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71.
BACKGROUND: Patchy stomatal conductance is a poorly understood and little-studied phenomenon. It is relatively common, yet it appears to be detrimental to water-use efficiency under some conditions and has no immediately obvious physiological function of any kind. Much of the difficulty in studying patchy stomatal conductance is tied to its unpredictability, both in occurrence and in characteristics. SCOPE AND CONCLUSIONS: Statistical analyses of the variability of stomatal patchiness reveal remarkable similarities to structures and behaviours found in locally connected networks of dynamic units that perform tasks. Such systems solve problems that reside at the level of the entire network despite the absence of a central processor or a mechanism for directly sharing information over the entire system. Frequently, task performance is emergent, in the sense that no unit independently performs the task. Because each unit in the network can communicate with only its immediate neighbours, problem solving is accomplished by the states of the individual units self-organizing into synchronized, collective patterns. In some cases, patches of states form and move coherently over the network, thus providing a means for distantly separated parts of the network to communicate. Often, exactly what form these patches take and how they move as the units synchronize is highly unpredictable. In analogy with such networks, it is suggested that stomatal patchiness may be a signature that plants optimize gas exchange in a more sophisticated and adaptive manner than if performed by their individual stomata independently. 相似文献
72.
Meinzer FC Woodruff DR Domec JC Goldstein G Campanello PI Gatti MG Villalobos-Vega R 《Oecologia》2008,156(1):31-41
Stomatal regulation of transpiration constrains leaf water potential (ΨL) within species-specific ranges that presumably avoid excessive tension and embolism in the stem xylem upstream. However,
the hydraulic resistance of leaves can be highly variable over short time scales, uncoupling tension in the xylem of leaves
from that in the stems to which they are attached. We evaluated a suite of leaf and stem functional traits governing water
relations in individuals of 11 lowland tropical forest tree species to determine the manner in which the traits were coordinated
with stem xylem vulnerability to embolism. Stomatal regulation of ΨL was associated with minimum values of water potential in branches (Ψbr) whose functional significance was similar across species. Minimum values of Ψbr coincided with the bulk sapwood tissue osmotic potential at zero turgor derived from pressure–volume curves and with the
transition from a linear to exponential increase in xylem embolism with increasing sapwood water deficits. Branch xylem pressure
corresponding to 50% loss of hydraulic conductivity (P
50) declined linearly with daily minimum Ψbr in a manner that caused the difference between Ψbr and P
50 to increase from 0.4 MPa in the species with the least negative Ψbr to 1.2 MPa in the species with the most negative Ψbr. Both branch P
50 and minimum Ψbr increased linearly with sapwood capacitance (C) such that the difference between Ψbr and P
50, an estimate of the safety margin for avoiding runaway embolism, decreased with increasing sapwood C. The results implied a trade-off between maximizing water transport and minimizing the risk of xylem embolism, suggesting
a prominent role for the buffering effect of C in preserving the integrity of xylem water transport. At the whole-tree level, discharge and recharge of internal C appeared to generate variations in apparent leaf-specific conductance to which stomata respond dynamically. 相似文献
73.
Saji S Bathula S Kubo A Tamaoki M Kanna M Aono M Nakajima N Nakaji T Takeda T Asayama M Saji H 《Plant & cell physiology》2008,49(1):2-10
To understand better the plant response to ozone, we isolated and characterized an ozone-sensitive (ozs1) mutant strain from a set of T-DNA-tagged Arabidopsis thaliana ecotype Columbia. The mutant plants show enhanced sensitivity to ozone, desiccation and sulfur dioxide, but have normal sensitivity to hydrogen peroxide, low temperature and high light levels. The T-DNA was inserted at a single locus which is linked to ozone sensitivity. Identification of the genomic sequences flanking the T-DNA insertion revealed disruption of a gene encoding a transporter-like protein of the tellurite resistance/C(4)-dicarboxylate transporter family. Plants with either of two different T-DNA insertions in this gene were also sensitive to ozone, and these plants failed to complement ozs1. Transpiration levels, stomatal conductance levels and the size of stomatal apertures were greater in ozs1 mutant plants than in the wild type. The stomatal apertures of ozs1 mutant plants responded to light fluctuations but were always larger than those of the wild-type plants under the same conditions. The stomata of the mutant and wild-type plants responded similarly to stimuli such as light, abscisic acid, high concentrations of carbon dioxide and ozone. These results suggest that OZS1 helps to close stomata, being not involved in the responses to these signals. 相似文献
74.
Anita Roth-Nebelsick 《Trees - Structure and Function》2005,19(3):251-265
Stomatal frequency is often observed to vary inversely with atmospheric CO2 concentration (pCO2). The response is due to (1) individual phenotypic plasticity and (2) evolutionary change, depending on the time scale. Evolutionary responses occur more frequently than individual responses and individual responses are more pronounced under subambient pCO2 levels than under elevated pCO2 (CO2 ceiling). The evolutionary response appears therefore to be a valuable device for determining past pCO2. Since tree leaves often represent a conspicuous and rich resource of fossil material, they are increasingly important in this respect. Additionally, certain tree species are considered to represent living fossils and therefore valuable sources of ancient stomatal data. There are, however, numerous difficulties which have to be considered such as: (1) high variance of the data, especially for fossil material, (2) interspecific differences of the response, (3) the CO2 ceiling and (4) differences between short-term and long-term responses. Whereas the qualitative pCO2 signal of stomatal frequency appears to be reliable, quantitative pCO2 reconstruction has to be performed with caution. The results of a number of studies which used stomatal frequency as a pCO2 sensor demonstrate good agreement with the results obtained with other proxy data. Current techniques are based on transfer functions which calibrate the fossil data with extant material. It is suggested that a mechanistic approach including physical as well as physiological processes could improve pCO2 reconstruction. Furthermore, the topic of the influence of pCO2 on stomatal frequency is significant not only for reconstructing past pCO2 but also with respect to the climate-biosphere interrelationship. 相似文献
75.
植物能够对生长环境产生生态适应性,这种适应性可从气孔导度、光合速率、水分利用效率等生态指标上反映出来。为了研究葡萄蒸腾特性对弱光环境的适应性变化,本试验以‘京玉’葡萄幼苗(Vitis vinefera cv. Jingyu)为试验材料,通过遮光处理(2个处理,分别遮光65%和85%)营造弱光环境,测定了在弱光环境下生长的葡萄叶片蒸腾速率、气孔导度、水分利用效率对光照强度的响应,同时用扫描电镜技术观察了气孔的发育。结果表明,弱光环境下生长的葡萄幼苗,叶片的水势较高,但水分利用效率较低,叶片蒸腾速率和气孔导度变化对光照强度的响应缓慢,而自然光下生长的葡萄叶片则反应较迅速。通过对气孔结构的研究发现,与自然光照环境下生长的植株相比,在弱光环境下生长的葡萄幼苗,叶片下表皮的气孔横轴变宽,大小气孔之间差异减少,气孔外突,表皮细胞变大甚至扭曲,角质层变薄。说明葡萄幼苗能够对弱光环境产生适应性变化,其蒸腾特性的变化与其气孔结构的变化相关,具有一致性。 相似文献
76.
Estimates of the extent of the discrimination against13CO2 during photosynthesis (A) on a global basis were made using gridded data sets of temperature, precipitation, elevation, humidity and vegetation type. Stomatal responses to leaf-to-air vapour mole fraction difference (D, leaf-to-air vapour pressure difference divided by atmospheric pressure) were first determined by a literature review and by assuming that stomatal behaviour results in the optimisation of plant water use in relation to carbon gain. Using monthly time steps, modelled stomatal responses toD were used to calculate the ratio of stomatal cavity to ambient CO2 mole fractions and then, in association with leaf internal conductances, to calculate A. Weighted according to gross primary productivity (GPP, annual net CO2 asimilation per unit ground area), estimated A for C3 biomes ranged from 12.9 for xerophytic woods and shrub to 19.6 for cool/cold deciduous forest, with an average value from C3 plants of 17.8. This is slightly less than the commonly used values of 18–20. For C4 plants the average modelled discrimination was 3.6, again slightly less than would be calculated from C4 plant dry matter carbon isotopic composition (yielding around 5). From our model we estimate that, on a global basis, 21% of GPP is by C4 plants and for the terrestrial biosphere as a whole we calculate an average isotope discrimination during photosynthesis of 14.8. There are large variations in A across the globe, the largest of which are associated with the precence or absence of C4 plants. Due to longitudinal variations in A, there are problems in using latitudinally averaged terrestrial carbon isotope discriminations to calculate the ratio of net oceanic to net terrestrial carbon fluxes. 相似文献
77.
Malcolm B. Wilkins 《Planta》1991,185(3):425-431
The role of the epidermis in the generation of the endogenous circadian rhythm of CO2 exchange in leaves of Bryophyllum fedtschenkoi has been examined. At 25° C the rhythm of CO2 output exhibited by whole leaves kept in continuous darkness and an initially CO2-free air stream also occurs in isolated pieces of mesophyll. The sensitivity to light of the rhythms in whole leaves and in isolated mesophyll appears to be identical. At 15° C, however, no rhythm is observed in isolated mesophyll tissue, despite there being a conspicuous rhythm in intact leaves. The rhythm of net CO2 assimilation in whole leaves kept in continuous light and a stream of normal air at either 25° C or at 15° C is abolished by removal of the epidermis, although at 15° C and under the higher of the two light levels used, there is an indication that rhythmicity may begin to reappear after the third day of the experiment. Thus, only under certain environmental conditions is the rhythm of CO2 exchange in Bryophyllum leaves independent of the epidermis. The results indicate that the rhythm of carbon dioxide fixation in continuous darkness and CO2-free air is generated primarily in the mesophyll cells, whereas the rhythm in continuous light and normal air is generated in the stomatal guard cells or in an interaction of these cells with the mesophyll cells.Abbreviation PEPCase
phosphoenolpyruvate carboxylase 相似文献
78.
Carbon-water balance and patchy stomatal conductance 总被引:11,自引:0,他引:11
Stomata govern carbon-water balance by simultaneously controlling photosynthesis (A) and transpiration (E). It is unclear how patchy stomatal conductance influences this control. Cowan and Farquhar showed that for a given water
supply available during a fixed time interval, carbon gain is maximized by a pattern of stomatal behavior that keeps the partial
derivative of A with respect to E constant. This result implies that spatially uniform stomatal conductance is optimal (provided photosynthetic performance
and environmental conditions are spatially uniform), so patchy stomatal conductance should be detrimental to carbon-water
balance. However, these results required that the curvature of A versus E be uniformly negative. Using mathematical arguments and computer modeling, we show that (1) this caveat is violated under
some environmental conditions, (2) water-use efficiency (A/E) is nearly unaffected, and can actually be improved, by patchiness under these conditions, and (3) patchiness has most often
been observed under conditions similar to these. These results imply that under many conditions, patchiness may not significantly
influence carbon-water balance, consistent with recent work suggesting patchiness may be common but unobserved. Additionally,
we discuss implications of these results that muddle the definition of `optimal' in the context of plant gas exchange in some
situations, and extend the work of Cowan and Farquhar under conditions causing positive curvature in A versus E.
Received: 15 May 1998 / Accepted: 14 October 1998 相似文献
79.
湿度对葡萄,樱桃离体繁殖植株气孔行为和移栽成活率的影响 总被引:1,自引:0,他引:1
本文通过葡萄和樱桃不同品种离体植株气孔在繁殖不同时期对多种关闭诱导因素的反应,研究了气孔不能关闭的原因和提高植株移栽成活率的影响因素。材料和方法选用二倍 相似文献
80.
Understanding how photosynthetic capacity acclimatises when plants are grown in an atmosphere of rising CO2 concentrations will be vital to the development of mechanistic models of the response of plant productivity to global environmental change. A limitation to the study of acclimatisation is the small amount of material that may be destructively harvested from long-term studies of the effects of elevation of CO2 concentration. Technological developments in the measurement of gas exchange, fluorescence and absorption spectroscopy, coupled with theoretical developments in the interpretation of measured values now allow detailed analyses of limitations to photosynthesisin vivo. The use of leaf chambers with Ulbricht integrating spheres allows separation of change in the maximum efficiency of energy transduction in the assimilation of CO2 from changes in tissue absorptance. Analysis of the response of CO2 assimilation to intercellular CO2 concentration allows quantitative determination of the limitation imposed by stomata, carboxylation efficiency, and the rate of regeneration of ribulose 1:5 bisphosphate. Chlorophyll fluorescence provides a rapid method for detecting photoinhibition in heterogeneously illuminated leaves within canopies in the field. Modulated fluorescence and absorption spectroscopy allow parallel measurements of the efficiency of light utilisation in electron transport through photosystems I and IIin situ.Abbreviations A
net rate of CO2 uptke per unit leaf area (µmol m–2 s–1)
- Asat
light-saturated A
- A820
change in absorptance of PSI on removal of illumination (OD)
- c
CO2 concentration in air (µmol mol–1)
- ca
c in the bulk air; ci, c in the intercellular spaces
- ce
carboxylation efficiency (mol m–2 s–1)
- E
transpiration per unit leaf area (mol m–2 s–1)
- F
fluorescence emission of PSII (relative units)
- Fm
maximal level of F
- Fo
minimal level of F upon illumination when PSII is maximally oxidised
- Fs
the steady-state F following the m peak
- Fv
the difference between Fm and Fo
- F'm
maximal F' generated after the m peak by addition of a saturating light pulse
- F'o
the minimal level of F' after the m peak determined by re-oxidising PSII by far-red light
- g1
leaf conductance to CO2 diffusion in the gas phase (mol m–2 s–1)
- g'1
leaf conductance to water vapour diffusion in the gas phase (mol m–2 s–1)
- kc and ko
the Michaelis constants for CO2 and O2, respectively, (µmol mol–1);
- Jmax
the maximum rate of regeneration of rubP (µmol m–2 s–1)
- l
stomatal limitation to CO2 uptake (dimensionless, 0–1)
- LCP
light compensation point of photosynthesis (µmol m–2 s–1)
- oi
the intercellular O2 concentration (mmol mol–1)
- Pi
cytosol inorganic phosphate concentration
- PSI
photosystem I
- PSII
photosystem II
- Q
photon flux (µmol m–2 s–1)
- Qabs
Q absorbed by the leaf
- rubisCO
ribulose 1:5 bisphosphate carboxylase/oxygenase; rubP, ribulose 1:5 bisphosphate; s, projected surface area of a leaf (m2)
- Vc,max
is the maximum rate of carboxylation (µmol m–2 s–1)
- Wc
the rubisCO limited rate of carboxylation (µmol m–2 s1)
- Wj
the electron transport limited rate of regeneration of rubP (µmol m–2 s–1)
- Wp
the inorganic phosphate limited rate of regeneration of rubP (µmol m–2 s–1)
-
absorptance of light (dimensionless, 0–1)
- a
of standard black absorber 1, of leaf
- s
of integrating sphere walls
- , CO2
compensation point of photosynthesis (µmol mol–1)
-
the specificity factor for rubisCO carboxylation (dimensionless)
- ,
convexity of the response of A to Q (dimensionless 0–1)
-
the quantum yield of photosynthesis on an absorbed light basis (A/Qabs; dimensionless)
-
the quantum yield of photosynthesis on an incident light basis (A/Q; dimensionless)
- app
the maximum
- m
the maximum
- m,app
the photochemical efficiency of PSII (dimensionless, 0–1)
- PSII,m
the maximum 相似文献