a b s t r a c tTo examine the effects of vineyard soil management on soil C and N content and quality, we studied harrowed and grass-covered vineyards on a soil developed on plio-pleistocene, marine sediments. A soil naturally covered by grasses adjacent to the vineyards served as control. To reach this goal, we assessed (1) the distribution of C and N and their 13 C and 15 N signatures in different soil organic matter pools, (2) the amount of C and N as live and dead vine fine roots and their 13 C, 15 N and 14 C signatures, and (3) the stocks of C and N forms accumulated at two soil-depth intervals (0-50 and 50-100 cm).Independent of the soil management, the vines increased the total organic C and total N content in the deeper soil horizons because of root turnover and rhizodeposition processes. In the upper horizons, a greater organic matter accumulation was fostered by the presence of the grass cover and the absence of tillage. The grass cover favoured the organic C storage mainly in the form of particulate and highly stabilised organic matter (humic acids and humin), and reduced the soil N content by plant uptake, whereas the harrowing produced a greater abundance of fulvic acids, which were mainly ascribed to oxidative processes enhanced by the soil tillage. In both vineyard soils, decaying vine roots represented an important source of organic C and N, especially in the deepest horizons. Indeed, isotope analyses revealed a more intense degradation of the dead vine roots in the deeper soil portion, where they likely constituted the main substrate for soil microorganisms. In the deepest horizons of the grass-covered vineyard, the greater mean residence time of the decaying vine roots and the lower root production were attributed to the easily available energetic substrates supplied by grass root turnover and rhizodeposition, which were preferentially used by microorganisms. This fact fostered a larger C accumulation in the grass-covered than in the harrowed vineyard.

Aims: Facilitation has been reported in a wide range of plant communities, with evidence of positive interactions between beneficiary and nurse plants shifting during their ontogenetic development. This study explored the hypothesis that shrubs of Juniperus communis subsp. nana (thereafter Juniperus) play a crucial role in the successional sequence of plant communities acting as nurse for different species, but only after reaching a certain size. In addition, we examined whether plant-plant interaction changes during ontogenesis of these shrubs in the presence of contrasting disturbance regimes in terms of substrate stability. Location: Sibillini National Park, central Italy. The vegetation is semi-natural dry grasslands (92/43/EEC Habitats Directive: Habitat 6210 -Festuco-Brometalia).Methods: Field measurements were carried out to assess the effects of Juniperus on (1) the distribution of co-existing vascular species, (2) the above-and belowground microclimate, and (3) changes in soil fertility and hydrology.Results: The capacity of Juniperus shrubs to facilitate heterospecific plants considerably increases during its ontogenetic development, i.e. small shrubs mainly compete for resources with local vegetation, whereas large shrubs act as nurse plants for herbaceous and especially for woody species. The facilitation effect was slight, albeit significantly higher in the disturbed area than in the more stable one. Juniperus was able to promote the formation of an island of fertility under its canopy by accumulating a considerable amount of organic matter, N, P, Ca 2+ , Mg 2+ and K + in a few decades. Juniperus shrubs improve soil hydrological properties and mitigate the daily range of soil temperature, reducing the exposure of co-existing plants to high temperatures and water loss through soil evaporation, particularly during the growing periods in spring and summer.Conclusions: This study demonstrates that biogenic amelioration of soil quality, coupled with the mitigation of below-canopy microclimatic conditions, control the establishment and growth of co-existing plants during Juniperus shrub development.

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