Tropical rain forests have been severely affected by deforestation. As a consequence, a fragmented landscape results with several fragments of different sizes (mainly < 10 ha) and shapes immersed into a matrix of non favorable conditions for natural vegetation, such as cattle ranching and croplands. It is well known that fragmentation effects on diversity and species richness are directly related to fragment size in aboveground communities. However, belowground communities show contradictory results, particularly, arbuscular mycorrhizal fungi (AMF) are one of the most important soil organisms, due to their mutualistic relationship with a great number of plant groups; being seedlings the most sensitive stage to them . Some studies have emphasized that plant and AMF community structure are directly correlated. In this context, our main goal was to describe and correlate both seedling and AMF community structure and composition in fragments of different sizes and to evaluate the conservation status of this fragmented landscape. We selected seven fragments of different sizes, and established seven randomly distributed plots in the centre of each one; we collected soil and sampled all seedlings in each plot. All estimates were done with AMF spore number. We calculated mean estimated species richness, and diversity per fragment, also we analyzed seedlings and AMF composition among fragments. We performed regression and correlation analyses on these data.
Results/Conclusions We found a total of 168 plant species and 44 AMF species. Results show that all fragments included shade tolerant plant species. Contrary to other studies, we found that mean diversity and observed species richness of seedlings were significant and inversely related to fragment size, and AMF showed the same trend. Overall seedling and AMF estimated species richness (values fluctuated between 14 and 21 and between 4.85 and 7.14, respectively) were significant and negatively correlated, and fragment size did not explain this result as in the case of observed species richness. Glomus tenebrosum and Acaulospora scrobiculata seemed to be related with the dominance of Nectandra ambigens and Brosimum alicastrum. These results point out a great forest regeneration potential of small fragments that can be related to a well conserved AMF community, a large connectivity among fragments and a microenvironmental fragment heterogeneity.
