Strong leaf morphological, anatomical, and physiological responses of a subtropical woody bamboo (Sinarundinaria nitida) to contrasting light environments

Dwarf bamboos are an important understory component of the lowland and montane forests in the subtropical regions of Asia and South America, yet little is known about their physiology and phenotypic plasticity in response to changing light environments. To understand how bamboo species adapt to different light intensities, we examined leaf morphological, anatomical, and physiological differentiation of Sinarundinaria nitida (Mitford) Nakai, a subtropical woody dwarf bamboo, growing in open and shaded natural habitats in the Ailao Mountains, SW China. Compared with leaves in open areas, leaves in shaded areas had higher values in leaf size, specific leaf area, leaf nitrogen, and chlorophyll concentrations per unit area but lower values in leaf thickness, vein density, stomatal density, leaf carbon concentration, and total soluble sugar concentration. However, stomatal size and leaf phosphorus concentration per unit mass remained relatively constant regardless of light regime. Leaves in the open habitat exhibited a higher light-saturated net photosynthetic rate, dark respiration rate, non-photochemical quenching, and electron transport rate than those in the shaded habitat. The results of this study revealed that the bamboo species exhibited a high plasticity of its leaf structural and functional traits in response to different irradiances. The combination of high plasticity in leaf morphological, anatomical, and physiological traits allows this bamboo species to grow in heterogeneous habitats.     

Photosynthesis in leaves of the juvenile and adult phase of ivy (Hedera helix)

Abstract Photosynthetic and anatomical parameters of leaves from the juvenile and adult part of an ivy plant (Hedera helix L.) have been determined and compared with each other. Light-saturated net photosynthesis (per unit leaf area) was about 1.5 times higher in adult leaves than in juvenile ones. The lower photosynthetic capacity of juvenile leaves was caused by a lower stomatal and especially a lower residual conductance to the CO₂-transfer. This corresponds with anatomical features of the leaves, i.e. lower stomatal frequency, fewer chloroplasts per cell, and – most important – thinner leaves, as well as with a less efficient photosynthetic apparatus measured as Hill reaction of isolated broken chloroplasts and activity of ribulose bisphosphate carboxylase. No differences in the respiration in light (relative to net photosynthesis) and in the CO₂-compensation concentration could be detected between the two leaf types. These observed anatomical and photosynthetic parameters of the juvenile and adult ivy leaves resemble those reported for shade and sun leaves, respectively, although the leaves investigated originated from the same light environment.     

Stomatal and nonstomatal limitations to net photosynthesis in seedlings of woody angiosperms

Comparative responses of net photosynthesis (A) to water stress in woody species from a variety of habitats were studied to assess the relationship between photosynthetic attributes and drought tolerance. Stomatal and nonstomatal limitations to A were compared in three-month-old white oak (Quercus alba L.), post oak (Quercus stellata Wangenh.), sugar maple (Acer saccharum Marsh.), and black walnut (Juglans nigra L.) seedlings during a drying cycle. Relative stomatal limitation of photosynthesis (I) was less than 50% in all species except for Q. stellata seedlings subjected to severe water stress. No significant changes in I were observed in Q. alba and J. nigra before, during, and after drought. In A. saccharum, I was generally low and decreased significantly under water stress. Under well-watered conditions, A was highest in Q. stellata, intermediate in Q. alba, and lower in A. saccharum and J. nigra. High A in well-watered Q. stellata was associated with high stomatal conductance and carboxylation efficiency, whereas low A was associated with low stomatal conductance and carboxylation efficiency in A. saccharum and low stomatal conductance, low carboxylation efficiency, and high CO₂ compensation point in J. nigra. Under severe water stress, A, carboxylation efficiency, and stomatal conductance decreased substantially in all species; however, Q. stellata had the highest carboxylation efficiency and lowest CO₂ compensation point under these conditions. After 5 days at high soil moisture after drought, stomatal and mesophyll components of A in A. saccharum and J. nigra had not recovered to predrought levels, whereas they had completely recovered in Q. stellata and Q. alba. The photosynthetic apparatus, especially mesophyll components, of drought-tolerant Quercus species showed either less inhibition under water stress, superior recovery to predrought capacity, or both. Exposure of the leaves to ¹⁴CO₂ indicated apparent asymmetric stomatal closure for mildly water-stressed seedlings, but not for leaves of well-watered, severely stressed, or rehydrated plants. These results suggest that patchy stomatal closure under mild water stress might be important for water stress-induced inhibition of photosynthesis, but not under the more severe water stress imposed in this study.     

Leaf plasticity in response to light of three evergreen species of the Mediterranean maquis

Morphological, anatomical, biochemical and physiological traits of sun and shade leaves of adult Quercus ilex, Phillyrea latifolia and Pistacia lentiscus shrub species co-occurring in the Mediterranean maquis at Castelporziano (Latium) were studied. Fully expanded sun leaves had 47% (mean of the three species) greater leaf mass area (LMA) and 31% lower specific leaf area (SLA) than shade leaves. Palisade parenchyma thickness contributed on an average 42% to the total leaf thickness, spongy layer 43%, upper epidermal cells 5%, and upper cuticle thickness 3%. Stomatal size was greater in sun (25.5 μm) than in shade leaves (23.6 μm). Total chlorophyll content per fresh mass was 71% greater in shade than in sun leaves, and nitrogen content was the highest in sun (13.7 mg g⁻¹) than in shade leaves (11.8 mg g⁻¹). Difference of net photosynthetic rates (P _N) between sun and shade leaves was 97% (mean of the three species). The plasticity index (sensu Valladares et al., New Phytol 148:79–91, 2000a) was the highest for physiological leaf traits (0.86) than for morphological, anatomical and biochemical ones. Q. ilex had the highest plasticity index of morphological, anatomical and physiological leaf traits (0.37, 0.28 and 0.71, respectively) that might explain its wider ecological distribution. The higher leaf plasticity of Q. ilex might be advantageous in response to varying environmental conditions, including global change.     

青藏高原不同海拔3种菊科植物叶片结构变化及其生态适应性

采用常规石蜡制片技术和显微观察方法,对分布于青藏高原祁连山东部山地冷龙岭3600—4400 m不同海拔高度的蒲公英(Taraxacum mongolicum Hand-Mazz)、火绒草(Leontopodium leontopodioides(Willd.)Beauv)和美丽风毛菊(Saussurea superba Anthony)的叶片形态解剖结构进行了研究,并探讨了其对海拔高度的响应及生态适应性。结果表明:随海拔高度的升高,3种植物气孔器外拱盖内缘、角质层纹饰、气孔与表皮细胞的位置关系以及上、下表皮气孔器内缘呈现不同的变化趋势;火绒草上、下表皮气孔密度随海拔升高而增加,而蒲公英和美丽风毛菊的气孔密度则降低;3种植物上、下表皮气孔指数随海拔高度的增加均未出现规律性变化;3种植物叶片厚度、上下表皮厚度、上下角质层厚度、栅栏细胞系数均随海拔升高而增加;解剖学指标之间大多呈明显的协同进化;叶片结构,尤其是气孔密度对海拔高度变化表现出较大的可塑性。研究表明3种植物采取不同的响应机制来适应海拔高度的变化,植物对高原环境变化的适应具有多样性。     

LIGHT,TEMPERATURE AND SALINITY EFFECTS ON GROWTH,LEAF ANATOMY AND PHOTOSYNTHESIS OF DISTICHLIS SPICATA (L.) GREENE

The effects of light, temperature, and salinity on growth, net CO₂ exchange and leaf anatomy of Distichlis spicata were investigated in controlled environment chambers. When plants were grown at low light, growth rates were significantly reduced by high substrate salinity or low temperature. However, when plants were grown at high light, growth rates were not significantly affected by temperature or salinity. The capacity for high light to overcome depressed growth at high salinity cannot be explained completely by rates of net photosynthesis, since high salinity caused decreases in net photosynthesis at all environmental conditions. This salinity-induced decrease in net photosynthesis was caused largely by stomatal closure, although plants grown at low temperature and low light showed significant increases in internal leaf resistance to CO₂ exchange. Increased salinity resulted in generally thicker leaves with lower stomatal density but no significant differences in the ratio of mesophyll cell surface area to leaf area. Salinity and light during growth did not significantly affect rates of dark respiration. The mechanisms by which Distichlis spicata tolerates salt appear to be closely coulpled to the utilization of light energy. Salt-induced leaf succulence is of questionable importance to gas exchange at high salinity in this C₄ species.     

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.     

Variation in leaf traits at different altitudes reflects the adaptive strategy of plants to environmental changes

Leaf anatomical traits play key roles in plant functions and display evolutionary adaptive changes to suit the surrounding environment. To reveal the adaptive mode and mechanisms of plants in response to global warming, we analyzed leaf morphology and anatomical structures in three different species, Epilobium amurense Hausskn., Pedicularis densispica Franch., and Potentilla fulgens Wall. ex Hook., growing along an elevational gradient (3,000–4,600 m) in the Yulong Mountains. The results showed leaf length and width decreased, whereas leaf thickness increased with increasing altitude in all three species. Thickness of leaf upper epidermis, lower epidermis, palisade and spongy mesophyll, and main vein increased with rising altitude. Stomatal density in each species increased with rising elevation. These results illustrate that plants can adapt to the environmental changes that accompany high altitudes by decreasing leaf area and increasing leaf thickness, mesophyll tissue thickness, and stomatal density. Such morphological and anatomical plasticity would lead to lower transpiration rates, enhanced internal temperature and water status, and improved photosynthetic capability.     

遮阴对高山杜鹃叶片解剖和光合特性的影响

为了解高山杜鹃对光能的需求和适应性,该研究以盆栽3 a生高山杜鹃品种cv. Furnivall's Daughter为材料,探讨了遮阴对高山杜鹃叶片解剖结构和光合特性的影响。结果表明:光照强度对高山杜鹃品种cv. Furnivall's Daughter叶片的气孔密度没有显著影响,其气孔密度范围在299.70~327.22个·mm~(-2)之间,但光照对气孔开度和单个气孔器的面积影响显著,100%全光照和30%全光照处理植株分别具有最小和最大的叶片气孔开度。在处理的光强范围内,随着光强减弱,叶片厚度、栅栏组织厚度、海绵组织厚度以及上、下表皮厚度逐渐降低,有利于提高叶片的光能利用效率。100%全光照处理下,高山杜鹃叶片的光饱和点(LSP)、净光合速率(P_n)、饱和光合速率(P_(max))、气孔导度(Gs)、蒸腾速率(Tr)均较低,遮阴处理有效提高了Pn、P_(max)、G_s、T_r和光能利用效率(LUE),且30%全光照处理植株的叶片光补偿点(LCP)、暗呼吸速率(Rd)最低,而LSP、P_n、P_(max)、G_s、T_r和LUE最高。这表明高山杜鹃在云南昆明地区的最适光照条件是30%左右的全光照,在高山杜鹃的栽培及应用中,应采取适当的遮阴措施以满足其生长的最佳光照条件。     

Leaf anatomical responses to light in five tropical moraceae of different successional status

We characterized the leaf anatomical characteristics and maximum assimilation rates of five neotropical Moraceae of different genera and successional positions. Plants were grown under different light levels and transferred to high light, simulating canopy openings. Total blade thickness increased with irradiance among all species, and thicker blades were developed when plants were switched. However, blade thickness, and the extent to which it was modified, was independent of the species’ successional position and did not predict photosynthetic performance. Palisade thickness was a good predictor of maximum photosynthetic rate, but only on a species-specific basis. Overall, leaf thickening with increasing irradiance was associated more with structural than with photosynthetic changes. The early successionals Cecropia obtusifolia and Ficus insipida exhibited similarly high photosynthetic plasticity and acclimation values, but differed in their leaf anatomical traits. The late successional Poulsenia armata produced the most anatomically plastic leaves, but failed to acclimate either anatomically or photosynthetically when transferred to higher light levels.     

Acclimation responses to high light by Guazuma ulmifolia Lam. (Malvaceae) leaves at different stages of development

• The re‐composition of deforested environments requires the prior acclimation of seedlings to full sun in nurseries. Seedlings can overcome excess light either through the acclimation of pre‐existing fully expanded leaves or through the development of new leaves that are acclimated to the new light environment. Here, we compared the acclimation capacity of mature (MatL, fully expanded at the time of transfer) and newly expanded (NewL, expanded after the light shift) leaves of Guazuma ulmifolia Lam. (Malvaceae) seedlings to high light.
• The seedlings were initially grown under shade and then transferred to full sunlight. MatL and NewL were used for chlorophyll fluorescence and gas exchange analyses, pigment extraction and morpho‐anatomical measurements.
• After the transfer of seedlings to full sun, the MatL persisted and acclimated to some extent to the new light condition, since they underwent alterations in some morpho‐physiological traits and maintained a functional electron transport chain and positive net photosynthesis rate. However, long‐term exposure to high light led to chronic photoinhibition in MatL, which could be related to the limited plasticity of leaf morpho‐anatomical attributes. However, the NewL showed a high capacity to use the absorbed energy in photochemistry and dissipate excess energy harmlessly, attributes that were favoured by the high structural plasticity exhibited by these leaves.
• Both the maintenance of mature, photosynthetically active leaves and the production of new leaves with a high capacity to cope with excess energy were important for acclimation of G. ulmifolia seedlings.

     

Light response in seedlings of a temperate (<Emphasis Type="Italic">Quercus petraea</Emphasis>) and a sub-Mediterranean species (<Emphasis Type="Italic">Quercus pyrenaica</Emphasis>): contrasting ecological strategies as potential keys to regeneration performance in mixed marginal populations

In order to understand better the ecology of the temperate species Quercus petraea and the sub-Mediterranean species Quercus pyrenaica, two deciduous oaks, seedlings were raised in two contrasting light environments (SH, 5.3% full sunlight vs. HL, 70% full sunlight) for 2 years, and a subset of the SH seedlings were transferred to HL (SH–HL) in the summer of the second year. We predicted that Q. pyrenaica would behave more as a stress-tolerant species, with lower specific leaf area (SLA), allocation to leaf mass, and growth rate and less responsiveness to light in these metrics, than Q. petraea, presumed to be more competitive when resources, especially light and water, are abundant. Seedlings of Q. petraea had larger leaves with higher SLA, and exhibited a greater relative growth rate (RGR) in both SH and HL. They also displayed a higher proportion of biomass in stems (SMF), and a lower root to shoot ratio (R/S) in HL than those of Q. pyrenaica, which sprouted profusely, and had higher rates of photosynthesis (A_n) and stomatal conductance (g_wv), but lower whole-plant net assimilation rate (NAR). On exposure to a sudden increase in light, SH–HL seedlings of both species showed a short period of photoinhibition, but fully acclimated photosynthetic features within 46 days after transference; height, main stem diameter, RGR and NAR all increased at the end of the experiment compared to SH seedlings, with these increases more pronounced in Q. petraea. Observed differences in traits and responses to light confirmed a contrasting ecology at the seedling stage in Q. petraea and Q. pyrenaica in consonance with differences in their overall distribution. We discuss how the characteristics of Q. petraea may limit the availability of suitable regeneration niches to microsites of high-resource availability in marginal populations of Mediterranean climate, with potential negative consequences for its recruitment under predicted climatic changes.     

Carbon dioxide assimilation of hardwood seedlings in relation to community dynamics in central illinois

Summary Field measurements of net assimilation and respiration for seedlings of four hardwood species were made periodically over a growing season with soil moisture tension maintained between 0 and 0.75 bar. Total net assimilation per day was significantly greater for Acer saccharum than either Quercus rubra or Quercus alba and for Quercus macrocarpa as compared with Q. rubra, when measurements were made under natural shade conditions and light intensity varied from 80 to 120 ft-c. Mean light compensation points determined under canopy shade were 50.3, 53.5, 87.2, and 102.5 ft-c., respectively, for Acer saccharum, Quercus macrocarpa, Q. rubra, and Q. alba. In a 0.04-hectare canopy opening, total net assimilation per day was not significantly different between Q. rubra, Q. alba, and A. saccharum but was significantly greater for Q. macrocarpa than Q. alba and A. saccharum. Relationships between photosynthetic efficiency and successional characteristics of these species are inferred from the data.     

Stomatal and Mesophyll Limitations to Photosynthesis in One Evergreen and One Deciduous Mediterranean Oak Species

In the evergreen Quercus rotundifolia and the co-existing deciduous Q. faginea we studied the diurnal variations in photosynthetic capacity (P _max), measured as the rate of O₂ evolution at photon and CO₂ saturation, and in the rate of net CO₂ assimilation (P _N) in the field during the period of maximum photosynthetic activity. Our aim was to check the contribution of stomatal and non-stomatal limitations to the diurnal variation in photosynthesis, and to study the differences between both species. Q. faginea leaves displayed lower mass per unit area and higher nitrogen content than Q. rotundifolia leaves. The maximum stomatal conductance and P _N in the field were higher in Q. faginea than in Q rotundifolia. Also P _max of Q. faginea was higher than that of Q. rotundifolia. Both species attained in the field a high percentage of the P _max (around 82 % for Q. faginea and 73 % for Q. rotundifolia). This indicates reduced stomatal limitation of photosynthesis under favourable conditions, especially in Q. faginea. P _N underwent a sharp decrease towards mid-day in association with increase in the atmospheric vapour pressure deficit and decrease in the leaf water potential. P _max was also reduced during mid-day. This demonstrated the contribution of mesophyll limitations to the P _N in the two species under stress. The mesophyll limitation of photosynthesis seemed to be similar for both species, independently from the differences in leaf traits between them.     

Development of a photosynthesis model with an emphasis on ecological applications

Summary A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is used to describe net photosynthesis daily time courses in Prunus armeniaca. Net photosynthesis rates are calculated in response to incident light intensity, leaf temperature, air carbon dioxide concentration, and leaf diffusion resistance measured at five minute intervals. The steady-state calculations closely approximate the observed net photosynthesis rates for a broad range of weather conditions and leaf stomatal behavior.     

Growth,biomass distribution and CO2 exchange of northern hardwood seedlings in high and low light: relationships with successional status and shade tolerance

The physiology, morphology and growth of first-year Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. seedlings, which differ widely in reported successional affinity and shade tolerance, were compared in a controlled high-resource environment. Relative to late-successional, shade-tolerant Acer and Ostrya species, early-successional, shade-intolerant Betula species had high relative growth rates (RGR) and high rates of photosynthesis, nitrogen uptake and respiration when grown in high light. Fire-adapted Quercus rubra had intermediate photosynthetic rates, but had the lowest RGR and leaf area ratio and the highest root weight ratio of any species. Interspecific variation in RGR in high light was positively correlated with allocation to leaves and rates of photosynthesis and respiration, and negatively related to seed mass and leaf mass per unit area. Despite higher respiration rates, early-successional Betula papyrifera lost a lower percentage of daily photosynthetic CO₂ gain to respiration than other species in high light. A subset comprised of the three Betulaceae family members was also grown in low light. As in high light, low-light grown Betula species had higher growth rates than tolerant Ostrya virainiana. The rapid growth habit of sarly-successional species in low light was associated with a higher proportion of biomass distributed to leaves, lower leaf mass per unit area, a lower proportion of biomass in roots, and a greater height per unit stem mass. Variation in these traits is discussed in terms of reported species ecologies in a resource availability context.     

Flag Leaf Photosynthesis of Triticum aestivum and Related Diploid and Tetraploid Species

Rates of net photosynthesis of the flag leaves of 15 genotypesof wheat and related species were measured throughout theirlife, using intact leaves on plants grown in the field. At thestage when rates were maximal, they were in general highestfor the diploid species, intermediate for the tetraploidspeciesand lowest for Triticum aestivum (means of 38, 32 and 28 mgCO₂ dm^–2 h^–1 respectively). Rates were stronglynegatively correlated with leaf area, leaf width and the meanplan area per mesophyll cell and positvely correlated with stomatalfrequency and number of veins per mm of leaf width. The differencesamong species in these attributes were mainly related to ploidylevel. It was not possible to determine the relative importanceof each anatomical feature, though the changes in stomatal frequencyhad only slight effects on stomatal conductance and the observeddifferences in rates of photosynthesis were much greater thanwould be expected from those in stomatal conductance alone. There was genetic variation in rates of light dependent oxygenevolution of isolated protoplasts and intact chloroplasts butno difference attributable to ploidy. The mean rate, 91 µmolO₂ mg^–1 chlorophyll h^–1, equivalent to 3.9 mg CO₂mg^-1chlorophyll h^-1 was considerably less than the rate of photosynthesisin comparable intact leaves, which was 7.2 mg CO₂ mg^–1chlorophyll h^–1. The total above-ground dry matter yields were least for thewild diploids T. urartu and T. thauodar and the wild tetraploidT. dicoccoides, but the other wild diploids produced as muchdry matter as the hexaploids. The prospects of exploiting differences in photosynthetic ratein the breeding of higher yielding varieties are discussed. Triticum aestivum L., wheat, Aegilops spp, photosynthesis, stomatal conductance, stomatal frequency, polyploidy     

Light acclimation at the end of the growing season in two broadleaved oak species

The ability of plants to increase their net CO₂ assimilation rate in response to increased irradiance is due to morphological and physiological changes, which might be related to their shade tolerance and leaf ontogeny, but few studies have considered morphology and physiology. Two sympatric oak species (the shade-tolerant Q. petraea and the comparatively shade-intolerant Q. pyrenaica) were grown in hydroponic solution in low-light (LL) and high-light (HL) conditions. 5 months after leaf expansion under these conditions, half of the LL plants were transferred to high light (TLH). Transfer of Q. pyrenaica, from low- to high light led to photoinhibition and after 21 days in higher light there was little acclimation of the maximum rate of carboxylation (V_Cmax) or the maximum rate of electron transport (J_max). Q. pyrenaica TLH plants showed lower stomatal conductance at all times compared to plants growing in LL. Stomatal closure was the main limitation to photosynthesis after transfer in Q. pyrenaica. The increase in evaporative demand upon TLH did not affect hydraulic conductivity of Q. pyrenaica. In contrast, the more shade-tolerant Q. petraea showed a greater degree of acclimation of gas exchange in TLH than Q. pyrenaica and two weeks after transfer gas-exchange rates were as high as in LL plants. In Q. petraea, the most important changes occurred at the level of leaf biochemistry with significant increase in V_Cmax that decreased the J_max/V_Cmax ratio below values recorded in HL plants. However, this potential increase in photosynthesis was at least partially hamstrung by a decrease in internal conductance, which highlights the importance of internal conductance in acclimation to higher light in mature leaves. Neither oak species reached the photosynthetic rates of HL plants; however a trend towards leaf acclimation was observed in Q. petraea while the transfer was harmful to the leaves of Q. pyrenaica developed in the shade.     

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。     

Diffusional limitations explain the lower photosynthetic capacity of ferns as compared with angiosperms in a common garden study

Ferns are thought to have lower photosynthetic rates than angiosperms and they lack fine stomatal regulation. However, no study has directly compared photosynthesis in plants of both groups grown under optimal conditions in a common environment. We present a common garden comparison of seven angiosperms and seven ferns paired by habitat preference, with the aims of (1) confirming that ferns do have lower photosynthesis capacity than angiosperms and quantifying these differences; (2) determining the importance of diffusional versus biochemical limitations; and (3) analysing the potential implication of leaf anatomical traits in setting the photosynthesis capacity in both groups. On average, the photosynthetic rate of ferns was about half that of angiosperms, and they exhibited lower stomatal and mesophyll conductance to CO₂ (g_m), maximum velocity of carboxylation and electron transport rate. A quantitative limitation analysis revealed that stomatal and mesophyll conductances were co‐responsible for the lower photosynthesis of ferns as compared with angiosperms. However, g_m alone was the most constraining factor for photosynthesis in ferns. Consistently, leaf anatomy showed important differences between angiosperms and ferns, especially in cell wall thickness and the surface of chloroplasts exposed to intercellular air spaces.