Diurnal measurements of sap velocity were made in 50-, 90-, 150- and 230-year-old mountain ash (Eucalyptus regnans F. Muell.) forests in the North Maroondah catchment (southeast Australia) over the periods January 8, 1990 to April 4, 1990 and October 29, 1990 to April 16, 1991. Over the two periods, daily mean sap velocities for the four forests, in order of increasing age, were 11.5, 11.4, 9.9 and 11.8 cm h(-1) respectively. Daily mean sap velocity did not differ significantly among the 50-, 90- and 230-year-old plots. However, in the 150-year-old trees it was significantly smaller by an average of 14%. Sap velocity varied diurnally and also between positions within individual trees and among trees both within and between stands. Despite this variability, the sampling intensity and duration were sufficient to establish that behavior was highly correlated among individuals within plots. There was a significant decline with age in the overstory sapwood conducting area of these forests. In order of increasing age, the values were 6.7, 6.1, 4.2 and 4.0 m(-2) ha(-1), respectively. When combined with daily mean sap velocity, these data allowed the calculation of overstory water use. Over the experimental period, water use of the overstory decreased with age ranging, on average, from 1.86 mm day(-1) for the 50-year-old plot to 0.81 mm day(-1) for the 230-year-old plot. Mean daily water use for the two intermediate-aged forests was 1.67 and 1.00 mm day(-1), respectively. Annual water use decreased with forest age from 679 mm for the 50-year-old stand to 296 mm for the 230-year-old stand. This difference corresponds to 3.8 x 10(3) m(3) ha(-1). The annual water use of the intermediate-aged stands was 610 and 365 mm for the 90- and 150-year-old stands, respectively.
Photosynthesis-irradiance response curves and leaf nitrogen contents were measured weekly by destructive sampling over the life cycles of leaves 10, 15, 20 and 25 of sunflower plants (cv. Prosol 35) grown in large pots in the open under optimum conditions of temperature and high irradiance. Individual leaf responses were adequately described by a hyperbola of three parameters, viz. Pmax, the rate of photosynthesis in saturating irradiance; R, the rate of dark respiration adjusted for temperature (30�C); and ε, the apparent quantum efficiency of photosynthesis at low irradiance. Pmax (range 0-40 μmol CO2 m-2 s-1) and R (0-4 μmol CO2 m-2 s-1) were non-linearly related to nitrogen content per unit leaf area (NL) (range 0.3-2.9 g N m-2) across all leaf positions and for all leaf ages. ε (mean value 0.050 mol mol-1, s.e. 0.001) was independent of NL. The equations for net photosynthesis derived from pot studies were shown to explain (r2 =0.80) leaf photosynthesis in a crop of the same cultivar over a wide range of NL and irradiance.
A balanced fertilizer treatment -equivalent to that optimal for pasture development on the infertile sandy soils of the Coastal Lowlands of south-eastern Queensland -was applied to a heathland stand on North Stradbroke Island in 1968, 3 years after the vegetation had been razed by bushfire. The fertilized and control plots were examined in detail in 1968 (before application of fertilizer), in 1969 and in 1976. Eight years after fertilizer treatment the heath species have declined in density and/or biomass. The native grass, Themeda australis, responded to fertilizer and is expanding into gaps as the heath species die. A few composites and grasses are invading the fertilized plots.
Two crops of Sherpa wheat grown in successive years, but under contrasting seasonal conditions, were subjected to comprehensive environmental and biological measurement. An analysis is made of the changing state of water in the soil-plant system and of the consequent growth and the development of grain yield. The early pattern of growth was strongly influenced by moderate restriction in the availability of soil water (> - 200 J kg -1) and was associated with a marked shift in the allocation of growth resources in favour of root development. In both years, but more so in the second, grain filling proceeded under rapidly increasing plant water stress and senescence of productive photosynthesizing area. An analysis of the quantitative consistency of the biological and environmental data is attempted by the application of a published model of crop growth to the experimental data.
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