Gas exchange, photochemical efficiency, and leaf water potential (Ψl) of Salix matsudana (non-indigenous species), S. microstachya and S. gordejevii (indigenous species) were studied in Hunshandak Sandland, China. Ψl of all the three species decreased from 06:00 to 12:00, and increased afterwards. S. matsudana showed higher values of Ψl than others. Net photosynthetic rate (PN) and stomatal conductance (gs) of S. matsudana were the lowest among all, with the maximum PN at 10:00 being 75% of that of S. gordejevii. Compared with the indigenous species, the non-indigenous S. matsudana had also lower transpiration rate (E) and water use efficiency (WUE). The values of Fv/Fm in all the species were lower from 06:00 to 14:00 than those after 14:00, indicating an obvious depression in photochemical efficiency of photosystem 2 in both non-indigenous and native species. However, it was much more depressed in S. matsudana, the non-indigenous tree. PN was positively correlated to gs and negatively related to Ψl. The relationship between gs and vapour pressure difference (VPD) was exponential, while negative linear correlation was found between gs and Ψl. and M. Z. Liu ... [et al.].
We studied water relations and gas exchange in six almond genotypes grafted on GF677 in response to withholding irrigation for 14 days and a subsequent 10-day rehydration period. The responses to drought stress significantly differed in the almond genotypes; the tolerant plants were distinguished and monitored. Leaf relative water content (RWC) decreased by more than 23%, leaf water potential dropped to less than -4.3 MPa, and electrolyte leakage increased to 43% in dehydration-sensitive genotypes. Photosynthesis (PN) and stomatal conductance (gs) of drought-sensitive genotypes were significantly reduced by 70% and 97% in response to water deficiency. Water stress significantly enhanced wateruse efficiency up to 10 folds in drought-tolerant almonds. The difference between leaf temperature and its surrounding air temperature (ΔT) increased significantly to more than 187% under water stress in drought-tolerant genotypes. In addition, the reduction in the g s and further ability to preserve RWC were involved probably in drought-tolerance mechanism in almond. Negative significant correlations were found between ΔT, PN, and gs. Based on the correlations, we suggested that ΔT could be used as a simple measurement for monitoring water stress development in the irrigation management of almond orchards. In conclusion, ‘Supernova’ and the Iranian genotypes ‘6-8’ and ‘B-124’, were found to be more droughttolerant compared with other genotypes in this experiment., S. Karimi, A. Yadollahi, K. Arzani, A. Imani, M. Aghaalikhani., and Obsahuje bibliografii
The effect of CO2 increase on gas exchange and water-use effíciency (WUE) in three temperate deciduous species (Fagus crenata, Ginkgo biloba and Alnus firma) under gradually-developing drought-stress was assessed. Seedlings were grown within transparent open-top cabinets and maintained for 4 monťhs at mean CO2 concentrations of either 350 (ambient; C350) or 700 pmol moT’ (elevated; C700) and combined with five water regimes [leaf water potential, higher than -0.3 (well- watered), -0.5 and -0.8 (moderate drought), -1.0 and lower than -1.2 MPa (serious drought-stress)]. Increase in CO2 concentration induced a 60 % average increase in net photosynthetic rate (P^) under well-watered conditions. The effect of C700 became more pronounced with drought stress established, with an 80 % average increase in at as low as -0.8 MPa; leaf conductance to water vapour transfer (gs) and transpiration rate (£), however, were significantly decreased. Consequently, WUE increased under drought, through drought stress affected potential E sooner than potential P^. The interaction of CO2 x drought stress on WUE was significant in that Pn was stimulated while E in C700 enriched plants resembled that of C350 plants under drought. Hence if a doubling of atmospheric CO2 concentration occurs by the mid 2U* century, then greater P^ in F. crenata, G. biloba and^. firma may be expected and the drought susceptibility of these species will be substantially enhanced.
Leaf gas exchange and plant water relations of three co-occurring evergreen Mediterranean shrubs species, Quercus ilex L. and Phillyrea latifolia L. (typical evergreen sclerophyllous shrubs) and Cistus incanus L. (a drought semi-deciduous shrub), were investigated in order to evaluate possible differences in their adaptive strategies, in particular with respect to drought stress. C. incanus showed the highest annual rate of net photosynthetic rate (PN) and stomatal conductance (gs) decreasing by 67 and 69 %, respectively, in summer. P. latifolia and Q. ilex showed lower annual maximum PN and gs, although PN was less lowered in summer (40 and 37 %, respectively). P. latifolia reached the lowest midday leaf water potential (Ψ1) during the drought period (-3.54±0.36 MPa), 11 % lower than in C. incanus and 19 % lower than in Q. ilex. Leaf relative water content (RWC) showed the same trend as Ψ1. C. incanus showed the lowest RWC values during the drought period (60 %) while they were never below 76 % in P. latifolia and Q. ilex; moreover C. incanus showed the lowest recovery of Ψ1 at sunset. Hence the studied species are well adapted to the prevailing environment in Mediterranean climate areas, but they show different adaptive strategies that may be useful for their co-occurrence in the same habitat. However, Q. ilex and P. latifolia by their water use strategy seem to be less sensitive to drought stress than C. incanus. and A. Bombelli, L. Gratani.
Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-line formation at a global scale. We studied gas exchange and water relations of Polylepis tarapacana in the field, considering the possible effects of water stress limitations imposed on net photosynthetic rate (PN). Daily courses of microclimatic variables, gas exchange, and leaf water potential were measured in both dry-cold and wet-warm seasons at an altitude of 4 300 m. Marked differences in environmental conditions between seasons resulted in differences for the dry-cold and wet-warm seasons in mean leaf water potentials (-1.67 and -1.02 MPa, respectively) and mean leaf conductances (33.5 and 58.9 mmol m-2 s-1, respectively), while differences in mean PN (2.5 and 2.8 μmol m-2 s-1, respectively) were not as evident. This may be related to limitations imposed by water deficit and lower photon flux densities during dry and wet seasons, respectively. Hence P. tarapacana has coupled its gas exchange characteristics to the extreme daily and seasonal variations in temperature and water availability of high elevations. and C. García-Núñez ... [et al.].
In two hybrids of sorghum (Sorghum bicolor Moench.), C51 and C42, high nitrogen concentration (HN) increased net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) of well watered (HW) plants. Water stressing (LW plants) resulted in low PN, gs, and E in both hybrids, but the values were still higher in HN plants as compared to low nitrogen-grown (LN) plants. Intercellular CO2 concentration (Ci) increased in droughted plants. This increase was much higher in LN plants as compared to HN plants. Instantaneous water use efficiency was lower in LN plants as a consequence of a greater effect of water stress on photosynthesis. Leaf water potential was reduced by water stress in all treatments. Analysis of chlorophyll a fluorescence at room temperature showed that photosystem 2 (PS2) was rather tolerant to the water stress imposed. Water stress caused a slight decrease in the efficiency of excitation capture by open PS2 reaction centres (Fv/Fm). The in vivo quantum yield of PS2 photochemistry (ΦPS2) and the photochemical quenching coefficient (qP) were slightly reduced, while the nonphotochemical quenching coefficient (qN) was increased under the water stress. However, in hybrid C42 these characters were little or not affected by the water stress.
Plant traits of Malcolmia littorea growing at the Botanic Garden of Rome and transplanted from the wild population developing along the Latium coast (Italy) were analyzed. The highest photosynthetic rates [PN, 22.5 ± 0.5 μmol(CO2) m-2 s-1], associated to the highest chlorophyll content (Chl, 60 ± 5 SPAD units), and respiration rates [R, 11.1 ± 0.2 μmol(CO2) m-2 s-1] were reached in spring, when mean air temperature (Tm) was in the range 17°C to 23°C. PN, Chl, and R decreased by 86, 38, and 59% in summer when mean maximum air temperature (Tmax) was 30.3 ± 2.6°C. Leaf water potential decreased by 34% in summer compared to the spring value, and it was associated to a relative water content (RWC) of 74 ± 4%, and to a water-use efficiency (WUE) of 2.15 ± 0.81 μmol(CO2) mmol-1(H2O). Moreover, also low air temperatures determined a significant PN and R decreases (by 52 and 40% compared to the maximum, respectively). Responsiveness of gross photosynthetic rate (Pg) to R was higher than that to PN as underlined by the slope of the regression line between the two variables. The results underlined a low tolerance to both high- and low air temperatures of M. littorea. The selected key traits (R, WUE, Chl) by the discriminant analysis might be used to monitor the M. littorea wild population in the long time. The ex situ cultivated plants could be propagated and used to increase the individuals number of the wild population. and L. Gratani ... [et al.].
European beech (Fagus sylvatica L.) seedlings of three different origins were used to evaluate the effect of water deficit and recovery during the most vulnerable phase of forest tree life. Gas-exchange characteristics and fluorescence rapid light curves were studied in the seedlings from a warm region (PV1, 530 m a.s.l.), seedlings from a moderately warm region (PV2, 625 m a.s.l.), optimal for beech, and in seedlings from a cool region (PV3; 1,250 m a.s.l.). Changes in photosynthetic characteristics caused by water deficit were similar, but their intensity was dependent on the origin of the seedlings. Simulation of drought conditions by the interruption of watering led to a decrease in the efficiency of primary photochemistry in PSII, with the most significant decrease in the PV2 seedlings. Conversely, water deficit affected most significantly gas exchange in PV3, where the recovery process was also the worst. The PV1 demonstrated the highest resistance to water deficit. Drought-adaptation of beech seedlings at non-native sites seems to be linked to water availability and to the origin of the beech seedlings., E. Pšidová, Ľ. Ditmarová, G. Jamnická, D. Kurjak, J. Majerová, T. Czajkowski, A. Bolte., and Obsahuje bibliografii
The responses of gas exchange and chlorophyll fluorescence of field-growing Ulmus pumila seedlings to changes in simulated precipitation were studied in Hunshandak Sandland, China. Leaf water potential (Ψwp), net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) were significantly increased with enhancement of precipitation from 0 to 20 mm (p<0.01), indicating stomatal limitation of U. pumila seedlings that could be avoided when soil water was abundant. However, PN changed slightly when precipitation exceeded 20 mm (p>0.05), indicating more precipitation than 20 mm had no significant effects on photosynthesis. Maximum photochemical efficiency of photosystem 2, PS 2 (Fv/Fm) increased from 0.53 to 0.78 when rainfall increased from 0 to 10 mm, and Fv/Fm maintained a steady state level when rainfall was more than 10 mm. Water use efficiency (WUE) decreased significantly (from 78-95 to 23-27 µmol mol-1) with enhancement of rainfalls. PN showed significant linear correlations with both gs and Ψwp (p<0.0001), which implied that leaf water status influenced gas exchange of U. pumila seedlings. The 20-mm precipitation (soil water content at about 15 %, v/v) might be enough for the growth of elm seedlings. When soil water content (SWC) reached 10 %, down regulation of PS2 photochemical efficiency could be avoided, but stomatal limitation to photosynthesis remained. When SWC exceeded 15 %, stomatal limitation to photosynthesis could be avoided, indicating elm seedlings might tolerate moderate drought. and Y.-G. Li ... [et al.].
Net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), and leaf water potential (Ψl) of an annual pioneer C4 grass (Agriophyllum squarrosum) were compared under different simulated precipitation events in a field of Hunshandak Sandland, China. The increase of soil water content (SWC) had significant effect on these physiological traits (p<0.001). In the vegetative stage, the values of PN, E, and gs went up sharply when SWC increased at the beginning, while they went down with continuous increase of SWC. PN, E, and gs increased 1.4, 1.7, and 1.7 fold, respectively, with SWC range from 6.7 to 11.6 %. In the reproductive stage, similar trends were found, except for the climate with a higher SWC. This indicated that A. squarrosum was very sensitive to the small increment of SWC which might have a large photosynthetic potential. Ψl increased by about 8 % as the SWC changed from 6.7 to 8.8 %, and then maintained a steady level when the SWC was higher than 8.8 %, while the values of PN, E, and gs kept increasing even after this SWC. This might indicate that the adjustment of Ψl response to the changes of SWC lagged that of the photosynthetic parameters. and M. Z. Liu ... [et al.].