M. S. Jimenez

Effects of thinning on throughfall in Canary Islands pine forest — the role of fog

Throughfall was monitored over a one-year period in a 48-year-old Pinus canariensis plantation on the northern side of the island of Tenerife, nine years after light thinning (mean 15% of basal area (BA)) or heavy thinning (mean 56% of BA). Three plots of each treatment (light thinning, heavy thinning, no thinning) were studied, using a randomized block design. Mean total throughfall over the year of study was about 2.0 times the incident rainfall in the control plots, about 2.2 times rainfall in the lightly thinned plots, and about 1.8 times incident rainfall in the heavily thinned plots. The high throughfall-to-rainfall ratios are as expected, given the importance of fog entrapment in these forests. The statistical analysis indicated that the observed differences in throughfall are attributable to the treatments, not to plot topography. Throughfall showed significant relationships with actual BA, surface roughness (as tree height variability) and leaf area index (LAI), all of which varied significantly among treatments (as expected). Our results are unexpected as heavy thinning led to a long-term decline, not increase, in throughfall. The explanation for this result is the importance of fog entrapment may mean that reducing LAI and surface roughness (height variability) has a negative effect on throughfall. The long period elapsed between thinning and throughfall estimation means that LAI of light thinning plots exceeded pre-thinning values, and then throughfall values.

Influence of canopy position, needle age and season on the foliar gas exchange of Pinus canariensis

We investigated the seasonal variation in the gas exchange of current and 1-year-old needles in the upper sun and lower shade crown of adult Pinus canariensis trees. In general, current year needles displayed lower gas exchange rates than the 1-year-old needles. In both needle age classes, gas exchange was significantly lower in the shade than in the sun crown. However irrespective of crown position and needle age, maximum daily net photosynthesis, transpiration, and stomatal conductance for water vapour were generally higher during the wet and cold winter as compared to the dry and hot summer. These higher gas exchange values obtained during the cold and wet season can mainly be explained by higher soil-water availability and lower evaporative demand as compared to the warm and dry seaon. In addition, we also observed a displacement in the temperature optimum of net photosynthesis towards lower temperatures during the cold and wet season as compared to the warm and dry season. The observed gas exchange characteristics indicate a conservative water saving strategy and thus allowing P. canariensis needles to maintain a positive carbon gain even at periods of high evaporative demand and low soil-water availability.

Element contents and stress-physiological characterization of Pinus canariensis needles in Mediterranean type field stands in Tenerife

Abstract Contents of Ca, Mg, K, Na, S, Cl, P, N, pigments, ascorbic acid, glutathione, and tocopherol together with chlorophyll fluorescence were measured in needles of Pinus canariensis trees growing at four field stands at 4 different altitudes at the south-eastern slope of the Teide in Tenerife. S contents reflected impacts of SO 2 at lower altitudes. Via Na and Cl contents the influence from the sea was assessed up to 1000 m. Above 1000 m we found higher levels of ascorbic acid, less chlorophyll, higher carotenoid/chlorophyll-ratios, and lower α/β-carotene ratios. This pattern suits in a picture of elevated oxidative stress these trees are responding to. Decreases in Fv/Fm-ratios of chlorophyll fluorescence below 0.80 reflecting damages in the photosynthetic apparatus were only found at one site at 1500 m, where altitude stress was probably amplified by drought stress.

Succulence and CAM relationships in Aeonium genus

The CAM has been tested in six species of the Aeonium genus by studying the diurnal fluctuation of organic acids, pH and night fixation of CO2. The existence of a mesophyll structure able to support this metabolism has been shown as well as a congruent periodicity in the pool of cell starch.We have calculated the S, ES and Sm indices in the six species. A series of regression equations of different grades and types were calculated and shown to have correlation coefficients statistically significant. This allows us to confirm the suitability of the Sm index as a rapid test to establish the CAM as postulated by former authors.ResumenSe ha comprobado el CAM en seis especies del género Aeonium, mediante el estudio de las fluctuaciones diurnas del acervo de ácidos orgánicos, de las oscilaciones periódicas de pH y de la captura nocturna de CO2, al mismo tiempo que se ha verificado en ellas le existencia de una estructura del mesófilo capaz de soportar este metabolismo y una periodicidad congruente en el acervo de almidón celular.Se han calculado asimismo los índices S, ES y Sm de especímenes de las seis especies y se ha podido establecer una serie de ecuaciones de regresión de distinto tipo y grado, a unos niveles de significación, que permiten postular, en el citado material, la idoneidad del índice Sm como prueba rápida del metabolismo ácido de las crasuláceas, confirmando de este modo las teorías de los primeros autores.