Effects of night warming on spruce root around non-growing season vary with branch order and month

The Root is an important plant organ and has high heterogeneity; how it responds to global warming is yet to be answered. This study examined the growth and physiological responses of fine roots to warming around the non-growing season. Plants from 4-year-old Picea asperata were grown under experimental warming conditions. A detailed investigation was conducted by measuring biomass, triphenyltetrazolium chloride (TTC) reducing capacity, carbon (C) and nitrogen (N) concentration, non-structural carbohydrate (NSC) of the primal five branch order roots in early (April) and late (September) growing seasons as well as in the non-growing season (December). Warming promoted fine root growth in April and fine root turnover was mostly in the first four orders. It decreased root C, N concentration in the early and late growing seasons but increased N concentration in the non-growing season. Moreover, it increased NSC concentration (especially soluble sugar) in April but decreased its concentration (soluble sugar and starch) in December. TTC reducing capacity in April was higher than in the other 2 months. The effect of warming on tree roots varied with its branch order and month. The lower order (first three or four order, in general) roots were sensitive to warming, especially in April (early part of growing season) and December (non-growing season). Warming accelerated the carbon input from root to soil. It is indicated that any changes in winter temperatures could alter the sink strength of terrestrial ecosystems considerably. Moreover, TTC reducing capacity could reflect more information about root, but it was more sensitive than N concentration.