Examinando por Autor "Jacobs, Douglass F."

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An exponential fertilization dose–response model to promote restoration of the Mediterranean oak Quercus ilex
(Springer Link, 2015-06-18) Uscola Fernández, Mercedes; Salifu, K Francis; Oliet-Palá, Juan A; Jacobs, Douglass F.
Nursery nitrogen (N) fertilization influences seedling N reserves, morphology, photosynthesis rate and stress tolerance and frequently enhances outplanting performance. Although mineral nutrition is a critical aspect of seedling quality, fertility targets of Mediterranean sclerophylous species have not been thoroughly quantified. We sought to define those fertility targets for seedlings of Quercus ilex, a key species in Mediterranean areas. Nine fertility treatments, ranging from 0 to 200 mg N seedling−1 applied under an exponential regime were tested in a greenhouse dose response trial in which phosphorus (P) and potassium (K) were increased in the same proportion as N (15N:5P:15K). Height and diameter growth were measured weekly, and biomass and nutritional status were analyzed at the end of culture (24 week). Plant growth and nutritional response to increased fertilization followed a curvilinear pattern depicting phases that ranged from deficiency to luxury consumption. Seedling dry mass production was maximized at 125 mg N seedling−1 (sufficiency level). N content and concentration increased with fertilization, reaching a maximum at 200 mg N seedling−1 (luxury consumption). P and K concentrations peaked at 75 and 25 mg N, respectively, suggesting a dilution effect of these nutrients. Root volume increased linearly up to 100 mg N and declined thereafter. The sufficiency level for Q. ilex (125 mg of applied N seedling−1) is notably higher than for other Quercus species from other biomes but intermediate to other Mediterranean Quercus species. No toxicity was observed at the highest treatment rate (200 mg N) suggesting that increased exponential N rates along with greater P and K proportions than those used in our experiment may further maximize nutrient storage.
Cold and heat tolerances of hybrids for restoration of the endangered Juglans cinerea L
(Springer Science + Business Media, 2021) Brennan, Andrea N; Uscola Fernández, Mercedes; Joly, Robert J; Jacobs, Douglass F.
• Key message Hybrids had overall intermediate cold and heat tolerances compared to their progenitors, Juglans cinerea and Juglans ailantifolia . Differences in hybrids were small compared to J. cinerea though, indicating that when considering extreme temperature tolerances, hybrids might be usesd in some restoration circumstances. However, hybrids might exceed their cold tolerance in especially cold areas, such as J. cinerea’s northern range limits. • Context Hybridization could incorporate traits for surviving detrimental global changes. Juglans cinerea, an endangered North American tree species, can hybridize with non-native Juglans ailantifolia Carr. Evidence indicates their hybrids could hold resistance to the fungal disease threatening J. cinerea. Consequently, the hybrids are being evaluated for restoration use, but to be effective, they must survive in J. cinerea’s distribution. An ecophysiological evaluation could contribute to predicting potential hybrid utilization areas. • Aims To provide a relative comparison of the cold and heat tolerances among J. cinerea provenances and between J. cinerea, J. ailantifolia, and their hybrids. • Methods In the cold test, twigs were subjected to five freeze treatments and resulting damage was estimated using electrolyte leakage. In the heat test, leaflets were subjected to six hot water bath treatments and damage was estimated using chlorophyll fluorescence. • Results Within J. cinerea, trees from colder areas exhibited less cold damage than those from warmer areas. Differences in heat damage did not occur among hardiness zones. Juglans cinerea exhibited greatest cold tolerance, J. ailantifolia exhibited greatest heat tolerance, and hybrids were intermediate. • Conclusion Differences in the cold and heat tolerances of J. cinerea and its hybrids were overall minimal, although greater in cold tolerance.
Drought tolerance and acclimation in Pinus ponderosa seedlings: the influence of nitrogen form
(Oxford, 2020-04-25) Sigala, José Angel; Uscola Fernández, Mercedes; Oliet-Palá, Juan A; Jacobs, Douglass F.
Drought is a limiting factor to forest regeneration and restoration, which is likely to increase in intensity and duration under future climates. Nitrogen (N) nutrition is related to drought-resistance mechanisms in trees. However, the influence of chemical N form (inorganic and organic N) on physiological traits related to drought resistance has been sparsely studied in conifer seedlings. We investigated the effect of N forms on morpho-physiological traits of Pinus ponderosa Dougl. ex Laws. seedlings and subsequent influences in drought tolerance and acclimation. One-year-old seedlings were fertilized during 10 weeks at 9 mM N with different N forms [either NH4+, NO3− or organic N (amino acids mixture)] in their second year of growth. After fertilization, we measured traits associated with intrinsic drought tolerance (shoot water relations, osmotic regulation, photosynthesis and cell membrane stability). Seedlings were then subjected to an 8-week drought period at varying drought intensities to evaluate plant acclimation mechanisms. We demonstrated that P. ponderosa seedlings could efficiently use amino acids as a primary N source, showing similar performance to those grown with inorganic N forms. Nitrogen form influenced mainly drought-acclimation mechanisms rather than intrinsic drought tolerance. Osmotic potential at saturation (Ψπsat) was marginally affected by N form, and a significant relationship between proline concentration in needles and Ψπsat was found. During acclimation, seedlings fertilized with organic N minimized needle senescence, retained more nutrients in the oldest needles, had maximum increments in proline concentration and hastened the development of water-use efficiency mechanisms compared with those fertilized with inorganic N sources. Our results suggest an improved physiological drought acclimation of organic N-fertilized seedlings.
Environmental stress under climate change reduces plant performance, yet increases allelopathic potential of an invasive shrub
(Springer Link, 2020-05-24) Medina-Villar, Silvia; Uscola Fernández, Mercedes; Pérez-Corona, Mª Esther; Jacobs, Douglass F.
Exotic invasive plant species (EIPS) may succeed in part because they release allelochemicals that are novel to native plants (Novel Weapons Hypothesis). Plant allelopathic effects may increase under abiotic and biotic stresses based on The Stress Hypothesis of Allelopathy (TSHA). Lonicera maackii is an aggressive EIPS in the Midwestern USA, able to affect native flora by means of allelopathy. We aimed to test the role of intraspecific competition, as biotic stress, and expected future climate conditions (i.e. intense floods in spring; hotter and drier conditions in summer), as abiotic stress, on the performance and allelopathic potential of L. maackii. We grew L. maackii plants, collected from the field (field plants) or germinated from seeds in a greenhouse (seedlings), with or without intraspecific competition and under simulated present and expected future (1) spring (intense flooding vs no flooding) and (2) summer conditions. We subsequently measured plant performance variables, such as Fv/Fm (an indicator of plant stress), plant biomass, and concentration of pigments, carbon and nitrogen; and allelopathic potential (i.e. the effect of L. maackii leaf extracts and conditioned substrates on the germination of two herb species). In accordance with TSHA, intense flooding stressed L. maackii (Fv/Fm < 0.7), reduced its biomass, and increased its allelopathic potential. In summer, L. maackii plants were more stressed (lower average Fv/Fm) under future summer conditions and intraspecific competition than under present conditions without competitors, but they had similar allelopathic potential. This suggests the presence of a stress threshold from which allelopathic potential does not increase further. Intraspecific competition more negatively affected the performance of seedlings (e.g. plant mass reduction) than field plants, but only increased the allelopathic potential of the latter. Our results indicated that the negative effects of intense flooding on L. maackii performance could be counteracted by the benefit gained in plant–plant competition by means of increased allelopathic potential. The complex role of abiotic and biotic conditions on L. maackii performance and allelopathy are also discussed.
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.
Nitrogen recovery in planted seedlings, competing vegetation, and soil in response to fertilization on a boreal mine reclamation site
(Science Direct, 2016-01-15) Sloan, Joshua L.; Uscola Fernández, Mercedes; Jacobs, Douglass F.
Field fertilization during reforestation often yields variable results, particularly on harsh restoration sites. An improved understanding of the recovery of applied nitrogen (N) under different fertilization practices should aid in developing more effective fertilizer prescriptions. We evaluated field establishment of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx.) seedlings as well as N recovery within planted seedlings, soil, and competing vegetation on a mine reclamation site in the oil sands region of northern Alberta in response to immediately available fertilizer (IAF) and polymer-coated controlled-release fertilizer (CRF) applications. 15N-enriched urea was applied as IAF and as a polymer-coated CRF (20 g N seedling−1 and 4 g N seedling−1, respectively) to each species. Seedling survival, growth, and nutritional status, along with occurrence of competing vegetation and plant and soil 15N recovery were quantified after the first field season. Seedlings receiving CRF exhibited increased diameter and organ dry mass relative to the IAF and control treatments. Both IAF and CRF promoted comparable increases in seedling N status, and fertilizer type did not influence within-seedling 15N allocation. Neither IAF nor CRF affected vegetation cover or dry mass. Recovery of fertilizer-derived 15N was low, with much of the recovered 15N remaining in soils and only small amounts observed in seedlings and competing vegetation for both fertilizer treatments. Findings indicate that directed root zone application of CRF promotes first-year seedling growth and nutritional responses similar to or better than those induced by broadcast IAF applications, but at substantially lower N application rates. Our results suggest that a shift from broadcast IAF to targeted soil applications of CRF may produce similar or improved early seedling growth and nutrient uptake on reclamation sites, while greatly reducing overall quantities of N applied during the regeneration phase, much of which appears to be lost from the site of application regardless of fertilizer type.
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.