Differential leaf expansion can enable hydraulic acclimation to sun and shade

Although leaf size is one of the most responsive plant traits to environmental change, the functional benefits of large versus small leaves remain unclear. We hypothesized that modification of leaf size within species resulting from differences in irradiance can allow leaves to acclimate to different photosynthetic or evaporative conditions while maintaining an efficient balance between hydraulic supply (vein density) and evaporative demand. To test this, we compared the function and anatomy of leaf hydraulic systems in the leaves of a woody angiosperm (Toona ciliata M. Roem.) grown under high and low irradiance in controlled conditions. Our results confirm that in this species, differential leaf expansion regulates the density of veins and stomata such that leaf hydraulic conductance and stomatal conductance remain proportional. A broader sample of field-grown tree species suggested that differences in leaf venation and stomatal traits induced by sun and shade were not regulated by leaf size in all cases. Our results, however, suggest that leaf size plasticity can provide an efficient way for plants to acclimate hydraulic and stomatal conductances to the contrasting evaporative conditions of sun and shade.     

叶脉网络功能性状及其生态学意义

叶脉网络结构是叶脉系统在叶片里的分布和排列样式。早期叶脉网络结构研究主要集中在其分类学意义上; 近年来叶脉网络功能性状及其在植物水分利用上的意义已成为植物生态学研究的热点。该文介绍了叶脉网络功能性状的指标体系(包括叶脉密度、叶脉直径、叶脉之间的距离、叶脉闭合度等), 综述了叶脉网络功能性状与叶脉系统功能(包括水分、养分和光合产物等物质运输、机械支撑和虫害防御等)的关系, 叶脉网络功能性状与叶片其他功能性状(包括比叶重、叶寿命、光合速率、叶片大小、气孔密度等)的协同变异和权衡关系, 以及叶脉网络功能性状随环境因子(包括水分、温度、光照等)的变化规律等方面的最新研究进展。此外, 叶脉网络功能性状的研究成果也被应用于古环境重建、城市交通规划、流域规划及全球变化研究中。由于叶脉网络功能性状是环境因子与系统发育共同作用的结果, 未来开展分子—叶片—植物—生态系统等多尺度的叶脉网络功能性状研究, 理清叶脉网络功能性状与气孔失水—茎干导水—根系吸水等植物水分利用的关系, 将为预测植物及生态系统对全球变化的响应提供新的启示。     

Acclimation to humidity modifies the link between leaf size and the density of veins and stomata

The coordination of veins and stomata during leaf acclimation to sun and shade can be facilitated by differential epidermal cell expansion so large leaves with low vein and stomatal densities grow in shade, effectively balancing liquid‐ and vapour‐phase conductances. As the difference in vapour pressure between leaf and atmosphere (VPD) determines transpiration at any given stomatal density, we predict that plants grown under high VPD will modify the balance between veins and stomata to accommodate greater maximum transpiration. Thus, we examined the developmental responses of these traits to contrasting VPD in a woody angiosperm (Toona ciliata M. Roem.) and tested whether the relationship between them was altered. High VPD leaves were one‐third the size of low VPD leaves with only marginally greater vein and stomatal density. Transpirational homeostasis was thus maintained by reducing stomatal conductance. VPD acclimation changed leaf size by modifying cell number. Hence, plasticity in vein and stomatal density appears to be generated by plasticity in cell size rather than cell number. Thus, VPD affects cell number and leaf size without changing the relationship between liquid‐ and vapour‐phase conductances. This results in inefficient acclimation to VPD as stomata remain partially closed under high VPD.     

兰州北山不同坡向刺槐叶脉密度与气孔性状的关联性分析

植物叶脉和气孔性状的关系反映了叶片的水力特性, 对认识它们与植物水分利用有关的生理功能间的关系及其调控作用具有重要意义。该文利用GIS (geographic information system)与实验生态学相结合的方法, 采用标准化主轴估计方法, 研究了兰州市北山不同坡向人工林刺槐(Robinia pseudoacacia)叶脉密度与气孔密度、气孔大小的关系。结果表明: 随着坡向由南坡向东坡、西坡和北坡转变, 植被群落的郁闭度、高度和土壤含水量呈逐渐增加的趋势, 刺槐的净光合速率(P_n)、蒸腾速率(T_r)、光合有效辐射(PAR)、叶脉密度和气孔密度呈逐渐减小的趋势, 气孔与叶面积呈逐渐增大的趋势; 各个坡向的刺槐叶脉密度与气孔密度呈显著正相关关系, 与气孔大小呈显著负相关关系, 且在南坡达到极显著相关关系。生长在南坡的刺槐具有高的叶脉密度和密而小的气孔, 生长在北坡的刺槐具有低的叶脉密度和疏而大的气孔。不同坡向刺槐叶脉密度与气孔特征间的资源分配模式, 反映了植物在异质性生境中根据其功能需求在自身性状之间进行投资权衡机制的优化。     

Correlation analysis between vein density and stomatal traits of Robinia pseudoacacia in different aspects of Beishan Mountain in Lanzhou

AimsThe relationship between leaf venation and stomatal traits reflects leaf water potential of plants, and is fundamental to probe the relationship between physiological functions and water use. Our objective was to study the changes in the relationship between venation density and stomatal traits (stomatal density and stomatal length) in Robinia pseudoacacia with the changes in slope aspects.MethodsIn Beishan Mountain of Lanzhou in Gansu Province, China, 20 transects were laid out horizontally along the contour at intervals of 50 m from an elevation of 1550-1750 m in four different slope aspects, and 12 plots were set up along each transect at intervals of 5 m. A handed GPS (global positioning system) was used to measure latitude, longitude and altitude at each plot. Community characteristics, including crown density, tree height and soil moisture, were investigated. Robinia pseudoacacia within all plots were sampled and used for measurements of individual leaf area, venation density, stomatal density and stomatal length in laboratory in each plot. The 240 plots were categorized into groups of southern, eastern, western and northern aspects, and the standardized major axis (SMA) estimation method was then used to examine the relationship between the stomatal density, stomatal length and vein density.Important findings The results showed that with a change of the aspect from south to east, west, and north, the crown density, average tree height and soil moisture of the plant community increased, while leaf net photosynthetic rate (P_n), transpiration rate (T_r), photosynthetically active radiation (PAR), vein density and stomatal density decreased. In addition, stomatal length and individual leaf area increased. Venation density of each aspect of R. pseudoacacia was positively correlated with stomatal density (p < 0.05) and negatively with stomatal length (p < 0.05). These correlations were strongest in south slope (p < 0.01).     

高粱、紫苏叶脉密度与光合特性的关系

叶脉是植物叶片光合作用水分输送的重要结构。为阐述叶脉与光合特性之间的关系,以C4植物高粱(Sorghum bicolor)、C3植物紫苏(Perilla frutescens)为实验材料研究了叶脉密度和光合特性之间的关系。结果表明,与紫苏相比,高粱叶片叶脉密度大,导水能力强,蒸腾速率高,但气孔密度小。进一步分析表明,高粱叶片近轴侧气孔密度占总气孔的比例明显高于紫苏。叶脉密度大的高粱具有较高的净光合速率;而紫苏叶脉密度小,净光合速率也较低。由此表明,较高的叶脉密度有利于支持较高的光合速率,但研究表明叶脉密度和气孔密度可能不存在严格的协同变异关系。研究结果对理解植物光合作用适应有重要意义。     

基部被子植物气孔性状与叶脉密度的关联进化

植物叶片通过气孔的水分蒸腾散失和叶脉的水分供应达到水分平衡,而基部被子植物在进化过程中叶片水分供应和蒸腾散失是否达到平衡或关联进化还缺乏了解。本研究以11种基部被子植物为材料,测定了气孔密度、气孔长度、叶脉密度和叶片厚度4个叶片性状,并结合系统发育树,利用系统发育独立对比的方法分析这些性状之间的关联进化。结果显示：沿进化方向,气孔密度和叶脉密度逐渐增加,而气孔长度和叶片厚度有减小的趋势;无论是否考虑系统发育的影响,气孔密度都与叶脉密度呈显著正相关关系,说明二者之间存在关联进化,并证实了基部被子植物叶片水分平衡假说;气孔密度和长度、叶脉密度均与叶片厚度呈显著线性相关,但在去除系统发育的影响后这种线性相关关系不再显著,说明叶片厚度与其它三个叶片性状不存在关联进化。本研究结果还表明,叶片的水分供应和散失乃至CO2通透性的平衡主导着基部被子植物叶片结构和功能的进化。     

Kinetic characterization of reduced pyridine nucleotide dehydrogenases (duroquinone-dependent) in cucurbita microsomes

Stomatal conductances of normally oriented and inverted leaves were measured as light levels (photosynthetic photon flux densities) were increased to determine whether abaxial stomata of Vicia faba leaves were more sensitive to light than adaxial stomata. Light levels were increased over uniform populations of leaves of plants grown in an environmental chamber. Adaxial stomata of inverted leaves reached maximum water vapor conductances at a light level of 60 micromoles per square meter per second, the same light level at which abaxial stomata of normally oriented leaves reached maximum conductances. Abaxial stomata of inverted leaves reached maximum conductances at a light level of 500 micromoles per square meter per second, the same light level at which adaxial stomata of normally oriented leaves reached maximum conductances. Maximum conductances in both normally oriented and inverted leaves were about 200 millimoles per square meter per second for adaxial stomata and 330 millimoles per square meter per second for abaxial stomata. Regardless of whether leaves were normally oriented or inverted, when light levels were increased to values high enough that upper leaf surfaces reached maximum conductances (about 500 micromoles per square meter per second), light levels incident on lower, shaded leaf surfaces were just sufficient (about 60 micromoles per square meter per second) for stomata of those surfaces to reach maximum conductances. This `coordinated' stomatal opening on the separate epidermes resulted in total leaf conductances for normally oriented and inverted leaves that were the same at any given light level. We conclude that stomata in abaxial epidermes of intact Vicia leaves are not more sensitive to light than those in adaxial epidermes, and that stomata in leaves of this plant do not respond to light alone. Additional factors in bulk leaf tissue probably produce coordinated stomatal opening on upper and lower leaf epidermes to optimally meet photosynthetic requirements of the whole leaf for CO₂.     

Decline of leaf hydraulic conductance with dehydration: relationship to leaf size and venation architecture

Across plant species, leaves vary enormously in their size and their venation architecture, of which one major function is to replace water lost to transpiration. The leaf hydraulic conductance (K(leaf)) represents the capacity of the transport system to deliver water, allowing stomata to remain open for photosynthesis. Previous studies showed that K(leaf) relates to vein density (vein length per area). Additionally, venation architecture determines the sensitivity of K(leaf) to damage; severing the midrib caused K(leaf) and gas exchange to decline, with lesser impacts in leaves with higher major vein density that provided more numerous water flow pathways around the damaged vein. Because xylem embolism during dehydration also reduces K(leaf), we hypothesized that higher major vein density would also reduce hydraulic vulnerability. Smaller leaves, which generally have higher major vein density, would thus have lower hydraulic vulnerability. Tests using simulations with a spatially explicit model confirmed that smaller leaves with higher major vein density were more tolerant of major vein embolism. Additionally, for 10 species ranging strongly in drought tolerance, hydraulic vulnerability, determined as the leaf water potential at 50% and 80% loss of K(leaf), was lower with greater major vein density and smaller leaf size (|r| = 0.85-0.90; P < 0.01). These relationships were independent of other aspects of physiological and morphological drought tolerance. These findings point to a new functional role of venation architecture and small leaf size in drought tolerance, potentially contributing to well-known biogeographic trends in leaf size.     

Morphological and stomatal responses of Norway spruce foliage to irradiance within a canopy depending on shoot age

Morphological and stomatal responses of Norway spruce (Picea abies) foliage to light availability were studied in respect to shoot age. Needle minor diameter (D(1), anatomical width), major diameter (D(2), anatomical thickness), dry weight (M), and tissue density index (I(D)) increased, and needle flatness (Fl) and specific leaf area (SLA) decreased with foliage age, while shade foliage demonstrated higher morphological plasticity as compared to sun foliage. Needle minor diameter, dry weight, and the ratio of total to projected leaf area increased, and needle flatness and specific leaf area decreased with daily average photosynthetic photon flux density (Q(D)). The current-year foliage exhibited the highest variation with irradiance, while the morphological plasticity decreased with needle ageing. The morphological characteristics of needles were independent of irradiance if Q(D) was above 300 μmol m(-2) s(-1). D(1) was the only linear needle characteristic which significantly changed with light availability within a canopy, and thus determined needle flatness, SLA, as well as the ratio of total to projected leaf area (TLA/PLA). Needle flatness was a characteristic responding most sensitively to the photosynthetic photon flux density, R(2) was 0.68, 0.44, and 0.49 for the current-year, 1-year-old, and 2-year-old foliage, respectively. TLA/PLA ranged from 2.2 to 4.0 depending on D(1). Variation in SLA in response to light availability can be attributed to changes both in needle shape and tissue density. Stomatal responses to photosynthetic photon flux density (Q(P)) depended on foliage type (sun or shade) and age. Sun needles demonstrated higher daily maximum leaf conductances to water vapour compared to shade needles. The shade needles responded more sensitively to changes in Q(P) at dawn and sunset than the sun needles, while older needles of both foliage types exhibited faster stomatal responses. The light-saturation of leaf conductance (g(L)) was achieved by 20 μmol m(-2) s(-1) for shade foliage, and approximately by 50 μmol m(-2) s(-1) for sun foliage. As a rule, g(L) changed in response to irradiance faster in the evening, i.e. at decreasing irradiance. Stomata were not usually completely closed in the dark before sunrise and after sunset, the phenomenon being more pronounced in older shoots and sun needles. Nightly water losses from spruce foliage are attributable primarily to older shoots, and are related to age-dependent changes in stomatal responsiveness.     

不同水分处理下喀斯特土层厚度异质性对两种草本叶片解剖结构和光合特性的影响

为了探究不同水分处理下草本植物对喀斯特土层厚度变化的叶片形态建成和光合生理响应,以黑麦草(Lolium perenne L.)和苇状羊茅(Festuca arundinacea Schreb.)为研究对象,通过盆栽水分受控试验,研究了3种水分处理[正常供水(W_(ck)),减水1组(D1)和减水2组(D2)]下3种土层厚度[浅土组(S_S)、对照组(S_(CK))和深土组(S_D)]对两种草本叶片解剖结构和光合特性的影响。结果表明:(1)正常供水下(W_(ck)),黑麦草和苇状羊茅在浅土组(S_S)的气孔密度和气孔限制值(Ls)均显著高于对照组(S_(CK)),净光合速率(Pn)、胞间CO_2浓度(Ci)和蒸腾速率(Tr)降低;在深土组(S_D),两种植物的气孔密度都有所下降,黑麦草的叶脉密度、Pn和Tr均低于对照组,而苇状羊茅的叶脉密度和Pn表现出增加;(2)D1水分条件下,黑麦草在浅土组的气孔密度较对照组增加,叶脉密度、Pn和Tr均降低,而苇状羊茅的气孔密度有所降低,叶脉密度、Pn和Tr未受到显著影响;在深土组中,黑麦草的气孔密度不变,叶脉密度增加,而Pn和Tr均降低;苇状羊茅的气孔密度降低,但叶脉密度、Pn和Tr均升高;(3)D2水分条件下,两种植物在浅土组的叶脉密度较对照组均增加,气孔密度、Pn和Tr均受到抑制;在深土组,黑麦草的远轴面气孔密度较对照组下降,两种植物的其他指标未受到明显影响。可见,在不同水分条件下,植物的叶片解剖结构和光合特性对不同土层厚度的响应不一,且不同物种间也有差异。总体上随着水分减少,土层厚度降低对植物的光合抑制作用增强,而厚度增加对深根植物的光合促进作用和对浅根植物的光合抑制作用先增强后减弱。植物气孔和叶脉性状特征随水分条件的变化在一定程度上与叶面积和叶片宽度的变化有关。     

Non-linear response of stomata in Pinus koraiensis to tree age and elevation

Knowledge on variations in stomata is useful in reflecting leaf physiological characteristics of CO₂ uptake and water transpiration, and predicting the responses of plants to future climate change. Stomatal density and number of stomatal rows (current-year, 1- and 2-year-old needles) in relation to tree age (ranging from 25 to 320 years old), elevation (ranging from 738 to 1,380 m a.s.l.), and sun exposure (sun and shade exposure) were investigated in Pinus koraiensis trees. Stomatal density and number of stomatal rows in relation to tree age and elevation showed a humped curve with the maximum values at intermediate levels of tree age (210 years old) and elevation (1,050 m a.s.l.), respectively. Needle age but not sun exposure significantly affected the stomatal density across tree ages and elevations. Our results suggest that variations in stomatal density of Pinus koraiensis needles are related to ontogenetic growth and environmental factors.     

Hydraulic analysis of water flow through leaves of sugar maple and red oak

Leaves constitute a substantial fraction of the total resistance to water flow through plants. A key question is how hydraulic resistance within the leaf is distributed among petiole, major veins, minor veins, and the pathways downstream of the veins. We partitioned the leaf hydraulic resistance (R(leaf)) for sugar maple (Acer saccharum) and red oak (Quercus rubra) by measuring the resistance to water flow through leaves before and after cutting specific vein orders. Simulations using an electronic circuit analog with resistors arranged in a hierarchical reticulate network justified the partitioning of total R(leaf) into component additive resistances. On average 64% and 74% of the R(leaf) was situated within the leaf xylem for sugar maple and red oak, respectively. Substantial resistance-32% and 49%- was in the minor venation, 18% and 21% in the major venation, and 14% and 4% in the petiole. The large number of parallel paths (i.e. a large transfer surface) for water leaving the minor veins through the bundle sheath and out of the leaf resulted in the pathways outside the venation comprising only 36% and 26% of R(leaf). Changing leaf temperature during measurement of R(leaf) for intact leaves resulted in a temperature response beyond that expected from changes in viscosity. The extra response was not found for leaves with veins cut, indicating that water crosses cell membranes after it leaves the xylem. The large proportion of resistance in the venation can explain why stomata respond to leaf xylem damage and cavitation. The hydraulic importance of the leaf vein system suggests that the diversity of vein system architectures observed in angiosperms may reflect variation in whole-leaf hydraulic capacity.     

Leaf Photosynthetic Rate of Tropical Ferns Is Evolutionarily Linked to Water Transport Capacity

Ferns usually have relatively lower photosynthetic potential than angiosperms. However, it is unclear whether low photosynthetic potential of ferns is linked to leaf water supply. We hypothesized that there is an evolutionary association of leaf water transport capacity with photosynthesis and stomatal density in ferns. In the present study, a series of functional traits relating to leaf anatomy, hydraulics and physiology were assessed in 19 terrestrial and 11 epiphytic ferns in a common garden, and analyzed by a comparative phylogenetics method. Compared with epiphytic ferns, terrestrial ferns had higher vein density (D_vein), stomatal density (SD), stomatal conductance (g_s), and photosynthetic capacity (A_max), but lower values for lower epidermal thickness (LET) and leaf thickness (LT). Across species, all traits varied significantly, but only stomatal length (SL) showed strong phylogenetic conservatism. A_max was positively correlated with D_vein and g_s with and without phylogenetic corrections. SD correlated positively with A_max, D_vein and g_s, with the correlation between SD and D_vein being significant after phylogenetic correction. Leaf water content showed significant correlations with LET, LT, and mesophyll thickness. Our results provide evidence that A_max of the studied ferns is linked to leaf water transport capacity, and there was an evolutionary association between water supply and demand in ferns. These findings add new insights into the evolutionary correlations among traits involving carbon and water economy in ferns.     

Limitations to photosynthesis in coffee leaves from different canopy positions.

Limitations to photosynthesis were explored in leaves from four canopy positions of field-grown, unshaded coffee (Coffea arabica L.), a tropical tree species classified as shade-obligatory. Overall, compared to shade (lower) leaves, sun (upper) leaves had higher net carbon assimilation rate (A) (4.5 against 2.0mumolm(-2)s(-1) at most) associated with higher electron transport rate (due to a greater irradiance availability) but unrelated to stomatal and mesophyll conductances, which were similar regardless of leaf position. Neither physiological variable directly involved with photosynthetic carbon gain nor those involved with light capture were able to adjust themselves to match the capacity of the photosynthetic machinery to the light supply. We concluded that: (i) there was no major difference in photosynthetic capacity between sun and shade leaves; (ii) the intrinsic low A in coffee was greatly associated with remarkable low diffusive limitations rather than with biochemical or photochemical constraints; and (iii) morphological (e.g., variations in specific leaf area and leaf inclination) or anatomical plasticity should be of greater acclimative value than physiological plasticity as a mean of coffee leaves to respond to changing irradiance.     

Ecophysiological adaptability of four tree species in the southern subtropical evergreen broad-leaved forest to warming

Aims The subject of this study was to investigate warming effects on leaf stomatal traits, anatomical structure and photosynthetic traits of four common tree species in subtropical evergreen broad-leaved forest of southern China, and to compare their physiological adaptability to warming. Our study aims to provide a theoretical basis for better predicting the tree growth of native forests in a warming climate.Methods One-year-old seedlings of Syzygium rehderianum, Ormosia pinnata, Castanopsis hystrix and Schima superba were selected and exposed to two levels of temperature (ambient temperature and infrared heater warming). Leaf stomatal traits, anatomical structure and photosynthetic characteristics were measured to represent the abilities of stomatal regulation, leaf tissue regulation and nutrient maintenance, respectively.Important findings For Syzygium rehderianum, warming decreased its leaf sponge tissue thickness, photosynthetic nitrogen-use efficiency (PNUE) and photosynthetic phosphorous-use efficiency (PPUE). Seedling of O. pinnata exposed to warming showed increased stomatal conductance, photosynthetic rate, PNUE and PPUE, but decreased stomatal density, leaf thickness and palisade tissue thickness. For C. hystrix, warming decreased the stomata size, but did not affect its photosynthetic rate. Seedling of Schima superba exposed to warming showed lower stomata density, leaf palisade tissue thickness, photosynthetic rate, PNUE and PPUE, but higher stomata size. These results suggested that O. pinnata, Syzygium rehderianum and Schima superba could reduce their leaf thickness to acclimate to warming conditions. The abilities of stomatal regulation, nutrient maintenance, photosynthetic rate and PNUE varied among these tree species. Warming would be beneficial for the growth of O. pinnata due to increased photosynthetic rate, PNUE and PPUE, while not for Syzygium rehderianum and Schima superba, the two dominant tree species of native forests. This study indicated that, with projected climate change, O. pinnata may replace Syzygium rehderianum and Schima superba as a new dominant tree species in the subtropical evergreen broad-leaved forest for its stronger adaptability to warming.     

Effect of local irradiance on CO(2) transfer conductance of mesophyll in walnut

The acclimation responses of walnut leaf photosynthesis to the irradiance microclimate were investigated by characterizing the photosynthetic properties of the leaves sampled on young trees (Juglans nigraxregia) grown in simulated sun and shade environments, and within a mature walnut tree crown (Juglans regia) in the field. In the young trees, the CO(2) compensation point in the absence of mitochondrial respiration (Gamma*), which probes the CO(2) versus O(2) specificity of Rubisco, was not significantly different in sun and shade leaves. The maximal net assimilation rates and stomatal and mesophyll conductances to CO(2) transfer were markedly lower in shade than in sun leaves. Dark respiration rates were also lower in shade leaves. However, the percentage inhibition of respiration by light during photosynthesis was similar in both sun and shade leaves. The extent of the changes in photosynthetic capacity and mesophyll conductance between sun and shade leaves under simulated conditions was similar to that observed between sun and shade leaves collected within the mature tree crown. Moreover, mesophyll conductance was strongly correlated with maximal net assimilation and the relationships were not significantly different between the two experiments, despite marked differences in leaf anatomy. These results suggest that photosynthetic capacity is a valuable parameter for modelling within-canopies variations of mesophyll conductance due to leaf acclimation to light.     

Allometric co-variation of xylem and stomata across diverse woody seedlings

Leaf stomatal density is known to co-vary with leaf vein density. However, the functional underpinning of this relation, and how it scales to whole-plant water transport anatomy, is still unresolved. We hypothesized that the balance of water exchange between the vapour phase (in stomata) and liquid phase (in vessels) depends on the consistent scaling between the summed stomatal areas and xylem cross-sectional areas, both at the whole-plant and single-leaf level. This predicted size co-variation should be driven by the co-variation of numbers of stomata and terminal vessels. We examined the relationships of stomatal traits and xylem anatomical traits from the entire plant to individual leaves across seedlings of 53 European woody angiosperm species. There was strong and convergent scaling between total stomatal area and stem xylem area per plant and between leaf total stomatal area and midvein xylem area per leaf across all the species, irrespective of variation in leaf habit, growth-form or relative growth rate. Moreover, strong scaling was found between stomatal number and terminal vessel number, whereas not in their respective average areas. Our findings have broad implications for integrating xylem architecture and stomatal distribution and deepen our understanding of the design rules of plants' water transport network.     

Stomatal function,density and pattern,and CO2 assimilation in Arabidopsis thaliana tmm1 and sdd1‐1 mutants

• Stomata modulate the exchange of water and CO₂ between plant and atmosphere. Although stomatal density is known to affect CO₂ diffusion into the leaf and thus photosynthetic rate, the effect of stomatal density and patterning on CO₂ assimilation is not fully understood.
• We used wild types Col‐0 and C24 and stomatal mutants sdd1‐1 and tmm1 of Arabidopsis thaliana, differing in stomatal density and pattern, to study the effects of these variations on both stomatal and mesophyll conductance and CO₂ assimilation rate. Anatomical parameters of stomata, leaf temperature and carbon isotope discrimination were also assessed.
• Our results indicate that increased stomatal density enhanced stomatal conductance in sdd1‐1 plants, with no effect on photosynthesis, due to both unchanged photosynthetic capacity and decreased mesophyll conductance. Clustering (abnormal patterning formed by clusters of two or more stomata) and a highly unequal distribution of stomata between the adaxial and abaxial leaf sides in tmm1 mutants also had no effect on photosynthesis.
• Except at very high stomatal densities, stomatal conductance and water loss were proportional to stomatal density. Stomatal formation in clusters reduced stomatal dynamics and their operational range as well as the efficiency of CO₂ transport.

     

南亚热带常绿阔叶林4个树种对增温的生理生态适应能力比较

以红枝蒲桃(Syzygium rehderianum)、海南红豆(Ormosia pinnata)、红锥(Castanopsis hystrix)和木荷(Schima superba) 4种南亚热带常绿阔叶林典型树种为研究对象, 采用红外-箱式增温的方法, 研究4个树种叶片气孔性状(表征气孔调节能力)、叶片解剖结构(表征叶片组织调节能力)和光合特征(表征养分维持能力)对增温的响应情况, 比较不同树种在增温背景下的生理生态适应能力, 为预测该地区森林植物在全球变暖情形下的生长变化趋势提供理论依据。结果表明: 增温后, 红枝蒲桃叶片海绵组织厚度减小, 且光合氮利用效率(PNUE)和光合磷利用效率(PPUE)降低; 海南红豆气孔导度增大、气孔密度减小以及叶片厚度和栅栏组织厚度减小, 同时光合速率、PNUE和PPUE升高; 红锥气孔大小缩小, 但光合速率不变; 木荷气孔增大而密度减小, 栅栏组织厚度减小, 光合速率、PNUE和PPUE降低。综上所述, 红枝蒲桃、海南红豆和木荷能够通过降低叶片厚度来适应高温环境, 不同物种的气孔调节、养分维持、光合速率和光合养分利用效率对增温的响应存在差异。增温有利于固氮植物海南红豆的生长, 但不利于传统优势树种木荷和红枝蒲桃的生长。因此, 在未来气候变暖的情况下, 固氮植物海南红豆由于具有较强的适应能力, 在南亚热带常绿阔叶林中可能会取代木荷和红枝蒲桃等成为新的优势树种。