【目的】探究不同施肥处理下无患子细根垂直分布特征与形态差异,以及氮(N)、磷(P)、钾(K)对细根生长的影响及其交互作用,为中国南方地区广泛种植的生物质能源树种无患子的科学培育提供支撑。【方法】以福建省三明市建宁县 8年生无患子原料林为研究对象,对N、P、K肥料各设置 3个水平,采用“3414”随机区组设计进行配方施肥试验,共 14个处理,以不施肥为对照(CK),设置 3个区组,共 42个处理小区,每小区 5株作为重复。分别在2015年生长季末、2016年花期前、2016年果实迅速生长期按照配比开沟施 3次肥料,2016年12月在每个处理小区选取 4株平均标准木样株,在距树1 m处分 3层(0~20 cm、≥20~40 cm、≥40~60 cm)采集林地土柱样品,研究各处理 3层土壤内的细根分布规律及细根形态。【结果】无患子细根主要分布在0~20 cm土层,呈各土层逐层递减的规律,0~20 cm土层细根生物量(fine root biomass, FRB)及根长密度(fine root length density, FRLD)是 ≥20~40 cm土层的1.51~2.52倍和1.82~2.25倍,是 ≥40~60 cm土层的6.29~13.17倍和6.03~9.31倍。无患子FRB、FRLD、细根表面积(fine root surface area, FRSA)及细根平均直径(fine root average diameter, FRAD)均随着N、P、K施肥量的增加呈先增加后平缓降低的变化趋势,而细根比根长(fine specific root length, SRL)随着施肥量的增加表现为先降低再急剧增加而后平稳降低的变化规律。对根系促进效果最佳的N2P2K2处理在0~20 cm土层的FRB及FRLD较不施肥(CK)分别显著提高了152%和164%,≥20~40 cm土层较不施肥(CK)分别显著提高了242%和161%,≥40~60 cm土层较CK分别显著提高了385%和135%。【结论】无患子FRB、FRLD和FRSA在0~60 cm土层范围内逐层递减,有明显的垂直分布特点。在缺P条件下施用N肥和K肥对无患子根系生长影响效果较小,需要在一定范围内增加土壤养分有效性以促进无患子细根生长及生物量积累。施肥量较为充足时,无患子能够根据 ≥40~60 cm土层土壤养分资源有效性调整细根分布结构,以充分吸收养分。N和P的交互作用对FRB、FRLD、FRAD和SRL的影响达极显著水平,与无患子细根生长的相关性较大。在配方施肥处理下无患子细根生长的拟合模型分析基础上建议施N肥693 kg/hm²、施P肥321 kg/hm²、施K肥432 kg/hm²。

【Objective】This study aimed to investigate the root distribution characteristics and morphological differences in soapberry (Sapindus mukorossi) under different fertilization treatments. We also aimed to analyze the effects of nitrogen (N), phosphorus (P) and potassium (K) on the fine root growth and their interactions, so as to provide a support for the scientific cultivation of S. mukorossi, which is a widely planted biomass species in Southern China. 【Method】Using the eight-year-old forest in Jianning County, Sanming City in Fujian Province, as the research object, three levels of N, P and K fertilizers were set and a total of 14 treatments were conducted using the “3414” randomized block design. Among them, using no fertilization as the blank control (CK), three blocks were set up with 42 treatment plots and five trees per plot as repetition. At the end of the growing season in 2015, before the blooming period in 2016 and during the rapid growth period of fruits in 2016, fertilizer was applied in ditches, according to the specified proportions, in three rounds. In December 2016, four standard wood samples were selected from each treatment plot. Soil column samples were collected in three layers (0-20 cm, ≥20-40 cm and ≥40-60 cm) at a distance of 1 m from the trees. The distribution and morphology of the fine roots in the three soil layers of each treatment were studied. 【Result】The fine roots were mainly distributed within the 0-20 cm soil layer and gradually declined in the other two layers. The fine root biomass (FRB) and length density (FRLD) of the 0-20 cm layer were 1.51-2.52 times and 1.82-2.25 times higher, respectively, than the ≥20-40 cm soil layer, and 6.29-13.17 times and 6.03-9.31 times, respectively, compared to those of the ≥40-60 cm soil layer. FRB, FRLD, fine root surface area (FRSA), and fine root average diameter (FRAD) tended to increase initially and then decrease before becoming steady as the N, P and K fertilizer rates increased. Meanwhile, with the increase in fertilization, specific root length (SRL) decreased initially, before increasing sharply, and then decreasing steadily. Compared to CK, the FRB and FRLD of the N2P2K2 treatment clearly increased by 152% and 164%, respectively, in the 0-20 cm soil layer. Meanwhile, the FRB and FRLD also evidently increased by 242% and 161%, respectively, in the ≥20-40 cm soil layer, and significantly increased by 385% and 135%, respectively, in the ≥40-60 cm soil layer (P<0.05). 【Conclusion】 The FRB, FRLD and FRSA of S. mukorossi decreased gradually and had obvious vertical distribution characteristics in the 0-60 cm soil layer. Under the condition of P deficiency, N and K fertilizers were less effective on the root growth, and it was necessary to increase soil nutrient availa-bility to promote the fine root growth and biomass accumulation to some degree. When the amount of fertilizer was sufficient, this species could adjust the distribution structure of fine roots according to the availability of soil nutrient resources in the ≥40-60 cm layer and fully absorb nutrients. The interaction between N and P had a significant effect on the FRB, FRLD, FRAD and SRL, and was significantly correlated with the growth rate of fine roots. The fitting model of fine roots proposed that the most ideal amount of fertilization is N 693, P 321 and K 432 kg/hm².