Morphophysiological aspects of ornamental sunflowers cultivated in different growing seasons under semi-arid conditions

ABSTRACT Knowledge of how climatic conditions affect plant morphophysiology is essential for understanding how to manage the growth cycles of different crops. The aim of this study was to evaluate the effects of the growing seasons in a semi-arid area on the morphophysiological variables of ornamental sunflower plants. The experiment was carried out in a randomized block design in a split-plot arrangement with four replicates. Six cultivars (‘Bonito de Outono Sortido’, ‘Sol Noturno’, ‘Sol Vermelho’, ‘Jardim Amarelo Alto’, ‘Girassol F1 Sunbright Supreme’ and ‘Girassol F1 Vincents Choice’) were evaluated in the main plots and two different growing seasons (GS) in the subplots (GS1 - warm climate and GS2 - mild climate). Evaluations of gas exchange, chlorophyll indices, and leaf surface area were carried out at the reproductive stage (R5.5). The cultivation of ornamental sunflowers in semi-arid regions was significantly affected by the growing season. Changes in gas exchange variables and the morphophysiology of ornamental sunflower plants in the two growing seasons reflected the high phenotypic plasticity characteristic of this species. The cultivation of ornamental sunflowers under semi-arid conditions in the growing season, when air temperature and solar radiation are high, could be limited due to elevated transpiration rates. Therefore, it is recommended that they are grown mainly during the moderate climatic season in semi-arid regions.

摘要 明晰气候条件对植物形态生理特性的作用机制，是优化不同作物生长周期管理方案的核心前提。本研究旨在探究半干旱地区不同生育期对观赏向日葵形态生理指标的影响。本试验采用裂区设计的随机区组方案，设置4次重复。主区设置6个观赏向日葵品种（‘Bonito de Outono Sortido’、‘Sol Noturno’、‘Sol Vermelho’、‘Jardim Amarelo Alto’、‘Girassol F1 Sunbright Supreme’以及‘Girassol F1 Vincents Choice’），副区设置2个不同生育期（GS1——暖温气候，GS2——温和气候）。于生殖生长期（R5.5）测定了气体交换参数、叶绿素指数与叶面积。半干旱地区观赏向日葵的种植受生育期影响显著。两个生育期内观赏向日葵气体交换参数与形态生理特性的变化，体现了该物种典型的高表型可塑性。在半干旱地区气温与太阳辐射较高的生育期种植观赏向日葵，可能因蒸腾速率升高而受到生长限制。因此，半干旱地区的观赏向日葵种植建议优先安排在气候温和的生育期开展。