Effects of Elevated Carbon Dioxide Plus Chronic Warming on Plant Nitrogen Relations and Leaf Hyponasty

Autor: Jayawardena, Dileepa M.
Jazyk: angličtina
Rok vydání: 2020
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Popis: Atmospheric carbon-dioxide (CO2) enrichment is largely the cause of current global warming. Hence, in the future, organisms will experience the interactive effects of elevated CO2 (eCO2) and chronic warming rather than their individual effects. Though individual effects of eCO2 or chronic warming on plant responses have been studied in some detail, interactive effects of eCO2 and chronic warming on plant responses such as nitrogen (N) relations (uptake, translocation, assimilation) and leaf hyponasty (upward bending of leaves) have been rarely studied. Therefore, the goals of my dissertation work included (1) investigation of eCO2 plus chronic warming on plant N relations, using tomato (Solanum lycopersicum L. cv. Big Boy) and wheat (Triticum aestivum L. cv. Glenn) followed by a meta-analytic review, and (2) investigation of eCO2 plus chronic warming on leaf hyponasty and subsequent effects of hyponasty on plant growth, using tomato and other economically-important species. These goals were achieved by growing plants in a full-factorial experimental design, using two levels of CO2 (ambient vs. elevated) and two temperature regimes (near-optimal vs. supra-optimal) in controlled-environment growth chambers. In all experimental trials conducted, eCO2 plus warming inhibited tomato vegetative growth, whereas warming alone inhibited growth to a smaller extent, and eCO2 alone increased growth. One potential reason for inhibition of plant growth at eCO2 plus warming could be the observed increase in leaf hyponasty. Warming or eCO2 alone caused modest leaf hyponasty, whereas eCO2 plus warming caused severe leaf hyponasty, which correlated with decreased leaf area and biomass. This could be explained by decreased light interception, and thus in situ photosynthesis, as leaves became more vertically-oriented. Severe hyponasty driven by eCO2 plus warming was observed only in the compound-leaved species tested, but not in the simple-leaved species tested. Tomato plants grown at eCO2 plus warming also had the lowest nitrate (NO3-) and ammonium (NH4+) -uptake rates, as well as the lowest root-to-shoot net-N translocation. Moreover, eCO2 plus warming decreased whole-plant N assimilation in tomato, which was mainly driven by the inhibition of whole-plant NO3- assimilation. However, tomato plants grown at eCO2 plus warming had higher in vitro activities of key N-assimilation enzymes (an index of assimilation capacity) and higher % carbon (C) and N levels in roots, indicating that inhibition of N assimilation was not due to the damage to these enzymes nor due to resource limitation for root functions. Thus, in tomato, eCO2 plus warming may decrease N uptake and assimilation in large part because of reduced whole-plant growth, and thus N demand, caused by leaf hyponasty. In wheat, plant growth, %N, protein concentration, and root N-uptake rates were each significantly affected only by CO2, while N- and NO3--assimilation were significantly affected only by warming. However, plants grown at eCO2 plus warming had the lowest concentrations of N and protein, and, hence, lower nutritional quality, with decreased protein concentration at eCO2 plus warming likely due to the inhibition of N assimilation. A comprehensive meta-analysis of the effects of eCO2 plus warming on plant N relations further supported the above-mentioned experimental observations. According to the meta-analysis, eCO2 alone or in combination with warming reduced shoot %N (more so at ≥300 vs. 2), while root %N was significantly reduced only by eCO2; warming alone often increased shoot %N, but mostly did not affect root %N. Though root N-uptake rate was unaffected by eCO2, eCO2 plus warming decreased N-uptake rate, while warming alone increased it. Similar to %N, protein concentration decreased with eCO2 in shoots and grain (but not roots), increased with warming in grain, and decreased with eCO2 and warming in grain. These results show that in the future, two key variables of climate change, eCO2 and chronic warming, will have the potential to interactively disrupt plant N metabolism and reduce nutritional quality of some economically important species. Therefore, when developing crops for future climates, transgenic, genetic engineering, and traditional plant-breeding approaches should focus on generating genotypes with more-resilient N uptake and assimilation, and, in the case of tomato and other compound-leaved species, genotypes that exhibit less climate-change induced leaf hyponasty.
Databáze: Networked Digital Library of Theses & Dissertations
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