Grass species within South Africa show a photosynthetic subtype and phylogenetic response to rainfall gradients, with Panicoideae species (NADP-Me and NAD-Me) inhabiting mesic environments, while Aristidoideae species (NADP-Me) inhabit more arid environments. It is predicted that climate change will alter rainfall patterns within southern Africa, which could have implications for grassland distributions and functional composition. Globally, and in South Africa, species distributions indicates that NAD-Me species have a preference for more arid environments, but this may be complicated by phylogeny as most NAD-Me species belong to the Chloridoideae subfamily. Additionally, differences in the metabolism and energetic requirements of different carboxylation types are expected to confer different ecological advantages, such as drought tolerance, but the role of these different pathways is not well understood. Based on natural distribution and photosynthetic subtype differences, it was hypothesised that Panicoideae NADP-Me species would be less drought tolerant than Panicoideae NAD-Me and Aristidoideae NADP-Me species and that subtypes and lineages would show different drought recovery rates. Furthermore, drought sensitivity would be of a metabolic and not a stomatal origin and plants that maintained favourable leaf water status would be more drought tolerant and recover faster. This was tested experimentally by comparing Panicoideae species (NADP-Me and NAD-Me) and NADP-Me species (Panicoideae and Aristidoideae). Plants were subjected to a progressive 58 day drought period and a recovery phase where gas exchange, chlorophyll fluorescence and leaf water relations were measured at select intervals. In conjunction with this, a rapid drought experiment was performed on Zea mays (NADP-Me: Panicoideae) plants where similar parameters were measured. Photosynthetic drought and recovery responses showed both a subtype and phylogenetic response. Panicoideae species were less drought tolerant than Aristidoideae species, although Panicoideae NAD-Me showed better recovery rates than Panicoideae NADP-Me species, while Aristidoideae species recovered the quickest. Panicoideae NAD-Me and Aristidoideae species maintained higher leaf water status during drought which contributed to the maintenance of PSII integrity and thus facilitated rapid photosynthetic recovery. During drought Panicoideae species showed greater metabolic limitations over Aristidoideae species and for the first time, lower metabolic limitations were associated with osmotic adjustment. This is a novel finding whereby osmotic adjustment and the subsequent maintenance of leaf water are key to preventing metabolic limitations of photosynthesis in C₄ grasses. Results from the Z. mays rapid drought study showed the limitations to photosynthesis were exclusively metabolic and unlikely to be a direct consequence of turgor loss. It was apparent that the response to drought was stronger amongst lineages, as NADP-Me species from different subfamilies showed a significant difference in drought tolerances. Aristidoideae species’ exceptional drought tolerance and predicted increased aridification could favour these species over Panicoideae species under future climates.

Mycorrhizae have been used in restoration for decades. However, studies assessing the use of mycorrhizae in Bromus tectorum-invaded areas of the Great Basin are limited. Two greenhouse pot experiments were conducted to assess the role of mycorrhizae in sagebrush restoration. The first objective (Chapter 2) was to determine the response of Pseudoroegneria spicatum, Elymus elymoides, and B. tectorum to mycorrhizal symbiosis by altering phosphorus, density, species, presence of mycorrhizae and water levels in a 5 factor design. To assess the mycorrhizal response, a variety of morphological and physiological traits were measured, such as tissue P concentration, specific root length, specific leaf area, carbon isotope discrimination, etc. The effects of the different treatment combinations were analyzed using ANOVA. The second objective (Chapter 3) was to determine the role of different inocula in competition between the three grasses. Species, density, and inoculum type were altered in a 3 factor design. Inoculum was cultured on Allium plants. The effect of locally cultured inoculum on the species was compared to the effect of commercial inoculum. The response of each species to mycorrhizae with different species compositions and densities was assessed. Morphological measurements were used to determine each species response to the different factor combinations. The effects of the different treatment combinations were analyzed using ANOVA. This research provides land managers with information regarding the efficacy of using local versus commercial inocula and whether they should use mycorrhizae in restoring their systems.

Trisetum spicatum (Poaceae) is circumboreal as well as bipolar in distribution. The species is comprised of both tetraploid and hexaploid cytotypes that display high morphological diversity. Previous taxonomic treatments have resulted in the separation of the species into a series of species, subspecies, varieties, races, and types. Many of these treatments were inconclusive, based on highly variable characters, and few specimens were examined. For instance, the characters of the inflorescence and relative stem pubescence are the characters most relied on for subspecific separation. These characters have been found to be extremely inconsistent, even within the same population. This study is concerned with the North American component of the species complex. Three-hundred and fifty herbarium specimens and field collections were measured for thirty-three characters. These data were analyzed numerically with basic statistics, cluster analysis, principal coordinate, and discriminant function techniques. The results indicate that extreme variation exists within the species complex with no distinct subgroups. The species was also analyzed genetically with isozyme electrophoresis. Eight populations were surveyed for five enzyme systems. These results indicate the species to possess complete allelic homogeneity within populations with few interpopulation differences. Previous recognition of the hexaploid as a distinct species is not supported morphologically or genetically. / Master of Science

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1964 M89 / Master of Science

LD2668 .T4 1962 O73

No description available.

Studies were conducted on Heteropogon contortus at three natural stands and a common nursery in southeast Arizona and under controlled conditions. The objective was to examine H. contortus growth and development and relate it to concurrently measured environmental variables, especially soil temperature. It was hypothesized that response to such environment variables would be sufficiently consistent to serve as an indicator of range site characteristics. Response to temperature of local accessions was examined under controlled conditions to confirm field observations and determine the possibility of ecotypic differences. Common nursery studies examined phenotypic response of local accessions plus others from outside the region, to examine ecotypic response. Major conclusions were that H. contortus distribution pattern varies among sites of different temperature and/or moisture regime. Sites where H. contortus is prominent have definite characteristics, associated with warm microsites at high elevations (southern aspects, increasing slope) and mesic microsites at low elevations (the borders of washes, roadsides or microdepressions). Growth was entirely associated with the current year, with no carry-over of vegetative tillers from previous years. Growth began in spring, but was soon restricted by depleted soil moisture. Major growth, flowering and seedling establishment occurred during summer rains. Growth ceased with the first frost. Seedling survival appeared temperature dependent at high elevations, extreme temperatures perhaps responsible for age structure differences among sites. Overall growth and development and microsite requirements appear sufficiently consistent for H. contortus presence and growth pattern to indicate range site characteristics, especially temperature. The response to temperature of H. contortus is typical of C4 species, the temperature threshold for leaf elongation being approximately 15 C. However, carry-over effects of cold nights together with warm days may reduce elongation. There is little ecotypic difference in response to temperature among local accessions. However, non-local material differs in cold tolerance (both more or less tolerant) and flowering date from local accessions. Some accessions may be more valuable for early-season growth than local accessions if H. contortus establishment is considered.

Salinity stress predisposed Penncross creeping bentgrass to cottony blight caused by P. aphanidermatum. Studies were conducted on the effects of salinity on the mycelial growth of P. aphanidermatum and on the growth of Penncross bentgrass. Mycelial growth increased significantly up to Ec levels of 7.1 ds/m when compared to mycelial growth at the control Ec levels of 0.5 ds/m. Plant growth was reduced to 50% of the control at Ec levels of 4.3 ds/m. 3-month-old Penncross bentgrass plants were inoculated and incubated at two differing temperatures. At 32 C, all plants died within 3 days regardless of salinity treatment. Rates of plant death were greatest at salinity levels over 2.8 ds/m. At 27 C, plants irrigated with water at Ec levels from 4.3 to 7.1 ds/m showed complete necrosis within 5 days, while treatments irrigated with tap water showed no disease symptoms.

No description available.