Enhanced Root Production as a Feed-forward Response to Soil Water Deficit in Field-grown Tomatoes

Abstract

Much research on the role of roots as ‘sensors’ of soil water deficits (SWD) has been with plants growing in small volumes of soil. We examined adaptive responses to SWD in processing tomatoes (Lycopersicon esculentum Mill.) growing in the field. The cv. Cannery Row was grown next to a rhizotron and trickle irrigated daily, except when water was withheld for 7 or 14 days during flowering in two deficit treatments. Rainfall was excluded.

Within 7 days of withholding irrigation, there was a substantial increase in root production, particularly in the subsoil. However, predawn and midday leaf water potentials did not differ between non-irrigated and control treatments until around day 9. Even by day 14 the SWD had not affected stomatal conductances, evapotranspiration, or plant dry mass. A rapid increase in root death rate followed the re- irrigation of each deficit treatment. New root production in the non-irrigated plots appeared sufficient to maintain an adequate supply of water to the shoots. If so, this could be an even more effective means of stress avoidance than reducing leaf and stem expansion rates. Our results appear to be the first practical demonstration that root systems may play such a feed-forward role.