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"Olivas, Steven T"
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Foliar Stoichiometry is Marginally Sensitive to Soil Phosphorus Across a Lowland Tropical Rainforest
The distribution of nutrients, both vertically and horizontally in a forest, has long been theorized to influence primary productivity. Working at La Selva Biological Station, Costa Rica, we gathered the most comprehensive foliar samples to date for a lowland tropical rainforest to measure horizontal and vertical trends in foliar nutrients. The mean traits of foliage from forest floor to top-of-canopy were determined at 45 plots placed across the landscape in a stratified random design. Area-basis foliar N and P for these vertically integrated columns varied by a factor of 3, while foliar N:P and mass-basis foliar N and P varied by a factor of 2. The variance in plot-level foliar N: P and P was best explained by total soil P, while variance in foliar N was best explained by soil pH (regression trees: r² ≥ 0.20, p ≤ 0.01). Other soil, topographic, and forest structure factors offered no additional explanatory power for variation of foliar nutrients from plot to plot. To explore vertical trends, we aggregated the data across the landscape into 2 m vertical segments. We found that foliar N: P was unrelated to height in the canopy, and that area-basis foliar N and P increased with height in the canopy (linear regression: r² = 0.82 and r² = 0.65 respectively, p < 0.0001 for both). We compared these vertical trends to those of the eight other elements quantified in the leaves, and the only other element enriched with height was potassium (K). Vertical nutrient enrichment was driven by increases in leaf mass per area (LMA), not mass-basis concentrations. Altogether, these findings suggest that, even in diverse tropical rainforests, foliar chemistry may reflect environmental constraints.
Journal Article
Integrating Aquatic Metabolism and Net Ecosystem CO2 Balance in Short- and Long-Hydroperiod Subtropical Freshwater Wetlands
How aquatic primary productivity influences the carbon (C) sequestering capacity of wetlands is uncertain. We evaluated the magnitude and variability in aquatic C dynamics and compared them to net ecosystem CO2 exchange (NEE) and ecosystem respiration (Reco) rates within calcareous freshwater wetlands in Everglades National Park. We continuously recorded 30-min measurements of dissolved oxygen (DO), water level, water temperature (Twater), and photosynthetically active radiation (PAR). These measurements were coupled with ecosystem CO2 fluxes over 5 years (2012–2016) in a long-hydroperiod peat-rich, freshwater marsh and a short-hydroperiod, freshwater marl prairie. Daily net aquatic primary productivity (NAPP) rates indicated both wetlands were generally net heterotrophic. Gross aquatic primary productivity (GAPP) ranged from 0 to − 6.3 g C m−2 day−1 and aquatic respiration (RAq) from 0 to 6.13 g C m−2 day−1. Nonlinear interactions between water level, Twater, and GAPP and RAq resulted in high variability in NAPP that contributed to NEE. Net aquatic primary productivity accounted for 4–5% of the deviance explained in NEE rates. With respect to the flux magnitude, daily NAPP was a greater proportion of daily NEE at the long-hydroperiod site (mean = 95%) compared to the short-hydroperiod site (mean = 64%). Although we have confirmed the significant contribution of NAPP to NEE in both long- and short-hydroperiod freshwater wetlands, the decoupling of the aquatic and ecosystem fluxes could largely depend on emergent vegetation, the carbonate cycle, and the lateral C flux.
Journal Article
El Niño Southern Oscillation (ENSO) Enhances CO2 Exchange Rates in Freshwater Marsh Ecosystems in the Florida Everglades
This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009-2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (-11 to -110 g CO2 m-2 yr-1) compared to El Niño and neutral years (-5 to -43.5 g CO2 m-2 yr-1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m-2 yr-1) except in one exceptionally wet year that was associated with an El Niño phase (-16 g CO2 m-2 yr-1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades.
Journal Article
19S Proteasome Subunits as Oncogenes and Prognostic Biomarkers in FLT3-Mutated Acute Myeloid Leukemia (AML)
26S proteasome non-ATPase subunits 1 (PSMD1) and 3 (PSMD3) were recently identified as prognostic biomarkers and potential therapeutic targets in chronic myeloid leukemia (CML) and multiple solid tumors. In the present study, we analyzed the expression of 19S proteasome subunits in acute myeloid leukemia (AML) patients with mutations in the FMS-like tyrosine kinase 3 (FLT3) gene and assessed their impact on overall survival (OS). High levels of PSMD3 but not PSMD1 expression correlated with a worse OS in FLT3-mutated AML. Consistent with an oncogenic role for PSMD3 in AML, shRNA-mediated PSMD3 knockdown impaired colony formation of FLT3+ AML cell lines, which correlated with increased OS in xenograft models. While PSMD3 regulated nuclear factor-kappa B (NF-κB) transcriptional activity in CML, we did not observe similar effects in FLT3+ AML cells. Rather, proteomics analyses suggested a role for PSMD3 in neutrophil degranulation and energy metabolism. Finally, we identified additional PSMD subunits that are upregulated in AML patients with mutated versus wild-type FLT3, which correlated with worse outcomes. These findings suggest that different components of the 19S regulatory complex of the 26S proteasome can have indications for OS and may serve as prognostic biomarkers in AML and other types of cancers.
Journal Article
Contrasting Photosynthetic Responses of Two Dominant Macrophyte Species to Seasonal Inundation in an Everglades Freshwater Prairie
The Everglades short-hydroperiod freshwater prairies exhibit strong reductions in CO
2
uptake that coincide with inundation, but the underlying basis is not fully understood. To address one of the processes potentially underlying this decline, we measured photosynthetic capacity of the dominant species, sawgrass (
Cladium jamaicense
) and muhly grass (
Muhlenbergia filipes
), during wet and dry seasons (2009–2012 and 2016–2017). The measurements in the seasonally inundated prairie were compared to those taken on a nearby rarely inundated levee situated 29 cm above the prairie with similar species composition. During the dry seasons, muhly grass exhibited a much higher photosynthetic capacity (28.5 μmol m
−2
s
−1
) than sawgrass (14.2 μmol m
−2
s
−1
), and no differences were found between the prairie and levee for either species. During the wet seasons when the prairie was inundated, photosynthetic capacity declined substantially (67%) in the prairie for muhly grass while it remained similar across seasons for sawgrass. Analyses of leaf reflectance, chlorophyll fluorescence and leaf nutrient indicated photosystem impairment was the main driver of photosynthetic capacity reduction for muhly grass when the ecosystem is inundated. Our study suggests that declines in photosynthesis of macrophytes, particularly muhly grass, contribute to low wet season productivity in Everglades short-hydroperiod freshwater prairies.
Journal Article
Effects of Fine-Scale Topography on CO2 Flux Components of Alaskan Coastal Plain Tundra: Response to Contrasting Growing Seasons
Arctic regions hold considerable reservoirs of soil organic carbon. However, most of this carbon is in a potential labile state, and expected changes in temperature and water availability could strongly affect the carbon balance of tundra ecosystems. Plant community composition and soil carbon are closely tied to microtopography and position relative to the water table. We evaluated CO2 fluxes and moss contribution to ecosystem photosynthesis in response to fine-scale topography across a drained lake bed in Barrow, Alaska, during two contrasting growing seasons. CO2 exchange was assessed through static chamber measurements in three vegetation classes distinguished by plant dominance and topographic position within low-centered polygons. Gross primary production (GPP) and ecosystem respiration (ER) were the lowest under high soil moisture conditions in 2006. ER responded more strongly to wet conditions, resulting in a larger summer sink in 2006 than in 2005 (64 vs. 17g CO2 m−2, respectively). Microsites responded differently to contrasting weather conditions. Low elevation microsites presented a strong reduction in ER as a result of increased water availability. A maximum of 48% of daytime GPP and 33% of seasonal daytime GPP was contributed by moss on average across microtopographic positions. The interaction between fine-scale microtopography and variation in temperature and water availability can result in considerable differences in CO2 sink activity of the polygonal tundra.
Journal Article
Responses of CO2 flux components of Alaskan Coastal Plain tundra to shifts in water table
The Arctic stores close to 14% of the global soil carbon, most of which is in a poorly decomposed state as a result of water‐saturated soils and low temperatures. Climate change is expected to increase soil temperature, affecting soil moisture and the carbon storage and sink potential of many Arctic ecosystems. Additionally, increased temperatures can increase thermokarst erosion and flooding in some areas. Our goal was to determine the effects that water table shifts would have on the CO2 sink potential of the Alaskan Coastal Plain tundra. To evaluate the effects of different water regimes, we used a large hydrological manipulation at Barrow, Alaska, where we maintained flooded, drained, and intermediate water levels in a naturally drained thaw lake basin over a period of three seasons: one pretreatment (2006) and two treatment (2007–2008) seasons. To assess CO2 flux components, we used 24 h chamber‐based measurements done on a weekly basis. Increased water table strongly lowered ecosystem respiration (ER) by reducing soil oxygen availability. Flooding decreased gross primary productivity (GPP), most likely by submerging mosses and graminoid photosynthetic leaf area. A decrease in water table increased GPP and ER; however, the increase in root and microbial activity was greater than the increase in photosynthesis, negatively affecting net ecosystem exchange. In the short term, ER is the CO2 flux component that responds most strongly to changes in water availability. Our results suggest that drying of the Alaskan Coastal Plain tundra in the short term could double ER rates, shifting the historic role of some Arctic ecosystems from a sink to a source of CO2.
Journal Article
Water uptake of Alaskan tundra evergreens during the winter-spring transition
PREMISE OF THE STUDY: The cold season in the Arctic extends over 8 to 9 mo, yet little is known about vascular plant physiology during this period. Evergreen species photosynthesize under the snow, implying that they are exchanging water with the atmosphere. However, liquid water available for plant uptake may be limited at this time. The study objective was to determine whether evergreen plants are actively taking up water while under snow and/or immediately following snowmelt during spring thaw. METHODS: In two in situ experiments, one at the plot level and another at the individual species level, ²H-labeled water was used as a tracer injected beneath the snow, after which plant stems and leaves were tested for the presence of the label. In separate experiments, excised shoots of evergreen species were exposed to ²H-labeled water for ~5 s or 60 min and tested for foliar uptake of the label. KEY RESULTS: In both the plot-level and the species-level experiments, some ²H-labeled water was found in leaves and stems. Additionally, excised individual plant shoots exposed to labeled water for 60 min took up significantly more ²H-label than shoots exposed ~5 s. CONCLUSIONS: Evergreen tundra plants take up water under snow cover, some via roots, but also likely by foliar uptake. The ability to take up water in the subnivean environment allows evergreen tundra plants to take advantage of mild spring conditions under the snow and replenish carbon lost by winter respiration.
Journal Article