Biogeochemical Cycles Research Articles

Deciphering the environmental adaptation and functional trait of core and noncore bacterial communities in impacted coral reef seawater

Microorganisms play pivotal roles in different biogeochemical cycles within coral reef waters. Nevertheless, our comprehension of the microbially mediated processes following environmental perturbation is still limited. To gain a deeper insight into the environmental adaptation and nutrient cycling, particularly within core and noncore bacterial communities, it is crucial to understand reef ecosystem functioning. In this study, we delved into the microbial community structure and function of seawater in a coral reef under different degrees of anthropogenic disturbance. To achieve this, we harnessed the power of 16S rRNA gene high-throughput sequencing and metagenomics techniques. The results showed that a continuous temporal succession but little spatial heterogeneity in the bacterial communities of core and noncore taxa and functional profiles involved in nitrogen (N) and phosphorus (P) cycling. Eutrophication state (i.e., nutrient concentration and turbidity) and temperature played pivotal roles in shaping both the microbial community composition and functional traits of coral reef seawater. Within this context, the core subcommunity exhibited a remarkably broader habitat niche breadth, stronger phylogenetic signals and lower environmental sensitivity when compared to the noncore taxa. Null model analysis further revealed that the core subcommunity was governed primarily by stochastic processes, while deterministic processes played a more significant role in shaping the noncore subcommunity. Furthermore, our observations indicated that changes in function related to N cycling were correlated to the variations in noncore taxa, while core taxa played a more substantial role in critical processes such as P cycling. Collectively, these findings facilitated our knowledge about environmental adaptability of core and noncore bacterial taxa and shed light on their respective roles in maintaining diverse nutrient cycling within coral reef ecosystems.

Soil fungal community has higher network stability than bacterial community in response to warming and nitrogen addition in a subtropical primary forest.

Soil microbes play a very important role in maintaining the function and health of forest ecosystems. Unfortunately, global change factors are profoundly affecting soil microbial structure and function. In this study, we found that climate warming promoted bacterial network stability and nitrogen deposition decreased bacterial network stability. Changes in bacterial network stability had strong effects on bacterial community functional potentials linked to metabolism, nitrogen cycling, and carbon cycling, which would change the biogeochemical cycle in primary forests.

Time-series metaproteogenomics of a high-CO2 aquifer reveals active viruses with fluctuating abundances and broad host ranges

Abstract Ecosystems subject to mantle degassing are of particular interest for understanding global biogeochemistry, as their microbiomes are shaped by prolonged exposure to high CO2 and have recently been suggested to be highly active. While the genetic diversity of bacteria and archaea in these deep biosphere systems have been studied extensively, little is known about how viruses impact these microbial communities. Here, we show that the viral community in a high-CO2 cold-water geyser (Wallender Born, Germany) undergoes substantial fluctuations over a period of 12 days, although the corresponding prokaryotic community remains stable, indicating a newly observed “infect to keep in check” strategy that maintains prokaryotic community structure. We characterized the viral community using metagenomics and metaproteomics, revealing 8,654 viral operational taxonomic units (vOTUs). CRISPR spacer-to-protospacer matching linked 278 vOTUs to 32 hosts, with many vOTUs sharing hosts from different families. High levels of viral structural proteins present in the metaproteome (several structurally annotated based on AlphaFold models) indicate active virion production at the time of sampling. Viral genomes expressed many proteins involved in DNA metabolism and manipulation, and encoded for auxiliary metabolic genes, which likely bolster phosphate and sulfur metabolism of their hosts. The active viral community encodes genes to facilitate acquisition and transformation of host nutrients, and appears to consist of many nutrient-demanding members, based on abundant virion proteins. These findings indicate viruses are inextricably linked to the biogeochemical cycling in this high-CO2 environment and substantially contribute to prokaryotic community stability in the deep biosphere hotspots.

Experimental Study on Ecological and Biogeochemical Role of Calcimycocavites in Understanding Carbon Fluxes in the Age of Global Warming and Climate Change

The present work reports the results of calcimycocavitological studies on the seashells from beaches of north Goa, India yielding distinct microfungal forms known as calcimycocavites which are important in global climate change studies. SEM studies of the calcareous shell fragments revealed the micro tunneling behavior of the fungi. Digital analysis of SEM images using Mountain Premium 7.2 software revealed the fine topography of calcimycocavites hyphae along with unidentified presumptive biomineral encrustations. The biodegradation of mycocavitogenic insoluble Calcium Oxalate by oxalotrophic members of bacterial communities may occur using bacterial Oxalate decarboxylase and formate dehydrogenase finally releasing Carbon Di Oxide and water and Calcium oxide to the local nutrient pool. Calcimycocavites may be thus involved in the biogeochemical cycling of Carbon and Calcium in the Ocean-Beach environment. The ecological, biological, and biogeochemical implications of the findings are presented concerning the possible role of calcimycocavites in Calcium and Carbon cycling by breakdown of the calcareous shells and release of inorganic and organic components in the ecosystem. The role of calcimycocavites is stressed in global climate studies.

Diversity and biogeography of dinoflagellates in the Kuroshio region revealed by 18S rRNA metabarcoding

Dinoflagellate is one of the most diverse and pervasive protists and a fundamental player in the marine food web dynamics and biogeochemical cycles. While possessing different nutritional strategies from purely autotrophy or heterotrophy to mixotrophy, some of them are also known as toxic harmful algal bloom (HAB) formers over the world. Despite their ordinariness, their diversity and biogeography are understudied in the open ocean compared with coastal region. As the first metabarcoding survey covering the Kuroshio current region from the offshore of Okinawa to the south of Honshu, we investigated the distribution of free-living dinoflagellates using the hypervariable V4 and V9 regions on 18S rRNA and their relation to ambient environments influenced by this oligotrophic but highly productive current in the northwest Pacific Ocean. We observed community structures differentiated by depth and nutrient concentrations. Most species annotated are autotrophic or mixotrophic and had a distribution correlated to warmer surface water, whereas heterotrophic species correlated to high nutrient levels or deeper layer. Our results also confirmed the overall high genetic diversity of dinoflagellates that decreased with depth and onshore. Most species present at stations offshore, and the relative abundance of HAB assemblages was lower at nutrient-rich stations on the continental shelf than stations influenced by the Kuroshio current, exhibiting the role of the Kuroshio transporting dinoflagellates including HAB species. To fully understand the dynamics of dinoflagellate communities in marine ecosystems, further seasonal monitoring is foremost for correlating dinoflagellates and environmental factors while completing the reference genomic database.

Temporal variations of biological nitrogen fixation and diazotrophic communities associated with artificial seaweed farms

Diazotrophic communities contribute inorganic nitrogen for the primary productivity of the marine environment by biological nitrogen fixation (BNF). They play a vital role in the biogeochemical cycle of nitrogen in the marine ecological environment. However, there is still an incomplete understanding of BNF and diazotrophs in artificial seaweed farms. Therefore, this study comprehensively investigated the temporal variations of BNF associated with Gracilariopsis lemaneiformis, as well as the diazotrophic communities associated with macroalgae and its surrounding seawater. Our results revealed that a total of 13 strains belonging to Proteobacteria and Bacteroidetes were identified as N2-fixing bacteria using azotobacter selective solid medium and nifH gene cloning. Subsequently, BNF and diazotrophic communities were characterized using the acetylene reduction method and high-throughput sequencing of the nifH gene, respectively. The results showed that nitrogenase activity and nifH gene abundance of epiphytic bacteria on G. lemaneiformis varied significantly among four different cultivation periods, i.e., Cultivation Jan. (CJ), Cultivation Feb. (CF), Cultivation Mar. (CM), Cultivation Apr. (CA). Among them, the nitrogenase activity and nifH gene abundance of epiphytic bacteria on G. lemaneiformis in CM were significantly higher than those in CJ, CF, and CA, indicating that the BNF of eiphytic bacteria on G. lemaneiformis was markedly enhanced. Combined with the data on environmental factors, it was found that the low concentration of nitrogen and phosphorus in CM might considerably boost the BNF of epiphytic bacteria in G. lemaneiformis. The sequencing results of the nifH gene showed that the α-diversity of diazotrophic communities associated with G. lemaneiformis and seawater in CM was higher than that in other cultivation periods. In addition, the diazotrophic communities on G. lemaneiformis were significantly different in CJ, CF, CM, and CA, and they were significantly diverse from diazotrophic communities in seawater. LEfSe analysis indicated that Rhodobacterales, Hyphomonadaceae, Robiginitomaculum, and Robiginitomaculum antarcticum within α-proteobacteria played a remarkable role in BNF in response to nitrogen nutrient deficiency. Taken together, these results provide a unique insight into the interaction between macroalgae and its epiphytic bacteria and lay a foundation for further research on the mechanism of action of nitrogen-cycling microorganisms associated with macroalgae.

Taxonomic diversity of extremophilic prokaryotes adapted to special environmental parameters in Hungary: a review.

The taxonomic and metabolic diversity of prokaryotes and their adaptability to extreme environmental parameters have allowed extremophiles to find their optimal living conditions under extreme conditions for one or more environmental parameters. Natural habitats abundant in extremophilic microorganisms are relatively rare in Hungary. Nevertheless, alkaliphiles and halophiles can flourish in shallow alkaline lakes (soda pans) and saline (solonetz) soils, where extreme weather conditions favor the development of unique bacterial communities. In addition, the hot springs and thermal wells that supply spas and thermal baths and provide water for energy use are suitable colonization sites for thermophiles and hyperthermophiles. Polyextremophiles, adapted to multiple extreme circumstances, can be found in the aphotic, nutrient-poor and radioactive hypogenic caves of the Buda Thermal Karst, among others. The present article reviews the organization, taxonomic composition, and potential role of different extremophilic bacterial communities in local biogeochemical cycles, based on the most recent studies on extremophiles in Hungary.

Short rotation willow to restore degraded marginal land and enhance climate resiliency within the Prairie Pothole Region: A potential nature-based solution

Short rotation willow (SRW) is a land management strategy involving the cultivation of rapidly growing, biomass-rich herbaceous-woody plants. This practice holds promise for renewable energy production, water quality preservation, carbon sequestration, greenhouse gas (GHG) mitigation, enhancement of soil extracellular enzyme activities (EEAs), and promotion of overall soil health. The rapid growth of SRW demands substantial water and nutrient resources, posing concerns when cultivated in marginal riparian lands within the Prairie Pothole Region (PPR), potentially leading to alterations in groundwater table (GWT) depth fluctuations, elevated soil salinity levels, and disruptions to biogeochemical cycles. Hence, this study comprehensively evaluated the effects of establishing SRW as a degraded marginal riparian land use practice in the PPR and attempted to answer several vital questions in the field and microcosm scale on soil hydrology, salinity, nutrients, soil organic carbon (SOC), GHG emissions, and EEAs involved in biogeochemical cycling. In a field experiment, the effects of SRW were evaluated by measuring the depth to GWT, groundwater and soil electrical conductivity (EC), macronutrients (N, P, K, and S), and SOC content in different fractions and chemical compositions during the first rotation (3-year cycle) compared with adjacent annual crop and pasture in two semi-arid PPR sites. In a microcosm experiment, GHG (CO2, CH4, and N2O) emissions and EEAs [β-glucosidase (BG), N-acetyl glucosaminidase (NAG), and alkaline phosphatase (AP)] were measured in intact soil cores treated with declining water tables and different groundwater salinity levels. No consistent land use impacts on GWT or soil EC were observed between sites. Land use in site B significantly impacted GWT depth, implying site-specific factors, such as topography and soil characteristics, may be dominant over land use effects. Under SRW, the levels of macronutrients in the soil varied but did not significantly reduce the overall nutrient content of the soil. Total SOC was highest in pasture; light fraction organic carbon and particulate organic carbon followed a similar land use pattern, i.e., pasture > SRW = annual crop. Land uses affected GHG emissions significantly in the order of pasture > annual crop = SRW. GHG emission varied with salinity and GWT but there was no interaction with land use practices. Soil EEAs were significantly impacted by different land uses, i.e., pasture > annual crop = SRW, suggesting that the effects resulted from associated SOC. Our microcosm experiment suggests that the SRW land use practice holds promise as a sustainable Nature-Based Solution for enhancing climate resiliency in PPR. It exhibits a lower global warming potential compared to annual crop and pasture. Therefore, widespread implementation of the SRW land use practice in degraded marginal land could help mitigate the effects of climate change in the region.

A revised model of global silicate weathering considering the influence of vegetation cover on erosion rate

Abstract. Silicate weathering, which is of great importance in regulating the global carbon cycle, has been found to be affected by complicated factors, including climate, tectonics and vegetation. However, the exact transfer function between these factors and the silicate weathering rate is still unclear, leading to large model–data discrepancies in the CO2 consumption associated with silicate weathering. Here we propose a simple parameterization for the influence of vegetation cover on erosion rate to improve the model–data comparison based on a state-of-the-art silicate weathering model. We found out that the current weathering model tends to overestimate the silicate weathering fluxes in the tropical region, which can hardly be explained by either the uncertainties in climate and geomorphological conditions or the optimization of model parameters. We show that such an overestimation of the tropical weathering rate can be rectified significantly by parameterizing the shielding effect of vegetation cover on soil erosion using the leaf area index (LAI), the high values of which are coincident with the distribution of leached soils. We propose that the heavy vegetation in the tropical region likely slows down the erosion rate, much more so than thought before, by reducing extreme streamflow in response to precipitation. The silicate weathering model thus revised gives a smaller global weathering flux which is arguably more consistent with the observed value and the recently reconstructed global outgassing, both of which are subject to uncertainties. The model is also easily applicable to the deep-time Earth to investigate the influence of land plants on the global biogeochemical cycle.

Analysis of nearly 3000 archaeal genomes from terrestrial geothermal springs sheds light on interconnected biogeochemical processes

Terrestrial geothermal springs are physicochemically diverse and host abundant populations of Archaea. However, the diversity, functionality, and geological influences of these Archaea are not well understood. Here we explore the genomic diversity of Archaea in 152 metagenomes from 48 geothermal springs in Tengchong, China, collected from 2016 to 2021. Our dataset is comprised of 2949 archaeal metagenome-assembled genomes spanning 12 phyla and 392 newly identified species, which increases the known species diversity of Archaea by ~48.6%. The structures and potential functions of the archaeal communities are strongly influenced by temperature and pH, with high-temperature acidic and alkaline springs favoring archaeal abundance over Bacteria. Genome-resolved metagenomics and metatranscriptomics provide insights into the potential ecological niches of these Archaea and their potential roles in carbon, sulfur, nitrogen, and hydrogen metabolism. Furthermore, our findings illustrate the interplay of competition and cooperation among Archaea in biogeochemical cycles, possibly arising from overlapping functional niches and metabolic handoffs. Taken together, our study expands the genomic diversity of Archaea inhabiting geothermal springs and provides a foundation for more incisive study of biogeochemical processes mediated by Archaea in geothermal ecosystems.

Higher diversity of sulfur-oxidizing bacteria based on soxB gene sequencing in surface water than in spring in Wudalianchi volcanic group, NE China.

Sulfur-oxidizing bacteria (SOB) play a key role in the biogeochemical cycling of sulfur. To explore SOB diversity, distribution, and physicochemical drivers in five volcanic lakes and twosprings in the Wudalianchi volcanic field, China. This study analyzed microbial communities in samples via high-throughput sequencing of the soxB gene. Physical-chemical parameters were measured, and QIIME 2 (v2019.4), R, Vsearch, MEGA7, and Mothur processed the data. Alpha diversity indices and UPGMA clustering assessed community differences, while heat maps visualized intra-sample variations. Canoco 5.0 analyzed community-environment correlations, and NMDS, Adonis, and PcoA explored sample dissimilarities and environmental factor correlations. SPSS v.18.0 tested for statistical significance. The diversity of SOB in surface water was higher than in springs (more than 7.27 times). We detectedSOB affiliated to β-proteobacteria (72.3 %), α-proteobacteria (22.8 %), and γ-proteobacteria (4.2 %) distributedwidely in these lakes and springs. Rhodoferax and Cupriavidus were most frequent in all water samples, whileRhodoferax and Bradyrhizobium are dominant in surface waters but rare in springs. SOB genera in both habitatswere positively correlated. Co-occurrence analysis identified Bradyrhizobium, Blastochloris, Methylibium, andMetyhlobacterium as potential keystone taxa. Redundancy analysis (RDA) revealed positive correlations betweenSOB diversity and total carbon (TC), Fe2+, and total nitrogen (TN) in all water samples. The diversity and community structure of SOB in volcanic lakes and springs in the Wudalianchivolcanic group were clarified. Moreover, the diversity and abundance of SOB decreased with the variation of wateropenness, from open lakes to semi-enclosed lakes and enclosed lakes.

Conception and parameterization of field-scale models for simulating ammonia loss from fertilized lands: a review

Conception and parameterization of field-scale models for simulating ammonia loss from fertilized lands: a review

Contribution of fluorescent primary biological aerosol particles to low-level Arctic cloud residuals

Abstract. Mixed-phase clouds (MPCs) are key players in the Arctic climate system due to their role in modulating solar and terrestrial radiation. Such radiative interactions rely, among other factors, on the ice content of MPCs, which is regulated by the availability of ice-nucleating particles (INPs). While it appears that INPs are associated with the presence of primary biological aerosol particles (PBAPs) in the Arctic, the nuances of the processes and patterns of INPs and their association with clouds and moisture sources have not been resolved. Here, we investigated for a full year the abundance of and variability in fluorescent PBAPs (fPBAPs) within cloud residuals, directly sampled by a multiparameter bioaerosol spectrometer coupled to a ground-based counterflow virtual impactor inlet at the Zeppelin Observatory (475 m a.s.l.) in Ny-Ålesund, Svalbard. fPBAP concentrations (10−3–10−2 L−1) and contributions to coarse-mode cloud residuals (0.1 to 1 in every 103 particles) were found to be close to those expected for high-temperature INPs. Transmission electron microscopy confirmed the presence of PBAPs, most likely bacteria, within one cloud residual sample. Seasonally, our results reveal an elevated presence of fPBAPs within cloud residuals in summer. Parallel water vapor isotope measurements point towards a link between summer clouds and regionally sourced air masses. Low-level MPCs were predominantly observed at the beginning and end of summer, and one explanation for their presence is the existence of high-temperature INPs. In this study, we present direct observational evidence that fPBAPs may play an important role in determining the phase of low-level Arctic clouds. These findings have potential implications for the future description of sources of ice nuclei given ongoing changes in the hydrological and biogeochemical cycles that will influence the PBAP flux in and towards the Arctic.

Arctic phytoplankton microdiversity across the marginal ice zone: Subspecies vulnerability to sea-ice loss

Seasonal phytoplankton blooms are important Arctic phenomena, contributing to global primary production and biogeochemical cycling. The decline in sea-ice extent and thickness favors a longer open-water period with impacts on phytoplankton dynamics. Arctic net productivity is influenced by microalgae living associated with sea ice, with distinct species thought to be favored by ice-covered and ice-free waters. In this study, we investigated the phytoplankton community structure in Baffin Bay, a semi-enclosed sea where Arctic and North Atlantic water masses interact. We compared communities from the ice-free Atlantic-influenced eastern, the marginal ice zone, and the ice-covered Arctic-influenced western Baffin Bay. The community was characterized using 18S rRNA high-throughput amplicon sequencing and flow cytometry cell counting, and compared to environmental data collected during the Green Edge campaign. We sampled 16 stations grouped by sectors according to sea-ice cover. In the sectors associated with sea ice, phytoplankton formed a highly diverse community of smaller taxa, which contrasted with a low-diversity community in ice-free sectors, dominated by larger centric diatoms and Phaeocystis pouchetii adapted to high light/low nutrient conditions. Several phytoplankton species were flagged as indicators for the under-ice and marginal ice zone sectors, including ice-associated taxa such as the diatoms Melosira arctica and Pseudo-nitzschia seriata, but also subspecies representatives of the early-blooming alga Micromonas polaris and the cryptophyte Baffinella frigidus. The strong association of certain taxa with under-ice and marginal ice zone sectors, including Pterosperma sp., Chrysochromulina sp., Micromonas polaris, and B. frigidus, suggest that they might be indicators of diversity loss due to ongoing sea-ice changes in Baffin Bay. We report new intra-species variability of Micromonas polaris suggesting that seasonal specialists could wax and wane over the bloom and non-bloom periods, highlighting the need for detailed year-long studies and the importance of microdiversity when assessing the diversity and distribution of polar phytoplankton.

“Air pollution from biomass burning in India”

Abstract Air Pollution is the most difficult challenge India is facing today and anthropogenic biomass burning (ABB) is one of the major and least understood sources leading to serious health and climate implications by affecting air quality, visibility, atmospheric chemistry, the Earth’s radiation budget, and biogeochemical cycling. Scientific understanding on the composition, chemistry, and regional dynamics of BB emissions is still limited constraining the implementation of appropriate research and policy interventions. The broad categories, associated complex emissions and spatio-temporal variations of ABB in India are discussed here. Major types of ABB prevalent year-round all over India include BB for cooking, heating purpose and open waste burning. Moreover, crop residue burning (CRB) in Indo-Gangetic Plain (IGP) during pre (April-May) and post-monsoon (October-November) seasons; CRB in South-India during January-February; forest fires in Central India and slash & burn agriculture in North-East India during March-May are the other dominant sources active during specific months and regions. Over the IGP, CRB along with other episodic ABB events and stagnant meteorology result in severe air quality and poor visibility (< ~300 m) with reported daily mean PM2.5 concentration shooting upto 15 times higher than Central Pollution Control Board standards. When compared with wheat residue burning, higher fire counts and emissions are reported during paddy residue burning events. During winters, BB contribution to 37% of aerosol oxidative potential in Delhi indicates its health implications. Meta-analysis of data obtained from representative source apportionment studies on PM10 shows >24% BB contribution in Assam, Ahmedabad, Kanpur, and Visakhapatnam; 20-24% in Patiala and Kolkata; 10-14% in Delhi. In PM2.5, BB contribution of >24% in Ahmedabad and Agra; 15-19% in Delhi, Mumbai, and Kolkata is reported while in PM1, BB contributed 19-24% in Kanpur, Patiala, and Assam and <10% in Delhi. Observed spatio-temporal variations in ABB sources and composition over India call for region specific solutions through airshed-based management.

Pengaruh Model Pembelajaran Problem Based Learning (PBL) Terhadap Hasil Belajar Peserta Didik Pada Sub Materi Daur Biogeokimia Di Kelas X SMA Negeri 1 Darangdan

This research aims to determine the effect of the Problem Based Learning (PBL) learning model on student learning outcomes in the Biogeochemical Cycle sub-material in Class X SMA Negeri 1 Darangdan. This research uses a quantitative approach with a Quasi Experimental research method with a Non Equivalent Control Group Design. The population in this study were all class X students of SMA Negeri 1 Darangdan, Purwakarta Regency. The sampling technique was Purposive Sampling with a sample of class X.9 as the experimental class which took part in learning by applying the Problem Based Learning (PBL) learning model and class The variables of this research include the independent variable, namely the Learning Model (PBL Learning Model vs. Conventional Learning Model) and the dependent variable, namely student learning outcomes in the Biogeochemical Cycle sub-material in Class X SMA Negeri 1 Darangdan. The data collection technique uses the Test Method. The instrument used is a multiple choice test. Learning outcome data were analyzed using the Independent Sample T-test. Learning Results of experimental class students achieved good characteristics and the control class only achieved adequate characteristics. The mean post-test for the experimental class was 83.1 and the mean post-test for the control class was 74.04. The results of the Independent Sample t-test show the value of tcount = 3.363 > ttable = 1.989. Because tcount > ttable, Ho is rejected and H1 is accepted, which means that there is a significant difference in student learning outcomes between classes that take part in learning using the Problem Based Learning (PBL) learning model and classes that take part in conventional learning. And also the Sig value. (2-tailed) < 0.05, namely 0.001. So it can be concluded that the Problem Based Learning (PBL) learning model influences student learning outcomes.

Litter decomposition rate response to multiple global change factors: A meta-analysis

Anthropogenic global change fundamentally impacts ecosystem biogeochemical cycling. Although litter decomposition is a crucial component of carbon (C) cycling, its response to diverse global change factors (GCFs) remains uncertain. In this research, we synthesized 1706 observations from 260 peer-reviewed publications to elucidate the effects of GCFs on litter decomposition rate (k) and the contribution of different variables to them. Overall, nitrogen (N) addition and drought significantly decreased k (−3.3 and −17.7%, respectively), phosphorus (P) addition, warming, and increased precipitation significantly increased k (6.7, 8.2, and 11.6%, respectively), while elevated CO2 had an insignificant effect on k (−0.6%). Combined GCFs had no significant effect on k except for warming*drought, and all combined factors mainly exhibited antagonistic interactions. Further analysis showed that k responses to GCFs were influenced by initial litter quality (C, N, C:N, P, cellulose, lignin, and vegetation types), soil properties (soil organic C, soil total N, soil total P, soil respiration and microbial biomass C), environmental factors (latitude, longitude, annual mean temperature, annual mean precipitation, ecosystem type, and climate type), and experimental methods (experiment type, richness, treatment method, fertilizer form, fertilizer rate, and experimental duration). Initial litter quality predominantly governed the k response to N addition (53.5%), while soil properties were more significant in regulating the P addition response (44.8%). Environmental factors largely determined k responses to warming, drought, and increased precipitation (50.6, 54.7, 46.9%). Moreover, the experimental methodology also played an important role in regulating k responses to GCFs, which explained 8.6, 23.6, 31.1, 23.7, and 29.7% of the variation of the responses of k to N addition, P addition, warming, drought, and increased precipitation. This meta-analysis offers improved global-scale nutrient cycling predictions under climate change and underscores the need for long-term, multi-factor, methodologically standardized experiments to accurately predict the influence of GCFs on litter decomposition.

Effect of coastal hypoxia on bacterial diversity as elucidated through 16S rRNA amplicon sequencing

The formation of oxygen-depleted zones in the bottom waters is one of the most widespread phenomena in coastal areas. Upwelling episodes along India’s west coast due to the southwest monsoon increase biological productivity, further lowering the dissolved oxygen in the upwelled waters, which intensifies annually between June and October. Here, we have determined the changes in the microbial community in response to the varying oxygen levels and other physicochemical parameters at the Candolim Time Series Station using high-throughput sequencing. Amplicon Sequence Variants across all the samples collected in different seasons were mostly affiliated to the phyla Proteobacteria, Actinobacteria, Bacteroidetes, Verrucomicrobia, Chloroflexi, Firmicutes and Planctomycetes, with the most dominant being Proteobacteria (21-41%). Statistical analysis revealed that microbial diversity differed significantly with changing DO, ammonia, nitrate and nitrite concentrations during different seasons. The microbial community shift due to seasonal hypoxia results in the differential biogeochemical cycling of essential nutrients, with certain years seeing redox conditions up to sulphate reduction while certain years seeing only nitrogen loss. Future global warming scenarios will serve as a big challenge for understanding the role of microbial diversity and its implications in the cycling of natural elements.

Precessional forcing of biogeochemical and nutrient cycling in the tropical western Pacific during the late Pleistocene

Unravelling the biogenic material export production and its relationship to surface ocean nutrient conditions, along with their external forcing, will provide insights into the ocean carbon biogeochemical cycle. In this study, we present data on coccolith particulate inorganic carbon (PIC) export production, coccolith carbon isotopic vital effects, and planktonic foraminifer cadmium to calcium ratio in the tropical western Pacific over the past 250 kiloyears (kyr). These proxies indicate the strength of the coccolith-based carbonate counter pump or coccolithophore productivity, and phosphate concentration in the surface ocean. Our results show that low phosphate concentration correlates with enhanced coccolith-based carbonate counter pump in the precessional band (a cyclicity of 19–23 kyr). Additionally, low phosphate concentration, which indicates high degree of phosphorus utilization, is coupled with enhanced nitrogen fixation, as shown by a nitrogen isotope record in the tropical western Pacific. Greater precipitation in Papua New Guinea (PNG) can occur during local insolation maxima, suggesting a dominant control of precession. This will in turn drive the biogeochemical and nutrient cycling in the tropical western Pacific. We propose that higher amounts of the PNG riverine input caused by greater precipitation can provide additional nutrients and trace element iron (Fe) for phytoplankton. An increased bioavailable Fe in the surface ocean can promote the growth of nitrogen-fixing diazotrophs, which results in a high degree of phosphorus utilization and relieves a potential nitrogen limitation. This may ultimately lead to increased biological productivity, e.g., the coccolith PIC.

Linking Upwelling Dynamics and Subsurface Nutrients to Projected Productivity Changes in the California Current System

AbstractGiven the importance of coastal upwelling systems to ocean productivity, fisheries, and biogeochemical cycles, their response to climate change is of great interest. However, there is no consensus on future productivity changes in these systems, which may be controlled by multiple drivers including wind‐driven and geostrophic transport, stratification, and source water properties. Here we use an ensemble of regional ocean projections and recently developed upwelling indices for the California Current System to disentangle these sometimes‐competing influences. Some changes are consistent among models (e.g., decreased mixed layer depth), while for others there is a lack of agreement even on the direction of future change (e.g., nitrate concentration in upwelled waters). Despite models' diverging projections of productivity changes, they agree that those changes are predominantly driven by subsurface nitrate concentrations, not by upwelling strength. Our results highlight the need for more attention to processes governing subsurface nutrient changes, not just upwelling strength.