Carbon Sequestration Monitoring In a Typical Mediterranean Vineyard

Many studies investigated the ability of terrestrial ecosystems in carbon sequestration, showing the importance to evaluate the agriculture contribution to the global carbon balance. It is recognized that agriculture sector is an important source of greenhouse gases, which many scientists agree is contributing to observed climate change. In addition, agriculture can play an important role in climate change mitigation, acting as a carbon sink and storing it in the soil and plant matter. Grapevine is one of the most important crops in the Mediterranean area, so it is essential to know its role in C emissions and sequestration, and to study the variability of the Net Ecosystem Exchange (NEE) depending on environmental factors. Eddy Covariance (EC) technique represents the standard methodology to directly measure energy, water, and carbon fluxes between ecosystem and the atmosphere. So far, few studies have been conducted to monitor fluxes over vineyard ecosystems, and previous studies only performed measurements for short periods (e.g., few weeks or in the growing season). Information are then missing on annual and inter-annual carbon balance variability for such ecosystems. The aim of this study was to investigate, at daily, monthly, seasonal, and annual scale, the vineyard behavior in acting as C source or sink. Three years of EC turbulent fluxes were monitored in a typical Mediterranean vineyard located in the South of Sardinia (Italy). Radiation and soil heat flux densities were also monitored by net radiometer and soil heat plates, respectively. Meteorological variables were collected by a weather station. Soil CO2 flux measurements were also performed periodically to separate the soil contribution to the global carbon balance. The energy balance closure method was used to evaluate measurements accuracy, and standard quality control tests were performed according to the FLUXNET community. In general, the vineyard acted as a carbon sink during the growing season (June-September), and as carbon source in fall and spring. A major amount of carbon was sequestrated in years characterized by favorable weather conditions and not limiting water availability, while the carbon uptake was reduced depending on high air temperature values and water stress conditions. The analysis also revealed the dependence of NEE by agronomic practices. Higher values of soil respiration were observed in fall, according to other Mediterranean ecosystems. In summer, measured values revealed that microbes and roots activities continued even under drought conditions. In addition, this study revealed that soil respiration is the key component in the carbon balance, given that it determines 60-80% of the loss of carbon as CO2. At annual scale, the vineyard acted as a carbon sink, even if significant differences have been observed during the three years depending on environmental factors. This study shows that grapevine ecosystems could greatly contribute in reducing carbon emissions, by absorbing more than 300 g C m-2 during the experiment period, and highlights the importance to include agriculture ecosystems in global carbon balance studies.