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Texas Tech University (2017)

Seedling development of forage species according to seral stage

Torres Sales, Aldo

Titre : Seedling development of forage species according to seral stage

Auteur : Torres Sales, Aldo

Université de soutenance : Texas Tech University

Grade : Doctor of Philosophy (PhD) 2017

Résumé partiel
Although seedling establishment has a significant role in the maintenance of plant diversity, productivity and biochemical cycles in the rangeland. However, little is known about the influence of environmental factors in the seedling establishment, as well as, the differences in the morphological development among species. Also, better understand of seedlings establishment becomes of crucial importance to improve the success of reseeding of natural ecosystems. This dissertation based its hypotheses that morphological differences exist between grasses species according to successional seral stage (late and mid-seral). The dissertation is divided into six pieces of research ; each one is showed as a chapter. In addition, in chapter 7 I have a general conclusion about the studies carried on this dissertation. Chapter 1 is shown a brief introduction about state-of-art about the profitability of risk of failures in the reseeding with native grasses of the United States. This chapter also introduces the challenges which we seek to be elucidated with this research. Chapter 2 is shown a literature review concerning the environmental and non-environmental factors that cause failures in the seedling establishment in the rangelands of the United States. In Chapter 3 we studied the effect of amount and frequency of watering events in two species : Blue grama (late seral) and Kleingrass(Mid-seral). The study was conducted in greenhouse conditions simulating the warm season temperature and humidity (May-August) in the South Plains of Texas. There were simulated three rainfall condition : Dry year, normal year and wet year based on Long-term Precipitation Average of Lubbock Texas. 120 days after planting the plants were washed from the pots with cold water and we measured the following variables : Biomass total (g of dry-matter), shoot and root length (mm). The data was subjected to analysis of variance and means were compared by Tukey test (P<0.05). Our results suggest the existence of an optimum range between frequency and amount of water inputted to the system of each plant species. This optimum range allows the seedling survival, establishment success, and initial development. Chapter 4 and Chapter 5 were conducted to evaluated the germination, survival, and morphological development of seedling in nine rangeland grasses species, being 3 for each seral stage (early, mid, and Late seral). In chapter 4 I analyzed the dates grouping the nine species in three groups according to seral stages (early, mid and late seral), and in Chapter 5 I analyzed the morphological development individually for each grass species. The study was conducted in germination chamber condition with sunlight simulation of 12 hours-long ; temperature (Day 33oC – Night 25oC), and air humidity (60%). There were used pots (123.31 cm3) filled with sterilized sand soil and watering with deionized water added Hoagland solution (0.25 strength). In total 144 seedlings were analyzed for each species, which represents 432 seedlings in each seral group during 12 times. Every day was accounted the germination and each 4 days we evaluated the seedling survival and development. In the evaluation the seedlings were washed from the pots with cold water and measured the following variables : Shoot length (mm), number of adventitious roots (mm), the length of seminal and adventitious roots (mm).

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