Factors affecting diurnal stem contraction in young Douglas-fir

Diurnal fluctuation in a tree's stem diameter is a function of daily growth and of the tree's water balance, as water is temporarily stored in the relatively elastic outer cambial and phloem tissues. On a very productive site in southwestern Washington, U.S.A., we used recording dendrometers to monitor stem diameter fluctuations of Douglas-fir at plantation ages 7 and 8 and related the fluctuations to environmental variables measured on-site. Growing-season diurnal stem contraction (DSC) averaged 0.21% of stem diameter, while dormant-season DSC averaged 0.03% of stem diameter. Maximum daily stem diameter generally occurred between 7:00 and 9:00 Pacific Standard Time (PST) and minimum stem diameter occurred between 17:00 and 20:00 PST. Diurnal stem contraction during the growing season was predicted by a model that included vapor pressure deficit and solar radiation (adjusted R² = 0.84). A similar model predicted DSC during the dormant season with an adjusted R² = 0.26. Soil water availability was high, and soil water content was not correlated with DSC. On four of the coldest winter days (mean daytime air temperature <0 °C), large decreases in stem diameter were observed. Recording dendrometers, used for continuous diameter measurements throughout the growing season, have the potential to provide important information not only on tree growth but also on a tree's water balance.     

Sulfite oxidase enzyme activity in soil

Several methods for measuring sulfite oxidases (EC 1.8.2.1 and EC 1.8.3.1) have been developed for microbial systems, but none have been systematically adopted for soils. We describe an assay method to measure sulfite oxidase in soil that is based on the use of potassium sulfite (K₂SO₃) serving as the substrate and electron donor, and potassium ferricyanide [K₃Fe(CN₆)] serving as the electron acceptor. Sulfite oxidase activity is expressed as micromoles of K₃Fe(CN)₆ reduced g^-1 soil 4 h^-1. Sulfite oxidase activity was linearly related to amount of soil in the assay (up to 3 g) and incubation time (up to 5 h). The average K _m value for K₂SO₃ serving as the substrate for the sulfite oxidase reaction in four diverse soils was 3.48 mM. The activation energy values calculated for soil sulfite oxidase ranged from 40.4 to 61.4 kJ mol^-1. The sulfite oxidase assay does not require any specialized equipment and is expected to be useful in studying biological sulfite oxidation in soils treated with sulfites or in naturally occurring soils where sulfur cycles between reduced (i.e., sulfite) and oxidized (i.e., sulfate) states due to flooding and drying.     

Potassium‐transport rate from root to shoot unrelated to potassium‐use efficiency in tomato grown under low‐potassium stress

Four tomato (Lycopersicon esculentum Mill.) strains (203, 474, 546, and 576) that are equally efficient in potassium (K) absorption, but different in efficiency of K use were studied using a continuously flowing solution culture to determine the importance of K‐transport rate from root to shoot in relation to K‐use efficiency. Strains 203 and 546 are inefficient in K use, ratios of K in shoots to roots were found to be three times higher than those of the two K‐use efficient strains 474 and 576 when grown under low‐K stress (0.1 mM). In addition, both the K concentrations and rates of K flow in xylem exudates of decapitated strains 203 and 546 were significantly higher than those of strains 474 and 576. These results suggest that high rates of K transport from roots to shoots are unrelated to K‐use efficiency in the tomato strains grown under low‐K stress. Further studies of K distributions in leaves and stems found that K concentrations in matured leaves and stems of the two efficient strains 474 and 576 were markedly lower than those of the two inefficient strains 203 and 546, while K in young and expanding leaves of the efficient strains were significantly higher than those of the inefficient strains, indicating that the ability to mobilize K from matured leaves to young and expanding leaves is an important factor that contributes to K‐use efficiency in tomato plants grown under low‐K stress.     

Nutrient Contribution and Release Kinetics of Vermicompost Amended Pine Bark

The composting of organic waste materials using earthworms yields the value-added product vermicompost (VC). The use of VC as a growing substrate amendment for containerized horticultural crop production is a sustainable nutrient management approach which can benefit crop production by providing plant nutrients and improving crop growth. In order to provide nutrient management guidelines for users of VC amended container substrates, a study was conducted to quantify nutrients supplied to substrates solution and to develop nutrient release kinetic models to predict plant available nutrient based on total initial loading rates. Experimental treatments and results were expressed on a volume basis (4-L container) for easy interpretation and application by growers of crops in containers.     

Water relations of the potato (Solanum tuberosum L.) cultivars Raritan and Shepody

Physiological responses to drought stress were evaluated in the potato cultivars Raritan and Shepody. Under well-watered conditions, Raritan exhibited a higher transpiration rate than Shepody. This higher rate could be related to a lower calculated stomatal resistance on abaxial leaf surfaces. Under drought stress conditions, Raritan consistently demonstrated superior performance over Shepody in the following areas: leaf water retention, epicuticular wax levels, desiccation tolerance and root growth. The estimated relative water content at a leaf water potential of-1.0 MPa was higher for Raritan than Shepody regardless of leaf age and may indicate a greater drought resistance in the former cultivar.     

A comparison of the water use of tree belts and pasture in recharge and discharge zones in a saline catchment in the Central West of NSW, Australia

Planting trees has been proposed as part of the solution to dryland salinity in Australia. The best location in the landscape and the spatial arrangement of trees however, is difficult to determine. This paper presents a case study of a field experiment that compared the water use of tree belts with that of pastures in recharge and discharge areas of a first order catchment in the Central West of NSW, Australia.The recharge tree belt and both pasture sites used very similar amounts of water but the discharge tree belt used double the water of the other three land uses by accessing groundwater. The discharge tree belt operated in an energy-limited environment, transpiring at a rate equivalent to atmospheric demand whereas the other three land uses were all water-limited. From a land management point of view, the establishment of more trees on the discharge site would have the biggest impact on reducing saline discharge and the least impact on the agricultural operations.     

Does growth temperature affect the temperature responses of photosynthesis and internal conductance to CO2? A test with Eucalyptus regnans

Internal conductance to CO(2) transfer from intercellular spaces to chloroplasts (g(i)) poses a major limitation to photosynthesis, but only three studies have investigated the temperature dependance of g(i). The aim of this study was to determine whether acclimation to 15 versus 30 degrees C affects the temperature response of photosynthesis and g(i) in seedlings of the evergreen tree species Eucalyptus regnans F. Muell. Six-month-old seedlings were acclimated to 15 or 30 degrees C for 6 weeks before g(i) was estimated by simultaneous measurements of gas exchange and chlorophyll fluorescence (variable J method). There was little evidence for acclimation of photosynthesis to growth temperature. In seedlings acclimated to either 15 or 30 degrees C, the maximum rate of net photosynthesis peaked at around 30 or 35 degrees C. Such lack of temperature acclimation may be related to the constant day and night temperature acclimation regime, which differed from most other studies in which night temperatures were lower than day temperatures. Internal conductance averaged 0.25 mol m(-2) s(-1) at 25 degrees C and increased threefold from 10 to 35 degrees C. There was some evidence that g(i) was greater in seedlings acclimated to 15 than to 30 degrees C, which resulted in seedlings acclimated to 15 degrees C having, if anything, a smaller relative limitation due to g(i) than seedlings acclimated to 30 degrees C. Stomatal limitations were also smaller in seedlings acclimated to 15 degrees C than in seedlings acclimated to 30 degrees C. Based on chloroplast CO(2) concentration, neither maximum rates of carboxylation nor RuBP-limited rate of electron transport peaked between 10 and 35 degrees C. Both were described well by an Arrhenius function and had similar activation energies (57-70 kJ mol(-1)). These findings confirm previous studies showing g(i) to be positively related to measurement temperature.     

Field experiments to assess approaches for spray drift incident investigation

BACKGROUND: Spray trials were conducted to determine the variation in primary spray drift deposition between trials under very similar conditions, in order to assess the feasibility of developing a computational tool to aid post‐event investigations of pesticide spray incidents. Pesticide deposition was examined by analysis of filter paper and vegetation samples. RESULTS: Considerable variation in the drift profile was found. The overall estimate of the spray drift decay term was ?1.13 (95% confidence interval ?1.02 to ?1.24), with statistically significant differences between plots. Variation in the drift profile between neighbouring essentially identical plots indicates the variation in deposition that might be expected over small distances. Vegetation samples were found to have considerably lower capture efficiency than filter papers. Importantly, degradation of pesticides was found to have little effect on the pesticide drift profile over a 14 day period. CONCLUSIONS: The levels of spatial variation in spray drift deposits between runs and plots observed in this study suggest serious limitations to the inferences that may be drawn from limited numbers of post‐incident samples. In particular, they would limit inferences about the spray conditions that could be drawn from an estimate of the drift profile derived from limited post‐incident samples. © Crown copyright 2009. Reproduced with permission of Her Majesty's Stationery Office. Published by John W iley & Sons, Ltd.