Lucia Rebello Dillenburg

Early growth of Brazilian pine (Araucaria angustifolia (Bertol.) Kuntze) in response to soil compaction and drought

Soil compaction leads to changes in soil physical properties such as density, penetration resistance and porosity, and, by consequence, affects root and plant growth. The initial growth of Brazilian pine is considered as being more affected by soil physical than chemical conditions, and the presence of a well-developed tap root system has been associated with this fact. A greenhouse experiment was conducted in order to evaluate the impact of soil compaction on the growth of Brazilian pine seedlings and on their susceptibility to a simulated drought period. In the first phase of the experiment, the effects of three levels of soil compaction on root morphology and plant growth were examined. Soil cylinders were artificially compacted in PVC tubes. Pre-germinated seeds were planted, and 147 days later 10 plants from each treatment were harvested for analysis. Higher values of soil density were associated with a shorter and thicker tap root. Growth of lateral roots and shoots remained unaffected at this stage. In the second phase, half of the plants (12) in each compaction treatment were drought-stressed by withholding water for a period of 77 days. Increased soil compaction again resulted in reduced length and increased diameter of the main tap root. This time, the effects were also extended to the lateral roots. Shoot extension growth and overall plant mass, however, increased with soil compaction. This greater mass accumulation in plants growing under increased soil compaction may be attributed to a more intimate contact between roots and soil particles. Drought stress reduced both root and shoot growth, but root mass was more negatively affected by drought stress in plants growing under high levels of soil compaction. Future investigations on the effects of soil compaction on the initial growth of Brazilian pine should include a wider range of compaction levels to better establish the relationship between soil physical parameters and plant growth.

Ajustes morfológicos e fisiológicos em plantas jovens de Araucária angustifolia (Bertol.) Kuntze em resposta ao sombreamento

This study evaluated the ability of plants of Araucaria angustifolia in adjusting some aspects of their morphology and physiology to different light conditions. Plants were submitted to full irradiance and shaded (90% reduction) conditions. During the course of a greenhouse experiment, four harvests were made (31, 49, 75 and 158 days after planting) and growth measurements of the shoot and roots were taken. A reduction in dry mass accumulation was observed in the shaded plants. These plants also had an initial enhancement of height growth, accumulated more chlorophyll, and, by the end of the experiment, had branched less and attained a greater leaf area ratio than the control plants. These morphological and physiological changes, which exhibited a temporally discontinuous expression, were interpreted as adjustments towards a more efficient light absorption and resource conservation under shading, which may contribute to the reported hade tolerance of the species.

Hypocotyl of seedlings of the large-seeded species Araucaria angustifolia: an important underground sink of the seed reserves

Araucaria angustifolia exhibits cryptogeal germination, where the root–hypocotyl axis emerges first and penetrates into the soil. In Araucaria bidwillii, the whole process of transferring reserves from the seed to the seedling takes place before shoot emergence, and there is a major storage of these reserves in the underground hypocotyl, which assumes a tuberous form. In A. angustifolia, the shoot emerges before seed reserves are depleted. Though it does not grow like a tuber, the hypocotyl of A. angustifolia grows thicker than the adjacent taproot during initial growth, and we hypothesize that it may act as a major sink for seed reserves during this stage. The study tests this hypothesis by evaluating changes in the mass of different plant parts during initial growth. Four harvests were conducted during a ~6-month period to compare the dry mass of different fractions (attached seed, seedling, its shoot and root and the hypocotyl) of seedlings growing under darkness and high light. While seed reserves were still being depleted, the hypocotyl mass showed an initial increase and then a reduction. This was more abrupt when light was available. After seed mass had stabilized, the mass of the hypocotyl continued to decrease in the dark-grown seedlings, but showed a second increase in the light-grown ones. Results confirm the hypothesis that the hypocotyl represents a major sink for the seed reserves of A. angustifolia, acting as an underground storage structure for the growing seedling. Its reserves seem to be important for sustaining initial shoot growth and might also act as a storage sink for photosynthates.

Effects of soil water availability on foliar water uptake of Araucaria angustifolia

Background and aimsFoliar water uptake has been reported for different species, including conifers living in drought-prone environments. We conducted three experiments to determine whether leaves might absorb mist water and how this affects the water relations of well-watered and water-stressed young plants of Araucaria angustifolia.MethodsThree independent experiments were conducted using well-watered and water-stressed plants: immersion of shoot in water for the quantification of water uptake, the short-term exposure of plants to deuterium-enriched artificial mist, followed by the evaluation of plant water status and δ2H of xylem and soil water, and the use of the heat ratio method to measure the sap flow in saplings submitted to artificial mist.ResultsFoliar water uptake was demonstrated in both groups of plants, but only water-stressed plants showed a significant improvement of shoot water status. Isotope analyses indicated release of mist water in water-stressed plants rhizosphere’s, and measurements of sap flow pointed to flow reversals in saplings exposed to mist, after a soil drought period.ConclusionsThe results confirm the capacity of A. angustifolia for absorbing water deposited in its leaves and demonstrate that leaf-absorbed water can be transported through the xylem to the soil close to the roots and improve plant water status.

Partição da competição por recursos do solo e radiação solar entre cultivares de soja e genótipos concorrentes

Plants compete for environmental resources located below and over soil surface. Physical separation of competition allows understanding the relative importance of each fraction, as well as identifying possible differences among species. The aim of this research was to separate the individual effects resulting from competition for soil or solar radiation resources, between soybean and concurrent plants. Thus, experiments using pots were carried out at UFRGS, in Porto Alegre-RS, in 2001 and 2002. The treatments tested resulted from the combinations of two concurrent genotypes (crop and competitor) and four competition conditions (absence of competition, competition for soil and solar radiation, competition for soil resources, and competition for solar radiation). Soybean cultivars IAS 5 and Fepagro RS 10 represented the crop, whereas radish forage and the soybean cultivar Fundacep 33 were the competitors tested. Morpho-physiological variables were evaluated in the soybean plants and radish forage. Growth of the soybean plants was most affected by soil resources competition, with RS 10 cultivar being more competitive than IAS 5.Radish forage did not interfere in the growth of soybean cultivars but it benefited from soybean presence.

Initial growth of Brazilian pine (Araucaria angustifolia) under equal soil volumes but contrasting rooting depths

Araucaria angustifolia is a critically endangered tall tree species of valuable wood, and field observations led to the suggestion that limitations imposed to the vertical growth of its tap root system greatly restrict the height of mature individuals. However, experimental studies dealing with the effects of soil depth on the species growth are mostly lacking. This study evaluated and compared the growth responses of young plants of A. angustifolia to distinct rooting depths but same soil volumes. Seeds were planted in pots of different heights and diameters, all containing 3 liters of soil mixture. Plants were submitted to four available rooting depths: 65 (T1), 35 (T2), 20 (T3), and 10 (T4) cm. There were eight experimental units in each treatment, arranged in a randomized complete block design, each block containing two units per treatment. Contrary to what was expected, the T3 and T4 plants had accumulated more mass and attained the same height as the other two groups, after a 10-month growth period in a green house. Those plants also had thicker stems, longer shoot branches, and thicker and longer lateral roots, which were interpreted as compensatory responses to increase plant anchorage and stability. The inverse relationship between rooting depth and plant mass was attributed to a down-regulation of shoot growth because or restricted lateral space and/or poor soil aeration of the longer and narrower pots. This experiment allowed us to demonstrate that is not the possibility of the tap root to grow deep into the soil that ensures a better growth to plants of A. angustifolia: provided that the offer of soil volume and resources are the same, the vertical extension of the tap root does not result in greater growth of the plants. In fact, much greater growth impairment is expected from lateral than from vertical restriction to root growth.

Water relations of tree species growing on a rock outcrop in the "Parque Estadual de Itapuã", RS

Foram examinadas neste estudo as relacoes hidricas das especies Myrsine umbellata Mart. ex A. DC., Dodonaea viscosa Jacq. e Erythroxylum argentinum O. E. Schulz, ocorrentes em um afloramento rochoso no Parque Estadual de Itapua, RS. Parâmetros ambientais (precipitacao, temperatura, agua no solo) e das plantas (potencial hidrico, deficit de pressao de vapor, condutância estomatica, transpiracao, condutância hidraulica, potencial osmotico e elasticidade da parede celular) foram coletados em cinco periodos e agrupados em dois conjuntos de dados: periodos umido e seco. Myrsine umbellata mostrou grande estabilidade dos parâmetros vegetais, incluindo a manutencao de altos potenciais hidricos de base (Ywpd) e de meio-dia (Ywmd), mesmo no periodo seco (-0,48 e -1,12 MPa, respectivamente), sugerindo a presenca de um sistema radicular profundo. Dodonaea viscosa e E. argentinum apresentaram menores Ywpd (-1,41 and -1,97 MPa, respectivamente) e maior fechamento estomatico no periodo seco, sugerindo um sistema radicular mais superficial. Exposicao diferenciada a seca do solo foi tambem corroborada pelos efeitos diferenciados da seca na condutância hidraulica folha-especifica da planta. Analises de correlacao indicaram fracas correlacoes entre Ywpd e gs. Erythroxylum argentinum foi a unica especie a mostrar ajuste osmotico em resposta a seca. Sugere-se que M. umbellata seja pouco tolerante a deficits hidricos, adotando uma estrategia de evitacao. Os menores Yw alcancados por D. viscosa e E. argentinum sugerem maior tolerância destas especies a seca.

Resprouting ability and intensity after damage in seedlings of the large-seeded species Araucaria angustifolia

The role of seed reserves on the ability to resprout and on the responses of resprouting in Araucaria angustifoliawas investigated. Seedlings were separated into three groups: plants which had their shoot damaged, a similar group in which damaged plants had their connection to the supporting seed removed, and a control group. All damaged seedlings resprouted, but those which remained connected to their seeds had a greater mass of resprouted shoots than the ones disconnected from their seeds. A greater accumulation of seed mass in the underground hypocotyl was a very distinct initial response to damage, but, on the long run, damaged plants were able to reestablish a biomass allocation pattern, which was very similar to the control plants. These results indicate that seed and underground reserves are important for the quantitative resprouting response of seedlings of Aangustifolia and for its ability to reestablish the functional balance when severely damaged.

Effects of different nitrogen sources on growth, chlorophyll concentration, nitrate reductase activity and carbon and nitrogen distribution in Araucaria angustifolia

The southern Brazilian highland plateau is a mosaic of two contrasting plant communities, Araucaria forests and grasslands, which differ in the relative abundances and spatial patterns of soil nitrate and ammonium. However, we still do not know the inorganic N preferences of one key species in this mosaic, Araucaria angustifolia, the dominant tree species in the Araucaria forests and an important tree species invading the adjacent grasslands. Growth responses measured in a greenhouse study demonstrated that the species prefers NH4+ over NO3- as an inorganic N source. When provided alone, NO3- induced N deficiency symptoms: increases in root: shoot ratio, root branching and leaf mass per area, thickening of the shoot apexes and decreased mass-based chlorophyll and N concentrations of the young leaves. Nitrate-based nutrition also affected the whole plant N and carbon (C) distribution: young leaves accumulated less N and showed a larger C:N ratio than mature leaves. The nitrate reductase activity (NRA) followed the pattern of root: shoot partitioning expected for temperate climate conifers (activity concentrated in roots). However, the presence of NRA even under sole NH4+ nutrition indicates that plants may show constitutive levels of the enzyme, or that low levels of NO3- (possibly formed by contamination of the growth media) can induce leaf NRA. We suggest that A. angustifolia has ammonium as a preferential inorganic N source, and that this preference may favor a more successful establishment in grassland than in forest areas.

Umidade do solo e fisiologia da soja afetados por estiagem em sistema de integração lavoura‑pecuária

The objective of this work was to evaluate the impact of grazing intensities after 11 years of an integrated crop‑livestock system, under no‑tillage, on soil moisture and soybean physiological parameters during a summer season affected by drought. The experiment was established in 2001 on a Rhodic Hapludox. Treatments consisted in the succession of soybean (summer) and a mixed pasture of black oat + Italian ryegrass (winter), under different beef‑cattle grazing intensities: intensive grazing, with 0.10‑m pasture height; moderate grazing, with 0.20‑m pasture height; and no grazing. During the soybean cycle, in the 2011/2012 crop season, rainfall was 40% of the climatological normal. The soil moisture was within the limits of available water both under moderate grazing and no grazing, at 0.00–0.50‑m soil depth, but, under intensive grazing, it was below the permanent wilting point, especially up to the grazing height of 0.20 m. Intensive grazing affected negatively the plant physiology parameters, reaching peaks of ‑2.5 MPa and +6°C for leaf water potential and leaf‑air temperature difference, respectively. Moderate grazing or the absence of grazing, during the winter season, results in similar physiological responses, contributing to soybean plant homeostasis.