Introduced cool-season grasses are dominant in Virginia's grasslands, but their high digestible energy and non-structural carbohydrate (NSC) levels pose a risk for horses prone to obesity and laminitis. Native warm-season grasses (NWSG) have lower digestible energy and NSC levels that may be more suitable for horses susceptible to laminitis. The overall objectives of this research were to 1) assess voluntary intake, toxicological response, and apparent digestibility of NWSG hays fed to horses; 2) evaluate the characteristics of three NWSG species under equine grazing; and 3) evaluate establishment strategies for NWSG and wildflowers in Virginia. For the first objective, a hay feeding trial was conducted with 9 Thoroughbred geldings in a 3 x 3 Latin square design. Voluntary dry matter intake of indiangrass (Sorghastrum nutans) and big bluestem (Andropogon gerardii) hays by horses were 1.3% and 1.1% of BW/d, significantly lower than orchardgrass (Dactylis glomerata), an introduced cool-season grass, at 1.7% of BW/d. Biomarkers for toxicity remained within acceptable ranges for all treatments. Apparent DMD did not differ among hays, ranging from 39 to 43%. Non-structural carbohydrate levels were below the maximum recommended concentration for horses susceptible to laminitis. For the second objective, a grazing trial was conducted comparing indiangrass (IG), big bluestem (BB), and eastern gamagrass (Tripsacum dactyloides) (EG) yields, forage losses, changes in vegetative composition, and effects on equine bodyweight. Nine, 0.1-hectare plots were seeded with one of the three native grass treatments, and each plot was grazed by one Thoroughbred gelding in two grazing bouts, one in July and another in September 2019. Indiangrass had the highest available forage, at 4340 kg/ha, compared with 3590 kg/ha from BB (P < 0.0001). Eastern gamagrass plots established poorly, and had only 650 kg/ha available forage during the experiment. Grazing reduced standing cover of native grasses in IG and BB treatments by about 30%, and trampled forage constituted 36-68% of groundcover in those plots after each grazing bout. Horses lost weight on all treatments, but tended (P=0.09) greater weight loss on the indiangrass treatment at 1.5 kg/d compared to 0.5 kg/d in the BB and EG treatments. For the third objective, three experiments were conducted to evaluate different strategies for establishing NWSG and wildflowers. The first experiment compared large grazed plots with or without a 2 oz/acre rate of the herbicide imazapic. Imazapic led to higher biomass and percent cover in plots seeded only with NWSG. For plots seeded with a mix of NWSG and wildflowers, imazapic reduced wildflower establishment and resulted in higher biomass and percent cover of weeds over the course of the experiment. The second experiment examined four rates of imazapic application for NWSG and wildflower establishment in small plots seeded with either NWSG or a NWSG and wildflower mix, and found biomass and percent cover of weeds was lowest at a 6 oz/acre rate, while NWSG biomass and cover did not differ between treatments. Wildflower establishment was again reduced by imazapic. The third establishment experiment compared four site preparation strategies for wildflower establishment and found tillage resulted in the most cover and biomass of wildflowers. / Doctor of Philosophy / Introduced cool-season grasses are dominant in Virginia's grasslands, but their high digestible energy and non-structural carbohydrate (NSC) levels pose a risk for horses prone to obesity and laminitis. Native warm-season grasses (NWSG) have lower digestible energy and NSC levels that may be more suitable for horses susceptible to laminitis. The overall objectives of this research were to 1) assess voluntary intake, toxicological response, and apparent digestibility of NWSG hays fed to horses; 2) evaluate the characteristics of three NWSG species under equine grazing; and 3) evaluate establishment strategies for NWSG and wildflowers in Virginia. For the first objective, a hay feeding trial was conducted with 9 Thoroughbred geldings in a 3 x 3 Latin square design. Voluntary dry matter intake of indiangrass (Sorghastrum nutans) and big bluestem (Andropogon gerardii) hays by horses were 1.3% and 1.1% of BW/d, significantly lower than orchardgrass (Dactylis glomerata), an introduced cool-season grass, at 1.7% of BW/d. Biomarkers for toxicity remained within acceptable ranges for all treatments. Apparent DMD did not differ among hays, ranging from 39 to 43%. Non-structural carbohydrate levels were below the maximum recommended concentration for horses susceptible to laminitis. For the second objective, a grazing trial was conducted comparing indiangrass (IG), big bluestem (BB), and eastern gamagrass (Tripsacum dactyloides) (EG) yields, forage losses, changes in vegetative composition, and effects on equine bodyweight. Nine, 0.1-hectare plots were seeded with one of the three native grass treatments, and each plot was grazed by one Thoroughbred gelding in two grazing bouts, one in July and another in September 2019. Indiangrass had the highest available forage, at 4340 kg/ha, compared with 3590 kg/ha from BB (P < 0.0001). Eastern gamagrass plots established poorly, and had only 650 kg/ha available forage during the experiment. Grazing reduced standing cover of native grasses in IG and BB treatments by about 30%, and trampled forage constituted 36-68% of groundcover in those plots after each grazing bout. Horses lost weight on all treatments, but tended (P=0.09) greater weight loss on the indiangrass treatment at 1.5 kg/d compared to 0.5 kg/d in the BB and EG treatments. For the third objective, three experiments were conducted to evaluate different strategies for establishing NWSG and wildflowers. The first experiment compared large grazed plots with or without a 2 oz/acre rate of the herbicide imazapic. Imazapic led to higher biomass and percent cover in plots seeded only with NWSG. For plots seeded with a mix of NWSG and wildflowers, imazapic reduced wildflower establishment and resulted in higher biomass and percent cover of weeds over the course of the experiment. The second experiment examined four rates of imazapic application for NWSG and wildflower establishment in small plots seeded with either NWSG or a NWSG and wildflower mix, and found biomass and percent cover of weeds was lowest at a 6 oz/acre rate, while NWSG biomass and cover did not differ between treatments. Wildflower establishment was again reduced by imazapic. The third establishment experiment compared four site preparation strategies for wildflower establishment and found tillage resulted in the most cover and biomass of wildflowers.

The breakdown of contaminants in soil resulting from microbial activity that is enhanced in the presence of the plant root zone, rhizosphere, has been termed rhizoremediation. To date, Australian native plants have not been assessed for their hydrocarbon rhizoremediation potential. The use of native plants offers an economically feasible and environmentally sustainable cleanup option for the rehabilitation and restoration of hydrocarbon contaminated sites in Australia. The aim of the study was to evaluate the potential of Australian native grass species for the rhizoremediation of aliphatic hydrocarbon contaminated soil from a mine site. Candidate Australian native grass species Poaceae were selected following the development of essential and desirable growth criteria. Nine perennial Australian grasses were evaluated for seedling emergence in sandy loam soil sourced from a mine site which was artificially contaminated with a 60:40 diesel/oil mix at concentrations of 30 000 mg/kg, 10 000 mg/kg, 5 000 mg/kg and 0 mg/kg control. Seedling emergence was not adversely affected by the presence of hydrocarbon contamination at the exposed concentrations for eight of the nine species studied p > 0.05. Three promising species were assessed for relative growth performance in diesel/oil contaminated 10 000 mg/kg, 5 000 mg/kg and uncontaminated control soils in greenhouse studies to assess their tolerance of aliphatic hydrocarbon contaminated soil. Cymbopogon ambiguus Lemon Scented grass is a summer growing perennial with widespread distribution throughout Australia including the region where the mine site is situated. Brachiaria decumbens Signal grass – naturalised - is adapted to humid tropical areas of Australia and is native to the site and sourced from seed banks. Microlaena stipoides Weeping grass var. Griffin is a cool season grass, widely distributed throughout Australia in moister regions. The three evaluated species survived for 120 days in the diesel/oil contaminated soil at the exposed concentrations without adverse growth affect p > 0.05. In some instances e.g. C. ambiguus growth stimulation occurred in the presence of contamination producing significantly more root biomass compared with the control p < 0.0001. Most hydrocarbon degradation is believed to occur through microbial processes, and so the plant-associated microbial community was examined in the three tolerant species. The assessment of the influence of grass on the abundance and activity of microorganisms in the rhizosphere revealed species-specific plant-induced changes in the soil microbial community. Selective enrichment of hydrocarbon degrading microorganisms was demonstrated in the rhizosphere soil of the Australian grasses tested, to varying degrees. C. ambiguus appeared to have the greatest influence on stimulation of hydrocarbon degrading microorganisms, followed by the cool season grass M. stipoides. B. decumbens showed consistently lower numbers of hydrocarbon degrading microorganisms in rhizosphere soil over time compared to the other two species p < 0.01. The influence of grasses on microbial community structure - defined as community DNA fingerprint - in diesel/oil contaminated soil suggested no new microbial population was favoured by the grasses - qualitative shift - rather there were relative quantitative changes in existing members of the microbial population. Soil lipase activity did not appear to be an optimal bioindicator of rhizoremediation and may encompass total soil microbial activity not exclusively the hydrocarbon degrading microorganisms of interest. The assessment of biodegradation of hydrocarbons in soil is essential to characterise the effectiveness of plant species in rhizoremediation. Residual diesel and oil concentrations as total petroleum hydrocarbons, TPH were measured using Gas Chromatography. The presence of single species successfully enhanced the removal of hydrocarbons from soil for all species. All showed significantly lower residual hydrocarbon concentrations than those in unplanted soil after 100 days p < 0.01. Significantly, it was not necessary to add N and P to achieve up to 90% reduction in hydrocarbon concentrations in the soil. The relative performance of each grass species varied. In soil planted with C. ambiguus hydrocarbon concentrations were reduced faster and to a greater extent than the other species studied, from 10 000 mg/kg to approximately 1 100 mg/kg TPH, 88% removal. Similar endpoint success was recorded for M. stipoides which facilitated 80% reduction in hydrocarbon concentrations. Interestingly, B. decumbens, the only naturalised species, did not perform as well as the other species, although still significantly better compared to unplanted controls, with hydrocarbon concentrations reduced to approximately 4 500 mg/kg, 49%. Hydrocarbon concentrations in unplanted control soil were reduced by 45% through natural biodegradation processes. Plant root and shoot tissue was periodically assessed for hydrocarbon accumulation and was shown to be negligible. A multispecies planted trial using C. ambiguus plus B. decumbens had no additional influence on total TPH removal. The final TPH removal efficiency in the multispecies trial was not significantly different p > 0.05 from that of the best single species performer of the two i.e. C. ambiguus. In a field application the planting of multiple species may still be desirable in order to preserve site biodiversity and assist rehabilitation of the area. A strong relationship between abundance of hydrocarbon degrading microorganisms in the rhizosphere and hydrocarbon biodegradation was demonstrated for all species p < 0.01. Those species which showed greatest stimulation of the microbial population resulted in enhanced TPH removal from soil. These species were the summer grass C. ambiguus and the winter species M. stipoides. This may allow for broader application both seasonally and geographically across Australia. B. decumbens showed successful rhizoremediation to a lesser degree, but may still be an option in multiple planting strategies. This investigation identified three Australian grass species from the nine evaluated that are candidates for further investigation for in situ rhizoremediation potential at field scale.

Pasture plants already adapted to acidic soil conditions are required as part of an integrated approach (with lime amelioration) to managing acid soils on the Tablelands of New South Wales, Australia. The objective of this thesis is to evaluate the usefulness of Austrodanthonia species for this purpose. The material evaluated in this study was collected during a previous survey of the distribution of Austrodanthonia on the Central, Southern and Monaro Tablelands of New South Wales. It was hypothesised that the genus Austrodanthonia has a wide range of tolerance to acid soils. A series of experiments that provided information on the growth and physiology of Austrodanthonia in relation to soil acidity, with a view to the identification and eventual domestication of the most promising plant material have been conducted through pot, hydroponics and field investigations. Firstly, soils were acidified or limed to obtain a range of soil pH and Al concentrations. This experiment showed that adding aluminium sulfate and calcium carbonate followed by washing excess salts with water is a simple, rapid and convenient method for adjusting soil pH for pot experiments. The pH of the amended soils remained relatively unchanged eight months after treatment. The experimental set-up also resulted in a wide range of soluble Al (2-52 mg/kg) across the soils. The relative Al-tolerance of 183 accessions from 15 Austrodanthonia species was tested in a pot experiment using a range of soil pH. Emergence, survival and growth of all accessions were drastically reduced by high soil acidity (pH 3.9, P < 0.001). About 11% of plants emerged at pH 3.9, whereas at pH 4.4 and 5.3, ~72% of plants emerged. Accessions exhibited large variation within and between species in their tolerance to soil acidity. From the species/accessions tested, 49 accessions from eight species were selected for further study (on the basis of being more acid tolerant). Hydroponic experiments conducted in the glasshouse evaluated: (i) formulation of nutrient solution with a stable pH, (ii) effectiveness of the formulation using tap water and deionised water and (iii) estimation of free ion activities of Al and Mn in the nutrient solution and their effects on Austrodanthonia growth. These experiments showed that a NO3-N/NH4-N ratio of 9:4 is the most appropriate ratio to obtain a stable pH 4.0 without affecting plant growth; that there was little difference between tap water and deionised water on the ionic effects of Al and Mn, and plant-size did not play a role on accession survival and that accessions of Austrodanthonia could grow well within a wide range of pH (3.5-5.5), Al (50-250 �M) and Mn (100-2000 �M). Growth of Austrodanthonia accessions declined under high acidity (pH < 3.5) and Al (300 �M), but tolerated high concentrations of Mn (2000 �M). Root-tips stained with hematoxylin grouped accessions in a similar way to the pot and hydroponic experiments for most of the accessions tested. The intensity of root staining with hematoxylin and the differential distribution of Al in the shoots and roots provided an indication that different tolerance mechanisms may be involved with Austrodanthonia accessions. It appears that both exclusion and internal mechanisms may operate for Al- and Mn-tolerance. A field experiment was conducted at Carcoar (33037�S, 149013�E, elevation 800 m) using gradients in soil pH and Al available on-site to grow selected accessions of Austrodanthonia. The accessions exhibited a range of responses to soil acidity. The accession responses to acidity from the pot and hydroponic experiments were similar to those obtained in the field, especially where Al was present as a low Al-challenge. Overall, this study shows that Austrodanthonia exhibits a wide range of acid tolerance between species and accessions within species. Among the species tested, A. duttoniana and A. fulva appeared to have the greatest commercial potential, because of their productivity and acid tolerance. The variability that exists in the accessions may be exploitable in breeding and selection programs for improved cultivars.

Pasture plants already adapted to acidic soil conditions are required as part of an integrated approach (with lime amelioration) to managing acid soils on the Tablelands of New South Wales, Australia. The objective of this thesis is to evaluate the usefulness of Austrodanthonia species for this purpose. The material evaluated in this study was collected during a previous survey of the distribution of Austrodanthonia on the Central, Southern and Monaro Tablelands of New South Wales. It was hypothesised that the genus Austrodanthonia has a wide range of tolerance to acid soils. A series of experiments that provided information on the growth and physiology of Austrodanthonia in relation to soil acidity, with a view to the identification and eventual domestication of the most promising plant material have been conducted through pot, hydroponics and field investigations. Firstly, soils were acidified or limed to obtain a range of soil pH and Al concentrations. This experiment showed that adding aluminium sulfate and calcium carbonate followed by washing excess salts with water is a simple, rapid and convenient method for adjusting soil pH for pot experiments. The pH of the amended soils remained relatively unchanged eight months after treatment. The experimental set-up also resulted in a wide range of soluble Al (2-52 mg/kg) across the soils. The relative Al-tolerance of 183 accessions from 15 Austrodanthonia species was tested in a pot experiment using a range of soil pH. Emergence, survival and growth of all accessions were drastically reduced by high soil acidity (pH 3.9, P < 0.001). About 11% of plants emerged at pH 3.9, whereas at pH 4.4 and 5.3, ~72% of plants emerged. Accessions exhibited large variation within and between species in their tolerance to soil acidity. From the species/accessions tested, 49 accessions from eight species were selected for further study (on the basis of being more acid tolerant). Hydroponic experiments conducted in the glasshouse evaluated: (i) formulation of nutrient solution with a stable pH, (ii) effectiveness of the formulation using tap water and deionised water and (iii) estimation of free ion activities of Al and Mn in the nutrient solution and their effects on Austrodanthonia growth. These experiments showed that a NO3-N/NH4-N ratio of 9:4 is the most appropriate ratio to obtain a stable pH 4.0 without affecting plant growth; that there was little difference between tap water and deionised water on the ionic effects of Al and Mn, and plant-size did not play a role on accession survival and that accessions of Austrodanthonia could grow well within a wide range of pH (3.5-5.5), Al (50-250 �M) and Mn (100-2000 �M). Growth of Austrodanthonia accessions declined under high acidity (pH < 3.5) and Al (300 �M), but tolerated high concentrations of Mn (2000 �M). Root-tips stained with hematoxylin grouped accessions in a similar way to the pot and hydroponic experiments for most of the accessions tested. The intensity of root staining with hematoxylin and the differential distribution of Al in the shoots and roots provided an indication that different tolerance mechanisms may be involved with Austrodanthonia accessions. It appears that both exclusion and internal mechanisms may operate for Al- and Mn-tolerance. A field experiment was conducted at Carcoar (33037�S, 149013�E, elevation 800 m) using gradients in soil pH and Al available on-site to grow selected accessions of Austrodanthonia. The accessions exhibited a range of responses to soil acidity. The accession responses to acidity from the pot and hydroponic experiments were similar to those obtained in the field, especially where Al was present as a low Al-challenge. Overall, this study shows that Austrodanthonia exhibits a wide range of acid tolerance between species and accessions within species. Among the species tested, A. duttoniana and A. fulva appeared to have the greatest commercial potential, because of their productivity and acid tolerance. The variability that exists in the accessions may be exploitable in breeding and selection programs for improved cultivars.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study was conducted at Campos de Cima da Serra physiographic region, Cambará do Sul, RS, Brazil. The objectives of these study were: to comparatively quantify, the length and the biomass of fine roots (≤ 2,0 mm) inside the soil and in the litter and relate comparatively, soil chemical and physical variables in a Pinus taeda L., with 15 years of age, stand, implanted in a 3 x 2 m spacing, in 1993 and in a native grass area close to it. Samples were obtained through the use of monoliths methods described by Böhm (1979), based on the digging 3 monoliths (25 cm x 25 cm x 40 cm each), distributed inside the stand and 3 in native grass area. Roots were separated from the soil through washing and catching; after they were distributed over a white sheet of paper, where with a digital camera supported by a support with fixed height, 2.045 images were obtained. With the aid of the software, the images were processed to quantify roots length. After this procedure, the roots were dried in an oven and then weighed for biomass determination. Fine roots total length in Pinus stand, in 40 cm soil profile, including litter layer, was 68413 km ha-1, where the most part of them was concentrated in the first 20 cm and in the litter. In native grass area, the total length in 40 cm soil profile, was 173550 km ha-1, 42,82% (74313 km ha-1) of the total length is concentrated in the layer 0 10 cm. The roots density in native grass is 234, 28% higher than in Pinus. In Pinus until 40 cm depth, 3,52 Mg ha-1 was counted for fine roots biomass. Native grass showed 5,628 Mg ha-1, almost twice of fine roots biomass in Pinus. In both areas, soil chemical conditions, showed correlation with roots length and biomass. In Pinus, the main factors were P>K>V>Mg>Ca, on the other hand, in native grass area, the main factors were P>K>Ca>Mg>V. The great presence of fine roots in Pinus litter is important for cycling process, nutrients and water availability. After forest harvesting, litter and residues layer should remain, aiming the maintenance of soil productive potential. / O presente estudo foi realizado no município de Cambará do Sul, RS, Brasil. Os objetivos do trabalho foram: quantificar comparativamente, o comprimento e a biomassa de raízes finas (≤ 2,0 mm) no solo e na serapilheira e relacionar comparativamente, variáveis químicas e físicas do solo em um povoamento de Pinus taeda L., com 15 anos de idade, e uma área de campo adjacente. A obtenção das amostras foi realizada através do método de monolitos descrito por Böhm (1979), a partir da escavação de 3 monolitos de 25 cm x 25 cm x 40 cm em cada área. As raízes foram separadas do solo através de lavagem e catação e, na seqüência, foram distribuídas sobre uma folha de papel branca, onde com o auxílio de uma câmera digital, apoiada em um suporte de altura fixa, obtiveram-se 2.045 imagens digitais. Com o auxilio de um software, as imagens foram processadas para quantificação do comprimento das raízes. Após, as raízes foram secas em estufa e, depois, pesadas para determinação da biomassa. O comprimento total de raízes finas no Pinus, no perfil de 40 cm do solo, incluindo-se a camada de serapilheira, foi de 68412 km ha-1, sendo que, a maior parte dessas se concentrou nos primeiros 20 cm de profundidade e na serapilheira. Na área de campo, o comprimento total de raízes finas, no perfil de 40 cm do solo, foi de 173550 km ha-1, 42,82% (74313 km ha-1) desse comprimento localiza-se na camada de 0 - 10 cm de profundidade. A densidade de raízes no campo é 234,28% maior do que no Pinus, destacando-se a camada de 0 - 10 cm, onde ocorreu a maior diferença. No Pinus até a profundidade de 40 cm, foram contabilizados 3,52 Mg ha-1 para biomassa de raízes finas. A área de campo apresentou 5,63 Mg ha-1, ou seja, praticamente o dobro da biomassa de raízes finas presente no Pinus. Nas duas áreas, as condições químicas do solo apresentaram maior correlação com o comportamento do comprimento e biomassa de raízes. No Pinus, destaca-se como principais fatores o P>K>V>Mg>Ca, por outro lado, na área de campo, destacam-se P>K>Ca>Mg>V. A grande presença de raízes finas na serapilheira do Pinus destaca a importância desta camada no processo de ciclagem, disponibilização de nutrientes e água. Após a colheita florestal, deve-se manter a camada de serapilheira e dos resíduos produzidos durante essa atividade, visando à manutenção do potencial produtivo do solo.