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Item The influence of phosphorus supply on below ground interferences between browntop and white clover : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1993) Pannell, Claire AstleyA low occurrence of white clover in pastures contributes to soil nitrogen (N) deficiency and a low quality feed for stock. There is evidence to suggest that competition for soil phosphorus (P) from roots of browntop plays an important role in determining the distribution of white clover in hill country swards. However, competition for soil P between roots of browntop and white clover has not been studied separately from other factors known to affect the growth and persistence of white clover (e.g., soil moisture, grazing management, shoot interferences (shading and physical impedance), and non-competitive root interferences). In hill country pastures, P level (phosphorus fertilisers), and defoliation (grazing management), are the main factors that can be changed by farmers to alter pasture botanical composition. The high cost of superphosphate has limited the potential of farmers to manipulate pastures using fertiliser applications. Therefore, it is important to know whether roots of browntop compete with roots of white clover for soil P, and whether a low supply of soil P will contribute to more severe competition from browntop roots. The possibility of non-competitive interferences occurring between roots of browntop and white clover must also be considered. How defoliation alters the balance of P acquisition between roots of browntop and white clover needs to be determined. Three techniques were employed to examine the nature of root interferences occurring between browntop and white clover: plant strategies; dual P isotope labelling; and a more traditional competitive settings trial using aerial partitions. Plant growth and root interferences were studied at a range of levels of soil P supply. Responses of growth and phosphorus uptake of browntop and white clover to increasing soil P supply were examined first, in the glasshouse, by growing monocultures of browntop and white clover in pots. Two mini-sward trials (one at deficient soil P supply, the other at adequate to luxury soil P supply) were carried out in the glasshouse to allow examination of root interactions (without shoot interactions). The basis of the experimental design was to determine the relative amounts of phosphorus-32 and -33 absorbed by a central row of plants (either browntop or white clover) from two adjacent soil spaces, one dominated by white clover roots, the other by browntop roots. 32P was injected into the soil on one side of the central row of plants, and 33P into the other side. 32p and 33p uptake was assessed by harvesting the shoots of the central plants, and counting the two isotopes. The competitive settings type trial compared the growth and P uptake of a single central plant in a small pot (no interference with other plants) with a central plant in a larger pot grown with roots associated with roots of plants of the same species (intraspecific association), or of the other species (interspecific association). Shoots of the central plant was separated from the shoots of outer plants by an aerial partition. The growth of browntop and white clover, and the nature of root interferences occurring within and between the two species was dependent on the level of soil P supply. However, the higher root density and specific root length (SRL) of browntop compared with white clover appeared to be the most important factor determining the success of browntop at all levels of soil P supply, regardless of whether or not browntop was grown with white clover. According to the plant strategy theory of Grime, browntop was found to be a stress tolerant plant. At low levels of P supply, the lower growth rate of browntop compared with white clover would be an important factor contributing to the dominance of browntop in hill country pastures. At adequate to luxury levels of soil P supply, shoot growth of browntop was more responsive than white clover, and browntop was capable of luxury consumption of P. The high growth rate and large demand for P contributed to the competitiveness of browntop at high P supply. However, the lower demand for P by white clover, and the high P supply may have enabled white clover to avoid competition with browntop. On unamended subsoil, browntop reduced P acquisition by white clover roots, and had a greater P uptake in the presence of roots of white clover than with roots of other browntop plants. Therefore, evidence of root competition for soil P from browntop with white clover was found. The competitive effect of browntop appeared to be due to browntop decreasing the availability of P in the soil, explained by browntop's ability to acquire more radioactive P from the soil than white clover. At low P supply (subsoil), P application, but not defoliation of browntop, reduced the competitiveness of browntop. At adequate P supply, the ability of browntop to acquire P was reduced by defoliation. The effect of defoliation was rapid (four days), and browntop was able to acquire P isotope to higher concentrations in the shoots than when undefoliated. Possibly the reduction of root competitiveness of browntop may be short-lived. Some interference, other than root competition, was occurring at intermediate to luxury levels of soil P supply, and may have masked the competitive effects of browntop. White clover appeared to benefit for P acquisition from growing with browntop, due to greater local root density compared with when growing with other white clover plants. Therefore, browntop and white clover appeared to gain mutual benefit for P acquisition from the presence of roots of the other species, and the competitive effects of browntop were not of overriding importance. The possibility of autotoxicity of white clover on its own root growth was discussed in relation to rhizosphere acidity effects on the toxicity of phenolics. At adequate to luxury levels of soil P supply, neither undefoliated browntop nor undefoliated white clover benefited from defoliation of adjacently growing white clover plants. However, at lower P supply, defoliation of white clover led to an increased P isotope acquisition by nearby browntop plants. Therefore, defoliation reduced the demand for soil P by white clover. Roots of browntop were not as tolerant of defoliation as white clover. In the field, the mat forming behaviour of browntop, physically impeding the growth of white clover and shading white clover stolons, would reduce the severity of competition for soil P between roots of browntop and white clover. Overall, root competition for P from browntop with white clover was found not to be as important as previously thought. The use of several experimental techniques allowed a clearer picture of the interferences that occur between browntop and white clover to be obtained. The nature of root interference changed with increasing P supply. The responses of browntop and white clover to increasing P supply was found to be enlightening when the plant strategy theory of Grime was used to compare browntop and white clover. However, the dual P isotope technique found plant interferences that were not detected by the other methods used (P response and competitive settings trial), and allowed interferences that were occurring simultaneously to be elucidated.Item Root restriction and root-shoot relationships in tomato (Lycopersicon esculentum Mill.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticultural Science at Massey University(Massey University, 1995) MacKay, Bruce R.; MacKay, Bruce R.The potential for controlling plant growth and productivity by manipulating root growth and development has not been realised because of a lack of understanding of how root growth influences shoot growth. Until such responses are understood, matching container design and volume to desired plant output will continue to be based solely on anecdotal evidence. A series of experiments were conducted to explore the role of physical root restriction on the vegetative growth and development of tomato (Lycopersicon esculentum Mill. 'Moneymaker'). Concurrent with these experiments, a statistical model was developed for non-destructively estimating leaf area, cluster analysis was adapted to improve experimental precision, and an improved form of growth analysis developed. Additionally, a review of oxygen and major nutrient uptake rates by tomato established the operational parameters of a hydroponic system developed specifically for the study. Rooted tomato cuttings were grown in 0.025 or 10 litre (control) containers in the hydroponic system. After 31 days in 0.025 litre containers, plants were de-restricted into either 0.05 or 10 litre containers, or retained in the 0.025 litre containers. Plants with physically restricted root systems had lower total plant biomass and total leaf area, were shorter in both height and total root length, and had fewer roots, leaves, and lateral shoots than unrestricted plants. Restriction reduced root number after 31 days, but reductions in root length and dry biomass did not occur until after 45 days. Leaf dry biomass was reduced in restricted plants after 45 days; reductions in stem height, leaf area, number and total dry biomass) were apparent after 67 days. Short periods (31 days) of root restriction had long term (67-99 days) effects on leaf growth. Leaf expansion was more sensitive than leaf biomass accumulation to root restriction. A strong linear relationship, independent of root restriction, was observed between the relative rates of root elongation and leaf expansion. Similar relationships with the relative rates of increase in root number and dry biomass were due to their covariance with root elongation. These data are consistent with the hypothesis that root elongation is functionally linked to leaf expansion via the synthesis of hormones in actively growing root apices. The influence of partial root restriction on leaf expansion was also examined. One or both halves of a split root system was enclosed in a 30 cm3 polyethylene cell. Leaf expansion was reduced in plants with only a portion of their total root system physically restricted. Compensatory growth in the unrestricted portion of the root systems resulted in total root growth at final harvest being similar to plants with all their root system unrestricted. Analysis of the relative rate of leaf expansion (RA) of individual leaves along the stem axis revealed two distinct phases in response to root restriction. In the first phase, apparent about 28 days after treatments were initiated (DAI) and observed in leaves that started expansion 3, 7, and 14 DAI, RA was reduced in plants with one or both root sub-systems in a restriction cell. The second phase, detected 42 DAI and observed in leaves that started expanding 21 and 28 DAI, was characterised by a higher RA in plants with a portion of their root system restricted compared to unrestricted plants. Proportionately more assimilate was partitioned to stems of plants with two restricted root sub-systems compared to plants with either a single or non-restricted root sub-system. No differences in leaf water potential or photosynthesis of leaves were observed among treatments. Conclusions drawn from these data support the involvement of chemical signals in maintaining coordination between root and shoot growth in container-grown plants. These conclusions are discussed with reference to the literature, and a model is proposed to explain root-shoot coordination in terms of root-sourced cytokinin and shoot-sourced auxin. Avenues for future research to test hypotheses arising from this model are identified and discussed, as are possible horticultural ramifications. Emphasis was placed in the study on improving analytical methodology of growth analysis of whole-plant studies. Experimental precision was increased in these experiments by using cluster analysis to allocate plants to blocks based on leaf area, with a developmental study showing that the mean coefficient of variation of groups formed from cluster analysis was between two and fives times smaller than that of groups formed from visual assessment. A statistical model for non-destructively estimating the leaf area of tomatoes was developed based on the length of the mib-rib of each compound leaf and its position on the stem. Although the model was accurate to within about 2.5% of actual leaf area, it was not stable in time. It was concluded that when non-destructive estimation of tomato leaf area is required, the prediction model must be developed while the main experiment is being conducted. A hybrid method of growth analysis, incorporating both functional and univariate statistical approaches, provided more flexibility and information than standard functional or classical analytical methods. The hybrid method yielded replicated estimates of growth analysis indices, providing opportunity for further evaluation of the derived data using multivariate analytical techniques including path, canonical correlation, and canonical discriminant analysis. keywords: allometric relationships, assimilate partitioning, biometrics. Chanter function, cluster analysis, containerised plants, hydroponics, leaf expansion, local error control, plant growth analysis, relative growth rate, Richards function.