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Abstract

To examine the effects of vineyard soil management on soil C and N content and quality, we studiedharrowed and grass-covered vineyards on a soil developed on plio-pleistocene, marine sediments. A soilnaturally covered by grasses adjacent to the vineyards served as control. To reach this goal, we assessed(1) the distribution of C and N and their13C and15N signatures in different soil organic matter pools, (2)the amount of C and N as live and dead vine fine roots and their13C,15N and14C signatures, and (3) thestocks 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 inthe 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 absenceof tillage. The grass cover favoured the organic C storage mainly in the form of particulate and highlystabilised 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 tooxidative processes enhanced by the soil tillage. In both vineyard soils, decaying vine roots represented animportant source of organic C and N, especially in the deepest horizons. Indeed, isotope analyses revealeda more intense degradation of the dead vine roots in the deeper soil portion, where they likely constitutedthe main substrate for soil microorganisms. In the deepest horizons of the grass-covered vineyard, thegreater mean residence time of the decaying vine roots and the lower root production were attributed tothe easily available energetic substrates supplied by grass root turnover and rhizodeposition, which werepreferentially used by microorganisms. This fact fostered a larger C accumulation in the grass-coveredthan in the harrowed vineyard.