Browsing by Author "Limmer, Matt A."
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Item Contrasting roles of rice root iron plaque in retention and plant uptake of silicon, phosphorus, arsenic, and selenium in diverse paddy soils(Plant and Soil, 2024-02-20) Linam, Franklin A.; Limmer, Matt A.; Seyfferth, Angelia L.Background and aims Iron (Fe) plaque on rice roots is a mixture of Fe oxide and oxyhydroxide minerals thought to protect rice from high levels of arsenic (As) in flooded paddy soils. Silicon (Si), phosphorus (P), and selenium (Se) also exist as oxyanions in rice paddies, but the impacts of Fe plaque on uptake of these nutrients are unknown. Methods We used natural variation in paddy soil chemistry to test how Si, P, As, and Se move from porewater to plaque to plant via multiple techniques. In a pot study, we monitored Fe plaque deposition and porewater chemistry in 5 different soils over time and measured plaque/plant chemistry and Fe plaque mineralogy at harvest. We normalized oxyanion concentrations by Fe to determine the preferential retention on plaque or plant uptake. Results Low phosphorus availability increased root Fe-oxidizing activity, while Fe, Si, P, As, and Se concentrations in plaque were strongly correlated with porewater. Plaque did not appreciably retain Si and Se, and the oxyanions did not compete for adsorption sites on the Fe plaque. Conclusion Root Fe plaque seems to protect rice from As uptake, does not interfere with Si and Se uptake, and roots adapt to maintain P nutrition even with retention of porewater P on plaque.Item Evaluation of quantitative synchrotron radiation micro-X-ray fluorescence in rice grain(Journal of Synchrotron Radiation, 2023-03-15) Limmer, Matt A.; Webb, Samuel M.; Seyffertha, Angelia L.Concentrations of nutrients and contaminants in rice grain affect human health, specifically through the localization and chemical form of elements. Methods to spatially quantify the concentration and speciation of elements are needed to protect human health and characterize elemental homeostasis in plants. Here, an evaluation was carried out using quantitative synchrotron radiation microprobe X-ray fluorescence (SR-µXRF) imaging by comparing average rice grain concentrations of As, Cu, K, Mn, P, S and Zn measured with rice grain concentrations from acid digestion and ICP-MS analysis for 50 grain samples. Better agreement was found between the two methods for high-Z elements. Regression fits between the two methods allowed quantitative concentration maps of the measured elements. These maps revealed that most elements were concentrated in the bran, although S and Zn permeated into the endosperm. Arsenic was highest in the ovular vascular trace (OVT), with concentrations approaching 100 mg kg−1 in the OVT of a grain from a rice plant grown in As-contaminated soil. Quantitative SR-µXRF is a useful approach for comparison across multiple studies but requires careful consideration of sample preparation and beamline characteristics.Item Hyperspectral Reflectance for Measuring Canopy-Level Nutrients and Photosynthesis in a Salt Marsh(Journal of Geophysical Research: Biogeosciences, 2022-11-04) Vázquez-Lule, Alma; Seyfferth, Angelia L.; Limmer, Matt A.; Mey, Paul; Guevara, Mario; Vargas, RodrigoSalt marsh ecosystems are underrepresented in process-based models due to their unique location across the terrestrial–aquatic interface. Particularly, the role of leaf nutrients on canopy photosynthesis (FA) remains unclear, despite their relevance for regulating vegetation growth. We combined multiyear information of canopy-level nutrients and eddy covariance measurements with canopy surface hyperspectral remote sensing (CSHRS) to quantify the spatial and temporal variability of FA in a temperate salt marsh. We found that FA showed a positive relationship with canopy-level N at the ecosystem scale and for areas dominated by Spartina cynosuroides, but not for areas dominated by short S. alterniflora. FA showed a positive relationship with canopy-level P, K, and Na, but a negative relationship with Fe, for areas associated with S. cynosuroides, S. alterniflora, and at the ecosystem scale. We used partial least squares regression (PLSR) with CSHRS and found statistically significant data–model agreements to predict canopy-level nutrients and FA. The red-edge electromagnetic region and ∼770 nm showed the highest contribution of variance in PLSR models for canopy-level nutrients and FA, but we propose that underlying sediment biogeochemistry can complicate interpretation of reflectance measurements. Our findings highlight the relevance of spatial variability in salt marshes vegetation and the promising application of CSHRS for linking information of canopy-level nutrients with FA. We call for further development of canopy surface hyperspectral methods and analyses across salt marshes to improve our understanding of how these ecosystems will respond to global environmental change. Plain Language Summary Canopy photosynthesis in salt marshes contributes to the carbon stored in these ecosystems; however, its relationship with canopy-level nutrients has been underrepresented in models. Reflectance from near surface remote sensing could be a cost-effective nondestructive tool to monitor canopy photosynthesis and associated nutrients in salt marshes. We combined canopy-level nutrient information with hyperspectral canopy reflectance to represent the spatial and temporal variability of canopy photosynthesis in a salt marsh in the Mid-Atlantic cost of the U.S. We found that local variability such as different salt marsh species have an influence on the relationship between canopy photosynthesis and associated nutrients, in consequence the most limiting nutrients for photosynthesis were phosphorus, potassium, and sodium. We propose that underlying sediment biogeochemistry can potentially obscure the expected relationships between plant nutrients and photosynthesis in remote sensing of coastal wetlands. These results open the possibility to use similar reflectance information from airborne or spaceborne platforms to explore these relationships at broader scales. Key Points - Local environmental variability influences the relationship of canopy nutrients with canopy photosynthesis in a salt marsh ecosystem - Sediment biogeochemistry can obscure expected relationships between plant nutrients and photosynthesis in remote sensing of coastal wetlands - Canopy surface hyperspectral remote sensing is a promising technique for studying vegetation dynamics of salt marshesItem Rice husk and husk biochar soil amendments store soil carbon while water management controls dissolved organic matter chemistry in well-weathered soil(Journal of Environmental Management, 2023-04-15) Linam, Franklin; Limmer, Matt A.; Ebling, Alina M.; Seyfferth, Angelia L.Rice agriculture feeds over half the world's population, and paddy soils impact the carbon cycle through soil organic carbon (SOC) preservation and production of carbon dioxide (CO2) and methane (CH4), which are greenhouse gases (GHG). Rice husk is a nutrient-rich, underutilized byproduct of rice milling that is sometimes pyrolyzed or combusted. It is unresolved how the incorporation of these residues affects C dynamics in paddy soil. In this study, we sought to determine how untreated (Husk), low-temperature pyrolyzed (Biochar), and combusted (CharSil) husk amendments affect SOC levels, GHG emissions, and dissolved organic matter (DOM) chemistry. We amended Ultisol paddy mesocosms and collected SOC and GHG data for three years of rice grown under alternate wetting and drying (AWD) conditions. We also performed a greenhouse pot study that included water management treatments of nonflooded, AWD, and flooded. Husk, Biochar, and CharSil amendments and flooding generally increased SOC storage and CH4 emissions, while nonflooded conditions increased N2O emissions and nonflooded and CharSil treatments increased CO2 emissions. All amendments stored ∼0.15 kg C m−2 y−1 more SOC than CH4 emissions (as CO2 equivalents), but the combustion of husk to produce CharSil resulted in the net release of CO2 which negates any SOC storage. UV–visible absorption/fluorescence spectroscopy from the pot study suggests that nonflooded treatment decreased DOM aromaticity and molecular size. Our data show that flooding and amendment of Husk and Biochar maximized C storage in the highly weathered rice paddy soil under study despite Husk increasing CH4 emissions. Water management affected dissolved organic matter chemistry more strongly than amendments, but this requires further investigation. Return of rice husk that is untreated or pyrolyzed at low temperature shows promise to close nutrient loops and preserve SOC in rice paddy soils. Graphical abstract available at: https://doi.org/10.1016/j.jenvman.2023.117936Item Unraveling the Mechanisms of Fe Oxidation and Mn Reduction on Mn Indicators of Reduction in Soil (IRIS) Films(Environmental Science and Technology, 2023-04-25) Limmer, Matt A.; Linam, Franklin A.; Evans, Abby E.; Seyfferth, Angelia L.Indicators of reduction in soil (IRIS) devices are low-cost soil redox sensors coated with Fe or Mn oxides, which can be reductively dissolved from the device under suitable redox conditions. Removal of the metal oxide coating from the surface, leaving behind the white film, can be quantified and used as an indicator of reducing conditions in soils. Manganese IRIS, coated with birnessite, can also oxidize Fe(II), resulting in a color change from brown to orange that complicates the interpretation of coating removal. Here, we studied field-deployed Mn IRIS films where Fe oxidation was present to unravel the mechanisms of Mn oxidation of Fe(II) and the resulting minerals on the IRIS film surface. We observed reductions in the Mn average oxidation state when Fe precipitation was evident. Fe precipitation was primarily ferrihydrite (30–90%), but lepidocrocite and goethite were also detected, notably when the Mn average oxidation state decreased. The decrease in the average oxidation state of Mn was due to the adsorption of Mn(II) to the oxidized Fe and the precipitation of rhodochrosite (MnCO3) on the film. The results were variable on small spatial scales (<1 mm), highlighting the suitability of IRIS in studying heterogeneous redox reactions in soil. Mn IRIS also provides a tool to bridge lab and field studies of the interactions between Mn oxides and reduced constituents.