Bianca A Santini, John G Hodgson, Ken Thompson, Peter J Wilson, Stuart R Band, Glynis Jones, Mike Charles, Amy Bogaard, Carol Palmer & Mark Rees

The relationships between plant traits tells us about the amount of resources species invest on a given trait. For example, thicker leaves are long-lived, but their construction is expensive for the plant and have lower photosynthetic rates than thin leaves. Another example, related to our study, is the triangular relationship found between seed mass and leaf area in woody species. This relationship tells us that small-seeded species can have either small or large leaves, whereas big-seeded species have large leaves. However, the combination of big seeds with small leaves does not occur. Again, this give us insights into resource allocation, in this case of the photosythates in a leaf and how are they distributed, either into small seeds or big seeds.

Indeed, resource allocation changes from species that live longer to those with shorter life-spans, and this will be reflected in the relationships between plant traits. For this reason, in this study, we wanted to know if the triangular relationship for seed mass and leaf area found in woody plants holds for annual species, which reproduce and die within a year, and invest most of their resources on reproduction. To test this, we used 401 annual species and, importantly, we incorporate indicators of habitat productivity and light into our study to test if these influence the relationship between these two traits.

Surprisingly, we found that the triangular relationship between seed mass and leaf area holds for annual species, and that the productivity of the habitat is driving this relationship. This is that in more productive habitats species with big leaves can either have either small or big seeds, whereas in low-productive habitats, species can only have small seeds and leaves. This suggest that in more productive habitats, which are also more competitive, species have more strategies for seed size/number selection. Our results show that despite the differences in their life cycle, plants conserve similar strategies across different life-forms, and that the productivity of the habitat plays an important role by driving and selecting for leaf and seed size.

Image caption: Photo provided by authors.
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