Canopy gaps are part of the natural regeneration cycle of tropical rainforests. A gap opening entails a number of cascading changes in micro-environment, soil and plant cover. The responses of plant communities to canopy gaps have been extensively studied but soil responses and especially soil biota responses are still poorly understood. The objective of this study was to analyse the response of soil microbiota microenvironment and plant community changes and their connection along early natural regeneration in natural gaps in Los Tuxtlas, Veracruz, Mexico. We used a space-for-time approach and located gaps of 1-15 years of regeneration. An intact forest site was selected in the neighbourhood of each gap to be used as its reference. On each gap and its reference site we marked a 5m x 5m plot and determined the size of the gap (when gap), slope, altitude, canopy openness, and light incidence in the center. Taxonomic identity and cover of plant species was measured in an area of 25m2. Soil water content, pH, organic matter, PO4-, NO3-, NH4+, were measured from three samples taken at 20 cm-depth to explore soil fertility and humidity changes, and fatty acid profiles to quantify the abundance of microbial groups within each plot.
Results/Conclusions
Despite some significant differences between the gap plots and the reference plots in specific sites, most results suggested minor changes in soil, microenvironment and vegetation along regeneration time and gaps did not differ in general from their references. Remarkably, tree cover regeneration was minimal in 15 years and most vegetation changes were observed in herbs. There was only a negative correlation between gap age and soil pH and a positive correlation with soil water content and NH4+. Multivariate analyses suggested that slope, the abundance of fungi, bacteria and fauna, and soil nitrate, were the most important variables explaining the variation among plots. Vegetation variables (density, dominance, basal area) and soil organic matter separated most forest reference sites from gap sites regardless of gap age. Altogether the results suggest that soil fertility and microbial abundance are important controlling factors of spatial variation in this forest but herbaceous vegetation changes drive the early regeneration stages in gap openings and buffer the environmental changes thereby dampening the effects of gaps on soil.