Evaluation of leaf features in forest trees: Methods,techniques, obtainable information and limits

Tree leaves are interfaces between the whole organism and the environment. Leaves display a series of attributes that are linked to specific functions (functional leaf traits—FLT) and/or show responses to biotic and abiotic stress factors (stress response traits, SRT), which can be subdivided into: (a) morphological traits; (b) chemical traits; (c) physiological traits; (d) symptoms. The analysis of FLT is a useful tool for tree species and provenance phenotyping, due to the adaptation of trees to environmental stress. Additionally, FLT can be used as response factor in long term and large spatial scales surveys of forest conditions. Despite these potential benefits of leaf traits in the assessment of ecosystem health and functioning, leaf sampling in forests is time-consuming and costly, especially in forests with a complex vertical and horizontal structure and in remote forest areas. Once a foliar sample has been collected, many different analyses can be carried out; however, analyses should be technically simple and able to be performed within one day following the leaf collection (i.e., on fresh samples), or after air-drying the leaves themselves (analysis of dried specimens). This paper reports the results of leaf sampling and foliar analyses carried out in previous research projects and revises the current state-of-the-art. The leaf traits that are easily obtainable from leaf sampling are listed, together with the operational procedures necessary for their measurement, described in a standardized protocol. Their ecological and functional relevance is discussed in relation to their potential information (as indicators of climatic stress, drought, air and soil pollution, tree light-use and competition, plant nutritional status, health and general plant stress conditions). Finally, this review provides suggestions for the elaboration and reporting of data, and proposes some guidelines to improve the effectiveness of foliar analysis in the assessment of forest ecosystem health, properties and functioning.     

Biochemical and molecular identification of Xanthomonas translucens pv. undulosa causing bacterial leaf streak of wheat in Punjab,Pakistan

Xanthomonas translucens pv. undulosa, (Xtu.), causal agent of Bacterial leaf streak (BLS) of wheat, was characterised through pathogencity, hypersensitivity, biochemical and molecular assays. Fifty symptomatic leaves of wheat were collected from eight agro-ecological zones of Punjab out of which 25 were isolated and purified. Maximum incidence and severity in Faisalabad were followed by Multan and Rahim Yar Khan. The pathogen isolated from diseased leaves was identified on the basis of colonies pattern, colour, biochemical and pathogencity test as X. translucens pv. undulosa and confirmed its pathogencity through pathogencity test. For molecular characterization, the bacterial 16S–23S rDNA spacer fragments were amplified by PCR with conserved primers (C1 and C2) and then in combination with specific primers (T1 & T2). 300?bp product amplified by C1 and C2 primer pair confirmed the presence of Xanthomonas, while specific primers T1 and T2 amplified a product of 200?bp, confirmed the presence of X. translucens pv. undulosa. This work will be quite helpful for wheat pathologist and breeders for future management strategy for this disease.     

Endogenous ascorbate restrains apoplastic peroxidase activity during sunflower leaf development

Several apoplastic enzymes have been implicated in the control of elongation growth of plant cells. Among them, peroxidases contribute to both loosening and stiffening of the cell wall. They appear to be regulated by various mechanisms, including the action of extracellular inhibitors. To obtain evidence of the role of the enzyme–inhibitor interaction during leaf development, the intercellular washing fluids from Helianthus annuus leaves of different ages were isolated using standard methods of vacuum infiltration and centrifugation. Peroxidase activities, assessed using tetramethylbenzidine as substrate, increased during leaf development, reaching a maximum value after the leaves were fully expanded. An inhibitor, chemically characterised as ascorbate, co‐localised with the enzyme in the apoplast. Moreover, there was a strong negative correlation between the action of peroxidase and the micromolar concentration of ascorbate in the apoplastic fluid. The results show that in growing leaves, the in planta ascorbate concentration is able to restrain peroxidase enzyme activity. Then, at the time of growth cessation, the loss of extracellular ascorbate relieves the inhibition on this enzyme that contributes to wall fixation.     

Different mechanisms explain feeding type-specific patterns of latitudinal variation in herbivore damage among diverse feeding types of herbivorous insects

To determine whether latitudinal variation in herbivore impact exists, we examined three major herbivorous insect feeding types (chewers, gallers, and miners) on/in leaves of Japanese beech. Herbivores were collected with litter traps deployed in forests across a latitudinal gradient of 10°. Leaf litter analyses demonstrated that chewing herbivory increased with increasing latitude of collection site. However, the densities of miners and gallers decreased with latitude. To test whether latitudinal variation in herbivore damage occurs in the absence of geographically differentiated environmental cueing (e.g., physical stresses or herbivore damage), we measured both genetically determined constitutive leaf traits and herbivore damage in a common-garden experiment. In this experiment, miner density decreased with latitude, but chewing herbivory did not vary latitudinally. Galler density was higher on trees from native provenances than on trees from unrelated provenances likely because of local adaptations. Leaf mass per unit area (LMA), tannin, and phenolics all decreased with latitude of provenance. The latitudinal variation in one constitutive leaf trait (LMA) best explained latitudinal variation in chewing herbivory. Thus, different mechanisms account for feeding type-specific patterns of latitudinal variation in herbivore damage among different herbivore feeding types.     

In vitro corm production in the saffron crocus (Crocus sativus L.)

Means to increase the reproductive capacity of Crocus sativus L., in vitro, are described. Cytokinins and auxin were found to be essential for development of bud explants. Ethylene and ethaphon pretreatments inhibited leaf development but induced corm production. Microsurgery of the apical bud combined with ethylene pretreatment increased both sprouting and corm production.     

Leaf phenology mediates provenance differences in herbivore populations on valley oaks in a common garden

1. Plants from different populations often display a variation in herbivore resistance. However, it is rarely understood what plant traits mediate such differences. 2. It was tested how leaf phenology affects herbivore populations in a 15‐year‐old common garden of valley oaks (Quercus lobata Née) with different populations and maternal parents from throughout the Q. lobata range. 3. The abundance of leaf miners (Stigmella sp. Shrank) and leaf phenology of oaks in the common garden was measured. 4. Leaf miner abundance varied among provenance locations (population), but not among maternal parents within populations. Leaf phenology varied by provenance location and maternal parent, and trees that leafed out earlier accrued higher leaf‐miner abundance. Path analysis indicated that leaf phenology was the likely driver of provenance and parental differences in resistance to leaf miners. 5. Understanding population differences is particularly important when considering transport of genotypes for ornamental or restoration purposes. The present study suggests that similarity in leaf phenology may be one factor that could be used to find genotypes with a similar herbivore resistance to local genotypes.     

Phylogeography and climatic niche evolution in live oaks (Quercus series Virentes) from the tropics to the temperate zone

Aim We investigated the phylogeography, geographical variation in leaf morphology, freezing tolerance and climatic niches of two widespread evergreen sister oak species (Quercus) in the series Virentes. Location South‐eastern USA, Mexico and Central America. Methods Nuclear microsatellites and non‐recombining nuclear and chloroplast DNA sequences were obtained from trees throughout the range of two sister lineages of live oaks, represented by Quercus virginiana in the temperate zone and Q. oleoides in the tropics. Divergence times were estimated for the two major geographical and genetic breaks. Differentiation in leaf morphology, analysed from field specimens, was compared with the molecular data. Freezing sensitivities of Q. virginiana and Q. oleoides populations were assessed in common garden experiments. Results The geographical break between Q. virginiana and Q. oleoides was associated with strong genetic differentiation of possible early Pleistocene origin and with differentiation in freezing sensitivity, climatic envelopes and leaf morphology. A second important geographical and genetic break within Q. oleoides between Costa Rica and the rest of Central America showed a mid‐Pleistocene divergence time and no differentiation in leaf morphology. Population genetic differentiation was greater but genetic diversity was lower within the temperate Q. virginiana than within the tropical Q. oleoides, and genetic breaks largely corresponded to breaks in leaf morphology. Main conclusions Two major breaks, one between Mexico and the USA at the boundary of the two species, and a more recent one within Q. oleoides between Honduras and Costa Rica, implicate climatic changes as potential causes. The latter break may be associated with the formation of the Cordillera de Guanacaste, which was followed by seasonal changes in precipitation. In the former case, an ‘out of the tropics’ scenario is hypothesized, in which the acquisition of freezing tolerance in Q. virginiana permitted colonization of and expansion in the temperate zone, while differences in climatic tolerances between the species limited secondary contact. More pronounced Pleistocene changes in climate and sea level in the south‐eastern USA relative to coastal Mexico and Central America may explain the greater population differentiation within temperate Q. virginiana and greater genetic diversity in tropical Q. oleoides. These patterns are predicted to hold for other taxa that span temperate and tropical zones of North and Central America.