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Abstract Temperature and salinity are important regulators of mangrove range limits and productivity, but the physiological responses of mangroves to the interactive effects of temperature and salinity remain uncertain. We tested the hypothesis that salinity alters photosynthetic responses to seasonal changes in temperature and vapor pressure deficit (D), as well as thermal acclimation _of leaf respiration in black mangrove (Avicennia germinans). To test this hypothesis, we grew seedlings of A. germinans in an outdoor experiment for ~ 12 months under four treatments spanning 0 to 55 ppt porewater salinity. We repeatedly measured seedling growth and in situ rates of leaf net photosynthesis (Asat) and stomatal conductance to water vapor (gs) at prevailing leaf temperatures, along with estimated rates of Rubisco carboxylation (Vcmax) and electron transport for RuBP regeneration (Jmax), and measured rates of leaf respiration at 25 °C (Rarea25). We developed empirical models describing the seasonal response of leaf gas exchange and photosynthetic capacity to leaf temperature and D, and the response of Rarea25 to changes in mean daily air temperature. We tested the effect of salinity on model parameters. Over time, salinity had weak or inconsistent effects on Asat, gs and Rarea25. Salinity also had little effect on the biochemical parameters of photosynthesis (Vcmax, Jmax) and individual measurements of Asat, gs, Vcmax and Jmax showed a similar response to seasonal changes in temperature and D across all salinity treatments. Individual measurements of Rarea25 showed a similar inverse relationship with mean daily air temperature across all salinity treatments. We conclude that photosynthetic responses to seasonal changes in temperature and D, as well as seasonal temperature acclimation of leaf R, are largely consistent across a range of salinities in A. germinans. These results might simplify predictions of photosynthetic and respiratory responses to temperature in young mangroves. 

Terrestrial ecosystems are increasingly enriched with resources such as atmospheric CO 2 that limit ecosystem processes. The consequences for ecosystem carbon cycling depend on the feedbacks from other limiting resources and plant community change, which remain poorly understood for soil CO 2 efflux, J CO2 , a primary carbon flux from the biosphere to the atmosphere. We applied a unique CO 2 enrichment gradient (250 to 500 µL L −1 ) for eight years to grassland plant communities on soils from different landscape positions. We identified the trajectory of J CO2 responses and feedbacks from other resources, plant diversity [effective species richness, exp(H)], and community change (plant species turnover). We found linear increases in J CO2 on an alluvial sandy loam and a lowland clay soil, and an asymptotic increase on an upland silty clay soil. Structural equation modeling identified CO 2 as the dominant limitation on J CO2 on the clay soil. In contrast with theory predicting limitation from a single limiting factor, the linear J CO2 response on the sandy loam was reinforced by positive feedbacks from aboveground net primary productivity and exp(H), while the asymptotic J CO2 response on the silty clay arose from a net negative feedback among exp(H), species turnover, and soil water potential. These findings support a multiple resource limitation view of the effects of global change drivers on grassland ecosystem carbon cycling and highlight a crucial role for positive or negative feedbacks between limiting resources and plant community structure. Incorporating these feedbacks will improve models of terrestrial carbon sequestration and ecosystem services.