Acclimation of photosynthesis and respiration to elevated atmospheric CO2 in two Scrub Oaks

Abstract For two species of oak, we determined whether increasing atmospheric CO₂ concentration (C_a) would decrease leaf mitochondrial respiration (R) directly, or indirectly owing to their growth in elevated C_a, or both. In particular, we tested whether acclimatory decreases in leaf‐Rubisco content in elevated C_a would decrease R associated with its maintenance. This hypothesis was tested in summer 2000 on sun and shade leaves of Quercus myrtifolia Willd. and Quercus geminata Small. We also measured R on five occasions between summer 1999 and 2000 on leaves of Q. myrtifolia. The oaks were grown in the field for 4 years, in either current ambient or elevated (current ambient + 350 µmol mol^?1) C_a, in open‐top chambers (OTCs). For Q. myrtifolia, an increase in C_a from 360 to 710 µmol mol^?1 had no direct effect on R at any time during the year. In April 1999, R in young Q. myrtifolia leaves was significantly higher in elevated C_a—the only evidence for an indirect effect of growth in elevated C_a. Leaf R was significantly correlated with leaf nitrogen (N) concentration for the sun and shade leaves of both the species of oak. Acclimation of photosynthesis in elevated C_a significantly reduced maximum RuBP‐saturated carboxylation capacity (V_{c max}) for both the sun and shade leaves of only Q. geminata. However, we estimated that only 11–12% of total leaf N was invested in Rubisco; consequently, acclimation in this plant resulted in a small effect on N and an insignificant effect on R. In this study measurements of respiration and photosynthesis were made on material removed from the field; this procedure had no effect on gas exchange properties. The findings of this study were applicable to R expressed either per unit leaf area or unit dry weight, and did not support the hypothesis that elevated C_a decreases R directly, or indirectly owing to acclimatory decreases in Rubisco content.     

Acclimation of photosynthesis in relation to Rubisco and non-structural carbohydrate contents and in situ carboxylase activity in Scirpus olneyi grown at elevated CO2 in the field

Stands of Scirpus olneyi, a native saltmarsh sedge with C₃ photosynthesis, had been exposed to normal ambient and elevated atmospheric CO₂ concentrations (C_a) in their native habitat since 1987. The objective of this investigation was to characterize the acclimation of photosynthesis of Scirpus olneyi stems, the photosynthesizing organs of this species, to long-term elevated C_a treatment in relation to the concentrations of Rubisco and non-structural carbohydrates. Measurements were made on intact stems in the Held under existing natural conditions and in the laboratory under controlled conditions on stems excised in the field early in the morning. Plants grown at elevated C_a had a significantly higher (30–59%) net CO₂ assimilation rate (A) than those grown at ambient C_a when measurements were performed on excised stems at the respective growth C_a. However, when measurements were made at normal ambient C_a, A was smaller (45–53%) in plants grown at elevated C_a than in those grown at ambient C_a. The reductions in A at normal ambient C_a, carboxylation efficiency and in situ carboxylase activity were caused by a decreased Rubisco concentration (30–58%) in plants grown at elevated C_a; these plants also contained less soluble protein (39–52%). The Rubisco content was 43 to 58% of soluble protein, and this relationship was not significantly altered by the growth CO₂ concentrations. The Rubisco activation state increased slightly, but the in situ carboxylase activity decreased substantially in plants grown at elevated C_a. When measurements were made on intact stems in the field, the elevated C_a treatment caused a greater stimulation of,A (100%) and a smaller reduction in carboxylation efficiency (which was not statistically significant) than when measurements were made on excised stems in the laboratory. The possible reasons for this arc discussed. Plants grown at elevated C_a contained more non-structural carbohydrates (25–53%) than those grown at ambient C_a. Plants grown at elevated C_a appear to have sufficient sink capacity to utilize the additional carbohydrates formed during photosynthesis. Overall, our results are in agreement with the hypothesis that elevated C_a leads to an increased carbohydrate concentration and the ensuing acclimation of the photo-synthetic apparatus in C₃ plants results in a reduction in the protein complement, especially Rubisco, which reduces the photosynthetic capacity in plants grown at elevated C_a, relative to plants grown at normal ambient C_a. Nevertheless, when compared at their respective growth C_a, Scirpus olneyi plants grown at elevated C_a in their native habitat maintained a substantially higher rate of photosynthesis than those grown at normal ambient C_a even after 8 years of growth at elevated C_a.     

Acclimation of photosynthesis, H2O2 content and antioxidants in maize (Zea mays) grown at sub-optimal temperatures

Maize plants were grown at 14, 18 and 20 °C until the fourth leaf had emerged. Leaves from plants grown at 14 and 18 °C had less chlorophyll than those grown at 20 °C. Maximal extractable ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity was decreased at 14 °C compared with 20 °C, but the activation state was highest at 14 °C. Growth at 14 °C increased the abundance (but not the number) of Rubisco breakdown products. Phosphoenolpyruvate carboxylase (PEPC) activity was decreased at 14 °C compared with 20 °C but no chilling-dependent effects on the abundance of the PEPC protein were observed. Maximal extractable NADP-malate dehydrogenase activity increased at 14 °C compared with 20 °C whereas the glutathione pool was similar in leaves from plants grown at both temperatures. Foliar ascorbate and hydrogen peroxide were increased at 14 °C compared with 20 °C. The foliar hydrogen peroxide content was independent of irradiance at both growth temperatures. Plants grown at 14 °C had decreased rates of CO₂ fixation together with decreased quantum efficiencies of photosystem (PS) II in the light, although there was no photo-inhibition. Growth at 14 °C decreased the abundance of the D1 protein of PSII and the PSI psaB gene product but the psaA gene product was largely unaffected by growth at low temperatures. The relationships between the photosystems and the co-ordinate regulation of electron transport and CO₂ assimilation were maintained in plants grown at 14 °C.     

Feedback limitation of photosynthesis of Phaseolus vulgaris L grown in elevated CO2

The capacity for photosynthesis is often affected when plants are grown in air with elevated CO₂ partial pressure. We grew Phaseolus vulgaris L. in 35 and 65 Pa CO₂ and measured photosynthetic parameters. When assayed at the growth CO₂ level, photosynthesis was equal in the two CO₂ treatments. The maximum rate of ribulose-1,5-bisphosphate (RuBP) consumption was lower in plants grown at 65 Pa, but the CO₂ partial pressure at which the maximum occurred was higher in the high-CO₂-grown plants, indicating acclimation to high CO₂. The acclimation of RuBP consumption to CO₂ involved a reduction of the activity of RuBP carboxylase which resulted from reduced carbamylation, not a loss of protein. The rate of RuBP consumption declined with CO₂ when the CO₂ partial pressure was above 50Pa in plants grown under both CO₂ levels. This was caused by feedback inhibition as judged by a lack of response to removing O₂ from the air stream. The rate of photosynthesis at high CO₂ was lower in the high-CO₂-grown plants and this was correlated with reduced activity of sucrose-phosphate synthase. This is only the second report of O₂-insensitive photosynthesis under growth conditions for plants grown in high CO₂.     

The sensitivity of C3 photosynthesis to increasing CO2 concentration: a theoretical analysis of its dependence on temperature and background CO2 concentration

The atmospheric CO₂ concentration has increased from the pre-industrial concentration of about 280 μmol mol⁻¹ to its present concentration of over 350 μmol mol⁻¹, and continues to increase. As the rate of photosynthesis in C₃ plants is strongly dependent on CO₂ concentration, this should have a marked effect on photosynthesis, and hence on plant growth and productivity. The magnitude of photo-synthetic responses can be calculated based on the well-developed theory of photosynthetic response to intercellular CO₂ concentration. A simple biochemically based model of photosynthesis was coupled to a model of stomatal conductance to calculate photosynthetic responses to ambient CO₂ concentration. In the combined model, photosynthesis was much more responsive to CO₂ at high than at low temperatures. At 350 μmol mol⁻¹, photosynthesis at 35°C reached 51% of the rate that would have been possible with non-limiting CO₂, whereas at 5°C, 77% of the CO₂ non-limited rate was attained. Relative CO₂ sensitivity also became smaller at elevated CO₂, as CO₂ concentration increased towards saturation. As photosynthesis was far from being saturated at the current ambient CO₂ concentration, considerable further gains in photosynthesis were predicted through continuing increases in CO₂ concentration. The strong interaction with temperature also leads to photosynthesis in different global regions experiencing very different sensitivities to increasing CO₂ concentrations.     

Whole plant respiration and photosynthesis of wheat under increased CO2 concentration and temperature: long-term vs. short-term distinctions for modelling

Short- and long-term effects of elevated CO₂ concentration and temperature on whole plant respiratory relationships are examined for wheat grown at four constant temperatures and at two CO₂ concentrations. Whole plant CO₂ exchange was measured on a 24 h basis and measurement conditions varied both to observe short-term effects and to determine the growth respiration coefficient (r_g), dry weight maintenance coefficient (r_m), basal (i.e. dark acclimated) respiration coefficient (r_g), and 24 h respiration:photosynthesis ratio (R:P). There was no response of r_g to short-term variation in CO2 concentration. For plants with adequate N supply, r_g was unaffected by the growth-CO₂ despite a 10% reduction in the plant's N concentration (%N). However, r_m was decreased 13%, and r_b was decreased 20% by growth in elevated CO₂ concentration relative to ambient. Nevertheless, R:P was not affected by growth in elevated CO₂. Whole plant respiration responded to short-term variation of ± 5 °C around the growth temperature with low sensitivity (Q₁₀= 1.8 at 15 °C, 1.3 at 30 °C). The shape of the response of whole plant respiration to growth temperature was different from that of the short term response, being a slanted S-shape declining between 25 and 30 °C. While r_m, increased, r_g decreased when growth temperature increased between 15 and 20 °C. Above 20 °C r_m became temperature insensitive while r_g increased with growth temperature. Despite these complex component responses, R:P increased only from 0.40 to 0.43 between 15° and 30 °C growth temperatures. Giving the plants a step increase in temperature caused a transient increase in R:P which recovered to the pre-transient value in 3 days. It is concluded that use of a constant R:P with respect to average temperature and CO₂ concentration may be a more simple and accurate way to model the responses of wheat crop respiration to ‘climate change’ than the more complex and mechanistically dubious functional analysis into growth and maintenance components.     

A mechanistic evaluation of photosynthetic acclimation at elevated CO2

Plants grown at elevated pCO₂ often fail to sustain the initial stimulation of net CO₂ uptake rate (A). This reduced, acclimated, stimulation of A often occurs concomitantly with a reduction in the maximum carboxylation velocity (V_c,max) of Rubisco. To investigate this relationship we used the Farquhar model of C₃ photosynthesis to predict the minimum V_c,max capable of supporting the acclimated stimulation in A observed at elevated pCO₂. For a wide range of species grown at elevated pCO₂ under contrasting conditions we found a strong correlation between observed and predicted values of V_c,max. This exercise mechanistically and quantitatively demonstrated that the observed acclimated stimulation of A and the simultaneous decrease in V_c,max observed at elevated pCO₂ is mechanistically consistent. With the exception of plants grown at a high elevated pCO₂ (> 90 Pa), which show evidence of an excess investment in Rubisco, the failure to maintain the initial stimulation of A is almost entirely attributable to the decrease in V_c,max and investment in Rubisco is coupled to requirements.     

Seventeen years of elevated CO2 exposure in a Chesapeake Bay Wetland: sustained but contrasting responses of plant growth and CO2 uptake

Increased atmospheric CO₂ concentration (Ca) produces a short‐term stimulation of photosynthesis and plant growth across terrestrial ecosystems. However, the long‐term response remains uncertain and is thought to depend on environmental constraints. In the longest experiment on natural ecosystem response to elevated Ca, we measured the shoot‐density, biomass and net CO₂ exchange (NEE) responses to elevated Ca from 1987 to 2003 in a Scirpus olneyi wetland sedge community of the Chesapeake Bay, MD, USA. Measurements were conducted in five replicated open‐top chambers per CO₂ treatment (ambient and elevated). In addition, unchambered control plots were monitored for shoot density. Responses of daytime NEE, Scirpus plant biomass and shoot density to elevated Ca were positive for any single year of the 17‐year period of study. Daytime NEE stimulation by elevated Ca rapidly dropped from 80% at the onset of the experiment to a long‐term stimulation average of about 35%. Shoot‐density stimulation by elevated Ca increased linearly with duration of exposure (r²=0.89), exceeding 120% after 17 years. Although of lesser magnitude, the shoot biomass response to elevated Ca was similar to that of the shoot density. Daytime NEE response to elevated Ca was not explained by the duration of exposure, but negatively correlated with salinity of the marsh, indicating that this elevated‐Ca response was decreased by water‐related stress. By contrast, circumstantial evidence suggested that salinity stress increased the stimulation of shoot density by elevated Ca, which highlights the complexity of the interaction between water‐related stresses and plant community responses to elevated Ca. Notwithstanding the effects of salinity stress, we believe that the most important finding of the present research is that a species response to elevated Ca can continually increase when this species is under stress and declining in its natural environment. This is particularly important because climate changes associated with elevated Ca are likely to increase environmental stresses on numerous species and modify their present distribution. Our results point to an increased resilience to change under elevated Ca when plants are exposed to adverse environmental conditions.     

Reversibility of photosynthetic acclimation of swiss chard and sugarbeet grown at elevated concentrations of CO2

Although leaf photosynthesis and plant growth are initially stimulated by elevated CO₂ concentrations, increasing insensitivity to CO₂ (acclimation) is a frequent occurrence. In order to examine the acclimation process, we studied photosynthesis and whole plant development in swiss chard (Beta vulgaris L. Koch ssp. ciela) and sugarbeet (Beta vulgaris L. ssp. vulgaris) grown at either ambient or twice ambient concentrations of CO₂. In an initial controlled environment study, photosynthetic acclimation to elevated CO₂ levels was observed in both subspecies 24 days after sowing (DAS) but was not observed at 42 and 49 DAS for sugarbeet or at 49 DAS for swiss chard. Although sugarbeet and swiss chard differed in root size and morphology, this was not a factor in the onset of photosynthetic acclimation. The reversal of photosynthetic acclimation that was observed in older plants grown at elevated CO₂, concentrations was associated with a rapid increase in root development (i.e. increased root: shoot [R/S] ratio), increased sucrose levels in sinks (roots) and no differences in total soluble leaf protein of either subspecies relative to the ambient CO₂ condition. In a second set of experiments, swiss chard and sugarbeet were grown in outdoor Plexiglass chambers at different times of the year (i.e. summer and early fall). Average 24-h temperature was 30.7 and 19.4°C for the summer and fall plantings, respectively. In agreement with the controlled environment study, lack of photosynthetic acclimation, determined from the response of photosynthesic rate to internal CO₂ concentration, was correlated with increased root biomass and sucrose concentration relative to the ambient condition. However, photo-synthetic acclimation was observed depending on the season, i.e. summer (swiss chard) or fall (sugarbeet), suggesting that acclimation was affected by environmental factors, such as temperature. Data from both experiments suggest that continued long-term photosynthetic stimulation may be dependent upon the ability of increased CO₂ to stimulate new sink development which would allow full utilization of the additional carbon made available in a high CO₂ environment.     

Growth at elevated CO2: photosynthetic responses mediated through Rubisco

Abstract. The global uptake of CO₂ in photosynthesis is about 120 gigatons (Gt) of carbon per year. Virtually all passes through one enzyme, ribulose bisphosphate carboxylase/oxygenase (rubisco), which initiates both the photosynthetic carbon reduction, and photorespiratory carbon oxidation, cycles. Both CO₂ and O₂ are substrates; CO₂ also activates the enzyme. In C₃ plants, rubisco has a low catalytic activity, operates below its K_m (CO₂), and is inhibited by O₂. Consequently, increases in the CO₂/O₂ ratio stimulate C₃ photosynthesis and inhibit photorespiration. CO₂ enrichment usually enhances the productivity of C₃ plants, but the effect is marginal in C₄ species. It also causes acclimation in various ways: anatomically, morphologically, physiologically or biochemically. So, CO₂ exerts secondary effects in growth regulation, probably at the molecular level, that are not predictable from its primary biochemical role in carboxylation. After an initial increase with CO₂ enrichment, net photosynthesis often declines. This is a common acclimation phenomenon, less so in field studies, that is ultimately mediated by a decline in rubisco activity, though the RuBP/P_i-regeneration capacities of the plant may play a role. The decline is due to decreased rubisco protein, activation state, and/or specific activity, and it maintains the rubisco fixation and RuBP/P_i regeneration capacities in balance. Carbohydrate accumulation is sometimes associated with reduced net photosynthesis, possibly causing feedback inhibition of the RuBP/P_iregeneration capacities, or chloroplast disruption. As exemplified by field-grown soybeans and salt marsh species, a reduction in net photosynthesis and rubisco activity is not inevitable under CO₂ enrichment. Strong sinks or rapid translocation may avoid such acclimation responses. Over geological time, aquatic autotrophs and terrestrial C₄ and CAM plants have genetically adapted to a decline in the external CO₂/O₂ ratio, by the development of mechanisms to concentrate CO₂ internally; thus circumventing O₂ inhibition of rubisco. Here rubisco affinity for CO₂ is less, but its catalytic activity is greater, a situation compatible with a high-CO₂ internal environment. In aquatic autotrophs, the CO₂ concentrating mechanisms acclimate to the external CO₂, being suppressed at high-CO₂. It is unclear, whether a doubling in atmospheric CO₂ will be sufficient to cause a de-adaptive trend in the rubisco kinetics of future C₃ plants, producing higher catalytic activities.     

Canopy photosynthesis of crops and native plant communities exposed to long-term elevated CO2

Abstract. There have been seven studies of canopy photosynthesis of plants grown in elevated atmospheric CO₂: three of seed crops, two of forage crops and two of native plant ecosystems. Growth in elevated CO₂ increased canopy photosynthesis in all cases. The relative effect of CO₂ was correlated with increasing temperature: the least stimulation occurred in tundra vegetation grown at an average temperature near 10°C and the greatest in rice grown at 43°C. In soybean, effects of CO₂ were greater during leaf expansion and pod fill than at other stages of crop maturation. In the longest running experiment with elevated CO₂ treatment to date, monospecific stands of a C₃ sedge, Scirpus olneyi (Grey), and a C₄ grass, Spartina patens (Ait.) Muhl., have been exposed to twice normal ambient CO₂ concentrations for four growing seasons, in open top chambers on a Chesapeake Bay salt marsh. Net ecosystem CO₂ exchange per unit green biomass (NCE_b) increased by an average of 48% throughout the growing season of 1988, the second year of treatment. Elevated CO₂ increased net ecosystem carbon assimilation by 88% in the Scirpus olneyi community and 40% in the Spartina patens community.     

Stomatal behaviour, photosynthesis and transpiration under rising CO2

Definitions of the variables used and the units are given in Table 1

The literature reports enormous variation between species in the extent of stomatal responses to rising CO₂. This paper attempts to provide a framework within which some of this diversity can be explained. We describe the role of stomata in the short-term response of leaf gas exchange to increases in ambient CO₂ concentration by developing the recently proposed stomatal model of Jarvis & Davies (1998 ). In this model stomatal conductance is correlated with the functioning of the photosynthetic system so that the effects of increases in CO₂ on stomata are experienced through changes in the rate of photosynthesis in a simple and mechanistically transparent way. This model also allows us to consider the effects of evaporative demand and soil moisture availability on stomatal responses to photosynthesis and therefore provides a means of considering these additional sources of variation. We emphasize that the relationship between the rate of photosynthesis and the internal CO₂ concentration and also drought will have important effects on the relative gains to be achieved under rising CO₂.  

  Table 1 . Abbreviations     

17.

CO₂ enrichment predisposes foliage of a eucalypt to freezing injury and reduces spring growth     

DAVID H. BARKER  BETH R. LOVEYS  JOHN J. G. EGERTON  HOLLY GORTON  WILLIAM E. WILLIAMS  & MARILYN C. BALL 《Plant, cell & environment》2005,28(12):1506-1515

Seedlings of Eucalyptus pauciflora, were grown in open-top chambers fumigated with ambient and elevated [CO₂], and were divided into two populations using 10% light transmittance screens. The aim was to separate the effects of timing of light interception, temperature and [CO₂] on plant growth. The orientation of the screens exposed plants to a similar total irradiance, but incident during either cold mornings (east-facing) or warm afternoons (west-facing). Following the first autumn freezing event elevated CO₂-grown plants had 10 times more necrotic leaf area than ambient CO₂ plants. West-facing plants had significantly greater (25% more) leaf damage and lower photochemical efficiency (F_v/F_m) in comparison with east-facing plants. Following a late spring freezing event east-facing elevated CO₂ plants suffered a greater sustained loss in F_v/F_m than west-facing elevated CO₂- and ambient CO₂-grown plants. Stomatal conductance was lower under elevated CO₂ than ambient CO₂ except during late spring, with the highest leaf temperatures occurring in west-facing plants under elevated CO₂. These higher leaf temperatures apparently interfered with cold acclimation thereby enhancing frost damage and reducing the ability to take advantage of optimal growing conditions under elevated CO₂.     

18.

Stomatal acclimation over a subambient to elevated CO₂ gradient in a C₃/C₄ grassland   总被引：1，自引：1，他引：1  

H. Maherali  C. D. Reid  H. W. Polley  H. B. Johnson  & R. B. Jackson 《Plant, cell & environment》2002,25(4):557-566

An investigation to determine whether stomatal acclimation to [CO₂] occurred in C₃/C₄ grassland plants grown across a range of [CO₂] (200–550 µmol mol^?1) in the field was carried out. Acclimation was assessed by measuring the response of stomatal conductance (g_s) to a range of intercellular CO₂ (a g_s–C_i curve) at each growth [CO₂] in the third and fourth growing seasons of the treatment. The g_s–C_i response curves for Solanum dimidiatum (C₃ perennial forb) differed significantly across [CO₂] treatments, suggesting that stomatal acclimation had occurred. Evidence of non–linear stomatal acclimation to [CO₂] in this species was also found as maximum g_s (g_smax; g_s measured at the lowest C_i) increased with decreasing growth [CO₂] only below 400 µmol mol^?1. The substantial increase in g_s at subambient [CO₂] for S. dimidiatum was weakly correlated with the maximum velocity of carboxylation (V_cmax; r² = 0·27) and was not associated with CO₂ saturated photosynthesis (A_max). The response of g_s to C_i did not vary with growth [CO₂] in Bromus japonicus (C₃ annual grass) or Bothriochloa ischaemum (C₄ perennial grass), suggesting that stomatal acclimation had not occurred in these species. Stomatal density, which increased with rising [CO₂] in both C₃ species, was not correlated with g_s. Larger stomatal size at subambient [CO₂], however, may be associated with stomatal acclimation in S. dimidiatum. Incorporating stomatal acclimation into modelling studies could improve the ability to predict changes in ecosystem water fluxes and water availability with rising CO₂ and to understand their magnitudes relative to the past.     

19.

Effects of elevated [CO₂] on photosynthesis in European forest species: a meta-analysis of model parameters   总被引：6，自引：6，他引：6  

B. E. Medlyn  F. -W. Badeck  D. G. G. De Pury  C. V. M. Barton  M. Broadmeadow  R. Ceulemans  P. De Angelis  M. Forstreuter  M. E. Jach  S. Kellomäki  E. Laitat  M. Marek  S. Philippot  A. Rey  J. Strassemeyer  K. Laitinen  R. Liozon  B. Portier  P. Roberntz  K. Wang &  P. G. Jstbid 《Plant, cell & environment》1999,22(12):1475-1495

The effects of elevated atmospheric CO₂ concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, process-based computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO₂] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (A_max), the potential electron transport rate (J_max), the maximum Rubisco activity (V_cmax) and leaf nitrogen concentration on mass (N_m) and area (N_a) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO₂]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO₂ concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters J_max and V_cmax of the order of 10%. This reduction in J_max and V_cmax was linked to the effects of elevated [CO₂] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO₂]. Tables of model parameter values for different European forest species are given.     

20.

Carbon gains by desiccation-tolerant plants at elevated CO₂     

Z. Tuba  Z. Csintalan  K. Szente  Z. Nagy  & J. Grace 《Functional ecology》1998,12(1):39-44

1. There have been no reports of the long-term responses of the desiccation-tolerant (DT) plants to elevated CO₂. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccation: a so-called poikilochlorophyllous desiccation-tolerant species (PDT). When the leaves of X. scabria are allowed to desiccate, the species shows many of the normal features of (P)DT plants.
2. However, the duration of photosynthesis in X. scabria is prolonged by 300% when the measurements are made at 700 as opposed to 350p.p.m. CO₂. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity. This response could have far-reaching implications for the success of such species in a future climate.
3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation. We show the desiccation responses of two common HDT species ( Cladonia convoluta and Tortula ruralis ) to elevated CO₂ for comparison. Both HDT species showed increased net CO₂ uptake in the material grown at high CO₂ by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation-tolerant plants will be among the main beneficiaries of a high CO₂ future.     

CO2 enrichment predisposes foliage of a eucalypt to freezing injury and reduces spring growth

Seedlings of Eucalyptus pauciflora, were grown in open-top chambers fumigated with ambient and elevated [CO₂], and were divided into two populations using 10% light transmittance screens. The aim was to separate the effects of timing of light interception, temperature and [CO₂] on plant growth. The orientation of the screens exposed plants to a similar total irradiance, but incident during either cold mornings (east-facing) or warm afternoons (west-facing). Following the first autumn freezing event elevated CO₂-grown plants had 10 times more necrotic leaf area than ambient CO₂ plants. West-facing plants had significantly greater (25% more) leaf damage and lower photochemical efficiency (F_v/F_m) in comparison with east-facing plants. Following a late spring freezing event east-facing elevated CO₂ plants suffered a greater sustained loss in F_v/F_m than west-facing elevated CO₂- and ambient CO₂-grown plants. Stomatal conductance was lower under elevated CO₂ than ambient CO₂ except during late spring, with the highest leaf temperatures occurring in west-facing plants under elevated CO₂. These higher leaf temperatures apparently interfered with cold acclimation thereby enhancing frost damage and reducing the ability to take advantage of optimal growing conditions under elevated CO₂.     

Stomatal acclimation over a subambient to elevated CO2 gradient in a C3/C4 grassland

An investigation to determine whether stomatal acclimation to [CO₂] occurred in C₃/C₄ grassland plants grown across a range of [CO₂] (200–550 µmol mol^?1) in the field was carried out. Acclimation was assessed by measuring the response of stomatal conductance (g_s) to a range of intercellular CO₂ (a g_s–C_i curve) at each growth [CO₂] in the third and fourth growing seasons of the treatment. The g_s–C_i response curves for Solanum dimidiatum (C₃ perennial forb) differed significantly across [CO₂] treatments, suggesting that stomatal acclimation had occurred. Evidence of non–linear stomatal acclimation to [CO₂] in this species was also found as maximum g_s (g_smax; g_s measured at the lowest C_i) increased with decreasing growth [CO₂] only below 400 µmol mol^?1. The substantial increase in g_s at subambient [CO₂] for S. dimidiatum was weakly correlated with the maximum velocity of carboxylation (V_cmax; r² = 0·27) and was not associated with CO₂ saturated photosynthesis (A_max). The response of g_s to C_i did not vary with growth [CO₂] in Bromus japonicus (C₃ annual grass) or Bothriochloa ischaemum (C₄ perennial grass), suggesting that stomatal acclimation had not occurred in these species. Stomatal density, which increased with rising [CO₂] in both C₃ species, was not correlated with g_s. Larger stomatal size at subambient [CO₂], however, may be associated with stomatal acclimation in S. dimidiatum. Incorporating stomatal acclimation into modelling studies could improve the ability to predict changes in ecosystem water fluxes and water availability with rising CO₂ and to understand their magnitudes relative to the past.     

Effects of elevated [CO2] on photosynthesis in European forest species: a meta-analysis of model parameters

The effects of elevated atmospheric CO₂ concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, process-based computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO₂] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (A_max), the potential electron transport rate (J_max), the maximum Rubisco activity (V_cmax) and leaf nitrogen concentration on mass (N_m) and area (N_a) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO₂]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO₂ concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters J_max and V_cmax of the order of 10%. This reduction in J_max and V_cmax was linked to the effects of elevated [CO₂] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO₂]. Tables of model parameter values for different European forest species are given.     

Carbon gains by desiccation-tolerant plants at elevated CO2

1. There have been no reports of the long-term responses of the desiccation-tolerant (DT) plants to elevated CO₂. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccation: a so-called poikilochlorophyllous desiccation-tolerant species (PDT). When the leaves of X. scabria are allowed to desiccate, the species shows many of the normal features of (P)DT plants.
2. However, the duration of photosynthesis in X. scabria is prolonged by 300% when the measurements are made at 700 as opposed to 350p.p.m. CO₂. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity. This response could have far-reaching implications for the success of such species in a future climate.
3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation. We show the desiccation responses of two common HDT species ( Cladonia convoluta and Tortula ruralis ) to elevated CO₂ for comparison. Both HDT species showed increased net CO₂ uptake in the material grown at high CO₂ by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation-tolerant plants will be among the main beneficiaries of a high CO₂ future.