East‐facing Helianthus annuus has maximal number and mass of kernel‐filled seeds: Seed traits versus head orientation. Issue 3 (29th June 2022)

• Record Type: Journal Article
• Authors: Takács, Péter; Slíz‐Balogh, Judit; Száz, Dénes; Horváth, Gábor
• Is Part Of: Plant-environment interactions. Volume 3:Issue 3(2022)
• Page Start: 130
• Page End: 139
• Publication Date: 2022-06-29
• Subjects: absorbed light energy -- eastward orientation -- Helianthus annuus -- inflorescence -- reproductive fitness -- seed number and mass -- seed traits -- sunflower; Plant ecology -- Periodicals; Plants -- Periodicals; 581.7
• DOI: 10.1002/pei3.10083
• Languages: English
• ISSNs: 2575-6265

Abstract

Abstract: After anthesis, the majority of mature sunflower ( Helianthus annuus ) inflorescences face constantly East, which direction ensures maximal light energy absorbed by the inflorescences in regions where afternoons are on average cloudier than mornings. Several theories have tried to explain the function(s) of this eastward orientation. Their common assumption is that eastward facing has certain advantages for sunflowers. In sunflower plantations, the capitulum of many plants can also face North, South, or upward. Large deviations from the conducive East direction can decrease the plant's reproductive fitness. A larger mass and number of seeds, for example, can guarantee safer seed germination and better early development of more offspring. Thus, our hypothesis was that the East facing of sunflower inflorescences ensures a larger seed number and mass compared to disoriented inflorescences. This idea was tested in a sunflower plantation, where we compared the number and mass of seeds in plants, the inflorescences of which were naturally or artificially oriented northward, eastward, southward, westward, or upward. Our study tested head diameter, seed weight, and seed number in a normal agronomic field setting being different from earlier investigations. The other difference was that we tested five head orientations and only East showed significantly increased seed weight and number. Using radiational computations, we showed that East facing ensures more absorbed light energy than other orientations, except upward. This finding can be one of the reasons for the maximal seed number and mass in East‐facing sunflower capitula. Although upward‐facing horizontal inflorescences absorbed maximal light energy, they had the fewest and lightest seeds probably because of the larger temperature and humidity as well as the too much sunlight, all three factors impairing the normal seed development. This study is the first that compares the seed traits of all head orientations of Helianthus annuus and proposes that the absorbed radiation could play a major role in the maximal seed number and mass of east‐facing heads. Abstract : Mature sunflower ( Helianthus annuus ) inflorescences no longer follow the Sun, and their majority face nearly East. This eastward orientation may have certain advantages for sunflowers. The eastern direction ensures maximal light energy absorbed by the inflorescences, if on average afternoons are cloudier than mornings, as is the usual meteorological situation averaged for decades. We hypothesized that the East facing of sunflower inflorescences ensures larger seed number and mass compared to disoriented inflorescences. In a sunflower plantation we found that East‐facing sunflower heads had much more and heavier seeds than heads facing North, South or West. Upward‐facing horizontal inflorescences had the fewest and lightest seeds, because they might have received too much sunlight which could impair the normal seed development.