How and why do species break a developmental trade-off? Elucidating the association of trichomes and stomata across species.

Premise: Previous studies have suggested a trade-off between trichome density (D _t ) and stomatal density (D _s ) due to shared cell precursors. We clarified how, when, and why this developmental trade-off may be overcome across species.
Methods: We derived equations to determine the developmental basis for D _t and D _s in trichome and stomatal indices (i _t and i _s ) and the sizes of epidermal pavement cells (e), trichome bases (t), and stomata (s) and quantified the importance of these determinants of D _t and D _s for 78 California species. We compiled 17 previous studies of D _t -D _s relationships to determine the commonness of D _t -D _s associations. We modeled the consequences of different D _t -D _s associations for plant carbon balance.
Results: Our analyses showed that higher D _t was determined by higher i _t and lower e, and higher D _s by higher i _s and lower e. Across California species, positive D _t -D _s coordination arose due to i _t -i _s coordination and impacts of the variation in e. A D _t -D _s trade-off was found in only 30% of studies. Heuristic modeling showed that species sets would have the highest carbon balance with a positive or negative relationship or decoupling of D _t and D _s , depending on environmental conditions.
Conclusions: Shared precursor cells of trichomes and stomata do not limit higher numbers of both cell types or drive a general D _t -D _s trade-off across species. This developmental flexibility across diverse species enables different D _t -D _s associations according to environmental pressures. Developmental trait analysis can clarify how contrasting trait associations would arise within and across species.
(© 2024 The Authors. American Journal of Botany published by Wiley Periodicals LLC on behalf of Botanical Society of America.)