【目的】西南桦(Betula alnoides)具有较高的经济价值和生态效益,是中国热带、亚热带地区重要的乡土速生阔叶树种。氮和磷的有效性和空间分布显著影响着植物生长和根系发育。笔者研究施肥对西南桦无性系生物量分配和根系形态的影响,筛选出优良西南桦无性系及适宜的施肥配方,为西南桦的科学培育提供参考。【方法】以西南桦4个无性系(编号分别为A5、FB4、FB4⁺、BY-1)组培苗为试验材料,采用完全随机区组设计,每个小区 25 株。设置氮(0、200、400 mg/株)和磷(0、70、140 mg/株)共9个组合处理,重复 3 次。以不施肥为对照。为防止苗木缺素,每株施钾量为332 mg。磷肥作为基肥一次性施入基质中,组培苗移栽成活1个月后,开始追施氮和钾肥,每次施肥间隔时间为7 d,共10次。最终苗木收获时,先分离出根系进行形态指标扫描,获得根长、根表面积、根体积和根平均直径,最后全株烘干用于测定各器官的生物量,比较不同施肥处理下西南桦无性系的生物量分配和根系形态差异。【结果】①不同无性系和施肥处理下西南桦幼苗的地上、地下和总生物量差异均达到显著水平,但无性系×施肥处理的交互作用不显著。施肥处理幼苗的地上、地下和总生物量较对照(不施肥)有明显的增幅。处理5(N 200 mg/株+P 70 mg/株)幼苗的地上、地下和总生物量最大,分别比其他施肥处理提高了11.27%~460.49%、7.14%~200.00%、10.57%~390.09%。进一步比较不同无性系,无性系FB4⁺的地上、地下和总生物量表现出明显的生长优势,分别是无性系A5、FB4和BY-1的1.14~1.21、1.22~1.31、1.15~1.22倍。②不同无性系和施肥处理下幼苗的根表面积、根平均直径和各根径等级细根的根长差异显著或极显著,且无性系×施肥处理的交互作用对根体积、根表面积、根平均直径和各根径等级细根(根径d>2 mm除外)的根长影响均极显著。施肥处理的幼苗根系形态参数均高于对照。在所有无性系中,处理5的根系形态参数均显著高于其他施肥处理,其根表面积、根平均直径、根体积和总根长,分别比其他施肥处理提高了0.77%~227.20%、2.13%~152.63%、0.60%~264.13%和4.53%~214.04%。进一步比较不同根径等级细根的根长,西南桦幼苗的小细根(0<d≤1 mm)、粗细根(1<d≤2 mm)和粗根(d>2 mm)的根长亦表现出处理5最大。无性系FB4⁺在处理5下的根系形态参数显著高于其他无性系和施肥组合。③总生物量与地上、地下生物量均呈极显著的正相关关系,这三者与根平均直径、总根长、根表面积、根体积亦分别表现为极显著的正相关关系。【结论】施肥显著促进了西南桦幼苗的生物量和根系生长发育,且存在无性系差异。综合幼苗的生物量和根系形态指标,认为西南桦无性系FB4⁺在处理5(N 200 mg/株+P 70 mg/株)条件下生长表现最优。

【Objective】 Betula alnoides is a native, fast-growing, broad-leaved tree species found in the tropical and subtropical regions of China, and it has a high economic value and ecological benefits. The availability and spatial distribution of nitrogen (N) and phosphorus (P) significantly affect plant growth and root development. By studying the effect of fertilization on biomass allocation and root morphology in B. alnoides clones, the optimum B. alnoides clone and fertilization treatments were screened to provide scientific guidance for cultivating B. alnoides. 【Method】 Four B. alnoides clones (A5, FB4, FB4⁺ and BY-1) were selected as research materials, and a completely randomized experimental design was conducted with nine treatments including three N levels (0, 200 and 400 mg/seedling) and three P levels (0, 70 and 140 mg/seedling) with three replications and 25 plants for each subplot. To prevent nutrient deficiency in seedlings, 332 mg/seedling potassium (K) was applied. P fertilizer was supplied to the medium as a basal fertilizer. The application of N and K fertilizers was initiated at 1 month after seedling transplantation and was conducted at intervals of 7 days for a total of 10 times. When the seedlings were harvested, the roots were separated and scanned to measure morphological indexes (root length, surface area, volume and mean diameter). Finally, whole plants were dried to determine the biomass of each part, and the biomass allocation and root morphology of B. alonoides clones under different fertilization treatments were compared. 【Result】 ① The above-ground, below-ground and total biomass were significantly affected by fertilization treatment and differed according to clones, but they were not influenced by the interaction between clones and fertilization treatment. Compared with the control treatment, the fertilization treatment significantly increased the above-ground, below-ground, and total biomass. Regardless of the clone, treatment 5 (200 mg/seedling N+70 mg/seedling P) resulted in the highest biomass among all treatments, which was 11.27%-460.49%, 7.14%-200.00% and 10.57%-390.09% higher than the other treatments for above ground, below ground, and total biomass, respectively. On further comparing different clones, FB4⁺ showed obvious growth advantages, with an above ground, below ground, and total biomass of 1.14-1.21, 1.22-1.31 and 1.15-1.22 times than those of other clones (A5,FB4 and BY-1), respectively. ② The root surface area, mean diameter and total length were significantly different among different clones and fertilization treatments. Except the total length of roots with a diameter of <2 mm, the interaction effect between clones and fertilization treatment resulted in significant differences in terms of root volume, surface area, mean diameter and total length. The fertilization treatment improved root morphology compared with the control treatment. In all clones, treatment 5 resulted in superior root morphological indexes than the other treatments, with values 0.77%-227.20%, 2.13%-152.63%, 0.60%-264.13% and 4.53%-214.04% higher than those of root surface area, mean diameter, volume and total length, respectively. On further comparing the total lengths of fine roots of different diameters, treatment 5 also produced the longest thin fine roots (0 < diameter ≤ 1 mm), thick fine roots (1 < diameter ≤ 2 mm), and coarse roots (diameter>2 mm) in B. alnoides seedlings. The clone FB4⁺ under treatment 5 exhibited the optimum root morphology among all combinations of clones and fertilization treatment. ③ There were significant positive correlations among the above ground, below ground and total biomass. Further, these three measures of biomass were positively correlated with root mean diameter, total length, surface area and volume. 【Conclusion】 Fertilization significantly increased biomass and promoted root growth ofB. alnoides seedlings, although there were differences among clones. Based on biomass and root morphological indexes, clone FB4⁺ and treatment 5 (200 mg/seedling N+70 mg/seedling P) exhibited the optimum growth performance for this tree species.