Inoculation with a soil fungus accelerates decomposition of avocado cv. Hass leaf litter in three plantations in Colombia

The objective of this study was to evaluate the effect of a fungal inoculation on the litter decomposition in three plantations of avocado (Persea americana) cv. Hass in Colombia at different altitudes (Támesis 1340 m, Jericó 1900 m, and Entrerríos 2420 m). These processes are key in the proper functioning of soil biogeochemical cycles. The litter was either uninoculated or inoculated with the fungus Mortierella sp., then transferred into litter bags and finally deposited in the field sites where remained for 430 days. Residual dry matter (RDM) and nutrient content was monitored overtime. Five regression models of litter decomposition were employed: single, double, and triple exponential models and two continuous models. Although, all models properly fitted the data variation, the double exponential was the most effective based on regression parameters (mean square error and Akaike index). In all three sites the rate of decomposition was higher when the litter was inoculated with the fungus. Thus, the RDM was significantly lower when the litter was inoculated with Mortierella sp. At day 430, the uninoculated RDM in Tamesis, Jerico, and Entrerrios was 0.48, 0.47, and 0.50, respectively; while the inoculated RDM was 0.47, 0.44, and 0.46, respectively. The rate of decomposition followed the decreasing sequence: Jericó > Támesis > Entrerríos. The nutrient release pattern was: K > Ca > Mg > N > P > Cu > Mn > Zn > Fe. While K was rapidly released, Ca, Mg, and N were slowly released; P, Cu, Mn, Zn, and Fe were immobilized during the decomposition process. However, fungal inoculation on the litter significantly reduced the magnitude of nutrient accumulation for P, Mg, S, Mn, and Zn. This effect was variable overtime and among sites. Litter N and P contents and the N:P ratio were good indicators of the decaying process.