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1.
A multiplicative model of stomatal conductance was developed and tested in two functionally distinct ecotypes of Acer rubrum L. (red maple). The model overcomes the main limitation of the commonly used Ball-Berry model (Ball et al. 1987) by accounting for stomatal behavior under soil drying conditions. We combined the Ball-Berry model with an integrated expression of abscisic acid (ABA)-based stomatal response to ABA concentration ([ABA]) in bulk leaf tissue (gfac), which coupled physiological changes at the leaf level with those in the root. The factor gfac = exp(-beta[ABA]L) incorporated the stomatal response to [ABA] into the Ball-Berry model by down regulating stomatal conductance (gs) in response to physiological changes in the root. The down regulation of gs is pertinent under conditions where soil drying may modify the delivery of chemical signals to leaf stomata. Model testing indicated that the multiplicative model was capable of predicting gs in red maple under wide ranges of soil and atmospheric conditions. Concordance correlation coefficients were high (between 0.59 and 0.94) for the tested ecotypes under three environmental conditions (atmospheric, rhizospheric and minimal stress). The study supported the use of gfac as a gas exchange function that controls water stress effects on gs and aids in the prediction of gs responses. 相似文献
2.
Coordinating leaf functional traits with branch hydraulic conductivity: resource substitution and implications for carbon gain 总被引：1，自引：0，他引：1
We studied relationships among branch hydraulic conductivity, xylem embolism, stomatal conductance (gs), foliar nitrogen (N) concentration and specific leaf area (SLA) of seven tree species growing at four temperate woodland sites spanning a 464-1350 mm rainfall gradient. Specifically, we examined the question: are gs and foliar N concentration coordinated with branch hydraulic conductivity and, if so, what are the implications for carbon assimilation? Area-based, light-saturated photosynthetic rate (Aa) was uniquely and positively correlated with gs and foliar N concentration. Multiple regression analyses showed that, when variability in SLA was controlled for, the (positive) partial slope for each predictor remained significant. In contrast, there was a negative correlation between gs and foliar N concentration such that, for any given Aa, leaves with a high gs allocated less N to foliage than leaves with a low gs. Foliar N concentration was negatively correlated with branch hydraulic conductivity, whereas gs was positively correlated with branch hydraulic conductivity. These relationships were also significant when variability in leaf area to sapwood area ratio, gs and SLA were controlled for in a multiple regression, suggesting that the relationships were unique and independent of other confounding factors. Trees with low water transport capacity were able to support a high Aa by increasing investment in foliar N. Resource substitution occurred such that there was a trade-off between gs and foliar N in relation to branch hydraulic conductivity. High Aa could be sustained through either a high branch hydraulic conductivity and hence high gs and a low allocation to foliar N, or the effect of a low branch hydraulic conductivity and hence low gs could be offset by a high allocation to foliar N. The results are discussed in relation to mechanisms for minimizing the negative effects of limited water availability on carbon gain. 相似文献
3.
To clarify mechanisms underlying variation in transpiration rate among deciduous broad-leaved tree species, we measured diurnal changes in stomatal conductance (gs) and leaf water potential, and calculated the maximum transpiration rate (Emax), leaf-specific hydraulic conductance (K(s-l)) and difference between the soil water potential and the daily minimum leaf water potential (Psis - Psi(l,min)). Pressure-volume (P-V) measurements were made on leaves. Saplings of eight broad-leaved tree species that are common in Japanese cool temperate forests were studied. Maximum transpiration rate varied significantly among species. There was a statistically significant difference in Psis - Psi(l,min), but not in K(s-l). Species with large Emax also had large Psis - Psi(l,min) and gs. The results of the P-V analyses showed that species with a large Psis - Psi(l,min) maintained turgor even at low leaf water potentials. The similar daily minimum leaf pressure potentials (Psip) across all eight species indicate that Psip values below this minimum are critical. Based on these results, we suggest that the leaf cell capacity for turgor maintenance strongly affects Psis - Psi(l,min) and consequently Emax via stomatal regulation. 相似文献
4.
Little is known about the effect of flowering on leaf photosynthesis. To understand why net photosynthesis (A(net)) is lower in Mangifera indica L. leaves close to inflorescences than in leaves on vegetative shoots, we measured nitrogen and carbohydrate concentrations, chlorophyll a fluorescence and gas exchange in recently matured leaves on vegetative terminals and on floral terminals of 4-year-old trees. We used models to estimate photosynthetic electron fluxes and mesophyll conductance (g(m)). Lower A(net) in leaves close to developing inflorescences was attributable to substantial decreases in stomatal conductance and g(m), and also in photosynthetic capacity as indicated by the decrease in the light-saturated rate of photosynthetic electron transport (J(max)). The decrease in J(max) was the result of decreases in the amount of foliar nitrogen per unit leaf area, and may have been triggered by a decrease in sink activity as indicated by the increase in the hexose:sucrose ratio. Parameters measured on leaves close to panicles bearing set fruits were generally intermediate between those measured on leaves on vegetative shoots and on leaves close to inflorescences, suggesting that the changes in A(net) associated with flowering are reversible. 相似文献
5.
We investigated how water and nutrient availability affect radiation-use efficiency (epsilon) and assessed leaf gas exchange as a possible mechanism for shifts in epsilon. We measured aboveground net primary production (ANPP) and annual photosynthetically active radiation (PAR) capture to calculate epsilon as well as leaf-level physiological variables (light-saturated net photosynthesis, Asat; stomatal conductance, gs; leaf internal CO2 concentration, Ci; foliar nitrogen concentration, foliar [N]; and midday leaf water potential, Psileaf) during the second (2001) and third (2002) growing seasons in sweetgum (Liquidambar styraciflua L.) and sycamore (Platanus occidentalis L.) stands receiving a factorial combination of irrigation and fertilization at the Savannah River Site, South Carolina. Irrigation and fertilization increased PAR capture (maximum increase 60%) in 2001 and 2002 for both species and annual PAR capture was well correlated with ANPP (mean r2 = 0.77). A decreasing trend in epsilon was observed in non-irrigated stands for sweetgum in 2001 and for sycamore in both years, although this was only significant for sycamore in 2002. Irrigated stands maintained higher gas exchange rates than non-irrigated stands for sweetgum in 2001 and for sycamore in both years, although foliar [N] and Psileaf were generally unaffected. Because Ci decreased in proportion to gs in non-irrigated stands, it appeared that greater stomatal limitation of photosynthesis was associated with decreased Asat. On several measurement dates for sweetgum in 2001 and for sycamore in both years, epsilon was positively correlated with gas exchange variables (Asat, gs, Ci) (r ranged from 0.600 to 0.857). These results indicate that PAR capture is well correlated with ANPP and that gas exchange rates modified by irrigation can influence the conversion of captured light energy to biomass. 相似文献
6.
目的]探究抑制剂对大叶黄杨生长的抑制作用以及对其叶片形态和光合作用的影响,为灌木绿篱的化学修剪提供技术指导。[方法]在北京林业大学林场苗圃采用3种生长抑制剂(多效唑(PP_(333))、三碘苯甲酸(TIBA)以及脱落酸(ABA))对密植成绿篱状的1年生大叶黄杨扦插苗进行叶面喷施,对其生长、叶片形态及光合作用等指标进行测定。[结果]3种抑制剂均有矮化植株、抑制新梢生长的作用,矮化效果最佳、抑制作用最强的为PP_(333),且高浓度PP_(333)对于高生长的抑制作用持效性较长。叶宽、叶厚以及叶面积在短期PP_(333)处理下高于对照。PP_(333)能提高大叶黄杨净光合速率,主要通过增加叶厚、气孔导度、叶肉导度及叶绿素含量来实现,并且PP_(333)使蒸腾速率提高的同时降低了水分利用效率。TIBA有显著减小叶长、叶宽的作用,但能使叶厚增加,且随浓度的增加作用效果增强,主要通过减小叶面积,降低叶肉导度、气孔导度、胞间CO_2浓度及叶绿素含量来降低净光合速率。ABA能增加叶面积(10 mg·L~(-1)处理除外)、叶长以及减小叶片厚度,通过抑制气孔导度、叶肉导度、叶绿素含量降低净光合速率。TI-BA及ABA均通过降低蒸腾速率,使水分利用效率提高。[结论]3种抑制剂均有矮化植株、抑制新梢生长的作用,并且影响叶片发育,进而影响叶片光合作用,且800 mg·L~(-1)的多效唑对大叶黄杨具有较好的正向作用。 相似文献
7.
To clarify interactions between stomatal responses to two simultaneous environmental changes, the rates of change in stomatal conductance were measured after simultaneously changing two environmental factors from the set of air humidity, leaf water potential (hydraulic environmental factors), air CO(2) concentration and light intensity (photosynthetic environmental factors). The stomatal responses to changes in leaf water potential were not significantly modified by any other simultaneous environmental change. A decrease in air humidity was followed by a decrease in stomatal conductance, and an increase in air humidity was followed by an increase in the conductance, irrespective of the character of the simultaneous change in the photosynthetic environmental factor. If the simultaneous change had an opposite effect on stomatal conductance, the rate of change in stomatal conductance was higher than the theoretical summed rate-the sum of the rate following one environmental change and the rate following another environmental change, measured separately. That is, the stomatal response to air humidity dominated over the responses to photosynthetic environmental factors. Yet, if the simultaneous change in photosynthetic factors had a codirectional effect on stomatal conductance, the rate of stomatal conductance change was lower than the theoretical summed rate. After a simultaneous change of two photosynthetic environmental factors, the rate of stomatal conductance change was very similar to the theoretical rate, if both the environmental changes had a codirectional effect on stomatal conductance. If the changes in the photosynthetic factors had opposite effects on stomatal conductance, the conductance increased, irrespective of the character of the increasing environmental factor. In drought-stressed trees, the rates of change in stomatal conductance tended to differ from the theoretical summed rates more than in well-watered trees. Stomatal closure following an increase in CO(2) concentration was the stomatal response that was most strongly suppressed by the response to another simultaneous environmental change. Six species of temperate deciduous trees were shown to be similar in their relations between the stomatal responses to two simultaneous environmental changes. The mechanism and ecological significance of the interactions between the two signal response pathways of stomata are discussed. 相似文献
8.
We sought to explain the declining distribution in the Balearic Islands of the endemic shrub Rhamnus ludovici-salvatoris R. Chodat, by comparing its photosynthetic response to drought with that of several widely distributed, competing Mediterranean species (R. alaternus L., Quercus ilex L., Pistacia lentiscus L., Q. humilis Mill. and P. terebinthus L.). All of the study species, except for the two Rhamnus species, avoided desiccation by rapidly adjusting their stomatal conductance at the onset of drought, and maintaining constant leaf relative water content. The two Rhamnus species showed desiccation-tolerant behavior; i.e., as drought progressed, their predawn leaf relative water content decreased simultaneously with stomatal closure. All four desiccation-avoiding species showed a significant positive correlation between leaf thermal dissipation (estimated by the fluorescence parameter NPQ (non-photochemical quenching)) and the de-epoxidation state of the xanthophyll cycle (DPS). The two Rhamnus species exhibited maximum DPS regardless of treatment, but only R. alaternus increased NPQ in response to drought. Rhamnus ludovici-salvatoris had a high ratio of photorespiration to photosynthesis and a low intrinsic water-use efficiency; traits that are likely to be unfavorable for plant productivity under arid conditions. It also had the lowest DPS and thermal dissipation among the six species. We conclude that the photosynthetic traits of R. ludovici-salvatoris account for its limited ability to compete with other species in the Mediterranean region. 相似文献
9.
This paper focuses on how canopy structure, its physiological functioning and the environment interact to control and drive the exchange of carbon dioxide (CO2) and water vapor between a temperate forest stand and the atmosphere. First, we present an overview of how temporal and spatial variations in canopy structure (e.g., leaf area index, species, leaf inclination angles, leaf clumping) and physiological functioning (e.g., maximal stomatal conductance, photosynthetic capacity) modulate CO2 and water vapor fluxes. Then, with the biophysical model CANOAK, we quantify the effects of leaf dimension and thickness, vertical variations in leaf area and photosynthetic capacity, leaf clumping, leaf inclination angles, photosynthetic capacity, stomatal conductance and weather on the annual sums of CO2, water vapor and sensible heat exchange. Finally, we discuss how much detail is needed in a model to predict fluxes of CO2 and water vapor with acceptable fidelity. 相似文献
10.
Comparison of photosynthetic induction and transient limitations during the induction phase in young and mature leaves from three poplar clones 总被引：1，自引：0，他引：1
Urban O Sprtová M Kosvancová M Tomásková I Lichtenthaler HK Marek MV 《Tree physiology》2008,28(8):1189-1197
We tested the hypothesis that leaf age affects photosynthetic induction, because conductance to CO2 diffusion usually decreases with increasing leaf age. Photosynthetic inductions, primarily determined by the light modulation of Rubisco activity and stomatal opening, were investigated in both young and mature leaves, as defined by leaf plastochron index (LPI), from three poplar clones: Populus alba L., P. nigra L. and P. x euramericana (Dode) Guinier. In all clones, maximum assimilation rates (A max), maximum stomatal conductance (G Smax) and dark respiration rates (RD) were higher in young leaves (LPI = 3-5) than in mature leaves (LPI = 10-14), and A max decreased from P. alba via P. x euramericana to P. nigra. The clones with high photosynthetic capacity had low induction states 60 s after leaf illumination (IS60; indicating a slow initial induction phase), and required less time to reach 90% photosynthetic induction (T90). In contrast, the clone with the lowest photosynthetic capacity (P. nigra) exhibited high IS60 (high initial induction state) but a long induction time (high T90). A comparison of mature leaves with young leaves revealed significantly (P < 0.01) lower IS60 values in mature leaves of P. nigra only, and significantly higher T90 values in mature leaves of P. alba only. In all clones, young leaves exhibited a lower percentage of maximum transient stomatal limitation during photosynthetic induction (4-9%) compared with mature leaves (16-30%). Transient biochemical limitation, assessed on the basis of the time constants of Rubisco activation (tau), was significantly higher in mature leaves than in young leaves of P. alba; whereas there were no significant differences in tau between young and mature leaves of the other poplar clones. Thus, our hypothesis that leaf age affects photosynthetic induction was confirmed at the level of transient stomatal limitation, which was significantly higher in mature leaves than in young leaves in all clones. For the induction parameters IS60, T90 and tau, photosynthetic induction was more clone-specific and was dependent on leaf age only in some cases, an observation that may apply to other tree species. 相似文献
11.
Diurnal and seasonal patterns of leaf gas exchange and water relations were examined in tree species of contrasting leaf phenology growing in a seasonally dry tropical rain forest in north-eastern Australia. Two drought-deciduous species, Brachychiton australis (Schott and Endl.) A. Terracc. and Cochlospermum gillivraei Benth., and two evergreen species, Alphitonia excelsa (Fenzal) Benth. and Austromyrtus bidwillii (Benth.) Burret. were studied. The deciduous species had higher specific leaf areas and maximum photosynthetic rates per leaf dry mass in the wet season than the evergreens. During the transition from wet season to dry season, total canopy area was reduced by 70-90% in the deciduous species and stomatal conductance (g(s)) and assimilation rate (A) were markedly lower in the remaining leaves. Deciduous species maintained daytime leaf water potentials (Psi(L)) at close to or above wet season values by a combination of stomatal regulation and reduction in leaf area. Thus, the timing of leaf drop in deciduous species was not associated with large negative values of daytime Psi(L) (greater than -1.6 MPa) or predawn Psi(L) (greater than -1.0 MPa). The deciduous species appeared sensitive to small perturbations in soil and leaf water status that signalled the onset of drought. The evergreen species were less sensitive to the onset of drought and g(s) values were not significantly lower during the transitional period. In the dry season, the evergreen species maintained their canopies despite increasing water-stress; however, unlike Eucalyptus species from northern Australian savannas, A and g(s) were significantly lower than wet season values. 相似文献
12.
Exploring the response differences of leaf physiology parameters to enhanced nitrogen deposition between saplings and trees is vital for predicting the variations of terrestrial ecosystem structure and function under future global climate change. In this study, the ecophysiological parameters of saplings and trees of Fraxinus mandshurica Rupr. were measured at different levels of nitrogen addition in a temperate forest. The results show that ecophysiological parameters maximum net photosynthetic rate(P_(max)), apparent quantum efficiency(a), dark respiration(R_d), light saturation point(L_(sp)), photosynthetic nitrogen use efficiency(PNUE),specific leaf area(SLA)and stomatal conductance under saturated light intensity(G_(smax)) were higher in saplings than in trees. These physiological parameters and not N_(leaf)(leaf nitrogen content)led to relatively lower P_(max) and R_d in trees. For both saplings and trees, low and median nitrogen addition(23 and 46 kg ha~(-1)a~(-1)) resulted in significant increases in Pmax, Rd, Lsp, Chl, PNUE, SLA and Gsmax. These parameters tended to decline under high additions of nitrogen(69 kg ha~(-1)a~(-1)),whereas Nleaf was always enhanced with increasing nitrogen. Variations in Pmax and Rd with increasing nitrogen were attributed to variations in the strongly related parameters of, Lsp, Chl, PNUE, SLA and Gsmax. Overall, the response sensitivity of physiological parameters to enhanced nitrogen levels was lower in trees compared with saplings. 相似文献
13.
We examined the principal differences in photosynthetic characteristics between sun and shade foliage and determined the relative importance of biochemical and stomatal limitations during photosynthetic induction. Temperate-zone broadleaf and conifer tree species, ranging widely in shade tolerance, were investigated from one locality in the Czech Republic. The study species included strongly shade-tolerant Abies alba Mill. and Tilia cordata Mill., less shade-tolerant Fagus sylvatica L. and Acer pseudoplatanus L. and sun-demanding Picea abies (L.) Karst. In the fully activated photosynthetic state, sun foliage of all species had significantly higher maximum CO(2) assimilation rates, maximum stomatal conductance and maximum rates of carboxylation than shade foliage. Compared with shade leaves, sun leaves had significantly higher nocturnal stomatal conductances. In all species, shade foliage tended to have higher induction states 60 s after leaf illumination than sun foliage. Sun and shade foliage did not differ in the rate of disappearance of the transient biochemical limitation during the induction phase. Longer time periods were required to reach 90% photosynthetic induction and 90% stomatal induction in sun foliage than in shade foliage of the less shade-tolerant F. sylvatica and A. pseudoplatanus and in sun-demanding P. abies; however, in sun foliage of the strongly shade-tolerant species T. cordata and A. alba, the time needed for photosynthetic induction was similar to, or less than, that for shade foliage. Shade but not sun needles of P. abies and A. alba had significantly slower induction kinetics than the broadleaf tree species. Among species, the sun-demanding P. abies exhibited the shortest stomatal induction times in both sun and shade leaves. Independently of shade tolerance ranking, the transient stomatal and total limitations that characterize photosynthetic induction were relieved significantly earlier in shade foliage than in sun foliage. Sun foliage generally exhibited a hyperbolic photosynthetic induction response, whereas a sigmoidal induction response was more frequent in shade foliage. The different relative proportions of transient biochemical and stomatal limitations during photosynthetic induction in sun and shade foliage indicate an essential role of stomata in photosynthetic limitation during induction, mainly in shade foliage, with a consequent influence on the shape of the photosynthetic induction curve. 相似文献
14.
We studied limitations caused by variations in leaf temperature and soil water availability on photosynthetic electron transport rates calculated from foliar chlorophyll fluorescence analysis (U) in a natural deciduous forest canopy composed of shade-intolerant Populus tremula L. and shade-tolerant Tilia cordata Mill. In both species, there was a positive linear relationship between light-saturated U (Umax) per unit leaf area and mean seasonal integrated daily quantum flux density (Ss, mol per square m per day). Acclimation of leaf dry mass per area and nitrogen per area to growth irradiance largely accounted for this positive scaling. However, the slopes of the Umax versus Ss relationships were greater on days when leaf temperature was high than on days when leaf temperature was low. Overall, Umax varied 2.5-fold across a temperature range of 20-30 degrees C. Maximum stomatal conductance (Gmax) also scaled positively with Ss. Although Gmax observed during daily time courses, and stomatal conductances during Umax measurements declined in response to seasonally decreasing soil water contents, was insensitive to prolonged water stress, and was not strongly correlated with stomatal conductances during its estimation. These results suggest that photorespiration was an important electron sink when intercellular CO2 concentration was low because of closed stomata. Given that xanthophyll cycle pool size (VAZ, sum of violaxanthin, antheraxanthin, and zeaxanthin) may play an important role in dissipation of excess excitation energy, the response of VAZ to fluctuating light and temperature provided another possible explanation for the stable Umax. Xanthophyll cycle carotenoids per total leaf chlorophyll (VAZ/Chl) scaled positively with integrated light and negatively with daily minimum air temperature, whereas the correlation between VAZ/Chl and irradiance was best with integrated light averaged over 3 days preceding foliar sampling. We conclude that the potential capacity for electron transport is determined by long-term acclimation of U to certain canopy light conditions, and that the rapid adjustment of the capacity for excitation energy dissipation plays a significant part in the stabilization of this potential capacity. Sustained high capacity of photosynthetic electron transport during stress periods provides an explanation for the instantaneous response of U to short-term weather fluctuations, but also indicates that U restricts potential carbon gain under conditions of water limitation less than does stomatal conductance. 相似文献
15.
Ontogenetic changes in stomatal and biochemical limitations to photosynthesis of two co-occurring Mediterranean oaks differing in leaf life span 总被引：1，自引：0，他引：1
A quantitative analysis was applied to the stomatal and biochemical limitations to light-saturated net photosynthesis under optimal field conditions in mature trees and seedlings of the co-occurring evergreen oak, Quercus ilex L., and the deciduous oak, Q. faginea Lam. Stomatal limitation to photosynthesis, maximal Rubisco activity and electron transport rate were determined from assimilation versus intercellular leaf carbon dioxide concentration response curves of leaves that were subsequently analyzed for nitrogen (N) concentration, mass per unit area, thickness and percent internal air space. In both species, seedlings had a lower leaf mass per unit area, thickness and leaf N concentration than mature trees. The root system of seedlings during their third year after planting was dominated by a taproot. A lower leaf N concentration of seedlings was associated with lower maximal Rubisco activity and electron transport rate and with assimilation rates similar to or lower than those of mature trees, despite the higher stomatal conductances and potential photosynthetic nitrogen-use efficiencies of seedlings. Consequently, stomatal limitation to photosynthesis increased with tree age in both species. In both seedlings and mature trees, a lower assimilation rate in Q. ilex than in Q. faginea was associated with lower stomatal conductance, N allocation to photosynthetic functions, maximal Rubisco activity and electron transport rate, and potential photosynthetic nitrogen-use efficiency but greater leaf thickness and leaf mass per unit area. Tree-age-related changes differed quantitatively between species, and the characteristics of the two species were more similar in seedlings than in mature trees. Despite higher stomatal conductances, seedlings are more N limited than adult trees, which contributes to lower biochemical efficiency. 相似文献
16.
Patterns of water relations, xylem sap abscisic acid (ABA) concentration ([ABA]) and stomatal aperture were compared in drought-sensitive black walnut (Juglans nigra L.) and black willow (Salix nigra Marsh.), less drought-sensitive sugar maple (Acer saccharum Marsh.) and drought-tolerant white oak (Quercus alba L.). Strong correlations among reduction in predawn water potential, increase in xylem sap [ABA] and stomatal closure were observed in all species. Stomatal response was more highly correlated with xylem [ABA] than with ABA flux. Xylem sap pH and ion concentrations appeared not to play a major role in the stomatal response of these species. Stomata were more sensitive to relative changes in [ABA] in drought-sensitive black walnut and black willow than in sugar maple and white oak. In the early stages of drought, increased [ABA] in the xylem sap of black walnut and black willow was probably of root origin and provided a signal to the shoot of the water status of the roots. In sugar maple and white oak, leaf water potential declined with the onset of stomatal closure, so that stomatal closure also may have occurred in response to the change in leaf water potential. 相似文献
17.
Quantifying stomatal and non-stomatal limitations to carbon assimilation resulting from leaf aging and drought in mature deciduous tree species 总被引：1，自引：0，他引：1
Gas exchange techniques were used to investigate light-saturated carbon assimilation and its stomatal and non-stomatal limitations over two seasons in mature trees of five species in a closed deciduous forest. Stomatal and non-stomatal contributions to decreases in assimilation resulting from leaf age and drought were quantified relative to the maximum rates obtained early in the season at optimal soil water contents. Although carbon assimilation, stomatal conductance and photosynthetic capacity (V(cmax)) decreased with leaf age, decreases in V(cmax) accounted for about 75% of the leaf-age related reduction in light-saturated assimilation rates, with a secondary role for stomatal conductance (around 25%). However, when considered independently from leaf age, the drought response was dominated by stomatal limitations, accounting for about 75% of the total limitation. Some of the analytical difficulties associated with computing limitation partitioning are discussed, including path dependence, patchy stomatal closure and diffusion in the mesophyll. Although these considerations may introduce errors in our estimates, our analysis establishes some reasonable boundaries on relative limitations and shows differences between drought and non-drought years. Estimating seasonal limitations under natural conditions, as shown in this study, provides a useful basis for comparing limitation processes between years and species. 相似文献
18.
Maximum Rubisco activities (V(cmax)), rates of photosynthetic electron transport (J(max)), and leaf nitrogen and chlorophyll concentrations were studied along a light gradient in the canopies of four temperate deciduous species differing in shade tolerance according to the ranking: Populus tremula L. < Fraxinus excelsior L. < Tilia cordata Mill. = Corylus avellana L. Long-term light environment at the canopy sampling locations was characterized by the fractional penetration of irradiance in the photosynthetically active spectral region (I(sum)). We used a process-based model to distinguish among photosynthesis limitations resulting from variability in fractional nitrogen investments in Rubisco (P(R)), bioenergetics (P(B), N in rate-limiting proteins of photosynthetic electron transport) and light harvesting machinery (P(L), N in chlorophyll and thylakoid chlorophyll-protein complexes). On an area basis, V(cmax) and J(max) (V(a) (cmax) and J(a) (max)) increased with increasing growth irradiance in all species, and the span of variation within species ranged from two (T. cordata) to ten times (C. avellana). Examination of mass-based V(cmax) and J(max) (V(m) (cmax) and J(m) (max)) demonstrated that the positive relationships between area-based quantities and relative irradiance mostly resulted from the scaling of leaf dry mass per area (M(A)) with irradiance. Although V(m) (cmax) and J(m) (max) were positively related to growth irradiance in C. avellana, and J(m) (max) was positively related to irradiance in P. tremula, the variation range was only a factor of two. Moreover, V(m) (cmax) and J(m) (max) were negatively correlated with relative irradiance in T. cordata. Rubisco activity in crude leaf extracts generally paralleled the gas-exchange data, but it was independent of light in T. cordata, suggesting that declining V(m) (cmax) with increasing relative irradiance was related to increasing diffusive resistances from the intercellular air spaces to the sites of carboxylation in this species. Because irradiance had little effect on foliar nitrogen concentration, the relationships of P(B) and P(R) with irradiance were similar to those of V(m) (cmax) and J(m) (max). Shade-intolerant species tended to have greater P(B) and P(R) and also larger V(a) (cmax) and J(a) (max) than more shade-tolerant species. However, for the whole material, P(B) and P(R) varied only about 50%, whereas V(a) (cmax) and J(a) (max) varied more than 15-fold, further emphasizing the importance of leaf anatomical plasticity in determining photosynthetic acclimation to high irradiance. Leaf chlorophyll concentrations and fractional nitrogen investments in light harvesting increased hyperbolically with decreasing irradiance to improve quantum use efficiency for incident irradiance. The effect of irradiance on P(L) was of the same order as its effect in the opposite direction on M(A), leading to either a constant model estimate of leaf absorptance with I(sum) or a slightly positive correlation. We conclude that leaf morphological plasticity is a more relevant determinant of foliage adaptation to high irradiance than foliage biochemical properties, whereas biochemical adaptation to low irradiance is of the same magnitude as the anatomical adjustments. Although shade-tolerant species did not have greater chlorophyll concentrations and P(L) than shade-intolerant species, they possessed lower M(A), and could maintain a more extensive foliar display for light capture with constant biomass investment in leaves. 相似文献
19.
Many woody species can be propagated from leafy cuttings. However, following rooting, cuttings of Corylus maxima Mill. cv. Purpurea do not always survive the transition from a highly supportive rooting environment (e.g., fog) to a more natural environment where evaporative demand is higher. We found that it is not the supply of water to leaves, but stomatal dysfunction that leads to severe water deficits in the rooted cuttings. Two hours after well-rooted cuttings were transferred from the rooting environment, we were able to relate visible signs of leaf water deficit to high stomatal conductance (g(s)) and low relative water content (R). Small expanding leaves (L3) had unusually high g(s) and lower R than fully expanded leaves (L1). Although high cuticular conductances (g(c)) were occasionally observed in L3, SEM confirmed that increased total leaf conductance (g) was mainly a result of abnormally wide stomatal opening. We measured changes in the ability of stomata to control water loss during rooting by determining stomatal responsiveness to leaf water deficit in detached L1 and L3 harvested from cuttings during the first 75 days after severance from stock plants. Reduced stomatal responsiveness was observed within 7 days of severance, prior to adventitious root formation, and was more pronounced in L3 than in L1. A period of acclimatization after rooting (no leaf wetting, but a vapor pressure deficit of 0.20 kPa) reduced g(s) by 50% in L3 but not in L1, and partially restored stomatal responsiveness in L1 but not in L3. After rooting, the original leaves on the cutting retained substantial capacity for photosynthesis (e.g., in L1, 8 micromol m(-2) s(-1) at a photosynthetic photon flux density of 400 micromol m(-2) s(-1)). The implications of the results for post-rooting acclimatization procedures are discussed. 相似文献
20.
We tested the hypothesis that branch hydraulic conductivity partly controls foliar stable carbon isotope ratio (delta13C) by its influence on stomatal conductance in Pinus monticola Dougl. Notching and phloem-girdling treatments were applied to reduce branch conductivity over the course of a growing season. Notching and phloem girdling reduced leaf-specific conductivity (LSC) by about 30 and 90%, respectively. The 90% reduction in LSC increased foliar delta13C by about 1 per thousand (P < 0.0001, n = 65), whereas the 30% reduction in LSC had no effect on foliar delta13C (P = 0.90, n = 65). Variation in the delta13C of dark respiration was similar to that of whole-tissues when compared among treatments. These isotopic measurements, in addition to instantaneous gas exchange measurements, suggested only minor adjustments in the ratio of intercellular to atmospheric CO2 partial pressures (ci/ca) in response to experimentally reduced hydraulic conductivity. A strong correlation was observed between stomatal conductance (gs) and photosynthetic demand over a tenfold range in gs. Although ci/ca and delta13C appeared to be relatively homeostatic, current-year leaf area varied linearly as a function of branch hydraulic conductivity (r2 = 0.69, P < 0.0001, n = 18). These results suggest that, for Pinus monticola, adjustment of leaf area is a more important response to reduced branch conductivity than adjustment of ci/ca. 相似文献