Study on water holding characteristics of litter under the main shrub types in the northern and southern mountains of Lanzhou City, northwest China

As ecological barriers, plantations of northern and southern mountains play an important role in soil and water conservation and regional climate improvement in Lanzhou City, Gansu Province. The aim of this study was to investigate the accumulation of litter and their water holding characteristics in different artificial shrubs in the northern and southern mountains of Lanzhou City. An investigation was conducted on the accumulation and water holding characteristics (water holding capacity, water holding rate, and water absorption rate) of the litter by field survey and laboratory soaking extraction under four main shrubs (Platycladus orientalis, Tamarix chinensis, Reaumuria soongorica, and Caragana rosea) in the northern and southern mountains of Lanzhou. The results showed that the accumulation amount of the litter under the shrubs ranged from 0.44 to 48.51 t·ha⁻¹, and in the order of C. rosea > P. orientalis > T. chinensis > R. soongorica. The storage percentage of undecomposed litter was greater than that of semi-decomposed litter, except for under C. rosea shrubs. The maximum water-holding rate of the litter ranged from 175.20% to 323.73%, which was the highest for T. chinensis and the lowest for C. rosea. The water-holding rate of the undecomposed litter was lower than that of the semi-decomposed litter. The maximum water-holding capacity of the litter ranged from 0.85 to 84.81 t·ha⁻¹, followed by C. rosea > P. orientalis > T. chinensis > R. soongorica. The water-holding capacities of C. rosea and P. orientalis were lower in undecomposed litter than in semi-decomposed litter, but the opposite was true for the T. chinensis shrub. The water absorption rate of the litter declined linearly within the first hour, after which the litter water absorption decreased slowly. The semi-decomposed litter had a higher water absorption rate than the un-decomposed litter. The maximum retaining amount of the litter ranged from 0.83 to 67.21 t·ha⁻¹, the effective retaining amount of the litter ranged from 0.70 to 54.49 t·ha⁻¹, the effective retaining depth ranged from 0.07 to 5.45 mm. and the order of the maximum litter retaining amount, the effective retaining amount and the effective depth in the different shrub types were C. rosea > P. orientalis > T. chinensis > R soongorica. Therefore, the C. rosea shrub has a high capacity for soil and water conservation in the northern and southern mountains of Lanzhou City.