The effects of topography on aboveground biomass and soil moisture at local scale in dryland grassland ecosystem, China

摘要

Water is the primary limiting factor for grassland vegetation in dryland regions. Topography is considered to play an important role in the distribution of soil moisture, which will significantly affect grassland ecosystems. To examine the response of soil water content (SWC) and aboveground biomass (AGB) of grassland vegetation to precipitation patterns and topography, a 6-year investigation was conducted during the period from 2012 to 2017 in a semiarid steppe of Inner Mongolia, China. The study area was divided into three parts based on the landscape position, i.e., top area (TA), slope area (SA) and bottom area (BA). The results suggested that SWC and AGB would be significantly affected by topography and precipitation patterns. A significant negative relationship was found between the SWC and the altitude of the sampling sites. In the dryer years (2013-2017), the AGB of the BA was significantly higher than that of the SA and TA. However, a non-significant difference was found for the AGB values between the three landscape positions in the wetter year (2012). During the growing season, variation of AGB and SWC was similar in 2014 but differed in 2015. AGB exhibited a significant positive relationship with SWC above a minimum value. Precipitation significantly affected the AGB of grassland, and moderate rainfall events were more effective than light rainfall events for grassland vegetation. Moreover, the distribution of species varied in different areas, which may result in the differences in the responses of AGB to soil moisture and precipitation. This study clarifies the effects of micro-topography on soil moisture and grassland ecosystems at a local scale in dryland regions, which provides useful information for grassland ecosystem management.