The responses of photosynthetic gas exchange, chlorophyll fluorescence, activities of antioxidant enzymes and lipid membrane peroxidation of two contrasting Picea asperata Mast. populations to 30% of full sunlight (shade) and full sunlight (sun) were investigated under well-watered and drought conditions. Two contrasting populations were from the wet and dry climate regions in China, respectively. For both populations tested, drought resulted in lower needle relative water content (RWC), CO 2 assimilation rate (A), stomatal conductance (gs) and effective PSII quantum yield (Y), and higher non-photochemical quenching (qN), superoxide dismutase (SOD), ascorbate peroxidase (APX) activities as well as malondialdehyde (MDA) levels and electrolyte leakage in sun plants, whereas these changes were not significant in shade plants. For the wet climate population, shade plants showed higher chlorophyll contents (Chla, Chlb and Chla þ b) than sun plants under both well-watered and drought conditions. Our study results implied that shade, applied together with drought, ameliorated the detrimental effects of drought. On the other hand, compared with the wet climate population, the dry climate population was more tolerant to drought in the sun treatment, as indicated by less decreases in A and mass-based leaf nitrogen content (N mass ), more responsive stomata, greater capacity for non-radiative dissipation of excitation energy as heat (analysed by qN), and higher level of antioxidant enzyme activities as well as lower MDA content and electrolyte leakage. These results demonstrated that the different physiological strategies were employed by the P. asperata populations from contrasting climate regions when the plants were exposed to drought and shade.

The effects of exogenous abscisic acid (ABA) on the acclimation of Picea asperata to water deficit were investigated in two populations originating from wet and dry climate regions of China. Exogenous ABA was sprayed onto the leaves, and changes in plant growth and structure, gas exchange, water use efficiency (WUE), endogenous ABA content, and antioxidant enzyme levels were monitored. The results demonstrated that ABA application affected the two P. asperata populations in different ways during the water deficit. ABA application resulted in significantly lower CO(2) assimilation rates (A) under water deficit in plants from the wet climate population, whereas there were no significant changes in this parameter in the dry climate population. On the other hand, ABA application significantly decreased the dry shoot biomass, stomatal conductance (g(s)), transpiration rate (E), and malondialdehyde (MDA) content, and it significantly increased the leaf mass per area (LMA), root/shoot ratio (Rs), fine root/total root ratio (Ft), WUE, ABA content, and the superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities under water-deficit conditions in the dry climate population, whereas ABA application did not significantly affect these parameters in the wet climate population. The results clearly demonstrated that sensitivity to an exogenous ABA application is population-dependent in P. asperata. Direct evidence is presented that variation in physiological mechanisms rather than different rates of ABA absorption explain the population differentiation in the sensitivity to exogenous ABA, and that the physiological basis for the amplified response to water deficit caused by exogenous ABA, present mainly in the dry climate population, is related to internal ABA accumulation. These results provide evidence for adaptive differentiation between populations of P. asperata, and they support the expected relationship between environmental heterogeneity and the magnitude of plastic responses in plant populations.

No abstract

No abstract

This study elucidated whether the beneficial effect of arbuscular mycorrhizal (AM) symbiosis was different in male and female Populus tomentosa Carrière trees. Female and male cuttings of P. tomentosa were treated with two AM fungal regimes, with or without an AM fungus (Glomus constrictum Trappe) inoculation, and with three salt regimes, no salt, low-salinity level (100 mmol·L–1 NaCl), and high-salinity level (200 mmol·L–1 NaCl). Our results showed that AM fungal colonization alleviated the salt-induced reduction in growth, gas exchange, photosynthetic pigment content, and nitrogen (N) and phosphorus (P) concentrations in the leaves, stems, and roots under low-salinity conditions. However, these effects were not alleviated under high-salinity conditions. AM fungal colonization was associated with a reinforcement of the activity of superoxide dismutase (SOD) and guaiacol peroxidase (GPx) and an inhibition of malondialdehyde (MDA) in treated plants of both genders under low-salinity conditions. Furthermore, sodium (Na+) and chlorine (Cl–) concentrations in tree organs were lower in the AM than the non-AM plants under the low-salinity condition in both sexes. AM fungal treatment may protect salt-stressed plants via the inhibition of salt-induced oxidative stress, which improves nutrient absorbance and inhibits Na+ transport from the roots to the shoots. In addition, small differences in plant growth induced by AM fungal colonization were observed between sexes, but significant gender differences were obtained in other parameters such as SOD and GPx activities and N and P concentrations.

No abstract

Keywords:carbon nitrogen ratio / photosynthetic nitrogen use efficiency / Populus cathayana / ultraviolet-b radiation / water use efficiency Abstract • The effects of drought, enhanced UV-B radiation and their combination on plant growth and physiological traits were investigated in a greenhouse experiment in two populations of Populus cathayana Rehder originating from high and low altitude in south-west China.• In both populations, drought significantly decreased biomass accumulation and gas exchange parameters, including net CO 2 assimilation rate (A), stomatal conductance (g s ), transpiration rate (E) and photosynthetic nitrogen use efficiency (PNUE). However, instantaneous water use efficiency (WUE i ), transpiration efficiency (WUE T ), carbon isotope composition (δ 13 C) and nitrogen (N) content, as well as the accumulation of soluble protein, UV-absorbing compounds and abscisic acid (ABA) significantly increased in response to drought. On the other hand, cuttings from both populations, when kept under enhanced UV-B radiation, showed very similar changes, as under drought, in all above-mentioned parameters.• Compared with the low altitude population, the high altitude population was more tolerant to drought and enhanced UV-B, as indicated by the higher level of biomass accumulation, gas exchange, water-use efficiency, ABA concentration and UV-absorbing compounds.• After one growing season of exposure to different UV-B levels and watering regimes, the decrease in biomass accumulation and gas exchange, induced by drought, was more pronounced under the combination of UV-B and drought. Significant interactions between drought and UV-B were observed in WUE i , WUE T , δ 13 C, soluble protein, UV-absorbing compounds, ABA and in the leaf and stem N, as well as in the leaf and stem C:N ratio.• Our results showed that UV-B acts as an important signal allowing P. cathayana seedlings to respond to drought and that the combination of drought and UV-B may cause synergistically detrimental effects on plant growth. Mots-clés :rapport carbone / azote / efficience photosynthétique d'utilisation de l'azote / Populus cathayana / rayonnement UV-B / efficience d'utilisation de l'eau Résumé -Variations intra-spécifiques de la réponse à la sécheresse de Populus cathayana sous atmosphère ambiante ou sous un rayonnement UV-B accru.• Les effets d'une sécheresse, d'une augmentation du rayonnement UV-B et de leur combinaison ont été étudiés sur la croissance et les caractéristiques physiologiques de plants de deux populations de Populus cathayana Rehder originaires de haute et basse altitude dans le sud-ouest de la Chine.• Dans les deux populations, la sécheresse a réduit de manière significative l'accumulation de biomasse et les échanges gazeux foliaires, y compris l'assimilation nette (A) de CO 2 , la conductance stomatique (g s ), la transpiration (E) et l'efficience photosynthétique d'utilisation de l'azote (PNUE). Toutefois, l'efficience instantanée d'utilisation de l'eau (WUE i ), l'efficience de transpiration (WUE T ), la com...

No abstract