Fruit effects on photosynthesis in Prunus persica

Seasonal measurements of net CO₂ assimilation, leaf conductance and mesophyll conductance were made in the field on mature, fruiting and defruited Prunus persica L. Batsch trees. During early stages of fruit growth there were no significant differences in leaf gas exchange characteristics between fruiting and defruited trees. During the early part of the last stage of fruit growth, CO₂ assimilation rates were 11–15% higher in fruiting trees than defruited trees. These increased assimilation rates corresponded with approximately 30% increases in leaf conductance and only minor changes in mesophyll conductances or leaf CO₂ assimilation capacity as indicated by leaf nitrogen content. It is concluded that under the field conditions of this study the fruit effect on photosynthesis is primarily related to stomatal behavior.     

The effects of soil and atmospheric drought on photosynthesis and stomatal control of gas exchange in three coniferous species

The responses of steady-state CO₂ assimilation rate (A), transpiration rate (E), and stomatal conductance (g_s) to changes in leaf-to-air vapour pressure difference (δW) on one hand and to increasing soil drought on the other hand were examined in 2-year-old seedlings of Pseudotsuga menziesii, Pseudotsuga macrocarpa and Cedrus atlantica. Analysing the data through A vs intercellular CO₂ molar fraction (c_i) graphs, we could determine stomatal and mesophyll contributions to changes in A as δW or soil drought were increased. Increasing soil drought affected g_s and mesophyll photosynthesis independently, since clearly distinct predawn leaf water potential (ψ_p) regions appeared in which either stomatal or mesophyll effects prevailed for explaining the changes in A. The two Pseudotsuga species exhibited a large ψ_P range (between ca -0.8 and -1.5 to -1.9 MPa) in which only stomata were responsible for the decrease in A. A dramatic decline in mesophyll photosynthesis was noticed starting from values as high as -1.2 MPa ( C. atlantica ), -1.5 MPa ( P. macrocarpa ) and -1.9 MPa ( P. menziesii ). Increasing ΔW at high soil water content led to a sharp decline in A primarily due to an alteration of mesophyll photosynthesis. Stomatal conductance for CO₂ diffusion was affected in a lesser extent and in close correlation with the changes in mesophyll photosynthesis, which could suggest the existence of a functional linkage between mesophyll photosynthesis and stomata. Surprisingly, the drought resistant P. macrocarpa exhibited the least conservative water use efficiency in response to the two types of drought. In this species drought adaptation seems to be mainly due to its high root growth and soil prospection ability.     

Photosynthesis, carbohydrate levels and chlorophyll fluorescence-estimated intercellular CO2 in water-stressed Casuarina equisetifolia Forst. & Forst.

The effect of long-term water stress on photosynthetic carbon metabolism in Casuarina equisetifolia Forst. & Forst. was analysed by measuring CO₂ assimilation, stomatal conductance, the quantum yield of photosystem II ( Φ _PSII), enzyme activities, and the levels of photosynthetic intermediates and carbohydrates. CO₂ assimilation decreased under water stress while the intercellular CO₂ concentration ( C _i) as estimated by gas exchange measurements remained high. However, the estimates of C _i from measurements of Φ _PSII suggest that the decrease in photosynthesis can be explained in terms of stomatal closure. Water stress decreased total stromal fructose-1,6-bisphosphatase activity and did not alter the activities and activation states of ribulose bisphosphate carboxylase oxygenase and NADP-dependent malate dehydrogenase (NADP-MDH). The concentration of photosynthetic metabolites, glucose, fructose and sucrose decreased, whereas starch concentrations increased under drought conditions.     

Photorespiration in C4 grasses remains slow under drought conditions

The CO₂-concentrating mechanism present in C₄ plants decreases the oxygenase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and, consequently, photorespiratory rates in air. Under drought conditions, the intercellular CO₂ concentration may decrease and cause photorespiration to increase. The C₄ grasses Paspalum dilatatum Poiret, Cynodon dactylon (L.) Pers. and Zoysia japonica Steudel were grown in soil and drought was imposed by ceasing to provide water. Net CO₂ assimilation ( A ) and stomatal conductance to water vapour decreased with leaf dehydration. Decreased carbon and increased oxygen isotope composition were also observed under drought. The response of A to CO₂ suggested that the compensation point was zero in all species irrespective of the extent of drought stress. A slight decrease of A as O₂ concentration increased above 10% provided evidence for slow photorespiratory gas exchanges. Analysis of amino acids contained in the leaves, particularly the decrease of glycine after 30 s in darkness, supported the presence of slow photorespiration rates, but these were slightly faster in Cynodon dactylon than in Paspalum dilatatum and Zoysia japonica . Although the contents of glycine and serine increased with dehydration and mechanistic modelling of C₄ photosynthesis suggested slightly increased photorespiration rates in proportion to photosynthesis, the results provide evidence that photorespiration remained slow under drought conditions.     

Effects of nitrogen deficiency on leaf photosynthetic response of tall fescue to water deficit

Abstract. The objective of the present work was to study the effect of nitrogen deficiency on drought sensitivity of tall fescue plants. The authors compared photosynthetic and stomatal behaviour of plants grown at either high (8 mol m⁻³) or low (0.5 mol m⁻³) nitrogen levels during a drought cycle followed by rehydration. Other processes investigated were stomatal and non-stomatal inhibition of leaf photosynthesis, water use efficiency and leaf rolling. Plants were grown in pots in controlled conditions on expanded clay. A Wescor in situ hygrometer placed on the leaf base outside the assimilation chamber permitted, simultaneously to leaf gas exchange measurements, monitoring of leaf water potential. Drought was imposed by withholding water from the pot. CO₂ uptake and stomatal conductance decreased and leaves started to roll at a lower leaf water potential in the high-N than in the low-N grown plants. Stomatal inhibition of leaf photosynthesis seemed larger in the low-N than in the high-N plants. Water-use efficiency increased more in the high-N than in the low-N grown plants during the drought. The decrease of photosynthesis was largely reversible after rehydration in low-N but not in high-N leaves. The authors suggest that low-N plants avoid water deficit rather than tolerate it.     

CO2 enrichment, drought stress and growth of Alaska pea plants (Pisum sativum)

The interaction of CO₂ enrichment and drought on water status and growth of pea plants was investigated. Pisum sativum L. (cv. Alaska) plants were grown from seeds in growth chambers using 350 and 675 μl I1 CO₂, a photon flux density of 600 μmol M-2 S-1, a 16 h photoperiod and a temperature regime of 20/14°C. The drought treatment was started at the beginning of branch initiation and lasted for 9 or 11 days. The water status of the plants was monitored daily by measuring total leaf water potential and stomatal conductance. The total leaf water potential of well-watered plants was not affected by the CO₂ level. Under draughting conditions total leaf water potential decreased, with a slower decrease under the high CO₂ regime, due, at least in part, to reduced stomatal conductance. Upon rewatering, total leaf water potential and stomatal conductance recovered within one day. High CO₂ counteracted the reduction in height and, to some extent, leaf area that developed in low CO₂ unwatered plants. Additional CO₂ had no effect on branch number and did not prevent the complete inhibition of branch development that resulted from drought stress. Removing the drought conditions resulted in a rapid recovery of the internal water status and also a rapid recovery of most, but not all, plant growth parameters.     

Elevated CO2 enhances stomatal responses to osmotic stress and abscisic acid in Arabidopsis thaliana

A , carbon assimilation rate
ABA, abscisic acid
Ci , intercellular space CO₂ concentration
g , leaf conductance
WUE, water use efficiency

Carbon dioxide and abscisic acid (ABA) are two major signals triggering stomatal closure. Their putative interaction in stomatal regulation was investigated in well-watered air-grown or double CO₂-grown Arabidopsis thaliana plants, using gas exchange and epidermal strip experiments. With plants grown in normal air, a doubling of the CO₂ concentration resulted in a rapid and transient drop in leaf conductance followed by recovery to the pre-treatment level after about two photoperiods. Despite the fact that plants placed in air or in double CO₂ for 2 d exhibited similar levels of leaf conductance, their stomatal responses to an osmotic stress (0·16–0·24 MPa) were different. The decrease in leaf conductance in response to the osmotic stress was strongly enhanced at elevated CO₂. Similarly, the drop in leaf conductance triggered by 1 μ M ABA applied at the root level was stronger at double CO₂. Identical experiments were performed with plants fully grown at double CO₂. Levels of leaf conductance and carbon assimilation rate measured at double CO₂ were similar for air-grown and elevated CO₂-grown plants. An enhanced response to ABA was still observed at high CO₂ in pre-conditioned plants. It is concluded that: (i) in the absence of stress, elevated CO₂ slightly affects leaf conductance in A. thaliana ; (ii) there is a strong interaction in stomatal responses to CO₂ and ABA which is not modified by growth at elevated CO₂.     

Photosynthesis affects following night leaf conductance in Vicia faba

Night-time stomatal opening in C₃ plants may result in significant water loss when no carbon gain is possible. The objective of this study was to determine if endogenous patterns of night-time stomatal opening, as reflected in leaf conductance, in Vicia faba are affected by photosynthetic conditions the previous day. Reducing photosynthesis with low light or low CO₂ resulted in reduced night-time stomatal opening the following night, irrespective of the effects on daytime stomatal conductance. Likewise, increasing photosynthesis with enriched CO₂ levels resulted in increased night-time stomatal opening the following night. Reduced night-time stomatal opening was not the result of an inability to regulate stomatal aperture as leaves with reduced night-time stomatal opening were capable of greater night-time opening when exposed to low CO₂. After acclimating plants to long or short days, it was found that night-time leaf conductance was greater in plants acclimated to short days, and associated with greater leaf starch and nitrate accumulation, both of which may affect night-time guard cell osmotic potential. Direct measurement of guard cell contents during endogenous night-time stomatal opening will help identify the mechanism of the effect of daytime photosynthesis on subsequent night-time stomatal regulation.     

Drought effects on photosynthesis and fluorescence in hard wheat cultivars grown in the field

Net photosynthesis of the flag leaf of hard wheat ( Triticum durum L. evs Valforte, Produra, Adamello, Karel, Appulo and El Amel from the collection of the Instituto di Cerealicultura. Foggia, Italy) of different water potential has been studied on three consecutive years. Net photosynthesis was measured in natural conditions with a LI-COR portable instrument and in saturating CO₂ with an oxygen electrode. Net photosynthesis and stomatal conductance were significantly lower in the unirrigated leaves. However, the ratio of intercellular CO₂, concentration (C₁) to ambient CO₃ concentration (C_a) around the stressed plants was similar to the irrigated control. The maximal rate of photosynthesis in saturating CO₂, (P_nmax). measured in the second year of the experiment, was quite close to photosynthesis under natural conditions, indicating that CO₂ supply was not limiting. These results suggest that altered mesophyll photosynthetic capacity, rather than stomatal closure, causes the observed reduction in photosynthesis in the unirrigated plants. The variable fluorescence yield (_v/F_m) in predarkened leaves measured for two consecutive years, did not show differences between treatments or between cultivars. However, the analysis of the slow transients, measured the last year of the experiment, showed a linear relation between the fluorescence decline from the maximum initial level (P) and maximum photosynthesis (P_nmax).     

Effects of manganese toxicity on leaf CO2 assimilation of contrasting common bean genotypes

Parameters related to leaf photosynthesis were evaluated in three genotypes of common bean ( Phaseolus vulgaris L.) with contrasting tolerance to Mn toxicity. Two short-term studies in solution culture were used to assess the effect of excess Mn on CO₂ assimilation in mature and immature leaves. Mn toxicity decreased total chlorophyll content only in immature leaves, with a consequent reduction of leaf CO₂ assimilation. Mature leaves that showed brown speckles characteristic of Mn toxicity, did not suffer any detriment in their capacity to assimilate CO₂, at least in a 4-day experiment. Stomatal conductance and transpiration were not affected by the presence of high levels of Mn in leaf tissue. Lower stomatal conductance and transpiration rates were observed only in leaves with advanced chlorosis. Differences among genotypes were detected as increased chlorosis in the more sensitive genotype ZPV-292, followed by A-283 and less chlorosis in the tolerant genotype CALIMA. Since CO₂ assimilation expressed per unit of chlorophyll was not different between high-Mn plants and control plants, we conclude that the negative effect of Mn toxicity on CO₂ assimilation can be explained by a reduction in leaf chlorophyll content.     

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     

12.

Non-stomatal limitation of CO₂ assimilation in three tree species during natural drought conditions   总被引：1，自引：0，他引：1  

G. M. Briggs  T. W. Jurik  D. M. Gates 《Physiologia plantarum》1986,66(3):521-526

The effect of drought on CO₂ assimilation and leaf conductance was studied in three northern hardwood species: Quercus rubra L., Acer rubrum L. and Populus grandidentata Michx. Leaf gas exchange characteristics at two CO₂ levels (320 and 620 μl I⁻¹) and temperatures from 20 to 35°C were measured at the end of a dry period and shortly after 10 cm of rainfall. The effects of drought varied with species, temperature and CO₂ level. Calculated values of internal CO₂ concentration showed little or no decline during drought. Differences in assimilation, before vs after the rains, were most apparent at the higher CO₂ level. These latter two observations indicate nonstomatal disruption of CO₂ assimilation during the dry period. In P. grandidentata there was a substantial interaction between drought and temperature, with a resultant shift in the temperature for maximum assimilation to lower temperatures during drought. During drought, internal CO₂ concentrations increased sharply in all three species under the combined conditions of high temperatures and the higher CO₂ level.     

13.

Diurnal variations of photosynthesis and dew absorption by leaves in two evergreen shrubs growing in Mediterranean field conditions   总被引：15，自引：0，他引：15  

SERGI MUNNÉ-BOSCH  SALVADOR NOGUÉS  & LEONOR ALEGRE 《The New phytologist》1999,144(1):109-119

The effects of summer drought, dew deposition on leaves and autumn rainfall on plant water relations and diurnal variations of photosynthesis were measured in two evergreen shrubs, rosemary ( Rosmarinus officinalis ) and lavender ( Lavandula stoechas ), grown in Mediterranean field conditions. Withholding water for 40 d caused a similar decrease in predawn shoot water potential (ψ_pd) from c. −0.4 to c. −1.3 MPa in both species, but a 50% decrease in the relative leaf water content in L. stoechas compared with 22% in R. officinalis . A similar decrease in CO₂ assimilation rates by c. 75% was observed in water-stressed plants of both species, although L. stoechas showed smaller photosynthesis: stomatal conductance ratio than R. officinalis (35 vs 45 μmol CO₂:mol H₂O). The relative quantum efficiency of photosystem II photochemistry also decreased by c. 45% at midday in water- stressed plants of both species. Nevertheless, neither L. stoechas nor R. officinalis suffered drought-induced damage to photosystem II, as indicated by the maintenance of the ratio F _v: F _m throughout the experiment, associated with an increase in the carotenoid content per unit of chlorophyll by c. 62% and c. 30%, respectively, in water-stressed plants. Only L. stoechas absorbed dew by leaves. In this species the occurrence of 6 d of dew over a 15-d period improved relative leaf water content by c. 72% and shoot water potential by c. 0.5 MPa throughout the day in water-stressed plants, although the photosynthetic capacity was not recovered until the occurrence of autumn rainfall. The ability of leaves to absorb dew allowed L. stoechas to restore plant water status, which is especially relevant in plants exposed to prolonged drought.     

14.

Diurnal regulation of photosynthesis in understory saplings   总被引：6，自引：1，他引：5  

ERIC L. SINGSAAS  DONALD R. ORT  & EVAN H. DeLUCIA 《The New phytologist》2000,145(1):39-49

Photosynthetic rates of plants grown in natural systems exhibit diurnal patterns often characterized by an afternoon decline, even when measured under constant light and temperature conditions. Since we thought changes in the carbohydrate status could cause this pattern through feedback from starch and sucrose synthesis, we studied the natural fluctuations in photosynthesis rates of plants grown at 36 and 56 Pa CO₂ at a FACE (free-air-CO₂-enrichment) research site. Light-saturated photosynthesis varied by 40% during the day and was independent of the light-limited quantum yield of photosynthesis, which varied little through the day. Photosynthesis did not correspond with xylem water potential or leaf carbohydrate build-up, but rather with diurnal changes in air vapor-pressure deficit and light. The afternoon decline in photosynthesis also corresponded with decreased stomatal conductance and decreased Rubisco carboxylation efficiency which in turn allowed leaf-airspace CO₂ partial pressure to remain constant. Growth at elevated CO₂ did not affect the afternoon decline in photosynthesis, but did stimulate early-morning photosynthesis rates relative to the rest of the day. Plants grown at 56 Pa CO₂ had higher light-limited quantum yields than those at 36 Pa CO₂ but, there was no growth–CO₂ effect on quantum yield when measured at 2 kPa O₂. Therefore, understory plants have a high light-limited quantum yield that does not vary through the day. Thus, the major diurnal changes in photosynthesis occur under light-saturated conditions which may help understory saplings maximize their sunfleck-use-efficiency.     

15.

Effects of elevated ozone on photosynthesis and stomatal conductance of two soybean varieties: a case study to assess impacts of one component of predicted global climate change   总被引：1，自引：0，他引：1  

E. Singh  S. Tiwari  & M. Agrawal 《Plant biology (Stuttgart, Germany)》2009,11(S1):101-108

Global climatic change scenarios predict a significant increase in future tropospheric ozone (O₃) concentrations. The present investigation was done to assess the effects of elevated O₃ (70 and 100 ppb) on electron transport, carbon fixation, stomatal conductance and pigment concentrations in two tropical soybean ( Glycine max L.) varieties, PK 472 and Bragg. Plants were exposed to O₃ for 4 h·day⁻¹ from 10:00 to 14:00 from germination to maturity. Photosynthesis of both varieties were adversely affected, but the reduction was higher in PK 472 than Bragg. A comparison of chlorophyll a fluorescence kinetics with carbon fixation suggested greater sensitivity of dark reactions than light reactions of photosynthesis to O₃ stress. The O₃-induced uncoupling between photosynthesis and stomatal conductance in PK 472 suggests the reduction in photosynthesis may be attributed to a factor other than reduced stomatal conductance. An increase in internal CO₂ concentration in both O₃-treated soybean varieties compared suggests that the reduction in photosynthesis was due to damage to the photosynthetic apparatus, leading to accumulation of internal CO₂ and stomatal closure. The adverse impact of O₃ stress increased at higher O₃ concentrations in both soybean varieties leading to large reductions in photosynthesis. This study suggests that O₃-induced reductions in photosynthesis in tropical and temperate varieties are similar.     

16.

Investigation of the limitations to photosynthesis induced by leaf water deficit in field-grown sunflower (Helianthus annuus L.)   总被引：1，自引：1，他引：0  

R. R. WISE  J. R. FREDERICK  D. M. ALM  †  D. M. KRAMER  J. D. HESKETH  A. R. CROFTS  D. R. ORT 《Plant, cell & environment》1990,13(9):923-931

Abstract. The diurnal cycling of leaf water potential (Ψ_leaf) in field-grown sunflower ( Helianthus annuus ) was used to investigate the cause of water deficitinduced limitation of net photosynthesis. Daily midafternoon decreases in Ψ_leaf of up to 1.5 MPa and in net photosynthesis of up to 50% were typical for irrigated sunflower during seed filling. These midafternoon values were lowered an additional 0.6 to 0.8 MPa by prolonged drought treatment. There was a nearly linear relationship between the decline in net photosynthesis and reductions in leaf conductance over the course of the day. Thus, it was unexpected to find that the low, midafternoon rates of photosynthesis were associated with the highest intercellular CO₂ concentrations. These and other observations suggest that the daily decline in photosynthesis represents a 'down regulation' of the biochemical demand for CO₂ that is coordinated with the diurnally developing need to conserve water, thus establishing a balanced limitation of photosynthesis involving both stomatal and non-stomatal factors. There were no indications that either short term (i.e. diurnal declines in Ψ_leaf) or long term (i.e. drought treatment) water deficits caused any damage or malfunctioning of photosynthesis. Rather, both the daily declines in photosynthesis and the nearly 25% decrease in leaf area induced by prolonged drought appeared to be well-controlled adaptive responses by field-grown sunflower plants to limited water availability.     

17.

Stomatal responses to CO₂ during a diel Crassulacean acid metabolism cycle in Kalanchoe daigremontiana and Kalanchoe pinnata     

SUSANNE VON CAEMMERER  & HOWARD GRIFFITHS 《Plant, cell & environment》2009,32(5):567-576

To investigate the diurnal variation of stomatal sensitivity to CO₂, stomatal response to a 30 min pulse of low CO₂ was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata , which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in p CO₂ in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low p CO₂. Stomata did not respond to a decreased p CO₂ in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO₂ was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal p CO₂, and suggest that in CAM species the diurnal variability in the responsiveness of stomata to p CO₂ could be explained by hypothesizing the existence of a single CO₂ sensor which interacts with other signalling pathways. When not perturbed by low p CO₂, CO₂ assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species.     

18.

Growth and physiological responses of canola (Brassica napus) to UV-B and CO₂ under controlled environment conditions   总被引：1，自引：1，他引：1  

Mirwais M. Qaderi  David M. Reid 《Physiologia plantarum》2005,125(2):247-259

Few studies have investigated the interaction of ultraviolet (UV)-B radiation and CO₂ concentration on plants. We studied the combined effects of UV-B radiation and CO₂ concentration on canola ( Brassica napus cv. 46A65) under four growth conditions – ambient CO₂ with UV-B (control), elevated CO₂ with UV-B, ambient CO₂ without UV-B, and elevated CO₂ without UV-B – to determine whether the adverse effects of UV-B are mitigated by elevated CO₂. Elevated CO₂ significantly increased plant height and seed yield, whereas UV-B decreased them. Elevated CO₂ ameliorated the adverse effects of UV-B in plant height. UV-B did not affect the physical characteristics of leaf but CO₂ did. Certain flower and fruit characteristics were affected negatively by UV-B and positively by CO₂. UV-B did not affect net photosynthesis, transpiration and stomatal conductance but decreased water use efficiency (WUE). Elevated CO₂ significantly increased net photosynthesis and WUE. Neither UV-B nor CO₂ affected chlorophyll (Chl) fluorescence. UV-B significantly decreased Chl b and increased the ratio of Chl a / b . Elevated CO₂ decreased only the ratio of Chl a / b . UV-B significantly increased UV-absorbing compounds while CO₂ had no effect on them. Both UV-B and CO₂ significantly increased epicuticular wax content. Many significant relationships were found between morphological, physiological, and chemical parameters. This study showed that elevated CO₂ can partially ameliorate some of the adverse effects of UV-B radiation in B . napus .     

19.

Exchange of oxygen and its role in energy dissipation during drought stress in tomato plants   总被引：10，自引：0，他引：10  

Silke Haupt-Herting  Heinrich P. F_ock 《Physiologia plantarum》2000,110(4):489-495

To elucidate how excess light energy is dissipated during water deficit, net photosynthesis (P_N), stomatal conductance (g_s), intercellular CO₂ concentration (c_i) and Chl a fluorescence were investigated in control and drought-stressed tomato plants ( Lycopersicon esculentum ). Gross O₂ evolution (E_o) and gross O₂ uptake (U_o) were determined by a mass spectrometric ¹⁶O/¹⁸O₂ isotope technique. Under drought stress P_N, g_s, c_i and U_o decline. While photochemical fluorescence quenching decreases under water deficit, non-photochemical quenching rises. The maximal efficiency of PSII measured in the dark is not affected by drought; however, in the light, E_o decreases under water deficit. The ratio P_N/E_o falls under stress while the ratio U_o/E_o increases. We conclude that tomato plants follow a double strategy to avoid photodamage under drought stress conditions: (1) a substantial portion of light energy is emitted as heat and PSII activity is downregulated. This results in a decrease in E_o as well as P_N and U_o. Despite reduced charge separation at PSII, the decline of CO₂ assimilation because of lowered stomatal conductance and metabolic changes results in the need of degrading excessive photosynthetic electrons. (2) Oxygen is used as an alternative electron acceptor in photorespiration or Mehler reaction and U_o rises relative to E_o.     

20.

Effect of elevated CO₂ on the stomatal distribution and leaf physiology of Alnus glutinosa   总被引：1，自引：1，他引：0  

I. POOLE  T. LAWSON  J. D. B. WEYERS  & J. A. RAVEN 《The New phytologist》2000,145(3):511-521

Variation in stomatal development and physiology of mature leaves from Alnus glutinosa plants grown under reference (current ambient, 360 μmol mol⁻¹ CO₂) and double ambient (720 μmol mol⁻¹ CO₂) carbon dioxide (CO₂) mole fractions is assessed in terms of relative plant growth, stomatal characters (i.e. stomatal index and density) and leaf photosynthetic characters. This is the first study to consider the effects of elevated CO₂ concentration on the distribution of stomata and epidermal cells across the whole leaf and to try to ascertain the cause of intraleaf variation. In general, a doubling of the atmospheric CO₂ concentration enhanced plant growth and significantly increased stomatal index. However, there was no significant change in relative stomatal density. Under elevated CO₂ concentration there was a significant decrease in stomatal conductance and an increase in assimilation rate. However, no significant differences were found for the maximum rate of carboxylation ( V _cmax) and the light saturated rate of electron transport ( J _max) between the control and elevated CO₂ treatment.     

Non-stomatal limitation of CO2 assimilation in three tree species during natural drought conditions

The effect of drought on CO₂ assimilation and leaf conductance was studied in three northern hardwood species: Quercus rubra L., Acer rubrum L. and Populus grandidentata Michx. Leaf gas exchange characteristics at two CO₂ levels (320 and 620 μl I⁻¹) and temperatures from 20 to 35°C were measured at the end of a dry period and shortly after 10 cm of rainfall. The effects of drought varied with species, temperature and CO₂ level. Calculated values of internal CO₂ concentration showed little or no decline during drought. Differences in assimilation, before vs after the rains, were most apparent at the higher CO₂ level. These latter two observations indicate nonstomatal disruption of CO₂ assimilation during the dry period. In P. grandidentata there was a substantial interaction between drought and temperature, with a resultant shift in the temperature for maximum assimilation to lower temperatures during drought. During drought, internal CO₂ concentrations increased sharply in all three species under the combined conditions of high temperatures and the higher CO₂ level.     

Diurnal variations of photosynthesis and dew absorption by leaves in two evergreen shrubs growing in Mediterranean field conditions

The effects of summer drought, dew deposition on leaves and autumn rainfall on plant water relations and diurnal variations of photosynthesis were measured in two evergreen shrubs, rosemary ( Rosmarinus officinalis ) and lavender ( Lavandula stoechas ), grown in Mediterranean field conditions. Withholding water for 40 d caused a similar decrease in predawn shoot water potential (ψ_pd) from c. −0.4 to c. −1.3 MPa in both species, but a 50% decrease in the relative leaf water content in L. stoechas compared with 22% in R. officinalis . A similar decrease in CO₂ assimilation rates by c. 75% was observed in water-stressed plants of both species, although L. stoechas showed smaller photosynthesis: stomatal conductance ratio than R. officinalis (35 vs 45 μmol CO₂:mol H₂O). The relative quantum efficiency of photosystem II photochemistry also decreased by c. 45% at midday in water- stressed plants of both species. Nevertheless, neither L. stoechas nor R. officinalis suffered drought-induced damage to photosystem II, as indicated by the maintenance of the ratio F _v: F _m throughout the experiment, associated with an increase in the carotenoid content per unit of chlorophyll by c. 62% and c. 30%, respectively, in water-stressed plants. Only L. stoechas absorbed dew by leaves. In this species the occurrence of 6 d of dew over a 15-d period improved relative leaf water content by c. 72% and shoot water potential by c. 0.5 MPa throughout the day in water-stressed plants, although the photosynthetic capacity was not recovered until the occurrence of autumn rainfall. The ability of leaves to absorb dew allowed L. stoechas to restore plant water status, which is especially relevant in plants exposed to prolonged drought.     

Diurnal regulation of photosynthesis in understory saplings

Photosynthetic rates of plants grown in natural systems exhibit diurnal patterns often characterized by an afternoon decline, even when measured under constant light and temperature conditions. Since we thought changes in the carbohydrate status could cause this pattern through feedback from starch and sucrose synthesis, we studied the natural fluctuations in photosynthesis rates of plants grown at 36 and 56 Pa CO₂ at a FACE (free-air-CO₂-enrichment) research site. Light-saturated photosynthesis varied by 40% during the day and was independent of the light-limited quantum yield of photosynthesis, which varied little through the day. Photosynthesis did not correspond with xylem water potential or leaf carbohydrate build-up, but rather with diurnal changes in air vapor-pressure deficit and light. The afternoon decline in photosynthesis also corresponded with decreased stomatal conductance and decreased Rubisco carboxylation efficiency which in turn allowed leaf-airspace CO₂ partial pressure to remain constant. Growth at elevated CO₂ did not affect the afternoon decline in photosynthesis, but did stimulate early-morning photosynthesis rates relative to the rest of the day. Plants grown at 56 Pa CO₂ had higher light-limited quantum yields than those at 36 Pa CO₂ but, there was no growth–CO₂ effect on quantum yield when measured at 2 kPa O₂. Therefore, understory plants have a high light-limited quantum yield that does not vary through the day. Thus, the major diurnal changes in photosynthesis occur under light-saturated conditions which may help understory saplings maximize their sunfleck-use-efficiency.     

Effects of elevated ozone on photosynthesis and stomatal conductance of two soybean varieties: a case study to assess impacts of one component of predicted global climate change

Global climatic change scenarios predict a significant increase in future tropospheric ozone (O₃) concentrations. The present investigation was done to assess the effects of elevated O₃ (70 and 100 ppb) on electron transport, carbon fixation, stomatal conductance and pigment concentrations in two tropical soybean ( Glycine max L.) varieties, PK 472 and Bragg. Plants were exposed to O₃ for 4 h·day⁻¹ from 10:00 to 14:00 from germination to maturity. Photosynthesis of both varieties were adversely affected, but the reduction was higher in PK 472 than Bragg. A comparison of chlorophyll a fluorescence kinetics with carbon fixation suggested greater sensitivity of dark reactions than light reactions of photosynthesis to O₃ stress. The O₃-induced uncoupling between photosynthesis and stomatal conductance in PK 472 suggests the reduction in photosynthesis may be attributed to a factor other than reduced stomatal conductance. An increase in internal CO₂ concentration in both O₃-treated soybean varieties compared suggests that the reduction in photosynthesis was due to damage to the photosynthetic apparatus, leading to accumulation of internal CO₂ and stomatal closure. The adverse impact of O₃ stress increased at higher O₃ concentrations in both soybean varieties leading to large reductions in photosynthesis. This study suggests that O₃-induced reductions in photosynthesis in tropical and temperate varieties are similar.     

Investigation of the limitations to photosynthesis induced by leaf water deficit in field-grown sunflower (Helianthus annuus L.)

Abstract. The diurnal cycling of leaf water potential (Ψ_leaf) in field-grown sunflower ( Helianthus annuus ) was used to investigate the cause of water deficitinduced limitation of net photosynthesis. Daily midafternoon decreases in Ψ_leaf of up to 1.5 MPa and in net photosynthesis of up to 50% were typical for irrigated sunflower during seed filling. These midafternoon values were lowered an additional 0.6 to 0.8 MPa by prolonged drought treatment. There was a nearly linear relationship between the decline in net photosynthesis and reductions in leaf conductance over the course of the day. Thus, it was unexpected to find that the low, midafternoon rates of photosynthesis were associated with the highest intercellular CO₂ concentrations. These and other observations suggest that the daily decline in photosynthesis represents a 'down regulation' of the biochemical demand for CO₂ that is coordinated with the diurnally developing need to conserve water, thus establishing a balanced limitation of photosynthesis involving both stomatal and non-stomatal factors. There were no indications that either short term (i.e. diurnal declines in Ψ_leaf) or long term (i.e. drought treatment) water deficits caused any damage or malfunctioning of photosynthesis. Rather, both the daily declines in photosynthesis and the nearly 25% decrease in leaf area induced by prolonged drought appeared to be well-controlled adaptive responses by field-grown sunflower plants to limited water availability.     

Stomatal responses to CO2 during a diel Crassulacean acid metabolism cycle in Kalanchoe daigremontiana and Kalanchoe pinnata

To investigate the diurnal variation of stomatal sensitivity to CO₂, stomatal response to a 30 min pulse of low CO₂ was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata , which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in p CO₂ in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low p CO₂. Stomata did not respond to a decreased p CO₂ in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO₂ was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal p CO₂, and suggest that in CAM species the diurnal variability in the responsiveness of stomata to p CO₂ could be explained by hypothesizing the existence of a single CO₂ sensor which interacts with other signalling pathways. When not perturbed by low p CO₂, CO₂ assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species.     

Growth and physiological responses of canola (Brassica napus) to UV-B and CO2 under controlled environment conditions

Few studies have investigated the interaction of ultraviolet (UV)-B radiation and CO₂ concentration on plants. We studied the combined effects of UV-B radiation and CO₂ concentration on canola ( Brassica napus cv. 46A65) under four growth conditions – ambient CO₂ with UV-B (control), elevated CO₂ with UV-B, ambient CO₂ without UV-B, and elevated CO₂ without UV-B – to determine whether the adverse effects of UV-B are mitigated by elevated CO₂. Elevated CO₂ significantly increased plant height and seed yield, whereas UV-B decreased them. Elevated CO₂ ameliorated the adverse effects of UV-B in plant height. UV-B did not affect the physical characteristics of leaf but CO₂ did. Certain flower and fruit characteristics were affected negatively by UV-B and positively by CO₂. UV-B did not affect net photosynthesis, transpiration and stomatal conductance but decreased water use efficiency (WUE). Elevated CO₂ significantly increased net photosynthesis and WUE. Neither UV-B nor CO₂ affected chlorophyll (Chl) fluorescence. UV-B significantly decreased Chl b and increased the ratio of Chl a / b . Elevated CO₂ decreased only the ratio of Chl a / b . UV-B significantly increased UV-absorbing compounds while CO₂ had no effect on them. Both UV-B and CO₂ significantly increased epicuticular wax content. Many significant relationships were found between morphological, physiological, and chemical parameters. This study showed that elevated CO₂ can partially ameliorate some of the adverse effects of UV-B radiation in B . napus .     

Exchange of oxygen and its role in energy dissipation during drought stress in tomato plants

To elucidate how excess light energy is dissipated during water deficit, net photosynthesis (P_N), stomatal conductance (g_s), intercellular CO₂ concentration (c_i) and Chl a fluorescence were investigated in control and drought-stressed tomato plants ( Lycopersicon esculentum ). Gross O₂ evolution (E_o) and gross O₂ uptake (U_o) were determined by a mass spectrometric ¹⁶O/¹⁸O₂ isotope technique. Under drought stress P_N, g_s, c_i and U_o decline. While photochemical fluorescence quenching decreases under water deficit, non-photochemical quenching rises. The maximal efficiency of PSII measured in the dark is not affected by drought; however, in the light, E_o decreases under water deficit. The ratio P_N/E_o falls under stress while the ratio U_o/E_o increases. We conclude that tomato plants follow a double strategy to avoid photodamage under drought stress conditions: (1) a substantial portion of light energy is emitted as heat and PSII activity is downregulated. This results in a decrease in E_o as well as P_N and U_o. Despite reduced charge separation at PSII, the decline of CO₂ assimilation because of lowered stomatal conductance and metabolic changes results in the need of degrading excessive photosynthetic electrons. (2) Oxygen is used as an alternative electron acceptor in photorespiration or Mehler reaction and U_o rises relative to E_o.     

Effect of elevated CO2 on the stomatal distribution and leaf physiology of Alnus glutinosa

Variation in stomatal development and physiology of mature leaves from Alnus glutinosa plants grown under reference (current ambient, 360 μmol mol⁻¹ CO₂) and double ambient (720 μmol mol⁻¹ CO₂) carbon dioxide (CO₂) mole fractions is assessed in terms of relative plant growth, stomatal characters (i.e. stomatal index and density) and leaf photosynthetic characters. This is the first study to consider the effects of elevated CO₂ concentration on the distribution of stomata and epidermal cells across the whole leaf and to try to ascertain the cause of intraleaf variation. In general, a doubling of the atmospheric CO₂ concentration enhanced plant growth and significantly increased stomatal index. However, there was no significant change in relative stomatal density. Under elevated CO₂ concentration there was a significant decrease in stomatal conductance and an increase in assimilation rate. However, no significant differences were found for the maximum rate of carboxylation ( V _cmax) and the light saturated rate of electron transport ( J _max) between the control and elevated CO₂ treatment.