Seasonal patterns of water relations and enzyme activity of the facultative CAM plant Portulacaria afra (L.) Jacq.

Abstract. Portulacaria afra (L.) Jacq. is a perennial facultative CAM species showing a seasonal shift from C₃ to CAM photosynthesis. The shift to CAM during the summer occurs despite continued irrigation of the plants. The authors examined the hypothesis that the seasonal shift to CAM occurred because of low transient water potentials. They measured changes in whole leaf water, osmotic and pressure potentials over the course of the shift. They also studied changes in enzyme activity to ascertain if PEP carboxylase and PEP carboxykinase were induced during the seasonal shift to CAM. Water potentials were high, from -0.1 to -0.5 MPa, predawn and midday, when the C₃ pathway of photosynthesis was utilized. Osmotic potentials were constant, from -0.7 to - 0.8 MPa, indicating very little change in turgor. P. afra shifted to CAM indicated by large diurnal acid fluctuations (300 400 meq m⁻²) despite C₃-like predawn water potentials. Midday water potentials usually decreased 0.2-0.7 MPa, while the osmotic potential remained unchanged or decreased slightly. Thus, a midday loss of turgor was associated with the use of the CAM pathway. The results support the hypothesis that the induction of CAM occurred due to low transient water potentials and may be partially mediated through the loss of turgor. The shift to CAM is only a partial induction with PEP carboxykinase showing high activity all year round while PEP carboxylase increases three-to five-fold over C₃ levels. Relatively high levels of CAM enzyme activity enables the utilization of the CAM pathway in the winter and spring in response to high daytime temperatures and increased evaporative demand. These results would lead to an increase in water use efficiency during such periods when compared to other inducible CAM species.     

Partitioning of photosynthetic electron flow between CO2 and O2 reduction in a C3 leaf (Phaseolus vulgaris L.) at different CO2 concentrations and during drought stress

Photosystem II chlorophyll fluorescence and leaf net gas exchanges (CO₂ and H₂O) were measured simultaneously on bean leaves (Phaseolus vulgaris L.) submitted either to different ambient CO₂ concentrations or to a drought stress. When leaves are under photorespiratory conditions, a simple fluorescence parameter F/ F_m (B. Genty et al. 1989, Biochem. Biophys. Acta 990, 87–92; F = difference between maximum, F_m, and steady-state fluorescence emissions) allows the calculation of the total rate of photosynthetic electron-transport and the rate of electron transport to O₂. These rates are in agreement with the measurements of leaf O₂ absorption using ¹⁸O₂ and the kinetic properties of ribulose-1,5bisphosphate carboxylase/oxygenase. The fluorescence parameter, F/F_m, showed that the allocation of photosynthetic electrons to O₂ was increased during the desiccation of a leaf. Decreasing leaf net CO₂ uptake, either by decreasing the ambient CO₂ concentration or by dehydrating a leaf, had the same effect on the partitioning of photosynthetic electrons between CO₂ and O₂ reduction. It is concluded that the decline of net CO₂ uptake of a leaf under drought stress is only due, at least for a mild reversible stress (causing at most a leaf water deficit of 35%), to stomatal closure which leads to a decrease in leaf internal CO₂ concentration. Since, during the dehydration of a leaf, the calculated internal CO₂ concentration remained constant or even increased we conclude that this calculation is misleading under such conditions.Abbreviations Ca, Ci ambient, leaf internal CO₂ concentrations - F_m, F_o, F_s maximum, minimal, steady-state fluorescence emission - F_v variable fluorescence emission - PPFD photosynthetic photon flux density - q_p, q_N photochemical, non-photochemical fluorescence quenching - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase     

Phloem transport in Picea abies (L.) Karst. in mid-winter

Summary Translocation of ¹⁴C assimilates was studied on four different transport systems of Picea abies branches after induced activation in January. ¹⁴CO₂ assimilation of terminal shoots for 48 h at 25° C resulted in phloem loading and basipetal transport of ¹⁴C photosynthate into the following, older shoot generations. ¹⁴C import was enhanced, when these older shoot generations were kept in the dark. Microautoradiographs of the labelled terminal shoots showed that ¹⁴C assimilates were exported from needles via sieve elements of the leaf traces and loaded into the latest increment of the axial secondary phloem. No ¹⁴C label appeared in the obliterated sieve cells or in the tracheids. In addition, ¹⁴C photosynthate accumulated densely in the chlorophyllous cells of the cortex and in cells of the resin ducts, indicating certain sink activity. In the darkened 2-year-old shoot, imported ¹⁴C photosynthate was concentrated in the functional secondary phloem, while some ¹⁴C label was unloaded into the latest xylem increment. When 6-year-old shoots were exposed to ¹⁴CO₂ for 48 h in the light, ¹⁴C assimilates accumulated in the phloem of the leaf trace and in the latest increment of the axial secondary phloem. However, a substantial amount of radioactivity was unloaded into ray cells and phloem parenchyma cells. Thus, the presence of functioning phloem in needles and twigs of P. abies during winter allows long-distance translocation and radial distribution of assimilates according to existing source-sink relations.     

Canopy throughfall of Picea abies (L.) Karst. as depending on trace gas concentrations

At six sites in central Germany consequences of SO₂, NO_X and O₃ deposition and of acid precipitation on canopy throughfall of sulphate, nitrate, ammonium, organic acids and of metal cations from Norway spruce crowns were investigated in the field. Measured canopy throughfall rates (mmol ion kg^-1 needle dw a^-1 are separated in (i) background ion throughfall rates in clean air and (ii) trace gas-(or acid interception)-dependent throughfall rates at ambient trace gas concentrations. Based on synchronously measured pollution, precipitation and canopy throughfall data, statistical response functions are given, which allow the separate estimation of annual rates of sulphur and nitrogen deposition into spruce canopies if only annual means of SO₂ or NO₂ concentrations in air are known. The specific SO₂ deposition rate of (0.841±0.214) mmol S kg^-1 needle dw a^-1 (nPa SO₂ Pa^-1)^-1 is 2.3 times higher than the specific stomatal SO₂ uptake. The NO₂-dependent nitrogen deposition of (2.464±0.707) mmol N kg^-1 needle dw a^-1 (nPa NO₂ Pa^-1)^-1 is 2.2 times higher than the specific stomatal NO_X (NO₂+NO) uptake. These ratios (2.32.2) are explained by the percentage of annual hours with open needle stomata. The shape of observed epicuticular SO₂ and NO_X deposition curves and of stomatal SO₂ and NO_X uptake curves are congruent. As for stomatal NO_X uptake, there is an apparent compensation point at (5 to 8) nPa NO₂ Pa^-1. There is significant SO₂-dependent canopy throughfall of Ca>K>Al>Mg>Fe in this order of relative importance. NO_X deposition in spruce canopies reduces K⁺ throughfall and it weakly promotes throughfall of Mn²⁺ and Zn²⁺. There was no significant codeposition of sulphate and ammonium and no ion exchange of intercepted H₃O⁺ with nutrient cations at the measured ambient pH values of the precipitation water. In the presence of O₃, throughfall of Mn²⁺ is reduced and throughfall of K⁺, Ca²⁺ and Al³⁺ is enhanced. In the cooperative presence of SO₂, NO₂ and O₃ pollution in the field there is a 1.3-fold increase of the annual K⁺ demand and a 1.5-fold Mg²⁺ demand of spruce canopies relative to the situation in clean air. This trace gas-dependent additional cation demand of spruce canopies corresponds to a needle loss percentage of (23 to 33)% if the additional K⁺ and Mg²⁺ throughfall could not be recycled in spruce ecosystems. Observed canopy thinning ranges from (13 to 26)% at the investigated six spruce stands.Abbreviations A_spec Specific needle surface area per kg needle dry matter (m²kg^-1 needle dw) - A_tot Total needle surface of spruce stands (ha ha^-1) - [gas]_a Ambient trace gas concentration (gas=SO₂; NO₂ or O₃) in air (nPa Pa^-1=ppb) - GP Number of days per annual growth period d a^-1) - IC_H30 ⁺ Acid interception rate (Eq H₃O⁺ kg^-1 needle dw a^-1) - k_o Trace gas-independent ion throughfall rate constant (mmol kg^-1 needle dw a^-1) - k_gas SO₂-,NO₂-or O₃-dependent ion throughfall rate per unit of trace gas pollution (mmol kg^-1 needle dw a^-1 (nPa Pa^-1)^-1) - k_H30 Specific H₃O⁺/Me⁺ exchange ratio (mol mol^-1) - L_o Background throughfall rate at [gas]_a=0 (mmol kg^-1 needle dw a^-1) - L_ion Canopy throughfall rate of ions (mmol kg^-1 needle dw a^-1) - L'_ion Trace gas dependent ion throughfall (mEq kg^-1 needle dw a^-1 (nPa Pa^-1)^-1) - LAI Leaf area index of the canopy (m² projected needle surface m^-2 ground) - Me⁺ Equivalents of metal cations (Eq) - N Stock of needles of spuce stands in the field (kg needle dw ha^-1) - P_% Percentage of needle loss relative to a healthy reference (%) - r Pearson correlation coefficient (no dimension) - R COO^--Sum of all organic anion equivalents Cat⁺ - An^- (Eq kg^-1 needle dw a^-1) - An^- Sum of all measured inorganic anion equivalents (Eq kg^-1 needle dw a^-1) - Cat⁺ Sum of all measured inorganic cation equivalents (Eq kg^-1 needle dw a^-1)     

Seasonal changes in the utilization and turnover of assimilation products in 8-year-old Scots pine (Pinus sylvestris L.) trees

Summary The present study aimed at a physiological understanding of the seasonal changes of the carbohydrate patterns and levels in the various tissues of 8-year-old Scots pine (Pinus sylvestris L.) trees growing under ambient climatic conditions in the botanical garden at Bayreuth. The photosynthates of selected twig sections were labelled by ¹⁴CO₂ fixation and after chase periods of 1 h up to 8 months, the distribution of radiocarbon in the whole trees was determined and the labelling of identified carbohydrates was compared with the levels of these compounds in the individual tissues. Bud break and sprouting in spring is exclusively supplied by the recent photosynthates of the previous year's needles. During summer assimilates of the old needles were utilized for secondary growth of the axial system while growth of the recent-year's shoots was supported by their own photosynthesis. In autumn, soluble carbohydrates were produced instead of starch, a major part of which in addition to recent photosynthates was utilized for root growth during the cold season. Another part of the autumnal storage material was incorporated into the cell walls of the latest xylem and phloem elements still in winter. A pronounced starch-oligosaccharide interconversion upon frost hardening, and its reversal in spring as has been described for deciduous trees, could not be observed. This was due to maintenance of photosynthetic capability even in the cold season and the replacement of consumed storage material especially in late winter and early spring by new photosynthates.     

Studies onArtemisia afra Jacq.: The phloem in stem and leaf

Summary The structure of the phloem was studied in stem and leaf ofArtemisia afra Jacq., with particular attention being given to the sieve element walls. Both primary and secondary sieve elements of stem and midvein have nacreous walls, which persist in mature cells. Histochemical tests indicated that the sieve element wall layers contained some pectin. Sieve element wall layers lack lignin. Sieve elements of the minor veins (secondary and tertiary veins) lack nacreous thickening, although their walls may be relatively thick. These walls and those of contiguous transfer cells are rich in pectic substances. Transfer cell wall ingrowths are more highly developed in tertiary than in secondary veins.     

Seasonal trends in leaf photosynthesis and stomatal conductance of drought stressed and nonstressed pearl millet as associated to vapor pressure deficit

Single leaf photosynthesis (Pn) and stomatal conductance (Cg) of drought stressed and nonstressed pearl millet [Pennisetum americanum (L.) Leeke] were measured across growth stages to determine if a pattern exists in Pn and Cg during the growing season and to evaluate the influence of air vapor pressure deficit (VPD_a) on the seasonal variations of Pn and Cg. Leaf photosynthesis and Cg were measured independently on pearl millet plants grown at the driest (drought stressed) and wettest (nonstressed) ends of a line-source irrigation gradient system. Well defined and predictable variations in both Pn and Cg were found across two growing seasons. Leaf photosynthesis of the nonstressed plants declined from a maximumof 25.8 mol m^–2 s^–1 at the flag leaf emergence (48 days after planting, DAP) to a minimum of 14.5 mol m^–2 s^–1 at physiological maturity. Stomatal conductance of the nonstressed plants peaked at the flowering and early grain fill stages and declined as plants approached maturity. In contrast, Pn and Cg of the stressed plants declined from a maximum at flag leaf emergence to a minimum at flowering and increased as plants approached maturity. High VPD_a during the flowering and grain fill stages induced stomatal closure and decreased Pn in the stressed plants. High mid-season VPD_a did not induce stomatal closure and did not reduce leaf photosynthesis in nonstressed plants. The lack of sensitivity of Pn to VPD_a in the nonstressed treatment suggests large air VPD such as that prevalent in southern Arizona does not limit the growth of irrigated pearl millet by limiting CO₂ assimilation.Abbreviations Cg stomatal conductance - DAP days after planting - Pn leaf photosynthesis - VPD_a air vapor pressure deficit - VPD_1-a leaf to air vapor pressure deficit Contribution of the Arizona Agricultural Experimental Station. Research supported in part by INTSORMIL/USAID.     

Differentiation among populations of Sedum wrightii (Crassulaceae) in response to limited water availability: water relations,CO2 assimilation,growth and survivorship

Summary Sedum wrightii is one of only a few species in the Crassulaceae for which there is evidence for a high degree of variability in the ratio of daytime to nighttime CO₂ assimilation. There are both environmental and genetic components to this variability. S. wrightii grows over a wide altitudinal gradient. The purpose of this study was to compare low, intermediate, and high altitude populations with respect to the degree of CAM expression and the capability to tolerate limited water availability. We utilized clonallyreplicated genotypes of plants from each population in common environment greenhouse experiments. Genetic differences among the populations were found in long-term water use efficiency, in 24 hour CO₂ exchange patterns, in biomass ¹³C values, in carbon allocation, and in water status and ultimately survival during prolonged drought. The differences among the populations appear to be closely related to differences in the native habitats. The low altitude, desert plants had the greatest ability to grow and survive under conditions of limited water availability and appear to have the greatest shift to nighttime CO₂ uptake during periods without water, while the high altitude plants had the poorest performance under these conditions and appear to shut down net carbon uptake when severely water limited.     

Carbon fixation and carbonic anhydrase activity in Haslea ostrearia (Bacillariophyceae) in relation to growth irradiance

The metabolic pathway of primary carbon fixation was studied in a peculiar pennate marine diatom, Haslea ostrearia (Bory) Simonsen, which synthesizes and accumulates a blue pigment known as “marennine”. Cells were cultured in a semi-continuous mode under saturating [350 μmol(photon) m⁻² s⁻¹] or non-saturating [25 μmol(photon) m⁻² s⁻¹] irradiance producing “blue” (BC) and “green” (GC) cells, characterized by high and low marennine accumulation, respectively. Growth, pigment contents (chlorophyll a and marennine), ¹⁴C accumulation in the metabolites, and the carbonic anhydrase (CA) activity of the cells were determined during the exponential growth phase. Growth rate and marennine content were closely linked to irradiance during growth: higher irradiance increased both growth rate and marennine content. On the other hand, the Chl a concentration was lower under saturating irradiance. The distribution between the Calvin-Benson (C₃) and β-carboxylation (C₄) pathways was very different depending on the irradiance during growth. Metabolites of the C₃ cycle contained about 70 % of the total fixed radioactivity after 60 s of incorporation into cells cultured under the non-saturating irradiance (GC), but only 47 % under saturating irradiance (BC). At the same time, carbon fixation by β-carboxylation was 24 % in GC versus about 41 % in BC, becoming equal to that in the C₃ fixation pathway in the latter. Internal CA activity remained constant, but the periplasmic CA activity was higher under low than high irradiance.     

Respiration and photosynthesis in cones of Norway spruce (Picea abies (L.) Karst.)

Summary Dark respiration and photosynthetic carbon dioxide refixation in purple and green Picea abies cones were investigated from budbreak to cone maturity. The rate of dark respiration per unit dry weight and CO₂ refixation capacity decreased during cone maturation. At the beginning of the growing season, photosynthetic CO₂ refixation could reduce the amount of CO₂ released by respiration in green and purple cones by 50% and 40%, respectively. The seasonal performance of the components of the cone carbon balance was calculated using information on the seasonal course of respiration, refixation capacity and the light response curves of cone photosynthesis, as well as the actual light and temperature regime in the field. The daily gain of CO₂ refixation reached 28%–34% of respiration in green and 22%–26% in purple cones during the first month of their growth, but decreased later in the season. Over the entire growth period refixation reduced carbon costs of cone production in both cone colour polymorphs by 16%–17%.     

Variable HCO 3 - affinity of Elodea canadensis Michaux in response to different HCO 3 - and CO2 concentrations during growth

Summary Elodea canadensis grows over a wide range of inorganic carbon, nutrient, and light conditions in lakes and streams. Affinity for HCO ₃ ^- use during photosynthesis ranged from strong to weak in Elodea collected from seven localities with different HCO ₃ ^- and CO₂ concentrations. The response to HCO ₃ ^- was also very plastic in plants grown in the laboratory at high HCO ₃ ^- concentrations and CO₂ concentrations varying from 14.8 to 2,200 M. Bicarbonate affinity was markedly reduced with increasing CO₂ concentrations in the growth medium so that ultimately HCO ₃ ^- use was not detectable. High CO₂ concentrations also decreased CO₂ affinity and induced high CO₂ compensation points (360M CO₂) and tenfold higher half-saturation values (800 M CO₂).The variable HCO ₃ ^- affinity is probably environmentally based. Elodea is a recently introduced species in Denmark, where it reproduces only vegetatively, leaving little opportunity for genetic variation. More important, local populations in the same water system had different HCO ₃ ^- affinities, and a similar variation was created by exposing one plant collection to different laboratory conditions.Bicarbonate use enabled Elodea to photosynthesize rapidly in waters of high alkalinity and enhanced the carbon-extracting capacity by maintaining photosynthesis above pH 10. On the other hand, use of HCO ₃ ^- represents an investment in transport apparatus and energy which is probably not profitable when CO₂ is high and HCO ₃ ^- is low. This explanation is supported by the findings that HCO ₃ ^- affinity was low in field populations where HCO ₃ ^- was low (0.5 and 0.9 m M) or CO₂ was locally high, and that HCO ₃ ^- affinity was suppressed in the laboratory by high CO₂ concentrations.Abbreviations DIC dissolved inorganic carbon (CO₂+ HCO ₃ ^- +CO ₃ ^- ) - CO₂ compensation point - K _1/2 apparent halfsaturation constant - P_{HCO 3} ^– interpolated photosynthesis in pure HCO ₃ ^- and zero CO₂ - P_max photosynthetic rate under carbon and light saturation     

Effects of temperature and CO2 enrichment on kinetic properties of NADP+-malate dehydrogenase in two ecotypes of Barnyard grass (Echinochloa crus-galli (L.) Beauv.) from contrasting climates

Summary The apparent energy of activation (E _a), Michaelis-Menten constant (K _mfor oxaloacetate), V _max/K _mratios and specific activities of NADP⁺-malate dehydrogenase (NADP⁺-MDH; EC 1.1.1.82) were analyzed in plants of Barnyard grass from Québec (QUE) and Mississippi (MISS) acclimated to two thermoperiods 28/22°C, 21/15°C, and grown under two CO₂ concentrations, 350 l l^-1 and 675 l l^-1. E _avalues of NADP⁺-MDH extracted from QUE plants were significantly lower than those of MISS plants. K _mvalues and V _max/K _mratios of the enzyme from both ecotypes were similar over the range of 10–30°C but reduced V _max/K _mratios were found for the enzyme of QUE plants at 30 and 40°C assays. MISS plants had higher enzyme activities when measured on a chlorophyll basis but this trend was reversed when activities were expressed per fresh weight leaf or per leaf surface area. Activities were significantly higher in plants of both populations acclimated to 22/28°C. CO₂ enrichment did not modify appreciably the catalytic properties of NADP⁺-MDH and did not have a compensatory effect upon catalysis or enzyme activity under cool acclimatory conditions. NADP⁺-MDH activities were always in excess of the amount required to support observed rates of CO₂ assimilation and these two parameters were significantly correlated. The enhanced photosynthetic performance of QUE plants under cold temperature conditions, as compared to that of MISS plants, cannot be attributed to kinetic differences of NADP⁺-malate dehydrogenase among these ecotypes.     

Growth and photosynthetic response of nine tropical species with long-term exposure to elevated carbon dioxide

Summary Seedlings of nine tropical species varying in growth and carbon metabolism were exposed to twice the current atmospheric level of CO₂ for a 3 month period on Barro Colorado Island, Panama. A doubling of the CO₂ concentration resulted in increases in photosynthesis and greater water use efficiency (WUE) for all species possessing C₃ metabolism, when compared to the ambient condition. No desensitization of photosynthesis to increased CO₂ was observed during the 3 month period. Significant increases in total plant dry weight were also noted for 4 out of the 5 C₃ species tested and in one CAM species, Aechmea magdalenae at high CO₂. In contrast, no significant increases in either photosynthesis or total plant dry weight were noted for the C₄ grass, Paspallum conjugatum. Increases in the apparent quantum efficiency (AQE) for all C₃ species suggest that elevated CO₂ may increase photosynthetic rate relative to ambient CO₂ over a wide range of light conditions. The response of CO₂ assimilation to internal C_i suggested a reduction in either the RuBP and/or Pi regeneration limitation with long term exposure to elevated CO₂. This experiment suggests that: (1) a global rise in CO₂ may have significant effects on photosynthesis and productivity in a wide variety of tropical species, and (2) increases in productivity and photosynthesis may be related to physiological adaptation(s) to increased CO₂.     

15N estimates of nitrogen fixation by white clover (Trifolium repens L.) growing in a mixture with ryegrass (Lolium perenne L.)

The ¹⁵N isotope dilution technique and the N difference method were used to estimate N₂ fixation by clover growing in a mixture with ryegrass, in a field experiment and a controlled environment experiment. Values obtained using N difference were approximately 25% lower than those estimated using ¹⁵N isotope dilution. In the field experiment there was a measured N benefit to grass growing with clover, equivalent to 42.7 kgN ha^-1. The grass in the mixture had a lower atom %¹⁵N content and a higher N content than grass in a monoculture; therefore values for N₂ fixation were different depending on choice of control plant i.e. monoculture or mixture grass. In the controlled environment experiment there were no significant differences between either the atom %¹⁵N contents or the N contents of monoculture grass and grass growing in a mixture with clover. It is concluded that there is a long term indirect transfer of N from clover to associated grass which can lead to errors in estimates of N₂ fixation.     

CO2 fixation in stem slices of Picea abies (L.) Karst: microautoradiographic studies

Summary Microautoradiography was used to show that chlorophyllous cells of young Picea abies stem slices are able to fix ¹⁴CO₂, in the dark as well as in the light. The amount of ¹⁴CO₂ fixed in the dark is much lower than that in the light. In the dark the concentration of radioactive label is equally high in all chlorophyllous cells of the stem. In the light, however, a gradient of radioactive assimilates extends from the stem surface to its centre, with the highest concentration being located in the phelloderm and the outer one-third of the cortex. This is in spite of even illumination and CO₂ supply across the whole stem slice. In the dark, stem slices with and without bark show the same amount of radioactive label in the chlorophyllous cells of xylem, perimedullary region and pith. In the light, however, the concentration of radioactive assimilates in these cells is much higher in stem slices with bark than in stem slices without bark. It is assumed therefore that light fixation products of phelloderm and cortex are transported radially into the tissue inside the cambium.     

Photosynthetic characteristics of mesophyll eells isolated from sunflower (helianthus annuus L.) leaves

Mesophyll cells were isolated from sunflower leaves by an enzymic procedure. The cell suspensions possessed high photosynthesis rates. The products of cell photosynthesis were similar to the products of leaf disc photosynthesis. The relatively high radioactivity incorporated into malate after ¹⁴CO₂ feeding suggests that PEP carboxylase might participate in CO₂ fixation. Sunflower leaf extracts possessed a PEP carboxylase activity slightly higher than that of other C₃ species. Inhibition of PEP carboxylase by maleate decreased cell photosynthesis by only 15% and the first products of cell photosynthesis were phosphorylated compounds. It is concluded that the high photosynthesis rates displayed by sunflower are not due to a parallel C₄ pathway of photosynthesis but are rather dependent, at least in part, on the activity, or the amount, of RuBP carboxylase.Abbreviations PVP polyvinylpyrrolidone - PDS potassium dextran sulfate - DTT dithiothreitol - PEG polyethyleneglycol - RuBP ribulose 1,5-bisphosphate - PEP phosphoenolpyruvate - Mes 2-(N-morpholino) ethanesulfonic acid - Hepes N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid     

Intra- specific variation in response of Jatropha (Jatropha curcas L.) to elevated CO2 conditions

Twenty genotypes of Jatropha collected from diverse eco-geographic regions from the states of Chhattisgarh (3), Andhra Pradesh (12), Rajasthan (4) and Uttarakhand (1) of India were subjected to elevated CO₂ conditions. All the genotypes showed significant difference (p < 0.05 and 0.01) in the phenotypic traits in both the environments (elevated and ambient) and genotype x environment interaction. Among the physiological traits recorded, maximum photosynthetic rate was observed in IC565048 (48.8 μmol m⁻² s⁻¹) under ambient controlled conditions while under elevated conditions maximum photosynthetic rate was observed in IC544678 (41.3 μmol m⁻² s⁻¹), and there was no significant difference in the genotype x environment interaction. Stomatal conductance (Gs) emerged as the key factor as it recorded significant difference among the genotypes, between the environments and also genotype x environment interaction. The Gs and transpiration (E) recorded a significant decline in the genotypes under the elevated CO₂ condition over the ambient control. Under elevated CO₂ conditions, the minimum values recorded for Gs and E were 0.03 mmol m⁻² s⁻¹ and 0.59 mmol m⁻² s⁻¹ respectively in accession IC565039, while the maximum values for Gs and E were 1.8 mmol m⁻² s⁻¹ and 11.5 mmol m⁻² s⁻¹ as recorded in accession IC544678. The study resulted in the identification of potential climate ready genotypes viz. IC471314, IC544654, IC541634, IC544313, and IC471333 for future use.     

Potential risks for European beech (Fagus sylvatica L.) in a changing climate

Over large areas of Europe, coniferous monocultures are being transformed into mixed forests by the re-introduction of broadleaf tree species belonging to the potential natural vegetation. One important species of interest in this changing forest policy is European beech (Fagus sylvatica). However, at present, this forest management directive has ignored potential adverse effects of global climate change on wide-spread re-introduction of beech to these areas. Average global surface temperatures have risen by approx. 0.8°C in the period between 1861 and 2005 and are expected to continue to increase until the end of this century by 1.5–5.8°C above the 1990 value. To estimate the climate change in the southern part of central Europe in future, we reviewed calculations from regional climate models. Temperature increase for the southern part of central Europe is projected to be up to 2°C within the next 40 years. In contrast, the annual precipitation will most likely remain constant over the same time period, but will experience significant changes in seasonal patterns. Rising intensities of individual precipitation events may result in increasing number and intensities of flooding events and reduced precipitation during the growing season in a higher frequency of summer droughts. Growth and competitive ability of European beech will not, necessarily, respond to increasing CO₂ concentrations but may be strongly impacted by intensive drought that occurs during the growing season. Seedlings as well as adult trees may suffer from xylem embolism, restricted nutrient uptake capacity and reduced growth under limited water availability. However, it remains uncertain to what extent other environmental factors (e.g. soil properties, competitive interactions) may modify the drought response of beech, thus either enhancing susceptibility or increasing drought tolerance and resilience potential. Water-logged soils, predicted during the spring for several regions due to higher than average precipitation, could negatively impact nutrient uptake and growth of beech. Whereas other dominant species as, e.g. oak are well adapted to that environmental stress, beech is known to be sensitive to water-logging and flooding. Thus, the competitive capacity of beech might—depending on the other environmental conditions—be reduced under the expected future climate conditions. Silvicultural practices must be aware today of the potential risks which a changing climate may impose on sustainable forest development.     

Responses of photosynthesis to irradiance and temperature in soybean,Glycine max (L.) Merr

The response of photosynthesis to irradiance and temperature during growth was investigated in two soybean genotypes. Soybean is a species that can modify its structure and metabolism so as to adapt to differing light conditions; its responses to rapid changes in irradiance are characterized by their flexibility. However, the temperature during growth can change the response to irradiance: moreover, there may be a marked interaction with genotype.The response of photosynthesis to irradiance consists of changes in leaf thickness, which bring about variations in the mesophyll resistance to CO₂ transfer. The increase in net photosynthesis per unit of leaf area is due to the increase in the amount of assimilating material beneath unit of area, as corroborated by the stability of the net photosynthesis per unit volume. Moreover, the response of photosynthesis to temperature is due to the mesophyll diffusion constant which decreases with the growth temperature.