The contribution of acorn and soil N to early development of Chinese cork oak (Quercus variabilis Blume) seedlings under contrasting soil fertility conditions

40 p.Several studies have addressed the role of soil fertility on acorn N remobilization during seedling growth, but have focused on very early development stages or have assessed remobilization at a coarse grain ontogenetic scale making it difficult to know the precise time when seedlings switch from acorn N to soil N use. We cultivated Quercus variabilis seedlings under two distinct soil N fertility and assessed their growth, acorn N remobilization, and absorption of soil N at five distinct development stages, spanning from the incipient shoot emergence to the completion of the second flush of growth. Acorn N contributed more to seedling N content than soil N at all development stages. Seedlings began to uptake substantial amounts of soil N after the completion of leaf expansion during the first shoot flush of growth, coinciding with a fine root area that reached 50% of the maximum value observed at the end of the study. Roots became less dependent on acorn N before shoots. Soil fertility, rather than seedling growth rate, determined soil N uptake after the completion of leaf expansion in the first shoot flush of growth. We conclude that the acorn is the primary N source for Q. variabilis seedlings until the completion of the first shoot flush of growth. Soil fertility does not significantly affect either the amount of N remobilized from acorns or the switch from acorn N to massive soil N use, suggesting a minimal effect of forest microhabitat fertility on acorn N utilization by Q. variabilis seedlings.Gobierno de EspañaComunidad de MadridNational Natural Science Foundation of ChinaChina Scholarship Counci

Acorn size is more important than nursery fertilization for outplanting performance of Quercus variabilis container seedlings

Small acorns are usually discarded for seedling cultivation because they reduce plant quality. This,however, can potentially reduce genetic diversity of plantations. The use of small acorns will result in the production ofa higher proportion of small seedlings containing low nutrient levels and having poor outplanting performance in oakcontainer seedlings. Nursery fertilization partially offsets the negative effect of small acorns on seedling attributes in thenursery but not on outplanting performance.Small acorns result in low-quality seedlings and so are usually discarded in artificial regeneration programs of oakspecies. This can potentially reduce genetic diversity of plantations. Nursery fertilization may compensate for the low quality of small-acorn seedlings.To assess whether nursery fertilization interacts with Quercus variabilis acorn size to determine seedling morphology and nutrition in the nursery and outplanting performance.Methods Acorns of three size classes were used to cultivate seedlings with or without fertilization. Seedling emergence, nursery morphology and nutrient status, and outplanting survival and growth were measured.National Natural Science Foundation of ChinaFundamental Research Funds for Central UniversitiesComunidad de Madri

Simulated predation of Quercus variabilis acorns impairs nutrient remobilization and seedling performance irrespective of soil fertility

Background and aims Predators may partially orcompletely consume Quercus spp. acorns, but effectson nutrient remobilization and seedling performance arepoorly understood. We investigated interactions betweensoil fertility and the removal of Quercus variabilisacorn cotyledons at different early developmental stageson seedling nutrition and development.Methods Seedlings were grown in two soils of contrastingfertility and the kinetics of acorn nitrogen, phosphorusand potassium remobilization, and seedling survival,growth and nutrient content were analyzed.Results Acorn mass and macronutrients decreased remarkably<2 weeks after emergence, with nitrogen andphosphorus remobilizing faster than potassium. Acornremoval at or 1 week after emergence inhibited seedlingsurvival, growth and fine root formation, whereas removalfrom 2 to 10 weeks after emergence had minor effects. Acorn macronutrient remobilization and effects of acorn removal on seedling performance were not reversed under high soil fertility. When acorns were removed &#8805; 2 weeks after emergence, fertilization increased root surface and seedling nitrogen content. Conclusions. Acorn nutrients are more important than soil nutrients during very early seedling development. Cotyledon damage at emergence impairs seedling performance despite no direct damage to the remainder of the seedling. This effect cannot be reverted by high soil fertility and has potential ecological and practical implications for oak regeneration.National Natural Science Foundation of ChinaComunidad de Madri

The role of stored carbohydrates and nitrogen in the growth and stress tolerance of planted forest trees

Plants store compounds that supplement external resources to maintain primaryfunctions. 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 functionaltypes 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 fineroots. Conifers used less remobilized resources than broadleaf species for fine root growth.New shoots/leaves were mostly comprised of remobilized N ([60 %) in conifers andbroadleaf deciduous species, while broadleaf evergreens relied more on soil N (\50 %remobilized N). In contrast, few differences among functional groups existed in the contributionof remobilized carbon (C) to new leaves/shoots, which comprised 28&-45 % ofstored C reflecting the importance of current photosynthesis and distinctions in C and N remobilization physiology. Organ source strength for remobilized N 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. Accumulation of stored resources 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 managementMinisterio de Ciencia e InnovaciónComunidad de MadridUniversidad de Alcal

Differential impact of hotter drought on seedling performance of five ecologically distinct pine species

Increasing temperature and drought intensity is inducing the phenomenon of so called &ldquo;hotter drought&rdquo;, which is expected to increase in frequency over the coming decades across many areas of the globe, and is expected to have major implications for forest systems. Consequences of hotter drought could be especially relevant for closely-related species overlapping their distributions, since differences in response can translate into range shifts. We assessed the effect of future climatic conditions on the performance of five ecologically distinct pine species common in Europe: Pinus halepensis, P. pinaster, P. nigra, P. sylvestris and P. uncinata. We hypothesised that Mediterranean species inhabiting dry, low-elevation sites will be less affected by the expected warming and drought increase than species inhabiting cold-wet sites. We performed a controlled-conditions experiment simulating current and projected temperature and precipitation and analysed seedling responses in terms of survival, growth, biomass allocation, maximum photochemical efficiency (Fv/Fm) and plant water potential (&Psi;). Either an increase of temperature or a reduction of water input alone reduced seedling performance, but the highest impact occurred when these two factors acted in combination. Warming and water limitation reduced &Psi;, whereas warming alone reduced biomass allocation to roots and Fv/Fm. However, species responded differentially to warmer and drier conditions, with lowland Mediterranean pines (P. halepensis and P. pinaster) showing higher survival and performance than mountain species. Interspecific differences in response to warmer, drier conditions could contribute to changes in the relative dominance of these pine species in Mediterranean regions where they co-occur and a hotter, drier climate is anticipated.Supported by Stirling-held EU Marie Curie (FP7-2011-IEF-300825

Root growth dynamics of Aleppo pine (Pinus halepensis Mill.) seedlings in relation to shoot elongation, plant size and tissue nitrogen concentration

Large and high nitrogen (N) concentration seedlings frequently have higher survival and growth in Mediterranean forest plantations than seedlings with the opposite traits, which has been linked to the production of deeper and larger root systems in the former type of seedlings. This study assessed the influence of seedling size and N concentration on root growth dynamics and its relation to shoot elongation in Aleppo pine (Pinus halepensis Mill.) seedlings. We cultivated seedlings that differed in size and tissue N concentration that were subsequently transplanted into transparent methacrylate tubes in the field. The number of roots, root depth, and the root and shoot elongation rate (length increase per unit time) were periodically measured for 10 weeks. At the end of the study, we also measured the twig water potential (psi) and the mass of plant organs. New root mass at the end of the study increased with seedling size, which was linked to the production of a greater number of new roots of lower specific length rather than to higher elongation rate of individual roots. Neither plant size nor N concentration affected root depth. New root mass per leaf mass unit, shoot elongation rate, and pre-dawn psi were reduced with reduction in seedling size, while mid-day psi and the root relative growth rate were not affected by seedling size. N concentration had an additive effect on plant size on root growth but its overall effect was less important than seedling size. Shoot and roots had an antagonistic elongation pattern through time in small seedlings, indicating that the growth of both organs depressed each other and that they competed for the same resources. Antagonism between shoot and root elongation decreased with plant size, disappearing in large and medium seedlings, and it was independent of seedling N concentration. We conclude that root and shoot growth but not rooting depth increased with plant size and tissue N concentration in Aleppo pine seedlings. Since production of new roots is critical for the establishment of planted seedlings, higher absolute root growth in large seedlings may increase their transplanting performance relative to small seedlings. The lack of antagonism between root and shoot growth in large seedlings suggests that these plants can provide resources to sustain simultaneous growth of both organs.Ministerio de Economía y CompetitividadMinisterio de Ciencia y EducaciónComunidad de Madri

Assessing the limiting factors of natural regeneration in Mediterranean planted hedgerows

12 p.Conservation and restoration of hedgerows promote biodiversity and multifunctionality in agricultural landscapes. However, in Mediterranean environments, natural regeneration of hedgerows is often poor, and factors hindering the establishment and growth of hedgerow woody species remain unclear. This study aimed to address this gap by (1) quantifying natural regeneration, including seedling establishment and resprouting of planted hedgerow species and the establishment of woody species coming from outside the hedgerows; and (2) experimentally assessing the impact of drought, herbivory, and herb competition on seedling establishment. We selected 12 planted, 11?13-year-old hedgerows in four sites in Central Spain to sample their natural regeneration. In addition, we transplanted 1,356 seedlings of Colutea arborescens L., Crataegus monogyna Jacq. and Rhamnus alaternus L. to two field sites under three treatments that were applied factorially for two years: irrigation to alleviate summer drought, protection against herbivory, and herb clipping to reduce competition with transplanted seedlings. We found that only 66 juveniles of woody species, including 29 of species that were not planted in the hedgerows, developed from seed germination, and 316 sprouts recruited spontaneously along 10 years (14 individuals ha?1 year?1 ). Of the transplanted seedlings, only 22% survived after two years with protection against herbivory strongly enhancing seedling survival. To a lesser extent, irrigation and herb competition affected survival through interactions with herbivory and species identity. Irrigation and protection against herbivores accelerated seedling growth. Survival and growth of C. arborescens (14%; seedling height = 12 ± 9 cm) were lower than those of C. monogyna (41%; 21 ± 11 cm) and R. alaternus (17%; 13 ± 8 cm). We conclude that natural regeneration in Mediterranean planted hedgerows is low, herbivory is the main limiting factor for seedling survival, especially for deciduous species, and summer drought and herb competition mostly limit growth. These findings have important implications for the conservation and restoration of hedgerows in Mediterranean environments.Comunidad de MadridUniversidad de Alcal

Remobilization of acorn nitrogen for seedling growth in holm oak (Quercus ilex), cultivated with contrasting nutrient availability

Summary The relative contribution of nitrogen (N) reserves from seeds or uptake by the roots to the growth and N content of young seedlings has received little attention. In this study, we investigated the contribution of N from the acorn or uptake by the roots to the N content of holm oak (Quercus ilex L.) seedlings and determined if remobilization of acorn N was affected by nutrient availability in the growing media. Q. ilex seedlings were cultivated for 3 months, until the end of the second shoot flush of growth, with three N fertilization rates: 8.6 mM N, 1.4 mM N or no fertilization. Fertilizer N was enriched in 15 N. Between 62 and 75% of the N contained in high and low fertilized seedlings, respectively, at the end of the second flush of growth was derived from the acorn. However, the dependence on acorn N was greater during the early root growth and first shoot flush of growth and decreased during the second shoot flush of growth, with root uptake contributing 32-54% of plant new N in this latter developmental stage in high and low fertilized plants, respectively. Fertilization rate did not affect the amount of N taken up during the earliest developmental stages, but it increased it during the second shoot flush of growth. Fertilization increased the mass of the shoot segment formed during the second shoot flush of growth and reduced the root mass, with no effect on whole plant growth. Remobilization of acorn N was faster in unfertilized plants than in fertilized plants. It is concluded that the holm oak seedlings depend greatly upon acorn N until the end of the second shoot flush of growth, that significant root N uptake starts at the beginning of the second shoot flush of growth and that acorn N remobilization is a plastic process that is accelerated under extremely low substratum nutrient content

Foliar absorption and root translocation of nitrogen from different chemical forms in seedlings of two Mediterranean trees.

Along with root uptake, plants can also absorb N through leaves. There are few comparative studieson the foliar absorption of N from different chemical forms of N in forest tree species. We comparedthe 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 mMN:15N-nitrate (NO3&#8722;),15N-ammonium (NH4+),15N-urea or13C and15N dual-labeled glycine. Cuticularconductance was used as a surrogate of cuticle permeability to water. Q. ilex had higher N foliar absorp-tion than P. hapelensis. Neither cuticular conductance nor shoot surface area explained N differences inabsorption rate between species, which were instead likely linked to differences in stomatal density andpresence of trichomes. In both species, foliar N absorption rate and N recovery differed among N forms:urea > NH4+&#8805; glycine &#8805; NO3&#8722;. Differences in N absorption rate among N forms were correlated with theirphysico-chemical properties. The strong positive relationship between15N and13C uptake together withdetection in shoots of intact dual-labeled glycine (measured by gas chromatography&#-mass spectrome-try), 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&amp;amp;amp;;8722#. Cuticularconductance 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.Comunidad de MadridAustralian Research Counci

Root uptake of inorganic and organic N chemical forms in two coexisting Mediterranean forest trees

Background and aims Plants differ in their ability to usedifferent nitrogen (N) chemical forms, these differencescan be related to their ecology and drive communitystructure. The capacity to uptake intact organic N hasbeen observed in plants of several ecosystems. However,soil organic N uptake by Mediterranean plants is unknowndespite organic N being abundant inMediterranean ecosystems. We compare the uptake ofdifferent N forms in two widespread coexistingMediterranean forest trees with contrasting ecophysiologicalcharacteristics: Quercus ilex and Pinus halepensis.Methods To estimate root uptake rate of eachN form weused equimolar solutions (1 mM N) of 15NO3-, 15NH4+ and 15N-13C glycine.Results NH4+ and glycine were taken up at a similarrate, but faster than NO3&#8722; in both species. Intact duallabeled glycine was found in both species, demonstratingthat both species can absorb intact organic N. Conclusions: Despite their ecological differences, both species had similar preference for N forms suggesting no 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.Ministerio de Educación y CienciaMinisterio de Ciencia e InnovaciónMinisterio de Economía y CompetitividadComunidad de Madri