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1.
Mature non-senescent leaves of evergreen species become gradually shaded as new foliage develops and canopy expands, but the interactive effects of integrated light during leaf formation (Q(int)G), current light (Q(int)C) and leaf age on foliage photosynthetic competence are poorly understood. In Quercus ilex L., we measured the responses of leaf structural and physiological variables to Q(int)C and Q(int)G for four leaf age classes. Leaf aging resulted in increases in leaf dry mass per unit area (M(A)), and leaf dry to fresh mass ratio (D(F)) and decreases in N content per dry mass (N(M)). N content per area (N(A)) was independent of age, indicating that decreases in N(M) reflected dilution of leaf N because of accumulation of dry mass (NA = N(M) M(A)). M(A), D(F) and N(A) scaled positively with irradiance, whereas these age-specific correlations were stronger with leaf growth light than with current leaf light. Area-based maximum ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylase activity (V(cmax)A), capacity for photosynthetic electron transport (J(max)A) and the rate of non-photorespiratory respiration in light (R(d)A) were also positively associated with irradiance. Differently from leaf structural characteristics, for all data pooled, these relationships were stronger with current light with little differences among leaves of different age. Acclimation to current leaf light environment was achieved by light-dependent partitioning of N in rate-limiting proteins. Mass-based physiological activities decreased with increasing leaf age, reflecting dilution of leaf N and a larger fraction of non-photosynthetic N in older leaves. This resulted in age-dependent modification of leaf photosynthetic potentials versus N relationships. Internal diffusion conductance (g(m)) per unit area (g(m)A) increased curvilinearly with increasing irradiance for two youngest leaf age classes and was independent of light for older leaves. In contrast, g(m) per dry mass (g(m)M) was negatively associated with light in current-year leaves. Greater photosynthetic potentials and moderate changes in diffusion conductance resulted in greater internal diffusion limitations of photosynthesis in higher light. Both area- and mass-based g(m) decreased with increasing leaf age. The decrease in diffusion conductance was larger than changes in photosynthetic potentials, leading to larger CO2 drawdown from leaf internal air space to chloroplasts (delta(c)) in older leaves. The increases in diffusion limitations in older leaves and at higher light scaled with age- and light-dependent increases in MA and D(F). Overall, our study demonstrates a large potential of foliage photosynthetic acclimation to changes in leaf light environment, but also highlights enhanced structural diffusion limitations in older leaves that result from leaf structural acclimation to previous rather than to current light environment and accumulation of structural compounds with leaf age. 相似文献
2.
Seasonal evolution of diffusional limitations and photosynthetic capacity in olive under drought 总被引:3,自引:1,他引:2
This study tests the hypothesis that diffusional limitation of photosynthesis, rather than light, determines the distribution of photosynthetic capacity in olive leaves under drought conditions. The crowns of four olive trees growing in an orchard were divided into two sectors: one sector absorbed most of the radiation early in the morning (MS) while the other absorbed most in the afternoon (AS). When the peak of radiation absorption was higher in MS, air vapour pressure deficit (VPD) was not high enough to provoke stomatal closure. In contrast, peak radiation absorption in AS coincided with the daily peak in VPD. In addition, two soil water treatments were evaluated: irrigated trees (I) and non-irrigated trees (nI). The seasonal evolution of leaf water potential, leaf gas exchange and photosynthetic capacity were measured throughout the tree crowns in spring and summer. Results showed that stomatal conductance was reduced in nI trees in summer as a consequence of soil water stress, which limited their net assimilation rate. Olive leaves displayed isohydric behaviour and no important differences in the diurnal course of leaf water potentials among treatments and sectors were found. Seasonal diffusional limitation of photosynthesis was mainly increased in nI trees, especially as a result of stomatal limitation, although mesophyll conductance (g(m)) was found to decrease in summer in both treatments and sectors. A positive relationship between leaf nitrogen content with both leaf photosynthetic capacity and the daily integrated quantum flux density was found in spring, but not in summer. The relationship between photosynthetic capacity and g(m) was curvilinear. Leaf temperature also affected to g(m) with an optimum temperature at 29 degrees C. AS showed larger biochemical limitation than MS in August in both treatments. All these suggest that both diffusional limitation and the effect of leaf temperature could be involved in the seasonal reduction of photosynthetic capacity of olive leaves. This work highlights the need for models of plant growth and ecosystem function to incorporate new parameters affecting the distribution of photosynthetic capacity in canopies. 相似文献
3.
Physiological effects of kaolin applications in well-irrigated and water-stressed walnut and almond trees 总被引:1,自引:0,他引:1
BACKGROUND AND AIMS: Kaolin applications have been used to mitigate the negative effects of water and heat stress on plant physiology and productivity with variable results, ranging from increased to decreased yields and photosynthetic rates. The mechanisms of action of kaolin applications are not clear: although the increased albedo reduces leaf temperature and the consequent heat stress, it also reduces the light available for photosynthesis, possibly offsetting benefits of lower temperature. The objective of this study was to investigate which of these effects are prevalent and under which conditions. METHODS: A 6% kaolin suspension was applied on well-irrigated and water-stressed walnut (Juglans regia) and almond (Prunus dulcis) trees. Water status (i.e. stem water potential, psi(s)), gas exchange (i.e. light-saturated CO2 assimilation rate, Amax; stomatal conductance, g(s)), leaf temperature (T(l)) and physiological relationships in treated and control trees were then measured and compared. KEY RESULTS: In both species, kaolin did not affect the daily course of psi(s) whereas it reduced Amax by 1-4 micromol CO2 m(-2) s(-1) throughout the day in all combinations of species and irrigation treatments. Kaolin did not reduce g(s) in any situation. Consequently, intercellular CO2 concentration (C(i)) was always greater in treated trees than in controls, suggesting that the reduction of Amax with kaolin was not due to stomatal limitations. Kaolin reduced leaf temperature (T(l)) by about 1-3 degrees C and leaf-to-air vapour pressure difference (VPD(l)) by about 0.1-0.7 kPa. Amax was lower at all values of g(s), T(l) and VPD(l) in kaolin-treated trees. Kaolin affected the photosynthetic response to the photosynthetically active radiation (PAR) in almond leaves: kaolin-coated leaves had similar dark respiration rates and light-saturated photosynthesis, but a higher light compensation point and lower apparent quantum yield, while the photosynthetic light-response curve saturated at higher PAR. When these parameters were used to model the photosynthetic response curve to PAR, it was estimated that the kaolin film allowed 63% of the incident PAR to reach the leaf. CONCLUSIONS: The main effect of kaolin application was the reduction, albeit minor, of photosynthesis, which appeared to be related to the shading of the leaves. The reduction in T(l) and VPD(l) with kaolin did not suffice to mitigate the adverse effects of heat and water stress on Amax. 相似文献
4.
5.
不同甘蔗品种叶片气孔对水分胁迫的响应 总被引:2,自引:0,他引:2
干旱是甘蔗面临最主要的环境胁迫之一,为了解不同甘蔗品种在干旱胁迫时的气孔响应,该研究以F172、GT21、YT93/159和 YL6四个抗旱性有显著差异的甘蔗品种为材料,采用桶栽,在伸长期进行四种不同程度的干旱胁迫(不浇水)处理:土壤持水量在①65%~70%为轻度干旱;②45%~50%为中度干旱;③25%~30%为重度干旱;④以土壤含水量为75%为对照(CK).检测不同品种不同处理甘蔗的叶片相对持水量变化,并利用扫描电镜技术观察甘蔗叶片下表皮气孔特性.结果表明:在干旱胁迫下,四个甘蔗品种叶片气孔导度急剧下降,重度干旱时耐旱性强的 F172和 GT21的气孔导度低于耐旱性弱的 YT93/159和 YL6的;复水后3 d,F172和 GT21的气孔导度上升至82.07和88.85 mmol·m-2·s-1,而 YT93/159和 YL6的仅有18.88和33.08 mmol·m-2·s-1.干旱还导致气孔下陷、闭合,气孔器的长、宽明显减小,且品种间气孔器长度变化差异显著;干旱胁迫下气孔密度增大,尤以耐旱性最强的 F172在重度干旱时达到显著差异.重度干旱时 F172与GT21的气孔闭合百分比是 YT93/159和 YL6近3~4倍.在水分胁迫下,叶片相对含水量降低,但 F172和GT21在重度干旱时仍可以保持相对较高的含水量,其它两个品种相对较低,尤以 YT93/159的最低.在复水后叶片含水量都有所恢复.这些研究结果表明不同甘蔗品种抗旱能力与叶片气孔特性和含水量密切相关. 相似文献
6.
Photosynthetic limitations in response to water stress and recovery in Mediterranean plants with different growth forms 总被引:10,自引:1,他引:9
* Whether photosynthesis is limited during water stress and recovery because of diffusive or biochemical factors is still open to debate, and apparent contradictions appear when various studies on species with different growth forms are compared. * Ten Mediterranean species, representing different growth forms, were subjected to different levels of water stress, the most severe followed by rewatering. A quantitative limitation analysis was applied to estimate the effects of water stress on stomatal (S(L)), mesophyll conductance (MC(L)) and biochemical limitations (B(L)). * Results confirmed a general pattern of photosynthetic response to water stress among C(3) plants when stomatal conductance (g(s)) is used as a reference parameter. As g(s) values decreased from a maximum to approx. 0.05 mol H(2)O m(-2) s(-1), the total photosynthetic limitation rose from 0 to approx. 70%, and this was caused by a progressive increase of both S(L) and MC(L) limitations, while B(L) remained negligible. When lower values of g(s) were achieved (total photosynthetic limitation increased from 70 to 100%), the contribution of S(L) declined, while MC(L) still increased and B(L) contributed significantly (20-50%) to the total limitation. * Photosynthetic recovery of severely stressed plants after rewatering showed a dominant role of MC(L), irrespective of the degree of photosynthesis recovery. 相似文献
7.
8.
Mature apricot (Prunus armeniaca L. cv. Búlida) trees, growing under field conditions, were submitted to two drip irrigation treatments: a control (T1), irrigated
to 100 % of seasonal crop evapotranspiration (ETc), and a continuous deficit (T2), irrigated to 50 % of the control throughout
the year. The behaviour of leaf water potential and its components, leaf conductance and net photosynthesis were studied at
three different times during the growing season, when they revealed a diurnal and seasonal pattern in response to water stress,
evaporative demand of the atmosphere and leaf age. The deficit-irrigated trees showed, among other effects, a pronounced decrease
in leaf water potential (ψw), decreased in leaf conductance (gs) and no osmotic adjustment. For this reason, gl and ψw can be considered good indicators of mature apricot tree water status and can therefore be used for irrigation scheduling. 相似文献
9.
Photosynthetic and Transpiration Rates of Soybean as Affected by Different Irradiances During Growth
The diurnal variation of net photosynthetic (PN) and transpiration (E) rates in soybean [Glycine max (L.) Merr. cv. Fukuyutaka] plants grown under 100, 50, or 25 % of full sun irradiance (I100, I50, I25 plants) were compared. In the morning, activities of the plants were measured at irradiances under which they grew. However, during the afternoon, all the plants were tested under full irradiance. The lower the growth irradiance, the lower PN, E, and mesophyll conductance values were found. Stomatal conductance was considerably lower in I25 plants only. Both the increase in specific leaf area (SLA) and the decrease in nitrogen content per leaf area unit contributed to the PN reduction of soybean plants grown under low irradiances. Though E of the plants grown under different irradiances differed less markedly than PN, the water use efficiency declined from I100 to I25. 相似文献
10.
Central paradigms of ecophysiology are that there are recognizable and even explicit and predictable patterns among species, genera, and life forms in the economics of water and nitrogen use in photosynthesis and in carbon isotope discrimination (delta). However most previous examinations have implicitly assumed an infinite internal conductance (gi) and/or that internal conductance scales with the biochemical capacity for photosynthesis. Examination of published data for 54 species and a detailed examination for three well-characterized species--Eucalyptus globulus, Pseudotsuga menziesii and Phaseolus vulgaris--show these assumptions to be incorrect. The reduction in concentration of CO2 between the substomatal cavity (Ci) and the site of carbon fixation (Cc) varies greatly among species. Photosynthesis does not scale perfectly with gi and there is a general trend for plants with low gi to have a larger draw-down from Ci to Cc, further confounding efforts to scale photosynthesis and other attributes with gi. Variation in the gi-photosynthesis relationship contributes to variation in photosynthetic 'use' efficiency of N (PNUE) and water (WUE). Delta is an information-rich signal, but for many species only about two-thirds of this information relates to A/gs with the remaining one-third related to A/gi. Using data for three well-studied species we demonstrate that at common WUE, delta may vary by up to 3 per thousand. This is as large or larger than is commonly reported in many interspecific comparisons of delta, and adds to previous warnings about simplistic interpretations of WUE based on delta. A priority for future research should be elucidation of relationships between gi and gs and how these vary in response to environmental conditions (e.g. soil water, leaf-to-air vapour pressure deficit, temperature) and among species. 相似文献
11.
Stomatal, mesophyll conductance and biochemical limitations to photosynthesis as affected by drought and leaf ontogeny in ash and oak trees 总被引:16,自引:2,他引:16
Gas exchange measurements were carried out on ash and oak trees in a forest plantation during three whole growing seasons characterized by different water availability (2001, 2002 and 2003). A quantitative limitation analysis was applied to estimate the effects of drought and leaf ontogeny on stomatal (SL) and non-stomatal limitations (NSL) to light-saturated net photosynthesis (Amax), relative to the seasonal maximum rates obtained under conditions of optimal soil water content. Furthermore, based on combined gas exchange and chlorophyll fluorescence measurements, NSL was partitioned into a diffusive (due to a decrease in mesophyll conductance, MCL) and a biochemical component (due to a decrease in carboxylation capacity, BL). During the wettest year (2002), the seasonal pattern of both Amax and stomatal conductance (gsw) was characterized in both species by a rapid increase during spring and a slight decline over the summer. However, with a moderate (year 2001) or a severe (year 2003) water stress, the summer decline of Amax and gsw was more pronounced and increased with drought intensity (30–40% in 2001, 60–75% in 2003). The limitation analysis showed that during the spring and the autumn periods SL, MCL and BL were of similar magnitude. By contrast, from the summer data it emerged that all the limitations increased with drought intensity, but their relative contribution changed. At mild to moderate water stress (corresponding to values of gsw > 100 mmol H2O m−2 s−1) about two-thirds of the decline in Amax was attributable to SL. However, with increasing drought intensity, NSL increased more than SL and nearly equalled it when the stress was very severe (i.e. with gsw < 60 mmol H2O m−2 s−1). Within NSL, MCL represented the main component, except at the most severe water stress levels when it was equalled by BL. It is concluded that diffusional limitations (i.e. SL + MCL) largely affect net assimilation during most of the year, whereas biochemical limitations are quantitatively important only during leaf development and senescence or with severe droughts. 相似文献
12.
The use of low [CO2 ] to estimate diffusional and non-diffusional limitations of photosynthetic capacity of salt-stressed olive saplings 总被引:9,自引:5,他引:4
In this study it has been shown that increased diffusional resistances caused by salt stress may be fully overcome by exposing attached leaves to very low [CO2] (~ 50 µmol mol?1), and, thus a non‐destructive‐in vivo method to correctly estimate photosynthetic capacity in stressed plants is reported. Diffusional (i.e. stomatal conductance, gs, and mesophyll conductance to CO2, gm) and biochemical limitations to photosynthesis (A) were measured in two 1‐year‐old Greek olive cultivars (Chalkidikis and Kerkiras) subjected to salt stress by adding 200 mm NaCl to the irrigation water. Two sets of A–Ci curves were measured. A first set of standard A–Ci curves (i.e. without pre‐conditioning plants at low [CO2]), were generated for salt‐stressed plants. A second set of A–Ci curves were measured, on both control and salt‐stressed plants, after pre‐conditioning leaves at [CO2] of ~ 50 µmol mol?1 for about 1.5 h to force stomatal opening. This forced stomata to be wide open, and gs increased to similar values in control and salt‐stressed plants of both cultivars. After gs had approached the maximum value, the A–Ci response was again measured. The analysis of the photosynthetic capacity of the salt‐stressed plants based on the standard A–Ci curves, showed low values of the Jmax (maximum rate of electron transport) to Vcmax (RuBP‐saturated rate of Rubisco) ratio (1.06), that would implicate a reduced rate of RuBP regeneration, and, thus, a metabolic impairment. However, the analysis of the A–Ci curves made on pre‐conditioned leaves, showed that the estimates of the photosynthetic capacity parameters were much higher than in the standard A–Ci responses. Moreover, these values were similar in magnitude to the average values reported by Wullschleger (Journal of Experimental Botany 44, 907–920, 1993) in a survey of 109 C3 species. These findings clearly indicates that: (1) salt stress did affect gs and gm but not the biochemical capacity to assimilate CO2 and therefore, in these conditions, the sum of the diffusional resistances set the limit to photosynthesis rates; (2) there was a linear relationship (r2 = 0.68) between gm and gs, and, thus, changes of gm can be as fast as those of gs; (3) the estimates of photosynthetic capacity based on A–Ci curves made without removing diffusional limitations are artificially low and lead to incorrect interpretations of the actual limitations of photosynthesis; and (4) the analysis of the photosynthetic properties in terms of stomatal and non‐stomatal limitations should be replaced by the analysis of diffusional and non‐diffusional limitations of photosynthesis. Finally, the C3 photosynthesis model parameterization using in vitro‐measured and in vivo‐measured kinetics parameters was compared. Applying the in vivo‐measured Rubisco kinetics parameters resulted in a better parameterization of the photosynthesis model. 相似文献
13.
Miconia albicans, a common evergreen cerrado species, was studied under field conditions. Leaf gas exchange and pre-dawn leaf water potential
(Ψpd) were determined during wet and dry seasons. The potential photosynthetic capacity (P
Npmax) and the apparent carboxylation efficiency (ε) dropped in the dry season to 28.0 and 0.7 %, respectively, of the maximum
values in the wet season. The relative mesophyll (Lm) and stomatal (Ls) limitations of photosynthesis increased, respectively, from 24 and 44 % in the wet season to 79 and 57 % at the peak of
the dry season when mean Ψpd reached −5.2 MPa. After first rains, the P
Npmax, ε, and Lm recovered reaching the wet season values, but Ls was maintained high (63 %). The shallow root system growing on stonemason limited by lateral concrete wall to a depth of
0.33 m explained why extreme Ψpd was brought about. Thus M. albicans is able to overcome quickly the strains imposed by severe water stress. 相似文献
14.
BACKGROUND AND AIMS: Bamboos have long-lived, evergreen leaves that continue to accumulate silica throughout their life. Silica accumulation has been suggested to suppress their photosynthetic activity. However, nitrogen content per unit leaf area (N(area)), an important determinant of maximum photosynthetic capacity per unit leaf area (P(max)), decreases as leaves age and senescence. In many species, P(max) decreases in parallel with the leaf nitrogen content. It is hypothesized that if silica accumulation affects photosynthesis, then P(max) would decrease faster than N(area), leading to a decrease in photosynthetic rate per unit leaf nitrogen (photosynthetic nitrogen use efficiency, PNUE) with increasing silica content in leaves. METHODS: The hypothesis was tested in leaves of Sasa veitchii, which have a life span of 2 years and accumulate silica up to 41 % of dry mass. Seasonal changes in P(max), stomatal conductance, N(area) and silica content were measured for leaves of different ages. KEY RESULTS: Although P(max) and PNUE were negatively related with silica content across leaves of different ages, the relationship between PNUE and silica differed depending on leaf age. In second-year leaves, PNUE was almost constant although there was a large increase in silica content, suggesting that leaf nitrogen was a primary factor determining the variation in P(max) and that silica accumulation did not affect photosynthesis. PNUE was strongly and negatively correlated with silica content in third-year leaves, suggesting that silica accumulation affected photosynthesis of older leaves. CONCLUSIONS: Silica accumulation in long-lived leaves of bamboo did not affect photosynthesis when the silica concentration of a leaf was less than 25 % of dry mass. Silica may be actively transported to epidermal cells rather than chlorenchyma cells, avoiding inhibition of CO2 diffusion from the intercellular space to chloroplasts. However, in older leaves with a larger silica content, silica was also deposited in chlorenchyma cells, which may relate to the decrease in PNUE. 相似文献
15.
The response of Brassica carinata hybrids and their parents to moisture stress at different growth stages was studied. B.
carinata 226 was found to be susceptible to stress at pre-flowering and post-flowering stages while B. carinata 241 at flowering
stage. Neither the changes in stomatal conductance nor in chlorophyll content could fully explain the reduction in net photosynthetic
rate (PN) induced by stress. B. carinata 241 had higher leaf water potential (ψw) although, it had lower PN compared to B. carinata 226. Both the parents had lower PN as well as leaf ψw. The stress response of PN in hybrids followed that in their respective female parents.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Yuhan Yang Qiangqiang Zhang Guanjun Huang Shaobing Peng Yong Li 《Plant, cell & environment》2020,43(6):1437-1451
Studies on the temperature (T) responses of photosynthesis and leaf hydraulic conductance (Kleaf) are important to plant gas exchange. In this study, the temperature responses of photosynthesis and Kleaf were studied in Shanyou 63 (Oryza sativa) and Yannong 19 (Triticum aestivum). Leaf water potential (Ψleaf) was insensitive to T in Shanyou 63, while it significantly decreased with T in Yannong 19. The differential Ψleaf − T relationship partially accounted for the differing gm–T relationships, where gm was less sensitive to T in Yannong 19 than in Shanyou 63. With different gm–T and Ψleaf–T relationships, the temperature responses of photosynthetic limitations were surprisingly similar between the two lines, and the photosynthetic rate was highly correlated with gm. With the increasing T, Kleaf increased in Shanyou 63 while it decreased in Yannong 19. The different Kleaf–T relationships were related to different Ψleaf–T relationships. When excluding the effects of water viscosity and Ψleaf, Kleaf was insensitive to T in both lines. gm and Kleaf were generally not coordinated across different temperatures. This study highlights the importance of Ψleaf on leaf carbon and water exchanges, and the mechanisms for the gm–T and Kleaf–T relationships were discussed. 相似文献
17.
随着城市化进程的加快, 臭氧(O3)已经成为中国夏季首要大气污染物。已有研究表明O3通过气孔进入叶片显著抑制光合作用, 影响陆地生态系统碳水循环过程。但是O3浓度升高对植物光合和气孔导度模型关键参数影响的研究仍然缺乏。该研究利用开顶式气室, 设置两个O3处理(CF, 过滤空气; E-O3, 未过滤空气+ 60 nmol·mol-1 O3), 选用4种常见的树木(茶(Camellia sinensis)、复叶槭(Acer negundo)、栾树(Koelreuteria paniculata)和蒙古栎(Quercus mongolica)), 通过测定叶片气体交换参数, 探究O3浓度升高对植物光合和气孔导度模型关键参数的影响。结果表明: O3浓度升高显著降低了4种植物的饱和光合速率和光合生化模型参数叶肉导度, 但是O3对光合生化模型参数最大羧化速率和最大电子传递速率的负效应在不同树种间存在差异。此外, 不同植物气孔导度对O3的响应也存在差异。通过对最优化气孔导度模型进行参数化, 结果表明O3显著提高了蒙古栎和复叶槭的斜率参数(g1), 并显著增加了茶的气孔导度模型截距参数(g0), 但降低了复叶槭的g0。在不同O3处理下4种树木的内源水分利用效率与g1呈显著线性负相关关系。综上所述, O3浓度升高显著影响光合生化和气孔导度模型关键参数。 相似文献
18.
Decline of photosynthetic capacity with leaf age in relation to leaf longevities for five tropical canopy tree species 总被引:2,自引:0,他引:2
The effect of leaf aging on photosynthetic capacities was examined for upper canopy leaves of five tropical tree species in a seasonally dry forest in Panama. These species varied in mean leaf longevity between 174 and 315 d, and in maximum leaf life span between 304 and 679 d. The light-saturated CO2 exchange rates of leaves produced during the primary annual leaf flush measured at 7-8 mo of age were 33-65% of the rates measured at 1-2 mo of age for species with leaf life span of < 1 yr. The negative regression slopes of photosynthetic capacity against leaf age were steeper for species with shorter maximum leaf longevity. In all species, regression slopes were less steep than the slopes predicted by assuming a linear decline toward the maximum leaf age (20-80% of the predicted decline rate). Maximum oxygen evolution rates and leaf nitrogen content declined faster with age for species with shorter leaf life spans. Statistical significance of regression slopes of oxygen evolution rates against leaf age was strongest on a leaf mass basis (r = 0.49-0.87), followed by leaf nitrogen basis (r = 0.48-0.77), and weakest on a leaf area basis (r = 0.35-0.70). 相似文献
19.
Almond plants (Amygdalus communis L. cv. Garrigues) were grown in the field under drip irrigated and non irrigated conditions. Leaf water potential () and leaf conductance (g1) were determined at three different times of the growing season (spring, summer and autumn). The relationships between and g1 in both treatments showed a continuous decrease of g1 as decreased in spring and summer. Data from the autumn presented a threshold value of (approx. –2.7 MPa in dry treatment, and approx. –1.4 MPa in wet treatment) below which leaf conductance remained constant. 相似文献
20.
Drought effects on photosynthesis and fluorescence in hard wheat cultivars grown in the field 总被引:4,自引:0,他引:4
Net photosynthesis of the flag leaf of hard wheat ( Triticum durum L. evs Valforte, Produra, Adamello, Karel, Appulo and El Amel from the collection of the Instituto di Cerealicultura. Foggia, Italy) of different water potential has been studied on three consecutive years. Net photosynthesis was measured in natural conditions with a LI-COR portable instrument and in saturating CO2 with an oxygen electrode. Net photosynthesis and stomatal conductance were significantly lower in the unirrigated leaves. However, the ratio of intercellular CO2 , concentration (C1 ) to ambient CO3 concentration (Ca ) around the stressed plants was similar to the irrigated control. The maximal rate of photosynthesis in saturating CO2 , (Pn max). measured in the second year of the experiment, was quite close to photosynthesis under natural conditions, indicating that CO2 supply was not limiting. These results suggest that altered mesophyll photosynthetic capacity, rather than stomatal closure, causes the observed reduction in photosynthesis in the unirrigated plants. The variable fluorescence yield (v /Fm ) in predarkened leaves measured for two consecutive years, did not show differences between treatments or between cultivars. However, the analysis of the slow transients, measured the last year of the experiment, showed a linear relation between the fluorescence decline from the maximum initial level (P) and maximum photosynthesis (Pn max). 相似文献