Simulating warmer and drier climate increases root production but decreases root decomposition in an alpine grassland on the Tibetan plateau

Background: Future ecosystem structure and function will largely depend on root responses to climate change. However, few studies have explored the responses of root production and decomposition to simultaneous warming and altered precipitation in high-latitude and high-altitude ecosystems. Methods: Using ingrowth core and root bag methods, we investigated root production and decomposition dynamics from 2013 to 2015 in a full-factorial warming (control, 1.5 ~ 1.8 °C warming) and precipitation (dry (−50% precipitation), ambient, and wet (+50% precipitation)) experiment established in 2011 in a Tibetan alpine grassland. Results: Warming and precipitation effects on root production were independent. Dry plus warming treatments increased root production, while wet treatments did not significantly affect root production. In contrast, root decomposition accelerated along the increasing precipitation gradient. Warming tended to decrease root decomposition under dry treatments but did not affect root decomposition under wet treatments. The different responses of root production among the treatments were mainly driven by changes in soil moisture, whereas those of root decomposition were mainly due to the changes in the root carbon nitrogen ratio, soil microbial biomass and soil moisture. Conclusions: Given that altered precipitation had contrasting effects on root production and decomposition, our findings indicate that root-derived carbon may accumulate in soils on the Tibetan Plateau where precipitation decreases but not in the areas with projected increasing precipitation under future warming.