M. Soledad Jiménez

Laurel forests in Tenerife, Canary Islands: the annual course of sap flow in Laurus trees and stand

Abstract Sap flow rate was continuously measured in six trees of Laurus azorica at the experimental site of laurel forest in Agua Garcia mountains, Tenerife, Canary Islands, over 1 year from June 1993 to May 1994. Sample trees were of different sizes and covered the whole range of species. A sigmoid-like relationship based on basal area was applied to scale up the transpiration data from sample trees to the whole stand. Maximum transpiration for the stand was 7 mm day−1. There was strong competition among the medium-sized trees in the high-density stand. The annual course of transpiration was very variable, owing to weather conditions, and was mainly controlled by the evaporative conditions. Contrasting with conditions in colder regions of the world with pronounced seasons, relatively high transpiration persisted over the mild winter. The annual total of transpiration was thus significantly higher, amounting to 636 mm year−1 (about 500 mm from April to October). Nevertheless, the transpiration represented only a small portion of stand water balance (65% of potential evaporation and 80% of annual precipitation in the open).

Laurel forests in Tenerife, Canary Islands. II. Leaf distribution patterns in individual trees

Abstract Branching pattern, leaf distribution (area, dry weight, number) and allometric relations on individual trees from a Canarian laurel forest have been analyzed. The following species were studied: Persea indica (L.) Spreng., Laurus azorica (Seub.) Franco, and Erica arborea L. Crown architecture was similar in all study species and corresponded to Rauhs’s model. In all species, leaf area was highly correlated to stem diameter. The vertical distribution of foliage was largely symmetrical and was roughly approximated by a Gaussian-like pattern which shifted upwards in dominant tree and downwards in suppressed tree. When radially viewed, most of the foliage area occurred roughly half the distance between the stem axis and the edge of the crown. However, radial leaf area indices, calculated for different areas of annulus around stems, showed a maximum closer to the stem.

Structure and ultrastructure of Pinus canariensis needles.

Summary The present study using light, transmission and scanning electron microscopy contains information about the structure of the needles of Pinus canariensis , an endemic pine of the Canary Islands. As a three-needled species, they have a triangular shape in transverse section being the abaxial side hemispherical. The deeply sunken stomata and the waxes covering the epidermal cells as well as the epistomatal chamber, constitute a good adaptation to the loss of water. The mechanical tissue below the epidermis contributes to a higher drought resistance and to maintain the shape of the long needles as a skeletic tissue. The ultrastructure of mesophyll cells, transfusion tissues as well as endoderrnis and resin ducts is also described. The results of this study should be used as reference data for further investigations of physiological, biochemical and ultrastructural responses of this species to environmental variations due to pollutants and different altitudinal and exposure situations.

Different surface characteristics of primary and secondary needles of Pinus canariensis

Summary Surface characteristics of primary and secondary needles of Pinus canariensis were investigated using scanning electron micro-scopy and gas chromatography to study structure and composition of epicuticular wax, cuticle micromorphology and the structure of stomata. Tubular waxes could be observed on the whole needle surface of the glaucous primary needles whereas on secondary needles they were restricted to the lower surface of young needles. Recrystallization resulted in comparable wax tubes and, addition-ally, plate like structures recrystallized from primary needle wax. Isolated cuticles of primary needles were tender and showed a simple stomata complex with six subsidiary cells whereas the cuticles of secondary needles were massive and revealed 9–12 subsidiary cells. In contrast to the cuplike epistomatal chamber of the primary needles that of the secondary needles was larger and often irregularly formed. Main constituents of the cuticular wax were ω-hydroxy-n-alkanoic acids, 10-nonacosanol and n-alkanoic acids with no differences in the qualitative composition between primary and secondary needles but with some differences in the quantitative pattern. The possible role of the investigated cuticular features in adaptive strategies of the needles to avoid light and water stress is discussed.

Effect of Extreme Temperature on Quantum Yield of Fluorescence and Membrane Leakage of the Canarian Endemic Pine (Pinus canariensis)

The effect of extreme temperature on the quantum yield of fluorescence and membrane leakage of Pinus canariensis growing in 5 stands at different altitudes and orientation in Tenerife (Canary Islands, Spain) was determined. Needles were collected from the field and transferred to the laboratory where they were kept in a closed chamber with water-saturated air overnight. Then they were exposed for 30 minutes in plastic bags in a water bath at temperature treatments with steps of 2K between 56 °C and -24 °C and the effect was determined immediately and 24 hours after the treatment by chlorophyll fluorescence and electrolyte leakage. Needles presented incipient damage at temperatures ranging from -5 to -10 °C depending on the altitude and orientation of the stand. The results were more evident when the measurements were done 24 hours after the cold treatment and values were consistent with the electrolyte leakage results. Different resistance to high temperature depending on the altitude and orientation was also found, varying the temperature for incipient damage from 42 to 44 °C detected with the fluorescence parameters but not with the leakage of electrolytes which was not found until 50 °C. The amplitude of thermal limits for photosynthetic efficiency alteration in needles of P. canariensis was relatively narrow and similar to that of evergreen Canarian laurel forest trees

Net below canopy fluxes in Canarian laurel forest canopies

Bulk precipitation, stemflow and throughfall were collected in a Canarian laurel forest (North Tenerife), and chemically analysed to determine the net below canopy fluxes. Annual negative fluxes were found for H þ ,N O 3 ,S O 4 and Cl 2 and annual positive fluxes for Ca 2þ ,M g 2þ ,K þ ,N a þ , HCO3 ,P O 42 and DOC. Negative fluxes for most of these ions have been reported previously but this is the first time that they have all been measured at the same time in one forest. The relative importance of atmospheric deposition and canopy leaching to net below canopy fluxes was evaluated using two approaches previously employed in this type of study. The first approach consisted of calculating total inputs, taking inputs as bulk precipitation or bulk precipitation plus the additional input from scavenging dry deposition by vegetation surfaces, corrected by the maximum and minimum leaching rate. The values obtained for inputs were very similar, possibly due to the minimum effect on scavenging particles by the canopy. In the second approach, linear regressions were developed for net below canopy fluxes and the variables related to dry deposition (antecedent dry period) and leaching (event quantity and duration, etc.); this showed that NO3 in net below canopy fluxes came from dry deposition, the rest of the elements from leaching, and SO42 from both. Similar results were obtained using both approaches. It was found that a simple linear regression model with event quantity as the independent variable can readily substitute the Lovett and Lindberg (1984) [J. Appl. Ecol. 21 (1984) 1013] model. The latter model was applied for separate internal and external sources in the case of SO42 . This forest differed greatly from other, previously studied forests. Large amounts of water were required for a positive flux (leaching), suggesting that the negative net below canopy fluxes of some elements were due to the low water regimes during the study year. Possible causes of this were the high value of the canopy saturation and the pattern of scattered rainfall, which led to extreme values of interception losses. The point at which the line representing the relationship between net below canopy fluxes and event quantity intersected the x axis varied depending on the leachable properties of the canopy ions. q 2002 Elsevier Science B.V. All rights reserved.

Effect of Dehydration on the Photosynthetic Apparatus of Sun and Shade Leaves of Laurel Forest Trees

In this work we study the effect of reduction in relative water content (RW C) on the chlorophyll fluorescence induction kinetics as well as on the membrane integrity, measured as electrolyte leakage, in sun and shade leaves of three Canarian laurel forest trees. No differences were found among the species and type of leaves, when the slow fluorescence kinetic parameters and electrolyte leakage were analyzed, values deviated from the normal ones at 70% and 40% RWC respectively. On the contrary, the photochemical efficiency of PSII was affected at higher values of RWC in sun leaves (90% and 52% RWC depending on the species) than in shade ones (40% RWC). These results indicate that the susceptibility of PSII to water deficit is different depending on species and environmental conditions where the leaves develop

Gas Exchange of Irrigated and Non-Irrigated Pinus canariensis Seedlings Growing Outdoors in La Laguna, Canary Islands, Spain

Chlorophyll fluorescence, gas exchange, water potential and relative water content were measured in the needles of five year old seedlings of Pinus canariensis in order to know their response to mild water stress. Two trial plots of ten plants per plot, of similar age and characteristics were irrigated daily until the experiment was undertaken, then one of the plots was left without watering while the other one was irrigated as before. After a week of treatment, the water potential at midday did not change in any of the irrigated or non-irrigated plants maintaining around -0 .4 MPa, and the relative water content changed from 93% in irrigated to 84% in non-irrigated seedlings. The stomatal conductance decreased 60% in non irrigated plants and as a result CO2 assimilation decreased by 50% and transpiration was reduced at a higher proportion (70% ), indicating a good control against water loss, before any change in water status in the needles could be observed suggesting an isohydric water economy in this plant