断根对杨树切口处细根根序形态与解剖结构的影响

Effect of root pruning on the morphological characteristics and anatomical structure among different branch orders of fine root in the incision of poplar

为探讨断根对杨树切口处不同根序细根的形态与解剖特征的影响效果,通过大田试验研究6倍胸径两侧(6-2)、8倍胸径两侧(8-2)与10倍胸径两侧(10-2)等不同断根处理对杨树切口处1-5级根形态参数与解剖学特征参数的影响.结果显示,与对照(未断根)相比,10-2处理1-5级根的表面积、体积和生物量变化较小,6-2处理则显著减小,而8-2处理显著增大.随着根序的增加,各处理的细根表面积、体积与生物量均呈递减的趋势,而直径与组织密度则呈递增的趋势.在断根处理中,8-2处理1-2级根的直径与组织密度最小,而3-5级根的直径、组织密度最大,并均与6-2和10-2处理差异达显著水平.同时,各处理不同根序细根的维管束直径与维管束-根直径比(维根比)随根序的增加而逐渐增大,其中8-2处理1-2级根的维管束直径与维根比显著小于6-2和10-2处理,而3-5级根则明显大于6-2、10-2处理.不同处理切口处1-2级根基本呈现初生结构的特征,从3级根开始出现木栓层且皮层脱落.此外,8-2处理的胸径、树高平均生长率显著高于其他处理,其中胸径平均生长率分别比CK、6-2和10-2处理高出44.67%、69.36%和46.34%,树高平均生长率分别高出47.31%、60.81%和38.46%.上述结果表明,3种断根强度对杨树切口处各序级细根的作用效果存在显著差异,其中8-2处理通过调节不同根序细根的组织密度、维管束直径、皮层厚度和维根比来增强根系的吸收能力与运输功能,更利于促进杨树林木的生长.

This study aimed to explore the effects of root pruning on the morphological characteristics and anatomical structure among different branch orders of fine root in the incision of Populus euramericana ‘Neva’. A field experiment was designed and performed, in which the root system of five-year-old poplar was manually pruned with a sharp spade at six, eight, and ten times of diameter at breast height (DBH) distance along both inter-row sides, to determine the effects of different root pruning treatments on the morphological parameters and anatomical trait parameters of the first five order roots in the incision of poplar. The results showed that, compared with those for CK (un-pruned), the surface area, volume, and biomass changed slightly from the first to fifth order roots in 10-2 treatment, obviously decreased in the 6-2 treatment, whereas significantly increased in the 8-2 treatment. The surface area, volume, and biomass of fine roots in each treatment showed a decreasing trend, whereas the diameter and tissue density tended to increase gradually with an increase of root order. The diameter and tissue density of the first two orders in the 8-2 treatment were the smallest, and those from the third to fifth order roots were the largest;statistically significant differences in these parameters were noted compared with 6-2 and 10-2 treatments. Further, the stele diameter and stele to root diameter ratio of different root orders in fine roots of every treatment increased gradually along with the increase of root order, and those of the first two orders in 8-2 treatment were significantly less than those in the 6-2 and 10-2 treatments, whereas the parameters from the third to fifth order roots were obviously higher than those in the 6-2 and 10-2 treatments. Fine roots of the first two orders in the incision of different treatments were of the primary structure, whereas fine roots from the third to fifth orders formed the secondary phellem layer, and the cortex fell off. Moreover, the average growth rates of DBH and tree height in 8-2 treatment were significantly higher than those in the other treatments, indicative of 44.67%, 69.36%, and 46.34% increases in average growth rates of DBH, and 47.31%, 60.81%, and 38.46% increases in average growth rates of tree height compared with those of CK, 6-2, and 10-2, respectively. In conclusion, significant differences were noted in the effects of three pruning intensities on the different orders of fine root in the incision of P. euramericana ‘Neva’, in which root pruning at distance of eight times of the DBH along both inter-row sides significantly enhanced the absorption ability and transport function of the root system and promoted the growth of P. euramericana ‘Neva’ by regulating the tissue density, stele diameter, cortex thickness, and stele to root diameter ratio of different orders of fine root in the incision.