Direct contribution by soil arthropods to nutrient availability through body and faecal nutrient content

Summary The direct contribution made by soil arthropods to nutrient dynamics was investigated in pine forests that differed in soil nutrient status. Nutrient concentrations (K⁺, Ca²⁺, Mg²⁺, PO ₄ ^3– , N, C) in the most abundant species and groups of arthropods in two Pinus nigra forests were compared, and distinct differences were found among taxonomic groups. In the rank order: collembolans, oribatides, isopods, diplopods, Ca²⁺ and Mg²⁺ concentrations increased, while N and C concentrations decreased. The nutrient concentrations in individuals of the same species but originating from the different forests were similar, except for the isopod Philoscia muscorum. The total and available nutrient concentrations in food and faeces of the collembolan Tomocerus minor and the isopod Philoscia muscorum were compared. The isopod faeces contained relatively less K⁺ and Mg²⁺, and more Ca²⁺, PO ₄ ^3– , and greater N availability, compared with the food material. The collembolan faeces showed a higher availability of all nutrients measured. The N species appeared to be changed by collembolans; their faeces contained high NO ₃ ^– concentrations, while their food contained relatively high concentrations of NH ₄ ⁺ . These findings were examined in relation to their significance for ecosystem functioning. It was concluded that about 12% of the total K⁺, PO ₄ ^3– , N and 2% of the Ca²⁺ in the organic layer was found in the mesofauna. It was calculated that faeces production by the collembolans resulted in a 2.4 times higher NO ₃ ^– availability in the forest floor.