Interspecific variation in root penetration abilities of 15 wild plants in the Mongolian steppe

Abstract

Vegetation disturbance and soil compaction by off-road vehicular traffic have been recognised as a serious environmental issue in arid regions. Vegetation recovery following such disturbances may depend on the ability of the plant roots to penetrate into the compacted soil. Here, we evaluated variation in root penetration ability in 15 wild plant species of the Mongolian steppe and analysed its contribution to plant establishment on the compacted soil. We expected that the roots of those species emerging during the early stages of vegetation recovery following soil compaction would exhibit greater penetration ability. Root penetration of each species was tested using wax layers of five different strengths. Root penetration ability (P50) was determined as the wax strength at which 50% of the individuals could penetrate the wax. P50 varied greater than three-fold among species and was high in Salsola collina, which is an early-successional species following soil compaction. However, contrary to expectation, the P50 was low in Artemisia frigida, which is an early-to mid-successional species following soil compaction, and it was highest in Stipa krylovii, which is a late-successional species in the Mongolian steppe. We concluded that the ability of the roots to penetrate a hard medium may not be a critical factor influencing plant establishment on the compacted soil in the field and that root penetration ability may not be an appropriate index for screening plant species suitable for the restoration of vegetation on the compacted soil.