RESUMEN
Deciduous trees prepare for winter by breaking up chlorophyll and other nitrogen-rich compounds, which are resorbed for storage. Timing is important as senescence too early will waste growing season, while senescence too late risks the loss of the leaf resources to frost. While plants of temperate and boreal regions use decreasing day length as a cue of approaching winter, we show that decreasing temperature may also play a role in the variability of leaf senescence. We investigated the timing of autumnal decrease in photosynthetic efficiency and the concentration of chlorophyll and total carotenoids in nine common lilac (Syringa vulgaris L.) trees over two consecutive years. Day length explained a greater proportion of photosynthetic efficiency, but temperature had a significant additional role, which seems to be related to individual differences. Precipitation and cloudiness did not explain photosynthetic efficiency. Photosynthetic efficiency was higher outside the canopy and at high and middle elevations than inside and low elevations of the canopy. Late onset of senescence led to a steeper decline in photosynthetic efficiency than early senescence. The onset of decline in photosynthetic efficiency differed between years, but there was no difference in the steepest rate of change in photosynthetic efficiency with respect to sampling year or location. Contributions of day-length vs temperature to leaf senescence have important consequences for the adaptability and invasibility of deciduous trees in a changing climate, especially at the edge of species distributions.
Asunto(s)
Fotosíntesis/fisiología , Hojas de la Planta/fisiología , Syringa/fisiología , Árboles/fisiología , Carotenoides/metabolismo , Clorofila/metabolismo , Estaciones del Año , Luz Solar , TemperaturaRESUMEN
To explore the toxicity and action mechanism of acute sulfur dioxide (SO2) on urban landscape plants, a simulated SO2 stress environment by using fumigation chamber involving increasing SO2 concentration (0, 25, 50, 100, 200â¯mgâ¯m-3) was carried out among three species. After 72â¯h of exposure, SO2-induced oxidative damage indicated by electrolyte leakage increased with higher dose of SO2. Meanwhile, SO2 decreased the contents of chlorophyll a, chlorophyll b and carotenoid and increased the contents of sulfur. Net photosynthetic rate (Pn) decreased as a result of stomatal closure when SO2 dose was lower than 50â¯mgâ¯m-3, out of this range, non-stomatal limitation play a dominant role in the decline of Pn. Simultaneous measurements of chlorophyll fluorescence imaging (CFI) also revealed that the maximal quantum efficiency of PSII photochemistry in dark-adapted state (Fv/Fm) and the realized operating efficiency of PSII photochemistry (Fq'/Fm') was reduced by SO2 in a dose-dependent manner. In addition, the maximum quantum efficiency of PSII photochemistry in light-adapted state (Fv'/Fm') and the PSII efficiency factor (Fq'/Fv') decreased when exposure to SO2. These results implied that acute SO2 exposure induced photoinhibition of PSII reaction centers in landscape plants. Our study also indicated that different urban landscape plant species resist differently to SO2: Euonymus kiautschovicus >â¯Ligustrum vicaryi >â¯Syringa oblata according to gas-exchange characteristics and chlorophyll fluorescence responses.
Asunto(s)
Euonymus/efectos de los fármacos , Ligustrum/efectos de los fármacos , Dióxido de Azufre/toxicidad , Syringa/efectos de los fármacos , Dióxido de Carbono/metabolismo , Clorofila/metabolismo , Clorofila A/metabolismo , Euonymus/fisiología , Fluorescencia , Ligustrum/fisiología , Fotosíntesis/efectos de los fármacos , Fotosíntesis/fisiología , Complejo de Proteína del Fotosistema II/metabolismo , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/metabolismo , Syringa/fisiologíaRESUMEN
In the present study, the effects of spring drought stress on physiological characteristics of leaves and roots for Populus alba, Ulmus pumila, Syringa oblata and Prunus sibirica were analyzed in Northwest Liaoning Province. The relationships between leaves and roots under drought stress were explored, and drought resistance of the four tree species was evaluated with the method of subordinate function and the gray correlative analysis. The results showed that there were significant differences in osmotic substances contents (soluble sugar, soluble protein and proline), antioxidative enzymes activities (SOD, POD and CAT) and malondialdehyde content among the four tree species and different organs (leaves and roots) (P<0.05). The average subordinative value in leaves increased in a sequence of P. sibirica (0.245), P. alba (0.346), S. oblata (0.412) and U. pumila (0.673), but it increased in roots in an order of U. pumila (0.315), P. sibirica (0.383), S. oblata (0.552) and P. alba (0.558). Meanwhile, the average subordinative value in leaves of P. alba, S. oblata and P. sibirica was lower than in roots, but it was higher in leaves than in roots of U. pumila. The association between physiological indexes and drought resistance showed an order of malondialdehyde > SOD > CAT > soluble protein > proline > soluble sugar > POD in leaves, and an order of malondialdehyde > soluble protein > soluble sugar > CAT > POD > proline > SOD in roots. These results indicated that the drought-resistant capability was different in leaves and roots of the four tree species. The roles of drought-resistance indexes were different between leaves and roots of the four tree species. Different management measures should be selected according to different organs of various tree species.
Asunto(s)
Sequías , Hojas de la Planta/fisiología , Raíces de Plantas/fisiología , Árboles/fisiología , China , Populus/fisiología , Prunus/fisiología , Estrés Fisiológico , Syringa/fisiología , Ulmus/fisiología , AguaRESUMEN
During leaf development, the increase in stomatal conductance cannot meet photosynthetic demand for CO2, thus leading to stomatal limitation of photosynthesis (Ls). Considering the crucial influences of stomatal development on stomatal conductance, we speculated whether stomatal development limits photosynthesis to some extent. To test this hypothesis, stomatal development, stomatal conductance and photosynthesis were carefully studied in both Syringa oblata (normal greening species) and Euonymus japonicus Thunb (delayed greening species). Our results show that the size of stomata increased gradually with leaf expansion, resulting in increased stomatal conductance up to the time of full leaf expansion. During this process, photosynthesis also increased steadily. Compared to that in S. oblata, the development of chloroplasts in E. japonicus Thunb was obviously delayed, leading to a delay in the improvement of photosynthetic capacity. Further analysis revealed that before full leaf expansion, stomatal limitation increased rapidly in both S. oblata and E. japonicus Thunb; after full leaf expansion, stomatal limitation continually increased in E. japonicus Thunb. Accordingly, we suggested that the enhancement of photosynthetic capacity is the main factor leading to stomatal limitation during leaf development but that stomatal development can alleviate stomatal limitation with the increase of photosynthesis by controlling gas exchange.
Asunto(s)
Euonymus/fisiología , Fotosíntesis , Estomas de Plantas/crecimiento & desarrollo , Estomas de Plantas/fisiología , Syringa/fisiología , Dióxido de Carbono/metabolismo , Clorofila/metabolismo , Cloroplastos/metabolismo , Ritmo Circadiano/fisiología , Tamaño de los Órganos , Fotones , Estomas de Plantas/anatomía & histología , Factores de TiempoRESUMEN
Using LI-6400 CO2 gas analysis system and by the methods of correlation analysis and multinomial regression, this paper studied the diurnal changes of Syringa oblata photosynthesis during different seasons and assessed the correlation between net photosynthetic rate and environmental factors. The results indicated that the photosynthetic rate showed a double-peak curve in spring and summer and a single peak curve in autumn. The major factors affecting the photosynthetic rate were the solar radiation and stomatal conductance in spring and summer, and the stomatal conductance and intercellular CO2 intensity in autumn. The related equation was also constructed in this paper.