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Öğe Biomass allocation and nutrient use efficiency in response to water stress: insight from experimental manipulation of balsam fir, concolor fir and white pine transplants(Springer, 2021) Koc, Ismail; Nzokou, Pascal; Cregg, BertPlants under water stress alter their normal morphological and physiological processes. However, biomass allocation and nutrient use efficiency remain largely unknown under the interactive effect of irrigation and fertilization for many economically important conifer species. In this study, we compared biomass allocation and resources use efficiency of two-year-old (plug+1) containerized balsam fir [Abies balsamea (L) Mill.] 'Cooks' and concolor fir [Abies concolor (Gord. & Glend.) Lindl. Ex Hildebr.] 'Cibola', and one-year-old bare-root white pine [Pinus strobus L.] transplants grown under variable watering and fertilization conditions. In a controlled greenhouse setting, transplants were submitted to three irrigation levels and two fertilization rates in a factorial experimental design. Fir species, mainly concolor fir, had a greater capacity to utilize water resulting in decreased stem water potential than white pine, leading to increased aboveground growth and shoot-to-root (S/R) ratio. White pine transplants had a higher assimilatory nutrient efficiency, nutrient use efficiency (NUE), root weight ratio, and a lower nitrogen availability index than the two fir species, suggesting a better ability to tolerate water stress. The high rates of fertilization increased nutrient concentration more than growth, suggesting luxury consumption. These results indicate that white pine responds to drought stress by closing their stomata and decreasing their S/R ratio to limit physiological activities, while the two fir species exhibit increased water uptake via expanded fine root networks, increasing the NUE and S/R ratio. However, there was no clear trend for the irrigation and fertilization interaction for NUE for three species, making it difficult to generalize responses.Öğe Combined effects of water stress and fertilization on the morphology and gas exchange parameters of 3-year-old Abies fraseri (Pursh) Poir(Springer Heidelberg, 2023) Koç, İsmail; Nzokou, PascalThree-year-old (plug + 2) containerized Fraser fir (Abies fraseri [Pursh] Poir.) seedlings were treated to various irrigation and fertilization regimes in a greenhouse factorial experiment. We assessed physiological and growth responses to these two factors' single and combined effects. Irrigation significantly (P < 0.05) affected relative height (RHG) and ground-level diameter growth (RDG) and some physiological parameters, including stomatal conductance (gs), stem water potential, net photosynthetic rate (Anet), intrinsic water use efficiency (WUE), transpiration rate (E), and photosynthetic pigments concentrations (Chls). Fertilization had only a significant effect on RDG. The increased fertilizer rates decreased some physiological parameters, including Anet, gs, and E, while increased fertilizer rates increased Chls and total nitrogen concentration (TKN). Chls and carotenoids usually increased through the treatment periods. The irrigation and fertilization interaction did not significantly affect RHG and RDG; however, the interaction significantly affected (P < 0.05) Anet, gs, E, and WUE. The interaction did not affect the TKN and Chls (P > 0.05). As a result, fertilization affected plant growth positively but caused some adverse effects on a few plant physiological functions, such as photosynthesis and Chls and carotenoid concentrations in plants under water stress. In our study, plant water status was the most critical parameter for growth and physiological processes compared to fertilization. Plants have the best responses to water stress in terms of physiological parameters under the interaction of low fertilization and increased irrigation. Under water-stress (375 ml irrigation per week), the medium fertilized (5.0 g N-1) treatment would be proposed as best morphologically and physiologically for 3-year-old Fraser fir seedlings.Öğe Do Various Conifers Respond Differently to Water Stress? A Comparative Study of White Pine, Concolor and Balsam Fir(Kastamonu Univ, 2022) Koç, İsmail; Nzokou, PascalAim of study: Two-year-old containerized balsam and concolor fir and one-year-old Eastern white pine transplants were grown under variable watering regimes with the goal of identifying plant morphological and some physiological traits under water stress. Area of study: This experiment was conducted in a greenhouse at the Tree Research Center on the Michigan State University campus, East Lansing, Michigan. Material and methods: Relative root collar diameter (RRCD), height growth (RHG), and root length (RRL) were measured as growth parameters. Stem water potential (psi), stomatal conductance (gs), net photosynthetic rate (Anet), intrinsic water use efficiency (iWUE=Anet/gs), foliar potassium ((K)+), and calcium (Ca+2) concentration were measured as physiological traits. Main results: Well-watered transplants had significantly higher RRCD, RHG, and RRL in fir species. Balsam fir and white pine transplants had a higher psi than concolor fir under severe stress. Fir species had higher Anet, gs, and a lower iWUE than white pine. White pine had a lower foliar K+ concentration, while balsam fir had the highest foliar Ca+2 concentration. Balsam fir had higher growth and Anet, gs, and iWUE under water stress due to their ability to maintain higher water uptake despite a reduced soil water content. Highlights: It is concluded that white pine has better drought tolerance because of the ability to withstand water stress through the mechanism of reduced photosynthetic activities and growth, minimize water loss, and increase water uptake.Öğe Gas Exchange Parameters of 8-Year-Old Abies fraseri (Pursh) Poir. Seedlings Under Different Irrigation Regimes(2022) Koç, İsmail; Nzokou, PascalEight-year-old Abies fraseri seedlings were grown under different irrigation regimes to determine how drought stress might affect the seedlings in terms of gas exchange parameters. In this study, net photosynthesis (Anet), transpiration rate (E), stomatal conductance (gs), intercellular CO2 (Ci), Ci to ambient CO2 (Ca) concentration ratio (Ci/Ca), intrinsic water use efficiency (iWUE), and water use efficiency (WUE) were measured on August 11 and 27. Irrigation and measurement time were statistically significant on all gas exchange parameters except WUE for irrigation and measurement time and Anet for measurement time. E and gs were significant under the irrigation and measurement time interactions. In this study, increasing irrigation generally decreased Anet, and gs, while increased E, iWUE, and Ci/Ca. On August 27, A. fraseri had higher Anet, gs, E, Ci, Ci/Ca, and lower iWUE values than August 11. However, there was a robust positive correlation between gs and Anet, while a negative correlation between gs and iWUE in A. fraseri seedlings. In general, prolonged water deficiency leads plants to decrease Anet, gs, and E while iWUE increases, contrary to the current study. A well-developed and deeper root system, especially in plants under less or no-irrigation regimes, may alleviate drought stress effects in the long run and provide an advantage in leaf gas exchange parameters. In addition, the fact that soil moisture did not differ much between treatments, although irrigation levels were different, may explain the similar behavior among individuals measured in terms of gas exchange parameters.Öğe Growth and physiological response of fraser fir [Abies fraseri (Pursh) Poir.] seedlings to water stress: Seasonal and diurnal variations in photosynthetic pigments and carbohydrate concentration(2012) Kulaç, Şemsettin; Nzokou, Pascal; Güney, Deniz; Cregg, Bert Michael; Turna, İbrahimFour-year-old seedlings of Abies fraseri [(Pursh) Poir] (fraser fir) were grown in semicontrolled conditions in hoop houses with five watering regimes (0.00, 0.62, 1.25, 2.50, and 3.70 cm/week) with the goal of determining the seasonal variation in the physiological response to drought stress. Drought stress was monitored by measuring predawn (?pd) and midday (?md) potentials in a subset of plants from each treatment. Physiological variables monitored were chlorophyll fluorescence (Fv/Fm), Chl a, Chl b, total carotenes, and total carbohydrate concentrations. Morphological characteristics including height growth, root collar diameter, and terminal shoot growth were also measured. Predawn stem water potential values were generally higher (-0.8 to -1.9 Mpa) than midday values (-1.3 to -2.9 Mpa). Irrigation consistently increased ?pd and ?md compared with nonirrigated treatments. Photosynthetic pigments (Chl a, Chl b, and carotenes) decreased midseason (14 July) and increased toward the end of the season (25 Aug.) in predawn and midday measurements. There was a significant effect (P < 0.05) of drought stress on photosynthetic pigment concentrations in predawn and midday samples in the late-season measurements (25 Aug.). These results were accompanied with a similar significant difference in Fv/Fm between non-irrigated and irrigated trees. We concluded that significant effects observed on photosynthetic pigment concentrations in some of the treatments did not affect carbohydrate concentrations. Exposure of A. fraseri to water stress did not cause a reduction in supply of metabolic carbohydrates; consequently, the decline and mortality in water-stressed plants can only be the result of hydraulic failure caused by xylem cavitation leading to cessation of water flow in tissues, desiccation, and cellular death. Further studies are needed to confirm these preliminary conclusions.Öğe Growth and Physiological Response of Fraser Fir [Abies fraseri (Pursh) Poke] Seedlings to Water Stress: Seasonal and Diurnal Variations in Photosynthetic Pigments and Carbohydrate Concentration(Amer Soc Horticultural Science, 2012) Kulaç, Şemsettin; Nzokou, Pascal; Güney, Deniz; Cregg, Bert Michael; Turna, İbrahimFour-year-old seedlings of Abies fraseri [(Pursh) Poir] (fraser fir) were grown in semicontrolled conditions in hoop houses with five watering regimes (0.00, 0.62, 1.25, 2.50, and 3.70 cm/week) with the goal of determining the seasonal variation in the physiological response to drought stress. Drought stress was monitored by measuring predawn (Psi pd) and midday (Psi md) potentials in a subset of plants from each treatment. Physiological variables monitored were chlorophyll fluorescence (F-v/F-m), ChI a, ChI b, total carotenes, and total carbohydrate concentrations. Morphological characteristics including height growth, root collar diameter, and terminal shoot growth were also measured. Predawn stem water potential values were generally higher (-0.8 to 1.9 Mpa) than midday values (-1.3 to 2.9 Mpa). Irrigation consistently increased Psi pd and Psi md compared with non-irrigated treatments. Photosynthetic pigments (ChI a, ChI b, and carotenes) decreased midseason (14 July) and increased toward the end of the season (25 Aug.) in predawn and midday measurements. There was a significant effect (P < 0.05) of drought stress on photosynthetic pigment concentrations in predawn and midday samples in the late-season measurements (25 Aug.). These results were accompanied with a similar significant difference in F-v/F-m between non-irrigated and irrigated trees. We concluded that significant effects observed on photosynthetic pigment concentrations in some of the treatments did not affect carbohydrate concentrations. Exposure of A. fraseri to water stress did not cause a reduction in supply of metabolic carbohydrates; consequently, the decline and mortality in water-stressed plants can only be the result of hydraulic failure caused by xylem cavitation leading to cessation of water flow in tissues, desiccation, and cellular death. Further studies are needed to confirm these preliminary conclusions.Öğe Growth response and nitrogen use physiology of Fraser fir (Abies fraseri), red pine (Pinus resinosa), and hybrid poplar under amino acid nutrition(Springer, 2013) Wilson, Alexa R.; Nzokou, Pascal; Güney, Deniz; Kulaç, ŞemsettinPlants can assimilate amino acids from soils. This has been demonstrated in controlled environments and soils of various forest ecosystems. However, the role of root-absorbed amino acids in plant nitrogen nutrition is still poorly understood. We investigated the agroecological performance and nutrient use physiology of two conifers (Abies fraseri and Pinus resinosa) and one hardwood species (hybrid poplar) under amino acid fertilization. Arginine fertilizer (arGrow(A (R)) Complete) was applied at varying rates (0, 56, 112, 224, and 336 kg N/ha) and compared to an inorganic control treatment (ammonium sulfate 112 kg N/ha). Parameters monitored included tree growth response, foliar nitrogen concentration, and inorganic nitrogen leaching below the rootzone. Results obtained indicate a significant growth and foliar nitrogen response to amino acid treatments, with increasing amino acid application leading to greater growth and foliar nitrogen. However, rates two to three times higher than that of the inorganic control were necessary to provide similar growth and foliar nitrogen responses. These observations were suggested to be due to competition with soil microbes for organic nitrogen, growth inhibition due to the presence of large concentrations of amino acids, or adsorption to cation exchange sites. Amino acid applications did not increase the leaching of inorganic nitrogen due either to the binding of positively charged arginine cations to exchange sites or rapid mineralization followed by plant assimilation. Mineral nitrogen collected in leachate samples increased with the application rate suggesting at least some mineralization in high amino acid application rates. We conclude that growth response and nitrogen use physiology of these species when treated with arginine are largely controlled by soil processes including microbial competition and adsorption. Further studies are being conducted to confirm these hypotheses.
