Changes of root biomass in response to a one-year temperature and precipitation alteration experiment in a tallgrass prairie

Background/Question/Methods Root production is the poorest understood process in ecosystem studies because of large variation among ecosystems and measuring methods. But it is important to have information about this process since it contributes to a large portion of the plant’s ability to sequestering carbon and responses sensitively to the environmental change. In a one year pulse experiment of warming and increased precipitation conducted on a tallgrass prairie, the interannual variance of the root production responsing to extreme climate fluctuation was investigated. A total of 20 plots were arranged in a randomized block design with 2 levels of temperature (ambient and 4^oC warming) and 2 levels of precipitation (ambient and 2x ambient). Soil profiles were sampled in November of the treatment year, the pre-treatment year, and the post-treatment year by two methods: direct soil coring and ingrowth coring. 

Results/Conclusions Results of the profile analysis showed significant treatment effect of warming on the root biomass, as well as an interaction effect with time. But no effects of doubled precipitation, warming plus doubled precipitation, and their interaction effects with time were found. Root:shoot ratios showed the same dynamic pattern. The root biomass increased significantly in the treatment year compared to the pre-treatment year, but decreased significantly in the post-treatment year. The strong treatment effect of warming was due to the significantly increased proportion of biomass allocated to the root of the plants to overcome the dryer soil caused by warming although there is no significant increase of total plant production. But this process left the legacy of the increasing root mortality to the post-treatment year. Doubled precipitation did not show direct effect on root production but mitigated the water demand of the plants under warming.