川滇高山栎灌丛萌生过程中的营养元素供应动态

萌生更新是森林更新的重要方式,是硬叶栎林受到干扰后植被恢复的主要机制。以位于青藏高原东南缘的川西折多山东坡川滇高山栎(Quercus aquifoliodes)灌丛为研究对象,调查分析了砍伐后灌丛萌生过程中基株根系和萌株生物量动态、营养元素含量,以及基株根系和土壤对萌株生长过程中的营养元素供应动态。结果表明,川滇高山栎灌丛平均地上和地下生物量分别为(11.25±0.92)t·hm-2和(34.85±2.02)t·hm-2,具有较大的根冠比(3.10:1);萌生过程中,萌株生物量呈线性增加趋势,以灌丛活细根生物量变化为最大,其次是活中根和活粗根,树桩和根蔸生物量变化最小;萌生过程中,灌丛细根和中根N、P含量表现为先增加、后降低的变化趋势,萌生初期树桩、粗根和根蔸中N和K的含量明显下降,根蔸中Ca含量略有下降,而P没有明显下降,根系Mg含量变化幅度较大,灌丛地下根系储存了较多的营养元素;土壤、树桩、粗根和根蔸是川滇高山栎灌丛砍伐后0-120天萌生生长的主要营养来源,砍伐后60天,萌株生长所需的营养除K元素主要来源于根系外,其余营养元素主要来源于土壤;在砍伐后60-120天,基株根系对萌株生长所需的N、K和Ca贡献较大,而对P和Mg的贡献较小;在砍伐后120-180天,根系除K元素对萌生生长还保持较大的贡献外,对其余营养元素的贡献均较小。高山栎林管理要注重加强地下根系的保护。

Dynamics of nutrient supply to sprouts from the roots and soil during sprouting of Quercus aquifoliodes shrublands,western Sichuan,China

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.