Shoot and root physiological responses to localized zones of soil moisture in cultivated and wild lettuce (Lactuca spp.)

Abstract

Cultivated crisphead lettuce (Lactuca sativa L.) has a shallower root system than its wild relative, Lactuca serriola L. The effects of localized soil water, at depth, on plant water relations, gas exchange and root distribution were examined in the two species using soil columns with the soil hydraulic‐ally separated into two layers, at (0–20 cm and 20–81) cm, but permitting root growth between the layers. Three treatments were imposed on 7‐week‐old plants, and maintained for 4 weeks: (i) watering, both layers to field capacity; (ii) drying the upper layer while watering the lower layer to field capacity, and (iii) drying both layers. Drying only 0–20 cm of soil had no effect on leaf water status, net photosynthesis, stomatal conductance or biomass production in L. serriola compared to a well‐watered control, but caused a short‐term reduction (10 d) in leaf water status and photosynthesis in L. sativa that reduced final shoot production. The different responses may be explained by differences in root distribution. Just before the treatments commenced, L. serriola had 50% of total root length at 20–80 cm compared to 35% in L. sativa. Allocation of total biomass to roots in L. serriola was approximately double that in L. sativa. The wild species could provide germplasm for cultivated lettuces to extract more soil water from depth, which may improve irrigation efficiency.

Sugar Accumulation along the Seminal Root Axis, as Affected by Osmotic Stress in Maize: A Possible Physiological Basis for Plastic Lateral Root Development

“…Taylor and Klepper (1974) reported that young cotton plants developed much deeper root systems under conditions of frequent superfi cial application of water to surface soil than those grown with suffi cient water. This type of promotion of rooting depth by surface irrigation was reported for lupin (Devries et al, 1989;Rodringues et al, 1995), soybean (Finn and Brun, 1980;Mason et al, 1982;Hoogenboom et al, 1987), maize (Robertson et al, 1980;Sharp and Davies, 1985;Newell and Wilhelm, 1987), lettuce (Gallardo et al, 1996) and sorghum (Burch et al, 1978). These results showed that the change in lateral root development, i.e.…”

The biology of Canadian weeds. 122. Lactuca serriola L.

“…Jackson (1995) suggested that these differences in root architecture may be due to inadvertent selection for lettuce cultivars with increased root growth in the surface zone where water and fertilizer are plentiful. Gallardo et al (1996) found that drying of the top 20 cm of soil had no effect on leaf water status, net photosynthesis or biomass production of L. serriola grown in 1-mlong cylinders, whereas biomass production, leaf water status and photosynthesis were reduced in L. sativa.…”

“…A gene for downy mildew resistance from L. serriola was incorporated into L. sativa cultivars Calmar and Valverde (Ryder and Whitaker 1976). Gallardo et al (1996) suggested that traits for root architecture associated with drought tolerance in L. serriola could be incorporated into cultivated lettuce to improve irrigation efficiency.…”

“…Werk and Ehleringer (1986b) experimentally manipulated stem leaf orientation in plants of L. serriola, and showed that vertical leaf orientation in a north-south plane (see Section 7a) reduces water loss without significantly reducing carbon gain, and results in higher reproductive output compared to a horizontal leaf orientation. Jackson (1995) and Gallardo et al (1996) compared root architecture and drought-tolerance in prickly lettuce and cultivated lettuce grown in soil columns in the greenhouse. L. serriola produced a deeper root system than L. sativa, with more laterals near the root tip and 50% of its total root length at the 20 to 80 cm depth.…”

“…(a) Climatic requirements -L. serriola is native to a summer-dry mediterranean climate (Gallardo et al 1996) considered a drought-tolerant species Ehrlinger 1985, 1986b). Prince et al (1978) noted that L. serriola is found primarily between latitudes 30 and 55 in the northern hemisphere.…”