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The function of landscape plants on the ecosystem can alleviate environmental issues of urbanization and global change. Global changes due to elevated CO 2 affect plant growth and survival, but there is a lack of quantitative methods to evaluate the adaptability of landscape plants to future climate conditions. Leaf traits characterized by leaf economic spectrum (LES) are the universal currency for predicting the impact on plant ecosystem functions. Elevated CO 2 usually leads to photosynthetic acclimation (PC), characterised by decreased photosynthetic capacity. Here, we proposed a theoretical and practical framework for the use of LES and PC to project the potential performance of landscape plants under future climatic conditions through principal component analysis, structural equation modelling, photosynthetic restriction analysis and nitrogen allocation analysis. We used wintersweet (an important landscaping species) to test the feasibility of this framework under elevated CO 2 and different nitrogen (N) supplies. We found that elevated CO 2 decreased the specific leaf area but increased leaf N concentration. The results suggest wintersweet may be characterized by an LES with high leaf construction costs, low photosynthetic return, and robust stress resistance. Elevated CO 2 reduced photosynthetic capacity and stomatal conductance but increased photosynthetic rate and leaf area. These positive physio-ecological traits, e.g., larger leaf area (canopy), higher water use efficiency and stress resistance, may lead to improved performance of wintersweet under the predicted future climatic conditions. The results suggest planting more wintersweet in urban landscaping may be an effective adaptive strategy to climate change., (© 2024 Scandinavian Plant Physiology Society.)

Elevated CO2 and warmer temperature occur simultaneously under the current climate change. However, their combined effects on the photosynthetic traits in boreal trees are not well understood. This study investigated the morphological and photosynthetic responses of yellow birch (Betula alleghaniensis Britt.) to a combined treatment of CO2 and temperature (ambient, ACT (400 μmol mol-1 CO2 and current temperature) vs elevated, ECT (750 μmol mol-1 CO2 and current +4 °C temperature)). It was found that ECT significantly reduced leaf-area based photosynthetic rate (An), maximum Rubisco carboxylation rate (Vcmax), photosynthetic electron transport rate (Jmax), leaf nitrogen concentration, respiration and mesophyll conductance. There were two interesting findings: first, the primary mechanism of photosynthetic limitation shifted from Ribulose-1,5-bisphosphate (RuBP) carboxylation (related to Vcmax) to RuBP regeneration (related to Jmax) in response to ECT, leading to decreased transition point (Ci-t and An-t) from RuBP carboxylation to regeneration; second, the increase in total leaf area in response to ECT more than compensated for the downregulation of leaf-area based photosynthesis, leading to greater biomass in ECT than in ACT. We proposed a new protocol for evaluating photosynthetic limitations by comparing the relative relationship between the transition point (Ci-t and An-t) and the photosynthetic rate at growth CO2 (Ci-g and An-g). Furthermore, we found that Jmax (RuBP regeneration) was the primary limitation to An under ECT., (© The Author(s) 2022. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

In response to global warming, trees are expected to shift their distribution ranges to higher latitudes. The range shift will expose them to novel environmental conditions, such as new photoperiod regimes. These factors can interact with rising atmospheric CO 2 ([CO 2 ]) to affect trees' physiology and growth. This study simulated future environmental conditions to investigate photosynthetic responses to changes in photoperiod regimes (seed origin [48°N], 52, 55, and 58°N) and [CO 2 ] (ambient 400 vs. elevated 1000 μmol mol -1 ) in white birch (Betula papyrifera Marsh.) seedlings. Our results show that elevated [CO 2 ] stimulated leaf photosynthesis (P n ) at the two lower latitudes (48 and 52°N). However, this stimulation by elevated [CO 2 ] was lost in the two higher latitudes (55 and 58°N). Elevated [CO 2 ] led to the downregulation of maximum Rubisco activity (V cmax ) for the two higher latitudes, and maximum electron transport rate (J max ) and triose phosphate utilization (TPU) at 58°N, while it enhanced J max and TPU for the two lower latitudes. Increased instantaneous water-use efficiency (IWUE) for the two lower latitudes was primarily attributed to the CO 2 stimulation of P n while the higher IWUE under the photoperiod regimes of 55 and 58°N latitudes was explained by reduced water loss. Photoperiod effects varied with [CO 2 ]: P n increased at the photoperiod regimes of 55 and 58°N in ambient [CO 2 ] while it tended to decline under these photoperiods in elevated [CO 2 ]. Our study suggests that the photosynthesis of white birch will likely respond negatively to northward migration or seed transfer in response to climate change., (© 2020 Scandinavian Plant Physiology Society.)

Global climate change is expected to affect how plants respond to their physical and biological environments. In this study, we examined the effects of elevated CO2 ([CO2]) and low soil moisture on the physiological responses of mountain maple (Acer spicatum L.) seedlings to light availability. The seedlings were grown at ambient (392 µmol mol(-1)) and elevated (784 µmol mol(-1)) [CO2], low and high soil moisture (M) regimes, at high light (100%) and low light (30%) in the greenhouse for one growing season. We measured net photosynthesis (A), stomatal conductance (g s), instantaneous water use efficiency (IWUE), maximum rate of carboxylation (V cmax), rate of photosynthetic electron transport (J), triose phosphate utilization (TPU)), leaf respiration (R d), light compensation point (LCP) and mid-day shoot water potential (Ψx). A and g s did not show significant responses to light treatment in seedlings grown at low soil moisture treatment, but the high light significantly decreased the C i/C a in those seedlings. IWUE was significantly higher in the elevated compared with the ambient [CO2], and the effect was greater at high than the low light treatment. LCP did not respond to the soil moisture treatments when seedlings were grown in high light under both [CO2]. The low soil moisture significantly reduced Ψx but had no significant effect on the responses of other physiological traits to light or [CO2]. These results suggest that as the atmospheric [CO2] rises, the physiological performance of mountain maple seedlings in high light environments may be enhanced, particularly when soil moisture conditions are favourable.

To study the effects of source-sink ratio and nutrient supply on photosynthetic acclimation to CO(2) elevation, we subjected white birch seedlings to two levels of nutrient supply (high vs. low) and CO(2) concentrations (ambient vs. doubled [CO(2)]) for two months and then shaded the lower canopy on half of the seedlings to reduce source/sink ratio for an additional month. The CO(2) elevation significantly increased P(n) and IWUE at both nutrient levels but the increase was greater in the high than low nutrient treatment. The CO(2) elevation resulted in a down-regulation of V(cmax) in the low nutrient treatment but up-regulation of J(max), TPU, [Formula: see text] and J(c) in the high nutrient after 3 months of treatment. Both the CO(2) elevation and high nutrient supply increased the partition of total electron transport to carboxylation at the expense of oxidation. The seedlings responded to the shading of the lower canopy by reducing biomass allocation to roots rather than making physiological adjustments to unshaded leaves in the upper canopy. Our results suggest that the direction of photosynthetic acclimation to CO(2) elevation in white birch was nutrient-dependent and an increase in sink strength could reduce the feedback inhibition of photosynthesis., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

To investigate the interactive effects of soil temperature (T(soil)) and nutrient availability on the response of photosynthesis to elevated atmospheric carbon dioxide concentration ([CO(2)]), white birch (Betula papyrifera Marsh.) seedlings were exposed to ambient (360 micromol mol(-1)) or elevated (720 micromol mol(-1)) [CO(2)], three T(soil) (5, 15 and 25 degrees C initially, increased to 7, 17 and 27 degrees C, respectively, 1 month later) and three nutrient regimes (4/1.8/3.3, 80/35/66 and 160/70/132 mg l(-1) N/P/K) for 3 months in environment-controlled greenhouses. Elevated [CO(2)] increased net photosynthetic rate (A(n)), instantaneous water-use efficiency (IWUE), internal to ambient carbon dioxide concentration ratio (C(i)/C(a)), triose phosphate utilization (TPU) and photosynthetic linear electron transport to carboxylation (J(c)), and it decreased actual photochemical efficiency of photosystem II (DeltaF/F(m)'), the fraction of total linear electron transport partitioned to oxygenation (J(o)/J(T)) and leaf N concentration. The low T(soil) suppressed A(n), transpiration rate (E), TPU, DeltaF/F(m)' and J(c), but it increased J(o)/J(T). The low nutrient treatment reduced A(n), IWUE, maximum carboxylation rate of Rubisco, light-saturated electron transport rate, TPU, DeltaF/F(m)', J(c) and leaf N concentration, but increased C(i)/C(a). There were two-factor interactions for C(i)/C(a), TPU and leaf N concentration, and a significant effect of CO(2) x T(soil) x nutrient regime on A(n), IWUE and J(c). The stimulations of A(n) and IWUE by elevated [CO(2)] were limited to seedlings grown under the intermediate and high nutrient regimes at the intermediate and high T(soil). For J(c), the [CO(2)] effect was significant only at intermediate T(soil) + high nutrient availability. No significant [CO(2)] effects were observed under the low T(soil) at any nutrient level. Our results support this study's hypothesis that low T(soil) would reduce the positive effect of high nutrient supply on the response of A(n) to elevated [CO(2)].

White birch (Betula papyrifera Marsh.) seedlings were grown under two carbon dioxide concentrations (ambient: 360 micromol mol(-1) and elevated: 720 micromol mol(-1)), three soil temperatures (5, 15 and 25 degrees C initially, increased to 7, 17 and 27 degrees C, respectively, 1 month later) and three moisture regimes (low: 30-40%; intermediate: 45-55% and high: 60-70% field water capacity) in greenhouses. In situ gas exchange and chlorophyll fluorescence were measured after 2 months of treatments. Net photosynthetic rate (A(n)) of seedlings grown under the intermediate and high moisture regimes increased from low to intermediate T(soil) and then decreased to high T(soil). There were no significant differences between the low and high T(soil), with the exception that A(n) was significantly higher under high than low T(soil) at the high moisture regime. No significant T(soil) effect on A(n) was observed at the low moisture regime. The intermediate T(soil) increased stomatal conductance (g(s)) only at intermediate and high but not at low moisture regime, whereas there were no significant differences between the low and high T(soil) treatments. Furthermore, the difference in g(s) between the intermediate and high T(soil) at high moisture regime was not statistically significant. The low moisture regime significantly reduced the internal to ambient CO2 concentration ratio at all T(soil). There were no significant individual or interactive effects of treatment on maximum carboxylation rate of Rubisco, light-saturated electron transport rate, triose phosphate utilization or potential photochemical efficiency of photosystem II. The results of this study suggest that soil moisture condition should be taken into account when predicting the responses of white birch to soil warming.

To study the effects of elevated CO2 concentration ([CO2]) on relationships between nitrogen (N) nutrition and foliar gas exchange parameters, white birch (Betula papyrifera Marsh.) seedlings were exposed to one of five N-supply regimes (10, 80, 150, 220, 290 mg N l(-1)) in either ambient [CO2] (360 micromol mol(-1)) or elevated [CO2] (720 micromol mol(-1)) in environment-controlled greenhouses. Foliar gas exchange and chlorophyll fluorescence were measured after 60 and 80 days of treatment. Photosynthesis showed a substantial down-regulation (up to 57%) in response to elevated [CO2] and the magnitude of the down-regulation generally decreased exponentially with increasing leaf N concentration. When measured at the growth [CO2], elevated [CO2] increased the overall rate of photosynthesis (P(n)) and instantaneous water-use efficiency (IWUE) by up to 69 and 236%, respectively, but decreased transpiration (E) and stomatal conductance (g(s)) in all N treatments. However, the degree of stimulation of photosynthesis by elevated [CO2] decreased as photosynthetic down-regulation increased from 60 days to 80 days of treatment. Elevated [CO2] significantly increased total photosynthetic electron transport in all N treatments at 60 days of treatment, but the effect was insignificant after 80 days of treatment. Both P(n) and IWUE generally increased with increasing leaf N concentration except at very high leaf N concentrations, where both P(n) and IWUE declined. The relationships of P(n) and IWUE with leaf N concentration were modeled with both a linear regression and a second-order polynomial function. Elevated [CO2] significantly and substantially increased the slope of the linear regression for IWUE, but had no significant effect on the slope for P(n). The optimal leaf N concentration for P(n) and IWUE derived from the polynomial function did not differ between the CO2 treatments when leaf N was expressed on a leaf area basis. However, the mass-based optimal leaf N concentration for P(n) was much lower in seedlings in elevated [CO2] than in ambient [CO2] (31.88 versus 37.00 mg g(-1)). Elevated [CO2] generally decreased mass-based leaf N concentration but had no significant effect on area-based leaf N concentration; however, maximum N concentration per unit leaf area was greater in elevated [CO2] than in ambient [CO2] (1.913 versus 1.547 g N m(-2)).

To investigate the interactive effects of atmospheric carbon dioxide concentration ([CO(2)]) and nutrition on photosynthesis and its acclimation to elevated [CO(2)], a two-way factorial experiment was carried out with two nutritional regimes (high- and low-nitrogen (N), phosphorus (P) and potassium (K)) and two CO(2) concentrations (360 and 720 ppm) with white birch seedlings (Betula papyrifera Marsh.) grown for four months in environment-controlled greenhouses. Elevated [CO(2)] enhanced maximal carboxylation rate (V(cmax)), photosynthetically active radiation-saturated electron transport rate (J(max)), actual photochemical efficiency of photosystem II (PSII) in the light (DeltaF/F(m)') and photosynthetic linear electron transport to carboxylation (J(c)) after 2.5 months of treatment, and it increased net photosynthetic rate (A(n)), photosynthetic water-use efficiency (WUE), photosynthetic nitrogen-use efficiency (NUE) and photosynthetic phosphorus-use efficiency (PUE) after 2.5 and 3.5 months of treatment, but it reduced stomatal conductance (g(s)), transpiration rate (E) and the fraction of total photosynthetic linear electron transport partitioned to oxygenation (J(o)/J(T)) after 2.5 and 3.5 months of treatment. Low nutrient availability decreased A(n), WUE, V(cmax), J(max), triose phosphate utilization (TPU), (/F(m)' - F)//F(m)' and J(c), but increased J(o)/J(T) and NUE. Generally, V(cmax) was more sensitive to nutrient availability than J(max). There were significant interactive effects of [CO(2)] and nutrition over time, e.g., the positive effects of high nutrition on A(n), V(cmax), J(max), DeltaF/F(m)' and J(c) were significantly greater in elevated [CO(2)] than in ambient [CO(2)]. In contrast, the interactive effect of [CO(2)] and nutrition on NUE was significant after 2.5 months of treatment, but not after 3.5 months. High nutrient availability generally increased PUE after 3.5 months of treatment. There was evidence for photosynthetic up-regulation in response to elevated [CO(2)], particularly in seedlings receiving high nutrition. Photosynthetic depression in response to low nutrient availability was attributed to biochemical limitation (or increased mesophyll resistance) rather than stomatal limitation. Elevated [CO(2)] reduced leaf N concentration, particularly in seedlings receiving low nutrition, but had no significant effect on leaf P or K concentration. High nutrient availability generally increased area-based leaf N, P and K concentrations, but had negligible effects on K after 2.5 months of treatment.

One-year-old jack pine (Pinus banksiana Lamb.) and current-year white birch (Betula papyrifera Marsh.) seedlings were grown in ambient (360 ppm) or twice ambient (720 ppm) atmospheric CO2 concentration ([CO2]) and at three soil temperatures (Tsoil = 7, 17 and 27 degrees C initially, increased to 10, 20 and 30 degrees C two months later, respectively) in a greenhouse for 4 months. In situ foliar gas exchange, in vivo carboxylation characteristics and chlorophyll fluorescence were measured after 2.5 and 4 months of treatment. Low Tsoil suppressed net photosynthetic rate (Pn), stomatal conductance (g(s)) and transpiration rate (E) in jack pine in both CO2 treatments and g(s) and E in white birch in ambient [CO2], but enhanced instantaneous water-use efficiency (IWUE) in both species after 2.5 months of treatment. Treatment effects on g(s) and E remained significant throughout the 4-month study. Low Tsoil reduced maximal carboxylation rate (Vcmax) and PAR-saturated electron transport rate (Jmax) in jack pine in elevated [CO2] after 2.5 months of treatment, but not after 4 months of treatment. Low Tsoil increased actual photochemical efficiency of photosystem II (PSII) in the light (DeltaF/Fm') in jack pine, but decreased DeltaF/Fm' in white birch after 4 months of treatment. In response to low Tsoil, photosynthetic linear electron transport to carboxylation (Jc) decreased in jack pine after 2.5 months and in white birch after 4 months of treatment. Low Tsoil increased the ratio of the photosynthetic linear electron transport to oxygenation (Jo) to the total photosynthetic linear electron transport rate through PSII (Jo/J(T)) in both species after 2.5 months of treatment, but the effects became statistically insignificant in white birch after 4 months of treatment. High Tsoil decreased foliar N concentration in white birch. Elevated [CO2] increased Pn, IWUE and Jc but decreased Jo/J(T) in both species at both measurement times except Jc in white birch after 2.5 months of treatment. Elevated [CO2] also decreased g(s) and E in white birch at high Tsoil, Vcmax in both species and triose phosphate utilization in white birch at low Tsoil after 4 months of treatment, and DeltaF/Fm' in white birch after 2.5 months of treatment. Elevated [CO2] also increased foliar N concentration in both species. Low Tsoil caused no permanent damage to PSII in either species, but jack pine responded and acclimated to low Tsoil more quickly than white birch. Photosynthetic down-regulation and a decrease in photosynthetic electron transport to photorespiration occurred in both species in response to elevated [CO2].

Trees may migrate northward in response to climate change and become exposed to new photoperiod and soil moisture regimes. This study assessed the impacts of photoperiod and its interaction with soil moisture and carbon dioxide concentration ([CO2]) on the hydraulic conductivity in jack pine ( Pinus banksiana Lamb.) and its vulnerability to xylem embolism. Seedlings were exposed to 400 vs. 950 μmol·mol−1 [CO2], 60%-70% vs. 30%-40% (of field capacity) soil moisture, and photoperiods of seed origin and 5° and 10° north of seed origin in greenhouses. Cavitation vulnerability curves were measured for determining the xylem pressure at which 50% hydraulic conductivity was lost (ΨPLC50). It was found that elevated [CO2] significantly increased hydraulic conductivity, whereas low soil moisture decreased it. Under elevated [CO2], the xylem became progressively more vulnerable to embolism with changes in photoperiod regime from the seed origin to 10° north of the seed origin, as indicated by the progressively less negative ΨPLC50. However, no such a trend was detected under the ambient [CO2]. The results suggest that the species may become less resistant to drought as the atmospheric [CO2] increases, hindering the northward migration or seed transfers. Even within its current natural distribution range, trees near its northern boundary of the range may be more vulnerable to embolism as the atmospheric [CO2] increases even without any change in moisture conditions. [ABSTRACT FROM AUTHOR]

Climate change will cause northward shifts of climate envelopes for boreal plants, however, the different photoperiod and soil moisture regimes at higher latitudes will likely influence the success of species migrations (natural and assisted). The objective of this study was to assess the effects of photoperiod regime and its interactions with soil moisture and carbon dioxide concentration ([CO2]) on the morpho-physiological processes in jack pine Pinus banksiana. One-year old seedlings were exposed to two [CO2] (400 and 950 μmol mol-1), two soil moistures (60-70% and 30-40% of field water capacity) and three photoperiod regimes (photoperiods at seed origin, 5° and 10° north of the seed origin) in environment controlled greenhouses. The impacts of photoperiod, soil moisture and elevated [CO2] on growth and physiological processes in the seedlings were examined. The results suggest that the response of jack pine to climate change will be complex under the interactive effects of northward migration associated longer photoperiod, soil moisture stress and elevated [CO2]. The longer photoperiod associated with higher latitudes under elevated [CO2] significantly advanced the budburst at both high and low soil moisture regimes, which may likely increase the risk of late spring frosts damage prior to and during budburst. The interactive effects of longer photoperiod and low soil moisture significantly increased the water use efficiency under elevated [CO2]. However, the significant 2- and 3-way interactions suggest that drought and longer photoperiods with northward migration will limit the positive effects of elevated [CO2] on growth and physiological processes in the species. These results might have important implications in assisted migration/seed transfer of the species following climate change. [ABSTRACT FROM AUTHOR]

Aims Some shade-tolerant understory tree species such as mountain maple (Acer spicatum L.) exhibit light-foraging growth habits. Changes in environmental conditions, such as the rise of carbon dioxide concentration ([CO2]) in the atmosphere and soil warming, may affect the performance of these species under different light environments. We investigated how elevated [CO2] and soil warming influence the growth and biomass responses of mountain maple seedlings to light availability. Methods The treatments were two levels of light (100% and 30% of the ambient light in the greenhouse), two [CO2] (392 µmol mol−1 (ambient) and 784 µmol mol−1(elevated)) and two soil temperatures (Tsoil) (17 and 22°C). After one growing season, we measured seedling height, root collar diameter, leaf biomass, stem biomass and root biomass. Important findings We found that under the ambient [CO2], the high-light level increased seedlings height by 70% and 56% at the low Tsoil and high Tsoil, respectively. Under the elevated [CO2], however, the high-light level increased seedling height by 52% and 13% at the low Tsoil and high Tsoil, respectively. The responses of biomasses to light generally followed the response patterns of height growth under both [CO2] and Tsoil and the magnitude of biomass response to light was the lowest under the elevated [CO2] and warmer Tsoil. The results suggest that the elevated [CO2] and warmer Tsoil under the projected future climate may have negative impact on the colonization of open sites and forest canopy gaps by mountain maple. [ABSTRACT FROM AUTHOR]

Abstract: CO2 elevation stimulates plant growth, which in turn demands more nutrients to sustain. Since the increase of demand for nitrogen (N), phosphorus (P) and potassium (K) may be in different proportions, the optimal N–P–K ratios at elevated [CO2] are likely different from those at the ambient [CO2]. This study investigated the effects of various N supply levels with constant and variable (constant P and K concentrations) N–P–K ratios under ambient and elevated [CO2] on black spruce (Picea mariana Mill. BSP) seedlings. One-year-old seedlings were exposed to two [CO2] (370 vs. 720μmolmol−1), two nutrient ratio regimes (constant vs. variable N/P/K ratios) and six N concentrations (10, 80, 150, 220, 290 and 360μmolmol−1) in four environmentally controlled greenhouses for 3.5months. Growth response to N varied with [CO2] and N/P/K ratios: under the elevated [CO2], height growth increased with increasing N supply when P and K concentrations were kept constant across different N levels, but it only increased when increasing N from 10 to 150μmolmol−1, and started to decline with further increase in N supply when N/P/K ratios were kept constant at different N levels; at the ambient [CO2], height growth was greatest at 150μmolmol−1 N and was generally greater at 220–360 than at 10 and 80μmolmol−1 N in both nutrient ratio treatments. The foliage to root ratio, shoot mass ratio and total biomass generally increased with increasing N supply but root mass ratio decreased. The smallest specific leaf area occurred at the lowest N supply when N/P/K ratios were kept constant but at 220μmolmol−1 N when P and K concentrations were kept constant across different N supplies. The results of leaf nutrient concentrations suggest that the elevated [CO2] increased demand for N, P and K and the increase for N was greater than P and K, altering the relationship between growth and nitrogen supply. Under the elevated [CO2], high N supplies resulted in growth suppression by critical toxicity content only in the constant N/P/K ratios treatment but low N supplies led to growth suppression by critical deficiency content in both nutrient ratio treatments. At the ambient [CO2], in contrast, N/P/K ratio treatments did not affect growth suppression by critical deficiency or critical toxicity content. Because elevated CO2 causes unequal increases in N, P and K demands, N–P–K ratios should be considered when modeling plant growth responses to elevated CO2. [Copyright &y& Elsevier]

CO2–light interactions can influence the competition among boreal plants, but are poorly understood. We investigated the effect of such interactions on the growth and biomass of 1-year-old black spruce (Sb) (Picea mariana (Mill.) BSP) and white spruce (Sw) (Picea glauca (Moench) Voss) grown with CO2 concentrations ([CO2]) of 360 and 720 µmol·mol–1 under 30%, 50%, and 100% light, in greenhouses. There were significant two-way and three-way interactions. Root collar diameter (RCD) of Sw decreased with decreasing light, while in Sb, there was no significant difference in RCD for plants grown under 50% or 30% light. Height was greater for plants grown under 100% light than if the plants were shaded. Elevated [CO2] increased RCD by 33% and enhanced stem volume by 67%, 98%, and 84% under 100%, 50%, and 30% light, respectively. The CO2 enhancement of total biomass was relatively higher under lower light, and greater for Sb than Sw. Elevated [CO2] decreased specific leaf area under 50% light only. Root mass was generally higher under 100% light than when shaded. Elevated [CO2] increased the root mass of Sb under 100% light, but decreased it under 30% light. Elevated [CO2] decreased the shoot/root ratio under 100% light, but increased it under 30% light. Our data suggest that raising [CO2] will likely increase species competitiveness under low light conditions, and that the increase will be greater in species that are relatively shade tolerant. [ABSTRACT FROM AUTHOR]

Abstract: This paper will discuss TRIPLEX-Flux, a process-based model that estimates net ecosystem production (NEP) as well as analyzing the level of sensitivity of the model''s response by simulating CO2 flux in an existing old black spruce BOREAS site in central Canada. The research objectives were: (1) to test the TRIPLEX-Flux model simulations against flux tower measurements; and (2) to examine parameter and input variable effects on model response via sensitivity analysis. Validation of NEP data at 30min intervals derived from tower and chamber measurements showed that the NEP data from the model corresponded well with the measured NEP from the BOREAS site (R 2 >0.65). Sensitivity analysis demonstrated different levels of sensitivity between morning and noon periods and from the current to doubled atmospheric CO2 concentrations. Additionally, the comparison of different algorithms to calculate stomatal conductance showed that the NEP predicted by the model using the iteration algorithm was consistent with the results using a constant C i/C a of 0.74 for current and 0.81 for doubled CO2 concentrations. Varying parameter and input variable values by ±10% resulted in a similar model response between morning and noon periods (less than or equal to 27.6% and 27.4%, respectively). Most parameters were more sensitive at noon than they were in the morning except for those that were correlated with air temperature, suggesting that air temperature has considerable influence over model sensitivity for these parameters/variables. Air temperature effect was greater under doubled than it was under current atmospheric CO2 concentrations. In contrast, model sensitivity to CO2 decreased under doubled CO2 concentrations. [Copyright &y& Elsevier]