Traits mediate drought effects on wood carbon fluxes

CO₂ fluxes from wood decomposition represent an important source of carbon from forest ecosystems to the atmosphere, which are determined by both wood traits and climate influencing the metabolic rates of decomposers. Previous studies have quantified the effects of moisture and temperature on wood decomposition, but these effects were not separated from the potential influence of wood traits. Indeed, it is not well understood how traits and climate interact to influence wood CO₂ fluxes. Here, we examined the responses of CO₂ fluxes from dead wood with different traits (angiosperm and gymnosperm) to 0%, 35%, and 70% rainfall reduction across seasonal temperature gradients. Our results showed that drought significantly decreased wood CO₂ fluxes, but its effects varied with both taxonomical group and drought intensity. Drought‐induced reduction in wood CO₂ fluxes was larger in angiosperms than gymnosperms for the 35% rainfall reduction treatment, but there was no significant difference between these groups for the 70% reduction treatment. This is because wood nitrogen density and carbon quality were significantly higher in angiosperms than gymnosperms, yielding a higher moisture sensitivity of wood decomposition. These findings were demonstrated by a significant positive interaction effect between wood nitrogen and moisture on CO₂ fluxes in a structural equation model. Additionally, we ascertained that a constant temperature sensitivity of CO₂ fluxes was independent of wood traits and consistent with previous estimates for extracellular enzyme kinetics. Our results highlight the key role of wood traits in regulating drought responses of wood carbon fluxes. Given that both climate and forest management might extensively modify taxonomic compositions in the future, it is critical for carbon cycle models to account for such interactions between wood traits and climate in driving dynamics of wood decomposition.     

Impacts of biogenic CO2 emissions on human health and terrestrial ecosystems: the case of increased wood extraction for bioenergy production on a global scale

Biofuels are a potentially important source of energy for our society. Common practice in life cycle assessment (LCA) of bioenergy has been to assume that any carbon dioxide (CO₂) emission related to biomass combustion equals the amount absorbed in biomass, thus assuming no climate change impacts. Recent developments show the significance of contributions of biogenic CO₂ emissions during the time they stay in the atmosphere. The goal of this article is to develop a global, spatially explicit method to quantify the potential impact on human health and terrestrial ecosystems of biogenic carbon emissions coming from forest wood extraction for biofuel production. For this purpose, changes in aboveground carbon stock (ΔC_forest) due to an increase in wood extraction via changes in rotation time are simulated worldwide with a 0.5° × 0.5° grid resolution. Our results show that both impacts and benefits can be obtained. When the extraction increase is reached by creating a longer rotation time, new growth is allowed resulting in carbon benefits. In a case study, we assessed the life cycle impacts of heat production via wood to determine the significance of including biogenic CO₂ emissions due to changes in forest management. Impacts of biogenic CO₂ dominate the total climate change impacts from a wood stove. Depending on the wood source country, climate change impacts due to heat production from wood either have an important share in the overall impacts on human health and terrestrial ecosystems, or allow for a large additional CO₂ sink.     

Methane emission from living tree wood

The time courses of CO₂, CH₄, and H2 accumulation and O2 absorption at the exposure of trunk wood samples taken from living trees of birch (Betula pendula Roth.), bird cherry tree (Padus avium Mill.), and pine (Pinus sylvestris L.) in the closed volume were studied. The activity of these processes at different temperatures (from 5 to 55°C) was also examined. The main components of gas exchange in all three tree species were O₂ absorption and CO₂ evolution. The fluxes of these gases were equal. In experiments with dehydration-hydration of wood samples, the intrawood origin of “woody” methane was established. Emission of CH₄ and H₂ from the wood depended on temperature. The temperature dependence of CH₄ emission was similar to the temperature dependence of wood respiration. The high correlation between CO₂, CH₄, and H₂ release and O₂ absorption was noted. The relationships between these gas-exchange parameters were not species-specific. Temperature maxima of CH₄ emission and the respiratory activity coincided. This implies that the highest methane emission should be expected in the period of the growth season most favorable for tree physiology. For the wood from all tree species, the ratio between released CH₄ and CO₂ volumes was close to 1: 160. This means that the annual methane emission from living tree is about 2 Mt C, attaining 4% of total methane emission from the territory of North Eurasia. However, taking into account a temperature dependence of methane exchange between the vegetation cover and atmosphere, we can expect that, at global climate warming, methane emission volume might be substantial.     

Sap flow in Scots pines growing under conditions of year-round carbon dioxide enrichment and temperature elevation

Starting in rrrr, individual trees of Scots pine (Pinus sylvestris L.) aged 30 years were grown in closed-top chambers and exposed to normal ambient conditions (CON), elevated CO₂ (Elev. C), elevated temperature (Elev. T) and a combination of elevated CO₂ and temperature (Elev. C + T). Using the constant-power heat balance method, sap flow was monitored simultaneously in a total of 16 trees, four for each treatment, over a 32 d period (after the completion of needle expansion and branch elongation in 1997). An overall variation in diurnal sap flow totals (F_t) was evident during the period of measurement (days 167–198, 1997) regardless of the treatments, with a range from 0·15 to 2·82 kg tree^–1 d^–1. Elev. C reduced F_t by 4·1–13·7% compared with CON on most days (P varies from 0·042 to 0·108), but slightly increased it on some days (P≥ 0·131), depending on the weather conditions. Although the decrease in F_t caused by Elev. C was statistically significant on only a few days (P≤ 0·042), the cumulative F_t for the 32 d decreased by 14·4% (P = 0·047), indicating that Elev. C may have an important influence on seasonal water use of the Scots pine. Analysis of the diurnal courses of sap flow combined with corresponding weather factors indicated that the CO₂-induced decrease in F_t could be largely attributed to an increase in stomatal sensitivity to vapour pressure deficit (VPD), whereas the CO₂-induced increase in F_t related to an increase in stomatal sensitivity to low light levels. Elev. T increased F_t by 11·2–35·6% throughout the measuring period and the cumulative F_t for the 32 d by 32·5% (P = 0·019), which could be largely attributed to the temperature-induced increase in current-year needle area and decrease in stomatal sensitivity to high levels of VPD. There were no significant interactive effects of CO₂ and temperature on sap flow, so that Elev. C + T had approximately the same F_t as Elev. T and similar diurnal patterns of sap flow, suggesting that the temperature factor played a dominant role in the case of Elev. C + T.     

Stem wood properties of Populus tremuloides, Betula papyrifera and Acer saccharum saplings after 3 years of treatments to elevated carbon dioxide and ozone

The aim of this study was to examine the effects of elevated carbon dioxide [CO₂] and ozone [O₃] and their interaction on wood chemistry and anatomy of five clones of 3‐year‐old trembling aspen (Populus tremuloides Michx.). Wood chemistry was studied also on paper birch (Betula papyrifera Marsh.) and sugar maple (Acer saccharum Marsh.) seedling‐origin saplings of the same age. Material for the study was collected from the Aspen Free‐Air CO₂ Enrichment (FACE) experiment in Rhinelander, WI, USA, where the saplings had been exposed to four treatments: control (C; ambient CO₂, ambient O₃), elevated CO₂ (560 ppm during daylight hours), elevated O₃ (1.5 × ambient during daylight hours) and their combination (CO₂+O₃) for three growing seasons (1998–2000). Wood chemistry responses to the elevated CO₂ and O₃ treatments differed between species. Aspen was most responsive, while maple was the least responsive of the three tree species. Aspen genotype affected the responses of wood chemistry and, to some extent, wood structure to the treatments. The lignin concentration increased under elevated O₃ in four clones of aspen and in birch. However, elevated CO₂ ameliorated the effect. In two aspen clones, nitrogen in wood samples decreased under combined exposure to CO₂ and O₃. Soluble sugar concentration in one aspen clone and starch concentration in two clones were increased by elevated CO₂. In aspen wood, α‐cellulose concentration changed under elevated CO₂, decreasing under ambient O₃ and slightly increasing under elevated O₃. Hemicellulose concentration in birch was decreased by elevated CO₂ and increased by elevated O₃. In aspen, elevated O₃ induced statistically significant reductions in distance from the pith to the bark and vessel lumen diameter, as well as increased wall thickness and wall percentage, and in one clone, decreased fibre lumen diameter. Our results show that juvenile wood properties of broadleaves, depending on species and genotype, were altered by atmospheric gas concentrations predicted for the year 2050 and that CO₂ ameliorates some adverse effects of elevated O₃ on wood chemistry.     

Photosynthesis, light and nitrogen relationships in a young deciduous forest canopy under open-air CO2 enrichment

Leaf photosynthesis (Ps), nitrogen (N) and light environment were measured on Populus tremuloides trees in a developing canopy under free‐air CO₂ enrichment in Wisconsin, USA. After 2 years of growth, the trees averaged 1·5 and 1·6 m tall under ambient and elevated CO₂, respectively, at the beginning of the study period in 1999. They grew to 2·6 and 2·9 m, respectively, by the end of the 1999 growing season. Daily integrated photon flux from cloud‐free days (PPFD_day,sat) around the lowermost branches was 16·8 ± 0·8 and 8·7 ± 0·2% of values at the top for the ambient and elevated CO₂ canopies, respectively. Elevated CO₂ significantly decreased leaf N on a mass, but not on an area, basis. N per unit leaf area was related linearly to PPFD_day,sat throughout the canopies, and elevated CO₂ did not affect that relationship. Leaf Ps light‐response curves responded differently to elevated CO₂, depending upon canopy position. Elevated CO₂ increased Ps_sat only in the upper (unshaded) canopy, whereas characteristics that would favour photosynthesis in shade were unaffected by elevated CO₂. Consequently, estimated daily integrated Ps on cloud‐free days (Ps_day,sat) was stimulated by elevated CO₂ only in the upper canopy. Ps_day,sat of the lowermost branches was actually lower with elevated CO₂ because of the darker light environment. The lack of CO₂ stimulation at the mid‐ and lower canopy was probably related to significant down‐regulation of photosynthetic capacity; there was no down‐regulation of Ps in the upper canopy. The relationship between Ps_day,sat and leaf N indicated that N was not optimally allocated within the canopy in a manner that would maximize whole‐canopy Ps or photosynthetic N use efficiency. Elevated CO₂ had no effect on the optimization of canopy N allocation.     

The influence of carbon dioxide-depletion on growth and sinking rate of two planktonic diatoms in culture

Growth in relation to CO₂-depletion and CO₂-enrichment was investigated for the freshwater diatoms Asterionella formosa and Fragilaria crotonensis in batch cultures. Algal concentration and pH were measured during growth cycles, and inorganic carbon quantities determined by potentiometric Gran titrations and from pH-alkalinity relationships. After the primary growth with CO₂-depletion and pH increase, successive CO₂-enrichments induced further such cycles and produced a final three- to fivefold increase in algal biomass over that of unenriched controls. The extent of CO₂-depletion, and pH rise, was greater in later cycles, indicative of some cellular adaptation. Values of pH reached 9·7 for Asterionella and 9·9 for Fragilaria. The lowest residual quantities of free CO₂ were 0·1 and 0·03 μmol 1^-1 for Asterionella and Fragilaria respectively, which were less than 0·05% of the corresponding residual quantities of total CO₂. The primary limitation of CO₂-uptake and growth was probably related to the concentration of free CO₂, given the relative excess of other major nutrients (N, P, Si) in he media used. Limited of CO₂-uptake could be restored without CO₂ additions if the CO₂ present was redistributed between its several forms (increasing free CO₂) by the addition of strong acid, although growth was still restricted.

Limitation of CO₂-uptake, either by CO₂-depletion or the addition of an inhibitor of photo-synthesis (DCMU), increased the sinking rate of Asterionella cells from 0·3 to 1 m day^-1. The possible ecological implications of CO₂-pH-growth and CO₂-pH-buoyancy relationships are discussed, which may contribute to the frequent paucity of diatoms during summer in manv productive lakes.     

Antagonistic fungal interactions influence carbon dioxide evolution from decomposing wood

Fungal species vary in the rate and way in which they decay wood. Thus, understanding fungal community dynamics within dead wood is crucial to understanding decomposition and carbon cycling. Mycelia compete for wood territory, by employing antagonistic mechanisms involving changes in morphology, and production of volatile and diffusible chemicals. This is metabolically costly, and may affect the rate of use of the resource. The metabolic rate during pairwise interactions between wood decay ascomycetes and basidiomycetes was determined by measuring CO₂ production. CO₂ evolution altered over time, but changes were combination-specific. In only two combinations – when the dominant competitor overgrew the opponent's territory as mycelia cords – did CO₂ evolution increase over the course of the whole interaction. In most interactions, CO₂ evolution increased only after complete replacement of one competitor, suggesting utilisation of the predecessor mycelium or differences in decay ability due to alteration of the resource by the predecessor. There was no relationship between rate of CO₂ evolution and combative ability nor outcome of interaction.     

Photosynthetic acclimation to long-term exposure to elevated CO2 concentration in Pinus radiata D. Don. is related to age of needles

The effects of CO₂ enrichment on photosynthesis and ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) in current year and 1-year-old needles on the same branch were studied on Pinus radiata D. Don. trees growing for 4 years in large, open-top chambers at ambient (36 Pa) and elevated (65 Pa) CO₂ partial pressures. At this age trees were 3·5–4 m tall. Measurements made late in the growing cycle (March) showed that photosynthetic rates at the growth CO₂ concentration [(pCO₂)_a] were lower in 1-year-old needles of trees grown at elevated CO₂ concentrations than in those of trees grown at ambient (pCO₂)_a. At elevated CO₂ concentrations V_cmax (maximum carboxylation rate) was reduced by 13% and J_max (RuBP regeneration capacity mediated by maximum electron transport rate) by 17%. This corresponded with photosynthetic rates at the growth (pCO₂)_a of 4·68 ± 0·41 μmol m^–2 s^–1 and 6·15 ± 0·46 μmol m^–2 s^–1 at 36 and 65 Pa, respectively (an enhancement of 31%). In current year needles photosynthetic rates at the growth (pCO₂)_a were 6·2 ± 0·72 μmol m^–2 s^–1 at 36 Pa and 10·15 ± 0·64 μmol m^–2 s^–1 at 65 Pa (an enhancement of 63%). The smaller enhancement of photosynthesis in 1-year-old needles at 65 Pa was accompanied by a reduction in Rubisco activity (39%) and content (40%) compared with that at 36 Pa. Starch and sugar concentrations in 1-year-old needles were not significantly different in the CO₂ treatments. There was no evidence in biochemical parameters for down-regulation at elevated (pCO₂)_a in fully fexpanded needles of the current year cohort. These data show that enhancement of photosynthesis continues to occur in needles after 4 years’ exposure to elevated CO₂ concentrations. Photosynthetic acclimation reduces the degree of this enhancement, but only in needles after 1 year of growth. Thus, responses to elevated CO₂ concentration change during the lifetime of needles, and acclimation may not be apparent in current year needles. This transitory effect is most probably attributable to the effects of developmental stage and proximity to actively growing shoots on sink strength for carbohydrates. The implications of such age-dependent responses are that older trees, in which the contribution of older needles to the photosynthetic biomass is greater than in younger trees, may become progressively more acclimated to elevated CO₂ concentration.     

The onset of photosynthetic acclimation to elevated CO2 partial pressure in field-grown Pinus radiata D. Don. after 4 years

The effects of CO₂ enrichment on photosynthesis and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rubisco) were studied in current year and 1‐year‐old needles of the same branch of field‐grown Pinus radiata D. Don trees. All measurements were made in the fourth year of growth in large, open‐top chambers continuously maintained at ambient (36 Pa) or elevated (65 Pa) CO₂ partial pressures. Photosynthetic rates of the 1‐year‐old needles made at the growth CO₂ partial pressure averaged 10·5 ± 0·5 μmol m^?2 s^?1 in the 36 Pa grown trees and 11·8 ± 0·4 μmol m^?2 s^?1 in the 65 Pa grown trees, and were not significantly different from each other. The photosynthetic capacity of 1‐year‐old needles was reduced by 25% from 23·0 ± 1·8 μmol m^?2 s^?1 in the 36 Pa CO₂ grown trees to 17·3 ± 0·7 μmol m^?2 s^?1 in the 65 Pa grown trees. Growth in elevated CO₂ also resulted in a 25% reduction in V_cmax (maximum carboxylation rate), a 23% reduction in J_max (RuBP regeneration capacity mediated by maximum electron transport rate) and a 30% reduction in Rubisco activity and content. Total non‐structural carbohydrates (TNC) as a fraction of total dry mass increased from 12·8 ± 0·4% in 1‐year‐old needles from the 36 Pa grown trees to 14·2 ± 0·7% in 1‐year‐old needles from the 65 Pa grown trees and leaf nitrogen content decreased from 1·30 ± 0·02 to 1·09 ± 0·10 g m^?2. The current‐year needles were not of sufficient size for gas exchange measurements, but none of the biochemical parameters measured (Rubisco, leaf chlorophyll, TNC and N), were effected by growth in elevated CO₂. These results demonstrate that photosynthetic acclimation, which was not found in the first 2 years of this experiment, can develop over time in field‐grown trees and may be regulated by source‐sink balance, sugar feedback mechanisms and nitrogen allocation.     

Tree ring responses to elevated CO2 and increased N deposition in Picea abies

Four- to seven-year-old spruce trees (Picea abies) were exposed to three CO₂ concentrations (280, 420 and 560 cm³ m^?3) and three rates of wet N deposition (0, 30 and 90 kg ha^?1 year^?1) for 3 years in a simulated montane forest climate. Six trees from each of six clones were grown in competition in each of nine 100 × 70 × 36 cm model ecosystems with nutrient-poor natural forest soil. Stem dises were analysed using X-ray densitometry. The radial stem increment was not affected by [CO₂] but increased with increasing rates of N deposition. Wood density was increased by [CO₂], but decreased by N deposition. Wood-starch concentration increased, and wood nitrogen concentration decreased with increasing [CO₂], but neither was affected by N deposition. The lignin concentration in wood was affected by neither [CO₂] nor N deposition. Our results suggest that, under natural growth conditions, rising atmospheric [CO₂] will not lead to enhanced radial stem growth of spruce, but atmospheric N deposition will, and in some regions is probably already doing so. Elevated [CO₂], however, will lead to denser wood unless this effect is compensated by massive atmospheric N deposition. If can be speculated that greater wood density under elevated [CO₂] may alter the mechanical properties of wood, and higher ratios of C/N and lignin/N in wood grown at elevated [CO₂] may affect nutrient cycles of forest ecosystems.     

DECREASED RATE OF GLUCOSE UTILIZATION BY RAT BRAIN IN VIVO AFTER EXPOSURE TO ATMOSPHERES CONTAINING HIGH CONCENTRATIONS OF CO2

—(1) The effects of exposure of rats to increased atmospheric concentrations of CO₂ on brain metabolism in vivo were studied. (2) After 2·5 min exposure to an atmosphere of 20% CO₂, the rate of glucose utilization by brain decreased from 0·61 μmol/min per g to 0·32 μmol/min per g and remained between 0·3 and 0·4 μmol/min per g for 60 min, the longest interval studied. O₂ utilization, calculated from the arteriovenous difference of O₂ across the brain and blood flow, was 3·5 μmol/min per g in controls and was 4·7 μmol/min per g after 5 min in the 20% CO₂ atmosphere. (3) The concentrations of glucose, glucose 6-phosphate and aspartate were increased during the first 10 min of CO₂ exposure whereas the concentrations of other glycolytic intermediates, tricarboxylic acid cycle intermediates and glutamate were decreased. The amount of endogenous substrate which disappeared during the first 10 min was sufficient, if used to supplement glucose as a fuel, to maintain the O₂ consumption at, or slightly above, the control level. Glutamate and lactate were quantitatively the most important energy sources. (4) The mechanism whereby‘CO₂ decreased the rate of glucose utilization is uncertain. The initial rise in glucose 6-phosphate and fall in fructose 1,6-diphosphate concentrations suggested that an inhibition of phosphofructokinase was responsible. However, after 60 min in 20% CO₂, the concentrations of both of these metabolites returned to normal while the rate of glucose utilization remained depressed.     

Photosynthesis of Ectocarpus siliculosus in red light and after pulses of blue light at high pH – evidence for bicarbonate uptake

Pulses of blue light cause stimulation of red light saturated photosynthesis in Ectocarpus siliculosus, because blue light activates the operation of a pathway for inorganic carbon (C_i) acquisition by inducing the mobilization of CO₂ from an intermediate metabolite. In the absence of exogenous C_i, photosynthetic rates roughly equal those of CO₂ release by respiration. In seawater of pH 9·5 (2·3 mol m^–3 total C_i, but concentrations of free CO₂ below 0·2 mmol m^–3), photosynthesis was clearly above these rates, although they were only ≈ 30% of those in normal seawater (≈ pH 8). The degree and the time course of the stimulations of photosynthesis by pulses of blue light were unaltered at high pH. Essentially the same characteristics were found after buffering or in the presence of acetazolamide, an inhibitor of extracellular carbonic anhydrase activity. Therefore, it is concluded that Ectocarpus is able to directly take up HCO₃^– in addition to CO₂ (uptake of CO₃^2– cannot be excluded). The dependence of photosynthesis on C_i at pH 9·5 was biphasic, with C_i below 0·2 mol m^–3 having no effect at all. In C_i-free seawater, the shapes of the stimulations after blue light pulses differed for pH 6, pH 8 and pH 9·5. At low pH, only the fast peak (maximum ≈ 5 min after blue light) was detected, whereas at high pH mainly the slow peak (maximum ≈ 20 min after blue light) was observed. At the intermediate pH 8, both peaks were present. As inhibition of total carbonic anhydrase by ethoxyzolamide brought out the fast peak of the stimulations at pH 9·5 it is concluded that the fast component was due to a transient disequilibrium of an intracellular pool of C_i which, after blue light, was fed by CO₂ released from the postulated storage intermediate.     

Effect of elevated [CO2] on stem wood properties of mature Norway spruce grown at different soil nutrient availability

The objective of the present study was to investigate the interactive effects of elevated [CO₂] and soil nutrient availability on secondary xylem structure and chemical composition of 41‐year‐old Norway spruce (Picea abies (L.) Karst.) trees. The nonfertilized and irrigated‐fertilized trees were, for 3 years, continuously exposed to elevated [CO₂] in whole‐tree chambers. Elevated [CO₂] decreased concentrations of soluble sugars, acid‐soluble lignin and nitrogen in stem wood, but the effects were not consistent between sampling height and/or fertilization. The effect of 2*ambient [CO₂] on wood structure depended on the exposure year and/or fertilization. Radial lumen diameter decreased and annual ring width increased in the second year of exposure (1999) in elevated [CO₂]. In the latter, the CO₂ effect was significant only in the nonfertilized trees. Stem wood chemistry and structure were significantly affected by fertilization. Fertilization increased the concentrations of nitrogen and gravimetric lignin, annual ring width, and radial lumen diameter. Fertilization decreased C/N ratio, mean ring density, earlywood density, latewood density, cell wall thickness, cell wall index, and latewood percentage. We conclude that elevated [CO₂] had only minor effects on wood properties while fertilization had more marked effects and thus may affect ecosystem processes and suitability of wood for different end‐use purposes.     

Carbon-based secondary metabolites and internal nitrogen pools in Populus nigra under Free Air CO2 Enrichment (FACE) and nitrogen fertilisation

The goal of this study was to investigate whether increased nitrogen use efficiency found in Populus nigra L. (Jean Pourtet) under elevated CO₂ would correlate with changes in the production of carbon-based secondary compounds (CBSCs). Using Free-Air CO₂ Enrichment (FACE) technology, a poplar plantation was exposed to either ambient (about 370 μmol mol⁻¹ CO₂) or elevated (about 550 μmol mol⁻¹ CO₂) [CO₂] for 5 years. After three growing seasons, the plantation was coppiced and half of the experimental plots were fertilized with nitrogen. CBSCs, total nitrogen and lignin-bound nitrogen were quantified in secondary sprouts in seasons of active growth and dormancy during 2 years after coppicing. Neither elevated CO₂ nor nitrogen fertilisation alone or in combination influenced lignin concentrations in wood. Soluble phenolics and soluble proteins in wood decreased slightly in response to elevated CO₂. Higher nitrogen supply stimulated formation of CBSCs and increased protein concentrations. Lignin-bound nitrogen in wood ranged from 0.37–1.01 mg N g⁻¹ dry mass accounting for 17–26% of total nitrogen in wood, thus, forming a sizeable nitrogen fraction resistant to chemical degradation. The concentration of this nitrogen fraction was significantly decreased by elevated CO₂, increased in response to nitrogen fertilisation and showed a significant CO₂ × fertilisation interaction. Seasonal changes markedly affected the internal nitrogen pools. Soluble proteins in wood were 52–143% higher in the dormant than in the growth season. Positive correlations existed between the biosynthesis of proteins and CBSCs. The limited responses to elevated CO₂ and nitrogen fertilisation indicate that growth and defence are well orchestrated in P. nigra and that changes in the balance of both resources—nitrogen and C—have only marginal effects on wood chemistry. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of carbon dioxide enrichment, ozone and nitrogen fertilization on cotton (Gossypium hirsutum L.) leaf and root composition

The objective of this study was to test whether elevated [CO₂], [O₃] and nitrogen (N) fertility altered leaf mass per area (LMPA), non‐structural carbohydrate (TNC), N, lignin (LTGA) and proanthocyanidin (PA) concentrations in cotton (Gossypium hirsutum L.) leaves and roots. Cotton was grown in 14 dm³ pots with either sufficient (0·8 g N dm ^{? 3}) or deficient (0·4 and 0·2 g N dm ^{? 3}) N fertilization, and treated in open‐top chambers with either ambient or elevated ( + 175 and + 350 μ mol mol ^{? 1}) [CO₂] in combination with either charcoal‐filtered air (CF) or non‐filtered air plus 1·5 times ambient [O₃]. At about 50 d after planting, LMPA, starch and PA concentrations in canopy leaves were as much as 51–72% higher in plants treated with elevated [CO₂] compared with plants treated with ambient [CO₂], whereas leaf N concentration was 29% lower in elevated [CO₂]‐treated plants compared with controls. None of the treatments had a major effect on LTGA concentrations on a TNC‐free mass basis. LMPA and starch levels were up to 48% lower in plants treated with elevated [O₃] and ambient [CO₂] compared with CF controls, although the elevated [O₃] effect was diminished when plants were treated concurrently with elevated [CO₂]. On a total mass basis, leaf N and PA concentrations were higher in samples treated with elevated [O₃] in ambient [CO₂], but the difference was much reduced by elevated [CO₂]. On a TNC‐free basis, however, elevated [O₃] had little effect on tissue N and PA concentrations. Fertilization treatments resulted in higher PA and lower N concentrations in tissues from the deficient N fertility treatments. The experiment showed that suppression by elevated [O₃] of LMPA and starch was largely prevented by elevated [CO₂], and that interpretation of [CO₂] and [O₃] effects should include comparisons on a TNC‐free basis. Overall, the experiment indicated that allocation to starch and PA may be related to how environmental factors affect source–sink relationships in plants, although the effects of elevated [O₃] on secondary metabolites differed in this respect.     

Influence of free air CO2 enrichment (EUROFACE) and nitrogen fertilisation on the anatomy of juvenile wood of three poplar species after coppicing

Populus × euramericana, P. alba, and P. nigra clones were exposed to ambient or elevated (about 550 ppm) CO₂ concentrations under field conditions (FACE) in central Italy. After three growing seasons, the plantation was coppiced. FACE was continued and in addition, one-half of each experimental plot was fertilised with nitrogen. Growth and anatomical wood properties were analysed in secondary sprouts. In the three poplar clones, most of the growth and anatomical traits showed no uniform response pattern to elevated [CO₂] or N-fertilisation. In cross-sections of young poplar stems, tension wood amounted to 2–10% of the total area and was not affected by elevated CO₂. In P. nigra, N-fertilisation caused an about twofold increase in tension wood, but not in the other clones. The formation of tension wood was not related to diameter or height growth of the shoots. In P. × euramericana N-fertilisation resulted in significant reductions in fibre lengths. In all three genotypes, N-fertilisation caused significant decreases in cell wall thickness. In P. × euramericana and P. alba elevated [CO₂] also caused decreases in wall thickness, but less pronounced than nitrogen. In P. nigra and P. × euramericana elevated [CO₂] induced increases in vessel diameters. These results show that elevated [CO₂] and N-fertilisation affect wood structural development in a clone specific manner. However, the combination of these environmental factors resulted in overall losses in cell wall area of 5–12% in all three clones suggesting that in future climate scenarios negative effects on wood quality are to be anticipated if increases in atmospheric CO₂ concentration were accompanied by increased N availability.     

Future wood productivity of Pinus radiata in New Zealand under expected climatic changes

The physiologically based growth model CenW was used to simulate wood‐productivity responses of Pinus radiata forests to climate change in New Zealand. The model was tested under current climatic conditions against a comprehensive set of observations from growth plots located throughout the country. Climate change simulations were based on monthly climate change fields of 12 GCMs forced by the SRES B1, A1B and A2 emission scenarios for 2040 and 2090. Simulations used either constant or increasing CO₂ concentrations corresponding to the different emission scenarios. With constant CO₂, there were only slight growth responses to climate change across the country as a whole. More specifically, there were slight growth reductions in the warmer north but gains in the cooler south, especially at higher altitudes. For sites where P. radiata is currently grown, and across the full suite of GCMs and emission scenarios, changes in wood productivity averaged +3% for both 2040 and 2090. When increasing CO₂ concentration was also included, responses of wood productivity were generally positive, with average increases of 19% by 2040 and 37% by 2090. These responses varied regionally, ranging from relatively minor changes in the north of the country to very significant increases in the south, where the beneficial effect of increasing CO₂ combined with the beneficial effect of increasing temperatures. These relatively large responses to CO₂ depend on maintenance of the current adequate fertility levels in most commercial plantations. Productivity enhancements came at the expense of some soil‐carbon losses. Average losses for the country were simulated to average 3.5% under constant CO₂ and 1.5% with increasing CO₂ concentration. Again, there were regional differences, with larger losses for regions with lesser growth enhancements, and lesser reductions in regions where greater productivity enhancements could partly balance the effect of faster decomposition activity.     

Annual wood production in a tropical rain forest in NE Costa Rica linked to climatic variation but not to increasing CO2

Increased atmospheric [CO₂] could theoretically lead to increased forest productivity (‘CO₂ fertilization’). This mechanism was hypothesized as a possible explanation for biomass increases reported from tropical forests in the last 30+ years. We used unique long‐term records of annually measured stands (eighteen 0.5 ha plots, 10 years) and focal tree species (six species, 24 years) to assess the effects of rainfall, temperature, and atmospheric [CO₂] on annual wood production in a neotropical rain forest. Our study area was a meso‐scale section (600 ha) of old‐growth Tropical Wet Forest in NE Costa Rica. Using the repeated remeasurements we directly assessed the relative effects of interannual climatic variation and increasing atmospheric [CO₂] on wood production. A remarkably simple two‐factor model explained 91% of the interannual variance in stand‐level tree growth; the statistically independent factors were total dry season rainfall (positive effect, r²=0.85) and night‐time temperature (negative effect, r²=0.42). Stand‐level tree mortality increased significantly with night‐time temperature. After accounting for dry season rainfall and night‐time temperature, there was no effect of annual [CO₂] on tree growth in either the stand or focal species data. Tree growth in this Tropical Wet Forest was surprisingly sensitive to the current range of dry season conditions and to variations in mean annual night‐time temperature of 1–2°. Our results suggest that wood production in the lowland rainforests of NE Costa Rica (and by extension in other tropical regions) may be severely reduced in future climates that are only slightly drier and/or warmer.     

PRIMARY PRODUCTION,CALCIFICATION, AND AIR-SEA CO2 FLUXES OF A MACROALGAL-DOMINATED CORAL REEF COMMUNITY (MOOREA,FRENCH POLYNESIA)1

Community metabolism and air-sea carbon dioxide (CO₂) fluxes were investigated in July 1992 on a fringing reef at Moorea (French Polynesia). The benthic community was dominated by macroalgae (85% substratum cover) and comprised of Phaeophyceae Padina tenuis (Bory), Turbinaria ornata (Turner) J. Agardh, and Hydroclathrus clathratus Bory (Howe); Chlorophyta Halimeda incrassata f. ovata J. Agardh (Howe); and Ventricaria ventricosa J. Agardh (Olsen et West), as well as several Rhodophyta (Actinotrichia fragilis Forskál (Børgesen) and several species of encrusting coralline algae). Algal biomass was 171 g dry weight· m^?2. Community gross production (P_g), respiration (R), and net calcification (G) were measured in an open-top enclosure. P_g and R were respectively 248 and 240 mmol Co₂·m^?2·d^?1, and there was a slight net dissolution of CaCO₃ (0.8 mmol · m^?2·d^?1). This site was a sink for atmospheric CO₂ (10 ± 4 mmol CO₂·m^?2·d^?1), and the analysis of data from the literature suggests that this is a general feature of algal-dominated reefs. Measurement of air-sea CO₂ fluxes in open water close to the enclosure demonstrated that changes in small-scale hydrodynamics can lead to misleading conclusions. Net CO₂ evasion to the atmosphere was measured on the fringing reef due to changes in the current pattern that drove water from the barrier reef (a C0₂ source) to the study site.