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Green sulfur bacteria (GSB) are a distinct group of anoxygenic phototrophic bacteria that are found in many ecological niches. Prosthecochloris, a marine representative genus of GSB, was found to be dominant in some coral skeletons. However, how coral-associated Prosthecochloris (CAP) adapts to diurnal changing microenvironments in coral skeletons is still poorly understood. In this study, three Prosthecochloris genomes were obtained through enrichment culture from the skeleton of the stony coral Galaxea fascicularis. These divergent three genomes belonged to Prosthecochloris marina and two genomes were circular. Comparative genomic analysis showed that between the CAP and non-CAP clades, CAP genomes possess specialized metabolic capacities (CO oxidation, CO2 hydration and sulfur oxidation), gas vesicles (vertical migration in coral skeletons), and cbb3-type cytochrome c oxidases (oxygen tolerance and gene regulation) to adapt to the microenvironments of coral skeletons. Within the CAP clade, variable polysaccharide synthesis gene clusters and phage defense systems may endow bacteria with differential cell surface structures and phage susceptibility, driving strain-level evolution. Furthermore, mobile genetic elements (MGEs) or evidence of horizontal gene transfer (HGT) were found in most of the genomic loci containing the above genes, suggesting that MGEs play an important role in the evolutionary diversification between CAP and non-CAP strains and within CAP clade strains. Our results provide insight into the adaptive strategy and population evolution of endolithic Prosthecochloris strains in coral skeletons.

Temperature is one of the fundamental environmental variables governing microbially mediated denitrification and anaerobic ammonium oxidation (anammox) in sediments. The GHG nitrous oxide (N2O) is produced during denitrification, but not by anammox, and knowledge of how these pathways respond to global warming remains limited. Here, we show that warming directly stimulates denitrification-derived N2O production and that the warming response for N2O production is slightly higher than the response for denitrification in subtropical sediments. Moreover, denitrification had a higher optimal temperature than anammox. Integrating our data into a global compilation indicates that denitrifiers are more thermotolerant, whereas anammox bacteria are relatively psychrotolerant. Crucially, recent summer temperatures in low-latitude sediments have exceeded the optimal temperature of anammox, implying that further warming may suppress anammox and direct more of the nitrogen flow towards denitrification and associated N2O production, leading to a positive climate feedback at low latitudes.

It has been estimated that more than 48% of global methane emissions from lakes and reservoirs occur at low latitudes (

Dinitrogen fixation (NF) by marine cyanobacteria is an important pathway to replenish the oceanic bioavailable nitrogen inventory. Light is the key to modulating NF; however, field studies investigating the light response curve (NF-I curve) of NF rate and the effect of light on diazotroph-derived nitrogen (DDN) net release are relatively sparse in the literature, hampering prediction using models. A dissolution method was applied using uncontaminated 15N2 gas to examine how the light changes may influence the NF intensity and DDN net release in the oligotrophic ocean. Experiments were conducted at stations with diazotrophs dominated by filamentous cyanobacterium Trichodesmium spp. in the western Pacific and the South China Sea. The effect of light on carbon fixation (CF) was measured in parallel using the 13C tracer method specifically for a station characterized by Trichodesmium bloom. Both NF-I and CF-I curves showed a Ik (light saturation coefficient) range of 193 to 315 µE m−2 s−1, with light saturation at around 400 µE m−2 s−1. The proportion of DDN net release ranged from ∼ 6 to ∼ 50 %, suggesting an increasing trend as the light intensity decreased. At the Trichodesmium bloom station, we found that the CF ∕ NF ratio was light-dependent and the ratio started to increase as light was lower than the carbon compensation point of 200 µE m−2 s−1. Under low-light stress, Trichodesmium physiologically preferred to allocate more energy for CF to alleviate the intensive carbon consumption by respiration; thus, there is a metabolism tradeoff between CF and NF pathways. Results showed that short-term (< 24 h) light change modulates the physiological state, which subsequently determined the C ∕ N metabolism and DDN net release by Trichodesmium. Reallocation of energy associated with the variation in light intensity would be helpful for prediction of the global biogeochemical cycle of N by models involving Trichodesmium blooms.

Stable isotopes (δ(15)N, δ(18)O) can serve as tracers for sources of nitrogen in the receiving environment. Hong Kong discharges ~3×10(6)m(3)d(-1) of treated wastewater into the ocean from 68 facilities implementing preliminary to tertiary treatment. We sampled treated sewage from 18 plants across 5 treatment types and examined receiving seawater from northeast Hong Kong. We analyzed nitrate and nitrite (NO3(-)+NO2(-), hereafter NOx) ammonium (NH4(+)), phosphate (PO4(+)) concentrations and δ(15)NNOx, δ(18)ONOx. Sewage effluents contained high mean nutrient concentrations (NO3(-)=260μmolL(-1), NH4(+)=1400μmolL(-1), PO4(+)=50μmolL(-1)) with some indication of nitrogen removal in advanced treatment types. Mean δ(15)NNOx of sewage effluents from all plants and treatment types (12‰) was higher than natural sources and varied spatially and seasonally. There was no overall effect of sewage treatment type on δ(15)NNOx. A mass balance model indicated that sewage (>68%) remains a dominant source of nitrate pollution in seawater in Tolo Harbor.

Fluvial sediment export from small mountainous rivers in Oceania has global biogeochemical significance affecting the turnover rate and export of terrestrial carbon, which might be speeding up at the recognized conditions of increased rainfall intensity. In this study, the historical runoff and sediment export from 16 major rivers in Taiwan are investigated and separated into an early stage (1970–1989) and a recent stage (1990–2010) to illustrate the changes of both runoff and sediment export. The mean daily sediment export from Taiwan Island in the recent stage significantly increased by >80% with subtle increase in daily runoff, indicating more sediment being delivered to the ocean per unit of runoff in the recent stage. The medians of the runoff depth and sediment yield extremes (99.0–99.9 percentiles) among the 16 rivers increased by 6.5%-37% and 62%-94%, respectively, reflecting the disproportionately magnified response of sediment export to the increased runoff. Taiwan is facing increasing event rainfall intensity which has resulted in chain reactions on magnified runoff and sediment export responses. As the globe is warming, rainfall extremes, which are proved to be temperature-dependent, very likely intensify runoff and trigger more sediment associated hazards. Such impacts might occur globally because significant increases of high-intensity precipitation have been observed not only in Taiwan but over most land areas of the globe.

International audience; Studies of submarine groundwater discharge (SGD) have been focused on passive margins with large floodplains [1]. SGD from active margins without substantial sediment cover remains unknown, but it is in the rapidly eroding highlands along these margins that the feedback between climate and weathering is most effective [2].In Taiwan, measured erosion and silicate weathering rates are amongst the highest in the world. In a representative section of the northeast coast of Taiwan, at the outlet of the Liwu river, we have explored the possible magnitude and pattern of SGD, and its implications for weathering budgets. The river drains 4 km of emergent mountain relief, with a further 5 km of submarine relief above the Pacific abyssal plain. In the Liwu catchment, 16±1% of the river discharge (averaged over 37 years of record) comes from a deep groundwater reservoir, and deep seated chemical weathering of silicates accounts for 38% of the riverine silicate weathering flux [3]. It is likely that the large inland hydraulic head drives submarine discharge from this deep groundwater reservoir and weathering reactor.We have used the radium quartet (228Ra, 226Ra, 224Ra, 223Ra) along with Temperature-Salinity (T-S) profiles on two 50 km West- East marine transects off the NE coast of Taiwan (

We report a new foraminifera-bound delta N-15 (FB-delta N-15) record from the South China Sea (SCS) extending back to 42 ka. This record shows a similar to 1.2 parts per thousand glacial-to-interglacial delta N-15 decrease, with a deglacial delta N-15 maximum similar to that observed in many bulk sedimentary delta N-15 records and in a Caribbean FB-delta N-15 record. The glacial-to-interglacial delta N-15 decrease is smaller than in the Caribbean record, indicating that at least half of the Caribbean delta N-15 decrease into the Holocene was regional, not global, supporting the interpretation of a Holocene increase in Atlantic nitrogen fixation. At the same time, the glacial-to-interglacial delta N-15 decrease observed in the SCS may also be explained as a regional signal of increasing nitrogen fixation into the Holocene. Other aspects of the SCS record suggest an effect of physical circulation on FB-delta N-15. FB-delta N-15 starts to increase toward its deglacial maximum before the last ice age ends, and it continues to decrease through the later Holocene, in contrast to the more pure glacial/deglacial/interglacial steps in the Caribbean record. These changes have parallels in other Pacific delta N-15 records, precessionally driven East Asian monsoon records, and the slow Holocene warming of SCS surface waters. In addition, the SCS record exhibits two one-point high-delta N-15 spikes in multiple foraminiferal species that coincide with apparent hydrographic events. Thinning or weakening of the thermocline, in the late glacial and early Holocene as well as during the noted events, may have yielded a higher delta N-15 for thermocline nitrate and thus a higher FB-delta N-15.

Rapidly eroding, coastal mountain belts, where steep rivers and submarine channels connect upland sources to nearby marine sinks are hotspots of organic carbon transfer from life biomass, soil and exhumed bedrock into geological storage. Using observations from the Southern Alps of New Zealand, and Taiwan, we have mapped this organic pathway to geological carbon sequestration, and can evaluate the magnitude and efficiency of transfers between sources and sinks. We demonstrate that POC is harvested by landsliding, but importantly also by common and widespread surface runoff on steep hillslopes. Although terrestrially sourced POC is found in many sedimentary environments associated with mountain belts and frontier basins, it appears to be most abundantly trapped and preserved in marine turbidites. The loss of all forms of POC in onward transport through short, steep routing systems to this repository is limited. This is in marked contrast to larger routing systems, in which only the most resilient forms of POC survive into long-term deposition.

We analyzed the high-resolution foraminifer isotope records, total organic carbon (TOC), and opal content from an Okinawa Trough core MD012404 in order to estimate the monsoon hydrography and productivity changes in the East China Sea (ECS) of the tropical western Pacific over the past 100,000 years. The variability shown in the records on orbital time scales indicates that high TOC intervals coincide with the increases of boreal May-September insolation driven by precession cycles (similar to 21 ka), implying a strong connection to the variations in monsoons. We also observed possibly nearly synchronous, millennial-scale changes of the ECS surface hydrography (mainly driven by salinity changes but also by temperature effects) and productivity coincident with monsoon events in the Hulu/Dongge stalagmite isotope records. We found that increased freshening and high productivity correlate with high monsoon intensity in interstadials. This study suggests that the millennial-scale changes in monsoon hydrography and productivity in the ECS are remarkable and persistent features over the past 100,000 years.