Optimal growth of euhalophytes requires moderate concentrations of salt and, in dicots, is associated with succulence of leaves and stems and accumulation of Na⁺ in plant tissues. Relative growth rate, water and cation content were studied in Sporobolus virginicus, a C₄ Chlorodoid grass, grown under different concentrations of NaCl. Optimal growth occurred at 100-150 mmol/L NaCl. and was not dependent on nitrogen levels or accompanied by accumulation of Na⁺ in leaves. Na:K ratios were lower in leaves and rhizomes than in roots indicating the possibility of discrimination in Na⁺ and K⁺ transport from roots to leaves. Water content of leaves and shoots was significantly greater in plants grown at optimal levels of salinity than in plants grown at sub or supra optimal salinity. Na⁺ and K⁺ concentrations in leaves contribute approximately 60% of osmolality. These results support the characterization of S. virginicus as a euhalophyte.

The work in this thesis provided critical information about the vacuolar Na⁺/H⁺ exchanger in Salicornia bigelovii with a goal to understand its role in plant salt tolerance. A cDNA (SbNHX1) was isolated and showed 87% identity to the Na⁺/H⁺ exchanger from the glycophyte, Arabidopsis thaliana. DNA blot analysis suggests the presence of a family of Na⁺/H⁺ exchangers in Salicornia bigelovii . An increase in SbNHX1 transcript was seen in shoots of 200 mM NaCl-grown plants compared to transcript levels in 5 mM NaCI-grown plants. To understand whether the SbNHX1 cDNA conferred increased salt tolerance by virtue of its unique sequence, the coding region of SbNHX1 was cloned for expression in Arabidopsis thaliana . Potential Ca⁺² regulation of vacuolar Na⁺/H⁺ exchange is shown using transport experiments. The isolation of a vacuolar Na+/H+ exchanger from Salicornia bigelovii and its functional expression in Arabidopsis thaliana will provide information on the salt tolerance mechanisms used by halophytes. (Abstract shortened by UMI.)

<p> Within Mediterranean ecosystems, conservation and restoration action is becoming increasingly necessary to preserve biological diversity within these working landscapes. Many of these systems have been managed to increase forage production through the removal of canopy trees and shrubs, resulting in understories dominated by herbaceous species. In California, woody plant regeneration can be constrained by exotic annual grasses, particularly in the presence of grazing. <i>Quercus douglasii</i> and other oak species are known to indirectly facilitate and provide spatial refuges to native plants through competitive suppression of herbaceous productivity. Mature trees can also compete with understory recruits and shrub species, limiting their occurrences to interstitial canopy gaps and resulting in reduced competition for resources. This study surveyed the overstory composition of 34 study plots at the Sierra Foothill Research and Extension Center to determine the effects of tree canopies on the occurrence and distribution of native woody species in the undergrowth. Because other studies have shown safesites, which include rock outcroppings, woodpiles, and nurse plants to facilitate woody plant establishment in this system, the microsites containing individual plants were recorded to determine the distribution of different woody species. Multivariate regressions showed that understory plant richness and abundance increased with higher levels of canopy cover, suggesting that mature trees play a role in maintaining understory diversity. The majority of stems were found growing directly underneath the canopy, with only one species established primarily in interstitial areas. Restoration strategies can utilize the natural distributions of woody species in the understory in order to increase the survival of plantings while continuing to manage these systems for multiple ecosystem services.</p>

<p> The high cost and environmental risks associated with non-renewable energy sources has caused an increased interest in, and development of renewable biofuels. Switchgrass (<i>Panicum virgatum</i> L.), a warm season perennial grass, has been investigated as a source of biofuel feedstock due to its high biomass production on marginal soils, its tolerance of harsh growing conditions, and its ability to provide habitat for wildlife and soil conservation cover. West Virginia contains vast expanses of reclaimed surface mine lands and could potentially benefit from the production of switchgrass as a biofuel feedstock. Furthermore, switchgrass production could satisfy Surface Mining Reclamation and Control Act of 1977 (SMCRA) requirements for reclamation bond release to mine operators. Three separate studies will be discussed in this thesis to determine if switchgrass grown on reclaimed surface mines can produce yields similar to yields from stands grown under normal agronomic conditions and what common surface mining reclamation practices may be most appropriate for growing switchgrass. The first study examined yield production of three commercially-available, upland switchgrass varieties grown on two reclaimed surface mines in production years two, three and four. The Hampshire Hill mine site, which was reclaimed in the late 1990s using top soil and treated municipal sludge, averaged 5,800 kg (ha-yr)^-1 of switchgrass compared to 803 kg (ha-yr)^-1 at the Hobet 21 site which was reclaimed with crushed, unweathered rock over compacted overburden. Site and variety interacted with Cave-in-Rock as the top performer at the more fertile Hampshire Hill site and Shawnee produced the highest yields at Hobet 21 (7,853 kg ha^-1 and 1,086 kg ha^-1 averaged across years, respectively). Switchgrass yields increased from 2009 to 2010, but declined from 2010 to 2011. Switchgrass yields from farmlands in this region averaged about 15000 kg (ha-yr)^-1 in the research literature, so switchgrass grown on reclaimed lands appears to be about 50% lower. A second study to determine optimal nitrogen and mulch rates for switchgrass establishment began in June 2011 on two newly-reclaimed surface mines. Both sites were seeded at a rate of 11.2 kg pure live seed (PLS) ha^-1 of Cave-in-Rock on replicated treatments of 0, 33.6 and 67.0 kg N ha^-1, and high and low mulch rates of mulch applied as hydromulch. Switchgrass cover, frequency and yield improved with the addition of any amount of N fertilizer compared to no N application. There was no significant difference in yield associated with high and low levels of N. We also observed that yields were not affected by application of additional mulch. The final study compared a one- and two-harvest system in the fourth year of production at the Hampshire Hill and Hobet 21 sites. There was no increase in yield production utilizing a two-harvest system (2922 kg (ha-yr)^-1, averaged across site) compared to a one-harvest system (3029 kg (ha-yr)^-1). The data also showed that re-growth collected from July to October in the two-harvest system added negligible yield and that yield collected in July was comparable in one- and two-harvest systems.</p>

<p> The vegetation associations in the Eastern San Cristobal Valley of Barry M. Goldwater Range-East (BMGR) were mapped using a combination of field surveys (relev&eacute;s) and interpretation of aerial imagery in order to contribute to ongoing mapping efforts of Barry M. Goldwater Range -East. Throughout the San Cristobal Valley, 149 relev&eacute; samples were collected to characterize the vegetation associations. Seventeen vegetation associations were identified and mapped, including a new <i>Larrea tridentata/Ambrosia dumosa/Grusonia kunzei</i> (Creosote bush-White bursage-Devil's cholla) association. Accuracy assessment of the map was conducted using a contingency table finding the map to be 82% accurate.</p><p> Route proliferation in the San Cristobal Valley of Barry M. Goldwater Range-East (BMGR) was also mapped and measured using remotely sensed imagery in geographic information systems and modeled with geographical variables in a multivariate regression. Throughout the San Cristobal Valley study site, 6,878 km of unauthorized routes were identified. Geographic explanatory variables distance from slopes greater than 34% (b = -3.252e-5, <i>p</i> &lt; 0.001) and the most influential variable distance from unauthorized routes (b = -0.006568, <i>p</i> &lt; 0.001) were tested for significance and influence in predicting unauthorized route density. The resulting model, built from the two significant geographic variables in a multivariate regression, was able to explain 57% of the variability in the data. The results from this study have shown that through the use of GIS and remote sensing, unauthorized route density can be predicted by geographic variables which can then be used to make future route management decisions.</p>

<p> The effective management of submersed aquatic macrophytes depends on understanding their reproductive biology. <i>Potamogeton crispus </i> L. (curlyleaf pondweed, Potamogetonaceae) produces numerous asexual propagules that make traditional management difficult. It has spread to roughly half of the counties in California (USA) from alpine habitats such as Lake Tahoe to the tidally influenced Sacramento-San Joaquin Delta. Studies were conducted from May 2012 till October 2012 at the bench and mesocosm scales in Davis and Sacramento, California, to explore the effects of benthic barrier control measures on the propagules (turions) of <i>Potamogeton crispus. </i> The first study examined the effects of three benthic barrier materials (jute, polyethylene and rubber) on turion sprouting. Jute benthic barrier material allows some light and oxygen through the fabric, while polyethylene allows oxygen, but not light. Rubber barrier material blocks light and oxygen exchange. Turion viability, as determined by sprouting, was then assessed post-treatment. Results showed no significant differences at the bench-scale for the untreated control (100% sprouting, SE=0%), jute (100% sprouting, SE=0%), or polyethylene treatments (96.9%, SE=2.1%) (n=16 for all treatments, &alpha; = 0.05). Rubber treatments resulted in 48.4% sprouting (SE= 10.6%; n=16). Results for the mesocosm experiments showed significant differences between the control and the jute and polyethylene treatments (control = 98.4% sprouting, SE= 1.6%; jute = 71.9% sprouting, SE= 4.5%; polyethylene= 70.3% sprouting, SE= 4.7%, n=16 for all treatments). Jute and polyethylene treatments were not significantly different in the mesocosm experiment. The mesocosm experiment with the rubber barrier significantly reduced sprouting (29.7% sprouting, SE= 6.1%; n=16) compared to other treatments. While light had minimal impact on sprouting, anoxia appeared to be the main factor inhibiting sprouting using benthic bottom barriers. Barrier induced anoxic stress combined with herbicides may potentially offer enhanced efficacy. The second study explored enhancement of the impermeable rubber barrier material with dilute acetic acid loaded into cassava starch "pearls". Turions were exposed for two weeks and then assessed for viability via post-treatment sprouting protocol with and without hydrosoil at the bench- and mesocosm-scale. Results for the bench-scale showed that the 20.8 mmol L^&ndash;1 acetic acid treatment was not significantly different (p=.4231) compared to the untreated control (Tukey HDS; p&le;0.05). However, the 41.6 mmol L^&ndash;1 acetic acid treatment was highly significantly different from the control (p-value &lt; 0.0001) at the bench-scale, but did not completely inhibit sprouting (mean sprouting of 31.25% (<i>SE</i>= 11.97)). Complete inhibition of sprouting turions occurred for both experiments at and above acetic acid concentrations of 83.3 mmol L^&ndash;1 (SE= 0). Results showed that tapioca starch saturated with acetic acid and combined with impermeable benthic barriers may offer an effective chemical treatment for the control of <i>Potamogeton crispus.</i> The final study examined hot water exposures under the barriers to kill and inhibit sprouting in turions. Heated water circulated under an insulated benthic bottom barrier may potentially offer a simple non-chemical rapid method to target surface propagules on the sediment, subterranean propagules and young plants. Heated water was used to treat <i>P. crispus</i> turions at the bench and mesocosm scales (25&deg;C, 40&deg;C, 50&deg;C, 60&deg;, 70&deg;C and 80&deg;C exposures for 30 to 300 seconds). Heated water exposures inhibited sprouting turions at 50&deg;C and 60&deg;C at the mesocosm and the bench scales, however, did not completely inhibit sprouting for all time exposures except at the bench-scale 60&deg;C treatment for 300 seconds. For 70&deg;C and 80&deg;C treatment exposures, there was a slight difference at the 30 second exposure mark, but at 60 second and beyond, all 70&deg;C and 80&deg;C treatments provided 100% inhibition. The cost to raise the temperature 60&deg;C from ambient water temperature under the contained limited volume under insulated barriers is estimated to be approximately $2 per 9.3 m² (100 ft²) for 5 minute treatments or $3459 ha^-1 ($1400 acre^-1).</p>

<p> Early detection of an invasive species facilitates control and eradication. Slender false brome <i>(Brachypodium sylvaticum)</i> was first discovered in the Santa Cruz Mountains of Central California in 2003 as a non-native grass in redwood forests, competing with native vegetation. The current infestation in the Santa Cruz Mountains, estimated to be 300 acres, is concentrated in San Mateo County and could be eradicated. This study sought to determine most likely locations of slender false brome in the Santa Cruz Mountains by assessing environmental attributes of known presence locations using species distribution modeling and Maxent software. The study used 1,320 species presence points collected in field surveys conducted from 2009 to 2012, GIS environmental layers covering a 940 km² study area, and the machine-learning program Maxent to identify slender false brome habitat at a 30 m resolution in the Santa Cruz Mountains. Maxent models successfully identified locations of potential distribution of slender false brome (training AUC = 0.961, test AUC = 0.960). Annual precipitation, average annual maximum or minimum temperature, and soils were the most important predictors. An independent dataset corroborated the performance of the Maxent model. Maxent could be used by land managers for targeting field surveys by predicting most likely <i> B. sylvaticum</i> habitat in the Santa Cruz Mountains.</p>

<p> The plant hormone auxin plays a major role in shaping plant morphology and development, but the gene networks regulating its synthesis and transport are incompletely known. The maize <i>BARREN INFLORESCENCE 1</i> (<i>BIF1</i>) gene has recently been cloned and shown to play an important role in the early stages of polar auxin transport. Auxin is synthesized in shoot tips and transported basipetally through the plant shoot and acts as a morphogen by facilitating the degradation of transcriptional repressors in a concentration dependent manner. The <i>AUX/IAA</i> gene family encodes transcriptional repressors that regulate a subset of plant developmental responses governed by the transcription of early auxin inducible genes in plants. Although the maize <i>BIF1</i> gene is a member of the <i>AUX/IAA</i> gene family, the co-ortholog(s) of <i> BIF1</i> in <i>Arabidopsis thaliana</i> was not known prior to this research.</p><p> Bayesian phylogenetic reconstruction placed maize <i>BIF1</i> in a clade sister to <i>Arabidopsis thaliana AtIAA15</i>. The <i> BIF1</i> lineage has undergone two gene duplications since the divergence of the early grasses. Molecular evolutionary analyses by maximum likelihood suggest that the <i>BIF1</i> alignment is under strong purifying selection with positive selection acting on a glutamine residue located in a functional region associated with <i>AUX/IAA</i> protein dimerization in one clade of <i>BIF1</i> paralogs, the <i>BIF1-Like2</i> (<i>BIF1L2</i>) clade. A character reconstruction analysis using maximum parsimony estimated an adenine to cytosine transversion at the base of the <i>BIF1L2</i> clade changed a glutamine into an alanine residue in this functional region. Expression of <i>BIF1</i> orthologs is conserved in floral meristems in the eudicot <i>AtIAA15</i> clade containing the taxa <i>Erianthe Guttata, Arabidopsis thaliana, Medicago truncatula</i>, however grass <i>BIF1L2</i> expression has diverged within the PACMAD &ndash; BEP clade, specifically in rice, where <i> BIF1L2</i> expression is reported to have moved into root tissue. These results suggest that <i>BIF1</i> paralogs has changed following a second round of gene duplication in the grasses. Taken together, a change in localized expression in these sequences, and positive selection acting on a glutamine-rich region of the protein-protein binding motif could imply that BARREN INFLORESCENCE1-like2 proteins are probably interacting with a new set or subset of AUXIN RESPONSE FACTOR (ARF) binding partners, and that neofunctionalization has occurred in the <i>BARREN INFLORESCENCE1-like2 </i> clade.</p>

<p> Developing maize kernels are vulnerable to colonization by microbes. When colonization allows proliferation of the microbe at the expense of the host, disease occurs. The ascomycete fungal pathogens <i>Aspergillus flavus</i> and <i>Fusarium verticillioides</i> are capable of colonizing maize kernels, causing ear rots and contamination of the kernel with mycotoxins. These diseases lead to significant losses of crop yield and quality, and constitute a threat to food safety and human health. Thus, the significance of these diseases has prompted extensive research efforts to understand these plant-parasite interactions. However, pathogenesis and resistance mechanisms remain poorly characterized, hampering the development of effective control strategies. No commercial maize lines are completely resistant to these fungi. We applied an integrated approach consisting of histology, in situ gene expression and transcriptional profiling to better understand the nature of the interactions that occur between maize kernels and these fungi. Maize inbred line B73 was hand pollinated and inoculated with either <i> A. flavus</i> or <i>F. verticillioides</i> by wounding the kernel with a needle bearing conidia. Histological staining of the kernel sections revealed fungal mycelium in kernels adjacent to the inoculation site by 48 hours post inoculation (hpi), and in all tissues at 96 hpi. Compared with <i>F. verticillioides, A. flavus</i> more aggressively colonized kernel tissue and formed a unique biofilm-like structure around the scutellum. Transcriptome profiling using RNA-sequencing (RNA-seq) coupled with pathway analysis showed that these fungi were recognized by the kernel tissues prior to visible colonization. Infection of the kernel by these fungi induced transcriptional changes in defense-related genes, hormone signaling networks, as well as primary and secondary metabolism pathways. To dissect tissue-specific responses of the kernel, RNA in situ hybridization and histological staining were carried out in adjacent serial sections. We found that two maize genes, <i>pathogenesis related protein, maize seeds (PRms)</i> and <i>shrunken-1 (Sh1) </i>, were expressed in the aleurone and scutellum during infection by these fungi. By staining the adjacent sections, we found that these genes were induced in the tissue before the establishment of fungal colonization. Integration of histology, in situ gene expression and transcriptional profiling to study pathogenesis of maize kernels by these two fungi revealed distinctive and common features between the two pathosystems, and provided information that will facilitate the development of resistance genotypes in maize.</p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7040. Adviser: Robert M. Skirvin. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.