Short term drying of half the root system reduces growth but not water status or photosynthesis in leaves of passionfruit (Passiflora sp.)

David Turner, C.M. Menzel, D.R. Simpson

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    The impact of soil water deficits and non-hydraulic root signals on the expansion, functioning and water status of leaves and the opening of flowers of passionfruit was studied in a series of pot experiments. Hydraulic and non-hydraulic signals were separated by withholding water from half the root system.The leaves of well-watered plants expanded in a sigmoid pattern to about 65 cm(2) over 15 to 18 days. Drying the whole root system stopped leaf expansion after 6 days, but did not change the pattern of leaf growth. Growth resumed after rewatering but the final leaf size was halved. As leaf growth slowed, the net photosynthesis, P-n, of mature leaves fell from 11 +/- 1 mu mol CO2 m(-2) s(-1) to less than zero as the leaves wilted. Leaf water potential, psi(1), of mature leaves at midday ranged from -0.9 MPa in well-watered plants to -3.1 to -3.7 MPa in wilted plants. After rewatering, psi(1) returned to -0.9 MPa within 1 day, but P-n took 3 days to return to control levels. A midday psi(1) of -1.5 MPa was associated with a 50% reduction in relative leaf expansion and net photosynthesis.Drying half of the root system reduced leaf expansion by 26%, compared with well-watered plants, and water use by 21 to 27%, without influencing psi(1) or P-n. Plants with half the root system dry for 13 days flowered earlier than well-watered plants but had the same number of open flowers 1 month after treatments ended, Non-hydraulic root signals affect leaf expansion and flowering in passionfruit.
    Original languageEnglish
    Pages (from-to)25-36
    JournalScientia Horticulturae
    Publication statusPublished - 1996


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