Examinando por Autor "Villar-Salvador, Pedro"

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Fast growth involves high dependence on stored resources in seedlings of Mediterranean evergreen trees
(Oxford, 2015-03-28) Uscola Fernández, Mercedes; Villar-Salvador, Pedro; Gross, Patrick; Maillard, Pascale
Background and Aims The carbon (C) and nitrogen (N) needed for plant growth can come either from soil N and current photosynthesis or through remobilization of stored resources. The contribution of remobilization to new organ growth on a whole-plant basis is quite well known in deciduous woody plants and evergreen conifers, but this information is very limited in broadleaf evergreen trees. This study compares the contribution of remobilized C and N to the construction of new organs in spring, and assesses the importance of different organs as C and N sources in 1-year-old potted seedlings of four ecologically distinct evergreen Mediterranean trees, namely Quercus ilex, Q. coccifera, Olea europaea and Pinus hapelensis. Methods Dual 13C and 15N isotope labelling was used to unravel the contribution of currently taken up and stored C and N to new growth. Stored C was labelled under simulated winter conditions. Soil N was labelled with the fertilization during the spring growth. Key results Oaks allocated most C assimilated under simulated winter conditions to coarse roots, while O. europaea and P. halepensis allocated it to the leaves. Remobilization was the main N source (>74 %) for new fine-root growth in early spring, but by mid-spring soil supplied most of the N required for new growth (>64 %). Current photosynthesis supplied >60 % of the C in new fine roots by mid-spring in most species. Across species, the proportion of remobilized C and N in new shoots increased with the relative growth rate. Quercus species, the slowest growing trees, primarily used currently acquired resources, while P. halepensis, the fastest growing species, mainly used reserves. Increases in the amount of stored N increased N remobilization, which fostered absolute growth both within and across species. Old leaves were major sources of remobilized C and N, but stems and roots also supplied considerable amounts of both in all species except in P. halepensis, which mainly relied on foliage formed in the previous growing season to supply stored resources. Conclusions Seedlings of Mediterranean evergreen trees have distinct C and N storage physiologies, with relative growth rate driving the contribution of remobilized resources to new growth. These differences may reduce competition and facilitate species coexistence.
Foliar absorption and root translocation of nitrogen from different chemical forms in seedlings of two Mediterranean trees
(Science Direct, 2014-08) Uscola Fernández, Mercedes; Villar-Salvador, Pedro; Oliet-Palá, Juan A; Warren, Charles R.
Along with root uptake, plants can also absorb N through leaves. There are few comparative studies on the foliar absorption of N from different chemical forms of N in forest tree species. We compared the foliar N absorption capacity in seedlings of two forest trees widespread in the Mediterranean basin, Quercus ilex and Pinus halepensis. Plants were sprayed with the following individual N forms at 40 mM N: 15N-nitrate (NO3 −), 15N-ammonium (NH4 +), 15N-urea or 13C and 15N dual-labeled glycine. Cuticular conductance was used as a surrogate of cuticle permeability to water. Q. ilex had higher N foliar absorption than P. hapelensis. Neither cuticular conductance nor shoot surface area explained N differences in absorption rate between species, which were instead likely linked to differences in stomatal density and presence of trichomes. In both species, foliar N absorption rate and N recovery differed among N forms: urea > NH4 + ≥ glycine ≥ NO3 −. Differences in N absorption rate among N forms were correlated with their physico-chemical properties. The strong positive relationship between 15N and 13C uptake together with detection in shoots of intact dual-labeled glycine (measured by gas chromatography–mass spectrometry), indicated that a significant fraction of glycine was absorbed intact by the seedlings. In both species, higher cuticular conductance was related to faster N absorption from all forms except NO3 −. Cuticular conductance had a stronger effect on N absorption from urea and NH4 + than N absorption from glycine, and the effects were more intense in Q. ilex than in P. halepensis. This suggests that variations in cuticle permeability in both species are determined by different mechanisms and that each N form was differently affected. Absorbed N was rapidly translocated to roots, with a larger proportion of N from organic forms being translocated than N from inorganic forms. Foliar fertilization increased plant N content, especially in urea fertilized plants, but direct foliar absorption only explained up to 10% of N content increase. This study demonstrates thattwo important Mediterranean foresttree species can absorb through their leaves both, inorganic and organic N forms. This has important ecological and applied implications, because all chemical forms of N are present in natural N deposition. Also results show that foliar N fertilization can play an important role for seedling N nutrition, and that the effect will have different impacts depending on the species.
Increase in size and nitrogen concentration enhances seedling survival in Mediterranean plantations. Insights from an ecophysiological conceptual model of plant survival
(Springer Link, 2012-04-24) Villar-Salvador, Pedro; Puértolas, Jaime; Cuesta, Bárbara; Peñuelas, Juan L; Uscola Fernández, Mercedes; Heredia-Guerrero, Norberto; Rey Benayas, José María
Reduction in size and tissue nutrient concentration is widely considered to increase seedling drought resistance in dry and oligotrophic plantation sites. However, much evidence indicates that increase in size and tissue nutrient concentration improves seedling survival in Mediterranean forest plantations. This suggests that the ecophysiological processes and functional attributes relevant for early seedling survival in Mediterranean climate must be reconsidered. We propose a ecophysiological conceptual model for seedling survival in Mediterranean-climate plantations to provide a physiological explanation of the frequent positive relationship between outplanting performance and seedling size and nutrient concentration. The model considers the physiological processes outlined in the plantation establishment model of Burdett (Can J For Res 20:415–427, 1990), but incorporates other physiological processes that drive seedling survival, such as N remobilization, carbohydrate storage and plant hydraulics. The model considers that seedling survival in Mediterranean climates is linked to high growth capacity during the wet season. The model is for container plants and is based on three main principles, (1) Mediterranean climates are not dry the entire year but usually have two seasons of contrasting water availability; (2) summer drought is the main cause of seedling mortality; in this context, deep and large roots is a key trait for avoiding lethal water stress; (3) attainment of large root systems in the dry season is promoted when seedlings have high growth during the wet season. High growth is achieved when seedlings can divert large amount of resources to support new root and shoot growth. Functional traits that confer high photosynthesis, nutrient remobilization capacity, and non-structural carbohydrate storage promote high growth. Increases in seedling size and nutrient concentration strongly affect these physiological processes. Traits that confer high drought resistance are of low value during the wet season because hinder growth capacity. We provide specific evidence to support the model and finally we discuss its implications and the factors that may alter the frequent increase in performance with increase in seedling size and tissue nutrient concentration.
Nitrogen form and concentration interact to affect the performance of two ecologically distinct Mediterranean forest trees
(Springer Link, 2013-12-24) Uscola Fernández, Mercedes; Oliet-Palá, Juan A; Villar-Salvador, Pedro; Díaz-Pinés, Eugenio; Jacobs, Douglass F.
Most studies examining inorganic N form effects on growth and nutrition of forest trees have been conducted on single species from boreal or temperate environments, while comparative studies with species from other biomes are scarce. We evaluated the response of two Mediterranean trees of contrasting ecology, Quercus ilex L. and Pinus halepensis Mill., to cultivation with distinct inorganic N forms. Seedlings were fertilized with different NH4 +/NO3 − proportion at either 1 or 10 mM N. In both species, N forms had small effects at low N concentration, but at high N concentration they markedly affected the plant performance. A greater proportion of NH4 + in the fertilizer at high N caused toxicity as it reduced growth and caused seedling death, with the effect being greater in Q. ilex than in P. halepensis. An increase in the proportion of NO3 − at high N strongly enhanced growth relative to low N plants in P. halepensis but had minor effects in Q. ilex. Relatively more NH4 + in the fertilizer enhanced plant P concentration but reduced K concentration in both species, while the opposite effect occurred with NO3 −, and these effects were enhanced under high N concentration. We conclude that species responses to inorganic N forms were related to their ecology. P. halepensis, a pioneer tree, had improved performance with NO3 − at high N concentration and showed strong plasticity to changes in N supply. Q. ilex, a late successional tree, had low responsiveness to N form or concentration.
Quercus ilex L
(Organismo Autónomo Parques Nacionales, Ministerio de Agricultura, Alimentación y Medio Ambiente, 2013) Villar-Salvador, Pedro; Nicolás Peragón, Juan Luis; Heredia-Guerrero, Norberto; Uscola Fernández, Mercedes
Descripción de la especie, técnicas de manejo y propagación, y uso en repoblaciones y restauraciones
Root uptake of inorganic and organic N chemical forms in two coexisting Mediterranean forest trees
(Springer Link, 2017-01-09) Uscola Fernández, Mercedes; Villar-Salvador, Pedro; Oliet-Palá, Juan A; Warren, Charles R.
Background and aims Plants differ in their ability to use different nitrogen (N) chemical forms, these differences can be related to their ecology and drive community structure. The capacity to uptake intact organic N has been observed in plants of several ecosystems. However, soil organic N uptake by Mediterranean plants is unknown despite organic N being abundant in Mediterranean ecosystems. We compare the uptake of different N forms in two widespread coexisting Mediterranean forest trees with contrasting ecophysiological characteristics: Quercus ilex and Pinus halepensis. Methods To estimate root uptake rate of each N form we used equimolar solutions (1 mM N) of 15NO3 −, 15NH4 + and 15N-13C glycine. Results NH4 + and glycine were taken up at a similar rate, but faster than NO3 − in both species. Intact dual labeled glycine was found in both species, demonstrating that both species can absorb intact organic N. Conclusions Despite their ecological differences, both species had similar preference for N forms suggesting no fundamental niche complementarity for N uptake. The higher preference for NH4 + and glycine over NO3 − possibly reflects adaptation to the differing proportions of N forms in Mediterranean soils.
The role of stored carbohydrates and nitrogen in the growth and stress tolerance of planted forest trees
(Springer Link, 2015-07-02) Villar-Salvador, Pedro; Uscola Fernández, Mercedes; Jacobs, Douglass F.
Plants store compounds that supplement external resources to maintain primary functions. We reviewed the role of stored non-structural carbohydrates (NSC) and nitrogen (N) in juvenile woody species for spring growth and cold and drought stress tolerance, which are crucial processes for early performance of forest plantations. Plant functional types differed in NSC and N partitioning and allocation to new growth. In general, however, new leaves/shoots were more enriched in remobilized resources than new fine roots. Conifers used less remobilized resources than broadleaf species for fine root growth. New shoots/leaves were mostly comprised of remobilized N (>60 %) in conifers and broadleaf deciduous species, while broadleaf evergreens relied more on soil N (<50 % remobilized N). In contrast, few differences among functional groups existed in the contribution of remobilized carbon (C) to new leaves/shoots, which comprised 28–45 % of stored C reflecting the importance of current photosynthesis and distinctions in C and N remobilization physiology. The amount of N remobilized by an organ was positively related to its contribution to seedling N content. However, leaves are priority N sources in evergreens, which remobilized more N than predicted by their contribution to seedling N content. In contrast, roots in broadleaf evergreens and conifers were poor contributors of remobilized N. Under low stress, spring growth has little effect on NSC reserves. However, prolonged and intense photosynthesis depression strongly reduces NSC. In contrast, N reserves usually decline after planting and their replenishment takes longer than for NSC reserves. Strong storage reduction can hinder seedling stress acclimation and survival capacity. Resource storage can be promoted in the nursery by arresting plant growth and supplying resources at a higher rate than seedling growth and maintenance rate. We conclude that the way in which woody plants manage stored resources drives their growth and stress tolerance. However, plant functional types differ in storage physiology, which should be considered in silvicultural management.