Root dynamics and water studies on Opuntia ficus-indica and O.robusta

[摘要] English: Over the last few years a great interest in cactus pear was shown in terms of both freshfruit and fodder production. However, there is a lack of knowledge on roots andtherefore this study aimed at determining the root dynamics in relation to soil-watercontent and to quantify or characterise the different root types for two Opuntia speciesnamely Opuntia ficus-indica (cultivar Morado) and 0. robusta (cultivar Monterey).This was carried out in the glasshouse (pots and root boxes) as well as in the field.Cactus pear planted in asbestos pots were used to determine the impact of soil-watercontent on root development and also their short time of recovery after rewetting thesoil. The water treatments included 0 to 25% depletion of plant available (PAW) (notstressed), 25 to 50% depletion of PAW (mildly stressed), 50 to 75% depletion ofPAW (moderately stressed) and 75 to 100% depletion of PAW (severely stressed).The root mass and root/shoot ratio decreased (P<0.05) with water stress for bothspecies. Water-use efficiency decreased for 0. ficus-indica and increased for 0.robusta with water stress. The root length, root length/root mass ratio and amount ofwater needed to fill the cladodes increased (P<0.05) with water stress for both species.The root boxes were used for observation and characterizing the different root typesand their response to soil drying and rewetting. Main roots grow up to 42 and 36 mmper day for Opuntia ficus-indica and 0. robusta respectively. The rain roots, whichdevelop after only one hour of rewetting the soil, grow only for three days until dyingdue to soil drying. The side roots also emerge in response to soil-water but dinersfrom rain roots in that they continue to grow until they die back as soil dries. Only 10to 14 mm water is needed to fill the cladodes after a water stress. The rain rootstherefore play an important role in rapid water up-take, which can fill the cladodesovernight.The root distribution with depth and distance was studied in the field, where rootmass, root length, root length/root mass relationship and root thickness were measuredat different depths and distances for each species. It has been found that most rootswere concentrated over the first 100 mm soil layer for both Opuntias. After only oneseason of establishment the root distribution can spread as far as 1.6 and 1.7 m fromthe stem for O. robusta and O. ficus-indica respectively. The root mass, root lengthand root thickness decreased (P<0.05) with depth and distance.In conclusion, the cactus pear is characterised by a shallow and extensive root system,which contributes a lot to its water-use efficiency. These characteristics make it moreappropriate for arid and semi-arid crop production. The marginal drier areas withshallow soils can therefore be utilised to their full potential by the cactus pear plant.

[发布机构] University of the Free State