As different as day and night: evidence from root lifespan

Abstract. Roots are key components of terrestrial ecosystem C cycling and play an important role in regulation of the response of terrestrial ecosystem to global climate warming, which occurs with greater warming magnitudes at night than during daytime across different regions on the Earth. However, there has been no detailed study to examine the effect of asymmetrical warming on root dynamics at the level of terrestrial ecosystem. To understand the effects of day and night warming on root lifespan in the semiarid temperate steppe in Northern China, a field study with a full factorial design including control, day warming, night warming and diurnal warming was conducted. The responses of root survivorship to day and night warming with modified rhizotron technique were monitored during the growing seasons of 2007–2009. We demonstrate, for the first time, that longevity of roots born in spring, summer and autumn showed different response to day, night and diurnal warming, and that day warming significantly prolonged the overall lifespan for the roots born in the growing seasons of 2007–2009 pooled as a whole, while night warning had no effect on the overall lifespan in the semi-arid grassland in Northern China. The differential response of root lifespan to day and night warming may be accounted for by the photoassimilate allocation as evidenced by that day and night warming had different effect on root non-structural carbohydrate content. This finding differed from other processes associated with ecosystem C cycle such as total ecosystem productivity, net ecosystem productivity and soil respiration. Thus our findings highlight that it is essential to incorporate the differential effects of day and night warming into the simulating and predicting the responses and feedbacks of terrestrial ecosystem C cycling to global warming.