Leaf Longevity Research Articles

A review of light interception in plant stands from leaf to canopy in different plant functional types and in species with varying shade tolerance

AbstractChanges in the efficiency of light interception and in the costs for light harvesting along the light gradients from the top of the plant canopy to the bottom are the major means by which efficient light harvesting is achieved in ecosystems. In the current review analysis, leaf, shoot and canopy level determinants of plant light harvesting, the light‐driven plasticity in key traits altering light harvesting, and variations among different plant functional types and between species of different shade tolerance are analyzed. In addition, plant age‐ and size‐dependent alterations in light harvesting efficiency are also examined. At the leaf level, the variations in light harvesting are driven by alterations in leaf chlorophyll content modifies the fraction of incident light harvested by given leaf area, and in leaf dry mass per unit area (MA) that determines the amount of leaf area formed with certain fraction of plant biomass in the leaves. In needle‐leaved species with complex foliage cross‐section, the degree of foliage surface exposure also depends on the leaf total‐to‐projected surface area ratio. At the shoot scale, foliage inclination angle distribution and foliage spatial aggregation are the major determinants of light harvesting, while at the canopy scale, branching frequency, foliage distribution and biomass allocation to leaves (FL) modify light harvesting significantly. FL decreases with increasing plant size from herbs to shrubs to trees due to progressively larger support costs in plant functional types with greater stature. Among trees, FL and stand leaf area index scale positively with foliage longevity. Plant traits altering light harvesting have a large potential to adjust to light availability. Chlorophyll per mass increases, while MA, foliage inclination from the horizontal and degree of spatial aggregation decrease with decreasing light availability. In addition, branching frequency decreases and canopies become flatter in lower light. All these plastic modifications greatly enhance light harvesting in low light. Species with greater shade tolerance typically form a more extensive canopy by having lower MA in deciduous species and enhanced leaf longevity in evergreens. In addition, young plants of shade tolerators commonly have less strongly aggregated foliage and flatter canopies, while in adult plants partly exposed to high light, higher shade tolerance of foliage allows the shade tolerators to maintain more leaf layers, resulting in extended crowns. Within a given plant functional type, increases in plant age and size result in increases in MA, reductions in FL and increases in foliage aggregation, thereby reducing plant leaf area index and the efficiency of light harvesting. Such dynamic modifications in plant light harvesting play a key role in stand development and productivity. Overall, the current review analysis demonstrates that a suite of chemical and architectural traits at various scales and their plasticity drive plant light harvesting efficiency. Enhanced light harvesting can be achieved by various combinations of traits, and these suites of traits vary during plant ontogeny.

The transcriptome of Populus in elevated CO2 reveals increased anthocyanin biosynthesis during delayed autumnal senescence

*The delay in autumnal senescence that has occurred in recent decades has been linked to rising temperatures. Here, we suggest that increasing atmospheric CO2 may partly account for delayed autumnal senescence and for the first time, through transcriptome analysis, identify gene expression changes associated with this delay. *Using a plantation of Populus x euramericana grown in elevated [CO2] (e[CO2]) with free-air CO2 enrichment (FACE) technology, we investigated the molecular and biochemical basis of this response. A Populus cDNA microarray was used to identify genes representing multiple biochemical pathways influenced by e[CO2] during senescence. Gene expression changes were confirmed through real-time quantitative PCR, and leaf biochemical assays. *Pathways for secondary metabolism and glycolysis were significantly up-regulated by e[CO2] during senescence, in particular, those related to anthocyanin biosynthesis. Expressed sequence tags (ESTs) representing the two most significantly up-regulated transcripts in e[CO2], LDOX (leucoanthocyanidin dioxgenase) and DFR (dihydroflavonol reductase), gave (e[CO2]/ambient CO(2) (a[CO2])) expression ratios of 39.6 and 19.3, respectively. *We showed that in e[CO2] there was increased autumnal leaf sugar accumulation and up-regulation of genes determining anthocyanin biosynthesis which, we propose, prolongs leaf longevity during natural autumnal senescence.

Auxin response factor 2 (ARF2) plays a major role in regulating auxin-mediated leaf longevity.

Auxin regulates a variety of physiological and developmental processes in plants. Although auxin acts as a suppressor of leaf senescence, its exact role in this respect has not been clearly defined, aside from circumstantial evidence. It was found here that ARF2 functions in the auxin-mediated control of Arabidopsis leaf longevity, as discovered by screening EMS mutant pools for a delayed leaf senescence phenotype. Two allelic mutations, ore14-1 and 14-2, caused a highly significant delay in all senescence parameters examined, including chlorophyll content, the photochemical efficiency of photosystem II, membrane ion leakage, and the expression of senescence-associated genes. A delay of senescence symptoms was also observed under various senescence-accelerating conditions, where detached leaves were treated with darkness, phytohormones, or oxidative stress. These results indicate that the gene defined by these mutations might be a key regulatory genetic component controlling functional leaf senescence. Map-based cloning of ORE14 revealed that it encodes ARF2, a member of the auxin response factor (ARF) protein family, which modulates early auxin-induced gene expression in plants. The ore14/arf2 mutation also conferred an increased sensitivity to exogenous auxin in hypocotyl growth inhibition, thereby demonstrating that ARF2 is a repressor of auxin signalling. Therefore, the ore14/arf2 lesion appears to cause reduced repression of auxin signalling with increased auxin sensitivity, leading to delayed senescence. Altogether, our data suggest that ARF2 positively regulates leaf senescence in Arabidopsis.

Leaf lifetime photosynthetic rate and leaf demography in whole plants of Ipomoea pes-caprae growing with a low supply of calcium, a 'non-mobile' nutrient.

The adaptive significance of leaf longevity has been established in relation to restrictive nutrients that can be retranslocated within the plant. However, the effect of deficiencies in ‘non-mobile’ nutrients on leaf lifespan and photosynthetic carbon gain is uncertain. Calcium is frequently given as an example of an essential nutrient with low phloem mobility that may alter the leaf senescence process. This study has been designed to estimate leaf lifespan, leaf production (Lp) and leaf death (Ld) rates, the age structure of leaves, and the decline in maximum photosynthetic rate (Amax) with age in plants of Ipomoea pes-caprae growing with a full supply of nutrients and with a low Ca supply. The Ca deficiency produced reductions in Lp and leaf lifespan compared with control plants. In spite of the differences in the demographic parameters between treatments in control and low-Ca plants, the percentage of leaves of a given leaf age class is maintained in such a way that the number of leaves per plant continues to increase. No relationship was found between Ca supply and Amax. However, the decline in Amax with leaf senescence was rather sudden in control plants compared with plants growing with a low Ca supply. The importance of simultaneously using the total leaf demographic census and the assimilation rate along with leaf lifespan data in order to understand the performance of whole plants under constrained conditions is discussed.

Identification of Arabidopsis stay-green mutants with a functional ethylene-response pathway

Natural or harvest-induced senescence is a major determinant factor causing crop losses. The plant hormone ethylene is a strong inducer of senescence and decreasing the ethylene response can reduce senescence, albeit often with undesirable pleiotropic effects. We took advantage of ethylene-induced leaf senescence as a tool to screen for late senescence Arabidopsis mutants that still have a functional ethylenesignalling pathway. Sixteen Arabidopsis onset of leaf death (old) mutants were selected that stayed green after treatment with ethylene. While all the mutants responded to ethylene in a triple response assay, ten mutants responded to the treatment in the same way as the wild type. These ten mutants showed limited pleiotropic effects when grown under standard growth conditions but nine mutants flowered slightly later than the wild type. Genetic characterisation of a subset of the mutants identified several independent loci controlling the leaf senescence process. The approach resulted in the isolation of several stay-green mutants with a functional ethylene response pathway. The late senescence mutants show extended leaf longevity and further research may advance the field of pre- or post-harvest senescence technology. The results, moreover, suggest that there is a correlation between senescence and floral induction. Keywords: Senescence, Arabidopsis, ethylene, mutant, shelf life

Does the invader Hieracium lepidulum have a comparative growth advantage over co-occurring plants? High leaf area and low metabolic costs as invasive traits

High leaf area has been associated statistically with plant invasiveness, but few studies have quantified metabolic costs of this trait. We have little information on whether high leaf area provides a universal growth advantage or an advantage only under limited conditions. We ask, do invasive Hieracium lepidulum and co-occurring aliens in New Zealand have higher leaf area and lower metabolic tissue costs than co-occurring native species? Invasive and co-occurring plants were grown under standard conditions across a resource availability gradient and leaf area ratio (LAR) estimated. To quantify metabolic costs of above- and below-ground plant tissues, construction costs based on heat of combustion (Wg), plant ash, and nitrogen content (Vg) were measured. Leaf longevity was measured as an index of nutrient use and metabolic efficiency. Hieracium lepidulum and invaders overall did have higher LAR than cooccurring native plant species. Tissue construction costs overlapped among invaders and native species; however, unlike in native species, tissue construction costs in both invaders were reduced at lower nutrient resource levels. This suggests that there would not be a universal growth advantage for invaders, rather there would be more pronounced growth advantage at lower nutrient resource levels. This is discussed in terms of the ecological context within which H. lepidulum and its co-occurring species are found.

Relictual distribution reaches the top: Elevation constrains fertility and leaf longevity in Juniperus thurifera

Juniperus thurifera populations are scattered throughout the western Mediterranean basin and are relictual from its Tertiary distribution due to progressive climatic warming since the last glacial period. To disentangle the factors responsible for its extremely low fertility we combined a microscale experimental design with a macroscale study. At the microscale we experimentally alleviated environmental stress by watering and fertilizing during two years a set of trees in one population. At macroscale we selected 11 populations across a geographical range and sampled them for three years. Macroscale patterns evidenced that both plant fertility and leaf longevity diminished with increasing elevation. Both microscale and macroscale illustrated the importance of water and nutrient availability on leaf growth and plant fertility: On the microscale experiments, regular supply of water and nutrients increased fruit-set by 300%. Macroscale showed that increases in resource availability (precipitation) resulted in reductions of seed abortion, although paralleled by increases in seed predation. Altogether, our results indicate that fertility is constrained both by elevation and by resource limitation. Therefore any potential lift in the elevational distribution limits will result in synergistic fertility reductions due to harder physical conditions and lower water and nutrient availability. Both will compromise future regeneration of this relictual species, although population decline might be buffered temporary thanks to longevity of adult trees.

Within-species correlations in leaf traits of three boreal plant species along a latitudinal gradient

Evergreen boreal plant species express high variability in their leaf traits. It remains controversial whether this within-species variability is constrained to the same leaf trait relationships as has been observed across species. We sampled leaves of three boreal evergreen woody species along a latitudinal gradient (from 57o56′N to 69o55′N). Leaf longevity (LL) of Pinus sylvestris L. and Vaccinium vitis-idaea L. correlated negatively with mean annual air temperature (MAT), whereas the LL of Ledum palustre L. was not affected by MAT. V. vitis-idaea and L. palustre had a negative relationship between leaf mass per area (LMA) and MAT. In P. sylvestris, the LMA–MAT relationship was positive. A negative correlation between LL and LMA was significant only for P. sylvestris. Leaf nitrogen concentration was positively related to leaf phosphorus concentration in all three species. Leaf potassium concentration was related to nitrogen concentration only in L. palustre, and to phosphorus concentration in P. sylvestris and L. palustre. Our results demonstrate that although within the studied species the variation in some of the leaf traits may have the same degree as interspecific variation, there is no such intercorrelation of leaf traits within the studied species as has been observed across species.

Size-dependent leaf area ratio in plant twigs: implication for leaf size optimization

Although many hypotheses have been proposed to explain variation in leaf size, the mechanism underlying the variation remains not fully understood. To help understand leaf size variation, the cost/benefit of twig size was analysed, since, according to Corner's rule, twig size is positively correlated with the size of appendages the twig bears. An extensive survey of twig functional traits, including twig (current-year shoots including one stem and few leaves) and leaf size (individual leaf area and mass), was conducted for 234 species from four broadleaved forests. The scaling relationship between twig mass and leaf area was determined using standardized major axis regression and phylogenetic independent comparative analyses. Leaf area was found to scale positively and allometrically with both stem and twig mass (stem mass plus leaf mass) with slopes significantly smaller than 1.0, independent of life form and habitat type. Thus, the leaf area ratio (the ratio of total leaf area to stem or twig mass) decreases with increasing twig size. Moreover, the leaf area ratio correlated negatively with individual leaf mass. The results of phylogenetic independent comparativeanalyses were consistent with the correlations. Based on the above results, a simple model for twig size optimization was constructed, from which it is postulated that large leaf size-twig size may be favoured when leaf photosynthetic capacity is high and/or when leaf life span and/or stem longevity are long. The model's predictions are consistent with leaf size variation among habitats, in which leaf size tends to be small in poor habitats with a low primary productivity. The model also explains large variations in leaf size within habitats for which leaf longevity and stem longevity serve as important determinants. The diminishing returns in the scaling of total leaf area with twig size can be explained in terms of a very simple model on twig siz

Interspecific variation of functional traits in a CAM-tree dominated sandy coastal plain

Question: Although the restinga vegetation lies adjacent to the species-rich Atlantic Rainforest, fewer species thrive due to low available resources of the sandy substrate. We asked whether there is a specific set of functional traits related to the ability to attain high dominance in a restinga dominated by a CAM photosynthesis tree. Location: Restinga of Jurubatiba National Park, north of the state of Rio de Janeiro, Brazil. Methods: We chose traits that are commonly used in large screenings, leaf mass per area (LMA), leaf longevity (LL) and leaf nitrogen concentration (LNC). We also measured the functional traits, midday leaf water potential (Ψmin), pressure-volume curves, nitrogen isotope discrimination (δ15N) and chlorophyll fluorescence. We compared species using ANOVA and ordination analysis. Results: The two most dominant species differed from subordinate species in terms of leaf succulence (SUC) and Ψmin. However, they were also significantly different from each other in LMA, SUC, leaf thickness and LNC. Ψmin and δ15N had the strongest loadings on the third ordination axis, which, despite explaining only 18.2% of total variance, was the only axis reflecting variation in species dominance. Conclusions: Despite high interspecific variation, the most common traits of the leaf economic spectrum were not directly associated with variation in species dominance. In contrast, the bulk modulus of elasticity, Ψmin and δ15N were important not only to track the connection between plant traits and environmental factors, but also between plant traits and community structure.

Capping invertase activity by its inhibitor

Since the initial biochemical study of a putative invertase inhibitor half a century ago, it has remained as a puzzle as whether such an inhibitory protein indeed limits invertase activity in vivo and, if it does, what is the developmental or physiological significance of such an interaction? Recently, we demonstrated that an invertase inhibitor, INVINH1, specifically inhibited cell wall invertase activity in tomato and Arabidopsis. Silencing INVINH1 expression in tomato released a significant amount of extra cell wall invertase activity. This posttranslational elevation of invertase activity resulted in a blockage of ABA-induced leaf senescence and an increase in fruit sugar levels and seed weight. Here, we discuss the implication of the findings and propose a model that the invertse inhibitor may act as a key modulator in controlling leaf longevity and seed development to ensure success during plant evolution. This may be achieved by optimizing carbon and nitrogen allocation and sugar signaling via interaction between invertase and inhibitor. The discoveries open up exciting new areas for exploring fundamental questions in sugar signaling, carbon allocation and plant development as well as avenues for improving crop productivity.

Leafing patterns and leaf traits of four evergreen shrubs in the Patagonian Monte, Argentina

We assessed leafing patterns (rate, timing, and duration of leafing) and leaf traits (leaf longevity, leaf mass per area and leaf-chemistry) in four co-occurring evergreen shrubs of the genus Larrea and Chuquiraga (each having two species) in the arid Patagonian Monte of Argentina. We asked whether species with leaves well-defended against water shortage (high LMA, leaf longevity, and lignin concentration, and low N concentration) have lower leaf production, duration of the leafing period, and inter-annual variation of leafing than species with the opposite traits. We observed two distinctive leafing patterns each related to one genus. Chuquiraga species produced new leaves concentrated in a massive short leafing event (5–48 days) while new leaves of Larrea species emerged gradually (128–258 days). Observed leafing patterns were consistent with simultaneous and successive leafing types previously described for woody plants. The peak of leaf production occurred earlier in Chuquiraga species (mid September) than in Larrea species (mid October–late November). Moreover, Chuquiraga species displayed leaves with the longest leaf lifespan, while leaves of Larrea species had the lowest LMA and the highest N and soluble phenolics concentrations. We also observed that only the leaf production of Larrea species increased in humid years. We concluded that co-occurring evergreen species in the Patagonian Monte displayed different leafing patterns, which were associated with some relevant leaf traits acting as plant defenses against water stress and herbivores. Differences in leafing patterns could provide evidence of ecological differentiation among coexisting species of the same life form.

Differences in the structure, growth and survival of Parasenecio yatabei ramets with contrasting water relations on the slope of a stream bank

Abstract Parasenecio yatabei (Asteraceae), a summer‐green perennial herb, is widely distributed on sloping mountain stream banks in cool‐temperate zone forests of Japan. We investigated the growth pattern, leaf longevity and leaf water relations of vegetatively independent plants (ramets) growing in two contrasting soil water conditions, that is, upper and lower stream banks (U ramets and L ramets, respectively). The objective of the present study was to clarify the physiological and morphological responses of the ramets to soil water conditions. Dry matter allocation to subterranean parts was higher in U ramets than in L ramets. The U ramet leaves survived for approximately 2 months longer than L ramet leaves. The ratio of subterranean part to aerial part dry matter was greater in U ramets than L ramets. Leaf mass per leaf area (LMA) tended to be greater in U ramets than L ramets throughout the growing season. The leaf bulk modulus of elasticity at full hydration was significantly higher in U ramets. Thus, ramet growth patterns and morphological traits varied with changing soil water conditions. The greater longevity of U ramet leaves may play a role in compensating for the reduced annual net carbon gain caused by lower photosynthetic activity. U ramets growing in environments with less water availability achieved high water‐use efficiency by a high passive water absorption capacity via a progressed root system and high productivity via longer leaf longevity with higher LMA and elasticity. Therefore, P. yatabei growing along mountain streams could have the ability to colonize the upper bank through higher survivorship based on these traits.

Species properties and recovery from disturbance: Forest herbs buried by volcanic tephra

AbstractQuestion: How do forest herb species differ from each other in their spatial and temporal dynamics during recovery from volcanic disturbance, and how are dynamics related to species traits?Location: Northeast of Mount St. Helens, Washington, USA.Methods: Following deposition of volcanic tephra in 1980, we measured herb density and cover in permanent 1‐m2 plots during 1980‐2005 in three old‐growth forests with differing tephra depths. For 26 species, we calculated the frequency of plots with residuals (individuals that survived the eruption) versus re‐establishment on the tephra, timing of establishment, turnover, influence of nearby conspecific plants, importance of three components of cover increase, and relationship of flowering frequency to succession.Results: Tephra depth affected species behavior. Deep tephra produced fewer residuals, a greater increase in shoot size, and more shoot turnover; favored species that established late; and allowed establishment of early seral herbs. Nearby presence of conspecifics increased permanence of first establishment and rate of plot occupancy. Most species spread significantly in deep tephra but not in shallow tephra. Among species, frequency of flowering increased with fewer residuals, later establishment, and higher turnover. Species behavior seldom differed among growth forms based on leaf longevity and vegetative spread.Conclusion: Population dynamics at the small‐plot scale differed from those of the entire population. The timing and permanency of establishment and mechanism of expansion differed among species and with tephra depth. There was some consistency among species with similar habitat breadth and degree of flowering, but little consistency associated with the usual growth form classification.

Controls on declining carbon balance with leaf age among 10 woody species in Australian woodland: do leaves have zero daily net carbon balances when they die?

* Here, we evaluated how increased shading and declining net photosynthetic capacity regulate the decline in net carbon balance with increasing leaf age for 10 Australian woodland species. We also asked whether leaves at the age of their mean life-span have carbon balances that are positive, zero or negative. * The net carbon balances of 2307 leaves on 53 branches of the 10 species were estimated. We assessed three-dimensional architecture, canopy openness, photosynthetic light response functions and dark respiration rate across leaf age sequences on all branches. We used YPLANT to estimate light interception and to model carbon balance along the leaf age sequences. * As leaf age increased to the mean life-span, increasing shading and declining photosynthetic capacity each separately reduced daytime carbon gain by approximately 39% on average across species. Together, they reduced daytime carbon gain by 64% on average across species. * At the age of their mean life-span, almost all leaves had positive daytime carbon balances. These per leaf carbon surpluses were of a similar magnitude to the estimated whole-plant respiratory costs per leaf. Thus, the results suggest that a whole-plant economic framework, including respiratory costs, may be useful in assessing controls on leaf longevity.

Distribution and evolutionary trends of photoprotective isoprenoids (xanthophylls and tocopherols) within the plant kingdom

The earliest land photosynthesis would have increased the risk of photo-oxidations and the demand of anti-oxidative protection. In this work, we aimed to determine the evolutionary trends in photoprotection across a wide representation of the plant kingdom and to verify whether the non-ubiquitous lutein-epoxide (Lx) cycle is a polyphyletic or an ancient character. Carotenoids and alpha-tocopherol (alpha-toc) were analysed by HPLC in 266 species. Phylogenetic analyses of the presence of photoprotective compounds and zeaxanthin-epoxidase (ZE) sequences were performed. Violaxanthin-cycle pigments (VAZ) and alpha-toc were taxonomically ubiquitous. Ancient groups showed higher contents of VAZ than vascular plants, while alpha-toc showed the opposite pattern. Lutein-epoxide was present in 45% of the species. It showed a remarkable variation across groups but with a clear increasing trend from algae to basal angiosperms. Lutein-epoxide was also related to woody trait and leaf longevity. No correlation between the presence of Lx and recurrent mutations in ZE sequences, including the duplications, was found. Thus, there is an evolutionary trend to increase the content of alpha-toc and to decrease the total amount of VAZ pigments. Absence of Lx in algae discards an ancestral origin. Present results are also inconsistent with a polyphyletic origin of Lx in angiosperms.

Biomass and aboveground net primary production in a subtropical mangrove stand of Kandelia obovata (S., L.) Yong at Manko Wetland, Okinawa, Japan

Biomass and aboveground net primary production (ANPP) in a monospecific pioneer stand of a mangrove Kandelia obovata (S., L.) Yong were quantified. The estimated biomasses in leaves, branches, stems, roots, aboveground and total were 5.61 (3.68%), 28.8 (18.9%), 46.1 (30.2%), 71.8 (47.2%), 80.5 (52.8%) and 152 Mg ha−1 (100%), respectively. Stem phytomass increment per tree was estimated using allometric relationships and stem analysis. Stem volume without bark of harvested trees showed a strong allometric relationship with D0.12H (D0.1, diameter at a height of one-tenth of tree height H) (R2 = 0.924). Annual stem volume increment per tree showed a strong allometric relationship with D0.12H (R2 = 0.860). Litterfall rate ranges from 3.87 to 56.1 kg ha−1 day−1 for leaves and 0.177 to 46.2 kg ha−1 day−1 for branches. Seasonal changes of litterfall rate were observed, which showed a peak during wet season (August–September). Total annual litterfall was estimated as 10.6 Mg ha−1 year−1, in which 68.2% was contributed by the leaves. The ANPP in the K. obovata stand was 29.9–32.1 Mg ha−1 year−1, which is ca. 2.8–3.0 times of annual litterfall. The growth efficiency (aboveground biomass increment/LAI) was 5.35–5.98 Mg ha−1 year−1. The low leaf longevity (9.3 months) and high growth efficiency of K. obovata makes it a highly productive mangrove species.

Growth, crown architecture and leaf dynamics of saplings of five mangrove tree species in Ranong, Thailand

We investigated the regeneration pattern of mangrove forests, considering the corre- spondence between growth strategies (i.e. sapling growth, crown architecture, leaf dynamics) of 5 canopy-dominant species and the disturbance regime in Ranong, Thailand. Individual canopy gap size and percent gap area were greater in the Sonneratia alba-Avicennia alba (SA) zone, which is located on the most seaward fringe, than in the other inland zones. In canopy gaps, the seaward species S. alba and A. alba showed a higher relative height growth rate than the inland species Rhizophora apiculata, Bruguiera gymnorhiza and Xylocarpus granatum. Under closed canopies, the seaward species showed greater mortality, presumably due to their low shade tolerance, while the inland species demonstrated a net growth in spite of the dark conditions. Leaf longevity of sunlit saplings increased from seaward to inland species. The 2 seaward species had well-branched, slen- der and deeper crowns, while R. apiculata and B. gymnorhiza had wider and flatter crowns, and X. granatum had less-branched, smaller crowns. Phenotypic traits were correlated with each species' growth strategy (potential growth rate and shade tolerance), which corresponded to the disturbance regime in each vegetation zone. Many large gaps may enhance the abundance of S. alba and A. alba in the SA zone, and a few small gaps may prevent establishment and growth of light-demanding species in the inland zones. Accordingly, the correspondence of disturbance regime and growth strategies of canopy-dominant species provides an advantage for successful regeneration, and may contribute to the maintenance of the present species composition in each vegetation zone.

Ontogenetic changes in leaf phenology of two co‐occurring Mediterranean oaks differing in leaf life span

AbstractLarge differences in leaf physiology and morphology between ontogenetic stages of a single woody species have often been observed. Far less attention, however, has been devoted to studying the ontogenetic changes observed in leaf phenology patterns, despite the relevance of leaf phenology in determining the leaf carbon balance and leaf and plant mortality. Leaf emergence patterns and leaf longevity were studied in the saplings and mature trees of the evergreen Quercus ilex and the deciduous Quercus faginea. Our aim here was to analyze and interpret the possible tree‐age related differences in these leaf traits. Unlike the adults, in which only one flush of leaf growth was observed, several leaf cohorts were produced within each year in the saplings. Sapling leaves showed a lower mean duration than those of the adults. However, Q. faginea saplings exhibited large plasticity in leaf longevity, which was not seen in the case of Q. ilex. The differences in leaf emergence patterns and in leaf longevity between growth stages seemed to be related to differences in resource availability for leaf production and in leaf mass per unit area, respectively. We propose that the sequential leaf development in saplings may be an important mechanism enabling tree species to cope with resource limitation in the early stages of life.

SPRAYING OF SUCROSE ON THE GREENHOUSE-GROWN ROSE AND ITS EFFECTS ON THE VASE LIFE OF THE CUT FLOWERS CV. ALEXANDER

SPRAYING OF SUCROSE ON THE GREENHOUSE-GROWN ROSE AND ITS EFFECTS ON THE VASE LIFE OF THE CUT FLOWERS CV. ALEXANDER