Photosynthetic capacity in a central Amazonian rain forest

The vertical profile in leaf photosynthetic capacity was investigated in a terra firme rain forest in central Amazonia. Measurements of photosynthesis were made on leaves at five levels in the canopy, and a model was fitted to describe photosynthetic capacity for each level. In addition, vertical profiles of photosynthetic photon flux density, leaf nitrogen concentration and specific leaf area were measured. The derived parameters for maximum rate of electron transport (J(max)) and maximum rate of carboxylation by Rubisco (V(cmax)) increased significantly with canopy height (P < 0.05). The highest J(max) for a single canopy level was measured at the penultimate canopy level (20 m) and was 103.9 &mgr;mol m(-2) s(-1) +/- 24.2 (SE). The highest V(cmax) per canopy height was recorded at the top canopy level (24 m) and was 42.8 +/- 5.9 &mgr;mol m(-2) s(-1). Values of J(max) and V(cmax) at ground level were 35.8 +/- 3.3 and 20.5 +/- 1.3 &mgr;mol m(-2) s(-1), espectively. The increase in photosynthetic capacity with increasing canopy height was strongly correlated with leaf nitrogen concentration when examined on a leaf area basis, but was only weakly correlated on a mass basis. The correlation on an area basis can be largely explained by the concomitant decrease in specific leaf area with increasing height. Apparent daytime leaf respiration, on an area basis, also increased significantly with canopy height (P < 0.05). We conclude that canopy photosynthetic capacity can be represented as an average vertical profile, perturbations of which may be explained by variations in the environmental variables driving photosynthesis.     

Influence of male cones on early season vegetative growth of Pinus contorta trees

On average, branches of Pinus contorta Dougl. bearing male cones had 35 fewer needle pairs than equivalent vegetative branches, and significantly fewer differentiated primordia (i.e., male cones + needle pairs + sterile cataphylls). It was estimated that the formation of male cones results in a 27-50% reduction in the number of needles per male cone-bearing branch. In early spring, branches bearing male cones had on average 23% (0.44 g) more dry weight than vegetative branches. On average, 95% of the dry weight of male cone-bearing branches was allocated to the terminal shoot (54% of which was male cones) and 5% to the lateral shoots. By comparison, vegetative branches allocated 85% of their total dry weight to the terminal shoot and 15% to the lateral shoots. These findings suggest that male cones may reduce the photosynthetic potential of the trees which bear them.     

Influence of female cones on the vegetative growth of Pinus contorta trees

Branches of Pinus contorta Dougl. bearing two-year-old female cones initiated fewer lateral buds than vegetative branches. However, the number of lateral shoots that differentiated and grew was not reduced on female cone-bearing branches. Neither the number nor the weight of female cones influenced the length of the terminal shoot. The total length of all lateral shoots was positively associated with the weight of two-year-old female cones. Branch units with two-year-old female cones produced significantly more total dry weight in the current year than vegetative branch units. There was, however, no significant reduction in the dry weight of terminal and lateral shoots. Branches bearing female cones allocated between 17 and 45% of the current year's dry weight to two-year-old cones and between 1 and 5% was allocated to one-year-old female cones. Female cones therefore apparently do not reduce the photosynthetic potential of trees. The influence of female cones compared with male cones on the growth of trees is discussed.     

Effect of elevated [CO(2)] and varying nutrient application rates on physiology and biomass accumulation of Sitka spruce (Picea sitchensis)

Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings were supplied with solutions containing nitrogen (N) at 0.1 x or 2 x the optimum rate (low-N and high-N supply, respectively) and grown either outside in a control plot or inside open-top chambers and exposed to ambient (355 &mgr;mol mol(-1)) or elevated (700 &mgr;mol mol(-1)) CO(2) concentration ([CO(2)]). Gas exchange measurements, chlorophyll determinations and nutrient analysis were made on current-year (< 1-year-old) shoots of the upper whorl after the seedlings had been growing in the [CO(2)] treatments for 17 months and the nutrient treatments for 6 months. Total seedling biomass and biomass allocation were assessed at the end of the experiment. Nutrient treatment had a significant effect on the light response curves, irrespective of [CO(2)] or chamber treatment; seedlings supplied with high-N rates had higher net photosynthetic rates than seedlings supplied with low-N rates. The degree of photosynthetic stimulation in response to elevated [CO(2)] was larger in seedlings receiving high-N rates than in seedlings receiving low-N rates. Light-saturated net photosynthesis of seedlings grown and measured in elevated [CO(2)] was 26% higher than that of seedlings grown and measured in ambient [CO(2)]. There was no significant effect of [CO(2)] or chamber treatment on the CO(2) response curves of seedlings receiving High-N supply rates. In contrast, analysis of the CO(2) response curves of seedlings receiving Low-N supply rates showed acclimation to elevated [CO(2)]. Both maximum rate of carboxylation (V(cmax)) and maximum electron transport capacity (J(max)) were lower and J(max)/V(cmax) higher in seedlings in the elevated [CO(2)] treatment. There was no effect of elevated [CO(2)] on stomatal conductance, although it was highly dependent on foliar [N], ranging from ~60 mmol m(-2) s(-1) at ~1.5 g N m(-2) to 200 mmol m(-2) s(-1) at ~5 g N m(-2). In the high-N and low-N treatments, foliar N concentration was 10 and 28% lower in seedlings grown in elevated [CO(2)] than in seedlings grown in ambient [CO(2)], respectively. There was no [CO(2)] effect on foliar phosphorus concentration ([P]). Chlorophyll concentration increased with increasing N supply in all treatments. There was no significant effect of elevated [CO(2)] on specific leaf area. Chlorophyll concentration expressed either on an area or dry mass basis for a given foliar [N] was higher in seedlings grown in elevated [CO(2)] than in seedings grown in ambient [CO(2)]. Elevated [CO(2)] increased total biomass accumulation by 37% in seedlings in the high-N treatment but had no effect in seedlings in the low-N treatment. There was a proportionally bigger allocation of biomass to roots of seedlings in the elevated [CO(2)] + low-N supply rate treatment compared with seedlings in other treatments. This resulted in a reduction in aboveground biomass compared with corresponding seedlings grown in ambient [CO(2)].     

Accounting for uncertainty in pedotransfer functions in vulnerability assessments of pesticide leaching to groundwater

A simulation tool for site-specific vulnerability assessments of pesticide leaching to groundwater was developed, based on the pesticide fate and transport model MACRO, parameterized using pedotransfer functions and reasonable worst-case parameter values. The effects of uncertainty in the pedotransfer functions on simulation results were examined for 48 combinations of soils, pesticides and application timings, by sampling pedotransfer function regression errors and propagating them through the simulation model in a Monte Carlo analysis. An uncertainty factor, f(u), was derived, defined as the ratio between the concentration simulated with no errors, c(sim), and the 80th percentile concentration for the scenario. The pedotransfer function errors caused a large variation in simulation results, with f(u) ranging from 1.14 to 1440, with a median of 2.8. A non-linear relationship was found between f(u) and c(sim), which can be used to account for parameter uncertainty by correcting the simulated concentration, c(sim), to an estimated 80th percentile value. For fine-textured soils, the predictions were most sensitive to errors in the pedotransfer functions for two parameters regulating macropore flow (the saturated matrix hydraulic conductivity, K(b), and the effective diffusion pathlength, d) and two water retention function parameters (van Genuchten's N and alpha parameters). For coarse-textured soils, the model was also sensitive to errors in the exponent in the degradation water response function and the dispersivity, in addition to K(b), but showed little sensitivity to d. To reduce uncertainty in model predictions, improved pedotransfer functions for K(b), d, N and alpha would therefore be most useful.     

Testing MACRO (version 5.1) for pesticide leaching in a Dutch clay soil

Testing of pesticide leaching models against comprehensive field-scale measurements is necessary to increase confidence in their predictive ability when used as regulatory tools. Version 5.1 of the MACRO model was tested against measurements of water flow and the behaviour of bromide, bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] and imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] in a cracked clay soil. In keeping with EU (FOCUS) procedures, the model was first calibrated against the measured moisture profiles and bromide concentrations in soil and in drain water. Uncalibrated pesticide simulations based on laboratory measurements of sorption and degradation were then compared with field data on the leaching of bentazone and imidacloprid. Calibrated parameter values indicated that a high degree of physical non-equilibrium (i.e. strong macropore flow) was necessary to describe solute transport in this soil. Comparison of measured and simulated bentazone concentration profiles revealed that the bulk of the bentazone movement in this soil was underestimated by MACRO. Nevertheless, the model simulated the dynamics of the bentazone breakthrough in drain water rather well and, in particular, accurately simulated the timing and the concentration level of the early bentazone breakthrough in drain water. The imidacloprid concentration profiles and its persistence in soil were simulated well. Moreover, the timing of the early imidacloprid breakthrough in the drain water was simulated well, although the simulated concentrations were about 2-3 times larger than measured. Deep groundwater concentrations for all substances were underestimated by MACRO, although it simulated concentrations in the shallow groundwater reasonably well. It is concluded that, in the context of ecotoxicological risk assessments for surface water, MACRO can give reasonably good simulations of pesticide concentrations in water draining from cracking clay soils, but that prior calibration against hydrologic and tracer data is desirable to reduce uncertainty and improve accuracy.     

A B-cell targeting virus disrupts potentially protective genomic methylation patterns in lymphoid tissue by increasing global 5-hydroxymethylcytosine levels

The mechanisms by which viruses modulate the immune system include changes in host genomic methylation. 5-hydroxymethylcytosine (5hmC) is the catalytic product of the Tet (Ten-11 translocation) family of enzymes and may serve as an intermediate of DNA demethylation. Recent reports suggest that 5hmC may confer consequences on cellular events including the pathogenesis of disease; in order to explore this possibility further we investigated both 5-methylcytosine (5mC) and 5hmC levels in healthy and diseased chicken bursas of Fabricius. We discovered that embryonic B-cells have high 5mC content while 5hmC decreases during bursa development. We propose that a high 5mC level protects from the mutagenic activity of the B-cell antibody diversifying enzyme activation induced deaminase (AID). In support of this view, AID mRNA increases significantly within the developing bursa from embryonic to post hatch stages while mRNAs that encode Tet family members 1 and 2 reduce over the same period. Moreover, our data revealed that infectious bursal disease virus (IBDV) disrupts this genomic methylation pattern causing a global increase in 5hmC levels in a mechanism that may involve increased Tet 1 and 2 mRNAs. To our knowledge this is the first time that a viral infection has been observed to cause global increases in genomic 5hmC within infected host tissues, underlining a mechanism that may involve the induction of B-cell genomic instability and cell death to facilitate viral egress.     

Metallothionein induction in cultured fibroblasts and liver of a marine flatfish,the turbot,Scophthalmus maximus

Intraperitoneal injection of turbot with Cd induced the synthesis of a low molecular weight hepatic Cd-binding protein and a 500bp mRNA, which hybridised to a plaice metallothionein (MT) cRNA probe. The Cd-binding protein displayed cross-reactivity in a competitive ELISA with antiserum raised against rainbow trout MT and had the characteristic amino acid composition, metal stoichiometry and spectral characteristics of a Class I MT. Only one isoform was apparent on ion exchange chromatography. Southern blot analysis of DNA cleaved with four restriction enzymes suggested that only a single MT gene is present in turbot.In an established turbot fibroblast cell line, Cd induced MT mRNA and MT levels in a dose and time-dependent manner. MT was also induced by Cu, Hg and Zn but not Pb exposure. Physiological concentrations of glucocorticoids and sex hormones did not induce MT synthesis, although at high concentrations a positive response to corticosterone, dexamethasone, hydrocortisone or progesterone was observedin vitro indicating the possible presence of a functional steroid regulatory element in the fish MT gene.Abbreviations used AMP adenosine monophosphate - CHSE chinook salmon embryo - DMSO dimethyl sulphoxide - HPLC high performance liquid chromatography - KB kenacid blue - MT metallothionein - Mr molecular weight (kDaltons) - NR neutral red - PEG polyethylene glycol - RTH rainbow trout hepatoma - SDS sodium dodecyl sulphate - SSC 0.15M NaCl, 0.015M sodium citrate - TF turbot fibroblast