Date of Award

Winter 3-2021

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Natalie Clay

Abstract

NaCl salinization in inland ecosystems is increasing globally due to anthropogenic activity and may alter organism abundances and ecosystem processes. Because sodium is an essential nutrient for heterotrophs but not required by autotrophs, this salinization can alter species abundance and performance. Riparia may be particularly sensitive to increases in salinization. Here, I examined the Sodium Subsidy-Stress Hypothesis, which states that deviations from an organism’s optimal nutrient target can decrease abundance and performance, by studying the effects of NaCl salinization on plant chemistry, productivity, and decomposition rates in riparia. First, I selected three focal common riparian plants (water oak: Quercus nigra, cottonwood: Populus deltoides, and kale: Brassica sp.) to test the prediction that riparian plants will uptake and store sodium in their tissues. Plants received either 300ml low-level (0.05%) NaCl solution or just H2O weekly. After three months, plants watered with NaCl solutions were ~2-3 times more enriched in sodium than controls but had no effects on productivity. The sodium-enriched plant tissues (leaves and stems) were then used to test the prediction that sodium-enriched plant tissues will decompose faster in riparia. These plant tissues along with artificial substrates (100% cellulose sponges either enriched in 0.05% NaCl or just H2O) were placed in three and five inland riparia respectively in Texas and Louisiana. However, decomposition rates did not differ between sodium-enriched and control treated plant and artificial tissues for any species or tissue type at any of the locations. Lastly, I tested the impacts of a gradient of NaCl addition on plant biochemistry and productivity in a common woody riparian species (water oak: Q. nigra). Oaks were watered with 0%, 0.05%, 0.1%, and 0.4% NaCl water solutions. After three months I found that oaks watered with higher NaCl solutions had higher tissues sodium concentrations and reduced leaf biomass and stem growth. Increases in NaCl salinization can lead to alterations in plant biochemistry as well as decreases in plant species abundances and productivity. Similar decomposition rates in sodiumenriched and non-enriched leaf litter suggest that either detrital communities in southcentral United States may not be sodium-limited or detrital committees are not sensitive to differences in leaf litter sodium concentrations. Riparia are seeing increases in global salinization, which can alter dead organic matter quality and quantity.

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