Dear, you will find some good information from these two references.see full details online.

1.Root exudation and root development of lettuce (Lactuca sativa L. cv. Tizian) as affected by different soils

G. Neumann, S. Bott, [...], and K. Smalla

Additional article information

Abstract

Development and activity of plant roots exhibit high adaptive variability. Although it is well-documented, that physicochemical soil properties can strongly influence root morphology and root exudation, particularly under field conditions, a comparative assessment is complicated by the impact of additional factors, such as climate and cropping history. To overcome these limitations, in this study, field soils originating from an unique experimental plot system with three different soil types, which were stored at the same field site for 10 years and exposed to the same agricultural management practice, were used for an investigation on effects of soil type on root development and root exudation. Lettuce (Lactuca sativa L. cv. Tizian) was grown as a model plant under controlled environmental conditions in a minirhizotrone system equipped with root observation windows (rhizoboxes). Root exudates were collected by placing sorption filters onto the root surface followed by subsequent extraction and GC-MS profiling of the trapped compounds. Surprisingly, even in absence of external stress factors with known impact on root exudation, such as pH extremes, water and nutrient limitations/toxicities or soil structure effects (use of sieved soils), root growth characteristics (root length, fine root development) as well as profiles of root exudates were strongly influenced by the soil type used for plant cultivation. The results coincided well with differences in rhizosphere bacterial communities, detected in field-grown lettuce plants cultivated on the same soils (Schreiter et al., this issue). The findings suggest that the observed differences may be the result of plant interactions with the soil-specific microbiomes.

Keywords: lettuce, root exudates, root morphology, soil effects

2.

Plant and Soil

April 1974, Volume 40, Issue 2, pp 381–391

The effect of irrigation on the length, weight, and diameter of lettuce roots

Author:

H. R. Rowse

Summary

The total fibrous-root length of mature field-grown lettuces, which were protected from rainfall and not irrigated after establishment was less than 75 per cent of that of irrigated plants, although the corresponding root weights were very similar. Non-irrigated plants had thicker roots, less roots near the soil surface, and more at depth. Up to the time that the roots started to die, about two weeks before the lettuce were mature, the variation of root length with depth and time is described by a simple logarithmic expression. re]19730803

You may use WinRhizo system. Please also check the attached files.

Dr. Alexander Diaz of the Universidad Militar Nueva Granada in Colombia has been assessing the impact of compost on lettuce plants (Lactuca sativa L. Var Crespa) by measuring leaf area with the CI-202 Portable Laser Leaf Area Meter.