Giant rosettes are ones of the most striking features of the vegetation in the high tropical Andes, with Coespeletia moritziana reaching the highest altitudes up to 4,600 m a.s.l. Different from other giant rosettes, this species grows on rock outcrops with poorly developed soils and where water availability may be limited. Two questions are addressed in this study: How does this species respond in terms of water relations to maintain favorable gas-exchange conditions? Considering that adult plants rely on a water-reserving central pith, how do early stages respond to this environment’s extreme conditions? Water relations and gas-exchange studies were carried out on juveniles, intermediate and adult C. moritziana plants during wet and dry seasons in Páramo de Piedras Blancas at 4,200 m a.s.l. Adult plants maintained higher leaf water potentials (ΨL) during the wet season, however, no differences between stages were found for the dry season. Minimum dry season ΨL were never near the turgor loss point in any of the stages. Juveniles show a more strict stomatal control during the dry season to maintain a favorable water status. Net photosynthesis significantly decreased in intermediate and juvenile stages from wet to dry seasons. Our results suggest that
C. moritziana resists more extreme conditions compared to other Andean giant rosettes., F. Rada, A. Azócar, A. Rojas-Altuve., and Obsahuje bibliografii
In order to address the question of how elevated CO2 concentration (EC) will affect the water relations and leaf anatomy of tropical species, plants of Jatropha gossypifolia L. and Alternanthera crucis (Moq.) Bondingh were grown in five EC open top chambers (677 μmol mol-1) and five ambient CO2 concentration (AC) open top chambers (454 μmol mol-1) with seasonal drought. No effect of EC was found on morning xylem water potential, leaf osmotic potential, and pressure potential of plants of J. gossypifolia. In A. crucis EC caused a significant increase in morning xylem water potential of watered plants, a decrease in osmotic potential, and an increase of 24-79 % in pressure potential of moderately droughted plants. This ameliorated the effects of drought. Stomatal characteristics of both leaf surfaces of J. gossypifolia and A. crucis showed time-dependent, but not [CO2]-dependent changes. In J. gossypifolia the thickness of whole leaf, palisade parenchyma, and spongy parenchyma, and the proportion of whole leaf thickness contributed by these parenchymata decreased significantly in response to EC. In A. crucis EC caused an increase in thickness of whole leaf, bundle sheath, and mesophyll, while the proportion of leaf cross-section comprised by the parenchymata remained unchanged. These effects disappeared with time under treatment, suggesting that acclimation of the leaf anatomy to the chambers and to EC took place in the successive flushes of leaves produced during the experiment. and E. Rengifo, R. Urich, A. Herrera.
We studied the seasonal changes in water relations, chlorophyll a fluorescence, and leaf saccharide contents of the tropical flood-tolerant trees Acosmium nitens, Campsiandra laurifolia, Eschweilera tenuifolia, Symmeria paniculata, and Psidium ovatifolium. Xylem water potential increased with flooding to a larger extent than leaf sap osmotic potential in all the species, and soluble sugars contributed up to 66 % of osmotic potential at maximum flooding. Starch was accumulated in leaves. Maximum quantum yield of photosystem 2 decreased in emerged leaves, values being always higher than 0.76. Daily maximum net photosynthetic rate and leaf conductance decreased in all the species. This reduction was associated in all the species but S. paniculata with the absence of a compensatory increase in non-photochemical quenching. and E. Rengifo, W. Tezara, A. Herrera.
Haloxylon ammodendron, Calligonum mongolicum, Elaeagnus angustifolia, and Populus hosiensis had different adaptations to limited water availability, high temperature, and high irradiance. C. mongolicum used water more efficiently than did the other species. Because of low transpiration rate (E) and low water potential, H. ammodendron had low water loss suitable for desert conditions. Water use efficiency (WUE) was high in E. angustifolia, but high E and larger leaf area made this species more suitable for mesic habitats; consequently, this species is important in tree shelterbelts. P. hosiensis had low WUE, E, and photosynthesis rates, and therefore, does not prosper in arid areas without irrigation. High irradiances caused photoinhibition of the four plants. The decrease of photochemical efficiency was a possible non-stomata factor for the midday depression of C. mongolicum. However, the species exhibited different protective mechanisms against high irradiance under drought stress. H. ammodendron and C. mongolicum possessed a more effective antioxidant defence system than E. angustifolia. These three species showed different means of coping with oxidative stress. Hence an enzymatic balance is maintained in these plants under adverse stress conditions, and the concerted action of both enzymatic and non-enzymatic reactive oxygen species scavenging mechanisms is vital to survive adverse conditions. and J. R. Gong ... [et al.].
Among various epiphytic ferns found in the Brazilian Atlantic Forest, we studied Vittaria lineata (L.) Smith (Polypodiopsida, Pteridaceae). Anatomical characterization of the leaf was carried out by light microscopy, fluorescence microscopy, and scanning electron microscopy. V. lineata possesses succulent leaves with two longitudinal furrows on the abaxial surface. We observed abundant stomata inside the furrows, glandular trichomes, paraphises, and sporangia. We examined malate concentrations in leaves, relative water content (RWC), photosynthetic pigments, and chlorophyll (Chl) a fluorescence in control, water-deficient, and abscisic acid (ABA)-treated plants. Plants subjected to drought stress (DS) and treated by exogenous ABA showed significant increase in the malate concentration, demonstrating nocturnal acidification. These findings suggest that V. lineata could change its mode of carbon fixation from C3 to the CAM pathway in response to drought. No significant changes in RWC were observed among treatments. Moreover, although plants subjected to stress treatments showed a significant decline in the contents of Chl a and b, the concentrations of carotenoids were stable. Photosynthetic parameters obtained from rapid light curves showed a significant decrease after DS and ABA treatments., B. D. Minardi, A. P. L. Voytena, M. Santos, Á. M. Randi., and Obsahuje bibliografii
Midday measurements of single leaf gas exchange rates of upper canopy leaves of soybeans grown in the field at 350 (AC) and 700 (EC) µmol(CO2) mol-1 in open topped chambers sometimes indicated up to 50 % higher net photosynthetic rates (PN) measured at EC in plants grown at AC compared to EC. On other days mean PN were nearly identical in the two growth [CO2] treatments. There was no seasonal pattern to the variable photosynthetic responses of soybean to growth [CO2]. Even on days with significantly lower PN in the plants grown at EC, there was no reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase, chlorophyll, or soluble protein contents per unit of leaf area. Over three years, gas exchange evidence of acclimation occurred on days when either soil was dry or the water vapor pressure deficit was high (n = 12 d) and did not occur on days after rain or on days with low water vapor pressure deficit (n = 9 d). On days when photosynthetic acclimation was evident, midday leaf water potentials were consistently 0.2 to 0.3 MPa lower for the plants grown at EC than at AC. This suggested that greater susceptibility to water stress in plants grown at EC cause the apparent photosynthetic acclimation. In other experiments, plants were grown in well-watered pots in field chambers and removed to the laboratory early in the morning for gas exchange measurements. In these experiments, the amount of photosynthetic acclimation evident in the gas exchange measurements increased with the maximum water vapor pressure deficit on the day prior to the measurements, indicating a lag in the recovery of photosynthesis from water stress. The apparent increase in susceptibility to water stress in soybean plants grown at EC is opposite to that observed in some other species, where photosynthetic acclimation was evident under wet but not dry conditions, and may be related to the observation that hydraulic conductance is reduced in soybeans when grown at EC. The day-to-day variation in photosynthetic acclimation observed here may account for some of the conflicting results in the literature concerning the existence of acclimation to EC in field-grown plants. and J. A. Bunce, R. C. Sicher.
Seedlings of Cyamopsis tetragonoloba were grown on Petri dishes either in water or water plus 3 % PEG-6000 to induce water stress. The senescing cotyledons experiencing the stress exhibited loss in contents of leaf proteins and chlorophyll (Chl) and a decline in oxygen evolution. The effect of PEG treatment was more pronounced at moderate (MI) than low (LI) irradiance. The stress-induced loss in the activity of superoxide dismutase and increase in the thylakoid lipid peroxidation accompanied a change in the physical status of the bilayer membrane as demonstrated by an enhancement of room temperature Chl a fluorescence polarization and decrease in energy transfer efficiency in pigment assembly. This resulted in a sustained decrease in photosystem 2 activity blocking channels of energy utilization. The absorbed quanta, thus unutilized, were excess even at MI, leading to photoinhibitory response. and P. M. Deo, U. C. Biswal, B. Biswal.
Responses to drought were studied using two maize inbred lines (B76 and B106) and a commercial maize hybrid (Zea mays L. cv. Silver Queen) with differing resistance to abiotic stress. Maize seedlings were grown in pots in controlled environment chambers for 17 days and watering was withheld from one half the plants for an additional 11 days. On the final treatment date, leaf water potentials did not differ among genotypes and were -0.84 and -1.49 MPa in the water sufficient and insufficient treatments, respectively. Greater rates of CO2 assimilation were retained by the stress tolerant maize inbred line, B76, in comparison to the other two genotypes 11 days after watering was withheld. Rates of CO2 assimilation for all three genotypes were unaffected by decreasing the measurement O2 concentration from 21 to 2% (v/v). Activities of phosphoenolpyruvate carboxylase (PEPC), NADP-malic enzyme (NADP-ME), and NADP malate dehydrogenase were inhibited from 25 to 49% by the water deficiency treatment. Genotypic differences also were detected for the activities of NADP-ME and for PEPC. Changes of transcript abundance for the three C4 pathway enzymes also varied among watering treatments and genotypes. However, examples where transcripts decreased due to drought were associated with the two stress susceptible genotypes. The above results showed that enzymes in the C4 photosynthetic pathway were less inhibited by drought in stress tolerant compared to stress susceptible maize genotypes., R. Sicher, J. Bunce, J. Barnaby, B. Bailey., and Obsahuje bibliografii
Effects of water and nitrogen (N) supply on growth and photosynthetic response of B. carinata were examined in this study. Plant growth and related characteristics varied significantly in response to the availability of water and nitrogen. B. carinata maximized the utilization efficiency of the most limiting resources by developing physiological adaptations, such as changes in root and leaf development. The utilization of water and N was tightly linked with the availability of each resource. Instantaneous water-use efficiency (WUE) was always greater in plants with high-N nutrition [50, 100, and 150 kg(N) ha-1] than in the low-N-treated plants
[0 kg(N) ha-1] in all watering treatments. Instantaneous N-use efficiency (PNUE) decreased significantly with increasing water stress in all N treatments. Seed yield is significantly related to PNUE (p>0.05) but not WUE (p<0.05). The positive relationship between leaf net photosynthetic rate (PN) and seed yield suggests that PN can be used as an important tool for selection of new strains with high seed yield. and X. Pan ... [et al.].
Environmental conditions that promote photorespiration are considered to be a major driving force for the evolution of C4 species from C3 ancestors. The genus Flaveria contains C3 and C4 species as well as a variety of intermediate species. In this study, we compare the water-use efficiency of intermediate Flaveria species to that of C3 and C4 species. The results indicate that under both well-watered and a drought-stress condition, C3-C4 and C4-like intermediacy in Flaveria species improve water-use efficiency as compared to C3 species. and M. C. Dias, W. Brüggemann.