A geostatistical approach to estimate probability of occurrence of Tuber melanosporum in relation to some soil properties

This study concerned an experimental truffle bed of downy oaks infected by the ectomycorrhizal fungus Tuber melanosporum and planted in 1983. The pres ence of T. melanosporum creates rounded areas with little herbaceous cover, termed "brulis", where carpophores are found. The investigation was aimed at relating the occurrence and carpophore production of T. melanosporum to soil properties, i.e., organic matter, structure, aeration and fertility, e xpressed in terms of total organic C, aggregate size classes, DTPA-extracta ble Fe and Mn, and host plant height. Data were processed by multivariate g eostatistical techniques. A linear model of coregionalization (LMC) includi ng (i) a nugget effect, (ii) a short-range spherical structure with a range of 7 m and (iii) a long-range spherical structure with a range of 32 m, wa s fitted to the experimental direct and cross-variograms of the investigate d properties. Factorial kriging analysis (FKA) was used to separate the sou rces of variation of the data according to the spatial scale at which they operate, and to summarize and map them in terms of spatial factors. An indi cator approach was adopted to estimate and map the conditional probability of presence and fructification of T. melanosporum. The visual comparison be tween the spatial pattern of the long-range structure of the first regional ized factor with the probability map of finding brulis plus carpophore prod uction revealed some interesting relationship and suggested that T. melanos porum may prefer a soft and well-aerated soil environment to grow. (C) 2000 Elsevier Science B.V. All rights reserved.