Are phenolic compounds released from the Mediterranean shrub <i>Cistus albidus</i> responsible for changes in N cycling in siliceous and calcareous soils?

• We studied the effects of Cistus albidus leaf leachates on nitrogen-cycling processes in two siliceous soils (granite and schist) and one calcareous soil. We compared those effects with gross N-transformation rates in soils sampled underneath Cistus. • Soils amended with leachates and soils sampled under Cistus had higher NH4+ immobilization and lower nitrification compared with control soils. Gross N mineralization increased under Cistus but decreased in soils amended with leachates. These effects were especially strong in granite soil. • To determine whether phenolic compounds were causing those effects, we incubated granite soils with leachate and a leachate fraction containing only nonphenolic compounds. Nonphenolic compounds increased NH4+ immobilization and decreased gross nitrification, while decreases in gross N mineralization were estimated to be caused by phenolic compounds. • Our results show that although phenolic compounds leached from green foliage changed gross N mineralization, their effects on net N rates were eclipsed by the changes produced by polar nonphenolic compounds such as carbohydrates. Plant nonphenolic compounds may drive N cycling under Cistus.