The number, distribution, size, and function of stomata and wettability of the sweet cherry (Prunus avium L.) fruit surface were investigated.
The number of stomata per fruit differed significantly among sweet cherry cultivars, ranging from 143 26 per fruit in ‘Adriana’ to 2124 142 per fruit in ‘Hedelfinger’. The number of stomata per fruit was not affected by fruit mass (‘Burlat’). For a given cultivar, the stylar scar region had the highest stomatal density, followed by ventral suture or cheek.
The stem cavity region was essentially astomatous. Stomatal density decreased as distance from the scar increased.
Cross-sectional areas of stomatal pores had a log-normal distribution and differed among cultivars, with medians ranging from 39.0 to 105.2 mm2 for ‘Van’ and ‘Sam’, respectively. The length/width ratio of stomatal pores increased in the course of a day in early stage II, but not in mature stage III fruit.
Treating exocarp segments with ABA (0.1 mM) or sucrose (1 M) decreased length/ width ratios of stomatal pores in early stage II fruit, but not in the mature stage III, suggesting that stomata were non-functional at maturity.
Contact angles of 1 ml water droplets (71 mN m 1) with the sweet cherry fruit surface averaged 92:4 0:6 ðn 1⁄4 164Þ across years and cultivars and did not differ between regions (cheek, suture vs. stylar end). The critical surface tension of the sweet cherry fruit was not affected by developmental stage (stage II vs. mature stage III ‘Burlat’ fruit) or cultivar, and averaged 24.9 mN m 1 making Poiseuille-flow of water through open stomata unlikely.
We analysed the impact of elevated CO2 on water relations, water use efficiency and photosynthetic gas exchange in barley (Hordeum vulgare L.) under wet and drying soil conditions. Soil moisture was less depleted under elevated compared to ambient [CO2]. Elevated CO2 had no significant effect on the water relations of irrigated plants, except on whole plant hydraulic conductance, which was markedly decreased at elevated compared to ambient CO2 concentrations.
The values of relative water content, water potential and osmotic potential were higher under elevated CO2 during the entire drought period. The better water status of water-limited plants grown at elevated CO2 was the result of stomatal control rather than of osmotic adjustment.
Despite the low stomatal conductance produced by elevated CO2, net photosynthesis was higher under elevated than ambient CO2 concentrations. With water shortage, photosynthesis was maintained for longer at higher rates under elevated CO2 . The reduction of stomatal conductance and therefore transpiration, and the enhancement of carbon assimilation by elevated CO2 , increased instantaneous and whole plant water use efficiency in both irrigated and droughted plants.
Thus, the metabolism of barley plants grown under elevated CO2 and moderate or mild water deficit conditions is benefited by increased photosynthesis and lower transpiration. The reduction in plant water use results in a marked increase in soil water content which delays the onset and severity of water deficit.
Bennettites are an abundant and frequently well- preserved component of many Mesozoic fossil floras, often playing an important ecological role in flood plain vegetation communities.
During a recent study focusing on stomatal indices of Triassic–Jurassic fossil plants, it became evident that the leaf fragments of two bennettite genera Anomozamites Schimper (1870) emend. Harris (1969) and Pterophyllum Brongniart (1825) display a significant overlap of leaf shape as well as cuticular characters.
Owing to the preference of recognition of single taxa (ideally species) for the stomatal method, we use a database of 70 leaf fragments of Anomozamites and Pterophyllum compressions from five isotaphonomic Late Triassic sedimentary beds of Astartekløft in East Greenland to test whether leaf and cuticle fragments of the two genera can be separated using a range of quantitative and qualitative morphological and statistical analyses.
None of the observed characters – including stomatal frequencies – could be applied to separate the fragments of the two genera into well-defined groups. Our results therefore indicate that fragmented material and dispersed cuticles cannot be utilized to distinguish between Anomozamites or Pterophyllum at the genus level, but that instead these cuticle fragments may be used interchangeably as stomatal proxies.
Classification of fossil leaves into either of these genera is thus only possible given adequate preservation of macro-morphology and is not possible based solely on cuticle morphology.
We suggest that this large inter- and intra-generic morphological variation in both leaf and cuticle traits within Anomozamites and Pterophyllum may be related to the bennettites’ role as understory plants, experiencing a range of micro-environmental conditions, perhaps depending mainly on sun exposure.
Based on the results obtained in this study, we conclude that Anomozamites and Pterophyllum cuticle fragments can be employed interchangeably in palaeo [CO2] reconstructions based on the stomatal method, thus potentially annexing a plethora of bennettitalean fossil plant material as CO2 proxies, including dispersed cuticles.
Recent paleoatmospheric reconstructions of CO2 concentration have utilized the observed physiological relationship between atmospheric CO2 and stomatal frequency (which can be reported as SI, stomatal index, or as SD, stomatal density; Fig. 1; Kürschner et al. 1996; Wagner et al., 1999; Retallack, 2001; Royer et al., 2001; Beerling & Royer, 2002; Beerling etal., 2002; Beerling, 2002; Wagner etal., 2002). Over relatively small ranges of pCO2 such as the historical range of atmospheric increase, the response of SI is approximately linear and negative (Wagner et al., 1996; Royer et al., 2001; Beerling, 2002). Most workers have begun to recognize a ‘nonlinear response’ in more recent observations of SI at higher CO2 concentrations, and applied empirical nonlinear calibrations to fossil leaf data. In some such studies, fossil data have been extrapolated beyond the range of CO2 measured, or to CO2 concentrations represented by relatively few modern observations (Table 1). In efforts to describe this relationship, several nonlinear calibrations of SI measurements of modern leaves grown at variable CO2 concentrations have been made using a sigmoidal regression function for Betula and Quercus (Kürschner et al., 1997), a second-order polynomial for Ginkgo (Retallack, 2001), and an inverse expression for Ginkgo and Metasequoia (Royer et al., 2001). Extrapolations to include data derived from paleosol stable isotopic measurements have used a logarithmic function for Ginkgo (Beerling & Royer, 2002). A nonlinear response of gaseous diffusion through stomatal pores is intuitive with an understanding of the fundamental laws governing diffusion. A new model presented here, based on the solution to the general diffusion equation for stomatal pores, provides a physically based relationship between SI and atmospheric CO2 that follows an inverse power function.
Question: Is stomatal regulation specific for climate and tree species, and does it reveal species-specific responses to drought? Is there a link to vegetation dynamics?
Location: Dry inner alpine valley, Switzerland
Methods:Stomatal aperture of Pinus sylvestris, Quercus pubescens, Juniperus communis and Picea abies were continuously estimated by the ratio of measured branch sap flow rates to potential transpiration rates (adapted Penman-Monteith single leaf approach) at 10-min intervals over four seasons.
Results:Stomatal aperture proved to be specific for climate and species and revealed distinctly different drought responses: Pinusstomata close disproportionately more than neighbouring species under dry conditions, but has a higher stomatal aperture than the other species when weather was relatively wet and cool. Quercus keeps stomata more open under drought stress but has a lower stomatal aperture under humid conditions. Juniperus was most drought-tolerant, whereas Picea stomata close almost completely during summer.
Conclusions: The distinct microclimatic preferences of the four tree species in terms of stomatal aperture strongly suggest that climate (change) is altering tree physiological performances and thus species-specific competitiveness. Picea and Pinus currently live at the physiological limit of their ability to withstand increasing temperature and drought intensities at the sites investigated, whereas Quercus and Juniperus perform distinctly better. This corresponds, at least partially, with regional vegetation dynamics: Pinus has strongly declined, whereas Quercus has significantly increased in abundance in the past 30 years. We conclude that stomatal aperture provides an indication of a species’ ability to cope with current and predicted climate.
Association of potassium ions with stomatal movements is reported here for 22 different plants. These include Ophioglossum engelmanni, Ginkgo biloba, and Pinus sylvestris. In all 22 plants potassium migrates into the guard cells when stomata open in response to light.
In addition, potassium migration into guard cells also occurs with night opening in Crassula argentea and.with rhythmic opening in Mimosa pudica. Potassium inside the guard or subsidiary cells, conventionally detected through light microscopic observations of epidermal peels treated with sodium cobaltinitrite reagent, may also be mapped by x-ray microanalysis of such histochemically treated peels, as was the case in this study.
In addition to the potassium migration, we also show the movement of chloride as an accompanying anion in Ophioglossum engelmanni, Ginkgo biloba, Plantago rugelii, Begonia sp., and Avena sativa. Eight plants are shown to accumulate potassium inside the stomatal initials or cells of immature stomatal apparatuses;ordinary, immature epidermal cells do not show such an accumulation of potas- sium. A list in the discussion indicates all the plants in which potassium fluxes associated with stomatal movements have so far been established, including the new examples reported in this paper.