Influence of girdling on growth of litchi (Litchi chinensis) roots during cold-dependent floral induction

•Root growth increased during floral induction but decreased during flower development.•Girdling suppressed the growth of distal roots but induced that of proximal roots.•The reduction of starch and sucrose caused by girdling accounted for the suppression of distal roots growth.•More fine roots were distributed in shallower soil layers where the roots showed more rapid responses to cold and the girdling treatment.•Root growth is more sensitive to carbohydrate availability than floral inductive-cold. Girdling is extensively applied to promote litchi flowering via the acceleration of bud dormancy and accumulation of carbohydrate in terminal shoots and leaves, but little is known about the response of root growth to girdling treatment during low temperature-mediated floral induction. In this study, litchi plants were girdled before exposure to inductive-cold in the field, and the growth of roots were monitored until floral initiation. The results showed that the length density and growth rate of fine roots increased during cold-dependent floral induction in the entire soil profile, but significantly decreased during flower development. The girdling treatment suppressed the emergence and growth of distal roots but induced that of proximal roots. More fine roots were distributed in shallower soil layers (15–45 cm) where the roots showed more rapid responses to cold and the girdling treatment. Roots reduced starch and sucrose content across the floral induction period and in response to the girdling treatment, which possibly accounted for the suppression of distal root growth. It is suggested that litchi root growth is more sensitive to carbohydrate availability than cold temperatures during floral induction.