primary producers, but not always adequately recognized, for example, due to methodological limitations. In this study, we combined flow cytometry and metabarcoding to investigate seasonal and spatial patterns of picophytoplankton abundance and community composition in the Elbe estuary. Due to the mixing of freshwater and seawater and the tidal currents this ecosystem is characterized by typical estuarine features such as salinity gradients and high turbidity. Picophytoplankton (mostly picoeukaryotes such as Mychonastes and Minidiscus) contributed on average 70% (SD = 14%) to the total phytoplankton counts. In summer picocyanobacteria (e.g., Synechococcus) played a more significant role. The contributions of picophytoplankton to the total phytoplankton were particularly high from summer to winter as well as in the mid estuary. However, at salinities of around 10 PSU in the mixing area of freshwater and seawater, the proportion of picophytoplankton was comparably low (average 49%, SD = 13%). Our results indicate that picophytoplankton prevail in the Elbe estuary year-round with respect to cell counts. Picophytoplankton could occupy important niche positions to maintain primary production under extreme conditions where larger phytoplankton might struggle (e.g., at high or low temperature, high turbidity, and in areas with high grazing pressure) and also benefit from high nutrient availability here. However, we did not find evidence that they played a particularly significant role at the salinity interface. Our study highlights the importance of including picophytoplankton when assessing estuarine phytoplankton as has been suggested for other ecosystems such as oceans.

Pulsed wind-driven control of phytoplankton biomass at a groundwater-enriched nearshore environment

Along some Mediterranean coastal areas and other world regions, nutrient and chlorophyll concentrations often show gradient increases of up to one order of magnitude perpendicular to the coast. This nearshore stripe, extending a few hundred meters from the coast, is enriched by submarine groundwater discharges (SGD) containing elevated nutrient concentrations that may eventually sustain high biomass phytoplankton blooms. During a survey carried out in the summer of 2018, we examined the short-term (hours) variability of the phytoplankton biomass (measured as chlorophyll; Chl) in response to environmental changes associated with SGD and wind forcing in the nearshore waters of Palma Beach (Mediterranean Sea). Continuous CTD records revealed a general salinity decline indicative of SGD along the shoreline. Large and pulsed salinity fluctuations (i.e. 2–3 psu variations, 1–4 h) were observed each day that were consistent with offshore advection episodes of the lower salinity water retained in the nearshore (peak crosshore velocity 5–6 cm s−1). Chl near the shoreline was markedly higher than offshore (3.55 ± 1.29 and 0.68 ± 0.27 mg m−3 respectively) but recurrently fluctuated in the afternoon to up to >7 mg m−3. Primary production estimations showed that despite the higher production in the nearshore (50.29 ± 10.98 μmol O2 L−1 d−1, 4-fold offshore values) productivity per unit chlorophyll did not significantly vary (p > 0.01) therefore suggesting that, at this time scales, high biomass episodes in the nearshore are driven by an accumulation mechanism. Statistical analysis (CCA) demonstrates that Chl variability is largely explained (93 %) by variations in wind and current velocity. Our results provide evidence that the dynamics of this nearshore environment are modulated by the interplay between the shoreward wind-induced flow and the offshore directed density flow. This mechanism could explain the occurrence and episodic nature of high biomass blooms in the nearshore, as well as be an important factor influencing the microbial community structure at the coastal zone.

Anomalous 2022 deep-water formation and intense phytoplankton bloom in the Cretan area

Abstract. The Mediterranean Sea is a quasi-permanently stratified and oligotrophic basin with intense late-winter and early-spring phytoplankton blooms typically limited to few regions (i.e. northwestern Mediterranean Sea, the southern Adriatic Sea, and the Rhodes Gyre). In these areas, blooms are sustained by nutrient injection to surface layers by winter vertical mixing and convective processes. A markedly intense bloom was predicted in spring 2022 in an unusual area of the southeastern Mediterranean Sea (i.e. southeast of Crete) by the Mediterranean Sea Copernicus Marine Forecasting Centre (MED MFC) system. Combining Copernicus modelling and observation products, the 2022 event and a number of driving and concurrent features have been investigated in a multidisciplinary way. A noticeable cold spell that occurred in Eastern Europe at the beginning of 2022 has been identified as the main driver of an intense deep-water formation event, with associated high nutrient concentrations in the surface layers. Consequently, an extreme phytoplankton bloom that was 50 % more intense than usual occurred in the area southeast of Crete, starting nearly 1 month later than usual and lasting for 3–4 weeks. Impacts on primary production were also relevant in the 2022 event area and were 35 % higher than the climatological annual primary production. Furthermore, the documented link between primary productivity and fishery catches suggests possible consequences along the whole food chain up to the marine ecosystem in the eastern Mediterranean Sea.

Warming-induced soil moisture stress threatens food security in India.

Soil moisture (SM) interconnects various components of the Earth system and drives the land-atmosphere feedbacks and food production. However, around 40% of global vegetated land experiences SM drying. India is one of the global hotspots of land-atmosphere interactions and an extensively agrarian economy, but underexplored in terms of SM dynamics and its ramifications on food security. Here, we examine the mechanism of SM drying and its implications on cropland productivity in India based on remote sensing measurements and land surface model simulations in recent decades (2000-2019) and future projection of the 21st century. We find SM reduction predominantly in monsoon (4.5%) and winter (3%) seasons that areinthemajor agricultural seasonsofKharif and Rabi, respectively. Machine learning (ML)-based random forest (RF) reveals that temperature (T, 30.76%) is the dominant driver of SM variability, and then precipitation (P, 26.34%), evapotranspiration (ET, 26.08%) and surface greenness (16.82%). Concurrently, India experiences severe warming in terms of land (0.59 ℃/dec), soil (0.48 ℃/dec) and soil heat flux (SHF, 0.16 W/m2/dec) during 2000-2019. Partial correlation analysis between SM and T limiting the influence of P reveals a strong negative (> - 0.5) relationship in the agriculture intensive regions of Indo-Gangetic Plain (IGP) and South India (SI). Drying owing to warming and increased SHF, termed as warming-induced moisture stress, reduces gross primary productivity (GPP) (i.e. browning) and yield of major food crops of wheat, rain-fed rice, maize and soyabean, predominantly in SI and eastern IGP. Granger Causality shows that warming-induced soil moisture stress has a maximum temporal lag of 1month. In a warming world, the ever-growing population demands more food, and therefore, the warming-induced soil moisture stress is a serious threat to food security in India and similar agro-climatic regions of the world. This calls for climate-resilient agriculture, better agronomic management, improved irrigation and adoption of water-efficient crops.

Late Jurassic paleoenvironmental reconstruction based on stable oxygen isotopes in bulk carbonates from the Qiangtang Basin, eastern Tethys

A composite eastern Tethyan oxygen and carbon isotope curve reveals major climate changes through the Late Jurassic. Despite significantly lower values and different amplitudes in scale, the δ18O data from whole-rock carbonates present fluctuant temperature results similar with well-studied composite δ18O curves of diagenetically-screened biogenic calcites, and are possibly acceptable as a paleotemperature proxy. The paleoclimate trends imply a cool global Callovian-Oxfordian transition, a mid-Oxfordian warming, a late Oxfordian cooling, a turbulent Kimmeridgian climate, a warm earliest Tithonian and rapid early Tithonian cooling event. The climate shift from the earliest Tithonian warmth to the middle early Tithonian cool climate was up to 8 °C decrease in some regions. These paleoclimate changes are greatly consistent with the eustatic sea-level changes, biological evolutions and paleoatmospheric CO2 reconstructions, and are recorded by coeval carbon isotope perturbations relating to the organic carbon accumulations in marine sediments. Coupled δ18O and δ13C chemostratigraphy evidence that higher temperatures lead to more rapid continental weathering, increased nutrient-rich runoff into the oceans, and intensified marine productivity, resulting in increased organic‑carbon burial and more positive δ13C values in limestones. The decrease in primary productivity and burial rates during cooling periods is, in turn, commonly accompanied by low δ13C values.

PREVALENCE AND MOLECULAR CHARACTERIZATION OF ROTAVIRUS IN MEAT CUTS, AND MEAT HANDLERS IN SELECTED ABATTOIRS IN NAIROBI, KENYA

In Kenya, food screening exercises mostly applies to bacterial and parasitic agents, with enteric viral detection neglected. This study aimed to determine the prevalence and molecular characterization of rotavirus in beef/pork cuts and beef/pork handlers in 4 selected abattoirs in Nairobi. Rotavirus was preferred because of its high prevalence rates and its ability to cause pathophysiologic infective gastroenteritis in humans. It has diverse strains characterized as P and G genotypes based on the VP7 and VP4 proteins, respectively. This cross-section study involved the collection of a total of 467, (165) beef/pork cuts and (302) handlers fecal samples. Collected samples wereprepared before rotavirus identification. Prepared meat and stool suspensions were subjected to direct RNA extraction and EIA detection respectively. All the stool suspensionsand RNA extracted meat suspensions subjected to EIA and Two step RT-PCR were all non-reactive respectively. Therefore, there was no VP4 and VP7 genotyping for characterizationpurposes on confirmed primary PCR products. Eppicollect5 was also used to collect and store the descriptive data of study participants, and the analysis conducted using Power BI statistical software application. The studys findings, indicating no human rotaviral infections in meat cuts, enhance public health by reassuring consumers, guiding regulatory policies, emphasizing the need for ongoing surveillance, directing resources to pressing concerns, supporting safe food handling campaigns, establishing baseline data for future assessments, and encouraging best practices in both formal and informal markets.

In situ imaging of a kleptoplastidic ciliate thin layer indicates traditional sampling underestimates oceanic mixotroph biomass

Planktonic mixotrophs, including ciliates, are abundant, yet understudied, mediators of primary and secondary production in aquatic food webs. Here, we report high-resolution in situ observations of a thin layer—a vertically limited patch of high organism abundance—of the ciliate, Laboea strobila. Within the thin layer, peak L. strobila abundances were as high as 62,000 cells/L, six times higher than previously reported, and were strongly positively correlated with co-measured chlorophyll a concentrations, indicating that the organism indulged in kleptoplasty, retaining plastids from ingested algae. Estimates indicated L. strobila contributed to ~63–78% of chlorophyll a within the layer, in sharp contrast to conventional expectations that phytoplankton dominate this signature, suggesting that mixotroph biomass, and consequently, their contribution to marine ecosystems is widely underestimated. These observations also highlight the importance of pairing traditional approaches such as chlorophyll a measurements with high-resolution imaging for proper attribution of biomass proxies.

Quarry rock reef design features influence fish assemblage structure across a systematically heterogenous restoration reef

To restore an area of temperate rocky-reef degraded by sedimentation, scour, and burial, a large quarry rock reef, the Palos Verdes Restoration Reef (PVR), was built with a heterogenous design including high relief elements intended to increase fish biomass productivity and support a diverse reef community. The replicated design features provide a unique opportunity to study the effects of reef design on fish habitat use patterns. To determine how submodule scale habitat features are associated with variation in the assemblage structure of eleven focal fish species on the PVR we conducted diver-operated stereo-video surveys on all 18 PVR modules 9–13 months after construction. The highest mean densities of most focal fish species and highest total fish densities were observed on high and medium-relief reef submodules and their adjacent ecotones positioned on the offshore sides or ends of modules. These included the most abundant species on the PVR, the zooplanktivorous Blacksmith (Chromis punctipinnis), as well as the fishery species Kelp Bass (Paralabrax clathratus) and California Sheephead (Bodianus pulcher). On the inshore side of parallel modules, the reef and ecotone transects on low and medium relief submodules exhibited the lowest total mean fish densities, and consistently lower mean focal fish species densities. Focal fish species assemblages also differed between the reef and sand-rock ecotone transects. Reef-resident planktivorous fishes likely contribute to reef primary and secondary productivity through consumer mediated nutrient transport and are an important consideration in restoration reef design. Future reef restoration designs should consider incorporating replicated heterogeneous design features including the placement of higher relief elements relative to shore and current patterns as a special consideration for providing habitat for planktivorous reef-resident fishes.

Evolution of phosphate scouting in the terrestrial biosphere.

Chemistry assigns phosphorus and its most oxidized form, inorganic phosphate, unique roles for propelling bioenergetics and metabolism in all domains of life, possibly since its very origin on prebiotic Earth. For plants, access to the vital mineral nutrient profoundly affects growth, development and vigour, thus constraining net primary productivity in natural ecosystems and crop production in modern agriculture. Unlike other major biogenic elements, the low abundance and uneven distribution of phosphate in Earth's crust result from the peculiarities of phosphorus cosmochemistry and geochemistry. Here, we trace the chemical evolution of the element, the geochemical phosphorus cycle and its acceleration during Earth's history until the present (Anthropocene) as well as during the evolution and rise of terrestrial plants. We highlight the chemical and biological processes of phosphate mobilization and acquisition, first evolved in bacteria, refined in fungi and algae and expanded into powerful phosphate-prospecting strategies during land plant colonization. Furthermore, we review the evolution of the genetic and molecular networks from bacteria to terrestrial plants, which monitor intracellular and extracellular phosphate availabilities and coordinate the appropriate responses and adjustments to fluctuating phosphate supply. Lastly, we discuss the modern global phosphorus cycle deranged by human activity and the challenges imposed ahead. This article is part of the theme issue 'Evolution and diversity of plant metabolism'.

Species‐specific effects of leaf litter leachate on the aquatic microbial community and the ratio of heterotrophic to autotrophic biomass

Abstract Dissolved organic carbon (DOC) released from submerged leaf litter is an important allochthonous carbon source for heterotrophic bacteria that enhances the detrital food chain in freshwater ecosystems. In contrast, nitrogen (N), phosphorus (P) and micronutrients released during the leaching process support primary production and enhance the grazing food chain in these ecosystems. This study investigated how DOC and dissolved N and P from the leaf litter of two temperate broadleaf and two coniferous tree species affect heterotrophic and autotrophic biomass by incubating the freshwater microbial community in the culture media prepared from the leaf litter leachate. The results showed that heterotrophic biomass, including bacteria, heterotrophic‐flagellated protists and fungal zoospores, was the highest in the leaf litter leachate, which contained the highest DOC concentration relative to dissolved N and P (Japanese hemlock). In contrast, autotrophic biomass, including small algae, autotrophic flagellated protists and cyanobacteria, was associated with concentrations of dissolved N and P in the leaf litter leachates. Amendment of basal nutrients other than N and P, including micronutrients, trace elements and vitamins, increased autotrophic biomass in two leaf litter leachates (oak, Siebold's beech), suggesting that some elements other than N and P were deficient relative to the requirements of autotrophic organisms. These results indicated that the elemental composition of leaf litter leachates influences microbial community structure and heterotrophic versus autotrophic biomass in freshwater ecosystems. More importantly, the present results suggest that changes in forest vegetation surrounding freshwater ecosystems alter detritus‐based heterotrophic production relative to autotrophic production through the changes in the elemental composition (i.e. stoichiometry) of leaf litter inputs.

Wildfire Particulates Enhance Phytoplankton Growth and Alter Communities in the South China Sea Under Wind‐Driven Upwelling

AbstractExtreme wildfire events and cyclones are on the rise across tropical regions in response to climate change. Despite assumptions about their impact on phytoplankton through nutrient supplies, field evidence is lacking, and their combined effects remain unclear. In an on‐site microcosm experiment conducted in the Xisha Islands, South China Sea (SCS) after Typhoon Noru, we observed enhanced phytoplankton growth in response to exposure to total suspended particulates (TSP) from wildfires (2 mg/L and 6 mg/L) under wind‐driven upwelling conditions. Upwelled nutrients had a limited effect on Chl‐a concentration due to phosphate depletion, by contrast, wildfire TSP contributed nutrients enriched in nitrogen and phosphate, resulting in a 3.30–5.61‐fold increase in Chl‐a. However, upwelled nutrients increased the diatom‐to‐dinoflagellate ratio from the initial 11.0 to 12.7, TSP at low and high levels reduced the ratio to 0.3–0.8 and significantly altered the communities, with 61.8% of species, including two dominant diatoms, negatively correlated with N and/or P supplies. Species diversity declined significantly at high TSP levels. These findings suggest that enhanced primary productivity by wildfires may come at the cost of an altered phytoplankton community. This field study improves understanding of the effects of simultaneous occurrences of multiple extreme climate events on marine ecosystems.

Suspended Particulate Organic Matter Supports Mesopredatory Fish Across a Tropical Seascape

AbstractUnderstanding the sources of primary production supporting marine food webs is important for conserving critical habitats. However, the importance of allochthonous versus autochthonous production is often unclear. We identify the sources of primary production supporting three species of predatory fish (Lutjanus carponotatus, Lutjanus fulviflamma, and Lethrinus punctulatus) in the Dampier Archipelago, Western Australia. The proportions of mangrove, seagrass, macroalgae, and suspended particulate organic matter (SPOM) assimilated by fish of different life-history stages and from different habitats were determined using stable isotopes and Bayesian mixing models. While contributions of sources varied among species and habitats, we found that SPOM was an important energetic resource for both adults and juveniles of all three fish species. Juvenile L. carponotatus and L. punctulatus inhabiting macroalgal habitats assimilated more seagrass- and macroalgae-derived material than fish from coral or mangrove habitats, while reliance on mangrove carbon was generally limited overall. Assimilation of macrophyte-derived material decreased throughout ontogeny for L. carponotatus, while L. fulviflamma relied on a combination of SPOM and seagrass into adulthood. The contribution of macroalgae and SPOM to the diets of juvenile L. punctulatus and L. carponotatus from macroalgal habitats varied spatially but was unrelated to seascape configuration, habitat quality, or hydrodynamic conditions. While mixing models suggested a modest degree of trophic connectivity, cross-habitat trophic subsidies provided by macrophytes play a minor role in supporting the studied fish of either life-history stage. Instead, microalgal production predominantly fuels the productivity of predatory fish in this turbid, macrotidal system.

Assessing Drought Impacts on Gross Primary Productivity of Rubber Plantations Using Flux Observations and Remote Sensing in China and Thailand

Rubber (Hevea brasiliensis Muell.) plantations are vital agricultural ecosystems in tropical regions. These plantations provide key industrial raw materials and sequester large amounts of carbon dioxide, playing a vital role in the global carbon cycle. Climate change has intensified droughts in Southeast Asia, negatively affecting rubber plantation growth. Limited in situ observations and short monitoring periods hinder accurate assessment of drought impacts on the gross primary productivity (GPP) of rubber plantations. This study used GPP data from flux observations at four rubber plantation sites in China and Thailand, along with solar-induced chlorophyll fluorescence (SIF), enhanced vegetation index (EVI), normalized difference vegetation index (NDVI), near-infrared reflectance of vegetation (NIRv), and photosynthetically active radiation (PAR) indices, to develop a robust GPP estimation model. The model reconstructed eight-day interval GPP data from 2001 to 2020 for the four sites. Finally, the study analyzed the seasonal drought impacts on GPP in these four regions. The results indicate that the GPP prediction model developed using SIF, EVI, NDVI, NIRv, and PAR has high accuracy and robustness. The model’s predictions have a relative root mean square error (rRMSE) of 0.22 compared to flux-observed GPP, with smaller errors in annual GPP predictions than the MOD17A3HGF model, thereby better reflecting the interannual variability in the GPP of rubber plantations. Drought significantly affects rubber plantation GPP, with impacts varying by region and season. In China and northern Thailand (NR site), short-term (3 months) and long-term (12 months) droughts during cool and warm dry seasons cause GPP declines of 4% to 29%. Other influencing factors may alleviate or offset GPP reductions caused by drought. During the rainy season across all four regions and the cool dry season with adequate rainfall in southern Thailand (SR site), mild droughts have negligible effects on GPP and may even slightly increase GPP values due to enhanced PAR. Overall, the study shows that drought significantly impacts rubber the GPP of rubber plantations, with effects varying by region and season. When assessing drought’s impact on rubber plantation GPP or carbon sequestration, it is essential to consider differences in drought thresholds within the climatic context.