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1.
Stomatal versus biochemical limitations to dynamic photosynthetic performance in four tropical rainforest shrub species 总被引:6,自引:0,他引:6
Photosynthetic performance under dynamic light regimes was assessed in four different species of tropical shrubs from the
family Rubiaceae via field gas exchange measurements conducted on Barro Colorado Island, Panamá. Rates of photosynthetic induction
and induction loss were assessed throughout the day in both the wet and dry seasons in order to determine the relative roles
of stomata and biochemistry in limiting photosynthetic performance under transient light conditions. A high degree of coordination
was observed between stomatal conductance and biochemical capacity for CO2 assimilation during induction. Rates of biochemical and overall photosynthetic induction sharply decreased when initial stomatal
conductance fell below a narrow range of critical values. Time of day or season did not affect rates of biochemical deactivation
upon shading, but did influence stomatal closure, which often exerted a significant influence over induction loss in the darkness.
In measurements of total assimilation due to a 60-s light pulse, both biochemical activity and stomatal conductance were linearly
related to total CO2 uptake. Only during the mornings of the wet season was stomatal conductance consistently high enough to be non-limiting to
dynamic photosynthetic performance. At all other times, stomatal behavior exercised significant influence over induction times,
photosynthetic induction loss, and total CO2 uptake from 60-s light pulses.
Received: 17 March 1999 / Accepted: 26 October 1999 相似文献
2.
Photosynthetic sunfleck utilization potential of understory saplings growing under elevated CO<Subscript>2</Subscript> in FACE 总被引:3,自引:0,他引:3
Few studies have evaluated elevated CO2 responses of trees in variable light despite its prevalence in forest understories and its potential importance for sapling
survival. We studied two shade-tolerant species (Acer rubrum, Cornus florida) and two shade-intolerant species (Liquidambar styraciflua, Liriodendron tulipifera) growing in the understory of a Pinus taeda plantation under ambient and ambient+200 ppm CO2 in a free air carbon enrichment (FACE) experiment. Photosynthetic and stomatal responses to artificial changes in light intensity
were measured on saplings to determine rates of induction gain under saturating light and induction loss under shade. We expected
that growth in elevated CO2 would alter photosynthetic responses to variable light in these understory saplings. The results showed that elevated CO2 caused the expected enhancement in steady-state photosynthesis in both high and low light, but did not affect overall stomatal
conductance or rates of induction gain in the four species. Induction loss after relatively short shade periods (<6 min) was
slower in trees grown in elevated CO2 than in trees grown in ambient CO2 despite similar decreases in stomatal conductance. As a result leaves grown in elevated CO2 that maintained induction well in shade had higher carbon gain during subsequent light flecks than was expected from steady-state
light response measurements. Thus, when frequent sunflecks maintain stomatal conductance and photosynthetic induction during
the day, enhancements of long-term carbon gain by elevated CO2 could be underestimated by steady-state photosynthetic measures. With respect to species differences, both a tolerant, A. rubrum, and an intolerant species, L. tulipifera, showed rapid induction gain, but A. rubrum also lost induction rapidly (c. 12 min) in shade. These results, as well as those from independent studies in the literature, show that induction dynamics
are not closely related to species shade tolerance. Therefore, it cannot be concluded that shade-tolerant species necessarily
induce faster in the variable light conditions common in understories. Although our study is the first to examine dynamic
photosynthetic responses to variable light in contrasting species in elevated CO2, studies on ecologically diverse species will be required to establish whether shade-tolerant and -intolerant species show
different photosynthetic responses in elevated CO2 during sunflecks. We conclude that elevated CO2 affects dynamic gas exchange most strongly via photosynthetic enhancement during induction as well as in the steady state.
Received: 1 April 1999 / Accepted: 16 August 1999 相似文献
3.
Liubov Volkova Lauren T. Bennett Andrew Merchant Michael Tausz 《Trees - Structure and Function》2010,24(2):351-362
We examined the responses of two tree fern species (Dicksonia antarctica and Cyathea australis) growing under moderate and high light regimes to short-term water deficit followed by rewatering. Under adequate water supply,
morphological and photosynthetic characteristics differed between species. D. antarctica, although putatively the more shade and less drought adapted species, had greater chlorophyll a/b ratio, and greater water use efficiency and less negative δ13C. Both species were susceptible to water deficit regardless of the light regime showing significant decreases in photosynthetic
parameters (A
max, V
cmax, J
max) and stomatal conductance (g
s
) in conjunction with decreased relative frond water content (RWC) and predawn frond water potential (Ψpredawn). During the water deficit period, decreases in g
s
in both species started one day later, and were at lower soil water content, under moderate light compared with high light.
D. antarctica under moderate light was more vulnerable to drought than all other plants as was indicated by greater decreases in Ψpredawn, lowest stomatal conductance, and photosynthetic rates. Both tree fern species were able to recover after a short but severe
water stress. 相似文献
4.
Coupled response of stomatal and mesophyll conductance to light enhances photosynthesis of shade leaves under sunflecks
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Courtney E. Campany Mark G. Tjoelker Susanne von Caemmerer Remko A. Duursma 《Plant, cell & environment》2016,39(12):2762-2773
Light gradients within tree canopies play a major role in the distribution of plant resources that define the photosynthetic capacity of sun and shade leaves. However, the biochemical and diffusional constraints on gas exchange in sun and shade leaves in response to light remain poorly quantified, but critical for predicting canopy carbon and water exchange. To investigate the CO2 diffusion pathway of sun and shade leaves, leaf gas exchange was coupled with concurrent measurements of carbon isotope discrimination to measure net leaf photosynthesis (An), stomatal conductance (gs) and mesophyll conductance (gm) in Eucalyptus tereticornis trees grown in climate controlled whole‐tree chambers. Compared to sun leaves, shade leaves had lower An, gm, leaf nitrogen and photosynthetic capacity (Amax) but gs was similar. When light intensity was temporarily increased for shade leaves to match that of sun leaves, both gs and gm increased, and An increased to values greater than sun leaves. We show that dynamic physiological responses of shade leaves to altered light environments have implications for up‐scaling leaf level measurements and predicting whole canopy carbon gain. Despite exhibiting reduced photosynthetic capacity, the rapid up‐regulation of gm with increased light enables shade leaves to respond quickly to sunflecks. 相似文献
5.
The effects of leaf-air vapor pressure deficit (VPD) on the transient and steady-state stomatal responses to photon flux density (PFD) were evaluated in Piper auritum, a pioneer tree, and Piper aequale, a shade tolerant shrub, that are both native to tropical forests at Los Tuxtlas, Veracruz, México. Under constant high-PFD conditions, the stomata of shade-acclimated plants of both species were sensitive to VPD, exhibiting a nearly uniform decrease in gs as VPD increased. Acclimation of P. auritum to high light increased the stomatal sensitivity to VPD that was sufflcient to cause a reduction in transpiration at high VPD's. At low PFD, where gs was already reduced, there was little additional absolute change with VPD for any species or growth condition. The stomatal response to 8-min duration lightflecks was strongly modulated by VPD and varied between the species and growth light conditions. In P. aequale shade plants, increased VPD had no effect on the extent of stomatal opening but caused the rate of closure after the lightfleck to be faster. Thus, the overall response to a lightfleck changed from hysteretic (faster opening than closure) to symmetric (similar opening and closing rates). Either high or low VPD caused gs not to return to the steady-state value present before the lightfleck. At high VPD the value after was considerably less than the value before whereas at low VPD the opposite occurred. Shade-acclimated plants of P. auritum showed only a small gs response to lightflecks, which was not affected by VPD. Under sunfleck regimes in the understory, the stomatal response of P. aequale at low VPD may function to enhance carbon gain by increasing the induction state. At high VPD, the shift in the response enhances water use efficiency but at the cost of reduced assimilation. 相似文献
6.
Plants of the C4 tree species, Euphorbia forbesii, Sherff and the C3 tree species, Claoxylon sandwicense Muell-Arg., were grown in a full sun and a shade environment designed to simulate the understory of their native Hawiian forest habitat. When grown under shade conditions, both species exhibited a photosynthetic light response typical of shade plants with low light compensation points and low dark respiration rates. E. forbesii, however, exhibited greater acclimation of light saturated photosynthetic rates and no evidence of photoinhibition in high light. In contrast, quantum yields for CO2 uptake and chlorophyll contents were reduced in the high-light as compared to the low-light grown C. sandwicense plants. Both species exhibited similar changes in the intercellular CO2 response curves and chloroplast whole-chain electron transport capacities, suggesting that the underlying mechanisms of light acclimation are similar. Chloroplasts of E. forbesii exhibited large changes in ultrastructure, with much greater thylakoid membrane development in low than high light. In contrast, C. sandwicense exhibited different starch contents, but otherwise similar membrane development in high and low light. The results show that E. forbesii possesses a very flexible photosynthetic apparatus which may account for its ability to survive in the understory of shaded forests.Abbreviations gs =
stomatal conductance
- HL =
high light
- LL =
low light
- Pi =
intercellular CO2 partial pressure
- PFD =
photon flux density 相似文献
7.
Spatial and daily variation in photosynthetic water-use efficiency was examined in leaves of Betula pendula Roth with respect to distribution of hydraulic conductance within the crown, morphological properties of stomata, and water
availability. Intrinsic water-use efficiency (A
n/g
s) was determined from gas-exchange measurements performed both in situ in a natural forest stand and on detached shoots under
laboratory conditions. In intact foliage, sun leaves demonstrated significantly higher (P < 0.001) A
n/g
s than shade leaves, as photosynthesis in the lower canopy was chronically limited by low light availability. However, this
difference reversed in the mid-day period under sufficient irradiance (I > 800 μmol m−2 s−1): A
n/g
s averaged 28.8 and 24.0 μmol mol−1 (P < 0.01) for shade and sun leaves, respectively. This last finding coincided with the data obtained in laboratory conditions:
under equivalent leaf water supply and light, A
n/g
s in shade foliage was greater (P < 0.001) than in sun foliage across a wide range of irradiance. Thus, shade foliage of B. pendula is characterized by inherently higher A
n/g
s than sun foliage, associated with more conservative stomatal behavior, and lower soil-to-leaf (K
T) and leaf hydraulic conductances. Under unlimited light conditions, a within-crown trade-off between A
n/g
s and K
T becomes apparent. Differences in stomatal conductance between the detached shoots from sunlit and shaded canopy layers were
largely attributable to the variation in stomatal morphology; significant relationships were established with characteristics
combining stomatal size and density (relative stomatal surface, stomatal pore area index). Stomatal morphology is very likely
involved in long-term adjustment of photosynthetic WUE. 相似文献
8.
《Environmental and Experimental Botany》2007,59(2):160-165
A field study was conducted on a 5-year-old orchard of ‘Royal Gala’ apple (Malus domestica Borkh.) in Stellenbosch, South Africa, to investigate whether the measures employed to control sunburn in fruit, viz., evaporative cooling, Surround WP and 20% black shade net affect leaf photosynthetic gas exchange attributes in comparison to untreated control during the 2003/2004 season. Shade net significantly reduced midday leaf net photosynthetic rate (A) compared to evaporative cooling. Furthermore, shade net and Surround WP significantly reduced midday leaf stomatal conductance (gs) compared to evaporative cooling and control. Evaporative cooling increased light saturated photosynthetic rate by 27 and 24% compared to shade net and Surround WP, respectively. Light compensation point and dark respiration of shaded leaves were about a third of the other treatments and about 50% less than the control leaves, respectively. Shade net down-regulated photosynthetic capacity of the leaves as evidenced by lower maximum rate of carboxylation and light saturated rate of electron transport compared to control leaves. Sunburn control treatments reduced day respiration by 60–70% compared to the control. Response of A and gs to increasing temperature showed only slight increase in both A and gs with increasing temperature from 20 to 30 °C. A declined at 35 °C in Surround WP and shade net leaves while it declined at 40 °C in evaporatively cooled and control leaves. Evaporative cooling and control had higher gs than shade net and Surround WP at all leaf temperatures. In conclusion, shade net down-regulated photosynthetic reactions and Surround WP and shade net reduced leaf gs and increased the vulnerability of leaf A and gs to high temperature compared to evaporative cooling and control. 相似文献
9.
Light saturated photosynthesis (A) in field saplings of shade tolerant, intermediate, and intolerant tree species was analyzed
for stomatal and nonstomatal limitations to test differences between species and sun and shade phenotypes during drought.
Throughout the study, photosynthesis was highest and mesophyll limitations of A (Lm) lowest in the intolerant species in both open and understory habitats. The shade tolerant species exhibited the only drought-related
decreased A and increased Lm in the open, and the greatest drought-related decreased A and increased Lm in the understory. Few species exhibited significant habitat or drought-related differences in stomatal conductance to CO2 (gc), but even slight decreases in gc during drought were associated with large increases in stomatal limitations to A (Lg). Combined changes in Lm and Lg resulted in increased relative stomatal limitation to A (l
g) in several species during drought. Nevertheless, the overall lack of stomatal closure allowed for nonstomatal limitations
to play a major role in reduced A during drought. Higher leaf N was associated with shallower slope of the l
g versus gc relationship, an indication of greater A capacity. Photosynthetic capacity tended to be greater in the intolerant species
than the tolerant species, and it tended to decrease during drought primarily in the shade tolerant species in the understory.
Findings in the literature suggest that carbon reduction reactions may be more susceptible to drought than photosynthetic
light reactions. If so, reduced carbon reduction capacity of shade tolerant species or shade phenotypes may predispose them
to drought conditions, which suggests a mechanism behind the well-recognized tradeoff between drought tolerance and shade
tolerance of temperate tree species.
Received: 20 October 1995 / Accepted: 20 February 1996 相似文献
10.
We assessed the daily time‐courses of CO2 assimilation rate (A), leaf transpiration rate (E), stomatal conductance for water vapour (gs), leaf water potential ( Ψ w) and tree transpiration in a wet and a dry season for three late‐stage canopy rainforest tree species in French Guiana differing in leaf carbon isotope composition ( δ 13C). The lower sunlit leaf δ 13C values found in Virola surinamensis ( ? 29·9‰) and in Diplotropis purpurea ( ? 30·9‰), two light‐demanding species, as compared to Eperua falcata ( ? 28·6‰), a shade‐semi‐tolerant species, were clearly associated with higher maximum gs values of sunlit leaves in the two former species. These two species were also characterized by a high sensitivity of gs, sap flow density (Ju) and canopy conductance (gc) to seasonal soil drought, allowing maintenance of high midday Ψ w values in the dry season. The data for Diplotropis provided an original picture of increasing midday Ψ w with increasing soil drought. In Virola, stomata were extremely sensitive to seasonal soil drought, leading to a dramatic decrease in leaf and tree transpiration in the dry season, whereas midday Ψ w remained close to ? 0·3 MPa. The mechanisms underlying such an extremely high sensitivity of stomata to soil drought remain unknown. In Eperua, gs of sunlit leaves was non‐responsive to seasonal drought, whereas Ju and gc were lower in the dry season. This suggests a higher stomatal sensitivity to seasonal drought in shaded leaves than in sunlit ones in this species. 相似文献
11.
In three tropical rain forest light environments in Sabah, Malaysia, we compared photosynthesis in seedlings of ten climax
tree species with putatively differing shade tolerances. The objectives of the study were (a) to characterise the range of
photosynthetic responses in ten species of the Dipterocarpaceae and (b) to elucidate those photosynthetic characteristics
that might provide a basis for niche partitioning. Seedlings were acclimated (c. 7 months) in three light environments; understorey, partial shade and a gap (140 m2). The light environments represented a gradation in median diurnal (0630–1830 hours) photon flux density (PFD) ranging from
understorey (4.7 μmol m−2 s−1), through partial shade (21.2 μmol m−2 s−1) to gap (113.7 μmol m−2 s−1). Integrated diurnal PFD were in the sequence gap > partial shade > understorey (15.2, 4.7, 1.3 mol m−2 day−1, respectively). In gap-acclimated plants, species differed in the photosynthetic light-response variables apparent quantum
yield, dark respiration rate, light compensation point, net saturated leaf assimilation rate (A
sat), and in stomatal conductance (g
s sat) when assimilation rate (A) was saturated. A light-demanding pioneer species (Macaranga hypoleuca) and a shade-demanding understorey species (Begonia sp.) had, respectively, higher and lower A
sat and g
s sat than the dipterocarp species. In high-light conditions A
sat and g
s sat were strongly positively correlated in dipterocarp species. Differing photosynthetic characteristics of gap-acclimated plants
suggest that, in these dipterocarp species, different rates of carbon fixation may be an important factor contributing towards
niche partitioning. Mean integrated diurnal A (A
diurnal) in the gap, partial shade and understory were, respectively, 122.9, 52.7, 20.5 mmol m−2 day−1. Differences occurred in A
diurnal of dipterocarp species between light environments. When Macaranga was included, differences in A
diurnal were evident in the gap and partial shade, and in both cases were attributed to the pioneer. For the variable A
diurnal, there was of a shift in the rank position of Macaranga among light environments, but a shift did not occur among the dipterocarp species. Results from this study are consistent
with the idea that rates of carbon fixation per unit leaf area may contribute towards niche differentiation between the climax
and single pioneer species, but not within the group of climax species. Other physiological and/or carbon allocation factors
may be involved in any niche partitioning; dipterocarp species often have inherently different growth rates and susceptibility
to herbivory. As an alternative to niche partitioning, dipterocarp species may co-exist in natural light environments as a
result of habitat disequilibrium or purely stochastic processes.
Received: 2 April 1997 / Accepted: 13 July 1997 相似文献
12.
Summary Demography and physiology of two broad-leaved understory tropical herbs (Marantaceae) were studied in gaps and shaded understory in large-scale irrigated and control treatments during the dry season at Barro Colorado Island (BCI), Panama. Because photosynthetic acclimation potential may not predict light environments where tropical species are found, we studied a suite of physiological features to determine if they uniquely reflect the distribution of each species. Calathea inocephala and Pleiostachya pruinosa grow and reproduce in gaps, persist in shade, and have equivalent rates of leaf production. Calathea leaves survived 2 to 3 times as long as leaves of Pleiostachya and plants of Pleiostachya were 6 to 8 times more likely to die as plants of Calathea during 3.5 years of study. Pleiostachya had lowest survival in shade and when not irrigated during the dry season, while Calathea survived well in both habitats and both treatments. Pleiostachya had higher photosynthetic capacity and stomatal conductance than Calathea and acclimated to gaps by producing leaves with higher photosynthetic capacity. Calathea had lower mesophyll CO2 concentrations than Pleiostachya. Both species had similar dark respiration rates and light compensation points, and water-use and nitrogen-use efficiencies were inversely related between species. Species showed no differences in leaf osmotic potentials at full turgor. Calathea roots were deeper and had tuberous swellings.Leaf-level assimilation and potential water loss are consistent with where these species are found, but photosynthetic acclimation to high light does not reflect both species' abilities to grow and reproduce in gaps. Pleiostachya's gap-dependent, rapid growth and reproduction require high rates of carbon gain in short-lived leaves, which can amortize their cost quickly. High rates of water loss are associated with reduced longevity during drought. Calathea's roots may confer greater capacitance, while its leaves are durable, long-lived and have lower water loss, permitting persistence long after gap closure. 相似文献
13.
Direct and acclimatory responses of stomatal conductance to elevated carbon dioxide in four herbaceous crop species in the field 总被引:3,自引:0,他引:3
James A. Bunce 《Global Change Biology》2001,7(3):323-331
In order to separate the net effect of growth at elevated [CO2] on stomatal conductance (gs) into direct and acclimatory responses, mid‐day values of gs were measured for plants grown in field plots in open‐topped chambers at the current ambient [CO2], which averaged 350 μmol mol?1 in the daytime, and at ambient + 350 μmol mol?1[CO2] for winter wheat, winter barley, potato and sorghum. The acclimatory response was determined by comparing gs measured at 700 μmol mol?1[CO2] for plants grown at the two [CO2]. The direct effect of increasing [CO2] from 350 to 700 μmol mol?1 was determined for plants grown at the lower concentration. Photosynthetic rates were measured concurrently with gs. For all species, growth at the higher [CO2] significantly reduced gs measured at 700 μmol mol?1[CO2]. The reduction in gs caused by growth at the higher [CO2] was larger for all species on days with low leaf to air water vapour pressure difference for a given temperature, which coincided with highest conductances and also the smallest direct effects of increased [CO2] on conductance. For barley, there was no other evidence for stomatal acclimation, despite consistent down‐regulation of photosynthetic rate in plants grown at the higher [CO2]. In wheat and potato, in addition to the vapour pressure difference interaction, the magnitude of stomatal acclimation varied directly in proportion to the magnitude of down‐regulation of photosynthetic rate through the season. In sorghum, gs consistently exhibited acclimation, but there was no down‐regulation of photosynthetic rate. In none of the species except barley was the direct effect the larger component of the net reduction in gs when averaged over measurement dates. The net effect of growth at elevated [CO2] on mid‐day gs resulted from unique combinations of direct and acclimatory responses in the various species. 相似文献
14.
《Environmental and Experimental Botany》2009,65(3):232-238
Transient and steady state responses of leaf gas exchange (photosynthesis (A) and stomatal conductance to water vapor (gs)) to marked changes in photosynthetic photon flux density (PPFD) were studied for two invasive [Cynodon dactylon (L.) Pers. and Sorghum halepense (L.) Pers.] and two non-invasive, native [Bothriochloa ischaemum (L.) Keng and Chrysopogon gryllus (Torn.) Trin.] perennial C4 grass species from semiarid temperate grasslands or croplands. Following an abrupt drop in PPFD from 1300 to 270 μmol photon m−2 s−1, the two invasive species reduced gs to a greater extent than A, resulting in higher intrinsic photosynthetic water use efficiency (PWUE = A/gs) at low, compared to high-light conditions. For non-invasives, a comparable drop in gs and A led to invariant PWUE, which was lower than that for the invasive group under low light. The duration and speed of stomatal closure was similar for the four species. However, unlike the other grasses, the noxious weed S. halepense exhibited a negligible net loss in PWUE during the high-to-low light transition. Responses of the native B. ischaemum were mostly intermediate between those of the two invasive species and the non-invasive C. gryllus, which is in agreement with the species’ ecological intermediacy: non-invasive but often reaches local dominance following a disturbance. With a sudden reverse change in PPFD photosynthetic light induction was not faster for invasives than for non-invasives. These results indicate more efficient water use under variable light for invasive compared to non-invasive perennial C4 grasses which may contribute to their success in semiarid temperate habitats with a heterogeneous light regime. Yet, rapid photosynthetic light induction appears to be of less importance in such environments. 相似文献
15.
Transient and steady state responses of leaf gas exchange (photosynthesis (A) and stomatal conductance to water vapor (gs)) to marked changes in photosynthetic photon flux density (PPFD) were studied for two invasive [Cynodon dactylon (L.) Pers. and Sorghum halepense (L.) Pers.] and two non-invasive, native [Bothriochloa ischaemum (L.) Keng and Chrysopogon gryllus (Torn.) Trin.] perennial C4 grass species from semiarid temperate grasslands or croplands. Following an abrupt drop in PPFD from 1300 to 270 μmol photon m?2 s?1, the two invasive species reduced gs to a greater extent than A, resulting in higher intrinsic photosynthetic water use efficiency (PWUE = A/gs) at low, compared to high-light conditions. For non-invasives, a comparable drop in gs and A led to invariant PWUE, which was lower than that for the invasive group under low light. The duration and speed of stomatal closure was similar for the four species. However, unlike the other grasses, the noxious weed S. halepense exhibited a negligible net loss in PWUE during the high-to-low light transition. Responses of the native B. ischaemum were mostly intermediate between those of the two invasive species and the non-invasive C. gryllus, which is in agreement with the species’ ecological intermediacy: non-invasive but often reaches local dominance following a disturbance. With a sudden reverse change in PPFD photosynthetic light induction was not faster for invasives than for non-invasives. These results indicate more efficient water use under variable light for invasive compared to non-invasive perennial C4 grasses which may contribute to their success in semiarid temperate habitats with a heterogeneous light regime. Yet, rapid photosynthetic light induction appears to be of less importance in such environments. 相似文献
16.
Differential coordination of stomatal conductance,mesophyll conductance,and leaf hydraulic conductance in response to changing light across species
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Stomatal conductance (gs) and mesophyll conductance (gm) represent major constraints to photosynthetic rate (A), and these traits are expected to coordinate with leaf hydraulic conductance (Kleaf) across species, under both steady‐state and dynamic conditions. However, empirical information about their coordination is scarce. In this study, Kleaf, gas exchange, stomatal kinetics, and leaf anatomy in 10 species including ferns, gymnosperms, and angiosperms were investigated to elucidate the correlation of H2O and CO2 diffusion inside leaves under varying light conditions. Gas exchange, Kleaf, and anatomical traits varied widely across species. Under light‐saturated conditions, the A, gs, gm, and Kleaf were strongly correlated across species. However, the response patterns of A, gs, gm, and Kleaf to varying light intensities were highly species dependent. Moreover, stomatal opening upon light exposure of dark‐adapted leaves in the studied ferns and gymnosperms was generally faster than in the angiosperms; however, stomatal closing in light‐adapted leaves after darkening was faster in angiosperms. The present results show that there is a large variability in the coordination of leaf hydraulic and gas exchange parameters across terrestrial plant species, as well as in their responses to changing light. 相似文献
17.
Limitation of coffee leaf photosynthesis by stomatal conductance and light availability under different shade levels 总被引:2,自引:0,他引:2
In agroforestry systems, the effect of shade trees on coffee net photosynthesis (A
n) has been the object of debates among coffee scientists. In this study, we undertook over 600 coffee A
n “spot” measurements under four different artificial shade levels (100, 72, 45 and 19% of full solar irradiance) and analyzed
limitations to A
n by low light availability (photon flux density, PFD) and stomatal conductance (g
s). These gas exchange measurements were carried out during two consecutive coffee growing seasons in a commercial plantation
in the Orosi valley of Costa Rica. Levels of A
n were related to PFD and g
s in order to calculate envelope functions which were used to establish PFD or g
s limitations to A
n. Under the growing conditions of the present trial, mean leaf A
n remained stable for growth irradiance (GI) as low as 45% of full sun and decreased by ~20% at 19% GI. Limitation to A
n due to g
s was strong in full sun and decreasing with increasing shade levels. On the other hand, limitation due to PFD remained at
a similar level for all shade treatments. These different evolutions of limitations of A
n by PFD and g
s in response to shade explain the absence of a decrease in coffee leaf A
n with a shade level up to 55%. Consequently, these results confirm that Arabica coffee is a shade-adapted plant with leaves
that can maintain a high photosynthetic performance under low light availability. 相似文献
18.
Microstegium vimineum (Trin.) A. Camus, a shade-tolerant C4 grass, has spread throughout the eastern United States since its introduction in 1919. This species invades disturbed understory
habitats along streambanks and surrounding mesic forests, and has become a major pest in areas such as Great Smoky Mountains
National Park. The focus of this study was to characterize the photosynthetic induction responses of M. vimineum, specifically its ability to utilize low light and sunflecks, two factors that may be critical to invasive abilities and
survival in the understory. In addition, we were curious about the ability of a grass with the C4 photosynthetic pathway to respond to sunflecks. Plants were grown under 25% and 50% ambient sunlight, and photosynthetic
responses to both steady-state and variable light were determined. Plants grown in both 25% and 50% ambient sun became 90%
light saturated between 750–850 μmol m−2 s−1; however, plants grown in 50% ambient sun had significantly higher maximum steady-state photosynthetic rates (16.09 ± 1.37 μmol m−2 s−1 vs. 12.71 ± 1.18 μmol m−2 s−1). Both groups of plants induced to 50% of the steady-state rate in 3–5 min, while it took 10–13 min to reach 90% of maximum
rates, under both flashing and steady-state light. For both groups of plants, stomatal conductance during induction reached
maximum rates in 6–7 min, after which rates decreased slightly. Upon return to low light, rates of induction loss and stomatal
closure were very rapid in both groups of plants, but were more rapid in those grown in high light. Rapid induction and the
ability to induce under flashing light may enable this species to invade and dominate mesic understory habitats, while rapid
induction loss due to stomatal closure may prevent excess water loss when low light constrains photosynthesis. The C4 pathway itself does not appear to present an insurmountable barrier to the ability of this grass species to respond to sunflecks
in an understory environment.
Received: 21 February 1997 / Accepted: 10 October 1997 相似文献
19.
The photosynthetic response of juveniles of Decussocarpus rospigliosii, an emergent primary forest species and shade tolerant in its juvenile stages and Alchornea triplinervia, a gap-colonizing species of tropical cloud forest in Venezuela was studied. Daily courses of microenvironmental variables and gas exchange under contrasting light conditions (gap and understory) were carried out in their natural environment and transplanted to different light regimes (shade and sun) in the field. The photosynthetic response and some anatomical characteristics of plants from different treatments were analyzed in the laboratory. Photosynthetic rates were low for both species, and were negative during some diurnal periods, related to the low photosynthetically active radiation levels obtained at both gap (6% of total radiation) and understory (2%). A. triplinervia shows higher rates (1.5–3.0 molm-2
-1) than D. rospigliosii (0.7–1.1 molm-2s-1). Both species showed increased photosynthetic rates when grown in gaps. A. triplinervia did not adjust its maximum photosynthetic rates to the prevailing light conditions. In contrast, D. rospigliosii responded to increased light levels. Both species showed low light compensation points when grown under total shade. There was a partial stomatal closure generally during midday in D. rospigliosii. A. triplinervia presented lower leaf conductances, transpiration rates and lesser stomatal control. Some leaf anatomical characteristics, in both species, were affected by variations in the light regime (i.e. increased leaf thickness, leaf specific weight and stomatal density). These results suggest that both species have the ability to respond to variations in their natural light environments, therefore maintaining a favorable carbon balance during the day. 相似文献
20.
Physiological determinants of genotypic differences in carbon isotope discrimination in potato grown in well-watered conditions 总被引:1,自引:0,他引:1
R A. Jefferies 《The Annals of applied biology》1995,127(3):585-592
Carbon isotope discrimination (A), leaf conductance (gs), photosynthetic capacity, and plant growth were measured in well-watered, glasshouse-grown potato plants of clones from a cross made between diploid Solanum tuberosum and Solanum vernei. Clones showed significant differences (P < 0.001) in gs, Δ, stomatal density, root growth, and total dry matter production. Carbon isotope discrimination of genotypes was positively correlated (P < 0.001) with gs. There was no correlation between gs and stomatal density indicating that differences in gs reflected differences in stomatal aperture. Differences in rooting characteristics or in root/shoot ratio did not contribute to differences in gs or A. Genotypic differences in photosynthetic capacity were not statistically significant, and there was no correlation between A and photosynthetic capacity. Total dry matter production and A were positively correlated (P < 0.001) when differences in the time of plant emergence were included in the regression model. It is concluded that differences in A among potato genotypes is largely determined by gs, but confounding of gs and photosynthetic capacity reduces genotypic variation in A compared with that in gs. Total dry matter production is largely determined by processes other than carbon assimilation rate per unit area in individual leaves. Effective use of A as a character for selection in plant breeding depends on elucidating the effects that differences in stomatal characteristics have on crop production both in well-watered and in water-limited crops. 相似文献