Dynamics of soil microbial biomass and enzyme activities along a chronosequence of desertified land revegetation

Large-scale sand control and afforestation in the Mu Us Sandy land of China have greatly improved soil nutrients and physicochemical properties; however, little is known about their effects on soil biological properties. This study aimed to investigate the changes in soil microbial biomass and enzyme activities and their relationships with soil physicochemical properties during sand land rehabilitation. Soil samples were collected from the shrub and arbor plantations with an age sequence of 20, 30, and 51 years in Yulin at depths of 0-10 cm and 10-20 cm and with semi-fixed sand land selected as a control (0-year-old site). The soil physicochemical and biological properties in the 0-10 cm soil layer were significantly (P < 0.001) higher than in the 10-20 cm soil layer for all stand lands. The soil microbial biomass (e.g., microbial carbon and nitrogen) in the 0-10 cm and 10-20 cm layers greatly increased, by 1.58-5.59 times and 2.27-6.07 times, respectively, during the revegetation of shrub and arbor from 20 to 30 years on the control land. During the same period, the activities of soil catalase, urease, alkaline phosphatase and invertase also greatly increased, by 1.27-2.18, 0.59-1.23, 0.48-3.66 and 0.57-2.72 times in shrub land, respectively, whereas they increased by 1.51-2.73, 0.46-2.09, 0.97-2.79 and 2.00-6.65 times in arbor land, respectively, compared with the control land. However, during the 30-51 years of revegetation on the control land, the soil microbial biomass and all enzyme activities remained relatively stable or slightly increased in the arbor land, whereas they were reduced in the shrub land. The soil organic carbon (SOC), dissolved organic carbon (DOC), total nitrogen (TN) and available nitrogen (AN) contents also greatly increased after revegetation in the control land. Principal component analysis (PCA) also confirmed that most of the chemical and biological properties were influenced by the afforestation and showed coordinated variation between the analyzed parameters. Moreover, redundancy analysis (RDA) showed that the soil microbial biomass and enzyme activities were correlated with the changes of SOC, DOC and TN, whereas they were negatively correlated with the bulk density, pH and total potassium. Therefore, we concluded that revegetation by the establishment of both shrub and arbor plantations significantly improved soil biological properties. Moreover, SOC, DOC and TN were regarded as the key factors in the enhancement of soil biological activity during desertified land revegetation in the Mu Us Sandy land of China.