Implications of nurse species in mixed forest plantations management on soil fungal community diversity

Mixed plantations provide numerous benefits in terms of ecosystem and socioeconomic services, as well as on soil chemical and biological parameters; thus, a forest management allowing to recover overexploited soils is highly recommended. Although nurse species may deeply affect soil properties, few studies are present in literature assessing their role. A study site characterized by a mixed plantation established on a former agricultural area was selected in order to evaluate the impact of a specific forest management on marginal soils, with a special emphasis on the role of nurse species. The intercropping systems investigated feature two economically important species, Populus alba and Juglans regia, along with one of following nurse trees, Alnus cordata, Elaeagnus umbellata (both N-fixing species), and Corylus avellana. Each stand was replicated three times, and an adjacent agricultural field was included for comparison. Methodologically, topsoils (0-10 cm of depth) were sampled and several chemical and biological parameters determined. Fungal taxa, as well as fungal ecological guilds and their functional roles, were identified by means of metabarcoding analysis. Ectomycorrhizal fungi dominated tree consociations (53.5 %), while non-mycorrhizal saprophytes dominated the arable, control soil (5.3 %). TwoBlock Partial Least Squares showed differences both among tree consociations, where the presence of the Alnus cordata resulted in the highest concentration of organic carbon (19.10 f 1.8 mg g- 1), total nitrogen (1.78 f 0.1 mg g- 1), lignin (11.25 f 1.1 mg g- 1), cellulose (1.54 f 0.2 mg g- 1), and bioavailable phosphorus (8.99 f 1.2 mg kg- 1), as well as fluorescein diacetate hydrolase enzyme activity, and between tree consociation and the arable land. Thus, the utilization of Alnus cordata as a nurse species seems to be the best solution for a forest management capable of improving soil chemical and biological quality, providing a viable strategy for the restoration of marginal soils, particularly in a climate change scenario.