RESUMO

Potassium (K) is an essential element, which is often supplied to horticultural crops via foliar spraying. Some studies have investigated the effect of different foliar-applied K compounds; however, most studies have focussed on crop quality and yield parameters, or were performed with isolated leaf cuticles. The aim of this study was to evaluate the rates of the foliar ion penetration and leaf surface deposition of 130 mM K sprays of compounds with markedly different point of deliquescence (POD) and efflorescence (POE) values, the rates having been previously estimated in climate chamber trials. Shoots of field-grown, commercial olive trees were sprayed with K-nitrate (KNO3), K-sulphate (K2SO4), K-chloride (KCl), K-phosphate (K3PO4), K-carbonate (K2CO3) and K-bicarbonate (KHCO3), and leaf samples were collected after 3 and 24 h. Cation and anion concentrations were determined in the leaf tissues, and in a preliminary leaf water wash for estimating surface-deposited ion concentrations. No significant leaf tissue K increments were recorded between the K sprays. Olive tissue anion concentrations showed different patterns, and a chloride (Cl-) increase was detected 3 h after the foliar KCl supply. On the other hand, the foliar K applications led to leaf nitrate changes regardless of the K source supplied. High amounts of K and accompanying ions were recovered in the washing liquid of the foliar K-supplied leaves. Some foliar K treatments increased the leaf surface concentration of sulphate and chloride, suggesting a potential effect on leaf cell anion extrusion. Hence, despite no evidence of foliar K uptake, an effect of leaf anion concentrations was observed, indicating that foliar nutrient sprays may influence leaf and leaf surface anion balance.

RESUMO

Increasing CO2 air concentration may affect wettability, anatomy and ultra-structure of leaves of Patagonian forest species, evergreen and deciduous plants potentially responding differently to such CO2 increases. In this study, we analysed the wettability, anatomy and ultra-structure of leaves of Nothofagus antarctica (deciduous) and N. betuloides (evergreen) grown under high CO2 concentrations. Leaf wettability was affected by increasing CO2, in different directions depending on species and leaf side. In both species, soluble cuticular lipid concentrations per unit leaf area raised with higher CO2 levels. Stomatal parameters (density, size of guard cells and pores) showed different responses to CO2 increasing depending on the species examined. In both species, leaf tissues showed a general trend to diminish with higher CO2 concentration. Cuticle thickness was modified with higher CO2 concentration in N. betuloides, but not in N. antarctica leaves. In both species, chloroplasts were often damaged with the increase in CO2 concentration. Our results show that several surface and internal leaf parameters can be modified in association with an increase in atmospheric CO2 concentration which may very among plant species.

Assuntos

Dióxido de Carbono , Folhas de Planta , Dióxido de Carbono/análise , Regiões Antárticas , Molhabilidade , Folhas de Planta/fisiologia , Atmosfera

RESUMO

Nutrient resorption is crucial for mineral element conservation and efficiency of forest species, but knowledge on its significance and the mechanisms involved is still limited for most species and habitats. Focusing on the harsh conditions for plant growth and survival of southern Patagonia, a field study for comparing the rate of foliar resorption of macro-, micro-nutrients, and trace elements in coexisting Nothofagus pumilio and Nothofagus antarctica forests was performed. Forests located in three contrasting productivity sites (with different soil and climatic conditions) were selected, and mature, functional versus senescent leaves of both species were collected at two different dates of the growing season. Macro- (N, P, Ca, K, S, and Mg), micronutrients (B, Cu, Fe, Mn, Zn, and Ni), and trace elements (Al, Li, Pb, Rb, Sr, Ti, and Tl) were determined in foliar tissues. The mineral element concentrations of mature and senescent leaves were used for calculating the nutrient resorption efficiency (NuR). In general, and making an average of all sites and species, macro-nutrient resorption showed a decreasing trend for N > S = K > P > Mg, being Ca the only macro-nutrient with negative values (i.e., no resorption). Resorption of the majority of the elements did not vary between species in any of the evaluated sites. Variation across sites in nutrient resorption efficiency for most macronutrients, some micronutrients, and trace elements was observed for N. antarctica, whereas N. pumilio had a similar NuR for all experimental sites. On the other hand, regardless of the site or the species, some elements were not resorbed (e.g., B, Cu, Fe, Mn, Al, and Ti). It is concluded that both Nothofagus species performed similarly concerning their nutrient conservation strategy, when coexisting in the same mixed forest. However, no evidence was gained for an increased rate of foliar NuR in association with the sites subjected to more limiting soil and climatic conditions for plant growth.

RESUMO

Plant surfaces have a considerable degree of chemical and physical variability also in relation to different environmental conditions, organs and state of development. The potential changes on plant surface properties in association with environmental variations have been little explored so far. Using two model tree species (i.e., Quercus petraea, sessile oak and Fagus sylvatica, beech) growing in 'Montejo de la Sierra Forest,' we examined various traits of the abaxial and adaxial surface of leaves of both species collected at a height of approximately 15 m (top canopy), versus 3.5-5.5 m for beech and sessile oak, lower canopy leaves. Leaf surface ultra-structure was analyzed by scanning and transmission electron microscopy, and the surface free energy and related parameter were estimated after measuring drops of 3 liquids with different degrees of polarity and apolarity. The permeability of the adaxial and abaxial surface of top and bottom canopy leaves to CaCl2 was estimated by depositing 2 drops of 3-4 µl per cm2 and comparing the concentration of Ca in leaf tissues 24 h after treatment, and also Ca and Cl concentrations in the washing liquid. Higher Ca concentrations were recorded after the application of CaCl2 drops onto the veins and adaxial blade of top canopy beech leaves, while no significant evidence for foliar Ca absorption was gained with sessile oak leaves. Surprisingly, high amounts of Cl were recovered after washing untreated, top canopy beach and sessile oak leaves with deionised water, a phenomenon which was not traced to occur on lower canopy leaves of both species. It is concluded that the surface of the two species analyzed is heterogeneous in nature and may have areas favoring the absorption of water and solutes as observed for the veins of beech leaves.