Belowground dynamics in two olive varieties as affected by saline irrigation

Olive is a major tree crop found naturally in the Mediterranean basin, Asia and Africa, considered to be moderately salt-tolerant. Because most studies focus on aboveground parameters, detailed information regarding root-system functioning under salinity is scarce. We examined the belowground traits of two mature olive varieties (salt-tolerant Barnea and salt-sensitive Leccino) after 13 years of saline irrigation (EC 4.2dSm^-1) to better understand the causes underlying their diverging salt tolerance.Stem growth of Barnea variety was less impaired by salinity compared to Leccino trees. Fine-root regrowth was reduced in both varieties under salinity. Compared to growth under freshwater irrigation, the impairment was 10% higher for salt-stressed Leccino roots. However, Leccino trees may partially compensate smaller root systems under salinity by an increased specific root area. Median fine root lifespan was reduced by 12 days in Barnea variety under salinity but still remained higher than in Leccino trees under both irrigation treatments. Soil respiration around Leccino trees was twice as high as in the vicinity of Barnea trees.Root regrowth of the salt-tolerant Barnea variety was less constrained by salinity than Leccino's. Data on root longevity and soil respiration indicated that Leccino trees transfer more C belowground to rebuild and maintain their root system under both control and saline conditions. Subsequently, fewer C is available for aboveground growth, likely resulting in the previously reported lower stem growth and yield in Leccino trees.