Seasonal response of available nutrient content and enzyme activity in black soil surface to snow removal

Abstract: Snow cover patterns from climate change have profoundly dominated the soil physical structure and biochemical processes in farmland, as global warming is becoming much more serious in recent years. The resulting nutrient loss has posed a great threat to the black soil, a precious soil resource in China. Particularly, most black soils are distributed in seasonally frozen soil areas that are covered by snow all the year round. The snow cover has also some impacts on the black soils in these areas. Similarly, the soil nutrients and enzyme activities have a profound impact on the cycle process of soil materials in the growth and development of crops and grain yields. This study aims to further explore the seasonal response of the available nutrient content and enzyme activity in the black soil to the snow cover removal. Two experimental groups were divided in the study area, including the artificial snow cover removal, and the normal snow cover control group. A seven-month long-term field experiment was carried out to measure the soil temperature, moisture, organic matter content, available nitrogen content, available phosphorus content, invertase activity, and urease activity. The seasonal dynamics were then determined using the measured data. The results showed that the artificial snow removal led to a significant decrease in the soil temperature and soil moisture (P<0.05). At the same time, the artificial snow removal could greatly contribute to making the soil freezing and thawing time earlier, and significantly increased the number of soil freezing and thawing cycles, compared with the normal snow cover control group. In addition, the removal of artificial snow significantly increased the soil organic matter content, soil available nitrogen content, and soil available phosphorus content in early and late winter. However, the contents of soil organic matter, available nitrogen and phosphorus decreased significantly in late winter and early spring. There was also a significant decrease in the two soil enzyme activities of invertase and urease during most of the winter. The snow removal treatment decreased the activities of soil invertase and urease by more than 25.0% and 16.3%, respectively, compared with the normal snow cover control group. In addition, there were some differences in the controlling factors of soil invertase and urease activity in the whole winter and early spring. However, the soil's available nutrient content was the main controlling factor for the activities of two enzymes during most of the winter. In the future, global warming can lead to the reduction of snow cover in the middle and high latitudes of the world, some of which can have no snow cover, resulting in the different accumulation and release of soil available nutrients. The specific mechanism can be that the reduction of snow cover can cause the rapid accumulation of soil available nutrients in the early winter, and then gradually accumulate in the late winter, resulting in the loss of certain nutrients. This finding can also provide some theoretical support to the soil biochemical evolution under the condition of future climate warming.