skip to main content

Title: Interactive effects of light, CO2 and temperature on growth and resource partitioning by the mixotrophic dinoflagellate, Karlodinium veneficum
There is little information on the impacts of climate change on resource partitioning for mixotrophic phytoplankton. Here, we investigated the hypothesis that light interacts with temperature and CO 2 to affect changes in growth and cellular carbon and nitrogen content of the mixotrophic dinoflagellate, Karlodinium veneficum , with increasing cellular carbon and nitrogen content under low light conditions and increased growth under high light conditions. Using a multifactorial design, the interactive effects of light, temperature and CO 2 were investigated on K . veneficum at ambient temperature and CO 2 levels (25°C, 375 ppm), high temperature (30°C, 375 ppm CO 2 ), high CO 2 (30°C, 750 ppm CO 2 ), or a combination of both high temperature and CO 2 (30°C, 750 ppm CO 2 ) at low light intensities (LL: 70 μmol photons m -2 s -2 ) and light-saturated conditions (HL: 140 μmol photons m -2 s -2 ). Results revealed significant interactions between light and temperature for all parameters. Growth rates were not significantly different among LL treatments, but increased significantly with temperature or a combination of elevated temperature and CO 2 under HL compared to ambient conditions. Particulate carbon and nitrogen content increased in response more » to temperature or a combination of elevated temperature and CO 2 under LL conditions, but significantly decreased in HL cultures exposed to elevated temperature and/or CO 2 compared to ambient conditions at HL. Significant increases in C:N ratios were observed only in the combined treatment under LL, suggesting a synergistic effect of temperature and CO 2 on carbon assimilation, while increases in C:N under HL were driven only by an increase in CO 2 . Results indicate light-driven variations in growth and nutrient acquisition strategies for K . veneficum that may benefit this species under anticipated climate change conditions (elevated light, temperature and p CO 2 ) while also affecting trophic transfer efficiency during blooms of this species. « less
; ; ; ; ; ;
Anil, Arga Chandrashekar
Award ID(s):
Publication Date:
Journal Name:
Page Range or eLocation-ID:
Sponsoring Org:
National Science Foundation
More Like this
  1. Evidence has shown that individually feeding or reduced light can mitigate the negative effects of elevated temperature on coral physiology. We aimed to evaluate if simultaneous low light and feeding would mitigate, minimize, or exacerbate negative effects of elevated temperature on coral physiology and carbon budgets. Pocillopora damicornis, Stylophora pistillata, and Turbinaria reniformis were grown for 28 days under a fully factorial experiment including two seawater temperatures (ambient temperature of 25 °C, elevated temperature of 30 °C), two light levels (high light of 300 μmol photons m−2 s−1, low light of 150 μmol photons m−2 s−1), and either fed (Artemia nauplii) or unfed. Coral physiology was significantly affected by temperature in all species, but the way in which low light and feeding altered their physiological responses was species-specific. All three species photo-acclimated to low light by increasing chlorophyll a. Pocillopora damicornis required feeding to meet metabolic demand irrespective of temperature but was unable to maintain calcification under low light when fed. In T. reniformis, low light mitigated the negative effect of elevated temperature on total lipids, while feeding mitigated the negative effects of elevated temperature on metabolic demand. In S. pistillata, low light compounded the negative effects of elevated temperaturemore »on metabolic demand, while feeding minimized this negative effect but was not sufficient to provide 100% metabolic demand. Overall, low light and feeding did not act synergistically, nor additively, to mitigate the negative effects of elevated temperature on P. damicornis, S. pistillata, or T. reniformis. However, feeding alone was critical to the maintenance of metabolic demand at elevated temperature, suggesting that sufficient supply of heterotrophic food sources is likely essential for corals during thermal stress (bleaching) events.« less
  2. Accelerating erosion of the Alaska Beaufort Sea coast is increasing inputs of organic matter from land to the Arctic Ocean, and improved estimates of organic matter stocks in eroding coastal permafrost are needed to assess their mobilization rates under contemporary conditions. We collected three permafrost cores (4.5–7.5 m long) along a geomorphic gradient near Drew Point, Alaska, where recent erosion rates average 17.2 m year −1 . Down-core patterns indicate that organic-rich soils and lacustrine sediments (12–45% total organic carbon; TOC) in the active layer and upper permafrost accumulated during the Holocene. Deeper permafrost (below 3 m elevation) mainly consists of Late Pleistocene marine sediments with lower organic matter content (∼1% TOC), lower C:N ratios, and higher δ 13 C values. Radiocarbon-based estimates of organic carbon accumulation rates were 11.3 ± 3.6 g TOC m −2  year −1 during the Holocene and 0.5 ± 0.1 g TOC m −2  year −1 during the Late Pleistocene (12–38 kyr BP). Within relict marine sediments, porewater salinities increased with depth. Elevated salinity near sea level (∼20–37 in thawed samples) inhibited freezing despite year-round temperatures below 0°C. We used organic matter stock estimates from the cores in combination with remote sensing time-series data to estimate carbon fluxes for a 9 km stretch of coastlinemore »near Drew Point. Erosional fluxes of TOC averaged 1,369 kg C m −1  year −1 during the 21st century (2002–2018), nearly doubling the average flux of the previous half-century (1955–2002). Our estimate of the 21st century erosional TOC flux year −1 from this 9 km coastline (12,318 metric tons C year −1 ) is similar to the annual TOC flux from the Kuparuk River, which drains a 8,107 km 2 area east of Drew Point and ranks as the third largest river on the North Slope of Alaska. Total nitrogen fluxes via coastal erosion at Drew Point were also quantified, and were similar to those from the Kuparuk River. This study emphasizes that coastal erosion represents a significant pathway for carbon and nitrogen trapped in permafrost to enter modern biogeochemical cycles, where it may fuel food webs and greenhouse gas emissions in the marine environment.« less
  3. The Southern Ocean (SO) harbors some of the most intense phytoplankton blooms on Earth. Changes in temperature and iron availability are expected to alter the intensity of SO phytoplankton blooms, but little is known about how these changes will influence community composition and downstream biogeochemical processes. We performed light-saturated experimental manipulations on surface ocean microbial communities from McMurdo Sound in the Ross Sea to examine the effects of increased iron availability (+2 nM) and warming (+3 and +6 °C) on nutrient uptake, as well as the growth and transcriptional responses of two dominant diatoms, Fragilariopsis and Pseudo-nitzschia . We found that community nutrient uptake and primary productivity were elevated under both warming conditions without iron addition (relative to ambient −0.5 °C). This effect was greater than additive under concurrent iron addition and warming. Pseudo-nitzschia became more abundant under warming without added iron (especially at 6 °C), while Fragilariopsis only became more abundant under warming in the iron-added treatments. We attribute the apparent advantage Pseudo-nitzschia shows under warming to up-regulation of iron-conserving photosynthetic processes, utilization of iron-economic nitrogen assimilation mechanisms, and increased iron uptake and storage. These data identify important molecular and physiological differences between dominant diatom groups and add tomore »the growing body of evidence for Pseudo-nitzschia ’s increasingly important role in warming SO ecosystems. This study also suggests that temperature-driven shifts in SO phytoplankton assemblages may increase utilization of the vast pool of excess nutrients in iron-limited SO surface waters and thereby influence global nutrient distribution and carbon cycling.« less
  4. Hallam, Steven J. (Ed.)
    ABSTRACT Nitrite-oxidizing bacteria belonging to the genus Nitrospira mediate a key step in nitrification and play important roles in the biogeochemical nitrogen cycle and wastewater treatment. While these organisms have recently been shown to exhibit metabolic flexibility beyond their chemolithoautotrophic lifestyle, including the use of simple organic compounds to fuel their energy metabolism, the metabolic networks controlling their autotrophic and mixotrophic growth remain poorly understood. Here, we reconstructed a genome-scale metabolic model for Nitrospira moscoviensis ( i Nmo686) and used flux balance analysis to evaluate the metabolic networks controlling autotrophic and formatotrophic growth on nitrite and formate, respectively. Subsequently, proteomic analysis and [ 13 C]bicarbonate and [ 13 C]formate tracer experiments coupled to metabolomic analysis were performed to experimentally validate model predictions. Our findings corroborate that N. moscoviensis uses the reductive tricarboxylic acid cycle for CO 2 fixation, and we also show that N. moscoviensis can indirectly use formate as a carbon source by oxidizing it first to CO 2 followed by reassimilation, rather than direct incorporation via the reductive glycine pathway. Our study offers the first measurements of Nitrospira ’s in vivo central carbon metabolism and provides a quantitative tool that can be used for understanding and predicting theirmore »metabolic processes. IMPORTANCE Nitrospira spp. are globally abundant nitrifying bacteria in soil and aquatic ecosystems and in wastewater treatment plants, where they control the oxidation of nitrite to nitrate. Despite their critical contribution to nitrogen cycling across diverse environments, detailed understanding of their metabolic network and prediction of their function under different environmental conditions remains a major challenge. Here, we provide the first constraint-based metabolic model of Nitrospira moscoviensis representing the ubiquitous Nitrospira lineage II and subsequently validate this model using proteomics and 13 C-tracers combined with intracellular metabolomic analysis. The resulting genome-scale model will serve as a knowledge base of Nitrospira metabolism and lays the foundation for quantitative systems biology studies of these globally important nitrite-oxidizing bacteria.« less
  5. Youssef, Noha H. (Ed.)
    ABSTRACT Synechococcus elongatus UTEX 2973, the fastest-growing cyanobacterial strain known, optimally grows under extreme high light (HL) intensities of 1,500–2,500 μmol photons m −2 s −1 , which is lethal to most other photosynthetic microbes. We leveraged the few genetic differences between Synechococcus 2973 and the HL sensitive strain Synechococcus elongatus PCC 7942 to unravel factors essential for the high light tolerance. We identified a novel protein in Synechococcus 2973 that we have termed HltA for H igh l ight t olerance protein A . Using bioinformatic tools, we determined that HltA contains a functional PP2C-type protein phosphatase domain. Phylogenetic analysis showed that the PP2C domain belongs to the bacterial-specific Group II family and is closely related to the environmental stress response phosphatase RsbU. Additionally, we showed that unlike any previously described phosphatases, HltA contains a single N-terminal regulatory GAF domain. We found hltA to be ubiquitous throughout cyanobacteria, indicative of its potentially important role in the photosynthetic lifestyle of these oxygenic phototrophs. Mutations in the hltA gene resulted in severe defects specific to high light growth. These results provide evidence that hltA is a key factor in the tolerance of Synechococcus 2973 to high light and will open new insightsmore »into the mechanisms of cyanobacterial light stress response. IMPORTANCE Cyanobacteria are a diverse group of photosynthetic prokaryotes. The cyanobacterium Synechococcus 2973 is a high light tolerant strain with industrial promise due to its fast growth under high light conditions and the availability of genetic modification tools. Currently, little is known about the high light tolerance mechanisms of Synechococcus 2973, and there are many unknowns overall regarding high light tolerance of cyanobacteria. In this study, a comparative genomic analysis of Synechococcus 2973 identified a single nucleotide polymorphism in a locus encoding a serine phosphatase as a key factor for high light tolerance. This novel GAF-containing phosphatase was found to be the sole Group II metal-dependent protein phosphatase that is evolutionarily conserved throughout cyanobacteria. These results shed new light on the light response mechanisms of Synechococcus 2973, improving our understanding of environmental stress response. Additionally, this work will help facilitate the development of Synechococcus 2973 as an industrially useful organism.« less