Impact of Tipula paludosa larvae on plant growth and the soil microbial community

An experiment was performed to study the effect of feeding by the larvae of Tipula paludosa (Meig.) on the plant biomass of two contrasting plant species and on the soil microbial community, under controlled conditions. Agrostis capillaris (L.) (bentgrass) and Trifolium repens (L.) (white clover), were grown in pots, in monoculture and as mixtures, containing soil from an upland grassland site in the UK. After plant establishment, larvae were added to half the pots at field density (480 larvae m−2). After 12 days, the pots were destructively harvested and the shoot biomass, root biomass and the soil microbial community (using plate counts and community level physiological profiles (CLPP)) were assessed. The presence of larvae significantly reduced shoot biomass in T. repens growing as monoculture. In pots containing a mixture of A. capillaris and T. repens, only the shoot biomass of the T. repens was significantly reduced. In the single species pots, the larvae significantly reduced the root biomass of both species. The soil microbial community structure changed in the presence of larvae resulting in a significant 10-fold increase in numbers of Pseudomonas spp. in the soil. Canonical variate analysis of the CLPP data also showed that microbial communities from the soils with larvae present had a greater utilisation of a number of sugars, amino acids and carboxylic acids. These changes may have arisen as a result of an increase in carbon exudation due to root severance or shoot herbivory, an increase in dead roots or due to larval decomposition or defecation. © 2003 Elsevier B.V. All rights reserved.