Nutrient-addition effects of volcanic-ash deposition in forest ecosystems:

<p>Non-crystalline minerals are formed through weathering processes from volcanic materials and strongly bind phosphorus (P), which may reduce the P availability for forest trees on volcanic soils. On the other hand, volcanic materials are a direct source of P and enhance soil total P. It has not been clarified how P availability and P cycling in forest ecosystems relate to non-crystalline minerals in volcanic soils. The objective of this study is to clarify the differences of soil nutrient availability and foliar nutrients of trees by comparing volcanic vs. non-volcanic soils. We selected eight secondary forests where Quercus serrata was dominant in Japan as study sites. We collected surface soils from three layers (0-5, 5-15, 15-30 cm depth) from each study site and canopy fresh leaves of Q. serrata. We measured the concentration of oxalate-extractable Al and Fe (Al_o and Fe_o), P fractions, and exchangeable-cations in soils and N and P in leaves. Both Al_o and Fe_o and soil nutrients (P fraction and exchangeable cations) were significantly higher in volcanic soils than in non-volcanic soils. Al_o + 1/2Fe_o was significantly correlated to NaOH-P (indicator of P bound to Al and Fe). Both plant available-P and NaOH-P were significantly positively correlated with foliar N and P concentrations. Estimated maximum heights of trees tended to be higher in volcanic soils. Our results indicated that the addition of volcanic ash directly increased soil P availability via increasing the pool of P and flux of P from recalcitrant and organic forms of P to available inorganic forms of P in soils.</p>