Divergent responses of plant biomass and diversity to short-term nitrogen and phosphorus addition in three types of steppe in Inner Mongolia, China

Background: Understanding the response of the plant community to increasing nitrogen（N） and phosphorus（P） inputs is helpful for managing and protecting grassland ecosystems in semiarid areas. However, information about different types of steppe responses to N and P availability in semiarid grasslands is limited. In 2017–2018, two field experiments were conducted with six levels of N(from 5 to 30 g N m-2 yr-1) and P(from 2.5 g to 15 g P m-2 yr-1) additions in three different temperate steppes, including meadow steppe（MS）, typical steppe（TS）, and desert steppe（DS）, in northern China to study the effects of these addition rates on community biomass and diversity.Results: Our results showed that plant biomass and diversity in the three steppe types in Inner Mongolia responded differently to elevated N and P inputs. Increasing P promoted aboveground and belowground biomass more than increasing N in the three temperate steppes. Short-term N and P additions reduced plant diversity to some extent, with the most pronounced decreases in MS and DS. It is noteworthy that there were response thresholds for plant diversity and biomass in response to N and P inputs in different steppe types(e.g., 10 g P m-2 yr-1). Furthermore, redundancy analysis and stepwise regression analysis revealed that changes in soil properties induced by nutrient addition and climate conditions jointly regulated changes in vegetation biomass and diversity.Conclusions: The plant biomass and diversity of three steppe types in Inner Mongolia respond divergently to elevated N and P inputs. Our results indicate that regional differences in climate and soil substrate conditions may jointly contribute to the divergent responses of plant biomass and diversity to short-term N and P addition. Our analyses provide new insights into managing and protecting grassland ecosystems. Considering that the effects of nutrient addition on plant diversity and productivity may have increasing effects over time, studies on long-term in situ nutrient addition are necessary.