Functional traits of arbuscular mycorrhizal fungi communities along succession in a tropical dry forest ecosystem
Functional traits in natural communities of arbuscular mycorrhizal fungi are poorly understood. Tropical dry forests are currently highly dynamic ecosystems due to continuous transformation and land cover change. The high environmental heterogeneity resulting from land conversion likely selects the AMF species present in each community as a function of the traits that are more relevant to each new environment. To test this hypothesis we 1) described the composition of AMF communities in field sites with different successional time, 2) measured some of their extraradical mycelium traits (hyphal length, hyphal allocation to diameter categories and mycelium activity) and 3) explored the relation between community composition, mycelium traits and environmental heterogeneity. We set up a greenhouse experiment to measure community mycelium traits in divided pots using the same disinfected soil. Native AMF communities from active pastures, successional fields of different age and old-growth forests (7 natural communities) were inoculated to a native generalist host. Mycelium traits were measured after four months of growth by microscopy and image analysis.
We found that AMF communities from this ecosystem shared on average 60% of their species. Morphotypes were predominantly thick-walled, ornamented and sporocarpic Glomerales. A cluster analysis divided the communities mainly into an early and and a late succession group but there were also sites of discordant age within each group and out-groups. We found that the early communities, exposed naturally to the driest and warmest environments, produced the thickest mycelium. Mid-succession communities, exposed to the coolest and more humid environments under low and thick canopy closure, presented the longest and finest mycelium. Late communities, exposed to intermediate levels of humidity and temperature, in a more structured canopy, showed intermediate values of most mycelium traits. Differences were, however, of small magnitude. We are currently investigating the plasticity of these traits under water stress, a factor that likely contributes to the shaping of AMF communities.