It is postulated that definition of the availability of nutrients in soil t for plant uptake, will not be satisfactory, unless there is consideration of the plant's role as the absorber. The amount of nutrients absorbed by plants from soil can be related to i) the initial concentration in the soil solution, ii) the capacity of the soil to maintain this concentration (the buffer power), iii) the ease of movement of the nutrient to an absorbing root, and iv) the plant demand. These ideas are the foundation of models which successfully describe the nutrient uptake by single roots, growing in an infinite quantity of soil. The aim of the present work was to extend the approach used to explain uptake by single roots, to complete root systems. The requirements for the work are: (i) a theoretical description of nutrient flow to an absorbing, multiple root system; (ii) experiments for examining the proposed hypotheses. When a root absorbs a nutrient, there is a depletion in the nutrient concentration at the root surface. In a system of many roots, the zones of nutrient depletion around each root overlap. This reduces the effective initial concentration in the soil solution. So, in a multiple root system, the soil around each root is limited. The extent of overlap depends on the diffusion coefficient of the nutrient, the plant demand, and the interroot distance. The consequence is a lowering of the concentration at each root surface, below that of a similar root absorbing alone. An electrical analogue (Sanders et al. 1971) of diffusion of solutes to groups of absorbing roots was used to simulate nutrient uptake by plants from soil. The analogue was particularly useful for investigating the general consequences of different plant and soil conditions. To interpret specific plant uptake data, a more flexible computer model of diffusion and mass flow to a root system of variable density, with any specified uptake properties, was developed. For workers interested in an accuracy of ± 20%, an equation for calculating uptake, by systems similar to those which the computer model treats, is presented, which can be solved on a desk calculator. To test the model, experimental data on nutrient uptake, root dimensions and distribution, and soil conditions, during the growth of whole plants in soil was obtained. The computer model predicted the measured plant uptake wall, when values of the plant demand coefficient (which related uptake rate to the external solution concentration) given is the literature, from solution culture work under similar conditions, were used. It is concluded that the theory is an adequate representation of the simple plant-soil system used in the experiments. The expression, relating plant demand to concentration in the soil solution, was simulated on the electrical analogue. The effects of pattern, density, radius and demand coefficient of roots, on the course of uptake of solutes, of varying degrees of mobility, were investigated. Quantitative interrelations between soil and plant characteristics were established, which are discussed in the light of earlier concepts of mobility and availability of nutrients in soil. The uptake of a solute by any root system is roughly determined by the plant demand coefficient and the product of the solute diffusion coefficient, D, the absorption time, t, and the root density, L. The product DtL, for potassium, may often be is the range where root pattern affects uptake. This can be estimated graphically. Theory suggests that the uptake rate of K and K is the plant experiments was reduced by interroot competition. In both experiments, if supply was by physical processes only, the plants were absorbing K from the soil near to a maximum rate, which was set by transport through the soil. In those circumstances, the rate of uptake into a plant is limited by the length of root. Movement through the soil was easily able to supply the plant's requirement of N, until the total quantity was exhausted. It is deduced that this will usually be the case in British arable soils. A major problem, in the experimental determination of plant uptake from soil, results from the inaccessibility of the roots. A technique was devised for estimating the length and pattern of living roots of individual plants, without excessive labour. Radioactive roots are detected by autoradiography as they intersect planes of soil, and the root length par unit volume and rooting pattern follow easily. If two plants are labelled with different isotopes, their root systems can be distinguished. Any spatial interactions between the root systems are detected by the method, and the causes can be inferred. If the roots are extracted from the soil, their length can be automatically measured with an Image Analysing Computer.

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Pepper plants (Capsicum annuum L.) were grown in field and a greenhouse in Arizona to determine the effects of water stress, root temperature, and exogenously applied growth regulators on cytokinin production and the resulting growth. Research showed that vegetative plants were significantly higher in cytokinin activity and growth parameters than fruiting plants. Also, in root-pruned fruiting plants, cytokinin activity was less than that of intact fruiting plants. In vegetative plants, the competition between removed sinks and the rest of the shoot was reduced and, hence, more cytokinin came from the roots to the shoots. Besides, additional carbohydrates were available and recycled to the roots. In respect to temperature effect, elevating temperature from 15 to 30°C had a pronounced effect of increasing the growth rate and cytokinin activity. The measured parameters declined when temperature exceeded 30°C. Temperatures between 25 and 30°C were found to be optimum. Under experimental conditions, growth regulators (Cytex® and Burst®) applied to the soil or foliage had no significant effect on growth rates or cytokinin activity in roots. Also, applying Burst® or kinetin to the nutrient medium had inconsistent and statistically nonsignificant effects on photosynthesis and transpiration.

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Bibliography: leaves 207-222 / xvi, 222 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1987

Orientador: Ivany Ferraz Marques Valio / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-10T07:14:10Z (GMT). No. of bitstreams: 1 Frigeri_RenitaBeteroCorrea_D.pdf: 1952747 bytes, checksum: 56334acb7a1f414b02ad8d99c78ee37c (MD5) Previous issue date: 2007 / Resumo: O crescimento de plântulas de espécies arbóreas tropicais, em ambientes com disponibilidade luminosa contrastante, depende de interações entre características morfológicas e fisiológicas. Dentre as várias alterações morfológicas que ocorrem em condições de baixa irradiância, uma é a razão de crescimento entre a raiz e a parte aérea. A razão raiz:parte aérea de plântulas pode ser indicativa de especialização a diferentes ambientes. No geral, quanto mais sombreado o ambiente, maior a alocação de biomassa para as folhas. O aumento da biomassa da parte aérea (folhas e caules) se faz em detrimento da biomassa das raízes. Com o objetivo de verificar os efeitos de diferentes níveis de irradiância na alocação diferencial de fotossintatos, entre a parte aérea e subterrânea de plântulas de algumas espécies arbóreas tropicais, foram analisados o papel dos cotilédones e da região apical do caule e raiz na alocação, o teor de amido e a translocação de compostos de carbono. Plântulas de Copaifera langsdorfii, Dalbergia nigra, Hymenaea courbaril, Myroxylon peruiferum, Peltophorum dubium e Poecilanthe parviflora, consideradas tolerantes ao sombreamento e Bauhinia longifolia, Enterolobium contortisiliquum, Erythrina speciosa, Piptadenia gonoacantha, Senna macranthera e Schizolobium parahyba, consideradas pioneiras, foram crescidas por aproximadamente 2 meses sob 4, 18, 50 e 100 % da irradiância total. O acúmulo de biomassa de todas as espécies estudadas aumentou em resposta ao aumento da disponibilidade luminosa, bem como as taxas de crescimento relativo e a assimilação líquida. Verificou-se, em geral, redução na razão raiz: parte aérea das plântulas sob baixa irradiância. Apesar deste padrão geral, as espécies estudadas variaram quanto à razão raiz:parte aérea. Plântulas de espécies consideradas tolerantes ao sombreamento como Myroxylon peruiferum, Poecilanthe parviflora e Hymenaea courbaril apresentaram pouca alteração na razão raiz:parte aérea entre os diferentes tratamentos. Bauhinia longifolia, Copaifera langsdorfii, Erythrina speciosa, Enterolobium contortisiliquum e Piptadenia gonoacantha destacaram-se pelas altas razões raiz:parte aérea sob altas irradiâncias. A remoção dos cotilédones das plântulas, da maioria das espécies estudadas, resultou em redução da biomassa total. No geral, não houve diferença significativa na fração de biomassa alocada ao caule, às raízes e às folhas e na razão raiz:parte aérea, com a remoção dos cotilédones. O acúmulo relativo de amido nas folhas não pareceu associado ao decréscimo na partição de biomassa para as raízes, nas plântulas das espécies analisadas. Plântulas de Erythrina speciosa, que pouco diferiram neste aspecto quando mantidas a 2 e 50 % da irradiância, apresentaram a maior alteração na razão raiz:parte aérea. Plântulas de Poecilanthe parviflora, que não alteraram significativamente a distribuição de massa seca entre raiz e parte aérea, diferiram significativamente quanto ao acúmulo relativo de amido nas duas irradiâncias. Aparentemente, a remoção parcial dos diferentes órgãos contribuiu pouco para a redução da biomassa total. No geral, as plântulas das espécies analisadas revelaram um crescimento compensatório em resposta à remoção, tanto sob baixa quanto alta irradiância. A razão raiz:parte aérea não foi alterada em relação às plântulas intactas. A avaliação da distribuição de compostos com carbono radioativamente marcados demonstrou que a direção do movimento dos assimilados nas plântulas de Erythrina speciosa, Poecilanthe parviflora e Enterolobium contortisiliquum, após 48 horas de aplicação, deu-se no sentido da folha aplicada para o caule e em menor proporção para a raiz, exceto em plântulas de Hymenaea courbaril que retiveram quase a totalidade de assimilados na folha aplicada. No geral, não se observou uma diferença marcante em termos de movimento de assimilados, em plântulas mantidas a 2 e 50 % da irradiância. Em resumo, as espécies consideradas pioneiras apresentaram mudanças morfológicas e fisiológicas mais amplas, revelando grande plasticidade e habilidade em adaptar-se às variadas intensidades luminosas a que foram submetidas, em relação às espécies secundárias que revelaram baixa plasticidade fenotípica, a qual geralmente está associada à tolerância ao sombreamento. Entretanto, verificou-se a existência de espécies com respostas intermediárias e variáveis em relação aos parâmetros analisados / Abstract: The growth of seedlings of rain-forest tree species, in environments with contrasting light availability depends on the interaction between morphological and physiological characteristics. Among the various morphological alterations which occur in low-irradiance conditions, one of them is the ratio of growth between the root and shoot. The root: shoot ratio of seedlings can be suggestive to specialization to different environments. In general, the more shadowed the environment is, bigger is the biomass allocation on the leaves. The increase of biomass on the leaf area (leaves and stalk) occurs due to biomass detriment on the roots. Aiming to verify the different radiation level effects in the differential allocation of photosynthates between the root and the shoot of seedlings from some rain-forest tree species, the role of cotyledons and the apical region in the stalk and root in the allocation, the starch tenor and the translocation of carbon compounds radiolabelled. Seedlings of Copaifera langsdorfii, Dalbergia nigra, Hymenaea courbaril, Myroxylon peruiferum, Peltophorum dubium e Poecilanthe parviflora, considered shade tolerant and Bauhinia longifolia, Enterolobium contortisiliquum, Erythrina speciosa, Piptadenia gonoacantha,, Senna macranthera e Schizolobium parahyba, considered pioneers, were grown for approximately two months under 4, 18, 50 and 100 % of total irradiance. The biomass accumulation increased in all the studied species in response to light availability increase as well as the relative growth rate and net assimilation rate. In general, it was observed a reduction in the root:shoot ratio of seedlings under low irradiance. Despite this general pattern, the studied species varied regarding the root:shoot ratio. Seedlings of species considered shading tolerant as Myroxylon peruiferum, Poecilanthe parviflora e Hymenaea courbaril did not present a significant change in the root: shoot ratio. Bauhinia longifolia, Copaifera langsdorfii, Erythrina speciosa, Enterolobium contortisiliquum e Piptadenia gonoacantha contrasted due to high root: shoot ratio under high irradiance. The removal of cotyledons from the seedlings, in most of the studied species, resulted in reduction of the total biomass. Generally, there was not significant difference in the biomass portion allocated in the stalk, in the root and in the leaves and in the root:shoot ratio, with the removal of cotyledons. The accumulation of starch in the leaves did not seem associated to the decrease of biomass partitioning to the seedlings roots in the analyzed species. Seedlings of Erythrina speciosa which little differed in this aspect when put under 2 and 50% of irradiance, presented a higher alteration in the root: shoot ratio. Seedlings of Poecilanthe parviflora, which did not alter significantly the distribution of dry mass between root and shoot, differed significantly in the relative accumulate of starch in both irradiance. Apparently, the partial removal of these different organs little contributed for the total biomass reduction. In general, the analyzed seedling species, revealed compensatory growth in response to removal, either under low or high irradiance. The root:shoot ratio was not altered compared to the intact seedlings. The analyses of distribution of carbon compounds radioactively marked, showed that the moving direction of the assimilate in the seedlings of Erythrina speciosa, Poecilanthe parviflora e Enterolobium contortisiliquum, after 48 hours of application, occurred in the application leaf to stalk way also in lower portion to the root except in seedlings of Hymenaea courbaril which retained almost all the assimilate in the applied leaf. In an overall, a distinct difference was not observed in assimilates flow in seedlings put under 2 to 50 % of irradiance. Altogether, the species considered pioneers presented more ample morphological and physiological changes, revealing great plasticity and ability in adapting to various light intensities which they were submitted. In relation to the secondary species which revealed low phenotypical plasticity to which is generally associated with shadow tolerating therefore, there was found the existence of species with intermediate variable according to the analyzed parameters / Doutorado / Doutor em Biologia Vegetal

The study was initiated to determine the effects of RGP and three levels on weed control: no weed control (control), herbaceous weed control (Oust), and woody and herbaceous weed control (Oust-Garlon) on three pine seedlots: pitch x loblolly pine hybrid (pxL-F2), Virginia Department of Forestry loblolly pine (VDF-Iob), and westvaco loblolly pine (WCO-Iob). Lateral roots had the greatest response to the Oust treatment compared to all other seedling parts. All seedlot and treatment interactions were associated with lateral roots. After one growing season the Oust treatment resulted in a 148% increase in lateral root biomass compared to the control treatment. Shoot biomass in the Oust treatment increased by 70% compared to the control. The ability to respond to weed control was related to RGP. Compared the loblolly pine seedlots the PxL-F2 had both significant higher RGP at planting and biomass accumulation in response to the Oust treatment. Compared to the loblolly pine seedlots the PxL-F2 lateral root biomass and total tree biomass increased by 44% and 30%, respectively. The addition of woody weed control to herbaceous weed control in the Oust-Garlon treatment did not result in significant increasings in loblolly pine seedling biomass compared to herbaceous weed control. Because of a to sensitivity to Garlon 4™ the (PxL-F2) had 22% reduction in total tree biomass in the Oust-Garlon treatment compared to the Oust treatment. Therefore, the control of woody weeds in pitch x loblolly pine plantations will need to be accomplished using another herbicide. / Master of Science

The interactions between soil physical properties, particularly soil structure and bulk density, and the rooting of four herbaceous crops grown for biomass on three common Piedmont soil series were examined. The effect of these crops on soil properties over time was also studied. The rooting of the biomass crops studied seemed to be affected by soil physical factors on two of the three soils. Even though bulk density on all three soils (Appling, Cecil, and Davidson) appeared high enough to drastically limit rooting, such limitations were found only at the Appling sites and, to a much lesser extent, at the Cecil sites. Well-developed soil structure seemed to be instrumental in the success of the biomass crops on these dense Piedmont soils. All of the species studied had vigorous root systems in well-structured, high-density soils. Weeping lovegrass (<i>Erogrostis cuxvula</i>) was particularly insensitive to high bulk densities. The root systems of switchgrass (<i>Panicum virgatum</i>), birdsfoot trefoil (<i>Lotus corniculatus</i>), and sericea lespedeza (<i>Lespedeza cuneata</i>) were all heavily influenced by the high densities of the nearly structureless Appling soils; but lovegrass roots were quite prolific there. For this reason lovegrass should be considered first for biomass production on similar marginal soils. All soils had higher organic matter contents after four years of biomass production. Soil nutrient concentrations, particularly soil K, were also higher, especially under switchgrass. Soil Ca and Mg contents were higher under the two legumes than under the two grasses. / Master of Science