Influence of plant maturity, shoot reproduction and sex on vegetative growth in the dioecious plant Urtica dioica

Background and Aims

Stinging nettle (Urtica dioica) is a herbaceous, dioecious perennial that is widely distributed around the world, reproduces both sexually and asexually, and is characterized by rapid growth. This work was aimed at evaluating the effects of plant maturity, shoot reproduction and sex on the growth of leaves and shoots.

Methods

Growth rates of apical shoots, together with foliar levels of phytohormones (cytokinins, auxins, absicisic acid, jasmonic acid and salicylic acid) and other indicators of leaf physiology (water contents, photosynthetic pigments, α-tocopherol and F_v/F_m ratios) were measured in juvenile and mature plants, with a distinction made between reproductive and non-reproductive shoots in both males and females. Vegetative growth rates were not only evaluated in field-grown plants, but also in cuttings obtained from these plants. All measurements were performed during an active vegetative growth phase in autumn, a few months after mature plants reproduced during spring and summer.

Key Results

Vegetative growth rates in mature plants were drastically reduced compared with juvenile ones (48 % and 78 % for number of leaves and leaf biomass produced per day, respectively), which was associated with a loss of photosynthetic pigments (up to 24 % and 48 % for chlorophylls and carotenoids, respectively) and increases of α-tocopherol (up to 2·7-fold), while endogenous levels of phytohormones did not differ between mature and juvenile plants. Reductions in vegetative growth were particularly evident in reproductive shoots of mature plants, and occurred similarly in both males and females.

Conclusions

It is concluded that (a) plant maturity reduces vegetative growth in U. dioica, (b) effects of plant maturity are evident both in reproductive and non-reproductive shoots, but particularly in the former, and (c) these changes occur similarly in both male and female plants.     

Diurnal changes in photosystem II photochemistry, photoprotective compounds and stress-related phytohormones in the CAM plant, Aptenia cordifolia

Acclimation of photosynthetic light reactions to daily changes in solar radiation requires adjustments in photosystem II photochemistry and may be affected by environmental stresses, such as drought. In this study, we examined the effects of a short-term, severe water deficit on diurnal variations in photosystem II photochemistry, photoprotective compounds (tocopherols and carotenoids, including the xanthophyll cycle) and stress-related phytohormones (abscisic acid and salicylic acid) in the CAM plant, Aptenia cordifolia L. f. Schwantes. Violaxanthin was rapidly converted to zeaxanthin under high light, the de-epoxidation state of the xanthophyll cycle reaching maximum levels of 0.95 at midday in irrigated plants. Under a higher photoprotective demand caused by water deficit, plants showed significant increases in abscisic acid and γ-tocopherol levels, which were followed by decreases in β-carotene and the F_v/F_m ratio at later stages of stress. Decreases in this ratio below 0.70 correlated with sustained increases in the de-epoxidation state of the xanthophyll cycle, which kept above 0.90 at night after 15 days of water deficit. In contrast to abscisic acid, salicylic acid levels kept constant under water deficit and showed a sharp decrease during the day both under irrigated and water stress conditions. We conclude that the CAM plant, A. cordifolia showed several strategies of acclimation to short-term water deficit, including abscisic acid and γ-tocopherol accumulation, as well as sustained increases in the de-epoxidation state of the xanthophyll cycle, which was tightly coupled to daily variations in photosystem II photochemistry. The differential accumulation of tocopherol homologues under water deficit and the diurnal fluctuations of salicylic acid levels in this CAM plant will also be discussed.     

Age-dependent changes in the functions and compositions of photosynthetic complexes in the thylakoid membranes of Arabidopsis thaliana

Photosynthetic complexes in the thylakoid membrane of plant leaves primarily function as energy-harvesting machinery during the growth period. However, leaves undergo developmental and functional transitions along aging and, at the senescence stage, these complexes become major sources for nutrients to be remobilized to other organs such as developing seeds. Here, we investigated age-dependent changes in the functions and compositions of photosynthetic complexes during natural leaf senescence in Arabidopsis thaliana. We found that Chl a/b ratios decreased during the natural leaf senescence along with decrease of the total chlorophyll content. The photosynthetic parameters measured by the chlorophyll fluorescence, photochemical efficiency (F _v/F _m) of photosystem II, non-photochemical quenching, and the electron transfer rate, showed a differential decline in the senescing part of the leaves. The CO₂ assimilation rate and the activity of PSI activity measured from whole senescing leaves remained relatively intact until 28 days of leaf age but declined sharply thereafter. Examination of the behaviors of the individual components in the photosynthetic complex showed that the components on the whole are decreased, but again showed differential decline during leaf senescence. Notably, D1, a PSII reaction center protein, was almost not present but PsaA/B, a PSI reaction center protein is still remained at the senescence stage. Taken together, our results indicate that the compositions and structures of the photosynthetic complexes are differentially utilized at different stages of leaf, but the most dramatic change was observed at the senescence stage, possibly to comply with the physiological states of the senescence process.     

The role of phytohormone signaling in ozone-induced cell death in plants

Ozone is the main photochemical oxidant that causes leaf damage in many plant species, and can thereby significantly decrease the productivity of crops and forests. When ozone is incorporated into plants, it produces reactive oxygen species (ROS), such as superoxide radicals and hydrogen peroxide. These ROS induce the synthesis of several plant hormones, such as ethylene, salicylic acid, and jasmonic acid. These phytohormones are required for plant growth, development, and defense responses, and regulate the extent of leaf injury in ozone-fumigated plants. Recently, responses to ozone have been studied using genetically modified plants and mutants with altered hormone levels or signaling pathways. These researches have clarified the roles of phytohormones and the complexity of their signaling pathways. The present paper reviews the biosynthesis of the phytohormones ethylene, salicylic acid, and jasmonic acid, their roles in plant responses to ozone, and multiple interactions between these phytohormones in ozone-exposed plants.Key words: cross-talk, ethylene, jasmonic acid, ozone, phytohormones, programmed cell death, salicylic acid, signaling pathways     

苗期玉米叶片碳氮平衡与干旱诱导的叶片衰老之关系

为了探究干旱诱导的碳氮平衡破坏与干旱诱导的叶片衰老之间的关系,该实验以8个在干旱胁迫下叶片衰老进程有明显差异的玉米品种为实验材料,采用PEG模拟干旱处理,通过测定光合速率、叶绿素含量和叶绿素荧光参数等叶片衰老指标以及非结构性碳水化合物(可溶性糖、淀粉)和全氮含量等变化,分析玉米中干旱诱导的叶片衰老与叶片中碳氮平衡(碳氮比)之间的关系。结果显示:(1)干旱胁迫下,8个玉米品种叶片净光合速率受到严重抑制,Fv/Fm大幅下降,叶绿素含量显著降低,说明干旱诱导了玉米叶片的衰老;(2)干旱诱导玉米叶片衰老的同时,8个玉米品种的叶片中可溶性糖含量显著升高,淀粉含量小幅上升,全氮含量大幅降低,碳氮比显著升高,碳氮平衡遭到了破坏;(3)8个玉米品种叶片的叶绿素含量与非结构性碳水化合物含量以及碳氮比呈极显著负相关关系,与全氮含量呈极显著正相关关系。因此,碳氮代谢与干旱诱导的叶片衰老紧密联系,碳氮平衡可能参与了干旱诱导的叶片衰老调控。     

Radiation Use Efficiency,Chlorophyll Fluorescence,and Reflectance Indices Associated with Ontogenic Changes in Water-Limited Chenopodium quinoa Leaves

Net photosynthetic rate, radiation use efficiency, chlorophyll (Chl) fluorescence, photochemical reflectance index (PRI), and leaf water potential were measured during a 25-d period of progressive water deficit in quinoa plants grown in a glasshouse in order to examine effects of water stress and ontogeny. All physiological parameters except F_v/F_m were sensitive to water stress. Ontogenic variations did not exist in F_v/F_m and leaf water potential, and were moderate to high in the other parameters. The complete recovery of photosynthetic parameters after re-irrigation was related with the stability in F_v/F_m. PRI showed significant correlation with predawn leaf water potential, F_m, and midday F_v/F_m. Thus PRI and Chl fluorescence may help in assessing physiological changes in quinoa plants across different developmental stages and water status.     

Influence of phytohormones on morphology and chlorophyll a fluorescence parameters in embryos of Fucus vesiculosus L. (Phaeophyceae)

While a variety of plant hormones from brown algae were described, there were few studies that examined the combined effects of these hormones on morphogenesis and photosynthetic physiology in developing fucoid embryos. We evaluated the effects of phytohormones to determine the extent, to which responses were similar to those of terrestrial plants. Kinetin, IAA, ABA, GA₃, and kinetin + IAA were added to seawater at a physiological concentration (1 mg/L), and embryos of Fucus vesiculosus L. were grown for 10 days. Photosynthetic activity of single embryos or embryo cells were characterized using the following fluorescence parameters: minimum fluorescence yield (F ₀), maximum quantum yield (F _v/F _m), relative maximum rate of electron transfer to photosystem II under saturation irradiances (rETR_max), photosynthetic efficiency under non-saturating irradiances (αETR) and saturation irradiance (E _k). In addition, embryo length and diameter and apical hair length and number were determined. Morphological changes associated with hormone treatments included an increase in the embryo length in the presence of IAA, an increase in the embryo diameter in the presence of IAA, kinetin, and kinetin + IAA, an increase in the maximum hair length and number in the presence of kinetin + IAA, and a decrease in the hair length and number in the presence of ABA. With respect to fluorescence parameters, significant effects of phytohormones included an increase in the F ₀ and F _v/F _m at kinetin treatment, a synergistic effect of kinetin + IAA on F _v/F _m, rETR_max, and αETR, a promotion of F _v/F _m by GA, and a decrease of the parameters by ABA. These results are consistent with the data on responses of land plants to the same hormones and suggest that brown algae have evolved regulatory mechanisms for morphogenesis and photosynthetic regulation similar to plants.     

Diurnal and seasonal variations in photosynthetic and morphological traits of the tree ferns Dicksonia antarctica (Dicksoniaceae) and Cyathea australis (Cyatheaceae) in wet sclerophyll forests of Australia

Steady state and dynamic responses of two tree fern species of contrasting origins, Dicksonia antarctica (of Gondwanan origin) and Cyathea australis (Pan-tropical), were studied over two consecutive years under field conditions in a wet sclerophyll forest of south-east Australia. Irrespective of their different origins, there were no significant differences in photosynthetic performance between the two species. Growth irradiance and leaf temperature, but not plant water status, was significantly related to photosynthetic and morphological traits. At a common leaf temperature, maximum light-use efficiency of photosystem II (F_v/F_m) was significantly lower in winter than in summer, suggesting some limitation to PSII efficiency potentially associated with cold winter mornings. Both species displayed seasonal acclimation in a number of measured photosynthetic parameters and frond traits (i.e. F_v/F_m, A_sat, g_s, N_A, total chlorophyll, SLA). Acclimation of stomatal density to spatial variation in growth irradiance seemed limited in both species, although stomatal pattern differed between species. Because there were no significant differences between the two species in photosynthetic parameters, both species can be described by common carbon gain and water use models at the leaf scale.     

Photosynthetic response to water stress and changes in metabolites in <Emphasis Type="Italic">Jasminum sambac</Emphasis>

Gas exchange, chlorophyll (Chl) fluorescence, and contents of some metabolites in two genotypes of jasmine (Jasminum sambac), single petal (SP) and double petal (DP) one, were analyzed during dehydration and re-hydration. Water stress significantly decreased net photosynthetic rate, stomatal conductance, and maximum photochemical efficiency (F_v/F_m) in both jasmine genotypes, but increased minimum fluorescence (F₀) only in DP-jasmine. Water stress also decreased starch content, while increased contents of total soluble sugars and proline in leaves of both genotypes. SP-jasmine demonstrated higher drought tolerance as evidenced by maintaining higher gas exchange and photochemical efficiency and lower alteration of metabolites than DP-jasmine. Recovery analysis revealed that drought-induced injury in photosynthetic machinery in jasmine plants was reversible. DP-jasmine exhibited a slow recovery of drought-induced impairment in photosynthetic activity and associated metabolites, suggesting that this genotype had lower capacity to adapt to water limited condition. Higher yield stability of SP-than that of DP-jasmine under rain-fed condition finally confirmed higher drought tolerance of SP-jasmine.     

Changes in photosynthetic capacity and polypeptide patterns during natural senescence and rejuvenation of <Emphasis Type="Italic">Cucurbita pepo</Emphasis> L. (zucchini) cotyledons

Natural senescence of Cucurbita pepo (zucchini) cotyledons was accompanied by a gradual degradation of reserve proteins (globulins) and an intensive decrease in the content of both large subunit (LSU) and small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The net photosynthetic rate, the primary photochemical activity of PSII, estimated by the variable fluorescence (F_v)/maximal fluorescence (F_m) ratio (F_v/F_m) and the actual quantum yield of PSII electron transport in the light-adapted state (ΦPSII) also progressively decreased during natural senescence. In contrast, the fraction of the absorbed light energy, which is not used for photochemistry (LNU) increased with progression of senescence. The decline in the photosynthetic rate started earlier in ontogenesis compared with the down-regulation of the functional activity of PSII, thus suggesting the existence of protective mechanisms which maintain higher efficiency of the photochemical electron transport reactions of photosynthesis compared with the dark reactions of the Calvin cycle during earlier stages of natural senescence. Decapitation of the epicotyl above the senescing cotyledons resulted in full recovery of the polypeptide profile in the rejuvenated cotyledons. In addition, the photosynthetic rate increased reaching values that exceeded those measured in juvenile cotyledons. The photochemical efficiency of PSII also gradually recovered, although it did not reach the maximum values measured in the presenescent cotyledons.     

Changes in Chlorophyll Fluorescence in Maize Plants with Imposed Rapid Dehydration at Different Leaf Ages

A comparison of the effects of a rapidly imposed water deficit with different leaf ages on chlorophyll a fluorescence and gas exchange was performed in maize (Zea mays L.) plants. The relationships between photosynthesis and leaf relative turgidity (RT) and ion leakage were further investigated. Leaf dehydration substantially decreased net photosynthetic rate (A) and stomatal conductance (G _s), particularly for older leaves. With dehydration time, F _v /F _m maintained a relatively stable level for youngest leaves but significantly decreased for the older leaves. The electron transport rate (ETR) sharply decreased with intensifying dehydration and remained at lower levels during continuous dehydration. The photochemical quenching of variable chlorophyll fluorescence (q _P) gradually decreased with dehydration intensity for the older leaves but increased for the youngest leaves, whereas dehydration did not affect the nonphotochemical chlorophyll fluorescence quenching (NPQ) for the youngest leaves but remarkably decreased it for the older leaves. The leaf RT was significantly and positively correlated with its F _v /F _m, ETR, and q _P, and the leaf ion leakage was significantly and negatively correlated with F _v /F _m and NPQ. Our results suggest that the photosynthetic systems of young and old leaves decline at different rates when exposed to rapid dehydration.     

Photosynthesis and protective mechanisms during ageing in transgenic tobacco leaves with over-expressed cytokinin oxidase/dehydrogenase and thus lowered cytokinin content

The content of cytokinins (CKs), the plant inhibitors of the final phase of plant development, senescence, is effectively controlled by irreversible degradation catalysed by cytokinin oxidase/dehydrogenase (CKX). In transgenic tobacco, denoted as AtCKX, with over-expressed CKX causing lowered CK content, we investigated changes in the time courses of chlorophyll (Chl) and xanthophyll (violaxanthin, antheraxanthin, zeaxanthin, neoxanthin, and lutein) contents. We also determined parameters of slow Chl fluorescence kinetics such as minimum Chl fluorescence yield in the darkadapted state F₀, maximum quantum yield of PS2 photochemistry (F_v/F_m), maximum ratio of quantum yields of photochemical and concurrent non-photochemical processes in photosystem 2 (PS2), F_v/F₀, non-photochemical quenching (NPQ), and effective quantum yield of photochemical energy conversion in PS2 (Φ₂). We used three different developmental leaf stages, old, mature, and young, and compared this with time courses of these characteristics in leaves with natural CK levels. The parameters F_v/F_m, F_v/F₀, and Φ₂ were unchanged during ageing in AtCKX plants in contrast to control ones where a significant decrease in old leaves was found. In control plants F₀ increased during ageing, but in the oldest leaf a considerable decrease was observed. This could indicate progressive damage to PS2 reaction centres and then detachment and rapid degradation of Chl. This is in agreement with time course of Chl content. NPQ decreased with age and was similar in both plant types. We observed a decline of xanthophyll contents in the oldest leaves in both plant types, but the contents were enhanced in AtCKX compared to control plants, especially of neoxanthin. The higher xanthophyll contents in the transgenic plants contribute to a better photoprotection and the fluorescence parameters indicated that photosynthetic apparatus was in better condition compared to control and it consequently postponed the onset of leaf senescence.     

Effect of gamma radiation on mutant induction of <Emphasis Type="Italic">Fagopyrum dibotrys</Emphasis> Hara

Agronomic traits, photosynthetic pigments, gas exchange, and chlorophyll (Chl) fluorescence parameters of red stem buckwheat (Fagopyrum dibotrys Hara) mutants induced by γ-radiation were compared with green control at seedling stage. Plant height, number of first-class branches, and rhizome biomass were inhibited significantly (p<0.01). Chl a, Chl b, and Chl a+b contents decreased with elevated dose of γ-rays, while increasing carotenoid content indicated that buckwheat was capable of adjusting to the radiation damage. Decrease in net photosynthetic rate was the result of both stomatal and non-stomatal limitations. Fluorescence parameters, such as F₀, F_m, F_v/F_m, F_v/F₀, Φ_PS2, electron transport rate, and photochemical quenching declined significantly (p<0.01) as compared with control due to photoinhibition, while non-photochemical quenching increased to enhance thermal dissipation. Lower parameters implied that leaf tissue was damaged significantly by high dose of γ-radiation and therefore leaf senescence was accelerated.     

Bioregulators protected photosynthetic machinery by inducing expression of photorespiratory genes under water stress in chickpea

Globally, water deficit is one of the major constraints in chickpea (Cicer arietinum L.) production due to substantial reduction in photosynthesis. Photorespiration often enhances under stress thereby protecting the photosynthetic apparatus from photoinhibition. Application of bioregulators is an alternative to counter adverse effects of water stress. Thus, in order to analyze the role of bioregulators in protecting the photosynthetic machinery under water stress, we performed an experiment with two contrasting chickpea varieties, i.e., Pusa 362 (Desi type) and Pusa 1108 (Kabuli type). Water deficit stress was imposed at the vegetative stage by withholding water. Just prior to exposure to water stress, plants were pretreated with thiourea (1,000 mg L^?1), benzyladenine (40 mg L^?1), and thidiazuron (10 mg L^?1). Imposed water deficit decreased relative water content (RWC), photosynthetic rate (P_N), quantum efficiency of PSII (F_v/F_m), and enhanced lipid peroxidation (LPO). However, bioregulator application maintained higher RWC, P_N, F_v/F_m, and lowered LPO under water stress. Expression of Rubisco large subunit gene (RbcL) was low under water stress both in the Kabuli and Desi type. However, bioregulators strongly induced its expression. Although poor expression of two important photorespiratory genes, i.e., glycolate oxidase and glycine decarboxylase H subunit, was observed in Desi chickpea under imposed stress, bioregulators in general and cytokinins in particular strongly induced their expression. This depicts that the application of bioregulators protected the photosynthetic machinery by inducing the expression of RbcL and photorespiratory genes during water deficit stress.     

Application of phytohormones during seed hydropriming and heat shock treatment on sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.) chilling resistance and changes in soluble carbohydrates

The objective of this study was to analyze the mechanism of some physiological processes accompanying acquisition of sunflower (Helianthus annuus L.) chilling resistance due to seeds hydropriming in the presence of salicylic acid, jasmonic acid, 24-epibrassinolide followed exposition of seeds to short-term heat shock treatment. The seeds were hydroprimed at 25 °C in limited amounts of water or solution of salicylic or jasmonic acid at 10^?2, 10^?3 and 10^?4 M concentration, 24-epibrassinolide at 10^?6, 10^?8 and 10^?10 M concentration. The seeds were incubated for 2 days, subjected to short-term heat shock (45 °C, 2 h) and chilled for 21 days at 0 °C. Sunflower chilling susceptibility and physiological responses were evaluated according to the inhibition of radicle growth, the inhibition of the number of lateral roots formation, the activity of catalase and changes in soluble carbohydrates in seedlings developing for 72 h at 25 °C. Hydropriming and short-term heat shock application explicitly reduced inhibition of roots as well as lateral roots development by allowing the germinating seeds to recover from the growth-inhibiting effects of chilling. Seeds hydropriming in solutions containing salicylic acid, jasmonic acid and 24-epibrassinolide followed heat shock treatment additionally promoted the activity of catalase and sugars metabolism, which stimulated seedlings development and alleviated the decrease of F _v/F _m caused by chilling conditions. These beneficial effects contributed to increased resistance of sunflower seedlings to chilling stress. The present study demonstrated that the most profitable effect on reducing negative effect of chilling may be achieved by short-term heat shock applied during hydropriming in water supplemented with 24-epiBL (10^?8 and 10^?10 M) or salicylic acid (10^?3 and 10^?4 M).     

The geometry of light interception by shoots of Heteromeles arbutifolia: morphological and physiological consequences for individual leaves

The influence of leaf orientation and position within shoots on individual leaf light environments, carbon gain, and susceptibility to photoinhibition was studied in the California chaparral shrub Heteromeles arbutifolia with measurements of gas exchange and chlorophyll fluorescence, and by application of a three-dimensional canopy architecture model. Simulations of light absorption and photosynthesis revealed a complex pattern of leaf light environments and resulting leaf carbon gain within the shoots. Upper, south-facing leaves were potentially the most productive because they intercepted greater daily photon flux density (PFD) than leaves of any other orientation. North-facing leaves intercepted less PFD but of this, more was received on the abaxial surface because of the steep leaf angles. Leaves differed in their response to abaxial versus adaxial illumination depending on their orientation. While most had lower photosynthetic rates when illuminated on their abaxial as compared to adaxial surface, the photosynthetic rates of north-facing leaves were independent of the surface of illumination. Because of the increasing self-shading, there were strong decreases in absorbed PFD and daily carbon gain in the basipetal direction. Leaf nitrogen per unit mass also decreased in the basipetal direction but on a per unit area basis was nearly constant along the shoot. The decrease in leaf N per unit mass was accounted for by an increase in leaf mass per unit area (LMA) rather than by movement of N from older to younger leaves during shoot growth. The increased LMA of older lower leaves may have contributed directly to their lower photosynthetic capacities by increasing the limitations to diffusion of CO₂ within the leaf to the sites of carboxylation. There was no evidence for sun/shade acclimation along the shoot. Upper leaves and especially south-facing upper leaves had a potential risk for photoinhibition as demonstrated by the high PFDs received and the diurnal decreases in the fluorescence ratio F _v/F _m. Predawn F _v/F _m ratios remained high (>0.8) indicating that when in their normal orientations leaves sustained no photoinhibition. Reorientation of the leaves to horizontal induced a strong sustained decrease in F _v/F _m and CO₂ exchange that slowly recovered over the next 10–15?days. If leaves were also inverted so that the abaxial surface received the increased PFDs, then the reduction in F _v/F _m and CO₂ assimilation was much greater with no evidence for recovery. The heterogeneity of responses was due to a combination of differences between leaves of different orientation, differences between responses on their abaxial versus adaxial surfaces, and differences along the shoot due to leaf age and self-shading effects.     

Salt tolerance of Hibiscus hamabo seedlings: a candidate halophyte for reclamation areas

In order to evaluate the salinity tolerance of Hibiscus hamabo Siebold & Zuccarini (Malvaceae), a candidate halophyte for reclamation areas, we analyze the effects of NaCl concentration, ranging from 0 to 500?mM, on the morphological, photosynthetic and chlorophyll fluorescent traits of this species. The optimal concentration for the germination of H. hamabo was 25?mM NaCl, and the optimal concentration for the survival and growth of H. hamabo ranged from 5 to 10?mM NaCl. Growth traits of H. hamabo at 25?mM, including the plant height, canopy diameter, number of leaves and width of the largest leaf, showed no statistical differences from the control. Net photosynthetic rate, stomatal conduction, light utilization efficiency, water utilization efficiency, maximal photosynthetic rate, light saturation point and chlorophyll content were the highest at 7.5?mM NaCl. F _v/F _m and F _v/F ₀ at 5 and 7.5?mM were significantly higher than the others, while F ₀ was significantly lower. F _m and F _v at NaCl concentrations ranging from 2.5 to 10?mM were significantly higher than the others. Pearson correlation analysis showed that the chlorophyll content, maximal photosynthetic rate and light saturation point were significantly positively correlated with the number of leaves, while F ₀ was significantly negatively correlated with the width of the largest leaf. Light compensation point was significantly negatively correlated with plant height, leaf number, width of the largest leaf and canopy diameter, and might be a good indicator for the salt tolerance of H. hamabo.