Effects of different mulching measures on the fine-root adaptation strategies of Amorpha fruticosa in saline soil

In order to provide a reference for soil improvement and revegetation in the saline wastelands of the Ningxia Irrigation Area, we investigated the effects of different mulching materials on the soil microenvironment and vertical distribution of the fine roots of Amorpha fruticosa. In 2016 and 2017, we examined the effects of mulching using three different mulch materials, namely, plastic mulch (PM), sand mulch (SM), and rice straw mulch (RSM), and compared these with a non-mulch control (CK). To assess the effects of mulching, we measured the following soil microenvironmental factors at depths from 0 to 60 cm: soil water content (SWC), soil temperature (ST), electrical conductivity of a saturated paste extract (ECe), soil organic carbon (SOC), and available nitrogen (AN). Plants under different mulches were sampled to analyze extensive strategies (fine root biomass and fine root length) and intensive strategies (specific root length and specific root area). The results revealed that in both years of the study, RSM retained the highest SWC with increases of 13.59%～14.38% at depths of between 0 and 60 cm. Compared with CK, PM and SM increased ST by 8.48%～20.17% and 5.07%～18.20%, respectively, whereas the use of RSM reduced ST due to its greater heat capacity and lower thermal diffusivity. PM (12.05%～45.10%) showed the best performance with respect to a reduction in EC_e at depths between 0 to 60 cm, followed by RSM (10.34%～34.73%) and SM (4.42%～19.61%). In both years, RSM promoted the largest increase in SOC, by 6.61%～9.22%. In 2016, PM and SM reduced SOC by 13.95% and 7.80%, respectively, whereas in 2017, respective increases of 7.07% and 5.77% were obtained using these mulches. In both years, all mulching treatments increased AN, in the order RSM (28.58%～48.20%) > PM (26.00%～39.39%) > SM (10.18%～24.40%). Fine roots in the 0 – 40 cm layer under PM showed the best performance with respect to extensive strategies, whereas those in the 40 – 60 cm layer performed best in terms of intensive strategies. These adaption would be beneficial with regards to acquiring larger amounts of resources in saline soils characterized by resource heterogeneity. Comparatively, we found that fine roots in the 0 – 40 cm showed the best intensive strategies under CK conditions. The findings of this study thus indicate that among the different mulches assessed, a plastic mulch would be the most effective in improving the saline soil environment, thereby enhancing performance of the fine roots of A. fruticosa in different soil layers with respect to two adaptive strategies.