An official website of the United States government
Abstract Spartina alterniflorahas a distinct flood‐adapted morphology, and its physiological responses are likely to vary with differences in tidal submergence. To understand these responses, we examined the impacts of tidal inundation on the efficiency of Photosystem II (φPSII) photochemistry and leaf‐level photosynthesis at different canopy heights through a combination of in situ chlorophyll fluorescence (ChlF), incident photosynthetically active radiation, and tide levels. Our result showed small declines (7%–8.3%) in φPSII for air‐exposed leaves when the bottom canopies were tidally submerged. Submerged leaves produced large reductions (30.3%–41%) in φPSII. Our results suggest that when submerged, PSII reaction centers inS. alternifloraleaves are still active and able to transfer electrons, but only at ∼20% of the typical daily rate. We attribute this reduction in φPSII to the decrease in the fraction of “open” PSII reaction centers (10% of the total) and the stomatal conductance rate caused by the tidal submergence. To our knowledge, this flooding induced leaf‐level reduction of φPSII forS. alterniflorain field settings has not been reported before. Our findings suggest that canopy‐level φPSII is dependent on the proportion of submerged versus emerged leaves and highlight the complexities involved in estimating the photosynthetic efficiency of tidal marshes.
more »
« less
Supporting Spartina : Interdisciplinary perspective shows Spartina as a distinct solid genus
More Like this
-
-
Summary Spatiotemporal patterns ofSpartina alterniflorabelowground biomass (BGB) are important for evaluating salt marsh resiliency. To solve this, we created the BERM (Belowground Ecosystem Resiliency Model), which estimates monthly BGB (30‐m spatial resolution) from freely available data such as Landsat‐8 and Daymet climate summaries.Our modeling framework relied on extreme gradient boosting, and used field observations from four Georgia salt marshes as ground‐truth data. Model predictors included estimated tidal inundation, elevation, leaf area index, foliar nitrogen, chlorophyll, surface temperature, phenology, and climate data. The final model included 33 variables, and the most important variables were elevation, vapor pressure from the previous four months, Normalized Difference Vegetation Index (NDVI) from the previous five months, and inundation.Root mean squared error for BGB from testing data was 313 g m−2(11% of the field data range), explained variance (R2) was 0.62–0.77. Testing data results were unbiased across BGB values and were positively correlated with ground‐truth data across all sites and years (r = 0.56–0.82 and 0.45–0.95, respectively).BERM can estimate BGB withinSpartina alterniflorasalt marshes where environmental parameters are within the training data range, and can be readily extended through a reproducible workflow. This provides a powerful approach for evaluating spatiotemporal BGB and associated ecosystem function.more » « less
-
Abstract Introduced species may homogenize biotic communities. Whether this homogenization can erase latitudinal patterns of species diversity and composition has not been well studied. We examined this by comparing nematode and microbial communities in stands of nativePhragmites australisand exoticSpartina alterniflorain coastal wetlands across 18° of latitude in China. We found clear latitudinal clines in nematode diversity and functional composition, and in microbial composition, for soils collected from nativeP. australis. These latitudinal patterns were weak or absent for soils collected from nearby stands of the exoticS. alterniflora. Climatic and edaphic variables varied across latitude in similar ways in both community types. InP. australisthere were strong correlations between community structure and environmental variables, whereas inS. alterniflorathese correlations were weak. These results suggest that the invasion ofS. alterniflorainto the Chinese coastal wetlands has caused profound biotic homogenization of soil communities across latitude. We speculate that the variation inP. australisnematode and microbial communities across latitude is primarily driven by geographic variation in plant traits, but that such variation in plant traits is largely lacking for the recently introduced exoticS. alterniflora. These results indicate that widespread exotic species can homogenize nematode communities at large spatial scales.more » « less
-
Abstract Salt marshes sequester a disproportionately large amount of carbon dioxide (CO2) from the atmosphere through high rates of photosynthesis and carbon burial. Climate change could potentially alter this carbon sink, particularly the response of vegetation to environmental stressors that can decrease photosynthesis. Midday depression of gross primary production (GPP), characterized by a decline in photosynthesis during midday, has been documented in multiple ecosystems as a response to drought, high temperatures, and other stressors linked to climate change. Yet, midday depression has not been thoroughly investigated in salt marsh ecosystems. Here, we show that the midday depression of GPP in aSpartina alterniflorasalt marsh on the Eastern Shore of Virginia was ubiquitous and occurred on 76% of the 283 days studied during the 2019–2022 growing seasons. GPP was estimated from eddy covariance measurements with flux partitioning. Using random forest, we found that the daily maximum tidal height and air temperature were the strongest predictors of midday depression of GPP, with lower high tides and warmer temperatures associated with more severe depression. This result suggests midday depression occurs when GPP decreases in the afternoon in response to salinity and water stress. To our knowledge, this is the first examination of midday depression of photosynthesis inS.alternifloraat the ecosystem scale. Our results highlight the potential of climate change to increase midday depression of photosynthesis and ultimately weaken the salt marsh carbon sink.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/ecy.2863
