Early season precipitation accounts for the variability of fine-root traits in a Tibetan alpine grassland

Root trait dynamics can reflect the adjustment in the strategy of plant roots in resource acquisition and energy storage when responding to climatic fluctuations. Under global change, the responses of root traits in climate sensitive ecosystems, e.g. high-elevation and cold Alpine ecosystems, remain unclear. To identify how climatic fluctuations drive the variations in the root traits in a Tibetan alpine grassland, we intensively investigated the temporal dynamic of root traits by biweekly measuring root length, root biomass and specific root length for three continuous years. The SRL showed strong seasonal patterns across three years, which did not support SRL considered as a constant in previous root system modeling, while as hypothesized, mean SRL in non-growing seasons was significantly higher than that in growing seasons by 17 %. The accumulative air temperature of growing or non-growing season exerted synchronic effects on the changes in root traits. Nevertheless, precipitation was observed to have the lag effects on root traits, showing that January-April accumulative precipitation was a major driver for the variations in the root length and root biomass respectively peaking in July and June each year. Distinguishingly, root length relied on the lag effect of precipitation; however, for root biomass, the continuous accumulative precipitation together with peak month, i.e. the January-June accumulative precipitation, was also significantly vital. Our results would have an important implication for predicting responses of belowground carbon cycling to global climate change.