Coordination among leaf and fine-root traits along a strong natural soil fertility gradient

Background and aims: Unravelling how fundamental axes of leaf and fine-root trait variation correlate and relate to nutrient availability is crucial for understanding plant distribution across edaphic gradients. While leaf traits vary consistently along soil nutrient availability gradients, the response of fine-root traits to the same gradients has yielded inconsistent results. Methods: We studied leaf and root trait variation among 23 co-occurring plant species along a 2-million-year soil chronosequence to assess how leaf and root traits coordinate and whether this axis of trait variation relates to soil fertility. Results: Leaf and root trait variation was primarily structured by mycorrhizal association types. However, when considering community-level traits weighted by plant species abundance, soil nutrient availability was an important driver of trait distribution. Leaves that support rapid growth on younger more fertile soils were associated with roots of larger diameter and arbuscular mycorrhizal colonization. In contrast, leaves that favor nutrient conservation on nutrient-impoverished soil were associated with greater root-hair length and phosphorus-mobilizing root exudates proxied by leaf manganese concentration. At the species level, leaf and root trait variation patterns deviated from the community-wide results, as leaves that support either rapid growth or survival were associated with a wide range of root trait syndromes. Conclusions: Our results highlight the challenge of generalizing a specific set of root-trait values that consistently meet the requirements of leaves supporting rapid growth or survival. Hence, the leaf economic spectrum's ability to capture variation in carbon gain may not be reflected by the root economic space.