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    A study of nitrogen fixation, nitrogen distribution and seed yield of selected legumes with two different growth types : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 1986) Laohasiriwong, Suwit
    Plant growth types of the determinate and indeterminate growth forms are commonly distinguished in many legume species. However, there do not appear to be many studies where direct comparisons have been made of the two growth types in relation to nitrogen fixation and nitrogen distribution. Furthermore, there are disagreements in the literature about the yield advantage of these two growth types. This study was initiated to identify the influence of different growth types of selected grain legumes on seed yield, nitrogen fixation, and nitrogen distribution. In addition, the emphasis was also put on finding amongst the measured parameters, one that had the greatest influence on the differences observed. Initially determinate and indeterminate growth types of bean (Phaseolus vulgaris) and soybean (Glycinemax), were studied in glasshouse conditions. The indeterminate cultivar of both species had higher leaf area and nodule dry weight, more root growth, accumulated more total dry weight and had higher yield than that of the determinate cultivar. In both species, the indeterminate cultivar accumulated more total plant nitrogen than the determinate cultivar. However, only the indeterminate soybean cultivar showed significantly more nitrogen fixation (Acetylene reduction) than that of the determinate cultivar. Subsequently the same soybean cultivars ('Matara' =determinate and 'Amsoy' =indeterminate) were studied in controlled environment conditions. The indeterminate cultivar produced higher vegetative dry-matter and seed yield than that of the determinate cultivar. The higher acetylene reduction activity of the indeterminate cultivar came primarily from a greater nodule mass. About 30-40% of seed nitrogen of both cultivar came from redistribution from vegetative parts, but the stem of the indeterminate cultivar re-distributed a higher proportion of nitrogen to the seed than that of the determinate cultivar. Among several plant characters measured (viz. the dry-weights of the roots, nodules, stems, leaves, and pods, the leaf area, acetylene reduction activity and the total plant nitrogen) leaf area was identified as the key factor in determining the difference between the two growth types. In order to determine the relative importance of leaf area as a factor influencing seed yield, nitrogen fixation and nitrogen distribution the leaf area of the indeterminate cultivar 'Amsoy' was manipulated by imposing different levels of partial leaf removal starting at the flowering stage. For one treatment, partial pod removal was also applied to induce a reduced demand of assimilate. Partial defoliation of the indeterminate cultivar reduced markedly the root growth and the number of branches, but nodule growth, acetylene reduction activity and nitrogen distribution was reduced to a lesser extent. Partial pod removal did not change the overall pattern of response. When about 6 0 % o f the leaves o f t he indeterminate cultivar were removed, seed yield was reduced by about 1 7 % and it was still significantly higher than the undefoliated determinate cultivar . There was no significant difference between the rates o f nitrogen accumulation in the pods under each treatment . The final seed nitrogen concentration was not affected by defoliation treatments nor was the partitioning of nitrogen to seed. I t was concluded that there were differences between the two growth types o f soybean for seed yield, nitrogen fixation, and nitrogen distribution. Leaf area was the most important parameter in determining these difference [sic]. The greater overlapping of vegetative and reproductive growth in the indeterminate cultivar seemed to be advantageous rather than disadvantageous. This longer period of vegetative growth enabled the indeterminate cultivar to produce a bigger source capacity which consequently supported more nitrogen fixation activity and produced higher seed yield. The possible implications to tropical agriculture were discussed and some future research topic s were also suggested .
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    Auxin action and cell elongation : a rational approach : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Plant Physiology at Massey University
    (Massey University, 1970) Penny, Pauline Elizabeth
    A method was developed to measure every minute the growth of a single segment excised from the elongating region of a plant. The method was used to determine the short term kinetics of growth in response to auxin addition. The method is not dependant on the use of hollow coleoptile tissue and the results are plotted as a growth rate against time. The technique has a resolution an order of magnitude higher than those in current use. The results show that there is a latent phase before auxin-induced increase in elongation rate occurs. After this latent phase, there is a rapid rise in rate to a maximum followed by a decrease and then usually a rise to a second maximum. Three hypotheses for explaining the growth rate curve are considered. It was found that neither RNA nor protein synthesis were required for the initial action of auxin but that protein synthesis became necessary within a few minutes after auxin addition. The apparent half-life of the protein whose synthesis is stimulated by auxin is about 12 min. This short half life suggests that, after the synthesis of the protein, there is a limited time during which it can act with auxin to increase elongation. A model which incorporated these results has been proposed and its relationship to the three hypothesis for explaining the growth rate curve is discussed.
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    Growth studies on defoliated Lotus pedunculatus cv. 'Grasslands Maku' : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 1978) Sheath, Gavin William
    This thesis reports on a series of experiments designed to study the response of 'Grasslands Maku' to defoliation and thereby extend the understanding of growth and production of Lotus pedunculatus. Morphological structuring, production and nonstructural carbohydrate status of 'Grasslands Maku' were assessed for different defoliation regimes in two separate field experiments. The relative importance of several residual plant factors and assimilate partitioning in early shoot regrowth, was studied in controlled environmental conditions. In the first field experiment, seasonal differences in the partitioning of growth were recorded, with the spring to mid-summer period being dominated by aerial shoot growth and the late-summer, autumn period by underground growth. Of the underground components, rhizome growth was the most responsive to seasonal and defoliation changes and it was this horizontal stem system that formed the basis of basal shoot initiation. Canopy growth became increasingly dominated by rhizome shoots as cutting height and frequency decreased and stubble shoots, stubble and dead matter declined. Following defoliation, regrowth was consistently slow during the first two to three weeks, thus production increases were achieved where regrowth intervals were extended and subsequent, higher growth rates were allowed to be expressed. Higher cutting improved shoot regrowth, particularly in the stubble shoot pool, but increased within-canopy dry matter losses that were related to death and decomposition processes, resulted in little, if any improvement in net productivity. Shoot regrowth responses resulting from higher cutting were primarily related to increases in the size of the residual shoot pools from which regrowth commenced. Residual shoot number and individual size were therefore important determinants of early regrowth. Any direct influence of residual nonstructural carbohydrate status on regrowth appeared to be principally confined to the rhizome shoot pool for the first few days of regrowth. The importance of accumulated starch would appear to be related to the provision of metabolic substrate for underground respiration during late autumn to early spring. Where defoliation is incomplete, residual stubble would appear to be an important source of current and redistributed assimilates during early regrowth. Following defoliation, redistribution of carbon compounds to shoot growth was principally confined to the rhizome shoot pool. Total shoot growth increasingly dominated the partitioning of current assimilates as plants recovered from defoliation. Where defoliation is incomplete it is proposed that assimilate utilization is a more important limitation to early shoot regrowth than assimilate supply. The defoliation responses recorded with 'Grasslands Maku' in these experiments are finally considered with regard to the role of L. pedunculatus in agriculture. Management guidelines are proposed and improved regrowth characteristics, necessary for any further extension of L. pedunculatus into grasslands farming, are suggested.
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    Ecology of pastoral communities in a heterogeneous environment : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Pastoral Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2000) López, Ignacio Fernando; López, Ignacio Fernando
    A group of studies was conducted to examine environmental variables and pasture components and their relationships in heterogeneous hill country pasture. Four studies were conducted in relation to the hill country grassland ecosystem of New Zealand. 1. The effects of long-term fertiliser-stocking rate and hill country slope category (LS Low slope, 0-12° MS Medium slope, 13-25° HS High slope, ?25°) on soil physical and fertility attributes and pasture production were examined. Field treatments, high fertility-high stocking rate (HH) and low fertility-low stocking rate (LN), have been applied to paddocks since 1975. Soil samples were taken from the slope categories of the two field treatments (microsites) and physical and fertility features were analysed. Dry matter production through the year was also measured from these units. The soil attributes that explained the largest percentage of the differences between microsites were water holding capacity (WHC), water conductivity (Kunsat), slope, soil compressibility (SC), bulk density (BD), Olsen-P, soil total nitrogen (Total-N) and soil rebound after compression (SR). Slope led to greater differences between soil features of microsites than fertiliser and stocking rate history. Dry matter production increased with increasing Total-N, Olsen-P, WHC and SC, and decreasing slope, Kunsat, BD and SR. 2. The presence of plant functional groups, species segregation and their relationship with soil features were analysed. The relationship between field condition and plant functional group was also examined. The evaluation was conducted in the same sites as the first study. The pasture botanical composition for each microsite was measured through the year and plant functional groups determined. The relationship between the presence of plant species and the soil attributes WHC, Kunsat, slope, SC, BD, Olsen-P, Total-N and SR (from the first study) and plant functional groups were studied, as well as the field condition-plant functional groups relationship. Seven functional groups were determined. High fertility grasses and Lolium perenne (Lp) were associated with LS and high availability of resources, while low fertility species were segregated to HS. Groups of species such as Agrostis capillaris (Ac) were indifferent to environmental changes. Functional groups proved to be good indicators of soil development. Field condition and plant functional groups were complementary concepts in grassland dynamic analyses. 3. Sheep grazing behaviour was examined in relation to slope category and plant species selection. The study was conducted in the same microsites as studies 1 and 2. Transects with marked tillers of Anthoxanthum odoratum (Ao), Ac and Lp were placed in the slope categories as follows: Ac and Lp in LS; Ac, Ao and Lp in MS; and Ac and Ao in HS. The evaluation was carried out during 4 weeks in each of Summer, Autumn, Winter and Spring, and records of grazed and ungrazed tillers were analysed. Pasture growth rates were calculated through the year. During Spring sheep grazed mainly the LS. With decreasing availability of pasture, sheep enlarged their grazing areas towards the HS. Species selection was only present during Winter when pasture availability was low. In Winter sheep also grazed in all slope categories and selected Lp over of Ac but showed no selection for Ao. 4. Ecotype segregation and plant phenotypic plasticity were examined. Plant material was collected from the extremes of the environmental gradient analysed in studies 1, 2 and 3 and grown in glasshouse conditions under five levels of phosphorus and three of nitrogen in the soil. The plants in each pot were cut on three occasions and total dry matter was calculated. Height, plant architecture, plant horizontal expansion and leaf growth were analysed for Cynosorus cristatus (Cc), Holcus lanatus (HI), Ac, Ao and Lp. Morphological and physiological differences were present between genotypes of Lp whereas only physiological genotypic differences existed in Ao and Cc. Consistent differences were not found between HI genotypes. Thus, Ao, Cc and Lp showed ecotype differentiation. Ac genotypes showed high plasticity with no ecotype differentiation.
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    Population studies of ultraviolet-B radiation responses in white clover (Trifolium repens L.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Palmerston North, New Zealand
    (Massey University, 2000) Hofmann, Rainer W.; Hofmann, Rainer W.
    White clover growing in New Zealand is experiencing increasing levels of ultraviolet-B (UV-B) radiation as a result of ozone depletion. This thesis reports a series of investigations on morphological and physiological responses to UV-B in various white clover populations. In addition, these studies examined UV-B responsiveness in combination with drought and consequences for insect herbivores. Plants were grown in controlled environment rooms with and without supplemental UV-B radiation at a dose of 13.3 kJ m-2 d-1, corresponding to a 25% mid-summer ozone depletion above Palmerston North, New Zealand. Morphological measurements included numerous attributes of plant growth and morphogenesis as well as several aspects of leaf structure. Physiological studies investigated both primary and secondary metabolic functions. In general, UV-B reduced components of white clover growth. The white clover populations showed a number of constitutive and UV-B-induced differences in many morphological and physiological attributes. UV-B sensitivity was mitigated by drought and was less pronounced with increasing duration of UV-B exposure. Bioassays revealed differential dietary effects of UV-B-treated foliage on the performance of lepidopteran insects. UV-B effects were also apparent under frequent defoliation. Comparisons of morphological and physiological features showed that white clover UV-B responsiveness was mainly linked to inherent differences in morphology and growth among the populations, while on a physiological level it was more the UV-B-induced differences that conferred UV-B tolerance. In particular, UV-B tolerance of the white clover populations was related to lower constitutive productivity. This was further linked to several constitutive leaf attributes, including small leaf size, small and lens-shaped epidermal cells as well as low leaf water potential. UV-B-induced features linked to UV-B tolerance included high percentage of leaf dry mass, accumulation of UV-absorbing compounds and of total flavonols (particularly quercetin glycosides) as well as increases in leaf water potential. UV-B tolerance was greatest in white clover populations adapted to multiple and severe stresses in the habitat of origin. This series of investigations was used to propose a functional framework, linking UV-B responsiveness to underlying specialisation of the white clover populations.