Relationship between intra-parcel variability and carbon allocation and sequestration in a mature Barbera (Vitis vinifera L.) vineyard ecosystem

In this three year study (2018-2020) we wanted to assess the degree of spatial variability of a small sized (1.2 ha) mature cv. Barbera vineyard managed as alternate permanent native grass and tillage and how such variability interacts, at either single vine and whole vineyard level, with net primary productivity (NPP) and net carbon balance (NCB). Pre-trial an NDVI based vigor map was derived from a satellite image taken at 5 m spatial res-olution, and levels of high vigor (HV) and low vigor (LV) were located. Each year ground truthing was performed on test vines chosen within each vigor zone for assessment of vegetative growth, yield components and main compositional parameters at harvest. Samples of each above ground vine organ (leaves, shoot clipping, canes, clusters) and clippings derived from grass mowing were dried in an oven to allow dry biomass assessment. Soil respiration (SR) was also measured at fixed positions each year a few times during the season using a portable gas exchange system and assuring representativeness of either tilled and grassed areas. Vine vigor given as pruning weight vine- 1 was 33% higher in HV plots; yet, most of the measured parameters revealed a significant vigor x year interaction which, however, showed a spreading nature meaning that HV vines consistently had higher yield components and malic acid concentration in juice as well as lower total soluble solids (TSS), pH, total anthocyanins and phenols than LV and such differences just varied in magnitude depending on the season. Within a common range of 2.5 to 5.5 kg m -1 of yield, LV achieved superior quality likely due to reduced vegetative competition, better cluster microclimate and much more constrained berry size.<br /> On a per vine basis, NCB confirmed a C sink function with 1.06 kgC vine -1 yr- 1, whereas the LV reached only 0.594kgC vine -1 yr- 1. These values almost halved at 0.522 and 0.312 kgC vine -1 yr- 1 for HV and LV, respec-tively, when C stored in clusters was subtracted. However, upgrading the NCB to the whole vineyard ecosystem, therefore including the SR contribution, turned the balance into a source mode (i.e. net C release) amounting at 455 and 512 gC m -2 yr- 1 for HV and LV, respectively. Under the specific trial conditions, SR demonstrated to be an overwhelming factor at directing the vineyard NCB into a source mode; the high vigor is indeed more conducive to better C performance as vine and grass biomass is increased. However, it should be taken into account that there is a superior limit beyond which such parameters cannot go if optimal grape maturity parameters need to be assured.