Adaptation to cold includes faster nitrogen resorption in Arabidopsis thaliana leaves

Kevin Sartori, Cyrille Violle, Denis Vile, François Vasseur, Pierre de Villemereuil, Justine Bresson, Lauren Gillespie, Leila Rose Fletcher, Lawren Sack, Elena Kazakou

This is a plain language summary of a Functional Ecology research article which is published here.

Schematic drawing illustrating selection on various traits by Arabidopsis

Resorption refers to the process by which plants recycle nutrients from senescing leaves. It is of particular interest for nitrogen due to the scarcity of its assimilable form in most ecosystems. 

Here we ask whether resorption is adaptive, meaning that resorption capacity covaries with plant strategies in contrasting environments, and also that its variation is genetically determined.

Classically, nitrogen resorption is evaluated by measuring the nitrogen resorption efficiency. It indicates the proportion of nitrogen that has been remobilized during leaf senescence, by comparing the leaf nitrogen quantity when the leaf is physiologically mature and after complete leaf senescence. 

Methods to measure nitrogen content are destructive, meaning that different leaves are used to measure mature and senescent leaf nitrogen content, leading to possible bias.

We improved the resolution of estimation of leaf nitrogen resorption by non-destructively tracking time dynamics of nitrogen concentration. In addition to the classical measurement of resorption efficiency, we thus computed the relative maximum resorption rate of nitrogen, i.e., the amount of nitrogen remobilized by a leaf per unit time and per unit nitrogen. We used the model plant species Arabidopsis thaliana to explore the underlying genetics

With our results, we emphasized the ecological and evolutionary meaning of leaf nitrogen resorption components. In particular, high resorption rates of nitrogen, rather than high resorption efficiency, are favored toward the northern and colder region of A. thaliana’s distribution. We found that genes known to ensure resorption in cold climates are associated with the resorption rate and are under natural selection. We provided evidence that the resorption rate is integrated into resource use strategies and growth syndrome at both the leaf and plant level. Overall, our results suggest the importance of the resorption rate for a better characterization of plant adaptation to the environment.

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