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1. Marine phytoplankton resilience may moderate oligotrophic ecosystem responses and biogeochemical feedbacks to climate change

   https://doi.org/10.1002/lno.12029  

   Martiny, Adam C.; Hagstrom, George I.; DeVries, Tim; Letscher, Robert T.; Britten, Gregory L.; Garcia, Catherine A.; Galbraith, Eric; Karl, David; Levin, Simon A.; Lomas, Michael W.; et al (February 2022, Limnology and Oceanography)

   Abstract Are the oceans turning into deserts? Rising temperature, increasing surface stratification, and decreasing vertical inputs of nutrients are expected to cause an expansion of warm, nutrient deplete ecosystems. Such an expansion is predicted to negatively affect a trio of key ocean biogeochemical features: phytoplankton biomass, primary productivity, and carbon export. However, phytoplankton communities are complex adaptive systems with immense diversity that could render them at least partially resilient to global changes. This can be illustrated by the biology of theProchlorococcus“collective.” Adaptations to counter stress, use of alternative nutrient sources, and frugal resource allocation can allowProchlorococcusto buffer climate‐driven changes in nutrient availability. In contrast, cell physiology is more sensitive to temperature changes. Here, we argue that biogeochemical models need to consider the adaptive potential of diverse phytoplankton communities. However, a full understanding of phytoplankton resilience to future ocean changes is hampered by a lack of global biogeographic observations to test theories. We propose that the resilience may in fact be greater in oligotrophic waters than currently considered with implications for future predictions of phytoplankton biomass, primary productivity, and carbon export. 

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2. Ocean Acidification and Climate Change as Determinants of Marine Phytoplankton Communities along the U.S. East Coast

   Huntsman, C; Gomes, H; Goes, J (December 2024, Proceedings American Geophysical Union)

   Goes, J (Ed.)

   As climate change and carbon dioxide (CO2) emissions continue to alter oceans, it is critical to understand how marine life will respond. Atmospheric CO2 dissolves into ocean water, beginning a series of chemical reactions that lower pH and deplete free carbonate ions—this phenomenon is called ocean acidification (OA). Marine phytoplankton impact ocean chemistry by performing photosynthesis and cycling carbon. They also form the base of marine food webs and are thus implicated in fishery productivity and human food security. As part of the National Oceanic and Atmospheric Administration's Ocean Acidification Program, this research aimed to document the progression of OA and its effects on marine life. The project combined data analysis, remote sensing, and laboratory experiments to understand phytoplankton community change. Data from scientific cruises in 2018 and 2022 were compared to investigate inter-annual variability in phytoplankton distribution, size, and efficiency. These cruises measured chemical and biological indicators, including pH, temperature, and pigments associated with particular plankton taxa. Water samples collected at various depths were imaged to gather phytoplankton cell counts. The findings demonstrate a clear pH gradient along the East Coast, with northern waters being significantly more acidic than southern waters. This difference is primarily driven by increased precipitation, land characteristics, and ocean current dynamics. Biological community structure and the photosynthetic efficiency of the phytoplankton sampled along the coast varied with latitude and time, demonstrating that continued climate change and intensifying acidification will affect phytoplankton distribution and consumption of CO2, with reverberations throughout the ocean and climate systems at large. 

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3. The Photophysiological Response of Nitrogen-Limited Phytoplankton to Episodic Nitrogen Supply Associated With Tropical Instability Waves in the Equatorial Atlantic

   https://doi.org/10.3389/fmars.2021.814663  

   Sherman, Jonathan; Subramaniam, Ajit; Gorbunov, Maxim Y.; Fernández-Carrera, Ana; Kiko, Rainer; Brandt, Peter; Falkowski, Paul G. (January 2022, Frontiers in Marine Science)

   In the Equatorial Atlantic nitrogen availability is assumed to control phytoplankton dynamics. However, in situ measurements of phytoplankton physiology and productivity are surprisingly sparse in comparison with the North Atlantic. In addition to the formation of the Equatorial cold tongue in the boreal summer, tropical instability waves (TIWs) and related short-term processes may locally cause episodic events of enhanced nutrient supply to the euphotic layer. Here, we assess changes in phytoplankton photophysiology in response to such episodic events as well as short-term nutrient addition experiments using a pair of custom-built fluorometers that measure chlorophyll a (Chl a ) variable fluorescence and fluorescence lifetimes. The fluorometers were deployed during a transatlantic cruise along the Equator in the fall of 2019. We hypothesized that the Equatorial Atlantic is nitrogen-limited, with an increasing degree of limitation to the west where the cold tongue is not prominent, and that infrequent nitrate injection by TIW related processes are the primary source alleviating this limitation. We further hypothesized phytoplankton are well acclimated to the low levels of nitrogen, and once nitrogen is supplied, they can rapidly utilize it to stimulate growth and productivity. Across three TIW events encountered, we observed increased productivity and chlorophyll a concentration concurrent with a decreased photochemical conversion efficiency and overall photophysiological competency. Moreover, the observed decrease in photosynthetic turnover rates toward the western section suggested a 70% decrease in growth rates compared to their maximum values under nutrient-replete conditions. This decrease aligned with the increased growth rates observed following 24 h incubation with added nitrate in the western section. These results support our hypotheses that nitrogen is the limiting factor in the region and that phytoplankton are in a state of balanced growth, waiting to “body surf” waves of nutrients which fuel growth and productivity. 

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4. Influence of soil heterogeneity on soybean plant development and crop yield evaluated using time-series of UAV and ground-based geophysical imagery

   https://doi.org/10.1038/s41598-021-86480-z  

   Falco, Nicola; Wainwright, Haruko M.; Dafflon, Baptiste; Ulrich, Craig; Soom, Florian; Peterson, John E.; Brown, James Bentley; Schaettle, Karl B.; Williamson, Malcolm; Cothren, Jackson D.; et al (December 2021, Scientific Reports)

   Abstract Understanding the interactions among agricultural processes, soil, and plants is necessary for optimizing crop yield and productivity. This study focuses on developing effective monitoring and analysis methodologies that estimate key soil and plant properties. These methodologies include data acquisition and processing approaches that use unmanned aerial vehicles (UAVs) and surface geophysical techniques. In particular, we applied these approaches to a soybean farm in Arkansas to characterize the soil–plant coupled spatial and temporal heterogeneity, as well as to identify key environmental factors that influence plant growth and yield. UAV-based multitemporal acquisition of high-resolution RGB (red–green–blue) imagery and direct measurements were used to monitor plant height and photosynthetic activity. We present an algorithm that efficiently exploits the high-resolution UAV images to estimate plant spatial abundance and plant vigor throughout the growing season. Such plant characterization is extremely important for the identification of anomalous areas, providing easily interpretable information that can be used to guide near-real-time farming decisions. Additionally, high-resolution multitemporal surface geophysical measurements of apparent soil electrical conductivity were used to estimate the spatial heterogeneity of soil texture. By integrating the multiscale multitype soil and plant datasets, we identified the spatiotemporal co-variance between soil properties and plant development and yield. Our novel approach for early season monitoring of plant spatial abundance identified areas of low productivity controlled by soil clay content, while temporal analysis of geophysical data showed the impact of soil moisture and irrigation practice (controlled by topography) on plant dynamics. Our study demonstrates the effective coupling of UAV data products with geophysical data to extract critical information for farm management. 

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5. Using the rapid A‐C _i response (RACiR) in the Li‐Cor 6400 to measure developmental gradients of photosynthetic capacity in poplar

   https://doi.org/10.1111/pce.13436  

   Lawrence, Erica H.; Stinziano, Joseph R.; Hanson, David T. (October 2018, Plant, Cell & Environment)

   Abstract The rapid A‐C_iresponse (RACiR) technique alleviates limitations of measuring photosynthetic capacity by reducing the time needed to determine the maximum carboxylation rate (V_cmax) and electron transport rate (J_max) in leaves. Photosynthetic capacity and its relationships with leaf development are important for understanding ecological and agricultural productivity; however, our current understanding is incomplete. Here, we show that RACiR can be used in previous generation gas exchange systems (i.e., the LI‐6400) and apply this method to rapidly investigate developmental gradients of photosynthetic capacity in poplar. We compared RACiR‐determined V_cmaxand J_maxas well as respiration and stomatal conductance (g_s) across four stages of leaf expansion inPopulus deltoidesand the poplar hybrid 717‐1B4 (Populus tremula × Populus alba). These physiological data were paired with leaf traits including nitrogen concentration, chlorophyll concentrations, and specific leaf area. Several traits displayed developmental trends that differed between the poplar species, demonstrating the utility of RACiR approaches to rapidly generate accurate measures of photosynthetic capacity. By using both new and old machines, we have shown how more investigators will be able to incorporate measurements of important photosynthetic traits in future studies and further our understanding of relationships between development and leaf‐level physiology. 

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