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We describe experiments to better understand how CH 4 oxidation rates by different methanotroph communities respond to changing CH 4 concentrations. We used a novel system of automatically monitored chambers to investigate the response of CH 4 oxidation rates in a New Zealand pasture and adjacent pine forest soil exposed to varying atmospheric CH 4 concentrations. Type II methanotrophs that dominate CH 4 oxidation in the forest soil became progressively saturated as CH 4 concentrations rose from ambient (1.8 ppmv) to 570 ppmv, as shown by a decrease in uptake efficiency from 20% to 2% removal. By contrast, CH 4 oxidation in the pasture soil where Type I methanotrophs dominate increased in proportion to the increase in CH 4 inlet concentration, oxidising about 2% of the inlet CH 4 flux throughout. Modelling based on Michaelis-Menten kinetics revealed that low-affinity (Type I) methanotrophs were solely responsible for CH 4 oxidation in pasture soils, whereas high affinity (Type II) methanotrophs only contributed about 10% of the CH 4 oxidation in the forest soil. Increased aeration status using a soil–perlite (1:1) mixture doubled CH 4 oxidation rates at both ambient (1.8 ppmv) and 40 ppmv atmospheric CH 4 . A similar volcanic soil previously exposed for 8 y to high CH 4 fluxes from a landfill had removal efficiencies consistently above 95% for atmospheric CH 4 concentrations up to 7500 ppmv when the CH 4 oxidation rate was7000 μg CH 4 kg −1 soil h −1 .

Dairy farm effluent ponds are a source of methane (CH 4 ), a potent greenhouse gas. Biofiltration, whereby CH 4 is oxidised by methanotrophic bacteria, is a potentially cost-effective CH 4 mitigation technology. We report on the performance of a field-scale biofilter treating dairy farm effluent pond CH 4 emissions for 16 months. This study is the first to report on the feasibility of using biofiltration to mitigate dairy waste CH 4 emissions. The 70-L filter comprised a 1:1 volumetric mixture of volcanic soil from a landfill and perlite. Biogas collected in a floating cover on a 4-m 2 section of the pond was directed through the biofilter's base. Air was pumped through the filter to supply oxygen to the methanotrophs. The filter's maximum CH 4 removal rate was 16 g m −3 h −1 (or 53 μg g −1 h −1 ), which is high compared with literature landfill soil oxidation rates (typically −1 h −1 ). At the trial's conclusion, the filter experienced acid accumulation, due to oxidation of H 2 S in the inlet biogas (evidenced by low pH [3.9] and high sulphate-S [1079 mg −1 kg −1 ] at the base of the filter compared with the top [pH = 4.6, sulphate-S = 369 mg −1 kg −1 ]). Nonetheless, the filter's oxidation rate peaked at the end of the experiment indicating negligible H 2 S impact on overall performance over the 16-month period. The results showed that a 50-m 3 filter would be needed to offset CH 4 emissions (approximately 720 g h −1 ) from a typical 1000-m 2 dairy effluent pond. As this calculation is based on the efficiency of a single experimental filter, field testing of replicate biofilters is needed to accurately establish full-scale filter sizing. Nonetheless, this study has shown that biofilter technology is feasible to mitigate dairy effluent pond CH 4 emissions. Current research is underway to make the filter more economically viable through design optimisation.

Age-related reductions in stand biomass accumulation are frequently observed in old-growth forests. The phenomenon may be caused by reduced production, increased mortality or both. The relative importance of production and mortality is not well studied, so the mechanisms controlling age-related decline of stand biomass accumulation remain unclear. In this study, conducted in a Quercus-dominated deciduous forest in the Northeastern USA, we examined whether age-related decline in stand above-ground biomass (AGB) accumulation could be explained by reduction of above-ground net primary production (NPP) (growth of surviving trees) that may be associated with (i) physiological constraints within individual trees or (ii) changes in stand structure, or by (iii) age-related, increasing tree mortality in stands up to 135years old. Few previous studies have tested these hypotheses simultaneously within the same forest. We did not find evidence for a reduction in individual tree growth associated with age-related physiological constraints, in terms of foliar carbon assimilation capacity, photosynthesis/respiration balance, nitrogen availability or hydraulic constraints on carbon gain. Over the period of 1937-2006, we did not observe alterations in stand structure, and the above-ground NPP of the Quercus forest was generally stable. However, we did find that the primary mechanism driving age-related decline of stand AGB accumulation was biomass loss due to the death of large, dominant trees. Our results indicate that shifts in mortality from the loss of small trees to the loss of large trees, rather than changes in above-ground NPP, drives age-related decline in stand AGB accumulation in this forest. Synthesis.We found that within the range of stand development stages analysed, the age-related decline of stand AGB accumulation in a Quercus-dominated forest was primarily due to mortality of large, dominant trees and not due to changes in above-ground NPP associated with tree physiology, individual tree growth or stand structure. This result indicates that tree demography and the influence of climate change on disturbances may need to be integrated into models to predict the change of above-ground carbon stock of some old-growth forests.

Soil methane (CH(4)) biofilters, containing CH(4)-oxidizing bacteria (methanotrophs), are a promising technology for mitigating greenhouse gas emissions. However, little is known about long-term biofilter performance. In this study, volcanic pumice topsoils (0-10 cm) and subsoils (10-50 cm) were tested for their ability to oxidize a range of CH(4) fluxes over 1 yr. The soils were sampled from an 8-yr-old and a 2-yr-old grassed landfill cover and from a nearby undisturbed pasture away from the influence of CH(4) generated by the decomposing refuse. Methane was passed through the soils in laboratory chambers with fluxes ranging from 0.5 g to 24 g CH(4) m(-3) h(-1). All topsoils efficiently oxidized CH(4). The undisturbed pasture topsoil exhibited the highest removal efficiency (24 g CH(4) m(-3) h(-1)), indicating rapid activation of the methanotroph population to the high CH(4) fluxes. The subsoils were less efficient at oxidizing CH(4) than the topsoils, achieving a maximum rate oxidation rate of 7 g CH(4) m(-3) h(-1). The topsoils exhibited higher porosities; moisture contents; surface areas; and total C, N, and available-P concentrations than the subsoils, suggesting that these characteristics strongly influence growth and activity of the CH(4)-oxidizing bacteria. Soil pH values and available-P levels gradually declined during the trial, indicating a need to monitor chemical parameters closely so that adjustments can be made when necessary. However, other key soil physicochemical parameters (moisture, total C, total N) increased over the course of the trial. This study showed that the selected topsoils were capable of continually sustaining high CH(4) removal rates over 1 yr, which is encouraging for the development of biofilters as a low-maintenance greenhouse gas mitigation technology.

We investigated seasonal variation in dark respiration and photosynthesis by measuring gas exchange characteristics on Pinus radiata and Populus deltoides under field conditions each month for 1 year. The field site in the South Island of New Zealand is characterized by large day-to-day and seasonal changes in air temperature. The rate of foliar respiration at a base temperature of 10 °C (R10) in both pine and poplar was found to be greater during autumn and winter and displayed a strong downward adjustment in warmer months. The sensitivity of instantaneous leaf respiration to a 10 °C increase in temperature (Q10) was also greater during the winter period. The net effect of this strong acclimation was that the long-term temperature response of respiration was essentially flat over a wide range of ambient temperatures. Seasonal changes in photosynthesis were sensitive to temperature but largely independent of leaf nitrogen concentration or stomatal conductance. Over the range of day time growth temperatures (5–32 °C), we did not observe strong evidence of photosynthetic acclimation to temperature, and the long-term responses of photosynthetic parameters to ambient temperature were similar to previously published instantaneous responses. The ratio of foliar respiration to photosynthetic capacity (Rd/Asat) was significantly greater in winter than in spring/summer. This indicates that there is little likelihood that respiration would be stimulated significantly in either of these species with moderate increases in temperature – in fact net carbon uptake was favoured at moderately higher temperatures. Model calculations demonstrate that failing to account for strong thermal acclimation of leaf respiration influences determinations of leaf carbon exchange significantly, especially for the evergreen conifer.

Summary • Dark respiration and photosynthesis were measured in leaves of poplar Populus deltoides × nigra (‘Veronese’) saplings to investigate the extent of respiratory and photosynthetic acclimation in pre-existing and newly emerged leaves to abrupt changes in air temperature. • The saplings were grown at three temperature regimes and at high and low nitrogen availabilities. Rates of photosynthesis and dark respiration (Rd) were measured at the initial temperature and the saplings were then transferred to a different temperature regime, where the plants remained for a second and third round of measurements on pre-existing and newly emerged leaves. • Acclimation of photosynthesis was limited following transfer to warmer or cooler growing conditions. There was strong evidence of cold and warm acclimation of Rd to growth temperature, but this was limited in pre-existing leaves. Full acclimation of Rd was restricted to newly emerged leaves grown at the new growth temperature. • These findings indicate that the extent of thermal acclimation differs significantly between photosynthesis and respiration. Importantly, pre-existing leaves in poplar were capable of some respiratory acclimation, but full acclimation was observed only in newly emerged leaves. The Rd/Amax ratio declined at higher growth temperatures, and nitrogen status of leaves had little impact on the degree of acclimation.

The objective of this study was to characterize the forest canopy in terms of species composition, tree size classes and spatial distribution of leaf area of a mature temperate rainforest to provide a basis for scaling up shoot-level processes of energy and mass exchange using a one-dimensional canopy model. Stem number per unit area was high (1660 stems ha −1 ) but species diversity was low ( n = 10). Two species ( Dacrydium cuppressinum and Weinmannia racemosa ) equally accounted for 70% of the stem numbers, with the remaining 30% distributed among the other eight tree species. However, D. cuppressinum alone accounted for 72% of basal area and 75% of crown volume. Across the site L e (“effective” leaf area index, uncorrected for foliage clumping and woody surface interceptance) varied between 2.2 and 5.6, with a mean value of 3.5. Half total woody surface area per unit ground area ( W ) was 1.1. The mean foliage clumping index within shoot elements ( γ E ) was 1.2, while that between shoot elements ( Ω E ) was 0.87, giving an overall foliage clumping factor ( Ω = Ω E / γ E ) of 0.73. After corrections for foliage clumping and woody surface interceptance, half total leaf area per unit ground area ( L hc = L e / Ω − W ) was 3.7. For individual shoots, γ E increased from 1.0 to 1.5 with height in the canopy, possibly reflecting shoot structural adaptation to local irradiance. Simulations with the canopy model over 1 year using mean clumping factors revealed that clumping reduced total canopy radiation interception by 5%. Shoot-level irradiance was reduced at the top of the canopy but increased in lower canopy layers resulting in a more even canopy irradiance distribution. This enhanced annual canopy photosynthesis by 8% over a canopy with randomly distributed foliage. When the simulations were repeated to include the observed variation of γ E with height, total canopy radiation absorption was 11% lower than for a random canopy and canopy photosynthesis was 12% greater than a random canopy. The combination of reduced canopy radiation absorption and increased photosynthesis due to foliage clumping resulted in a considerable enhancement of canopy light-use efficiency. These analyses reveal a significant advantage of clumped foliage over randomly distributed foliage in terms of carbon gain, even for a forest canopy with moderate leaf area index.

Un modele multi couche de canopee forestiere a ete utilise pour simuler les effets de changements des teneurs en azote foliaire et d'indice foliaire sur le bilan net annuel d'assimilation de carbone dans deux ecosystemes forestiers contrastes de Nouvelle Zelande, afin de reveler les mecanismes de regulation et de controle d'efficience d'utilisation de la lumiere par les canopees. Dans la foret primaire mixte conifere feuillue dominee par Dacrydium cupressinum, l'assimilation de carbone de la canopee est limite par la carboxylation, essentiellement du fait d'une faible disponibilite en elements mineraux. Cette assimilation est limitee par le transport d'electrons photosynthetiques dans le cas du peuplement buissonnant secondaire a base de Leptospennum scoparium/Kunzea ericoides. Le maximum d'assimilation de carbone se produit au printemps dans les deux cas. Au cours de l'annee, les gains induits dans la photosynthese par des augmentations simulees d'indice foliaire de 50 % ont ete largement contrebalances par les pertes dues a l'augmentation de respiration nocturne. Une simulation realiste dans laquelle l'indice foliaire etait augmente de 50 % et l'azote foliaire de 20 % (ce qui correspond a une augmentation de 10 % de l'azote total de la canopee) a conduit a une baisse du gain de carbone cumule sur l'annee. Etant donnees les contraintes imposees par l'environnement, les deux couverts semblent fonctionner a l'optimum de leur indice foliaire et de leur concentration en N et maximisent ainsi le gain annuel de carbone.

Whereas leaf gas exchange properties are important to assess carbon and water fluxes in ecosystems worldwide, information of this type is scarce for savanna species. In this study, gas exchange characteristics of 2 C4 grass species (Andropogon canaliculatus and Hyparrhenia diplandra) and 2 C3 tree species (Crossopteryx febrifuga and Cussonia arborea) from the West-African savanna of Lamto (Ivory Coast) were investigated in the field. Measurements were done in order to provide data to allow the parameterization of biochemically-based models of photosynthesis (for C4 and C3 plant metabolic types) and stomatal conductance ; and to compare gas exchange characteristics of coexisting species. No systematic difference was found between grass and tree species for reference stomatal conductance, under standard environmental conditions, or stomatal response to incident light or vapour pressure deficit at leaf surface. Conversely, grass species displayed higher water (1.5-2 fold) and nitrogen (2-5 fold) photosynthetic use efficiencies (WUE and NUE, ratio of net photosynthesis to transpiration and leaf nitrogen, respectively). These contrasts were attributed to the CO2 concentrating mechanism of C4 plants. When looking within plant life forms, no important difference was found between grass species. However, significant contrasts were found between tree species, Cussonia showing higher NUE and reference stomatal conductance than Crossopteryx. These results stress the need to account for functional diversity when estimating ecosystem carbon and water fluxes. In particular, our results suggest that the tree/grass ratio, and also the composition of the tree layer, could strongly affect WUE and NUE at the ecosystem scale in West African savannas.

Measurements of photosynthesis and respiration were made on leaves in summer in a Quercus rubra L. canopy at approximately hourly intervals throughout 5 days and nights. Leaves were selected in the upper canopy in fully sunlit conditions (upper) and in the lower canopy (lower). In addition, leaves in the upper canopy were shaded (upper shaded) to decrease photosynthesis rates. The data were used to test the hypothesis that total night-time respiration is dependent on total photosynthesis during the previous day and that the response is mediated through changes in storage in carbohydrate pools. Measurements were made on clear sunny days with similar solar irradiance and air temperature, except for the last day when temperature, especially at night, was lower than that for the previous days. Maximum rates of photosynthesis in the upper leaves (18.7lmolm � 2 s � 1 ) were approximately four times higher than those in the lower leaves (4.3lmolm � 2 s � 1 ) and maximum photosynthesis rates in the upper shaded leaves (8.0lmolm � 2 s � 1 ) were about half those in the upper leaves. There was a strong linear relationship between total night-time respiration and total photosynthesis during the previous day when rates of respiration were normalized to a fixed temperature of 201C, removing the effects of temperature from this relationship. Measurements of specific leaf area, nitrogen and chlorophyll concentration and calculations of the maximum rate of carboxylation activity, Vcmax, were not significantly different between upper and upper shaded leaves 5 days after the shading treatment was started. There were small, but significant decreases in the rate of apparent maximum electron transport at saturating irradiance, Jmax (P40.05), and light use efficiency, « (Po0.05), for upper shaded leaves compared with those for upper leaves. This suggests that the duration of shading in the experiment was sufficient to initiate changes in the electron transport, but not the carboxylation processes of photosynthesis. Support for the hypothesis was provided from analysis of soluble sugar and starch concentrations in leaves. Respiration rates in the upper shaded leaves were lower than those expected from a relationship between respiration and soluble sugar concentration for fully exposed upper and lower leaves. However, there was no similar difference in starch concentrations. This suggests that shading for the duration of several days did not affect sugar concentrations but reduced starch concentrations in leaves, leading to lower rates of respiration at night. A model

Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp-broadleaved forest in New Zealand, dominated by 100–400-year-old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth

Landfills that generate too little biogas for economic energy recovery can potentially offset methane (CH(4)) emissions through biological oxidation by methanotrophic bacteria in cover soils. This study reports on the CH(4) oxidation efficiency of a 10-year old landfill cap comprising a volcanic pumice soil. Surface CH(4) and CO(2) fluxes were measured using field chambers during three sampling intervals over winter and summer. Methane fluxes were temporally and spatially variable (-0.36 to 3044 mgCH(4)m(-2)h(-1)); but were at least 15 times lower than typical literature CH(4) fluxes reported for older landfills in 45 of the 46 chambers tested. Exposure of soil from this landfill cover to variable CH(4) fluxes in laboratory microcosms revealed a very strong correlation between CH(4) oxidation efficiency and CH(4)/CO(2) ratios, confirming the utility of this relationship for approximating CH(4) oxidation efficiency. CH(4)/CO(2) ratios were applied to gas concentrations from the surface flux chambers and indicated a mean CH(4) oxidation efficiency of 72%. To examine CH(4) oxidation with soil depth, we collected 10 soil depth profiles at random locations across the landfill. Seven profiles exhibited CH(4) removal rates of 70-100% at depths

Humans utilise about 40% of the earth’s net primary production (NPP) but the products of this NPP are often managed by different sectors, with timber and forest products managed by the forestry sector and food and fibre products from croplands and grasslands managed by the agricultural sector. Other significant anthropogenic impacts on the global carbon cycle include human utilization of fossil fuels and impacts on less intensively managed systems such as peatlands, wetlands and permafrost. A great deal of knowledge, expertise and data is available within each sector. We describe the contribution of sectoral carbon budgets to our understanding of the global carbon cycle. Whilst many sectors exhibit similarities for carbon budgeting, some key differences arise due to differences in goods and services provided, ecology, management practices used, landmanagement personnel responsible, policies affecting land management, data types and availability, and the drivers of change. We review the methods and data sources available for assessing sectoral carbon budgets, and describe some of key data limitations and uncertainties for each sector in different regions of the world. We identify the main gaps in our knowledge/data, show that coverage is better for the developed world for most sectors, and suggest how sectoral carbon budgets could be improved in the future. Research priorities include the development of shared protocols through site networks, a move to full carbon accounting within sectors, and the assessment of full greenhouse gas budgets. Fil: Smith, Pete. University Of Aberdeen. School Of Biological Sciences.; Reino Unido Fil: Nabuurs, Gert Jan. Wageningen University; Países Bajos Fil: Janssens, Iván A.. Universiteit Antwerp; Bélgica Fil: Reis, Stefan. Centre For Ecology And Hydrology; Reino Unido Fil: Marland, Gregg. Mid Sweden University.; Suecia Fil: Soussana, Jean-François. Instituto National de Recherches Agronomiques. Biopolymères Interactions Assemblages; Francia Fil: Christensen, Torben R.. Lund University; Suecia Fil: Heath, Linda. No especifíca; Fil: Apps, Mike. Pacific Forestry Centre; Canadá Fil: Alexeyev, Vlady. Russian Academy of Science; Rusia Fil: Fang, Jingyun. Peking University; China Fil: Gattuso, Jean Pierre. Observatoire Océanologique; Francia Fil: Guerschman, Juan Pablo. No especifíca; Fil: Huang, Yao. The Chinese Academy of Sciences; China Fil: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina Fil: Murdiyarso, Daniel. Center for International Forestry Research; Indonesia Fil: Ni, Jian. The Chinese Academy Of Sciences; China Fil: Nobre, Antonio. Instituto Nacional de Pesquisas da Amazônia; Brasil Fil: Peng, Changhui. Université du Québec a Montreal; Canadá Fil: Walcroft, Adrian. Crown Research Institutes. Landcare Research; Nueva Zelanda Fil: Wang, Shao Qiang. The Chinese Academy Of Sciences; China Fil: Pan, Yude. No especifíca; Fil: Zhou, Guang Sheng. The Chinese Academy Of Sciences; China

Seven methods, including measurements of photosynthesis (A) and stomatal conductance (g(s)), carbon isotope discrimination, ecosystem CO2 and water vapour exchange using eddy covariance and the use of a multilayer canopy model and ecosystem Keeling plots, were employed to derive estimates of intercellular CO2 concentration (Ci) across a range of spatial and temporal scales in a low productivity rain forest ecosystem dominated by the conifer Dacrydium cupressinum Lamb. in New Zealand. Estimates of shoot and canopy Ci across temporal scales ranging from minutes to years were remarkably similar (range of 274-294 micromol mol(-1)). The gradual increase in shoot Ci with depth in the canopy was more likely attributable to decreases in A resulting from lower irradiance (Q) than to increases in g, due to changes in air saturation deficit (D). The lack of marked vertical gradients in A and g(s) at saturating Q through the canopy and the low seasonal variability in environmental conditions contributed to the efficacy of scaling Ci. However, the canopy Ci estimate calculated from the carbon isotope composition of respired ecosystem CO2 (delta13CR; 236 micromol mol(-1)) was much lower than other estimates of canopy Ci. Partitioning delta13CR into four components (soil, roots, litter and foliage) indicated root respiration as the dominant (> 50%) contributor to delta13CR. Variable time lags and differences in isotopic composition during photosynthesis and respiration make the direct estimation of canopy Ci from delta 13CR problematic.

We quantified parameters for a model of leaf-level photosynthesis for olive, and tested the model against an independent dataset. Specific temperature-dependence parameters of the model for olive leaves were measured, as well as the relationship of the model parameters with area-based leaf nitrogen (N) content. The effect of soil water deficit on leaf photosynthesis was examined by applying two irrigation treatments to 29-year-old trees growing in a plantation: drip irrigation sufficient to meet the crop water requirements (I) and dry-farming (D). In both treatments, leaves had a higher photosynthetic capacity in April than in August. In August, photosynthetic capacity was lower in D trees than in I trees. Leaf photosynthetic capacity was linearly and positively related to leaf N content on an area basis (Na) and to leaf mass per unit area (LMA), and the regression slope varied with irrigation treatment. The seasonal reduction in Na was used in the model to predict photosynthesis under drought conditions. Olive leaves showed a clear limitation of photosynthesis by triose phosphate utilization (TPU) even at 40°C, and the data suggest that olive invests fewer resources in TPU than other species. The seasonal decrease in photosynthetic capacity moderated the stomatal limitation to carbon dioxide (CO2) fixation as soil water deficit increased. Further, it enabled leaves to operate close to the transition point between photosynthetic limitation due to RuBP carboxylation capacity and that due to RuBP regeneration capacity, and resulted in a near constant value of internal CO2 concentration from April to August. Under well watered conditions, N-use efficiency of the olive leaves was enhanced at the expense of reduced water-use efficiency., Financial support was provided by Spanish CICYT, Project HID96-342- CO4-01, and an MEC fellowship to Antonio Díaz-Espejo.

Summary • Here we develop and test a method to scale sap velocity measurements from individual trees to canopy transpiration (Ec) in a low-productivity, old-growth rainforest dominated by the conifer Dacrydium cupressinum. Further, Ec as a component of the ecosystem water balance is quantified in relation to forest floor evaporation rates and measurements of ecosystem evaporation using eddy covariance (Eeco) in conditions when the canopy was dry and partly wet. • Thermal dissipation probes were used to measure sap velocity of individual trees, and scaled to transpiration at the canopy level by dividing trees into classes based on sapwood density and canopy position (sheltered or exposed). • When compared with ecosystem eddy covariance measurements, Ec accounted for 51% of Eeco on dry days, and 22% of Eeco on wet days. • Low transpiration rates, and significant contributions to Eeco from wet canopy evaporation and understorey transpiration (35%) and forest floor evaporation (25%), were attributable to the unique characteristics of the forest: in particular, high rainfall, low leaf area index, low stomatal conductance and low productivity associated with severe nutrient limitation.

Responses of photosynthesis to carbon dioxide (CO2) partial pressure and irradiance were measured on leaves of 39-year-old trees of manuka (Leptospermum scoparium J. R. Forst. & G. Forst.) and kanuka (Kunzea ericoides var. ericoides (A. Rich.) J. Thompson) at a field site, and on leaves of young trees grown at three nitrogen supply rates in a nursery, to determine values for parameters in a model to estimate annual net carbon uptake. These secondary successional species belong to the same family and commonly co-occur. Mean (+/- standard error) values of the maximum rate of carboxylation (hemi-surface area basis) (Vcmax) and the maximum rate of electron transport (Jmax) at the field site were 47.3 +/- 1.9 micromol m(-2) s(-1) and 94.2 +/- 3.7 micromol m(-2) s(-1), respectively, with no significant differences between species. Both Vcmax and Jmax were positively related to leaf nitrogen concentration on a unit leaf area basis, and the slopes of these relationships did not differ significantly between species or between the trees in the field and young trees grown in the nursery. Mean values of Jmax/Vcmax measured at 20 degrees C were significantly lower (P < 0.01) for trees in the field (2.00 +/- 0.05) than for young trees in the nursery with similar leaf nitrogen concentrations (2.32 +/- 0.08). Stomatal conductance decreased sharply with increasing air saturation deficit, but the sensitivity of the response did not differ between species. These data were used to derive parameters for a coupled photosynthesis-stomatal conductance model to scale estimates of photosynthesis from leaves to the canopy, incorporating leaf respiration at night, site energy and water balances, to estimate net canopy carbon uptake. Over the course of a year, 76% of incident irradiance (400-700 nm) was absorbed by the canopy, annual net photosynthesis per unit ground area was 164.5 mol m(-2) (equivalent to 1.97 kg C m(-2)) and respiration loss from leaves at night was 37.5 mol m(-2) (equivalent to 0.45 kg m(-2)), or 23% of net carbon uptake. When modeled annual net carbon uptake for the trees was combined with annual respiration from the soil surface, estimated net primary productivity for the ecosystem (0.30 kg C m(-2)) was reasonably close to the annual estimate obtained from independent mensurational and biomass measurements made at the site (0.22 +/- 0.03 kg C m(-2)). The mean annual value for light-use efficiency calculated from the ratio of net carbon uptake (net photosynthesis minus respiration of leaves at night) and absorbed irradiance was 13.0 mmol C mol(-1) (equivalent to 0.72 kg C GJ(-1)). This is low compared with values reported for other temperate forests, but is consistent with limitations to photosynthesis in the canopy attributable mainly to low nitrogen availability and associated low leaf area index.

Two process-based models were used to identify the environmental variables limiting productivity in a pristine, mature forest dominated by rimu (Dacrydium cupressinum Sol. ex Lamb.) trees in South Westland, New Zealand. A model of canopy net carbon uptake, incorporating routines for radiation interception, photosynthesis and water balance was used to determine a value for quantum efficiency when climate variables were not limiting. The annual net carbon uptake by the canopy was estimated to be 1.1 kg C m(-2) and the quantum efficiency 22.6 mmol mol quanta(-1). This value of quantum efficiency, combined with other parameters obtainable from the literature, was then used in a model of forest productivity (3-PG), to simulate changes in net productivity and the allocation of carbon to tree components. The model was adjusted to match a measured stem increment of 10.6 Mg ha(-1) over a period of 13 years. To achieve this while maintaining a low, but stable value for leaf area index, it was necessary to set the site fertility rating very low and select high values for the parameters describing the proportional allocation of total carbon to roots. This approach highlighted nutrient availability as the principal constraint on productivity for the ecosystem and identified critical measurements that will be necessary for using the model to predict the effects of climate change on carbon sequestration. The low rates of carbon uptake and productivity are consistent with the low nutrient supply available from the highly leached, acid soils, most likely attributable to frequent saturation and a very shallow aerobic zone.

The three-dimensional (3-D) architecture of a peach tree (Prunus persica L. Batsch) growing in an orchard near Avignon, France, was digitized in April 1999 and again four weeks later in May 1999 to quantify increases in leaf area and crown volume as shoots developed. A 3-D model of radiation transfer was used to determine effects of changes in leaf area density and canopy volume on the spatial distribution of absorbed quantum irradiance (PAR(a)). Effects of changes in PAR(a) on leaf morphological and physiological properties were determined. Leaf mass per unit area (M(a)) and leaf nitrogen concentration per unit leaf area (N(a)) were both nonlinearly related to PAR(a), and there was a weak linear relationship between leaf nitrogen concentration per unit leaf mass (N(m)) and PAR(a). Photosynthetic capacity, defined as maximal rates of ribulose-1,5-bisphosphate carboxylase (Rubisco) carboxylation (V(cmax)) and electron transport (J(max)), was measured on leaf samples representing sunlit and shaded micro-environments at the same time that the tree crown was digitized. Both V(cmax) and J(max) were linearly related to N(a) during May, but not in April when the range of N(a) was low. Photosynthetic capacity per unit N(a) appeared to decline between April and May. Variability in leaf nitrogen partitioning between Rubisco carboxylation and electron transport was small, and the partitioning coefficients were unrelated to N(a). Spatial variability in photosynthetic capacity resulted from acclimation to varying PAR(a) as the crown developed, and acclimation was driven principally by changes in M(a) rather than the amount or partitioning of leaf nitrogen.

Photosynthetic light acclimation of leaves can result from (i) changes in mass-based leaf nitrogen concentration, Nm, (ii) changes in leaf mass:area ratio, Ma, and (iii) partitioning of total leaf nitrogen among different pools of the photosynthetic machinery. We studied variations in Nm and Ma within the crowns of two peach (Prunus persica L. Batsch) trees grown in an orchard in Portugal, and one peach tree grown in an orchard in France. Each crown was digitized and a 3-D radiation transfer model was used to quantify the intra-crown variations in time-integrated leaf irradiance,PARi. Nitrogen concentration, leaf mass:area ratio, chlorophyll concentration, and photosynthetic capacity were also measured on leaves sampled on five additional peach trees in the orchard in Portugal. The data were used to compute the coefficients of leaf nitrogen partitioning among carboxylation, bioenergetics, and light harvesting pools. Leaf mass:area ratio and area-based leaf nitrogen concentration, Na, were nonlinearly related toPARi, and photosynthetic capacity was linearly related to Na. Photosynthetic light acclimation resulted mainly from changes in Ma and leaf nitrogen partitioning, and to a lesser extent from changes in Nm. This behavior contrasts with photosynthetic light acclimation observed in other tree species like walnut (Juglans regia L.) in which acclimation results primarily from changes in Ma.

Gas exchange was measured on a pruned Pinus radiata D. Don hedge and on a long-branch P. radiata tree near Hamilton, New Zealand, in spring 1993 when soil water content was close to field capacity. Foliage at the end of long branches (9.0 m) showed a marked drop in net photosynthetic rate and stomatal conductance as the saturation deficit increased, whereas foliage on short branches (0.5 m) showed little change. Mean foliage delta(13)C was -30.1 per thousand for short branches and -26.3 per thousand for long branches. Foliage delta(13)C was correlated with branch length in two genetically improved P. radiata seedlots at four stocking densities. The multinodal seedlot had shorter branches and more (13)C-depleted foliage compared with branches and foliage from the long internode seedlot. There was a strong effect of stocking density on carbon isotope composition in both seedlots. We conclude that branch morphology affects foliage gas exchange properties and foliage carbon isotope composition.

International audience; Stable isotopes of atmospheric carbon dioxide (CO 2) contain a wealth of information regarding biosphere-atmosphere interactions. The carbon isotope ratio of CO 2 (δ 13 C) reflects the terrestrial carbon cycle including processes of photosynthesis, respiration, and decomposition. The oxygen isotope ratio (δ 18 O) reflects terrestrial carbon and water coupling due to CO 2-H 2 O oxygen exchange. Isotopic CO 2 measurements, in combination with ecosystem-isotopic exchange models, allow for the quantification of patterns and mechanisms regulating terrestrial carbon and water cycles, as well as for hypothesis development, data interpretation, and forecasting. Isotopic measurements and models have evolved significantly over the past two decades, resulting in organizations that promote model-measurement networks, e.g., the U.S. National Science Foundation's Biosphere-Atmosphere Stable Isotope Network , the European Stable Isotopes in Bio-sphere-Atmosphere Exchange Network, and the U.S. National Environmental Observatory Network. Unfortunately, technical limitations associated with atmospheric flask sampling and subsequent analyses via mass spectrometry have constrained high-frequency data useful for in-depth quantification of patterns and controls. As a consequence, state-of-the-art models of ecosystem stable isotope exchange have evolved beyond their counterpart measurement systems, leaving model assumptions vulnerable due to a lack of validation data sets. The recent development of laser-based systems for high-frequency, continuous sampling of CO 2 isotopologues (at least one atom with a different number of neutrons), i.e., 12 CO 2 , 13 CO 2 , and 12 C 16 O 18 O, allows, for the first time, rigorous model testing at compatible timescales. Numerous laser systems are in development and all have advantages and disadvantages ; however, all of them share the potential of having precision and accuracy on par with traditional flask/mass spectrometry techniques while providing continuous, high-frequency data (i.e.

Pinus radiata L. were grown in climate-controlled cabinets under three night/day temperature treatments, and transferred between treatments to mimic changes in growth temperature. The objective was to determine the extent to which dark respiration and photosynthesis in pre-existing and new needles acclimate to changes in growth temperatures. We also assessed whether needle nitrogen influenced the potential for photosynthetic and respiratory acclimation, and further assessed if short-term (instantaneous, measured over a few hours) respiratory responses are accurate predictors of long-term (acclimated, achieved in days–weeks) responses of respiration to changing temperature. Results show that respiration displayed considerable potential for acclimation. Cold and warm transfers resulted in some acclimation of respiration in pre-existing needles, but full acclimation was displayed only in new needles formed at the new growth temperature. Short-term respiratory responses were poor predictors of the long-term response of respiration due to acclimation. There was no evidence that photosynthesis in pre-existing or new needles acclimated to changes in growth temperature. N status of leaves had little impact on the extent of acclimation. Collectively, our results indicate that there is little likelihood that respiration would be significantly stimulated in this species as night temperatures increase over the range of 10–20°C, but that inclusion of temperature acclimation of respiration would in fact lead to a shift in the balance between photosynthesis and respiration in favour of carbon uptake.