Seabird guano and phosphorus fractionation in a rhizosphere with earthworms

<p>Soil phosphorus (P) is a critical nutrient for plant growth and is an important determinant of vegetation development and long-term ecosystem sustainability. We investigated the effects of rhizosphere-earthworm-guano interactions on soil P dynamics in a mesocosm involving two species of native New Zealand earthworms (<i>Megascolecidae </i>Sp.1 and <i>Maoridrilus transalpinus</i>) and introduced <i>Eisenia fetida</i>, in the context of inputs from seabird guano and the ecological restoration of a unique coastal sandplain forest. A fully factorial experimental design included a tall fibrous liliaceous perennial plant (New Zealand flax) growing in a low P forest soil, a guano-P amendment (with and without guano-P), and earthworm inoculation (with and without species of epigeics, endogeics and anecics). Soil dehydrogenase activity, CaCl2-P, citrate-P and HCl-P were significantly modified by earthworm-guano interactions, altering the P status of the original forest soil. Furthermore, interactions between the rhizosphere and earthworms stimulated transformation of soil P and guano P; the proportional importance of soil microbial biomass P, organic-P and more soluble P fractions were substantially modified. These findings show that rhizosphere-earthworm interactions are likely to mediate the supply, chemical forms and plant-availability of P, and are likely to have an important role in successional processes and the trajectory of ecological restoration in coastal forests of New Zealand.</p>