Freeze-thaw process induced by increased precipitation affects root growth of alpine steppe on the Tibetan Plateau

The response of vegetation productivity to precipitation is becoming a worldwide concern. Most reports on responses of vegetation to precipitation trends are based on the growth season. In the soil freeze/thaw process, the soil water phase and heat transport change can affect root growth, especially during the thawing process in early spring. A field experiment with increased precipitation (control, increased 25% and increased 50%) was conducted to measure the effects of soil water in early spring on above- and below-ground productivity in an alpine steppe over two growing seasons from June 2017 to September 2018. The increased 50% treatment significantly increased the soil moisture at the 10 cm depth, there was no difference in soil moisture between the increased 25% treatment and the control in the growing season, which was not consistent in the freeze/thaw process. Increased soil moisture during the non-growing season retarded root growth. Increased precipitation in the freezing-thawing period can partially offset the difference between the control and increased precipitation plots in both above- and below-ground biomass.