Control of transpiration in an irrigated Eucalyptus globulus Labill. plantation

Stomatal conductance and transpiration were measured concurrently in an irrigated Eucalyptus globulus Labill. plantation. Canopy stomatal conductance, canopy boundary layer conductance and the dimensionless decoupling coefficient (Ω) were calculated (a) summing the conductance of three canopy layers (g_c) and (b) weighting the contribution of foliage according to the amount of radiation received (g_c′). Canopy transpiration was then calculated from g_c and g_c′ for Ω = 1 (E_eq), Ω = 0 (E_imp) and by weighting E_eq and E_imp using Ω (E_Ω). E_eq, E_imp and E_Ω were compared to transpiration estimated from measurements of heat pulse velocity. The mean value of Ω was 0·63. Transpiration calculated using g_c and assuming perfect coupling (12·5 ± 0·9 mmol m^?2 s^?1) significantly overestimated measured values (8·7 ± 0·8 mmol m^?2 s^?1). Good estimates of canopy transpiration were obtained either (a) calculating E_Ω separately for the individual canopy layers or (b) treating the canopy as a single layer and using g_c′ in a calculation of E_imp (Ω = 0). The latter approach only required measurement of stomatal conductance at a single canopy position but would be unsuitable for use in combined models of canopy transpiration and assimilation. It should however, be suitable for estimating transpiration in forests regardless of the degree of coupling.     

Phenolic acclimation to ultraviolet-A irradiation in <Emphasis Type="Italic">Eucalyptus nitens</Emphasis> seedlings raised across a nutrient environment gradient

We investigated the effects of long-term acclimation of Eucalyptus nitens seedlings to ultraviolet-A (UV-A) irradiation (320–400 nm) on phenolic compounds (gallotannins, stilbenes, and flavonols), photochemical efficiency, and chlorophyll and carotenoid contents. Seedlings were raised under four nutrient regimes, ranging from low to high application rates, in an environment that included or excluded UV-A irradiance. Our aims were: to classify phenolic compounds that absorb in the UV-A and their relative contribution to total UV-A absorption; to identify how phenolic compounds respond to UV-A exposure and exclusion, and to determine how plant nutrient status affects acclimation of photo-and pigment-chemistry to UV-A exposure and exclusion. Gallotannins contributed to only a minor fraction of total absorption within the lower range (320–360 nm) of the UV-A spectrum. Stilbene and flavonol compounds dominated absorption within the 320–360 and 360–400 nm ranges, respectively. Contents of gallotannin were generally high in UV-A-exposed seedlings. Although there was a significant effect of UV-A on contents of stilbenes, a general response (across nutrient treatment comparisons) was not evident. Contents of flavonols were not affected by UV-A exposure. Contents of gallotannin, stilbene, and flavonols decreased from low to high nutrient-application treatments. There were no effects of UV-A on photochemical efficiency or pigment-chemistry.     

Physiological basis of spacing effects on tree growth and form in Eucalyptus globulus

We examine the effects of spacing and layout on the growth and form of 3- to 4-year-old Eucalyptus globulus in a farm forestry context. Four planting layouts were chosen. These represented the range commonly in use in farm forestry: block plantings (2Ǹ m), triple rows (2Ǹ m) at 10-m intervals, single rows (2᎒ m) and isolated trees (10᎒ m). The physiological significance of key results is interpreted in terms of changes in the parameters of a simple plantation growth model. Under conditions where levels of direct light are high, for example during summer, block-planted trees intercepted only 38% of the light intercepted by isolated trees. On a stand basis, however, the combination of incident radiation and ground coverage declined with lower stand densities. While stand leaf area index declined from around 6 to 1 with increased spacing, individual tree leaf areas rose from around 50 m² in block plantings to 150 m² in isolated trees. The proportion of above-ground biomass found in stems declined with increasing spacing as the mass in foliage and branches increased. Stems accounted for 65% of above-ground biomass in block-planted trees but only 35% in isolated trees. The contributions of leaves and branches correspondingly rose from 19% to 35% and from 16% to 29%, respectively. Changes in biomass distribution were accompanied by increasing branch number, branch thickness, flatter branch angles and the longer retention of lower branches with greater spacing. These changes have implications for the merchantability of the timber. The efficiency of above-ground radiation conversion was constant at 0.67 g MJ^-1 irrespective of spacing. We estimated that foliar maintenance respiration (R_m) accounted for about 90% of above-ground R_m. On a stand basis R_m costs block plantings 23.90 t DM ha^-1 year^-1 (50% annual above-ground photosynthetic production) compared with 6.22 t DM ha^-1 year^-1 (40% annual above-ground photosynthetic production) in stands of isolated trees.     

Expert opinion as 'validation' of risk assessment applied to calf welfare

Background  

Recently, a Risk Assessment methodology was applied to animal welfare issues in a report of the European Food Safety Authority (EFSA) on intensively housed calves.