A novel and high-throughput approach to assess photosynthetic thermal tolerance of kelp using chlorophyll α fluorometry.

Foundation seaweed species are experiencing widespread declines and localized extinctions due to increased instability of sea surface temperature. Characterizing temperature thresholds are useful for predicting patterns of change and identifying species most vulnerable to extremes. Existing methods for characterizing seaweed thermal tolerance produce diverse metrics and are often time-consuming, making comparisons between species and techniques difficult, hindering insight into global patterns of change. Using three kelp species, we adapted a high-throughput method - previously used in terrestrial plant thermal biology - for use on kelps. This method employs temperature-dependent fluorescence (T-F0 ) curves under heating or cooling regimes to determine the critical temperature (Tcrit ) of photosystem II (PSII), i.e., the breakpoint between slow and fast rise fluorescence response to changing temperature, enabling rapid assays of photosynthetic thermal tolerance using a standardized metric. This method enables characterization of Tcrit for up to 48 samples per two-hour assay, demonstrating the capacity of T-F0 curves for high-throughput assays of thermal tolerance. Temperature-dependent fluorescence curves and their derived metric, Tcrit , may offer a timely and powerful new method for the field of phycology, enabling characterization and comparison of photosynthetic thermal tolerance of seaweeds across many populations, species, and biomes.

An innovative approach to using an intensive field course to build scientific and professional skills.

This paper reports on the design and evaluation of Field Studies in Functional Ecology (FSFE), a two-week intensive residential field course that enables students to master core content in functional ecology alongside skills that facilitate their transition from "student" to "scientist." We provide an overview of the course structure, showing how the constituent elements have been designed and refined over successive iterations of the course. We detail how FSFE students: (1) Work closely with discipline specialists to develop a small group project that tests an hypothesis to answer a genuine scientific question in the field; (2) Learn critical skills of data management and communication; and (3) Analyze, interpret, and present their results in the format of a scientific symposium. This process is repeated in an iterative "cognitive apprenticeship" model, supported by a series of workshops that name and explicitly instruct the students in "hard" and "soft" skills (e.g., statistics and teamwork, respectively) critically relevant for research and other careers. FSFE students develop a coherent and nuanced understanding of how to approach and execute ecological studies. The sophisticated knowledge and ecological research skills that they develop during the course is demonstrated through high-quality presentations and peer-reviewed publications in an open-access, student-led journal. We outline our course structure and evaluate its efficacy to show how this novel combination of field course elements allows students to gain maximum value from their educational journey, and to develop cognitive, affective, and reflective tools to help apply their skills as scientists.

Foliar water uptake via cork warts in mangroves of the Sonneratia genus.

Foliar water uptake (FWU) occurs in plants of diverse ecosystems; however, the diversity of pathways and their associated FWU kinetics remain poorly resolved. We characterized a novel FWU pathway in two mangrove species of the Sonneratia genus, S. alba and S. caseolaris. Further, we assessed the influence of leaf wetting duration, wet-dry seasonality and leaf dehydration on leaf conductance to surface water (Ksurf ). The symplastic tracer dye, disodium fluorescein, revealed living cells subtending and encircling leaf epidermal structures known as cork warts as a pathway of FWU entry into the leaf. Rehydration kinetics experiments revealed a novel mode of FWU, with slow and steady rates of water uptake persistent over a duration of 12 hr. Ksurf increased with longer durations of leaf wetting and was greater in leaves with more negative water potentials at the initiation of leaf wetting. Ksurf declined by 68% between wet and dry seasons. Our results suggest that FWU via cork warts in Sonneratia sp. may be rate limited and under active regulation. We conclude that FWU pathways in halophytes may require ion exclusion to avoid uptake of salt when inundated, paralleling the capacity of halophyte roots for ion selectivity during water acquisition.