Responses of apple leaf stomata: a model for single leaves and a whole tree

Abstract. An empirical model of stomatal response to environmental factors was developed from measurements of stomatal conductance ( g _s) made in a leaf chamber under controlled conditions. Results presented in a companion paper (Warrit, Landsberg & Thorpe, 1980) indicated that the model could be written in terms of only two factors, photon flux density ( Q _p) and leaf to air vapour pressure gradient ( D ). The response of Q _p was hyperbolic and that to D linear; combining these the equation of the model is where g _r is a reference conductance, α is the slope of the response to D and β indicates the sensitivity of g _s response to Q _p. Values of α were 0.20 and 0.30 kPa⁻¹ in June and August; the corresponding values of β were 59 and 79 μmol m⁻² s⁻¹.
The model was tested against mean values of g _s obtained with a porometer in the field, using environmental measurements as inputs. Correspondence between measured and calculated values was good. Transpiration rates were calculated from the Penman-Monteith equation, with stomatal resistance values calculated from the model, and compared with gravimetric measurements of tree water use. It was shown that transpiration could be calculated with acceptable accuracy. The effects of variations in stomatal resistance on transpiration rates under a range of conditions were explored using the model and the Penman- Monteith equation.     

Responses of stomata to environmental factors-experiments with isolated epidermal strips of Polypodium vulgare

Summary Stomatal apertures of isolated and suitably conditioned epidermal strips of Polypodium vulgare are described as the stomata respond to the influences of temperature, air humidity, and water potential at the epidermal inner walls. Water stress as a result of reduced water potential in the substomatal airspace leads to narrower stomatal pores when water potential falls below -8 bar. Water potentials above this threshold value show minor influence. Stomatal responses to such water stress strongly interact with the responses to humidity changes in ambient air and to temperature. The linear dependence of stomatal apertures on the vapor saturation deficit of the air (closing) is shifted to lower values (more closed) by lower leaf bulk water potentials.Stomatal behavior depending on the temperature factor seems to be reversed by higher water stress. Without water stress, rising temperatures between 20 and 28° C are accompanied by further opening of the pores, whereas an increase of temperature within this range leads to narrowing of the stomata under the influence of lower water potentials within the substomatal airspace. It can be demonstrated that stomatal aperture values of Polypodium vulgare depending on temperature always describe optimum curves. With no water stress, closing does not occur before rather high temperatures are reached and above a broad range of maximal opening. Water stress, on the other hand, results in more pronounced narrowing of stomatal pores and shifts the onset to considerably lower temperatures.     

Responses of stomata to environmental factors-experiments with isolated epidermal strips of Polypodium vulgare

Summary Stomatal responses in isolated epidermis strips of the fern Polypodium vulgare to humidity and temperature were investigated. Movements were observed under a microscope, the epidermis being mounted in a climatized chamber above a water table, the gap between tissue and water being similar to that between epidermis and mesophyll in the intact leaf. Stomatal aperture increases as the water vapor deficit is decreased. The relationship is approximately linear until full aperture is reached. The speed of stomatal movement depends on the magnitude of the change in saturation deficit. Temperature also exerts a strong influence on stomatal aperture. Low temperature causes closure. Maximal opening occurs between about 20° C and 28° C. Higher temperature leads to a slight reduction in aperture. The temperature range corresponding to maximum apertures depends on the temperature that prevailed during cultivation of the plants. The data are used to construct three-dimensional graphs showing stomatal behavior under the simultaneous influence of temperature and humidity for plants of different precultivation. The possible mechanisms that lead to the observed stomatal reactions are discussed.     

Responses of stomata to changes in humidity

Summary Large areas of the lower epidermis of full-grown leaves of Polypodium vulgare (and Valerianella locusta) are normally separated from the mesophyll by an extensive subepidermal airspace. Epidermal stripes were prepared for experiments to simulate these conditions in order to investigate stomatal reactions. They were placed with their inner surface in contact with an airspace of uniformly high humidity. The outer surface was treated with air of varying degrees of humidity. The stomatal reactions were observed by microscope and the opening of the guard cells determined photographically.Treatment of the outer side of the epidermis with dry air led to a rapid closing of the stomata, whilst moist air caused opening. This induction of opening and closing movements could be repeated up to 15 times with the same stoma by changing the degree of humidity. Neighbouring groups of stomata showed different apertures according to their individual humidity conditions. The degree of aperture of the stomata depended on the water potential of the ambient air and also on the humidity conditions in the subepidermal airspace.The cause of this stomatal behaviour could lie in the peristomatal transpiration. In this way, the guard cells are able to function as humidity sensors which measure the difference in water potential inside and outside the leaf. Their aperture thus is controlled by their individual transpiration conditions. This controlling mechanism could be very important for the water economy of plants. They would appear to be able to reduce their transpiration through an increase in diffusion resistance of the stomata during decreasing humidity in the ambient air, without changing the water status of the whole leaf.     

Responses of stomata of barley and maize to phenylmercuric acetate

A reduction of stomatal aperture in light was found in leaves of maize after they had been treated with 10“3-5 m phenylmercuric acetate (PMA). Complete closure of the stomata in darkness was prevented, whilst there was total closure in the controls. Higher PMA concentrations had bigger effects. The relative water content (RWC) of barley tissues was slightly reduced 12 hours after treatment with PMA. The transpiration rate observed on PMA-treated barley plants was lower in light and higher in darkness than in untreated plants. Water saturation deficit (WSD) was higher by about 5%, and water holding capacity (WHC) lower (25%) than in untreated plants. The results suggest that the concentration of PMA normally applied as an antitranspirant is unfavourable for healthy growth of maize and barley.     

Responses of stomata of senescing and nonsenescing leaves of Nicotians glauca to changes in intercellular concentrations of leaf carbon dioxide

Abstract. Gas exchange measurements were performed to test the hypothesis that failure of stomata to open in senescing leaves of Nicotiana glauca is caused by elevated concentrations of carbon dioxide in the intercellular spaces of leaf mesophyll tissue (c_i). Senescing leaves selected for experiments were completely chlorotic and lacked positive rates of photosynthesis. When stomata in detached epidermis from senescing leaves were illuminated in CO2-free air, they opened to similar apertures as those in detached epidermis from nonsenescing leaves. To compare the effects of changes in c_i on stomatal responses of the two leaf types, leaf 'flags' of either nonsenescing or senescing leaves were illuminated at a photosynthetic photon flux density of 500 μmol m⁻² s⁻¹ in a gas exchange cuvette. Leaf temperatures were maintained at 23.5 ± 0.5°C, and vapour pressure differences between leaves and the air were maintained between 0.70 and 0.75kPa. C_i was adjusted by changing external concentrations of carbon dioxide in air circulating through the cuvette. Conductances and photosynthetic rates of nonsenescing leaves changed in response to changes in c_i, but neither the conductances nor the photosynthetic rates of senescing leaves were affected significantly by changes in q. We conclude that guard cells of senescing leaves of Nicotiana glauca do not lose the capacity to respond to changes in carbon dioxide concentration and that increases in c_i resulting from declining rates of mesophyll photosynthesis are not the sole cause of maintenance of stomatal closure during leaf senescence. The data suggest that factors external to guard cells may prevent them from responding to changes in carbon dioxide concentrations in intact senescing leaves.     

Hybrid poplar stomata unresponsive to changes in environmental conditions

Summary The factors affecting stomatal conductance (g_s) of I-214 (Populus euramericana) and a hybrid poplar, Peace (P. koreana x P. trichocarpa), were examined in the field and under controlled environment conditions. Unusual opening of the stomata was observed with Peace leaves at all positions. Ontogenetic changes in g_s were similar between these two poplar species in the light. However, the dark/light ratio of g_s in Peace poplar varied from 0.58 to 1.23 with the insertion level while that of I-214 poplar was zero except for the third leaf from the top. The g_s of I-214 poplar changed with time of the day, varying from 0.74 mol m^-2s^-1 in the morning to zero at night, while the g_s of Peace poplar changed only from the minimum value of 0.23 mol m^-2s^-1 at night to the maximum of 0.48 mol m^-2s^-1 in the morning. Under severe water stress, below -1.5 MPa, which decreased the g_s of I-214 poplar to almost zero, the g_s of Peace poplar remained about onethird of that observed with well-watered leaves. Exposure to a relatively high concentration of O₃ caused the g_s of I-214 poplar to decrease nearly to zero but had no effect on the g_s of Peace. Stomata of Peace poplar were not affected by ABA and the g_s did not change even with 10^-4 M ABA, while the g_s of I-214 decreased to almost zero on the application of this concentration of ABA.     

Responses of leaf miners to atypical leaf production patterns

Abstract. 1. Larvae of two bivoltine species of leaf-mining Lepidop-tera, Acrocercops sp. and Neurobathra strigifinitella (Clem.), restrict feeding to young, second-flush leaves of their host trees in north Florida.
2. During 1980 and 1981, densities of both species varied greatly among thirty small water oaks ( Quercus nigra ), as did timing and extent of secondary leaf production.
3. In both years leaf-miner density at the end of the first generation (mid-August) was positively correlated with secondary leaf production.
4. Five trees abscised their leaves and reflushed new ones at atypical times of the growing season. When refoliation coincided with emergence of ovipositing adults, Acrocercops sp. and N.strigifinitella densities increased dramatically, indicating that both species are at times limited by availability of young leaves.
5. By staggering termination of diapause these leaf miners can exploit a temporally variable resource.     

Responses of individual stomata in Ipomoea pes-caprae to various CO2 concentrations

The responses of individual stomata to CO₂ concentrations ranging from 0 to 900 μmol mol⁻¹ air were analysed in Ipomoea pes-caprae L. Sweet (Convolvulaceae). The stomata were directly observed using a measurement system that permitted continuous observation of stomatal movement under controlled light and CO₂ conditions. A CO₂ concentration of 350 μmol mol⁻¹ or higher induced stomatal closure, whereas concentrations below 350 μmol mol⁻¹ did not. The time lag before stomatal closure decreased with increasing CO₂ concentration, as did the steady-state aperture of the stomata after a change in CO₂ concentration. However, the rate of stomatal closure increased with increasing CO₂ concentration. Therefore, not only the stomatal closure rate but also the time from the CO₂ concentration change to the beginning of stomatal closure changed with increasing CO₂ concentration. These results suggest that atmospheric CO₂ may be the stimulus for the closure of guard cells. No significant differences were observed between adaxial and abaxial stomata in terms of their responses to CO₂. However, heterogeneous responses were detected between neighbouring stomata on each leaf surface.     

Mutual diffusional interference between adjacent stomata of a leaf

The mutual diffusional interference between adjacent stomata in laminar flow over a leaf is shown to play a decisive role in determining overall transpiration. The magnitude of this interference varies with the interaction of the vapor diffusional shells forming above each stoma and the air flow over the leaf. The interference decreases with increasing incident radiation and wind velocity. The effect of interference on the stomatal resistance to diffusion plays a major role in the overall variations in transpiration.     

植物叶片最大羧化速率及其对环境因子响应的研究进展

植物叶片最大羧化速率对环境因子的响应关系是陆地生态系统生产力与碳收支研究的重要方面。论文从测定方法、影响因子与模拟模型3方面综述了植物叶片最大羧化速率及其对环境因子响应研究的最新进展,指出现有的植物叶片最大羧化速率对单个环境因子的响应研究严重制约着陆地生态系统生产力的准确评估。为弄清植物叶片最大羧化速率对环境因子的综合响应关系,迫切需要加强以下研究:(1)植物叶片最大羧化速率的生物与环境控制机制研究;(2)生物与环境因子协同作用下的植物叶片最大羧化速率定量模拟及其尺度化研究;(3)植物叶片最大羧化速率的环境因子阈值研究。     

From leaf to label: A robust automated workflow for stomata detection

1. Plant leaf stomata are the gatekeepers of the atmosphere–plant interface and are essential building blocks of land surface models as they control transpiration and photosynthesis. Although more stomatal trait data are needed to significantly reduce the error in these model predictions, recording these traits is time‐consuming, and no standardized protocol is currently available. Some attempts were made to automate stomatal detection from photomicrographs; however, these approaches have the disadvantage of using classic image processing or targeting a narrow taxonomic entity which makes these technologies less robust and generalizable to other plant species. We propose an easy‐to‐use and adaptable workflow from leaf to label. A methodology for automatic stomata detection was developed using deep neural networks according to the state of the art and its applicability demonstrated across the phylogeny of the angiosperms.
2. We used a patch‐based approach for training/tuning three different deep learning architectures. For training, we used 431 micrographs taken from leaf prints made according to the nail polish method from herbarium specimens of 19 species. The best‐performing architecture was tested on 595 images of 16 additional species spread across the angiosperm phylogeny.
3. The nail polish method was successfully applied in 78% of the species sampled here. The VGG19 architecture slightly outperformed the basic shallow and deep architectures, with a confidence threshold equal to 0.7 resulting in an optimal trade‐off between precision and recall. Applying this threshold, the VGG19 architecture obtained an average F‐score of 0.87, 0.89, and 0.67 on the training, validation, and unseen test set, respectively. The average accuracy was very high (94%) for computed stomatal counts on unseen images of species used for training.
4. The leaf‐to‐label pipeline is an easy‐to‐use workflow for researchers of different areas of expertise interested in detecting stomata more efficiently. The described methodology was based on multiple species and well‐established methods so that it can serve as a reference for future work.

     

马占相思林冠层气孔导度对环境驱动因子的响应

利用Granier热消散探针在2003年10月测定了广东鹤山丘陵地马占相思林14株样树的树干液流,同时监测林冠上方的光合有效辐射、空气湿度和气温,结合树木的形态和林分的结构特征,计算马占相思的整树蒸腾(E)、林分总蒸腾(E_t)以及冠层平均气孔导度(g_c),分析树形特征与整树水分利用的关系、冠层气孔导度对光合有效辐射(PAR)和空气水汽压亏缺(D)的响应.结果表明,整树蒸腾与胸径(P＜0.0001)、边材面积(P＜0.0001)和冠幅(P=0.0007)以自然对数的形式、与树高(P=0.014)以幂函数的形式呈现显著正相关.冠层气孔导度最大值(g_cmax)随D的上升呈对数函数下降(P＜0.0001),对光合有效辐射的响应则呈双曲线函数增加(P＜0.0001).液流测定系统能提供连续和准确的整树和林分蒸腾速率值,经严格数学推导公式计算,最终可求出冠层气孔导度,是研究森林水分利用与环境因子相互关系的有效方法.     

玉米叶片气孔及花环和维管束结构对水分胁迫的响应

采用盆栽种植,以玉米品种郑单958为试验材料,设置对照（CK）、轻度（LS）、中度（MS）和重度（SS）水分胁迫 (土壤含水量分别为田间持水量的75%～85%、65%～75%、55%～65%、45%～55%)4个水分梯度,从气孔开度的调控、花环结构的变化、叶片维管束水分运输等方面研究了玉米对土壤水分胁迫的应激反应.结果表明：随着水分胁迫程度的不断加剧,气孔保卫和副卫细胞中过氧化氢(H₂O₂)的积累量逐渐增多,应用荧光染色定位也发现H₂O₂荧光强度逐渐增强,而气孔开度和气孔导度均逐渐减小.同时,花环的正常结构被破坏,花环细胞排列凌乱且体积逐渐变小,维管束鞘细胞变得不规则;大维管束断面面积、木质部面积以及韧皮部细胞数均减少,总的叶片和上、下表皮的厚度逐渐变薄.此外,花环细胞和维管束鞘细胞中叶绿体数目减少,且在中度胁迫下花环细胞中叶绿体的分布发生了变化,由紧贴细胞质膜内侧环靠细胞壁分布向偏细胞中心扩散.发现玉米气孔关闭可能是由保卫细胞和副卫细胞中的H₂O₂共同调节,副卫细胞中的H₂O₂对保卫细胞主导的气孔关闭具有协同作用.总之,在水分胁迫下,玉米通过改变叶片花环结构和厚度、叶绿体的分布,减小木质部和韧皮部面积等降低叶片表面水势,促进气孔关闭,减少体内水分散失,以减轻干旱胁迫对其伤害.     

The interaction of hormonal and environmental factors in leaf senescence

The work concerns the senescence of isolated young leaves of oats (Avena sativa) floated on water or solutions. Senescence is rapid in darkness but slow in white light; the effect of light is not due to photosynthesis, but is paralleled by stomatal opening. Closure of the stomata by osmotic or chemical means makes senescence in light proceed as fast as in darkness, while opening the stomata in darkness by cytokinins, fusicoccin,etc., delays senescence to rates typical of light. The osmotic closure in light is mediated by abscisic acid, and since this also accumulates in darkness it appears as a major factor controlling senescence. Efflux of ions into the solution; indicating increased permeability, occurs almost in parallel with senescence. Senescence in light is accelerated by 1-aminocyclopropane-l-carboxylic acid (ACC) and inhibited by cobalt, silver or aminoethoxyvinyl glycine (AVG) which interfere with ethylene production or action; however, ethylene’s role is unclear because some reagents, including kinetin, that delay senescence, actually increase ethylene production. At the endogenous level, therefore, ethylene may not be a limiting factor. Finally, a new ethylene-generating system is described in which the dehydrogenation of linoleic acid is coupled through manganese to the oxidation of ACC; it is probably activein vivo.     

Responses of Porphyra linearis (Rhodophyta) to environmental factors under controlled culture conditions

The effect of environmental parameters on the growthof Porphyra linearis gametophytes was examinedunder controlled conditions, and related to themultilinear regression growth model recently developedfor this seaweed under coastal conditions in theeastern Mediterranean. Growth chambers, a gradienttable, special culture devices and analytical methodswere combined for this culture study.The major factors significantly controlling thegrowth rate of the P. linearis gametophytein glass dishes were: photoperiod, temperature, agein culture, photosynthetic photon flux (PPF), salinityand water dynamics. Maximal growth occurred underdaylength of 12 h, medium temperature (15–20 ^°C), low PPF (70–140 mol photon m^-2s^-1), ambient salinity (30–40 ppt), 1–3 h ofdaily air exposure, and water velocity of 4 cm s^-1.Photosynthesis and respiration rates weredominantly affected by daylength and temperature,while the concentration of pigments was dominantlyaffected by PPF and temperature.These conditions correspond well to the optimalnatural growth environment of this local species andare in agreement with the optimum estimated throughthe recently developed outdoor mathematical growthmodel.     

Responses of Odonata chromatophores to environmental stimuli

Responses to change in temperature and light intensity were studied in three species of Australian Odonata using time-lapse photography. In each species, responses to temperature are dependent on both the instantaneous temperature and the direction of temperature change. At temperatures below those which produce unstable colour phases, the change to dark phase takes about 9 hr and is constant in rate. The reverse change is directly temperature dependent and can be much more rapid. Responses to change in light intensity are attributable to the heating effect of light rather than to true light sensitivity. All colour changes show wide individual variation in both rate and amount. They are slightly affected by temperature acclimation but are unaffected by prevailing weather, time of year, geographic location, or age.     

Responses of cariogenic streptococci to environmental stresses

To persist in the oral cavity, bacteria must be able to tolerate rapid and substantial environmental fluctuations, particularly in pH and nutrient source and availability. Various species of Streptococcus, one of the most abundant genera in the mouth, are associated with oral health, as well as with dental caries. Cariogenic streptococci depend on a biofilm lifestyle for survival and persistence in the oral cavity and have developed sophisticated mechanisms to cope with environmental stresses. Here, we analyze the primary factors that allow these bacteria to emerge as significant members of tooth biofilms during adverse conditions. Our focus is on the molecular mechanisms of biofilm formation, stress tolerance and sugar metabolism by pathogenic oral streptococci, mainly Streptococcus mutans. Overlaps in the roles and regulation of these virulence attributes are highlighted and areas of research that deserve further investigation are proposed.     

滨柃叶功能性状对环境因子的响应

植物叶功能性状能反映植物对不同环境的响应及适应策略。以福建省福州市平潭海坛岛、大练岛、大怀屿的滨柃(Eurya emarginata)为研究对象,通过测定滨柃16项叶功能性状及14项环境因子,分析了环境因子对滨柃叶功能性状的影响。结果表明：(1)滨柃叶功能性状变异系数介于2.26%—25.78%,其中叶体积变异程度最大(25.78%),叶含水量变异程度最小(2.26%)。不同海岛滨柃大部分叶功能性状存在显著的差异性(P<0.05),说明滨柃叶片功能性状多样性丰富,其对异化环境表现出较强的适应性;(2)不同海岛的土壤因子指标间差异显著(P<0.05);(3)通过系统聚类可将30份滨柃聚为两类,海坛岛和大练岛为一类,大怀屿为一类,结果与海岛类型和地理分布相吻合;(4)冗余分析表明,滨柃的叶功能性状主要受郁闭度、土壤全钾、土壤有效磷、海拔、速效钾及碱解氮等环境因子的影响。研究结果表明滨柃叶片功能性状可通过一定的性状变异和性状组合,以及与环境因子间的相互作用弥补生境的不足,较好地适应海岛恶劣环境,研究结果有助于理解滨柃对不同海岛生境的响应特征及其在海岛的生态策略,对探究滨柃的资源利...