Internal Regulation of Nutrient Uptake by Relative Growth Rate and Nutrient-Use Efficiency

DOI: 10.1007/3-540-27675-0_4
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Available from: Vincent Gutschick, Oct 13, 2014
    • "This can be due to increased photosynthesis at higher temperatures, where the extra fixed carbon is allocated belowground to sustain new root growth (Pregitzer and King 2005). However, high temperatures often increase evapotranspiration and lead to drought, and low soil moisture reduces nutrient availability and nutrient uptake in the rooting zone, thus decreasing nutrient uptake rates (Gutschick and Pushnik 2005). Even though elevated CO 2 is expected to increase plant growth, this increase may not be sustained in the long term if nutrients or water are limited. "
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    ABSTRACT: Ecosystems exposed to elevated CO2 are often found to sequester more atmospheric carbon due to increased plant growth. We exposed a Danish heath ecosystem to elevated CO2, elevated temperature and extended summer drought alone and in all combinations in order to study whether the expected increased growth would be matched by an increase in root nutrient uptake of NH4+-N and NO3- -N. Root growth was significantly increased by elevated CO2. The roots, however, did not fully compensate for the higher growth with a similar increase in nitrogen uptake per unit of root mass. Hence the nitrogen concentration in roots was decreased in elevated CO2, whereas the biomass N pool was unchanged or even increased. The higher net root production in elevated CO2 might be a strategy for the plants to cope with increased nutrient demand leading to a long-term increase in N uptake on a whole-plant basis. Drought reduced grass root biomass and N uptake, especially when combined with warming, but CO2 was the most pronounced main factor effect. Several significant interactions of the treatments were found, which indicates that the responses were nonadditive and that changes to multiple environmental changes cannot be predicted from single-factor responses alone.
    No preview · Article · Jan 2014 · Functional Plant Biology
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    ABSTRACT: The effects of inorganic nitrogen (N) nutrition (NH4+, NO3− or both) at equimolar (0.5 mM) concentration on growth, biomass allocation, mineral element concentration, N-uptake kinetics and nitrate reductase activity were assessed in hydroponically grown Cyperus laevigatus and Phormium tenax. Both species grew well with both NH4+ and NO3− as the sole N source, but the mean growth rate of C. laevigatus (RGR = 0.12 d−1) was significantly higher than that of P. tenax (RGR = 0.02 d−1). However, the RGR of C. laevigatus was higher when supplied with NH4+, either alone or in combination with NO3−, than when supplied with NO3− alone, whereas the RGR of P. tenax was indifferent to nitrogen source. The nitrogen uptake rate of C. laevigatus was generally higher (2–3-fold for NH4+ and 4–14-fold for NO3−) than that of P. tenax in concert with its higher growth rate. Both species had higher uptake capacity and higher affinity for NH4+ than for NO3−. The mean maximum uptake velocity (Vmax) for NH4+ was 99 and 41 μmol g−1 root DM h−1 for C. laevigatus and P. tenax, respectively, as opposed to a Vmax for NO3− of 24 and 3.4 μmol g−1 root DM h−1 for C. laevigatus and P. tenax, respectively. P. tenax had significantly lower affinities for both NH4+ and NO3− than C. laevigatus indicating that P. tenax are adapted to sites with relatively high N availability, as opposed to C. laevigatus, which via its high-affinity uptake systems can grow at sites with lower N availability. Both shoots and roots of both species had nitrate reductase activity, particularly when plants were fed with NO3−. P. tenax seemed to be more sensitive to NH4+ nutrition than C. laevigatus since tissue concentrations of mineral elements were lower in roots of plants supplied with NH4+. Our results suggest that the indifference to N nutrition provides C. laevigatus and P. tenax with the ability to grow well in periodically inundated areas with fluctuating and variable N sources. However, C. laevigatus may be better adapted than P. tenax to grow in permanently inundated soils with high NH4+ concentrations, whereas P. tenax may be better adapted to grow at high NO3− condition.
    Full-text · Article · Apr 2013 · Aquatic Botany
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    ABSTRACT: Background and aims Accurate predictions of nutrient acquisition by plant roots and mycorrhizas are critical in modelling plant responses to climate change. Methods We conducted a field experiment with the aim to investigate root nutrient uptake in a future climate and studied root production by ingrowth cores, mycorrhizal colonization, and fine root N and P uptake by root assay of Deschampsia flexuosa and Calluna vulgaris. Results Net root growth increased under elevated CO2, warming and drought, with additive effects among the factors. Arbuscular mycorrhizal colonization increased in response to elevated CO2, while ericoid mycorrhizal colonization was unchanged. The uptake of N and P was not increased proportionally with root growth after 5 years of treatment. Conclusions While aboveground biomass was unchanged, the root growth was increased under elevated CO2. The results suggest that plant production may be limited by N (but not P) when exposed to elevated CO2. The species-specific response to the treatments suggests different sensitivity to global change factors, which could result in changed plant competitive interactions and belowground nutrient pool sizes in response to future climate change.
    Full-text · Article · Aug 2013 · Plant and Soil
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