The Tamaulipan thornforests of south Texas and northeast Mexico are an ecologically and economically important conservation hotspot. Thornforest restoration is limited by native tree and shrub seedling availability for planting. Seedling shortages arise from low seed availability and knowledge gaps regarding best practices for germinating and growing the 70+ thornforest species desired for restoration plantings. To fill key knowledge gaps, we investigated three ecologically important thornforest species with low or highly variable germination or seedling survival rates: Ebenopsis ebano, Cordia boissieri, and Zanthoxylum fagara. For each, we quantified the effects of different dosages of chemical seed treatments used to promote germination (sulfuric acid, SA; gibberellic acid, GA; indole-3-butyric acid, IBA) on germination likelihood and timing. We also quantified the effects that these chemical seed treatments, soil media mixture type, and soil warming had on seedling survival, growth, and root morphology. Ebenopsis germination peaked (>90%) with 40–60 min SA treatment. Cordia germination peaked (40%) with 100 mg/L GA treatment. Zanthoxylum germination was negligible across all treatments. Seed molding was rare but stirring during SA treatment reduced Ebenopsis molding by 4%. Ebenopsis seedling survival, height, leaf count, and root morphology were minimally affected by seed treatments, generally reduced by warming, and influenced by soil mix, which also mediated responses to warming. These results suggest improvements to existing practices that could increase Ebenopsis germination by 10–20% and potentially double Cordia germination.

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Lygodium microphyllum is an invasive exotic plant species taking over many sites in freshwater and moist habitats in Florida. Managing it has been a significant challenge for land resource managers and researchers due to its extensive rapid invasion. To assess the effects of soil pH on growth, nutrient uptake, and mycorrhizal colonization in the roots of L. microphyllum, we conducted a 60-day greenhouse experiment by growing it in pots filled with pH-adjusted soils to a range from 4.5 to 8.0. L. microphyllum was able to survive and grow at all soil pH levels; however, final biomass, relative growth rate, photosynthesis, and specific leaf area were all greater in soil pH 5.5-6.5 compared to the other treatments. Correspondingly, nitrogen concentration was also related to these four plant parameters. Root colonization by mycorrhizal fungi was higher in soil pH 5.5-7.5 and lowest for plants growing in 4.5 or 8.0 and was correlated with plant growth parameters as well as elemental concentration in the leaves. Soil pH 8.0 was not strong enough for a pronounced growth decline, thus further increasing soil pH could provide a desired outcome and merit further investigation, although its potential negative impact on native flora (both plants and microorganisms) would need to be assessed.

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Many farms use leguminous cover crops as a nutrient management strategy to reduce their need for nitrogen fertilizer. When they are effective, leguminous cover crops are a valuable tool for sustainable nutrient management. However, the symbiotic partnership between legumes and nitrogen fixing rhizobia is vulnerable to several abiotic and biotic stressors that reduce nitrogen fixation efficiency in real world contexts. Sometimes, despite inoculation with rhizobial strains, this symbiosis fails to form. Such failure was observed in a 14-acre winter cover crop trial in the Rio Grande Valley (RGV) of Texas when three legume species produced no signs of nodulation or nitrogen fixation. This study examined the role of nitrogen, phosphorus, moisture, micronutrients, and native microbial communities in the nodulation of cowpea (Vigna unguiculata L. Walp) and assessed arbuscular mycorrhizal fungi as an intervention to improve nodulation. Results from two controlled studies confirm moisture and native microbial communities as major factors in nodulation success. Micronutrients showed mixed impacts on nodulation depending on plant stress conditions. Nitrogen and phosphorus deficiencies, however, were not likely causes, nor was mycorrhizal inoculation an effective intervention to improve nodulation. Inoculation method also had a major impact on nodulation rates. Continued research on improved inoculation practices and other ways to maximize nitrogen fixation efficiency will be required to increase successful on-farm implementation.