Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisor: J. Thomas Sims, College of Agriculture and Natural Resources. Includes bibliographical references.

High external Pi could reduce the fold of induction of GmSOS1 and GmCNGC by salinity stress, while posses no effect on other gene candidates. The possible effects on the repression of GmSOS1 and GmCNGC by high external Pi were discussed according to the current understandings on their roles in the salt stress responses. / In this study, phenotypical, physiological, cellular and molecular investigations were carried out to delineate the interactive effects of salinity and external Pi in "Pi tolerant" soybeans. The ultimate goals are to provide essential scientific background for practicing soybean cultivation in saline lands and to explore the possibility to improve the salt tolerance together with P-deficiency tolerance of soybeans. / It was found that high external Pi could reduce the salt tolerance capability of 15 "Pi tolerant" soybean germplasms. Such detrimental effect was common among soybeans, regardless of the type (cultivated versus wild), the salt tolerant capability in optimum Pi level, and the sensitivity to Pi level (Pi tolerant versus Pi sensitive). / Salinity is a major abiotic stress significantly reducing crop yield. Moreover, high salinity in soil is usually accompanied with deficiency of available phosphorus (P). Supplementation of inorganic phosphate (Pi) could be an agricultural strategy to enhance crop production on saline lands. However, ionic components in soil often interact to each other to affect the final growth performance of plants. / Soybean is an important crop that is sensitive to both high salinity and P deficiency in soil. Based mainly on the studies using "Pi sensitive" soybean cultivars, physiological investigations concluded that high external Pi could reduce the salt tolerance via excessive accumulation of P and chloride in the foliar tissues. "Pi tolerant" and "Pi sensitive" are relative terms to describe the response of a soybean cultivar to 1.6mM Pi when grown in non-saline nutrient solutions. The "Pi sensitive" cultivars developed a reddish-brown discoloration on their leaves and exhibited retarded growth. By contrast, the "Pi tolerant" cultivars thrived under high Pi supplements. / The physiological mechanism underlining such interaction in "Pi tolerant" soybeans was distinct from that in "Pi sensitive" cultivars. At the in planta level, high level of external Pi external Pi diminished when de-rooted plants were used, suggesting that the root is the primary organ interacting with Pi in the growth medium. Two cell models, including soybean suspension cells and the tobacco Bright-Yellow-2 cell line, were also employed to study the effects of high external Pi at the cellular level. Consistent to the results using the whole plant, high external Pi uplifted cellular sodium ion uptake and reduced cell viability under salinity stress. / To identify the possible molecular targets of high external Pi, the expression of 12 gene candidates in roots of "Pi tolerant" soybean was investigated in response to NaCl stress supplemented with 0.2mM Pi or 2mM Pi. The putative functions of these gene candidates are involved in: (a) Na+ and/or K+ transportation (GmSOS1, GmNHX; GmGLR3, GmCNGC, GmNKCC and GmAKT1); (b) regulation of ion homeostasis (GmSAL1, GmCIPK1 and GmSCA1); and (c) energetic system for the operation of ion transporters (GmAHA1, GmVHA-C and GmVP1). / Phang, Tsui Hung. / "June 2008." / Adviser: Lam Hon Ming. / Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1525. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 132-157). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Typewritten copy Includes bibliographical references

Phosphorus (P) limitations to agricultural productivity commonly occur in Australian soils and have largely been overcome by the use of inorganic fertilisers. However, studies have shown that most of the P taken up by plants is from native P pools. The turnover of P and native soil organic matter may be strongly affected by drying and rewetting (DRW). Rewetting dry soil results in a pulse of respiration activity and available nutrients. In Mediterranean-type climates surface soils naturally undergo recurrent DRW cycles. In southern Australia, soils experience DRW due to erratic rainfall within the growing season, and short, high intensity thunderstorms also during summer periods. The principal objective of this thesis was to determine the significance of dry-rewet events, for altering P availability and cycling in agricultural soils in Australia. Soils representing a wide range of soil types and climatic zones of southern Australia, showed large flushes in carbon (C) mineralisation after a single DRW event. For some soils these were comparable with reported values, however large variability in flush size between soils was observed. Soils that commonly experience DRW did not appear to be more resilient to DRW than soils from areas with fewer DRW events. Even when soils had relatively small respiration flushes, as a result of low soil organic matter, a high proportion of the soil C was mineralised after rewetting. Soil physiochemical properties (total C, total N, organic C, humus, microbial biomass P, organic P, sand and silt) were correlated to the size of the flush, hence nutrient availability and soil texture appear to primarily determine flush size. Therefore, the influence of climate on DRW may relate to determining the quantity of organic matter and microbial biomass that is available for turnover. Different size and composition of the microbial biomass within the same soil matrix were achieved by adding three different C substrates (glucose, starch and cellulose at 2.5 g kg-¹) at 5 times over 25 weeks. The treatments showed disparate responses to DRW, due to greater biomass (larger flushes) and effects of community composition, highlighting the central role of the soil microbes in DRW processes. When subjected to multiple DRW events these soils showed smaller rewetting respiration flushes with subsequent rewetting events. In contrast, the amount of P released after rewetting was the same. This study showed that increases in P after rewetting were transient and rapid immobilisation of P by microbes occurred, which may limit the availability to plants. The composition of the microbial community was changed by DRW with a reduction in fungi and gram negative bacteria, showing that certain species are more susceptible to DRW than others. Closer investigation at 2 hourly intervals after rewetting confirmed the transient nature of P flushes. The response in microbial respiration after rewetting was immediate, with the highest activity occurring within the first 2 h. Phosphorus availability was increased by DRW but remained stable over the following 48 h incubation period. The study highlights the rapid nature of changes in available nutrients after rewetting. Furthermore, while potentially only a small component of the P flush that occurred, the DRW soil had higher levels of P than most incubated soil at 48 h, this would be potentially available for plant uptake or movement with the soil solution. Long-term water regimes (continuously moist or air-dry, or DRW occurring at different times during incubation) that were imposed on two soils from different climatic regions over a 14 wk period, did not alter available nutrient (P and C) pools or the size of the microbial biomass. However, these long-term water regimes determined the respiration response of the soils to experimental DRW. The largest flushes occurred in the treatment with the longest dry period, and confirm findings of reported studies that the response of a soil at rewetting is determined by the length of the period that it is dried. Microbial biomass was little affected by experimental DRW, but showed large changes in C:P ratio. Thus, changes in physiological state or community composition may be more affected by DRW than the size of the microbial biomass. Microbial communities were altered by DRW irrespective of climatic history (warm wet summer and temperate Mediterranean), however these changes were not related to specific groups of organisms. In addition, the disparate respiration responses and inhibition of phosphatase by DRW, indicate that functional changes may be induced by DRW but can not be sufficiently explained by quantifying available nutrient pools or the microbial biomass. The use of wheat seedlings bio-indicators of P availability after the long-term water regimes, confirmed that plant available P was altered by DRW, indicated by differences in growth, although the large variability in seedling growth made it difficult to quantify these differences. However, the distribution of labile P, available at planting, in soil and plant pools at harvest, showed that long-term water regimes increased P allocation in plant tissue in one soil and decreased it in another. Furthermore, only a small fraction of the labile P present at planting was taken up by plants, which confirms the superior ability of soil microbes to immobilise P that is released by DRW. Nevertheless, since the long-term water regimes increased P availability, this may be transported via surface water or leaching. DRW is important for C and P turnover in soils of southern Australia. However, P flushes occur rapidly after rewetting and are transient. Therefore, DRW appears to have only minor consequences for P availability to plants. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1321018 / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008

Nodal sections of the winter-hardy 'John Franklin' rose cultivar from field-grown plants were cultured on a modified Murashige and Skoog (MS) nutrient medium. Very high levels of contamination from the surface of the initial sections required that plants be grown under greenhouse conditions. Rose plantlets obtained from subsequent subcultures were used for the first time in a radiotracer experiment with $ sp{32}$P to study the kinetics of phosphorus (P) uptake as a function of temperature of the nutrient medium. P uptake increased with time for rooted and non-rooted plantlets in a linear fashion that did not reach an equilibrium value even after 96 hours of exposure. An analysis of variance revealed that the plantlets with roots absorbed significantly greater amounts of P at the 0.01 level compared with non-rooted plantlets at 22$ sp circ$C. P uptake was significantly higher at the 0.05 level, for rooted versus non-rooted plantlets at 33$ sp circ$C. There was no significant difference in P uptake by rooted and non-rooted plantlets at 3$ sp circ$C. Interaction between time of exposures and rooting was found to be significant at 22$ sp circ$C and 33$ sp circ$C at the 0.01 level. The results indicated that the root system, previously thought to be inefficient in the nutrient absorption, played a key role in absorbing P from the nutrient medium at optimum temperature.

Lowland rice production is expanding throughout South-East Asia necessarily onto soils of poorer nutrient status with a resulting decrease in yields. An understanding of the nutrient status of the rice rhizosphere is essential for the development of appropriate management practices to increase rice yields. Phosphorus (P) deficiency is one aspect of rice nutrition. Increased rice root respiration and P uptake efficiency, and an increase in H$ sp{+}$ released from roots and enhanced solubility of calcium phosphates are two possible mechanisms of tolerance to low P levels. These mechanisms were evaluated but could not be used as single tests to differentiate among cultivars for tolerance to P deficiency. Phosphorus reactions in the soil may be confounded by the chemistry of iron (Fe). Iron and P interactions in the rice rhizosphere were investigated using a Philippine paddy soil. Root loss of oxygen (O$ sb2$) into the rhizosphere caused the oxidation of Fe$ sp{2+}$ and the concurrent release of H$ sp{+}$. Root release of H$ sp{+}$ from cation-anion uptake imbalances also contributed to the acidification of the rhizosphere. Accumulation of Fe$ sp{3+}$ was found next to the root plane. Depletion of acid-soluble P coincided with the zone of acidification. Rice plants were able to utilize the acid-soluble P fraction during growth.

The radiotracer methodology was combined with the Hoagland solution culture of growing soybean in a greenhouse to investigate the absorptions of phosphorus (P), calcium (Ca), and sodium (Na) as a function of salinity. Salt stress was varied by using zero to 120 mM NaCl. The research was initiated because of a need to increase soybean production in the saline soils of the semi-arid regions of the world. Although P absorption increased with time at each concentration of NaCl, increasing its concentrations ([NaCl]) to 120 mM reduced P uptake considerably. The addition of inorganic P (Pi) to the salt medium improved P absorption significantly (P < 0.0001) in stem, petiole, and roots. Polynomial regressions showed the relationship between 22Na activity and [NaCl] for leaves and petiole to be cubic (R2 = 1) while in the stem a quadratic relationship prevailed. A maximum of P and Na absorption was observed at 40 mM NaCl. The relationship between 32P activity and increasing [NaCl] was linear for the roots (a positive slope) and the stem (a negative slope). 45Ca and 32P dual labelling part of the experiments failed to produce results because an unexpectedly high degree of tissue quenching which prevented from obtaining the minimum counting requirements for separation. Shoot fresh and dry weights decreased linearly with increasing [NaCl] as did the root fresh and dry weights. Leaf chlorophyll content during the last week of the final harvest showed a linear relationship with time. Chlorophyll increased with time linearly when the growth medium contained zero and 40 mM NaCl; whereas a negative slope was obtained for 80 and 120 mM NaCl. It seems that P fertilization of the soil could ameliorate the salt effect. 22 Na uptake results indicated that there is a mechanism for exclusion of Na from soybean plant parts.

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