水分胁迫下高粱叶片的渗透调节与延伸生长的关系

高粱抗旱品种3197B比不抗旱品种三尺三在水分胁迫条件下ψ_S下降低。在相同ψ_S时,3197B相对含水量高于三尺三。水分胁迫期间,3197B能始终维持比三尺三较高的ψ_P。在中度和严重水分胁迫时,3197B几种渗透物质积累均高于三尺三,其中可溶性糖和K~ 对渗透调节贡献最大。水分胁迫下,3197B正展开叶渗透调节能力较强,ψ_P维持较高,临界膨压低,叶片扩张性能小、故生长速率随ψ_W下降较慢。     

玉米叶片生长部位渗透调节和生长的生物物理参数变化

玉米叶片生长部位随着水分胁迫加剧ψ_w降低、LER减慢。LER从最大到零,快速干旱处理的ψw从-0.55降至-0.85 MPa;缓慢干旱处理ψ_w从-0.88降至-1.13 MPa。在任何一种LER下,缓慢干旱处理的ψ_s比快速干旱处理更低,生长停止时,前者为-1.57 MPa,而后者为-1.30MPa。缓慢干旱叶片尽管在更低ψ_w下,仍能维持一定膨压,保持一定的生长速率。经历长时间水分胁迫会改变细胞延伸生长的生物物理参数,增大临界膨压(0.08～0.09 MPa)。这是水分胁迫植株,在一定ψ_p下生长速率减慢的原因。     

Water Relations and Leaf Anatomy of the Tropical Species,Jatropha gossypifolia and Alternanthera crucis,Grown Under an Elevated CO2 Concentration

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 mol mol^–1) and five ambient CO₂ concentration (AC) open top chambers (454 mol 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.     

Comparison between two methods of generating pressure—volume curves

Abstract. Pressure—volume (P—V) curves were generated on roots and shoots of coastal Douglas fir [ Pseudotsuga menziesii (Mirb.) Franco] seedlings using two procedures. In the first (Method A), samples were dehydrated inside a pressure chamber. Exuded stem sap was collected and weighed at successive pressure increases to derive the P—V curve. In the second method (Method B). excised samples were allowed to dry outside the pressure chamber by evapotranspiration. They were weighed periodically to determine sap loss and their corresponding balance pressures were determined in a pressure chamber in order to derive the P—V curve.
Estimates of volume averaged osmotic potential at full turgor and water potential at zero turgor which were derived graphically from the P—V curves, were different for each method. In general, estimates were more negative in Method A, by as much as 1.5 MPa in one case. Also, Method B did not record an osmotic adjustment in seedlings which were subjected to severe water stress while Method A did.     

Hydraulic redistribution of soil water in two old-growth coniferous forests: quantifying patterns and controls

Although hydraulic redistribution of soil water (HR) by roots is a widespread phenomenon, the processes governing spatial and temporal patterns of HR are not well understood. We incorporated soil/plant biophysical properties into a simple model based on Darcy's law to predict seasonal trajectories of HR. We investigated the spatial and temporal variability of HR across multiple years in two old-growth coniferous forest ecosystems with contrasting species and moisture regimes by measurement of soil water content (theta) and water potential (Psi) throughout the upper soil profile, root distribution and conductivity, and relevant climate variables. Large HR variability within sites (0-0.5 mm d(-1)) was attributed to spatial patterns of roots, soil moisture and depletion. HR accounted for 3-9% of estimated total site water depletion seasonally, peaking at 0.16 mm d(-1) (ponderosa pine; Pinus ponderosa) or 0.30 mm d(-1) (Douglas-fir; Pseudotsuga menziesii), then declining as modeled pathway conductance dropped with increasing root cavitation. While HR can vary tremendously within a site, among years and among ecosystems, this variability can be explained by natural variability in Psi gradients and seasonal courses of root conductivity.     

Leaf age and salinity influence water relations of pepper leaves

Plant growth is reduced under saline conditions even when turgor in mature leaves is maintained by osmotic adjustment. The objective of this study was to determine if young leaves from salt-affected plants were also osmotically adjusted. Pepper plants (Capsicum annuum L. cv. California Wonder) were grown in several levels of solution osmotic potential and various components of the plants' water relations were measured to determine if young, rapidly growing leaves could accumulate solutes rapidly enough to maintain turgor for normal cell enlargement. Psychrometric measurements indicated that osmotic adjustment is similar for both young and mature leaves although osmotic potential is slightly lower for young leaves. Total water potential is also lower for young leaves, particularly at dawn for the saline treatments. The result is reduced turgor under saline conditions at dawn for young but not mature leaves. This reduced turgor at dawn, and presumably low night value, is possibly a cause of reduced growth under saline conditions. No differences in leaf turgor occur at midday. Porometer measurements indicated that young leaves at a given salinity level have a higher stomatal conductance than mature leaves, regardless of the time of day. The result of stomatal closure is a linear reduction of transpiration.     

Field studies of water relations and photosynthesis in Scots pine.

Needle water potential at noon and diurnal variation in needle water potential was measured with a pressure chamber during the growth seasons (1974, 1975 and 1976) in a 20-year-old stand of Scots pine (Pinus sylvestris L.), subjected to daily irrigation and nutrient treatments at Jädraås, in central Sweden (60°50'N).
In unstressed conditions there was little difference in water potential amongst the treatments. However, during a dry spell in 1976 the diurnal curves of water potential in the control and combined irrigated and fertilized treatment diverged by up to 6 bar in the middle of the day. Irrigation alone resulted in higher midday water potentials (Ψ_n) than in the controls only during this period. At other times in 1974, 1975 and early 1976, the values of Ψ_n in the irrigated treatment were similar to the controls. Fertilization alone resulted in higher Ψ_n than in the controls in both 1975 and 1976 during both wet and dry periods. However, the largest difference between treatment and control occurred in the combined, irrigated and fertilized treatment during the dry spell in 1976.
Several possible explanations for the effect of fertilization on leaf water potential are discussed, including changes in hydraulic conductivity and water storage. The most likely explanation is a reduced transpiration rate as a result of more effective stomatal control of water loss.     

Water relations of Capsicum genotypes under water stress

Pepper species and cultivars, Capsicum annuum cv. Bell Boy, C. annuum cv. Kulai and C. frutescens cv. Padi, differing in drought tolerance were investigated for their water relations, stomatal responses and abscisic acid (ABA) content during water stress. C. frutescens cv. Padi exhibited a greater osmotic adjustment than C. annuum cultivars. Stomatal conductance of cv. Bell Boy was more sensitive to water stress than that of cvs. Kulai and Padi. In all pepper genotypes, stomatal closure was triggered in the absence of a large decrease in leaf water status. ABA content in xylem sap and leaf was higher in C. annum cultivars compared to C. frutescens cv. Padi. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationship of antioxidant enzymes to ozone tolerance in branches of mature ponderosa pine (Pinus ponderosa) trees exposed to long-term, low concentration, ozone fumigation and acid precipitation

Seasonal activity of superoxide dismutase (SOD, EC 1.15.1.1). ascorbate peroxidase (APOD, EC 1.11.1.11) and guaiacol-oxidizing enzymes (GPODs, EC 1.11.1.7) was examined in needles of 12- to 15-year-old ponderosa pine (Pinus ponderosa Laws.) trees which received ozone (O₃) and acid precipitation treatment. Individual branches were enclosed in branch exposure chambers delivering either charcoal-filtered (O₃-reduced) air, ambient air, or air with twice ambient (2 x ambient) concentrations of O₃. Acid precipitation treatments were rain of pH 3.0 or 5.1 or no rain. Changes in antioxidant enzyme activity were not a consistent response to O₃ fumigation or acid precipitation, but when observed, they occurred most often in the O₃-sensitive clone and in symptomatic, fumigated branches. In the second year of fumigation. O₃ fleck symptoms appeared on needles of the sensitive clone as early as July and APOD activities were significantly increased by O₃ at all sampling dates. In the tolerant clone, antioxidant enzyme activities were not significantly changed by O₃ in the first season of fumigation (March to December 1990), not even during an episode when ambient O₃ concentrations reached 125 nl 1^?1 (240 nl 1^?1 in 2x ambient chambers). No foliar symptoms were observed on needles of the tolerant clone during this year. However, in the second year of fumigation (1992), O₃ fleck symptoms were observed on the tolerant clone and APOD activities were significantly increased in previous-year needles. The tolerant clone had SOD, APOD, and GPOD activities at least 40% higher than those of the sensitive clone before fumigation and 65, 178, and 119% higher, respectively, during both years of fumigation. The higher constitutive levels of these enzymes may have protected against foliar injury in 1990, however in 1992 we concluded that the stimulations in antioxidant enzyme activities observed in symptomatic branches of both clones were a consequence of O₃ injury. Total (intra- and extracellular) activities of the antioxidant enzymes did not appear to be good indicators of O₃ tolerance. Phenotypically, the O₃-tolerant clone was much more vigorous and in both years of fumigation, gas exchange rates were 30 to 71% higher than in the sensitive clone (P. D. Anderson, unpublished data). The greater vigor of the tolerant clone may allow more carbon allocation to protective and repair processes which include, but are not restricted to, the turnover of antioxidant enzymes and metabolites.     

Changes at panicle emergence in the water relations of a wetland and a dryland Japonica rice cultivar under wetland conditions

The diurnal and seasonal changes in plant water relations of two Japonica rice ( Oryza sativa L.) cultivars, Nipponbare and Tachiminori, were studied under flooded conditions at Kyoto University. The dryland cv. Tachiminori maintained higher predawn and midday leaf osmotic potentials relative to the wetland cv. Nipponbare during the vegetative stage, but the ranking was reversed after flowering. The relationship between leaf water potential and leaf osmotic potential showed that prior to panicle emergence Nipponbare was able to adjust osmotically to maintain turgor, whereas after heading there was little turgor maintenance. Tachiminori showed little difference in osmotic adjustment before and after panicle emergence. Fertilizer treatment during panicle development also helped to maintain the degree of osmotic adjustment in both cultivars.     

Measuring tree root respiration using (13)C natural abundance: rooting medium matters

Tree root respiration utilizes a major portion of the primary production in forests and is an important process in the global carbon cycle. Because of the lack of ecologically relevant methods, tree root respiration in situ is much less studied compared with above-ground processes such as photosynthesis and leaf respiration. This study introduces a new (13)C natural tracer method for measuring tree root respiration in situ. The method partitions tree root respiration from soil respiration in buried root chambers. Rooting media substantially influenced root respiration rates. Measured in three media, the fine root respiration rates of longleaf pine were 0.78, 0.27 and 0.18 mg CO(2) carbon mg(-1) root nitrogen d(-1) at 25 degrees C in the native soil, tallgrass prairie soil, and sand-vermiculite mixture, respectively. Compared with the root excision method, the root respiration rate of longleaf pine measured by the field chamber method was 18% higher when using the native soil as rooting medium, was similar in the prairie soil, but was 42% lower if in the sand-vermiculite medium. This natural tracer method allows the use of an appropriate rooting medium and is capable of measuring root respiration nondestructively in natural forest conditions.     

A comparison of the composite and repeat pressurization methods of pressure–volume analysis for shoots of four North American conifer species

Significantly different water relations attributes were derived for temperate conifers measured using the repeat pressurization (RP) and composite (CM) pressure–volume (PV) procedures. In the RP method, single shoots were measured 10–20 times for xylem water potential and mass during air-drying to produce each PV curve. In contrast, for CM PV curves 25–30 shoots were air-dried to relative water contents (R) ranging from 1.0 to 0.5 before being pressurized once. Aggregation of these 25–30 paired values produced single PV curves. Pinus banksiana, P. resinosa and Picea mariana, but not Pinus strobus, had lower full turgor osmotic potential, shallower slope of the linear segment of the PV curves and higher symplast fraction with the CM method. Data points along the linear segment of PV curves were obtained to lower R using the CM method. Reanalysis using similar R ranges eliminated differences between PV methods for Picea mariana but not Pinus banksiana and P. resinosa.     

A new visualization chamber to study the transient volumetric response of yeast cells submitted to osmotic shifts

A visualization chamber has been developed to analyze potential correlations between osmotic step increase on yeasts and the resultant cell volume decreases. Image analysis was used to characterize the step increases in the center of the chamber and to measure the changes in the cell volume. Step increases of different intensities have been performed on the yeast Saccharomyces cerevisiae. This device has allowed the kinetics of the volumetric evolution of the cells to be observed. The water exit flow rate from the cell was found to occur in the first 10 s following the hypertonic step change. Comparison of the time constants of the chamber and of the cell volume variations allowed to conclude that the time constant of the water transfer across the membrane was short (about 1 s). (c) 1994 John Wiley & Sons, Inc.     

A critical comparison of the pressure-probe and pressure-chamber techniques for estimating leaf-ceil turgor pressure in Kalanchoë daigremontiana

The aim of the present study was to test the accuracy of the pressure-chamber technique as a method for estimating leaf-cell turgor pressures. To this end, pressure-probe measurements of cell turgor pressure (P^cell) were made on mesophyll cells of intact, attached leaves of Kalanchoë daigremontiana. Immediately following these measurements, leaves were excised and placed in a pressure chamber for the determination of balance pressure (P^bal). Cell-sap osmotic pressure (?^cell) and xylem-sap osmotic pressure (?^xyl) were also measured, and an average cell turgor pressure calculated as P^cell=?^cell–?^xyl–P^bal. The apparent value of P^bal was positively correlated with the rate of increase of chamber pressure, and there was also a time-dependent increase associated with water loss. On expressing sap from the xylem, ?^xyl fell to a plateau value that was positively correlated with ?^cell. Correcting for these effects yielded estimates of P^bal and ?^xyl at the time of leaf excision. On average, the values of P^cell obtained with the two techniques agreed to within ±002 MPa (errors are approximate 95% confidence limits). If ?^xyl were ignored, however, the calculated turgor pressures would exceed the measured values by an average of 0.074 ± 0.012MPa, or 48% at the mean measured pressure of 0.155 MPa. We conclude that the pressure-chamber technique allows a good estimate to be made of turgor pressure in mesophyll cells of K. daigremontiana, provided that ?^xyl is included in the determination. The 1:1 relationship between the measured and calculated turgor pressures also implies that the weighted-average reflection coefficient for the mesophyll cell membranes is close to unity.     

Contrasting soil respiration in young and old-growth ponderosa pine forests

Three years of fully automated and manual measurements of soil CO₂ efflux, soil moisture and temperature were used to explore the diel, seasonal and inter‐annual patterns of soil efflux in an old‐growth (250‐year‐old, O site) and recently regenerating (14‐year‐old, Y site) ponderosa pine forest in central Oregon. The data were used in conjunction with empirical models to determine which variables could be used to predict soil efflux in forests of contrasting ages and disturbance histories. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. Soil CO₂ efflux at both sites showed large inter‐annual variability that could be attributed to soil moisture availability in the deeper soil horizons (O site) and the quantity of summer rainfall (Y site). Seasonal patterns of soil CO₂ efflux at the O site showed a strong positive correlation between diel mean soil CO₂ efflux and soil temperature at 64 cm depth whereas diel mean soil efflux at the Y site declined before maximum soil temperature occurred during summer drought. The use of diel mean soil temperature and soil water potential inferred from predawn foliage water potential measurements could account for 80% of the variance of diel mean soil efflux across 3 years at both sites, however, the functional shape of the soil water potential constraint was site‐specific. Based on the similarity of the decomposition rates of litter and fine roots between sites, but greater productivity and amount of fine litter detritus available for decomposition at the O site, we would expect higher rates of soil CO₂ efflux at the O site. However, annual rates were only higher at the O site in one of the 3 years (597 ± 45 vs. 427 ± 80 g C m^?2). Seasonal patterns of soil efflux at both sites showed influences of soil water limitations that were also reflected in patterns of canopy stomatal conductance, suggesting strong linkages between above and below ground processes.