No abstract

Salt spray is one of many abiotic factors that can influence plant productivity and species composition in coastal ecosystems. However, little is known about how marsh plants respond physiologically to the accumulation of sea aerosols on foliar tissues. In this study, experimental microcosms maintained in controlled greenhouse conditions were used to evaluate how low-(1.7 mg dm −2 day −1 , weekly averages) and high-(8.6 mg dm −2 day −1 ) salt-spray loads would influence plant-water relations in Spartina alterniflora (Loisel.). While no differences in plant performance (e.g., changes in biomass and leaf area) were observed between the treatments and control plants, a number of physiological modifications attributed to salt spray were observed. In general, salt-treated plants underwent significant decreases in water potential (Ψ) and osmotic potential (Ψ π ) and increases in leaf conductance (g) and bulk modulus of elasticity (ε). It is likely that these physiological responses were used to generate lower Ψ while maintaining osmotic and water homeostasis. That is, by decreasing Ψ π and increasing g and ε, more efficient water flow through the soilplant-atmosphere continuum can be achieved, thus generating lower Ψ without promoting loss of turgor.

The picocyanobacterium Prochlorococcus is a major contributor to primary production in tropical and temperate oceans. Division rates (μpop) of Prochlorococcus populations can be calculated by following their partially synchronized cell cycles, but one major source of error in these calculations is the estimation of the duration of the S and G2 phases, TSG2. Here we have used data generated by an individual‐based model (IBM) of the Prochlorococcus cell cycle to analyze an array of estimation methods and range of sample intervals to determine the best way to calculate μpop from time course data. Among the traditional methods using the cell cycle approach, areal median gave the best estimate of μpop; optimizing the IBM itself gave the best estimate overall. A size‐based matrix model also gave reasonable results, except at ultradian growth rates. These methods were applied to a time series in the Sargasso Sea to measure Prochlorococcus μpop in situ. The IBM was an effective test bed to investigate division rate estimates and provide recommendations for applying these estimates to field populations.