Variables affecting Suillus luteus fructification in ponderosa pine plantations of Patagonia (Argentina)

Suillus luteus is the most abundant wild edible mushroom harvested in Patagonian pine plantations from Argentina. Their fruitbodies are unevenly distributed in plantations but no studies have been carried out to investigate and quantify the macro- and micro-level environmental factors affecting their fructification in productive patches. The objective of this study was to determine the biotic and abiotic micro-environmental factors affecting the productivity of S. luteus fructification. The study was conducted in an even-aged (17–18 years) Pinus ponderosa plantation with sandy loam soil, very common in the region. Twelve plots with fructifications and 12 with no fructification were randomly selected to make comparative measurements. Crown cover (CROWN), percentage of herbaceous + small-shrubs cover (HERB) and species composition, percentage of duff cover (DUFFC), percentage of bare soil (BARE), decomposed + non-decomposed duff depth (TDUFFD), soil water content (SOILH), soil texture, pH in water, pH in NaF, organic matter percentage (OM), total nitrogen percentage, available phosphorus content, S–SO42− content, and exchangeable cations including Ca, Mg, K and Na were determined. Multiple logistic regression was used to select variables that explain presence or absence of fructifications, and a principal component analysis to further analyze the relationship between herbaceous species cover and fructification. The occurrence of fructifications was associated with a group of highly correlated variables (high HERB, OM and SOILH and low CROWN, DUFFC and TDUFFD), all determined by the irregular tree spatial pattern in plantation that impacts the quantity of light and water reaching the soil. Those variables related with chemical and physical soil properties, with the exception of OM and SOILH, explained little variation in the data set. The principal component analysis showed that plots with fructification presented higher Acaena ovalifolia and Stipa sp. cover, and that plots without fructification presented higher CROWN and TDUFFD. Pruning and thinning prior to complete canopy closure would maintain light and water reaching the soil and preventing duff accumulation by stimulating decomposition. If ponderosa plantations are managed for high production of S. luteus fructification, silvicultural treatments that include thinning should be implemented earlier.