ROOT DEMOGRAPHY IN KIWIFRUIT (ACTINIDIA-DELICIOSA)

A rhizotron was used to study fine-root demography in mature vines of kiwifruit (Actinidia deliciosa). The vines were grown in a deep, well drained, silt loam and received normal orchard management. Roots were measured from 10 to 160cm depth at biweekly intervals for 2 years. After an initial phase of rapid colonisation of the repacked soil behind the rhizotron windows, the total length of visible roots per vine remained quite steady. This apparent stability of the total belied fast and sustained localized turnover of the fine roots at all soil depths. Fifty-one per cent of the roots survived less-than-or-equal-to 28d, 69% died at an age less-than-or-equal-to 56d and only 8% survived > 252d. For each year, the cumulative length of roots grown was equivalent to about 2.75 times the maximum net length of roots visible. These may be the largest annual rates of root turnover vet reported. This has important ramifications for the carbon balance, mineral nutrition and water relations of the plant.