Background  The water-level fluctuation region in China's Three Gorges Reservoir (TGR) represents a disturbance zone that experiences cyclic exposure and inundation due to reservoir operations. This area has also experienced substantial erosion due to rainfall and wave effect. A special section of the slope with free face will be formed in water-level fluctuation zone because of the wave erosion. The section would suffer disintegration during the water level up. However, the influence of root on the soil disintegration of purple soil from the water-level fluctuation zone in TGR is still far from being fully understood.

Methods  Samples of purple soil collected from Zigui county, one of typical soil in the water-level fluctuation zone in TGR, were tested in the experiments. The soil samples were air-dried and gently sieved through a 5-mm sieve to remove the impurities such as roots and gravels in the soils. The soil was packed in the plant slot, 4.5 g of Cynodon dactylon seed was applied in each plant slot and sampled after growing 1 year. A home-made disintegration device was used to conduct the soil disintegration experiments with (RS) or without (CK) plant root under 10°, 20° and 30° conditions.

Results  The cumulative soil disintegration process for the CK and RS showed the similar trend as the steep increased in the rising limb and followed by the gradual increase and stable state with the increase of disintegration duration, while the disintegration rate process presented different trend between CK and RS. The cumulative soil disintegration in the whole duration and disintegration rate in the initial stage was significantly reduced because of the plant roots. The cumulative soil disintegration and the highest disintegration rate for the CK and RS enhanced with the increase of slope gradient. The plant root influence on the soil disintegration under lower middle (10° and 20°) slope was more than that under steep slope (30°). Comparing to the CK, the plant root eliminated over 50% of the occurrence of the soil disintegration of purple soil.

Conclusions  The plant root is sufficient to significantly affect soil disintegration process for both cumulative soil disintegration and disintegration rate. And the plant root is effective for preventing soil disintegration. The study will strengthen the understanding of mechanism and process of soil disintegration for water-level fluctuation region and provide a scientific basis for the sustainable use of the water and soil resources and the ecological construction in the TGR.