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Thesis (M.S.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 28, 2007) Includes bibliographical references.

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Wild Hordeum species, from the four genome groups of X, H, I and Y, were assessed for physiological traits associated with tolerance to salinity and waterlogging. When grown in saline conditions, a number of wild Hordeum species had exceptional ‘exclusion’ of Na+ and Cl- from the young leaves, and also maintained tissue K+ concentrations, compared with Hordum vulgare ssp. vulgare (cv. ‘Golf’). For example, at 150 mol m-3 NaCl, the K+:Na+ in youngest, fully expanded leaf blades of wild Hordeum species averaged 5.2, compared with 0.8 in H. vulgare. H. marinum was more salt tolerant than H. vulgare, with a relative growth rate 30% higher than H. vulgare at 150 mol m-3 NaCl. At 300 mol m-3 NaCl, glycinebetaine plus proline contributed to 15% of πsap in expanding leaf blades of H. marinum, compared with 8% in H. vulgare. When grown in stagnant conditions, 16 accessions (approximately half of those evaluated) formed a barrier to radial O2 loss (ROL) in basal zones of adventitious roots. In the Triticeae, this trait had previously only been described in one species, H. marinum. The barrier to ROL occurred only in accessions from wetland or intermediate habitats, and was also related to genome type, being present in accessions with the X or the H genome (Hordeum vulgare has the I genome). In stagnant conditions, aerenchyma formed was, on average; 22% in accessions with the X genome; 19% in those with the H genome; and 15 and 16% in those with the I or the Y genomes, respectively. The combination of a barrier to ROL and aerenchyma enhances longitudinal O2 movement in adventitious roots, permitting roots to penetrate deeper into anaerobic substrates. In H. marinum, induction of the barrier to ROL was associated with a 97% reduction in apparent O2 diffusivity across the external layers of the basal zones of roots, compared with near the root tip. The barrier results from physical resistance to radial O2 movement, although when roots were cooled to suppress respiration some additional leakage of O2 was detected, indicating respiration also contributes to the low rates of ROL from the basal regions of roots. Low radial O2 permeability in the roots of stagnantly-treated H. marinum was associated with secondary thickening, putatively lignin or suberin deposits, in the hypodermis. These changes in root structure, however, did not influence root hydraulic conductivity, assessed for individual adventitious roots and whole root systems. Thus, diversity amongst Hordeum species in expression of traits for tolerance to waterlogging (an inducible barrier to ROL and aerenchyma) and salinity (Na+ and Cl- ‘exclusion’) were documented in this study. Traits for root aeration did not compromise the capacity of roots to take up water, presumably being of importance for growth in soils with fluctuating water levels (i.e. wet/dry cycles). The high degree of salinity tolerance in several Hordeum species, and especially in H. marinum, is consistent with field observations that these species occur in salt affected areas

[Truncated abstract] Salinity and waterlogging interact to reduce the growth of most crop and pasture species. Species that are productive on saline-waterlogging land are needed for Australian farming systems. One option is Lotus tenuis, a perennial legume widely grown for pasture in the flood-prone and salt-affected Pampa region of Argentina. To identify mechanisms responsible for the adverse interaction between salinity and waterlogging, Lotus tenuis with a reputation for tolerance was compared with L. corniculatus, the most widely cultivated Lotus species. The physiology of salt and waterlogging tolerance in L. tenuis (4 cultivars) was evaluated, and compared with L. corniculatus (3 cultivars). Overall, L. tenuis cultivars accumulated less Na+ and Cl-, and more K+ in shoots than L. corniculatus cultivars, when exposed to 200 mM NaCl for 28 d in aerated or in anoxic (stagnant agar) solutions. In a NaCl dose response experiment (0 to 400 mM NaCl in aerated solution), Lotus tenuis (cv. Chaja) accumulated half as much Cl- in its shoots than L. corniculatus (cv. San Gabriel) at all external NaCl concentrations, and about 30% less shoot Na+ in treatments above 250 mM NaCl. Ion distributions in shoots were determined for plants at 200 mM NaCl; L. tenuis (cv. Chaja) accumulated about half as much Cl- in old leaves, young leaves and stems, compared with concentrations in L. corniculatus (cv. San Gabriel). There were not, however, significant differences between the two species for Na+ concentrations in the various shoot tissues under aerated NaCl treatment. '...' Therefore, during early stages of exposure to salinity, L. tenuis accumulated a higher proportion of total Na+ in the roots under combined stagnant-plus-NaCl treatment (55% versus 39% for L. corniculatus). Na+ transporters, particularly those relying on H+ gradients across membranes, which in turn require adequate ATP levels, could be impaired under O2 deficits that inhibit respiration. To study the effect of O2 deficiency on a Na+ transporter, an NHX1-like gene was cloned from L. tenuis and identity established via sequencing and yeast complementation studies. Real-time qPCR showed expression of NHX1 in L. tenuis roots increased under stagnant-plus-NaCl treatment, whereas it was reduced in L. corniculatus. Thus, maintaining O2 transport to roots, together with up-regulation of an NHX1-like gene for Na+ accumulation in vacuoles, contributes to tolerance of L. tenuis to combined salinity and waterlogging stresses. This study highlights the importance of minimising Cl- transport to shoots as a mechanism of salt tolerance and has identified a CCC-like gene in L. tenuis as a candidate for mediating root-to-shoot Cl- transport. Under combined stagnant-plus-NaCl treatment, control of Na+ transport is another mechanism contributing to tolerance in these Lotus species. Enhanced root aeration in L. tenuis maintains root Na+ transport processes, such as accumulation in vacuoles via NHX1-like genes, to diminish xylem loading to the shoot. Overall, this thesis has contributed new knowledge on the potential of Lotus tenuis as a saltland pasture and has significantly enhanced current understanding on the mechanisms of salinity and waterlogging tolerance in plants.

Winter cropping often does not realise its full potential in south-western Victoria, where waterlogging is a major problem on the poorly drained soils of conventional cultivation (CC) systems. Consequently, cropping has been undertaken on raised beds (RB) to reduce the risk of waterlogging. Initial reports on the yields of RB were encouraging. It was hypothesized that an improvement in soil properties of RB may account for their better performance compared to CC systems. / The aim of the thesis was to evaluate selected soil physical properties of RB and to make comparisons with other treatments (CC and pasture). The specific objectives were to: 1) evaluate plant growth and crop yield; 2) quantify soil water dynamics; 3) assess changes in the soil water retention characteristic (SWRC), soil strength and soil hydraulic properties; 4) describe pore pathways from solute transport; and 5) quantify soil macropore structure. / Measurements of volumetric water content (θv) were taken at 20, 40, 60 and 80 cm and at the soil surface. These data allowed the determination of the profile soil water deficit (SWD), which was found to be greater under the RB than the CC, although at times the pasture had the largest SWD. The RB mostly remained drier than the CC, but the response to rainfall in the surface θv was similar between treatments. Below average rainfall was received during the whole study period which resulted in drier than normal conditions. / There was no consistent difference in plant growth between crops on the RB and CC; e.g. in 2004 periods of waterlogging resulted in greater dry matter production on the RB; while drier conditions in 2003 saw better crop growth on the CC. Grain yield varied annually according to rainfall, and overall the treatment yields were similar. Analysis of regional yield data showed that there was no yield difference in years with average or below average rainfall, but years with higher rainfall favoured RB. / Little difference was found in the laboratory-derived SWRC, but in the field the RB were consistently drier at all depths and at 60 cm depth the CC had a saturated zone. The RB were found to have a lower soil strength characteristic within the surface 24 cm compared to the CC. The air-filled porosity (AFP) was higher in the RB while for long periods the CC were <10 per cent AFP. There was no significant difference between the treatments in unsaturated hydraulic conductivity (Kus) in the soil surface. Saturated hydraulic conductivity (Ks) in the subsoil was very small, although the RB had significantly greater Ks than the CC. / A solute transport experiment investigated the movement of a solute in large soil cores of the RB and CC treatments. Derived parameters from a transfer function model were used to assess the solute transport characteristics. This showed that under nearly saturated conditions the CC had significantly greater solute spreading than the RB. Furthermore, the transport volume (θst) to θv ratio was smaller in the RB which indicated a greater proportion of preferential flow. These and other data suggested that the RB had a better connected and more stable pore network. / Soil macropore structure was quantified using image analysis of resin-impregnated soil. Samples were taken twice; the first samples showed that the RB had improved pore connectivity, slightly greater porosity and a pore network with smaller sized pore components than the CC. In comparison, at the second sampling time the structural parameters of the two treatments were similar. / Uncertainty exists in the scenario of higher rainfall or of the longer-term changes of soil properties under RB cropping. Nevertheless after three years of measurements, this thesis concludes that most soil physical properties of RB are distinctly better for cropping than under CC systems.

Thesis (M.Ag.Sc. 1977) from the Department of Agronomy, University of Adelaide. / Includes bibliographical references (p. B1-B24).