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1.
Photosynthetic and stomatal responses to a soil drying cycle were examined in half-sib seedlings of four walnut (Juglans nigra L.) families. Well-watered seedlings of an Iowa seed source had significantly higher rates of net photosynthesis than seedlings from New York or Michigan sources. This superior photosynthetic potential was associated with both greater stomatal conductance and mesophyll capacity for CO(2) fixation. In a drying soil, net photosynthesis and leaf conductance to water vapor of all families declined substantially, even under mild water stress. These responses were more strongly related to soil water status, as estimated by predawn leaf water potential, than to leaf water potential at the time of gas exchange measurement. There were no differences among families in the pattern of gas exchange response to developing water stress; however, families differed in capacity for recovery of gas exchange from water stress following rehydration. Sensitivity of photosynthesis of black walnut seedlings to water stress may be associated with poor growth and survival of this species in xeric habitats. 相似文献
2.
Leaf growth, rate of leaf photosynthesis and tissue water relations of shoots of Eucalyptus marginata Donn ex Sm. (jarrah) seedlings were studied during a soil drying and rewatering cycle in a greenhouse experiment. Rates of leaf growth and photosynthesis were sensitive to water deficits. The rate of leaf growth decreased linearly with predawn leaf water potential to reach zero at -1.5 MPa. Rate of leaf growth did not recover completely within the first three days after rewatering. Midday photosynthetic rates declined to 40% of those of well-watered seedlings at a predawn leaf water potential of -1.0 MPa and reached zero at -2.2 MPa. Photosynthetic rate recovered rapidly following rewatering and almost fully recovered by the second day after rewatering. All tissue water relations parameters, except the bulk modulus of elasticity, changed significantly as the soil dried and recovered completely by the third day after rewatering. Changes in osmotic pressure at full turgor of 0.4 MPa indicated considerable capacity for osmotic adjustment. However, because there was little osmotic adjustment until predawn leaf water potential fell below -1.5 MPa, this capacity would not have enhanced seedling growth, although it may have increased seedling survival. The sensitivity of photosynthesis and relative water content to water deficits suggests that greenhouse-grown E. marginata seedlings behave like mesophytic plants, even though E. marginata seedlings naturally grow in a drought-prone environment. 相似文献
3.
Marron N Dreyer E Boudouresque E Delay D Petit JM Delmotte FM Brignolas F 《Tree physiology》2003,23(18):1225-1235
Responses to successive drought and re-watering cycles (1-3 cycles) were compared in greenhouse-grown cuttings of Populus x canadensis (Moench) clones, 'Luisa_ Avanzo' and 'Dorskamp.' Total leaf number increment rate, duration of leaf expansion, total and individual leaf area expansion rates and stomatal conductance were recorded periodically during the experiment. Soil water content (SWC) and predawn leaf water potential (Psi(WP)) were measured four times during each drought cycle. In parallel, relative leaf water content (RWC) and specific leaf area (SLA) were estimated on leaves collected from the top to bottom of each cutting. Under well-watered conditions, 'Luisa_Avanzo' and 'Dorskamp' differed in their patterns of leaf area expansion. Although duration of leaf expansion was similar between clones, 'Luisa_ Avanzo' exhibited higher total leaf number increment rates and individual leaf area increases than 'Dorskamp.' As a result, 'Luisa_Avanzo' cuttings reached larger individual and total leaf areas than 'Dorskamp.' 'Dorskamp' leaves had lower SLA than 'Luisa_Avanzo' leaves. In response to successive drought cycles, both clones underwent decreases in total leaf number increment rates and in total leaf area expansion rates, but both whole-plant and individual leaf areas were drastically reduced only in 'Luisa_Avanzo.' 'Dorskamp' maintained a constant leaf area as a result of an increase in the duration of leaf expansion during drought and a significant stimulation of individual leaf area expansion rate and total leaf number increment rate in response to re-watering. Drought caused a greater decrease in SLA in 'Luisa_Avanzo' than in 'Dorskamp.' Expanded leaves of 'Dorskamp' were constitutively dense or thick, or both, whereas leaves of 'Luisa_Avanzo' became dense or thick, or both, only in response to drought. In both clones, re-watering caused partial recovery of SLA to control values. Our data confirm previous field and greenhouse observations that 'Dorskamp' is more tolerant to successive drought and re-watering cycles than 'Luisa_Avanzo.' We conclude that this difference is mainly attributable to the plasticity of 'Dorskamp' after re-watering, rather than to clonal differences in drought responses. 相似文献
4.
Photosynthetic utilization of water and nitrogen in Ulmus americana L. seedlings was tightly linked with the relative availability of each resource. During periodic drying cycles, water use efficiency increased as predawn water potential fell from -0.5 to -2.0 MPa. During the later stages of such drying cycles, the relative contribution of stomatal limitations to the total net photosynthetic limitation appeared to be at its greatest, whereas biochemical limitations were predominant in well-watered plants grown under low nitrogen (N) availability. For any level of leaf water status, water use efficiency of photosynthesis (WUE) was always greater in plants with high leaf N content than in plants with low leaf N content. Photosynthetic nitrogen use efficiency (PNUE) was always greater in plants with low leaf N content than in plants with high leaf N content, for any level of water status. In combined N treatments and predawn water status classes, there was a significant inverse relationship between PNUE and WUE. 相似文献
5.
The atmospheric hydrocarbon budget is important for predicting ozone episodes and the effects of pollution mitigation strategies. Isoprene emission from plants is an important part of the atmospheric hydrocarbon budget. We measured isoprene emission capacity at the bottom, middle, and top of the canopies of a white oak (Quercus alba L.) tree and a red oak (Quercus rubra L.) tree growing adjacent to a tower in the Duke University Forest. Leaves at the top of the white oak tree canopy had a three- to fivefold greater capacity for emitting isoprene than leaves at the bottom of the tree canopy. Isoprene emission rate increased with increasing temperature up to about 42 degrees C. We conclude that leaves at the top of the white oak tree canopy had higher isoprene emission rates because they were exposed to more sunlight, reduced water availability, and higher temperature than leaves at the bottom of the canopy. Between 35 and 40 degrees C, white oak photosynthesis and stomatal conductance declined, whereas red oak (Quercus rubra) photosynthesis and stomatal conductance increased over this range. Red oak had lower rates of isoprene emission than white oak, perhaps reflecting the higher stomatal conductance that would keep leaves cool. The concentration of isoprene inside the leaf was estimated with a simplified form of the equation used to estimate CO(2) inside leaves. 相似文献
6.
Genotypic variation in photosynthesis and plant water relations during drought, and in leaf and seedling morphology were examined in greenhouse-grown Fraxinus pennsylvanica Marsh. (green ash) from five populations located along an east-west transect from New York State to South Dakota. During a 17-day drought, South Dakota seedlings, from the most xeric habitat, maintained the highest net photosynthesis and leaf conductance, and New York seedlings, from the most mesic habitat, exhibited the lowest net photosynthesis and leaf conductance. All populations except New York adjusted osmotically during the 17-day drought, by the end of which New York seedlings had the highest osmotic potentials at full and zero turgor. Tissue elasticity increased in New York seedlings, but decreased in Nebraska seedlings during the drought. Leaves of South Dakota seedlings were the most xerophytic. They were smaller in area and greater in thickness and specific mass than leaves of other sources. Leaves of New York seedlings were thinner than those of the other genotypes and among the largest. Seedlings from South Dakota were smaller than those of the other populations. 相似文献
7.
Diurnal and seasonal photosynthesis patterns were studied in poplar clones Populus tristis Fisch. x P. balsamfera L. cv. Tristis #1 (NC 5260) and Populus x euramericana (Dode) Guiner cv. Eugenei (NC 5326, Carolina poplar) during their first season in the field in a short rotation, intensive culture plantation. Photosynthetic rates were low in immature leaves; increased basipetally on the shoot and peaked in leaves that had recently reached full expansion; and thereafter declined in lower-crown leaves in both clones. Photosynthesis was associated with leaf age and stomatal conductance in immature leaves; adaxial photosynthetic photon flux density (PPFD) and leaf temperature in recently mature leaves; and leaf age and adaxial PPFD in lower-crown leaves. Diurnal photosynthesis patterns within trees were highly variable due to differential light interception among leaves. Results of clonal comparisons of photosynthetic rates were dependent on which leaves were pooled for comparison and how photosynthesis was expressed. Compared to Eugenei, Tristis produced smaller leaves which had higher unit-area photosynthesis rates. The more indeterminate Eugenei outgrew Tristis principally because it more fully utilized the growing season for leaf area production. Photosynthetic production integrated over the growing season was closely related to dry matter production in both clones. 相似文献
8.
Singsaas EL Laporte MM Shi JZ Monson RK Bowling DR Johnson K Lerdau M Jasentuliytana A Sharkey TD 《Tree physiology》1999,19(14):917-924
Because the rate of isoprene (2-methyl-1,3-butadiene) emission from plants is highly temperature-dependent, we investigated natural fluctuations in leaf temperature and effects of rapid temperature change on isoprene emission of red oak (Quercus rubra L.) leaves at the top of the canopy at Harvard Forest. Throughout the day, leaves often reached temperatures as much as 15 degrees C above air temperature. The highest temperatures were reached for only a few seconds at a time. We compared isoprene emission rates measured when leaf temperature was changed rapidly with those measured when temperature was changed slowly. In all cases, isoprene emission rate increased with increasing leaf temperature up to about 32 degrees C and then decreased with higher temperatures. The temperature at which isoprene emission rates began to decrease depended on how quickly measurements were made. Isoprene emission rates peaked at 32.5 degrees C when measured hourly, whereas rates peaked at 39 degrees C when measurements were made every four minutes. This behavior reflected the rapid increase in isoprene emission rate that occurred immediately after an increase in leaf temperature, and the subsequent decrease in isoprene emission rate when leaf temperature was held steady for longer than 20 minutes. We concluded that the observed temperature response of isoprene emission rate is a function of measurement protocol. Omitting this parameter from isoprene emission models will not affect simulated isoprene emission rates at mild temperatures, but can increase isoprene emission rates at high temperatures. 相似文献
9.
Container-grown black spruce (Picea mariana (Mill.) B.S.P.) seedlings were planted in trays containing a sand and peat mixture, and placed in a climate-controlled greenhouse. One group of seedlings was kept well-watered, and another group was subjected to three cycles of drought. Gas exchange analysis showed that mesophyll photosynthetic function was largely unimpaired by drought. In contrast, stomatal conductance was sensitive to drought, although it became less sensitive with each drought cycle. Both stomatal and mesophyll conductances increased with time in control and drought-stressed seedlings, but mesophyll conductance increased with time more rapidly than did stomatal conductance. Limitation of photosynthetic rate was dominated by the mesophyll. In control seedlings, relative stomatal limitation increased from 6 to 16% by the end of the experiment. In drought-stressed seedlings, relative stomatal limitation of photosynthesis reached 40% during the first drought, but decreased to near control values immediately after rewatering. Because the third, most severe drought had only a minor effect on stomatal conductance, relative stomatal limitation of photosynthesis was similar to that in control seedlings by the end of the experiment. Inhibition of ontogenetic change during drought stress may be responsible for the apparent acclimation of mesophyll photosynthetic processes. We conclude that it would be more effective to select for high photosynthetic capacity than for reduced stomatal sensitivity when breeding for increased drought resistance in black spruce seedlings. 相似文献
10.
Drought stress is one of the most important environmental factors affecting plant growth and survival. To date, most studies aim at understanding of post-stress physiological and anatomical adaptation to drought stress; however only few studies focus on plant recovery. In the present study, transpiration, shoot water potential, and anatomical and morphological measurements were performed on 4-year-old European beech seedlings with fully developed leaves. The seedlings were exposed to three levels of soil water potential (well-watered, moderate drought stress and severe drought stress) and followed by rewatering under greenhouse conditions. Reduced transpiration rates were observed in the stressed seedlings as a response to drought stress, whereas anatomical and morphological variables remained unchanged. Three days after rewatering, transpiration rates in both moderately and severely stressed seedlings recovered to the levels of those of well-watered seedlings. Drought stress promoted leaf budding, resulting in higher shoot dry mass of stressed seedlings. Our findings indicate that anatomical and morphological adaptations of European beech seedlings to drought stress are visibly limited during late-season growth stages. These results will help us to further understand factors involved in drought adaptation potential of European beech seedlings faced with expected climate-related environmental changes. To complete our findings, further experiments on plant recovery from drought stress should be focused on different periods of growing season. 相似文献
11.
We hypothesized that photosynthesis and growth of tropical vegetation at its most northern distribution in Asia (Xishuangbanna, SW China) is adversely affected by seasonal drought and chilling temperatures. To test this hypothesis, we measured photosynthetic and growth characteristics of Zizyphus attopensis Pierre seedlings grown in three contrasting forest microhabitats: the understory, a small gap and a large gap. Photosynthetic capacity (light-saturated photosynthetic rate (A(max)), maximum rate of carboxylation and electron transport rate) and partitioning of leaf nitrogen (N) into carboxylation and electron transport differed significantly among seasons and microhabitats. Specific leaf area (SLA) did not change seasonally, but differed significantly among microhabitats and showed a negative linear relationship with daily integrated photon flux (PPF(i)). In contrast, leaf N concentration per unit area (N(a)) changed seasonally but did not differ among microhabitats. Measurements of maximum PSII photochemical efficiency (F(v)/F(m)) indicated that chronic photoinhibition did not occur in seedlings in any of the microhabitats during the study. Photosynthetic capacity was greatest in the wet season and lowest in the cool season. During the cool and dry seasons, the reduction in A(max) was greater in seedlings grown in the large gap than in in the understory and the small gap. Close logarithmic relationships were detected between PPF(i), leaf N(a) and photosynthetic capacity. Stem mass ratio decreased, and root mass ratio increased, in the dry season. We conclude that seasonal acclimation in growth and photosynthesis of the seedlings was associated with changes in biochemical features (particularly N(a) and partitioning of total leaf N between the different photosynthetic pools) and biomass allocation, rather than with changes in leaf morphological features (such as SLA). Local irradiance is the main factor driving seasonal variations in growth and photosynthesis in the study area, where the presence of heavy fog during the cool and dry seasons limits irradiance, but supplies water to the soil surface layers. 相似文献
12.
短期干旱和复水对麻栎幼苗光合及叶绿素荧光的影响 总被引：2，自引：0，他引：2
麻栎是鲁中山区森林植被恢复的重要阔叶树种之一,本文以1年生麻标幼苗为试验对象,研究短期干旱和复水对其光合及叶绿素荧光等生理生态特征的影响。结果表明：在干旱胁迫初期,干旱组的各项指标均优于对照组,说明过高的土壤含水量并不利于麻栎幼苗的生长;随着土壤干旱程度的进一步加剧,幼苗的气孔导度减少,导致光合和蒸腾作用的下降,水分利用效率升高;胁迫末期各项光合指标均降到最低。从叶绿素荧光参数可以看出,干旱胁迫并未使幼苗的光合机构发生伤害,幼苗在适宜的水分条件时产生光合能力上调,当水分匮缺时,以叶黄素循环为主的非光化学淬灭耗散掉过剩的光能达到保护光合机构的目的。复水后麻栎幼苗的各项生理生态指标恢复正常,但气孔导度的增大存在一定的滞后效应,导致了水分利用效率的反冲,同时叶黄素库仍然维持较高水平,麻栎幼苗通过物理和化学的双重保护来抵御干旱胁迫和进行胁迫后的恢复。 相似文献
13.
Cuttings of hybrid Populus clones Tristis and Eugenei growing in pots in a greenhouse were treated with nitrogen fertilizer at two rates and subjected to repeated soil flooding or drying. Periodically, gas exchange measurements and radioimmunoassays, to determine abscisic acid (ABA) concentrations, were made on recently mature leaves.In both clones, photosynthesis and stomatal conductance were depressed five days after flooding, but leaf ABA concentrations remained relatively constant. In contrast, an initial, 9-day period of soil drying resulted in substantial ABA accumulation in leaves, which closely correlated with declines in photosynthesis and conductance. A second soil drying cycle of up to 9 days was less effective in modifying gas exchange and leaf ABA concentrations. High-N supply stimulated leaf ABA production as the soil dried. On the resumption of watering, gas exchange in Tristis recovered fully and rapidly and leaf ABA concentrations quickly returned to control values, whereas gas exchange in Eugenei recovered slowly and leaf ABA concentrations remained high for longer.Gas exchange in Eugenei was unaffected by soil drying until leaf ABA concentrations exceeded 100 ng g(dw) (-1), whereas Tristis showed a reduction in stomatal conductance and photosynthesis at leaf ABA concentrations of only 10 ng g(dw) (-1). A rise in internal CO(2) concentrations was associated with increased leaf ABA concentrations in Tristis, but not in Eugenei. Clonal differences in the relationship between gas exchange and leaf ABA concentration suggest contrasting physiological strategies for survival under prolonged drying conditions. 相似文献
14.
Many plants emit isoprene, a hydrocarbon that has important influences on atmospheric chemistry. Pathogens may affect isoprene fluxes, both through damage to plant tissue and by changing the abundance of isoprene-emitting species. Live oaks (Quercus fusiformis (Small) Sarg. and Q. virginiana Mill) are major emitters of isoprene in the southern United States, and oak populations in Texas are being dramatically reduced by oak wilt, a widespread fungal vascular disease. We investigated the effects of oak wilt on isoprene emissions from live oak leaves (Q. fusiformis) in the field, as a first step in exploring the physiological effects of oak wilt on isoprene production and the implications of these effects for larger-scale isoprene fluxes. Isoprene emission rates per unit dry leaf mass were 44% lower for actively symptomatic leaves than for leaves on healthy trees (P = 0.033). Isoprene fluxes were significantly negatively correlated with rankings of disease activity in the host tree (fluxes in leaves on healthy trees > healthy leaves on survivor trees > healthy leaves on the same branch as symptomatic leaves > symptomatic leaves; isoprene per unit dry mass: Spearman's rho = -0.781, P = 0.001; isoprene per unit leaf area: Spearman's rho = -0.652, P = 0.008). Photosynthesis and stomatal conductance were reduced by 57 and 63%, respectively, in symptomatic relative to healthy leaves (P < 0.05); these reductions were proportionally greater than the reductions in isoprene emissions. Low isoprene emission rates in symptomatic leaves are most simply explained by physiological constraints on isoprene production, such as water stress as a result of xylem blockage, rather than direct effects of the oak wilt fungus on isoprene synthesis. The effects of oak wilt on leaf-level isoprene emission rates are probably less important for regional isoprene fluxes than the reduction in oak leaf area across landscapes. 相似文献
15.
We used a localized ozone (O3) fumigation (LOF) system to study acute and short-term O(3) effects on physiological leaf traits. The LOF system enabled investigation of primary and secondary metabolic responses of similarly and differently aged leaves on the same plant to three different O3 concentrations ([O3]), unconfounded by other influences on O3 sensitivity, such as genetic, meteorological and soil factors. To simulate the diurnal cycle of O3 formation, current-year and 1-year-old Quercus ilex (L.) and Quercus pubescens (L.) leaves were fumigated with O3 at different positions (and hence, different leaf ages) on the same branch over three consecutive days. The LOF system supplied a high [O3] (300+/-50 ppb) on leaves appressed to the vents, and an intermediate, super-ambient [O3] (varying between 120 and 280 ppb) on leaves less than 30 cm from the vent. Leaves more than 60 cm from the O3 vent were exposed to an [O3] comparable with the ambient concentration, with a 100 ppb peak during the hottest hours of the day. Only leaves exposed to the high [O3] were affected by the 3-day treatment, confirming that Mediterranean oak are tolerant to ambient and super-ambient [O3], but may be damaged by acute exposure to high [O3]. Stomatal and mesophyll conductance and photosynthesis were all reduced immediately after fumigation with high [O3], but recovered to control values within 72 h. Both the intercellular and chloroplast CO2 concentrations ([CO2]) remained constant throughout the experiment. Thus, although treatment with a high [O3] may have induced stomatal closure and consequent down-regulation of photosynthesis, we found no evidence that photosynthesis was limited by low [CO2] at the site of fixation. One-year-old leaves of Q. ilex were much less sensitive to O3 than current-year leaves, suggesting that the low stomatal conductance observed in aging leaves limited O3 uptake. No similar effect of leaf age was found in Q. pubescens. Dark respiration decreased during the treatment period, but a similar decrease was observed in leaves exposed to low [O3], and therefore may not be an effect of O3 treatment. Light respiration, on the other hand, was mostly constant in ozone-treated leaves and increased only in leaves in which photosynthesis was temporarily inhibited by high [O3], preventing them from acting as strong sinks that recycle respiratory CO2 in the leaves. There was no evidence of photochemical damage in Q. ilex leaves, whereas Q. pubescens leaves exposed to a high [O3] showed limited photochemical damage, but recovered rapidly. Biochemical markers were affected by the high [O3], indicating accumulation of reactive oxygen species (ROS) and increased denaturation of lipid membranes, followed by activation of isoprene biosynthesis in Q. pubescens leaves. We speculate that the high isoprene emissions helped quench ROS and normalize membrane stability in leaves recovering from O3 stress. 相似文献
16.
Container-grown walnut seedlings (Juglans regia L.) were subjected to competition with rye grass (Lolium perenne L.) and to a 2-week soil drying cycle. One and 2 weeks after the beginning of the drought treatment, H2 18O (delta approximately equals +100%) was added to the bottom layer of soil in the plant containers to create a vertical H2 18O gradient. Rye grass competition reduced aboveground and belowground biomass of the walnut seedlings by 60%, whereas drought had no effect. The presence of rye grass reduced the dry weight of walnut roots in the upper soil layer and caused a 50% reduction in lateral root length. Rye grass competition combined with the drought treatment reduced walnut leaf CO2 assimilation rate (A) and leaf conductance (gw) by 20 and 39%, respectively. Transpiration rates in rye grass, both at the leaf level and at the plant or tiller level, were higher than in walnut seedlings. Leaf intrinsic water-use efficiency (A/gw) of walnut seedlings increased in response to drought and no differences were observed between the single-species and mixed-species treatments, as confirmed by leaf carbon isotope discrimination measurements. Measurement of delta18O in soil and in plant xylem sap indicated that the presence of rye grass did not affect the vertical profile of soil water uptake by walnut seedlings. Walnut seedlings and rye grass withdrew water from the top and middle soil layers in well-watered conditions, whereas during the drought treatment, walnut seedlings obtained water from all soil layers, but rye grass took up water from the bottom soil layer only. 相似文献
17.
Seasonal variability in basal isoprene emission factor (&mgr;g C g(-1) h(-1) or nmol m(-2) s(-1), leaf temperature at 30 degrees C and photosynthetically active radiation (PAR) at 1000 &mgr;mol m(-2) s(-1)) was studied during the 1998 growing season at Duke Forest in the North Carolina Piedmont. Emissions from eight upper-canopy white oak (Quercus alba L.) leaves were measured periodically from the onset of isoprene emission on Day of Year (DOY) 119 (April 29) to leaf senescence in late October (DOY 299). Emissions from four leaves were measured under basal conditions with a controlled-environment cuvette system equipped with 10-ml gas-tight syringes and a reduction gas detector. Emissions from the other four leaves were measured under ambient conditions with the same system. Emission rates from the four leaves measured under ambient conditions were adjusted to basal conditions based on the PAR and leaf temperature algorithms of Guenther et al. (1993). The seasonal onset of isoprene emission was in agreement with previous studies where cumulative degree days from the date of the last spring frost were used to estimate bud break, leaf expansion, and increase in basal emission factor (EF). Between DOY 141 (May 21) and 240 (August 28), mean meteorological conditions 6 to 18 h prior to the EF measurements (ambient PAR and temperature) explained up to 78% of the variability in mean basal EF between measurement periods. Summertime mean isoprene emission potential was reached on DOY 141 (May 21) and was maintained until DOY 240 (August 28), when isoprene emission began to decline monotonically as leaf senescence approached. The mean value for leaves measured under ambient conditions and adjusted to basal conditions for DOY 141-240 was 75.6 &mgr;g C g(-1) h(-1) (74.2-79.1), whereas the mean value for leaves measured under basal conditions was 72.9 &mgr;g C g(-1) h(-1) (64.7-88.9). Between DOY 141 and 240, daily mean isoprene EFs varied from 54 to 96 &mgr;g C g(-1) h(-1) (27 to 49 nmol m(-2) s(-1)). In agreement with previous work at this and other sites, basal isoprene emission rates of fully exposed leaves at the crown apex of this tree were about 20% higher than those of the selected leaves. The length of the period prior to measurement of isoprene emission, during which meteorology was correlated with basal EF, appeared to be related to the timing and periodicity of meteorological change, and probably explains quantitative differences in the length of this period among studies. The empirical equation that we derived for this effect explained variability in midday EFs at the study site, but its general applicability remains to be tested. Strong diurnal changes in EF (as high as a factor of 2) are implied in this study, and should be examined further. 相似文献
18.
Photosynthesis (A), water relations and stomatal reactivity during drought, and leaf morphology were evaluated on 2-year-old, sun- and shade-grown Prunus serotina Ehrh. seedlings of a mesic Pennsylvania seed source and a more xeric Wisconsin source. Wisconsin plants maintained higher A and leaf conductance (g(wv)) than Pennsylvania plants during the entire drought under sun conditions, and during the mid stages of drought under shade conditions. Compared to shade plants, sun plants of both sources exhibited a more rapid decrease in A or % A(max) with decreasing leaf water potential (Psi). Tissue water relations parameters were generally not significantly different between seed sources. However, osmotic potentials were lower in sun than shade plants under well-watered conditions. Following drought, shade plants, but not sun plants, exhibited significant osmotic adjustment. Sun leaves had greater thickness, specific mass, area and stomatal density and lower guard cell length than shade leaves in one or both sources. Wisconsin sun leaves were seemingly more xerophytic with greater thickness, specific mass, and guard cell length than Pennsylvania sun leaves. No source differences in leaf structure were exhibited in shade plants. Stomatal reactivity to sun-shade cycles was similar between ecotypes. However, well-watered and droughted plants differed in stomatal reactivity within and between multiple sun-shade cycles. The observed ecotypic and phenotypic variations in ecophysiology and morphology are consistent with the ability of Prunus serotina to survive in greatly contrasting environments. 相似文献
19.
The impact of drought conditioning on the ability of eight-week-old jack pine (Pinus banksiana Lamb.) seedlings to withstand drought was assessed. Two progressive cycles of drought conditioning significantly increased the survival of seedlings subjected to a subsequent prolonged drought. The in vivo accumulation of several root membrane proteins during drought conditioning was correlated with an increase in seedling survival. A group of root proteins, ranging in molecular mass from 43 to 47 kDa, increased accumulation during one cycle of drought conditioning and to a lesser extent during two cycles of drought conditioning. The accumulation of several low molecular mass membrane and soluble proteins also increased during drought conditioning, suggesting that these proteins may play an important role in the enhancement of drought tolerance. In vitro translation studies showed a general increase in the abundance of protein products encoded by mRNAs from drought-conditioned seedlings. Although the majority of the in vitro translation products appeared in both control and drought-conditioned seedlings, one mRNA encoding a 15 kDA translated protein was more prominent during the second cycle of drought conditioning. 相似文献
20.
Field measurements were made of leaf photosynthesis (A), stomatal conductance (g) and leaf water relations for sugar maple (Acer saccharum Marsh.) seedlings growing in a forest understory, small gap or large clearing habitat in southwestern Wisconsin, USA. Predawn water status, leaf gas exchange and plasticity in field and laboratory water relations characteristics were compared among contrasting light environments in a wet year (1987) and a dry year (1988) to evaluate possible interactions between light and water availability in these habitats. Leaf water potentials (Psi(leaf)) at predawn and midday were lower for clearing than gap or understory seedlings. Acclimation of tissue osmotic potentials to light environment was observed among habitats but did not occur within any of the habitats in response to prolonged drought. During a summer drought in 1988, decreases in daily maximum g (g(max)) and maximum A (A(max)) in clearing seedlings were correlated with predawn Psi(leaf), which reached a seasonal minimum of -2.0 MPa. Under well-watered conditions, diurnal fluctuations in Psi(leaf) of up to 2.0 MPa in clearing seedlings occurred along with large midday depressions of A and g. In a wet year, strong stomatal responses to leaf-to-air vapor pressure difference (VPD) in sunny habitats were observed over nine diurnal courses of gas exchange measurements on seedlings in a gap and a clearing. Increasing stomatal limitations to photosynthesis appeared to be responsible for the reduction in A at high VPD for clearing seedlings. In understory seedlings, however, low water-use efficiency and development of leaf water deficits in sunflecks was related to reduced stomatal limitations to photosynthesis relative to seedlings in sunny habitats. Predawn Psi(leaf) and VPD appear to be important factors limiting carbon assimilation in sugar maple seedlings in light-saturating irradiances, primarily through stomatal closure. The overall results are consistent with the idea that sugar maple seedlings exhibit "conservative" water use patterns and have low drought tolerance. Leaf water relations and patterns of water use should be considered in studies of acclimation and species photosynthetic performance in contrasting light environments. 相似文献