Roots are key components of C cycling in terrestrialecosystems and play an important role in the regulation of response ofterrestrial ecosystems to global climate warming, which is predicted tooccur with greater warming magnitudes at night than during daytime acrossdifferent regions on the Earth. However, there has been no detailed study toinvestigate the effect of asymmetrical warming on root dynamics at the levelof terrestrial ecosystems. To understand the effects of day and nightwarming 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 continuous warming was conducted using modified rhizotrontechnique during three growing seasons in 2007–2009. Our results show thatday, night and continuous warming had different effects on longevity ofroots born in spring, summer and autumn, and that day warming significantlyprolonged overall lifespan for the roots born in the three growing seasons,while night warning had no effect on overall lifespan. Day and night warminghad different effects on root non-structural carbohydrate content,suggesting that allocation of photoassimilate may account for thedifferential responses of root lifespan to day and night warming. Theseresults differ from other processes associated with ecosystems C cyclesuch as total ecosystem productivity, net ecosystem productivity and soilrespiration. Our findings highlight that it is essential to incorporate thedifferential effects of day and night warming on root dynamics intosimulating and predicting the responses and feedbacks of terrestrialecosystems C cycling to global warming.
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