| Summary: | <p class="Textbody"><em><span lang="EN-GB">Aim of study</span></em><em><span lang="EN-GB">: </span></em><span lang="EN-GB">in the context of niche construction theory, the investigation was aimed at assessing if truffle <em>brûlé</em> is a case of niche construction by testing if the disappearance of grasses in the <em>brûlé</em> induces a non-arbitrary perturbation in the soil physical environment and, in that case, which are the physical processes involved.</span></p><p class="Textbody"><em><span lang="EN-GB">Area of study</span></em><span lang="EN-GB">: a natural truffle bed located in the Italian Apennines inside an experimental truffle-producing area of the University of Perugia</span><span lang="EN-GB">.</span></p><p class="Textbody"><em><span lang="EN-GB">Material and methods</span></em><span lang="EN-GB">: Thr</span><span lang="EN-GB">ee aggregate size classes in the soil of a <em>brûlé </em>and of the neighbouring grass-covered area were determined with the wet-sieving technique in accordance with international standards. In the first part of the investigation, the area was sampled according to a systematic sampling design and the spatial patterns of aggregate size classes in the <em>brûlé</em> and in the neighbouring grass-covered area were compared by means of geostatistics. In the second part, </span><span lang="EN-GB">the suppression of grasses in the <em>brûlé</em> was mimicked in the laboratory by removing roots from a sample collected in the grass-covered area and the effect of freeze-thaw cycles was tested by comparing a control treatment to other </span><span lang="EN-GB">four treatments consisting in sub-samples equilibrated at a water tension of -2.5, -5, -10 and -20 kPa. Samples were </span><span lang="EN-GB">submitted to a number of freeze-thaw cycles equal to those recorded in the area, analysed for aggregate size distribution and compared with univariate ANOVA.</span></p><p class="Standard"><em><span lang="EN-GB">Main results</span></em><span lang="EN-GB">: The aggregate size classes larger than 0.25mm displayed a spatial pattern comparable to that of the <em>brûlé</em>, with sharp changes along the boundaries of the <em>brûlé</em> itself. The laboratory experiment showed that such changes are attributable to freeze-thaw cycles that in one winter season may produce a significant decrease in aggregate size compared to the grass-covered area. Both results indicate that the disappearance of grasses in the <em>brûlé</em> fulfils the requirement of perturbational niche construction.</span></p><p class="Textbody"><em><span lang="EN-GB">Research highlights</span></em><span lang="EN-GB">: the observed change of soil aggregation in the <em>brûlé</em> can be useful in delineating soils suitable for truffle farming and in creating suitable soil physical conditions for truffle production by exploiting freeze-thaw cycles after irrigation in winter.</span></p><p class="Standard"><strong><em><span lang="EN-GB">Keywords</span></em></strong><span lang="EN-GB">: aggregates; <em>brûlé</em>; niche construction; <em>Tuber</em>, soil structure.</span></p>
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