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Texas Tech University (2017)

Characterizing temporal ecophysiology for chemical management of huisache (Acacia farnesiana [L.] Willd.)

Teveni, Pablo Cortez

Titre : Characterizing temporal ecophysiology for chemical management of huisache (Acacia farnesiana [L.] Willd.)

Auteur : Teveni, Pablo Cortez

Université de soutenance : Texas Tech University

Grade : Doctor of Philosophy (PhD) 2017

Résumé partiel
Huisache (Acacia farnesiana [L.] Willd.), a pest tree species on rangelands throughout south Texas, is expanding in range and density and displacing more desirable forage grasses and forbs. It resists control via herbicide, fire, or mechanical methods through vigorous resprouting and prolific seed production. The objectives of my research were to 1) characterize the optimal timing and environmental conditions for effective herbicide control of huisache, 2) determine the optimum diurnally-fluctuating temperature conditions for huisache seed germination, and 3) determine the age at which seedlings’ cotyledon latent meristems are buried below the soil surface and plants attain resprouting ability. These objectives were addressed in three experiments. For the first, four huisache-invaded pastures with different soil textures from four counties along the Texas Coastal Bend region were used. On-site weather station data were gathered, and the average phenological stage of huisache was determined each month for each pasture ; shrubs from the average phenological stage were used for TNC (total nonstructural carbohydrate) analysis and herbicide treatment. Each month between April 2012 and November 2014, five shrubs per site were excavated, and the root crowns were collected, frozen, dried, ground, and analyzed for TNC. In addition, two herbicide formulations were foliar-applied to five to ten shrubs every month at the four sites from July 2012 to November 2014, and mortality was evaluated following two growing seasons. For the seed germination study, five 20-seed petri dish replicates were used in each of four seed temperature treatments, including : 35/25°C, 30/20°C, 25/15°C, and 20/10°C, under alternating 12-hour light/dark photoperiods in a growth chamber. For the seedling resprouting / cotyledon latent meristem burying study, ten (out of 240) greenhouse-grown plants were cut at soil level each month for 24 months to determine age of resprouting, and ten (out of 120) greenhouse-grown plants were examined every other month for 24 months to measure height of cotyledon latent meristem above (or below) soil level. All greenhouse plants that were selected each month (or every other month) were measured for height and dry mass (total or above-ground). Herbicide and TNC data were analyzed using a randomized complete block design ANOVA (with study site as blocking factor), with appropriate post hoc tests to separate means ; Akaike’s Information Criterion (AIC) was used to determine the best-fit model for mortality data. ANOVA for completely randomized design (with appropriate post-hoc tests) was used to analyze germination (daily and cumulative) and monthly change in cotyledon latent meristem height, and probit analysis and linear regression were used to analyze monthly changes in percentage of plants with cotyledon latent meristems at or below soil level and percentage of seedlings resprouting following top removal.

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