Soil fauna bioturbation along a successional gradient following swidden agriculture in the lowland tropical rainforests of New Guinea

Mesocosm studies in temperate soils indicate that soil fauna may promote accumulation of C in mineral soil. To test if this effect apply also in tropics we used field mesocosms that were either accessible or inaccessible to soil fauna. To explore potential interaction with traditional land use we locate these mesocosms along a succession gradient following traditional swidden agriculture in the lowland tropical rain forest of Papua New Guinea. Soil fauna densities did not show any significant changes along the succession gradient. Litter fall in primary forest was significantly higher than in younger succession stages. Litter stock on the soil surface follows the same pattern as litter fall. Litter stock was a few percent higher than annual litter fall suggests that litter removal from soil surface takes slightly over one year. Our Mesocosm experiment shows the same speed of litter removal (about one year). Litter removal from surface and its incorporation of organic matter into mineral soil is faster in the fauna treatment compared to the non-fauna treatment. Overall loss of C from the system was higher when fauna was absent. Fauna reduced overall loss of C from the soil in average for more then 40%. In conclusion soil fauna play important role in organic matter transformation and soil C storage in tropical ecosystem. Fauna removal sub-stantially reduce overall soil C storage.

Automated summary

Mesocosm studies indicate that soil fauna can promote C accumulation in temperate soils. To explore this effect in the tropics, we conducted field mesocosm experiments with and without soil fauna in a tropical rainforest in Papua New Guinea, along a succession gradient following traditional land use. The results showed that soil fauna densities did not vary significantly along the gradient, but litter fall and stock decreased with succession. In the presence of fauna, litter removal and organic matter incorporation into mineral soil were faster, leading to higher overall loss of C from the system.