Youfu Zhang

Effect of water stress on leaf photosynthesis, chlorophyll content, and growth of oriental lily

The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to increasing water stress were analyzed based on the net photosynthetic rate (Pn), stomatal conductance (gs), intercellular CO2 concentration (Ci), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (Ls) in the Horqin Sandy Land of western China. A photosynthesis-PAR response curve was constructed to obtain light-compensation and light-saturation points (LCP and LSP), the maximum photosynthetic rates (Pmax) and dark respiration rates (RD). The growth of lilies in the pots was analyzed after anthesis. Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied. The results indicated that drought stress not only significantly decreased Pn, E, gs, photosynthetic pigment content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (Pn)-PAR response curve. Drought stress increased LCP and RD and decreased LSP and Pmax. There were both stomatal and nonstomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and affected the diurnal pattern of gas exchange and Pn-PAR response curves, thereby reducing plant quality (lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin Sandy Land.

Tree ring δ18O's indication of a shift to a wetter climate since the 1880s in the western Tianshan Mountains of northwestern China

Central Asian droughts have drastically and significantly affected agriculture and water resource management in these arid and semiarid areas. Based on tree ring δ18O from native, dominant Schrenk spruce (Picea schrenkiana Fisch. et Mey.), we developed a 300 year (1710–2010) standard precipitation-evaporation index (SPEI) reconstruction from January to August for Chinas western Tianshan Mountains. The regression model explained 37.6% of the variation in the SPEI reconstruction during the calibration period from 1950 to 2010. Comparison with previous drought reconstructions confirmed the robustness of our reconstruction. The 20th century has been a relatively wet period during the past 300 years. The SPEI showed quasi 2, 5, and 10 year cycles. Several pluvials and droughts with covariability over large areas were revealed clearly in the reconstruction. The two longest pluvials (lasting for 12 years), separated by 50 years, appeared in the 1900s and the 1960s. The most severe drought occurred from 1739 to 1761 and from 1886 to 1911 was the wettest period since 1710. Compared to previous investigations of hydroclimatic changes in the western Tianshan Mountains, our reconstruction revealed more low-frequency variability and indicated that climate in the western Tianshan Mountains shifted from dry to wet in 1886. This regime shift was generally consistent with other moisture reconstructions for the northeastern Tibetan Plateau and northern Pakistan and may have resulted from a strengthened westerly circulation. The opposite hydrological trends in the western Tianshan Mountains and southeastern Tibetan Plateau reveal a substantial influence of strengthened westerlies and weakening of the Indian summer monsoon.

Inhibition of glutathione synthesis decreases chilling tolerance in Chorispora bungeana callus.

The possible roles of reduced glutathione (GSH) in chilling tolerance were studied in callus generated from a representative alpine plant, Chorispora bungeana Fisch. & C.A. Mey (C. bungeana). The callus grew well under low-temperature and chilling treatment led only to slight injury, as indicated by a low level of ion leakage (IL). Malondialdehyde measurements also were not elevated, however GSH was. Exogenously application of l-buthionine-(S R)-sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase (gamma-ECS), arrested the GSH accumulation induced by chilling and resulted in a significant decrease in cell growth and an increase in IL and malondialdehyde. These results implied that C. bungeana is a plant with a strong low-temperature tolerance mechanism, and the tolerance of C. bungeana may be associated with GSH accumulation. Under chilling treatment, the proportion of unsaturated fatty acid in the plasma membrane (PM) increased significantly in callus of C. bungeana mainly due to increases in C18:2 and C18:3, the membrane fluidity (indicated by DPH fluorescent polarization) however was maintained. High PM H(+)-ATPase activities were also induced by chilling. Exogenously application of BSO blocked the effects of chilling treatments on the changes of fatty acids and PM H(+)-ATPase activities, reducing the PM membrane fluidity. On the other hand, simultaneous application of GSH and BSO to callus under chilling treatments reversed the effects of BSO on the changes of fatty acids, PM fluidity and PM H(+)-ATPase activities. These results suggested that GSH induced by low-temperature treatments may confer chilling tolerance to C. bungeana, probably by increasing unsaturated fatty acid compositions and maintaining PM fluidity and high enzymatic activity.

Seasonal changes in non-structural carbohydrates and sucrose metabolism enzymes in two Sabina species

Evergreen plants need to store reserves to allow for their survival during the winter months and for new leaf growth in the following spring. In many of the tree species, these reserve functions are mainly carried out by starch, which is degraded to soluble carbohydrates during the dormant season to maintain active respiration and provide protection against freezing. In the present study, two evergreen woody plants, S. przewalskii Kom. (SP) and S. chinensis (Lin.) Ant.(SC), were used to investigate the patterns of seasonal variation in the concentrations of soluble sugars, sucrose, fructose and starch, and the activities of sucrose-phosphate synthase (SPS), sucrose synthase (SUSY), neutral invertase (NI) and soluble acid invertase (SAI). Foliar soluble sugar, sucrose, fructose, and starch concentrations were markedly higher in SC than in SP; moreover, the activities of SPS, SUSY, NI and SAI were also higher in SC than in SP. There were generally higher concentrations of soluble sugars, sucrose and fructose and SPS activities in the winter than in the summer for both Sabina trees, which was consistent with the necessity for protection against freezing; however, opposite results were found with regards to starch concentrations and the activities of SUSY, NI and SAI. In contrast with the activities of SUSY, NI and SAI, the negative correlation observed between SPS and air temperature was likely a reflection of its crucial role in the acquisition of freezing tolerance by sucrose metabolism in the winter. These results suggest that higher carbon reserves do not give S. chinensis (Lin.) Ant. a competitive advantage in tolerating cold temperatures and that only SPS, but not SUSY, NI and SAI, may play a positive role in freezing tolerance by increasing soluble sugar.

Qinghai spruce (Picea crassifolia) growth–climate response between lower and upper elevation gradient limits: a case study along a consistent slope in the mid-Qilian Mountains region

Tree-ring width chronologies are important records of climate change. Mounting evidence suggests that tree-ring climate response is elevation dependent. In this study, even-aged Qinghai spruce (Picea crassifolia Kom.) chronologies from six sites along a consistent slope in the Qilian Mountains region were selected to investigate altitudinal variability of growth–climate response. Results showed that growth–climate response of this species at different elevations was limited by identical factors. In the Qilian Mountains, P. crassifolia tree-ring growth was limited primarily by drought conditions which are determined by precipitation and temperature in the Qilian Mountains along the entire elevation gradient, exhibiting a positive correlation with PDSI in growth season, a positive correlation with precipitation in May and a negative correlation with the maximum temperature in June. Moreover, P. crassifolia recruitment dynamics coincided well with the temperature variations, suggesting that recruitment rates at different elevations were all primarily influenced by temperature. What was noteworthy was that the great decrease in the mean sensitivity and standard deviation of chronologies directly indicated that P. crassifolia climate–growth response weakened at higher elevations. Furthermore, tree-ring-climate correlation coefficients, and spatial correlation fields of tree-ring width indices to regional climate factors also significantly decreased at higher elevations, indicating that P. crassifolia climate–growth response at higher elevations was weaker than that at lower elevations. Additionally, response of P. crassifolia recruitment dynamics to changes in temperature decreased with increasing elevation, confirming results from chronology and response analyses that showed that P. crassifolia climate–growth response weakened at higher elevations.

Chlorophyll content, leaf gas exchange and growth of oriental lily as affected by shading

We evaluated the effects of light conditions on leaf gas exchange, chlorophyll content, and growth responses in the Oriental lily (Lilium auratum L.) cv. Sorbonne. The experiment involved application on increasing shade densities (0, 60, 75, and 80%) to Sorbonne, and was carried out in the Horqin Sandy Land of northern China. Shade tests showed that growth of the lily was primarily affected by the level of irradiance. Photoinhibition occurred in the 0 and 60% shade treatments, but not in the 75 and 80% shade treatments. Shade treatments led to increase in photosynthetic pigment content, enhancement in photosynthetic efficiency, and finally increase in the commercial value of the lily. Pn, on the other hand, was lowest in the 80% shade treatment. So irradiance less than that achieved in the 80% shade treatment limited carbon assimilation and led to decreased plant growth. Plants grown under 75% shade displayed the optimal traits determining commercial value (plant height, flower length, flower diameter). Trends in Pmax, AQY, LSP and LCP to shade confirmed that the lily is a shade-tolerant plant. Excessive light, therefore, was the primary factors limiting lily quality. Growth under conditions of 75% shade is recommended to improve photosynthetic efficiency and alleviate photodamage, thus increasing the commercial value of the lily grown in the Horqin Sandy Land.

Correlations of carbon isotope discrimination with element and ash contents in two Sabina evergreen trees in northwest China: patterns and implications

Foliar carbon isotope discrimination (Δ) is widely used as an integrator of physiological plant responses to environmental change. However, the relationship between foliar Δ and mineral nutrient accumulation is still not well-known. The foliar Δ, K, Ca, Mg, Si and ash contents of S. przewalskii Kom. (SP) and S. chinensis (Lin.) Ant. (SC), two over-winter trees distributed on high altitude plateaux and lower altitude plains, respectively, were measured at monthly intervals over two years under the same growing conditions to examine the genetic and seasonal variation in foliar nutrient concentrations in relation to foliar Δ. The foliar Δ, Mg, K and ash contents were markedly lower in SP than in SC, and the foliar Si content was significantly higher in SP than SC, while the differences in Ca contents between the two Sabina trees were not significant. There was higher foliar Δ in winter than in summer for both Sabina trees. Close negative correlations of foliar Δ with K and Mg content, and significant positive correlations between foliar Δ and Si contents, were observed in SP but not in SC. Thus, higher water-use efficiency of SP than of SC is related to higher Si and lower Mg and K contents that have positive effects on the reduction of transpiration rates or stomatal conductances. The results obtained by the present study will advance the understanding of the adaptive strategies of mineral nutrition and water use in harsh environments.

The effect and implication of human disturbances on altitudinal variation of non-structural carbohydrates in Kobresia pygmaea

Abstract Non-structural carbohydrates in plant organs can mirror the plant overall carbon supply status and balance and can also provide evidence for their health evaluation in the ecosystem. Non-structural carbohydrates in Kobresia pygmaea, one dominant herbaceous species on the Qinghai-Tibetan Plateau, were measured to investigate altitudinal variation in non-structural carbohydrate accumulations, as well as engineering disturbance on the stability of the alpine grassland ecosystem. An increasing trend with elevation in total soluble sugars, fructose, and sucrose was detected in the K. pygmaea growing in both undisturbed and disturbed sites. However, there were higher amounts and a more distinctly altitudinal trend of non-structural carbohydrates with a minor fluctuation in undisturbed sites compared to disturbed sites. In addition, the altitudinal trend of sucrose is similar to that in sucrose phosphate synthase and sucrose synthase activities, while it is opposite to that in neutral invertase and soluble acid invertase activities, suggesting that the sucrose accumulation was primarily related to its synthesis. These results revealed that human disturbance resulted in a reduced carbon supply and altered the balance of carbohydrate utilization in plants on the Qinghai-Tibetan Plateau.