Manuel Fernández

Plant water relations and edaphoclimatic conditions affecting acorn production in a holm oak (Quercus ilex L. ssp. ballota) open woodland

Acorn production patterns and the annual evolution of water relations parameters of Quercus ilex ssp. ballota (Desf.) Samp. in a dehesa (an open woodland forest) subject to various soil treatments (ploughing, ploughingxa0+xa0sowing, control) were studied in southwest Spain from June 2006 to December 2008. The effects of soil water holding capacity and effective soil depth on soil and plant water status and acorn production were also investigated. Water parameters showed significant differences between the ploughing treatment and the control, and there were also significant temporal differences. Xylem water potential ranged from −3.4xa0±xa00.1 to −0.7xa0±xa00.2xa0MPa, and cuticular transpiration was 62.4–192.9xa0mmolxa0H2Oxa0kg−1xa0s−1. Acorn production did not differ significantly according to soil treatment, and showed large intra-specific variability. Individual values ranged from 0 to 1,220xa0gxa0m−2 (fresh weight). Positive relationships were found between xylem water potential, cuticular transpiration and relative water content measured at midsummer, and acorn production during the three studied years. These results suggest that climatic conditions and soil water availability have a strong influence on plant water status, and therefore on acorn development during summer. The results also reflect the ability of this species to adapt to the Mediterranean climate by preserving water during dry periods, which to a large extent can be attributed to stomatal closure at high relative water content levels, and low cuticular transpiration during these periods.

Effects of Water and Nutrient Availability in Pinus pinaster Ait. Open Pollinated Families at an Early Age: Growth, Gas Exchange and Water Relations

Growth and physiological responses of Pinus pinaster Ait. to water and nutrient availability were compared in four open pollinated families of Arenas de San Pedro provenance (Central Iberian Peninsula), looking for more useful parameters and growing conditions to be included in early selection programmes of forest trees. Young seedlings were grown in a greenhouse, subjected to high and low water and nutrient regimes, during 14xa0weeks. Interfamily differences were significant with regard to growth, nutrient content and water-use efficiency (WUE): differences in growth were higher under more favourable growing conditions; gas exchange differences were higher in the short term (9xa0weeks), indicating a faster reaction to water stress of the better adapted families to these conditions; the highest growth rates were found in the families with the largest plasticity, highest WUE and highest nutrient content. Water regime and nutrients had significant effects on growth, δ13C, gas exchange and water relation parameters. For these parameters the ranking of the families was kept regardless the water × nutrient supply combination and there was not a significant familyxa0×xa0treatment interaction. In the long term (14xa0weeks) higher water supply and nutrient content significantly increased instantaneous WUE. The positive relationships between growth, intrinsic WUE (A/gwv) and δ13C demonstrate that it should be possible to use physiological parameters (e.g. gwv, δ13C) as a surrogate for the efficiency in the use of water, at least if short periods of water stress (up to 2xa0months long) were frequent, as it occurs in the Mediterranean basin. There was also some indication that the decrease in nitrogen or potassium supply led to increasing stomatal conductance and hence lower WUE.ResumenSe estudió la respuesta a la disponibilidad de agua y nutrientes, en cuatro familias de polinización abierta de Pinus pinaster Ait., de la procedencia española de Arenas de San Pedro, con el fin de buscar parámetros fisiológicos y de crecimiento, así como condiciones de cultivo idóneas, que puedan ser utilizados en los programas de selección temprana de la especie. Se cultivaron plantas en un invernadero durante 14 semanas, sometidas a cuatro tratamientos de disponibilidad de agua y nutrientes. Se obtuvieron diferencias significativas entre familias respecto a crecimiento, contenido en nutrientes y eficiencia en el uso del agua (WUE): las diferencias en crecimiento fueron mayores bajo condiciones de cultivo más favorables; las diferencias en intercambio gaseoso fueron más acusadas a las 9 semanas, indicando una mayor velocidad de reacción al estrés hídrico de aquellas familias más adaptadas a estas condiciones; las mayores tasas de crecimiento se obtuvieron en las familias con mayor plasticidad, WUE y contenido en nutrientes. Asimismo, el régimen de riego y fertilización resultó significativo respecto a crecimiento, δ13C, intercambio gaseoso y relaciones hídricas, manteniéndose el ranking entre familias en todos los tratamientos de cultivo ensayados, no siendo significativa, por tanto, la interacción genotipo x ambiente. A más largo plazo (14 semanas) WUE resultó favorecida por la aportación de agua y nutrientes. En especial para N y K, se encontró que la deficiencia en éstos tiende a aumentar la conductancia estomática, reduciendo con ello WUE. La correlación positiva entre crecimiento, WUE intrínsecay δ13C demuestra que el uso de parámetros fisiológicos (p.ej. gwv, δ13C) puede resultar útil en la estimación de WUE, al menos, para aquellas estaciones donde sean frecuentes cortos períodos de estrés hídrico (no más de dos meses), como ocurre en numerosas regiones de clima mediterráneo.

Influence of pruning and the climatic conditions on acorn production in holm oak (Quercus ilex L.) dehesas in SW Spain

Acorn production by Quercus ilex L. ssp. ballota (Desf.) Samp. in SW Spain was assessed, and variations between years and the influence of pruning on it were examined. To this end, an experimental study was conducted at two different sites (Calañas and San Bartolomé, in the province of Huelva) where trees were subjected to traditional (light, moderate or heavy) pruning and also to a new (crown-regeneration) pruning method. Acorn yield was quantified over a period of 5 years in the Calañas plot and 4 in the San Bartolomé plot, and found to average at 95.61 ± 0.76 g DM/m2, which is equivalent to 6.5 ± 0.05 kg DM/tree; however, yield figures varied markedly between years depending on the particular climatic conditions. The average acorn production was correlated with the water potential in mid summer (end of July); the annual, spring and autumn rainfall; and the actual evapotranspiration for the period from September (previous year) to August. No significant differences in acorn production between traditional pruning intensities were detected; in fact, there were only hints that heavy pruning might result in decreased acorn yields. The new pruning method used, crown-regeneration, seems promising with a view to increasing acorn yield; however, it should be tested on larger sample sizes before any final conclusions can be drawn in this respect. Based on the results, the present health status of holm oaks in southwestern Spain (a result of sustained decline) and the low value of firewood — which used to be a very important source of income from pruning a few decades ago -, the authors recommend reducing the frequency and intensity of pruning in the dehesas of the study area.RésuméLa production de glands par Quercus ilex L. ssp. ballota (Desf.) Samp. dans le sud ouest de l’Espagne a été mesurée, et l’influence de la taille sur les variations interannuelles a été examinée. Dans ce but, une étude expérimentales a été conduite dans deux sites (Calañas et San Bartolomé dans la province de Huelva) où des arbres ont été soumis à une taille traditionnelle (légère, modérée ou forte) et aussi à une nouvelle méthode de taille (régénération de couronne). La production de glands a été quantifiée sur une période de 5 ans sur le site de Calañas et de 4 ans sur celui de San Bartolomé et était en moyenne de 95,61 ± 0,76 g de matière sèche/m2, ce qui équivaut à 6,5 ± 0,05 kg de matière sèche/arbre. Cependant la production a varié de façon marquée entre années en relation avec les particularités climatiques. La moyenne de production de glands était corrélée avec le potentiel hydrique au milieu de l’été (fin juillet); avec les précipitations annuelles, du printemps et de l’automne, et avec 1’évapotranspiration pour les périodes allant de septembre (année précédente) à août. Aucune différence significative de production de glands n’a été détectée, entre les intensités de taille traditionnelle. La nouvelle méthode utilisée est prometteuse et permet une augmentation de la production de glands; cependant elle devra être testée sur des lots d’arbres plus importants avant d’arriver à des conclusions définitives sur ce sujet. Sur la base de ces résultats, en prenant en compte de l’état de santé actuel du chêne vert dans le sud ouest de l’Espagne (résultat d’un déclin prolongé) et la faible valeur actuelle du bois de feu qui était habituellement une source très importante de revenus provenant de la taille il y a quelques dizaines d’années, les auteurs recommandent la réduction de la fréquence et de l’intensité de la taille dans les dehesas.

Nursery fertilisation affects the frost-tolerance and plant quality of Eucalyptus globulus Labill. cuttings

Eucalyptus globulus is widely used in productive exotic plantations but the expansion of these plantations is limited by low temperatures, as its cold hardening capacity is limited (0.5 to 3.0 °C). It is not well understood how nursery fertilisation affects the field performance of plants. This led us to study the effect of three mineral nutrients (N, P and K) on both plant quality and frost tolerance. The experiment comprised eight growth treatments in which a high dose (H-) or a low dose (L-) of each nutrient was applied. Nitrogen was the nutrient that determined shoot growth, new root growth after transplanting (root egress), frost tolerance and field performance. Performance was better with treatment H-N than with treatment L-N, leaf nitrogen contents being 1.53 and 0.89% respectively. The effects of phosphorus and potassium were not significant between treatments for any parameter. The exception was P which, when interacting with N, favoured root egress for the H-N treatment. It was concluded that nursery fertilisation offers a management tool for eucalyptus growers concerned with plant stock quality.RésuméEucalyptus globulus est largement utilisé dans des plantations exotiques productives, mais l’expansion de ces plantations est limitée par les basses températures, étant donné que l’endurcissement potentiel au froid de cette espèce est limité (0,5 à 3,0 °C). On ne comprenait pas bien comment la fertilisation en pépinière pouvait affecter la performance en plantation des plants. Ceci nous a amené à étudier l’effet de trois nutriments minéraux (N, P et K) sur la qualité des plants et la résistance au froid. L’expérimentation a comporté huit traitements pour l’étude de la croissance pour lesquels une forte dose (H-) ou une faible dose (L-) de chaque nutriment a été apportée. L’azote a été le nutriment qui a déterminé la croissance de la pousse, la croissance de nouvelles racines après transplantation (émission de racines), la résistance au froid et la performance en plantation. Les performances étaient meilleures avec le traitement H-N que avec le traitement L-N, la teneur en azote des feuilles atteignant respectivement 1,53 et 0,89 %. Les effets du phosphore et du potassium n’ont été significatifs pour aucun des paramètres. L’exception a concerné le phosphore qui lorsqu’il était en interaction avec l’azote a favorisé l’émission de racines dans le traitement H-N. On conclut de cette étude que la fertilisation en pépinière offre un outil de gestion pour les producteurs d’eucalyptus confrontés au problème de la qualité des plants.

Autumn fertilization of Quercus ilex ssp. ballota (Desf.) Samp. nursery seedlings: effects on morpho-physiology and field performance

Abstract• BackgroundThe Holm oak (Quercus ilex ssp. ballota [Desf.] Samp.) is an evergreen tree widely distributed in the western Mediterranean Basin. Forest restoration programs using this species have enjoyed only limited success, and knowledge concerning the effect of fertilization on plant quality and post-transplantation response is sparse.• Methods We assessed the effect of autumn fertilization using different doses of nitrogen, phosphorus, and potassium (70.0xa0mgxa0N, 30.5xa0mg P and 58.1xa0mgxa0K during the growing phase for all plants; and 30.0 vs 1.5xa0mgxa0N, 13.1 vs 0.3xa0mg P and 24.9 vs 0.5xa0mgxa0K during the hardening phase, depending on the fertilization treatment) on the seedling characteristics and field performance of Holm oak.• Results and ConclusionsAutumn fertilization, especially with N, did not decrease plant quality but improved overall growth, root growth capacity, cold hardiness, and the nutritional content of nursery-grown seedlings. However, autumn fertilization had only a small effect on field performance, which was affected only by K fertilization, probably because of the adequate N and P nutrient status of all the plants and the mild weather conditions of the field plot. In our site, which had a mild winter climate, late autumn out-planting was more successful than was mid-winter out-planting.

Do ecological and silvicultural factors influence acorn mass in Holm Oak (southwestern Spain)

The effect of orientation, location, year, and pruning treatment on mean acorn mass in two open woodland experimental locations (Huelva, South-Western Spain) of Holm Oak (Quercus ilex L. subsp. ballota [Desf.] Samp.) was analyzed during 2001–2006. Data were analyzed by using a mixed linear model, where the covariates were tree size parameters (circumference at 80 cm height, crown size), topographic position (wet index and flow length), intraspecific competition, total acorn crops per tree (weight and number), and climatic parameters. Average estimated acorn mass was 3.17 g acorn−1 in the Calañas location and 4.12 g acorn−1 in the San Bartolomé location, with significant differences between locations, among individual trees and across years. Acorns from the south sides of trees were significantly heavier than those at other positions. The effect of pruning treatment and the interactions location × treatment and treatment × year were not significant. Our study provides no evidence that pruning affects acorn mass. None of the analyzed covariates related to tree size, topographic position and intraspecific competition explained the difference among trees, suggesting that heritable factors play an important role. Specific climatic parameters during September, the most important month for acorn growth, may explain the effects of year and location × year on acorn mass. In addition, there appeared to be a “trade-off” between acorn mass and number of acorns.

Nutrients return from leaves and litterfall in a mediterranean cork oak (Quercus suber L.) forest in southwestern Spain

The knowledge of the cycle of nutrients is fundamental for the correct comprehension of the tree–soil relationship and for an adequate forest management. In order to analyse the nutrients return from leaves and litterfall in a Mediterranean cork oak forest in southwestern Spain, 12 trees were randomly selected and litterfall collected for 2xa0years. Samples were taken monthly and separated in different fractions (leaves, twigs, catkins, acorns and miscellaneous), then leaves nutrients were analyzed. Simultaneously, we analyzed the nutrient content of living leaves from the same trees in each season during 1xa0year. The analyzed nutrients were C, N, P, K, Ca, Mg, Fe, Mn, S, Cu, Zn and Mo. Annual patterns of each nutrient in fallen leaves were characterized and compared with seasonal values of these nutrients in living leaves. Leaves fall has two annual maximum, first and most important in spring around April coinciding with renewal of foliar cover and second around October. Main concentration patterns of N, P and K are related with phenological patterns, in consequence minimum concentration in leaves fall were obtained in periods of growing and maximum litterfall. Concentrations of Ca, Fe and Mn increase with the age of the leaves and maximum concentrations were obtained before periods of maximum litterfall while concentrations of Cu, Mo and Mg stay stable. Seasonal analysis of nutrients in living leaves collected from the same trees in four different periods of the year allowed to corroborate the patterns of leaves fall and the probable osmotic function of K.

Autumn fertilization with nitrogen improves nutritional status, cold hardiness and the oxidative stress response of Holm oak (Quercus ilex ssp. ballota [Desf.] Samp) nursery seedlings

Holm oak (Quercus ilex ssp. ballota [Desf.] Samp) is one of the most important species in forest communities of the western Mediterranean Basin, but is very vulnerable to environmental stress during the first years of its life. In particular, summer drought and winter frosts limit the distribution, survival, and growth of Holm oak. These two stress factors can lead to plasmolysis and/or oxidative stress. We hypothesized that autumn fertilization with nitrogen (N) can improve plant tolerance to these abiotic stress factors and improve plant quality and therefore reforestation success. A 12-week autumn application of 30 or 60xa0mgxa0N (plus 70xa0mgxa0N applied to both treatments during the previous 28xa0weeks in the nursery, i.e. 100 and 130xa0mgxa0N in total, respectively) improved overall growth, root growth capacity, frost tolerance, and nutritional status of plants relative to plants given 0.0 and 1.5xa0mg autumnal N, and had no negative effect on seedling response to water stress. A very small increment in N doses during the autumn (1.5 vs. 0.0xa0mgxa0N) improved some morphological parameters, such as stem diameter (D) and shoot dry weight, and physiological parameters, such as total antioxidant activity. The highest autumnal N dose (60xa0mg) increased leaf nutrient content without decreasing the concentration, but had a tendency to reduce frost tolerance relative to seedlings given a lower autumnal N dose (30xa0mg).

Two provenances of Quercus ilex ssp. ballota (Desf) Samp. nursery seedlings have different response to frost tolerance and autumn fertilization

Despite evidences that Holm oak has a high plasticity and great adaptability, there is limited or contradictory knowledge of the morphological and physiological variability of this species. Holm oak has been widely used for reforestation projects in Mediterranean areas, but has frequently shown poor field performance. We hypothesized that Holm oak has inter-population differences in physiological responses to abiotic stressors that could affect reforestation success. The influence of nursery culture on the characteristics of Holm oaks from different provenances has not been explored in depth. Thus, we studied the effect of nursery autumn fertilization on morphological traits, frost tolerance, root growth potential, and nutritional status of two Spanish provenances of Holm oak, La Alcarria (a region with inland Mediterranean climate) and Sierra Morena Occidental (a region with a warm coastal Mediterranean climate). There were significant differences between the provenances in frost tolerance, biomass allocation, and leaf nutrient content, suggesting a role of genetic factors. The leaves of seedlings from La Alcarria had less visual damage at −12°C than seedlings from the warmer provenance (45% vs. 92%). Seedlings from La Alcarria, compared to those from Sierra Morena, had higher leaf P concentration (0.17% vs. 0.15%), greater stem diameter (3.1xa0mm vs. 2.7xa0mm), lower shoot-to-root dry mass ratio (0.46 vs. 0.53), and lower slenderness (4.03 vs. 5.31). For both provenances, N autumn fertilization improved growth, root growth potential, cold hardiness, and nutritional status of seedlings. We suggest that forest reforestation programs should consider to a greater extent Holm oak provenances and their tolerances to different abiotic stressors.

Effect of ecological factors on intra-annual stem girth increment of holm oak

Key messageThe intra-annual stem girth increment ofQuercus ilex is mainly driven by water availability and secondly by temperature. Tree size and competition modulate the growth response to climate.AbstractHolm oak (Quercus ilex ssp. ballota [Desf.] Samp.) is the most widespread species in the Iberian peninsula, being one of the most representative trees in forests and open woodlands. The analysis of stem girth increment of holm oak may provide valuable information about how Mediterranean ecosystems will respond to the forecasted climate changes. However, due to the variability of the Mediterranean climate, the knowledge of intra-annual patterns of growth is needed for a better understanding of the influence of the climatic variables at this scale. To this end, we used band dendrometers to measure monthly stem girth increments of 96 holm oak trees from 2003 to 2010, located in open woodlands and dense Mediterranean forests in southwestern Spain. We assessed the effects of climate, competition, topography, and initial stem diameter on stem girth increment. The major stem increment periods were in spring and autumn whereas increment rates were very low or even negative in winter and summer. Spring was not every year the season with the higher stem increments, but autumn when spring was very dry. Higher precipitation, soil moisture, and relative humidity had significant positive effects on stem increment, whereas higher temperature, reference evapotranspiration, and solar radiation had significant negative effects. Initial tree diameter and competition from nearby trees partly explained significant differences in stem increment of individual trees. Therefore, the forecasted climatic changes, in which decreased rainfall in spring and increased summer drought are expected in the Mediterranean region, may be a significant threat to the Q. ilex ecosystems.