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1. Transcriptional response of Emiliania huxleyi under changing nutrient environments in the North Pacific Subtropical Gyre

   https://doi.org/10.1111/1462-2920.14942  

   Alexander, Harriet ; Rouco, Mónica ; Haley, Sheean T. ; Dyhrman, Sonya T. ( February 2020 , Environmental Microbiology)

   The widespread coccolithophoreEmiliania huxleyiis an abundant oceanic phytoplankton, impacting the global cycling of carbon through both photosynthesis and calcification. Here, we examined the transcriptional responses of populations ofE. huxleyiin the North Pacific Subtropical Gyre to shifts in the nutrient environment. Using a metatranscriptomic approach, nutrient‐amended microcosm studies were used to track the global metabolism ofE. huxleyi. The addition of nitrate led to significant changes in transcript abundance for gene pathways involved in nitrogen and phosphorus metabolism, with a decrease in the abundance of genes involved in the acquisition of nitrogen (e.g. N‐transporters) and an increase in the abundance of genes associated with phosphate acquisition (e.g. phosphatases). Simultaneously, after the addition of nitrate, genes associated with calcification and genes unique to the diploid life stages ofE. huxleyisignificantly increased. These results suggest that nitrogen is a major driver of the physiological ecology ofE. huxleyiin this system and further suggest that the addition of nitrate drives shifts in the dominant life‐stage of the population. Together, these results underscore the importance of phenotypic plasticity to the success ofE. huxleyi, a characteristic that likely underpins its ability to thrive across a variety of marine environments.

    

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2. Uncovering the spatial heterogeneity of Ediacaran carbon cycling

   https://doi.org/10.1111/gbi.12222  

   Li, C. ; Hardisty, D. S. ; Luo, G. ; Huang, J. ; Algeo, T. J. ; Cheng, M. ; Shi, W. ; An, Z. ; Tong, J. ; Xie, S. ; et al ( December 2016 , Geobiology)

   Records of the Ediacaran carbon cycle (635–541 million years ago) include the Shuram excursion (SE), the largest negative carbonate carbon isotope excursion in Earth history (down to −12‰). The nature of this excursion remains enigmatic given the difficulties of interpreting a perceived extreme global decrease in the δ¹³C of seawater dissolved inorganic carbon. Here, we present carbonate and organic carbon isotope (δ¹³C_carband δ¹³C_org) records from the Ediacaran Doushantuo Formation along a proximal‐to‐distal transect across the Yangtze Platform of South China as a test of the spatial variation of theSE. Contrary to expectations, our results show that the magnitude and morphology of this excursion and its relationship with coexisting δ¹³C_orgare highly heterogeneous across the platform. Integrated geochemical, mineralogical, petrographic, and stratigraphic evidence indicates that theSEis a primary marine signature. Data compilations demonstrate that theSEwas also accompanied globally by parallel negative shifts of δ³⁴S of carbonate‐associated sulfate (CAS) and increased⁸⁷Sr/⁸⁶Sr ratio and coastalCASconcentration, suggesting elevated continental weathering and coastal marine sulfate concentration during theSE. In light of these observations, we propose a heterogeneous oxidation model to explain the high spatial heterogeneity of theSEand coexisting δ¹³C_orgrecords of the Doushantuo, with likely relevance to theSEin other regions. In this model, we infer continued marine redox stratification through theSEbut with increased availability of oxidants (e.g., O₂and sulfate) limited to marginal near‐surface marine environments. Oxidation of limited spatiotemporal extent provides a mechanism to drive heterogeneous oxidation of subsurface reduced carbon mostly in shelf areas. Regardless of the mechanism driving theSE, future models must consider the evidence for spatial heterogeneity in δ¹³C presented in this study.

    

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3. Contrasting ecosystem CO 2 fluxes of inland and coastal wetlands: a meta‐analysis of eddy covariance data

   https://doi.org/10.1111/gcb.13424  

   Lu, Weizhi ; Xiao, Jingfeng ; Liu, Fang ; Zhang, Yue ; Liu, Chang'an ; Lin, Guanghui ( August 2016 , Global Change Biology)

   Wetlands play an important role in regulating the atmospheric carbon dioxide (CO₂) concentrations and thus affecting the climate. However, there is still lack of quantitative evaluation of such a role across different wetland types, especially at the global scale. Here, we conducted a meta‐analysis to compare ecosystemCO₂fluxes among various types of wetlands using a global database compiled from the literature. This database consists of 143 site‐years of eddy covariance data from 22 inland wetland and 21 coastal wetland sites across the globe. Coastal wetlands had higher annual gross primary productivity (GPP), ecosystem respiration (R_e), and net ecosystem productivity (NEP) than inland wetlands. On a per unit area basis, coastal wetlands provided largeCO₂sinks, while inland wetlands provided smallCO₂sinks or were nearlyCO₂neutral. The annualCO₂sink strength was 93.15 and 208.37 g C m⁻²for inland and coastal wetlands, respectively. AnnualCO₂fluxes were mainly regulated by mean annual temperature (MAT) and mean annual precipitation (MAP). For coastal and inland wetlands combined,MATandMAPexplained 71%, 54%, and 57% of the variations inGPP,R_e, andNEP, respectively. TheCO₂fluxes of wetlands were also related to leaf area index (LAI). TheCO₂fluxes also varied with water table depth (WTD), although the effects ofWTDwere not statistically significant.NEPwas jointly determined byGPPandR_efor both inland and coastal wetlands. However, theNEP/R_eandNEP/GPPratios exhibited little variability for inland wetlands and decreased for coastal wetlands with increasing latitude. The contrasting ofCO₂fluxes between inland and coastal wetlands globally can improve our understanding of the roles of wetlands in the global C cycle. Our results also have implications for informing wetland management and climate change policymaking, for example, the efforts being made by international organizations and enterprises to restore coastal wetlands for enhancing blue carbon sinks.

    

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4. Use of the high‐affinity phosphate transporter gene, pstS , as an indicator for phosphorus stress in the marine diazotroph Crocosphaera watsonii ( Chroococcales , Cyanobacteria )

   https://doi.org/10.1111/jpy.12863  

   Pereira, Nicole ; Shilova, Irina N. ; Zehr, Jonathan P. ; Roleda, ed., M. ( May 2019 , Journal of Phycology)

   The marine diazotrophCrocosphaera watsoniiprovides fixed carbon (C) and nitrogen (N) to open‐ocean regimes, where nutrient deficiency controls productivity. The growth ofCrocosphaeracan be limited by low phosphorus (P) concentrations in these oligotrophic environments. Biomarkers such as the high‐affinityABCtransporter phosphate‐binding gene,pstS, are commonly used to monitor when such organisms are under P stress; however, transcriptional regulation of these markers is often complex and not well‐understood. In this study, we interrogated changes inpstStranscript levels inC. watsoniicells under P starvation, and in response to added dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), and changing light levels. We observed elevated relativepstStranscript levels inC. watsoniiWH8501 atDIPconcentrations below 60 and above 20 nmol · L⁻¹. Transcript levels were suppressed by both inorganic and bioavailable organic phosphorus; however, the P stress response was more sensitive toDIPthanDOPsources. Increasing light intensity resulted in increased relativepstStranscript abundances independently of low external P, and seemed to exacerbate the physiological effects of P stress. The variable response to different P compounds and rapid and transient influence of high light onpstStranscript abundances suggests thatpstSis an indicator of internal P status inCrocosphaera.

    

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5. Temporal and spatial transcriptomic and micro RNA dynamics of CAM photosynthesis in pineapple

   https://doi.org/10.1111/tpj.13630  

   Wai, Ching M. ; VanBuren, Robert ; Zhang, Jisen ; Huang, Lixian ; Miao, Wenjing ; Edger, Patrick P. ; Yim, Won C. ; Priest, Henry D. ; Meyers, Blake C. ; Mockler, Todd ; et al ( August 2017 , The Plant Journal)

   The altered carbon assimilation pathway of crassulacean acid metabolism (CAM) photosynthesis results in an up to 80% higher water‐use efficiency than C₃photosynthesis in plants making it a potentially useful pathway for engineering crop plants with improved drought tolerance. Here we surveyed detailed temporal (diel time course) and spatial (across a leaf gradient) gene and microRNA(miRNA) expression patterns in the obligateCAMplant pineapple [Ananas comosus(L.) Merr.]. The high‐resolution transcriptome atlas allowed us to distinguish betweenCAM‐related and non‐CAMgene copies. A differential gene co‐expression network across green and white leaf diel datasets identified genes with circadian oscillation,CAM‐related functions, and source‐sink relations. Gene co‐expression clusters containingCAMpathway genes are enriched with clock‐associatedcis‐elements, suggesting circadian regulation ofCAM. About 20% of pineapple microRNAs have diel expression patterns, with several that target keyCAM‐related genes. Expression and physiology data provide a model forCAM‐specific carbohydrate flux and long‐distance hexose transport. Together these resources provide a list of candidate genes for targeted engineering ofCAMinto C₃photosynthesis crop species.

    

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