Root capacity to penetrate compacted substrates and reach cracks. Methodological approach and application to plant colonisation on eroded slopes in semiarid areas

Abstract

This study describes a methodology to study the capacity of roots to penetrate substrates and reach cracks in a wide range of compactions. It also aims at determining the effects of root morphology, substrate resistance to penetration and depth of the most superficial substrate layer on root ability to penetrate and reach cracks in a compacted medium. The methodology is based on the use of wax discs made with different proportions of parafine and vaseline that determine different levels of resistance to penetration. A 2 x 2 x 5 full factorial design with three factors (root morphology: tap- vs. fibrous-roots, substrate depth: 3 vs. 7 mm and degree of resistance to penetration: 5 levels within the range 60-1500 kPa) was used to analyse their effects on the ability of roots to penetrate and reach cracks. Results indicate that resistance to penetration and substrate depth played a major role in the rate and velocity of root penetration. We found no effect of root morphology on the velocity of root penetration. Moreover, degree of compaction and root morphology were also relevant in the ability of roots to reach cracks. On the basis of these results, we discuss possible plant strategies that may explain the success of roadslope colonising species in semiarid environments. A mixed strategy that considers root penetration into the soil or crack detection by roots could be successful for plant establishment in roadfills, whereas the ability of roots to detect cracks in the limiting highly compacted superficial layers of roadcuts should be an advantage for plant establishment success on these latter slopes.