Fruit orchards potential as carbon (C) sinks is virtually unknown. Moreover, despite their importance in the Mediterranean area, few data are available about the effect of the reduction in water availability on fruit tree productivity. Here we report the effect of two different irrigation regimes on net primary (NPP) and net ecosystem (NEP) productivities of an apple orchard in northern Italy in 2006. Trees productivity and heterotrophic soil respiration were estimated by inventory and root exclusion methods, while belowground allocation with a C mass-balance approach. The NPP of the control (7.86 +/- 0.25 Mg C ha(-1); mean +/- SE) was significantly greater than that of water stressed trees (6.53 +/- 0.12 Mg C ha(-1)), and the ratio between above and below net primary productivity (ANPP/BNPP) was 1.88 and 0.98 respectively. However, the partitioning of ANPP and BNPP among aerial organs and among fine, coarse roots, and root litter was unaffected by the water regime. Although NEP was greater in the control than in stressed trees the C gain of the system after fruit removal (NEPafr) was unaffected by water availability. This study indicated an effect of water availability on C partitioning patterns above- and belowground, although there were no significant effects on the C sink potential as NEPafr.
