Effects of Scarification, Phytohormones, Soil Type, and Warming on the Germination and/or Seedling Performance of Three Tamaulipan Thornscrub Forest Species

Abstract

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.

Combined Effects of Scarification, Phytohormones, Stratification, and Soil Type on the Germination and/or Seedling Performance of Three Tamaulipan Thornscrub Forest Species

“…Native plant seedling availability is currently the greatest limiting factor for Tamaulipan thornforest restoration [ 15 ]. Current best practices for forest restoration in the Rio Grande Valley (RGV) of south Texas require the planting of seedlings, rather than seeds, and for all seedlings to be grown from locally collected seed to increase genetic diversity in these habitats while promoting locally adapted genotypes [ 16 ].…”

“…Native seed is only commercially available in small quantities and for a few of the 75+ species regularly planted for restoration, and wild collection and processing of native seed is both labor-intensive and requires significant expertise and local knowledge. Similarly, propagation of these 75+ native species from seed is also labor- and knowledge-intensive, and germination and/or seedling survival are often low or inconsistent, partly because many knowledge gaps remain about best practices for nursery propagation [ 15 ]. Consequently, nursery production of thornforest seedlings is high risk and difficult for commercial growers, which limits the number of qualified growers producing seedlings and creates a major bottleneck in reforestation capacity.…”

“…Consequently, nursery production of thornforest seedlings is high risk and difficult for commercial growers, which limits the number of qualified growers producing seedlings and creates a major bottleneck in reforestation capacity. Greater understanding of the horticultural techniques required to break seed dormancy, enhance germination, and maximize post-germination and post-transplant survival for Tamaulipan thornforest species is urgently needed [ 15 ].…”

“…In our previous study, Luera et al [ 15 ] performed a series of scarification and phytohormone trials to investigate the factors governing seed dormancy in three focal thornforest species: Ebenopsis ebano (Berl.) Barneby & Grimes (Texas ebony), Cordia boissieri A. DC.…”

Exogenous Antioxidants Enhance Seedling Growth and Yield of Artificially Aged Cabbage and Lettuce Seeds

“…It is crucial to assess the potential effects of seed pretreatments on subsequent seedling performance on the off chance that detrimental effects outweigh the beneficial effects on germination [34]. In our previous studies, we characterised the mechanisms of ageing and reinvigoration of cabbage (Brassica oleraceae) and lettuce (Lactuca sativa) seeds using exogenous antioxidant [17] and inorganic salt [15] solutions.…”