Effects of five Lacandon Maya agroforestry trees on soil nematode trophic group composition

The Lacandon Maya have managed their lands in Chiapas, Mexico for hundreds of years without long-term soil degradation by applying their traditional swidden agroforestry system. Lacandon land managers plant and care for a number of tree species during the fallow period in part to facilitate natural succession and enhance soil fertility. We evaluated the effects of five of these species (Poulsenia armata, Cedrela odorata, Enterolobium cyclocarpum, Swietenia macrophylla, and Lonchocarpus guatemalensis) on soil-dwelling nematodes, which play an important role in biogeochemical cycling. Only L. guatemalensis had a significant effect on the population of plant parasitic nematodes relative to the total nematode population, which demonstrates its potential utility in reducing pressures on plant growth and facilitating the regeneration of vegetation in secondary forests. In general, larger diameter trees tended to support larger nematode populations in nearby soils, possibly due to organic matter enrichment. Bacterivorous nematodes dominated the nematode community throughout succession, as is typical in agroecosystems with regular organic matter enrichment. However, counter to expectations, bacterivorous nematode dominance did not appear to be directly related to organic matter deposition in Lacandon agroforests. Nematode trophic group populations changed over time in secondary Lacandon agroforests, alternating between elevated and low populations in successive Lacandon agroforestry management stages. Our results demonstrate that the effects these trees have on soil fertility are likely species-specific and not necessarily a function of altering surrounding nematode communities. The inconclusiveness of our findings underscores the challenge of discriminating the individual species’ effects in the context of the agroforestry systems of which they are a part, particularly with regard to highly variable soil microfauna communities.