Plants Shed Flowers Because of Microbes That Affect Growth, Study Reveals

Flower yields are negatively impacted by microbes that grow on them. According to a recent study, this is the reason why plants quickly shed their flowers. The said study is a combination of plant microbiome analysis and field research.

The research, conducted by a team of scientists from Kyoto University in Japan together with the Centre for Research on Ecology and Forestry Applications (CREAF, Spain), is published in the open-access academic journal Metabarcoding and Metagenomics.

Zooming In on Flowers

The long-accepted theory is that flowers serve as the plant's reproductive system. However, perennial plants create their reproductive system from scratch each season. The flowers stay on the plant as long as they are required.

Previous studies have scrutinized the deviation in flower life spans among species. However, the previous studies focused primarily on the exchange between the benefit that the whole plant would get from maintaining their reproductive organs and the energy they would expend on developing and sustaining their flowers.

However, the team had already discovered a different angle to examine the phenomenon before the current study.

Their research was guided by the question of why plants invested their energy into producing delicate flowers which will wither in a matter of days as opposed to investing a little more of it to produce much more robust ones, increasing their chance of successful reproduction.

The author of the current study, Shoko Sakai, observed an intriguing relationship between flower longevity and temperature. The hotter the environment in which they bloom, the shorter the period a plant retains its flowers. Longtime experts have been aware of the phenomenon.

Microbes in the Flowers

Sakai proposed the idea that the cause of a flower's shortened lifespan must be antagonistic microbes present on flowers once the flower bud opens, such as fungi and bacteria. She didn't think it was a coincidence that microbes expand more quickly in hotter environments.

Microbes can find a variety of habitats in flowers. By exuding nectar, which is rich in sugars and frequently also contains other nutrients like amino acids and lipids, they draw pollinators. The stigma is a growth chamber for pollen tubes and a germination bed for pollen grains. It preserves the nutrients and humidity required for the growth of pollen tubes. Unsurprisingly, after a flower opens, the number of microbes grows more numerous over time.

Field Experiments

The researchers conducted field tests to identify what microbial communities would develop on flowers if their longevity was increased before drawing any conclusions.

They did this by extracting microbes from old flowers of wild ginger (Alpinia japonica), a species that grows in Japan and blooms in the early summer when the country's hot and muggy climate is perfect for microbial growth. The microbes were then spread to additional wild ginger plants, whose flowers had just begun to bloom.

The research team observed that the plant produced noticeably fewer fruits, which was consistent with their original hypothesis, even though there were no obvious disease symptoms on the flowers or fruits. In the study, the microbiomes of the plants reveal the presence of several bacterial groups evolving during the time that the flowers were still maintained by the whole plant system. These bacteria are referred to as "residents" of the plant because they can also be found on the flower buds of untreated flowers.

According to Sakai, the majority of research to date on flower characteristics has focused on how they interact with pollinators. Recent research has prompted the question of whether they have failed to consider the contributions of microbes in their investigations of floral traits. For instance, flower volatiles, frequently thought of as the main pollinator attractants, can suppress harmful microbes. Sakai says that they may have underestimated how deeply ingrained in the evolution of angiosperms the effects of microbes on plant reproductive ecology are, Phys Org reports.