A study involving three CREAF researchers has found that plants with low nitrogen and phosphorus concentrations in their leaves do not reproduce every year to enable them to reproduce on a huge scale in years in which conditions are right. Oaks, holm oaks and beeches are examples of trees that behave in such a way.

Until now, the scientific community had not conclusively determined why some plants do not reproduce on an annual basis, a phenomenon known as mast seeding. However, an article just published in the journal Nature Plants has solved the mystery. Plants that struggle to reproduce every year due to a lack of resources adopt a strategy of alternating years of extremely high seed production with years of poor or non-existent production. The practice has surprised the article’s authors, as skipping reproduction in any given year means a lost opportunity to spread seeds.

Staking everything on just a few years is a risky strategy for a plant.

Led by Marcos Fernández-Martínez from the University of Antwerp, the study described in the article found that the purpose of not reproducing in certain years is to make it possible to reproduce more effectively and with greater intensity in other years. “Mast seeding entails drawbacks in evolutionary terms, as staking everything on just a few years is a risky strategy”, explains Dr. Fernández-Martínez. “Plants do that when it takes them a number of years to accumulate the resources and nutrients they need to reproduce, and the only option open to them is to do so on a massive scale to guarantee success”, he adds. The scientists alongside whom he conducted the study include CREAF-based CSIC researchers Josep Peñuelas and Jordi Sardans and CREAF ecologist Josep Maria Espelta.

Climate and rainfall also affect reproduction

The researchers made their finding by looking at nitrogen and phosphorus concentrations in the leaves of 200 different species of plants across the world. Their results show that nitrogen and phosphorus are very closely connected with mast seeding, in that masting intensity is highest in plants with the lowest concentrations of the two nutrients.

“Over and above the influence of nutrients, we found that plants’ seed production tends to be more variable in climates with a high level of interannual variability in precipitation”, says Josep Peñuelas. This means that variability in a region’s rainfall is also a factor in the regularity with which plants reproduce. That finding is particularly relevant to the Mediterranean basin, where annual rainfall levels are predicted to become increasingly variable as a consequence of climate change.

Referenced article:

Fernández-Martínez, M., Pearse, I., Sardans, J. et al. Nutrient scarcity as a selective pressure for mast seeding. Nature Plants (2019) DOI: 10.1038/s41477-019-0549-y