Leaf manganese concentrations as a proxy for root carboxylate exudation: a first survey in phosphorus-limited South American temperate rainforests

Abstract

Background and aims

South American temperate rainforests primarily develop on volcanic soils with high total phosphorus (P) concentrations; however, the P availability is low for most plants due to strong sorption of P to soil particles. In response to this, certain plant species have evolved strategies involving the release of root carboxylates that mobilize soil P. However, studying root exudates in situ poses significant challenges, promoting recent studies to use leaf manganese concentration ([Mn]) as a proxy for rhizosheath carboxylate concentration. Therefore, we used leaf [Mn] to identify if plant species potentially utilize root carboxylates for P mobilization.

Methods

We collected leaf and soil samples from 50 plant families across four sites in Chile, analyzing leaf [Mn] to assess carboxylate-exudation patterns, using low leaf [Mn] fern species as negative references and species with high leaf [Mn] (≈ 500 mg kg⁻¹ dry weight) as positive references.

Results

The highest community-level leaf [Mn] was observed at the Rucamanque site, where soil P availability was the lowest. All species from the families Bromeliaceae, Myrtaceae, Nothofagaceae, and Winteraceae consistently exhibited high leaf [Mn], as we also observed for Podocarpus and Maytenus trees. With respect to plant life forms, trees, shrubs, and epiphytes generally had higher leaf [Mn] than ferns, mosses, and herbs.

Conclusions

Our findings suggest that plants in soils with low P availability exhibited both a greater frequency and higher average of leaf [Mn] than those in soils with greater P availability, indicating their potential reliance on carboxylate exudation for P acquisition.