Enrichment of soil nutrients and salt ions with different salinities under Tamarix chinensis shrubs in the Yellow River Delta

Abstract

In this study, we investigated the characteristics of soil salt ions and soil nutrients at different locations around Tamarix chinensis and with different salinity levels on a coastal beach of the Yellow River Delta. The findings help clarify the effects of T. chinensis growth on the enrichment rates of soil nutrients and salt ions. T. chinensis shrublands with low salinity (0.25 %), moderate salinity (0.51 %), and high salinity (1.03 %) on the coastal beach of the Yellow River Delta were studied. The available nitrogen (AN), available phosphorus (AP), available potassium (AK), total organic carbon (SOC), and levels of eight major salt ions were measured and analyzed at different locations around the T. chinensis plants. The results showed that soil salinity significantly affected the contents of soil nutrients and salt ions. Soil salinity, soil location, and their interaction had significant effects on the following contents of soil: AN, AP, SOC, K+, Na+, Cl−, and SO42− (P < 0.01). The soil nutrient contents differed significantly at different locations around a T. chinensis plant (P < 0.05), and the highest nutrient content was found under the center of the canopy, followed by that at the roots. The soil nutrient enrichment rates under different salinity levels were all greater than 1, and T. chinensis shrubs had the strongest enrichment capacity for SOC. The enrichment rates of AN, AK, and SOC under the center and edge of the canopy of T. chinensis were higher under moderate salinity than under low or high salinity; thus, T. chinensis produced a stronger “fertile island” effect under moderate salinity. Soil salinity and location had a significant impact on the enrichment of salt ions. Under low and moderate salinity, the enrichment rates of soil K+, Ca2+, and Mg2+ were all greater than 1, forming “salt islands,” whereas under high salinity, “salt basin” formed. In soil at different locations and with different salinity levels, T. chinensis produced a “salt basin” effect on Na+ and Cl− but a “salt island” effect on soil SO42− and HCO3–. The Na+ enrichment rates under low and moderate salinity were significantly lower than those under high salinity. In summary, T. chinensis shrubs under different salinity levels in the coastal beaches all exhibited the fertile island effect, which was most significant under moderate salinity. In the saline–alkali land on coastal beaches mainly containing Na+ and Cl−, T. chinensis had a salt basin effect on both ions; thus, T. chinensis shrubs significantly reduced the overall soil salinity.