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Resprouting woody species adapted to perturbations store large amounts of carbon reserves to sustain plant metabolism during and resprout following perturbations. However, it is not known how carbon sources and sinks re-adjust in response to perturbations. Here, we studied when and where different reserve pools were mobilized after an aboveground perturbation, and how were new assimilates used after resprouting. Leaf gas exchange, plant organ carbon isotopic composition (δ13C) and nonstructural carbohydrate concentrations [NSC] were measured over one year in Pinus canariensis saplings subjected to complete defoliation (D) or complete defoliation plus stem damage (DD). Growth stopped completely in D and DD trees by the second month after the treatment application and during subsequent crown development. Growth resumed in most trees (60%) by the end of the growing season. Relative to control (C) trees, stem xylem [starch] decreased in D and DD during resprouting of new buds. Stem and root [starch] were also lower during growth resumption in these trees. One year after aboveground damages, leaf and root δ13C were significantly lower in D and DD, whereas [starch] recovered to values of C trees, except in roots of DD trees. Mobilization of carbon reserves from woody organs allows for resprouting and contributes to crown regeneration, stem growth resumption and wound healing in DD trees. New 13C-depleted photoassimilates contribute to these processes, and to refilling carbohydrates reserves. High [starch], plasticity in growth during and recovery of [starch] after severe aboveground disturbance, highlights high resilience of P. canariensis to perturbation. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that fertilized containerized Pinus canariensis seedlings increases survival when planted in semiarid sites through the improvement of their physiological status during the establishment phase by an increment in root growth. Seedlings were cultured under two different regimes: traditional (in non-fertilized natural soil) and alternative (in fertilized peat). Morphological attributes and nitrogen content were measured before planting. Measurements of survival and growth in the plantation were made periodically for 2 years and physiological plant responses (leaf water potential, gas exchange and chlorophyll fluorescence) during the third summer after planting were tested and finally a set of plants were excavated to measure the same parameters as before planting. Seedlings cultivated using fertilized peat achieved the highest values for all of evaluated parameters. During the third dry season, big seedlings exhibited better physiological status. Therefore, enhanced root growth can result in better water uptake during the dry period thereby increasing survival and growth in the next few years after planting. A feed-back physiological model is proposed to explain P. canariensis establishment in a semiarid environment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]