Abstract:

Aims Sprouting is an efficient mechanism for forest regeneration to regain lost biomass after disturbances, and it is the main regeneration mechanism of some Quercus forests. Our objective was to study (a) root and sprout growth dynamics of Q. aquifoliodes shrubs after coppicing and (b) the supply of nutrients from the roots and the soil to the new sprouts.

Methods The sites selected were located on Zheduo Mountain of western Sichuan on the south-eastern fringe of the Tibetan Plateau. Post-fire, approximately 30-year Q. aquifoliodes shrubs were cut and sprouts and roots were sampled at 0, 30, 60, 90, 120, 150 and 180 days after coppicing. The roots were separated into fine roots (< 2.5 mm), medium roots (2.5-5.0 mm), coarse roots (> 5.0 mm), and taproot. Root biomass was investigated by excavating whole root systems and sprout biomass by harvesting. The concentrations of nutrient elements were determined by conventional methods. Nutrient supply to sprouts from the root and the soil was calculated based on change in nutrient content of the roots with time and accumulation of nutrients in the sprouts.

Important findings The mean aboveground and belowground biomass of Q. aquifoliodes shrubs was (11.25 ± 0.92) and (34.85 ± 2.02) t·hm^-2, respectively, giving a dry weight root: shoot ratio of 3.10. The biomass of sprouts linearly increased during the course of sprouting. Maximum biomasses of living fine and medium roots occurred in summer. No significant variation was observed for the stump and taproot biomasses. N and P concentrations in fine and medium roots increased in the first 60 days after harvesting; however, the stump, coarse roots and taproot decreased in N, K and Ca concentration. Of all nutrients, Mg showed the greatest variation in the root system. The root system stored much of the nutrient content. The soil, stump, coarse roots and taproots are the main nutrient sources for the initial growth of sprouts between harvesting and 120 days. All nutrients allocated to the sprouts, excluding K, were supplied by the soil between harvesting and 60 days. K was the nutrient most dependent on root reserves for the initial growth of sprouts. K, followed by Mg and Ca, is the nutrient most dependent on root reserves for sprout growth between 60 and 120 days, and the relative contribution of root to sprout P and Mg was very small in this period. Except for K, the soil is an important nutrient source between 120 and 180 days. The management of Q. aquifoliodes shrubs should focus on the protection of underground root systems.

Key words: biomass, nutrient element content, Quercus aquifoliodes, root nutrient reserves, sprouting