Environmental and genetic differentiation underlies divergence in phosphorus-acquisition strategies of Embothrium coccineum cultivated on volcanic substrates of contrasting age.

Phosphorus (P) limitation in volcanic soils imposes strong selective pressure on root traits that regulate nutrient acquisition, carbon allocation, and rhizosphere biochemical modification. In Proteaceae, P acquisition is often mediated by cluster roots and carboxylate exudation, yet it remains unclear whether environmentally and genetically differentiated populations within a species rely on contrasting structural and biochemical strategies. We tested whether Embothrium coccineum populations from contrasting environments differ genetically and in P-acquisition traits using two complementary approaches. First, ecological niche modeling and Amplified Fragment Length Polymorphism (AFLP) analyses characterized environmental and genetic structure across the species range. Second, a common-garden experiment compared seedlings from Northern, Central, and Southern populations grown in both recent and intermediate-age volcanic substrates, quantifying growth, cluster-root traits, leaf P and nitrogen, and whole-root-system carboxylate exudation. Niche modeling identified four bioclimatic strata, whereas AFLP analyses resolved two main genetic lineages; between-lineage Fixation Index (FST) values reached 0.214-0.249. Central seedlings consistently produced more cluster roots and, in the older-aged volcanic substrate, exhibited approximately 30% greater oxalate exudation than Northern and Southern seedlings; citrate was detected only in this population-substrate combination. In contrast, Southern seedlings showed limited cluster-root development but, in the recent-aged volcanic substrate, increased oxalate exudation two- and three-fold relative to Northern and Central seedlings, respectively, while simultaneously increasing foliar P concentration. Northern seedlings exhibited comparatively weak responses to substrate age. Our findings demonstrate that population differentiation in E. coccineum extends to key physiological mechanisms involved in nutrient acquisition and provide new insights into adaptive root function in Proteaceae growing on nutrient-impoverished volcanic soils.