Contrasting responses of cluster roots formation induced by phosphorus and nitrogen supply in Embothrium coccineum populations from different geographical origin

Abstract

Embothrium coccineum is a pioneer tree that produces cluster roots (CR) induced by phosphorus (P) or nitrogen (N) deficiency, but the role which both N and P play in CR formation for different E. coccineum populations is still unknown. We hypothesized that in E. coccineum, N influences the CR formation response, primarily induced by P limitation. However, this response depends on local adaptations to their specific conditions of geographic origin. Seedlings from three contrasting edaphoclimatic conditions (Northern, Central and Southern populations) were grown in hydroponic culture under high and low N supply and at five different P supply. Morphophysiological responses, including CR number, growth, biomass, P and N plant concentration, were studied. Our results showed that at high N supply, CR formation was stimulated with increased P supply, but just until it reaches a maximum of 5 μM, above this concentration CR formation decreases. However, at low N supply, a constitutive response was observed regardless of P supply. Moreover, each of these responses depends on the populations. Our study suggests that N drives CR formation induced by P supply and that a differential response exists among E. coccineum populations, that could be related to their origin edaphoclimatic conditions.