A multitrophic interaction: consequences of grazing on decomposition of needles of Pinus pinea L. by Ommatoiulus sabulosus L.

摘要

The aim of this study was to assess how the physical (needle fragmentation by trampling) and chemical (nutritional enrichment from faeces) changes brought about by grazing influence the consumption of needles of Pinus pinea L. by Ommatoiulus sabulosus L. Adult individuals of O. sabulosus were introduced into trays with pine needles subjected to four treatments: (i) intact needles, (ii) trampled needles, (iii) intact needles fertilized with liquid manure, and (iv) trampled needles fertilized with liquid manure. After 30 days, litter decomposition was determined as a function of mass loss over time. Biometric and chemical characteristics of the needles were also measured. The pine needle decomposition rate was significantly higher in the presence of O. sabulosus (20-40%) than in its absence, presenting in addition a significantly higher rate in the treatments enriched with nitrogen. Average needle length was significantly shorter in the trampled treatments (6.89 +/- 0.50 cm) than in those with intact needles (11.95 +/- 0.69 cm). With regard to leaf mass per area and resistance to breakage, no significant differences were found. The fertilized treatments presented significantly higher N content (50% higher) than those in the non-fertilized ones with a significantly lower C:N ratio. The results of the present study indicate that goat grazing (which produces both trampling and fertilization) favoured the consumption of pine needles by O. sabulosus, which thus influences, along with the microbial community, the decomposition rate of these needles and thereby promotes incorporation of N into the system.