Response of imidazolinone-resistant and -susceptible weedy rice populations to imazethapyr and increased atmospheric CO2

Abstract Background: Weedy rice (Oryza sativa L.) is the main weed of rice crop. The high genetic variability of weedy rice contributes to the high phenotypic diversity between biotypes and different responses to environmental stress. Objective: The present study aimed to evaluate the response of imidazolinone-susceptible and -resistant weedy rice populations to increased atmospheric [CO2]. Methods: The experiment was arranged in a complete randomized design with six replications. The treatments included two [CO2] concentration (700 and 400 μmol mol-1) and three treatments: resistant genotype (IMI-resistant) treated with imazethapyr; resistant genotype without imazethapyr, and a susceptible genotype without imazethapyr. Results: The IMI-resistant and -susceptible weedy rice responded similarly to [CO2] enrichment. Enhanced [CO2] increased competitive ability of the weedy rice populations tested, by means of increased plant height. Weedy rice seed production also increased with enhanced [CO2] by means of increased photosynthesis rate and reduced transpiration (increased water use efficiency). Increased seed production also means increased weed persistence as it increases the soil seedbank size. The application of imazethapyr on IMI-resistant weedy rice did not alter its response to [CO2]; conversely, increased [CO2] did not change the resistance level of weedy rice to imazethapyr. High [CO2] increased spikelet sterility, but this beneficial effect was negated by the overall increase in production of filled grains. Conclusions: Enhanced [CO2] concentrations increases weedy rice growth, photosynthesis rates, seed production and spikelet sterility; the imidazolinone application does not affect the response of weedy rice to enhanced [CO2] affects weedy rice response to imidazolinone herbicide.摘要 背景：杂草稻（Oryza sativa L.）是水稻栽培的主要杂草。杂草稻具有较高的遗传变异性，这使其不同生物型间呈现出丰富的表型多样性，且对环境胁迫的响应存在差异。 目的：本研究旨在评估抗咪唑啉酮类（imidazolinone-resistant）与咪唑啉酮敏感型（imidazolinone-susceptible）杂草稻种群对大气二氧化碳浓度（[CO2]）升高的响应。 方法：本实验采用完全随机设计，设置6次生物学重复。实验处理包含两种二氧化碳浓度（700 μmol mol⁻¹与400 μmol mol⁻¹），以及三种基因型处理：施用咪唑乙烟酸（imazethapyr）的抗咪唑啉酮基因型、未施用咪唑乙烟酸的抗咪唑啉酮基因型、未施用咪唑乙烟酸的敏感基因型。 结果：抗咪唑啉酮与敏感型杂草稻对二氧化碳浓度升高的响应趋势一致。大气二氧化碳浓度升高可通过提升株高，增强受试杂草稻种群的竞争能力。此外，二氧化碳浓度升高还可通过提高光合速率、降低蒸腾速率（提升水分利用效率），增加杂草稻的种子产量。种子产量的提升同时意味着土壤种子库规模扩大，进而增强杂草的田间存续能力。向抗咪唑啉酮杂草稻施用咪唑乙烟酸，并未改变其对二氧化碳浓度升高的响应；反之，二氧化碳浓度升高也未改变杂草稻对咪唑乙烟酸的抗性水平。高二氧化碳浓度会增加小穗不育率，但这一负面效应可通过饱合籽粒总产量的整体提升得到抵消。 结论：大气二氧化碳浓度升高可促进杂草稻的生长、提升其光合速率与种子产量，并增加小穗不育率；咪唑啉酮类（imidazolinone）除草剂的施用不会影响杂草稻对二氧化碳浓度升高的响应，而二氧化碳浓度升高也不会改变杂草稻对咪唑啉酮类除草剂的抗性水平。