Wheat production is the largest enterprise within the Australian grain industry, with an annual gross value of production of approximately $4 billion. However high temperature stress (>35°C) and zinc (Zn) deficiency in soils are a frequent occurrence across the Australian wheat belt and represent two of the most important environmental limitations to wheat production and grain quality. The work presented here has shown for the first time that Zn nutrition can provide wheat plants with a level of tolerance to high temperature stress. Field trials, along with controlled environment studies, showed that supplementary Zn nutrition improved photosynthetic activity during a high temperature event, by stabilising chlorophyll initial fluorescence, Fo. Since increases in Fo under heat stress are associated with an increase in lipid fluidity of the thylakoid membranes at high temperature, the results suggested that adequate Zn fertilisation could preserve membrane integrity during heat stress. Electron microscopy confirmed this hypothesis, and showed that adequate Zn nutrition could maintain the integrity of a number of cellular membranes during high temperature, including the tonoplast, chloroplast envelope and the thylakoid membranes. Measurements of canopy temperature depression showed an improvement in the evaporative cooling of the canopy with supplementary Zn nutrition in the Zn inefficient varieties, suggesting better soil water extraction under warm conditions. Supplementary Zn nutrition also increased the kernel weight of plants grown under warm conditions in the field, however this was unrelated to the improvement in photosynthetic ctivity. Nevertheless, results from both controlled environment and field experiments demonstrated that the detrimental effects of low Zn availability and high temperature on the yield of Zn inefficient or thermosensitive wheat varieties will be most damaging when these stresses occur in combination. Analysis of protein composition showed that supplementary Zn fertilisation increased the glutenin:gliadin ratio in the grain. This suggests that Zn fertilisation may improve the bread-making quality of wheat under conditions of Zn deficiency. The results also showed a negative association between grain Zn concentration and the number of days over 35°C during grain filling, which suggests that the negative effects of high temperature stress on grain protein composition will be compounded when plants are grown on soils of low Zn availability. This thesis represents a valuable contribution to the understanding of the relationships between micronutrient supply and environmental stress. Further studies should be undertaken to establish whether the protective effect of Zn on the photosynthetic apparatus will be maintained under consecutive heat stress events, to determine the ways in which Zn ions stabilise and protect bio- membranes under heat stress and to confirm the positive effects of Zn on grain protein composition and baking quality. / Thesis (Ph.D.)--School of Agriculture and Wine, 2004.

Thesis (M.Sc.) -- University of Western Sydney, Hawkesbury, 1999. / Thesis submitted for the degree of Master of Science. Includes bibliographical references (leaves 151-162).

Thesis (Ph.D.)--Murdoch University, 2005. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 258-296.

The current atmospheric CO2 partial pressure of 36 Pa is expected to nearly double by the end of the 21st Century.Increases of this magnitude are likely to profoundly change the biochemistry, growth and morphology of plants, particularly C3 species.The research in this thesis focuses on the micronutrient Zinc (Zn), because this element is associated with a number of macromolecules which play key roles in plant growth and development, particularly on the shoot apex.The main objective of the work was to study the influence of elevated CO2 Zn nutrition of rice in the vegetative phase.A second objective was to investigate whether high CO2 reduced Zn concentrations in grain of cv. Jarrah and a Japanese cultivar, Akitakomachi, grown in either controlled environments, or in the field in a FACE (Free Air CO2 Enrichment) experiment. The greater Zn use efficiency of cvv. IR8 and Jarrah at elevated CO2, and the fact that high CO2 completely overcame chronic Zn deficiency at low Zn supplies, indicates that it may be possible , under future CO2 scenarios, to produce rice in areas where low soil Zn availability currently limits yield. / Master of Science (Hons)

Transplanting is a common practice for many horticultural crops and some field crops. Recently, transplanted oilseed rape (Brassica napus L.) crops have been reported to be sensitive to zinc (Zn) deficiency. However, Zn nutrition in transplanted field crops has not been investigated in detail. The objectives of this present research were to investigate whether transplanting increases external Zn requirements of transplanted oilseed rape, and the mechanisms of root function, growth and Zn uptake after transplanting including rhizosphere modification capacity by plant roots. The second objective was to examine the relative effects of root pruning and transplanting on Zn responses of oilseed rape, and the third objective was to determine external and internal Zn requirements of transplanted oilseed rape for diagnosing and predicting Zn deficiency. An experiment on a low Zn sand (DTPA extractable Zn 0.14 mg kg-1) was set up to determine whether transplanted oilseed rape had a higher Zn requirement than that of direct-sown plants. Low Zn supply depressed shoot dry weight, however, root growth was relatively more strongly suppressed than shoots. Maximum root dry weight required much higher external Zn for transplanted plants compared to direct-sown plants, whilst shoot dry weight required a similarly low external Zn supply. In addition, transplanted plants were sensitive to zinc deficiency during the early post-transplanting growth, and the response weakened as the plants recovered from root injury or transplanting stress. However, the transplanted plants also experienced root pruning before transplanting and so in this experiment the higher Zn requirement could have been due to root pruning or transplanting or both. A further experiment was undertaken to determine the comparative external Zn requirements of direct-sown and transplanted plants in well-stirred chelate-buffered solution culture where a rhizosphere effect on plant availability of Zn forms is absent and the effects of poor root-soil contact on post-transplanting growth are minimized. In solution culture at the same level of Zn supplied, direct- sown plants produced higher shoot and root dry matter and greater root length than those of transplanted plants. However, since a higher external Zn requirement was found for transplanted plants in buffered solution culture than for direct- sown plants, it was concluded that the higher Zn requirement was not related to decreased rhizosphere modification, to greater demand for Zn or to poor root-solution contact, but rather to the time required for transplanted plants to recover from transplanting and root injury. The recovery of root function in solution culture was more rapid than that in soil culture and expressed as a higher Zn requirement for shoot as well as root growth. It suggested that the delay in root recovery in soil culture was due to slower absorption of Zn from the soil after transplanting than was the case in solution culture. Chelate-buffered nutrient solution culture and harvesting plants successively at 5 day intervals until 25 days after transplanting was used to examine the mechanisms of the recovery of root growth and function. In this experiment, the external Zn requirement of transplanted plants was investigated with unpruned or pruned root systems. Plants with unpruned root system and sufficient Zn supply exhibited faster recovery from transplanting than those with pruned root system plants. The results suggest that root pruning impaired Zn uptake by plant roots and slowed down the root and shoot growth after transplanting. Increased solution Zn partly alleviated the effects of root pruning and presumably this is a major reason why transplanted oilseed rape had a high external Zn requirement. However, root pruning also appeared to impair water uptake, and may have suppressed shoot growth through sequestering carbon for new root growth and through decreased phytohormone production by roots. Since rapid root recovery of transplanted plants is essential for successful of growth in the field, Zn application to the nursery bed was explored as a starter fertilizer to stimulate root growth after transplanting. The objective of this experiment was to determine whether increasing the seedbed Zn would stimulate new root growth of transplanted oilseed rape, and therefore would alleviate the need for increased external Zn for post-transplanting growth. Results showed that adequate Zn concentration in the seedbed promoted the post-transplanting growth by stimulating the new root growth especially increased root length, and also hastened the recovery of root systems. However, high Zn concentration at transplanting still had a more dominant effect in stimulating the new root growth of oilseed rape after transplanting. The final experiment was set up using rhizobags with three rates of Zn supply and unpruned or pruned root systems. The purpose of this study was to investigate the chemical change in the rhizosphere and non-rhizosphere or bulk soil and its relationship to the recovery of root function after transplanting, and also to identify and quantify the organic acids in soil extracts of direct-sown and transplanted plants. The rhizosphere soil pH was lower than that of non-rhizosphere soil, and the decrease of soil pH was suggested as the mechanism of the increase of Zn availability and mobility in the rhizosphere soil. Direct-sown plants were more efficient in utilizing Zn than those of transplanted plants especially compared to those of plants with pruned root system. Zinc deficient plants excreted higher concentration of organic acids particularly citric acid, suggesting this was a mechanism of Zn mobilization and Zn uptake by roots of oilseed rape. The main implications of the present study for the management of Zn nutrition of transplanted crops were: the need to increase the Zn application to crops in the nursery and at transplanting compared to direct-sown plants; the possibility that external requirements of other nutrients will be greater in transplanted crops also requires further consideration; and in cropping systems where transplanting is practised, greater attention should be given to the avoidance of root damage during the transplanting.

Thesis (Ph.D.)--Murdoch University, 2004. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 192-217.

Thesis (M.S.)--Mississippi State University. Department of Plant and Soil Sciences. / Title from title screen. Includes bibliographical references.

Zinc and manganese have long been considered as essential micronutrients to plant growth, yet the interactions of the two nutrients on growth and development of plants have not been elucidated in their entirety. Silicon is not classed as an essential element, but has been found to improve growth of a number of crops, particularly of the Poaceae family. A simple water culture hydroponic system was developed to monitor the growth and development of a fruit crop (Cucumber – Cucumis sativus) under deficient, adequate and excessive applications of zinc and manganese. Plant growth parameters were monitored including leaf growth, plant height, plant fresh and dry mass, yield, fruit size and fruit mass. Nutrient uptake was also measured using inductively coupled plasma emission spectroscopy, whilst chlorophyll was determined spectrophotometrically. Plant nutrient analyses were also conducted using inductively coupled plasma emission spectroscopy. Silicon was found to have a beneficial effect on the growth of cucumbers and was incorporated as a treatment for this crop along with zinc and manganese since foliar silicon sprays were able to correct the occurrence of mineral deficiency symptoms. Along with plant growth measurements, nutrient uptake, plant nutrient analysis and chlorophyll determination, plant tissue was also analysed using transmission electron microscopy to establish the impact of silicon applications on the cell ultra-structure of cucumbers. Electron micrographs showed an increased presence of plasmodesmata in treatments excluding silicon. Such increased plasmodesmata connections under silicon deficient conditions could increase translocation of cell solutes due to reduced cell longevity. Results also confirmed the essentiality of zinc and manganese on plant growth and development as typical deficiency symptoms were observed. Typical toxicity symptoms were also recorded. Rates of uptake of nutrients corresponded with leaf growth and enlargement as well as yield. The chlorophyll concentration was not a clear indicator of nutrient application level. Typically, manganese and zinc interacted with iron, magnesium, calcium and potassium, affecting their uptake into the plant dependent on the level of manganese and zinc applied. Although non-essential, silicon improved plant growth, but had neither a relationship with the other nutrients evaluated nor affected the physical growth and development of the plants. Manganese and zinc, as essential to plant growth and development, affect the visual appearance of the plant as well as affect the plant biochemically due to their involvement in many growth and development processes. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.