Using whole-plant chambers to estimate carbon and water fluxes in field-grown grapevines

There are limited studies available that have investigated the effects of different levels of water supply on the whole-plant gas exchange dynamics. The latter is related to the difficulty in measuring whole-canopy carbon fixation and water consumption, especially in field conditions. Whole-plant chambers can measure these fluxes, therefore the aims of this work were (i) to determine the relationship between whole-plant gas exchange compared to single leaf gas exchange; (ii) to validate whole-canopy chamber measurements using sap flow probes; (iii) to measure the effect of soil water availability on water use efficiency calculated from gas exchange measured using whole-plant chambers. For these purposes, an experiment was carried out during the 2014 season in an experimental vineyard using six-years-old plants of cv. Grenache. Two irrigation regimes were established, moderate irrigation (50 % ETo) and non-irrigation. Carbon fixation and transpiration were measured using whole-plant chambers at veraison and pre-harvest. Simultaneously, leaf gas exchange was measured at different canopy positions during the day in order to compare those measurements with the whole-plant chamber data. In parallel, sap flow measurements were continuously recorded using heat balance probes. Results showed that CO2 fixation measured at noon in sun exposed leaves oriented to the south presented the highest correlation coefficient with whole plant chamber data. Whole-plant transpiration measured with whole-plant chambers was slightly higher compared to the estimated from sap flow data in both irrigated and non-irrigated plants. In general intensive leaf-level measurements do not completely reflect the whole plant physiology, due to variability of leaf to leaf environmental conditions and plant regulation of gas exchange.