Vegetation on limestone bedrock is generally thought to have adapted to the low phosphorus (P) and manganese (Mn) availability due to the alkaline soils. However, this perception is based on studies in arid regions such as Europe and inland China. Recent studies in humid regions (e.g., Japan and Borneo) reported that limestone soils show extremely high P availability due to the decline of soil pH with progressive soil development under high precipitation. Yet soil pH rarely becomes ≤ 6 even in humid limestone soils, suggesting that Mn availability may still be low. So far only few studies examined physicochemical characteristics of limestone soils in humid regions, and nutrient-use and acquisition strategies of tree species growing in those environments are unknown.

We examined soil pH and P concentrations and plants’ strategies of P and Mn-use and acquisition at limestone and non-limestone vegetation in Ibuki (Shiga) and Atetsu (Okayama) in Japan where precipitation exceeds 1300mm year-1. We collected leaves for 16 species and rhizosphere and bulk soils for 7 species (3 individuals for each species). We hypothesized that in comparison with generalist tree species, species specialized to limestone soils (calcicole species) exhibited (i) lower foliar P resorption rates, and (ii) lower foliar Mn concentrations and higher Mn resorption rates, and (iii) greater ability to uptake Mn from soils by exudating organic acids from roots and acidifying rhizosphere soils.

Limestone soils had both higher pH and inorganic P concentrations than non-limestone soils. Phosphorus resorption rate was lower in calcicole species than generalist species (6.4 vs 54.7%). The calcicole species had very low foliar Mn concentrations compared to the generalist species (0.056 vs 0.56 mg kg-1). Soil pH was generally lower in the rhizosphere soils than the bulk soils (rhizosphere effects), but the effect did not vary between calcicole and generalist species. This suggests that rhizosphere effect is not important for Mn-acquisition strategy of calcicole species, and that calcicole species adapt to the low Mn availability in limestone soils by lowering the demand of Mn for growth rather than improving Mn uptake. Overall, results suggest that limestone soils in humid environment in Japan exhibit high P and low Mn availabilities, and that the calcicole species show a distinct strategy to adapt to limestone ecosystems by having very low P resorption rates and foliar Mn concentrations.