咖啡连作根际土壤水提液对其幼苗根系发育的影响

咖啡是世界三大饮料之一，营养丰富，经济价值高，深受消费者欢迎。咖啡是热区重要的多年生经济作物，长期的连作产生了严重的连作障碍，已成为影响咖农增收、制约产业可持续发展的严重问题，亟待解决。本研究采集咖啡园病株根际土壤，开展室内盆栽试验，研究其4个浓度的水提液（0、0.50、1.00和2.00 g/mL，分别表示为CK、T₁、T₂和T₃）对咖啡幼苗根系生长发育的影响，以期明晰咖啡连作障碍产生的机理，为克服咖啡连作障碍提供科学和试验依据。结果表明：发病植株根际土壤水提液导致其幼苗根系表皮细胞变小、排列更加紧密，并且随着浓度的升高，根系细胞壁及内膜系统逐渐被破坏，形成空腔；初生木质部细胞的木质化程度逐渐增加。根系鲜重、干重、总根长、根体积、根尖数、总根表面积以及根系活力均随根际土壤水提液浓度的升高而下降，T₂处理与CK相比差异显著（P<0.05），T₃处理差异极显著（P<0.01）。随着根际土壤水提液浓度的升高，根系木质素含量和相对电导率逐渐升高，T₁处理与CK相比，木质素含量增加29.53%，差异显著，T₂、T₃处理木质素含量分别增加42.38%、66.52%，差异均达极显著；T₂、T₃根系相对电导率分别增加34.40%、58.30%，差异均达极显著。根系可溶性蛋白含量随着土壤水提液浓度的升高呈现先升高后下降的变化趋势，T₂处理与CK相比，可溶性蛋白含量增加61.75%，差异显著。MDA含量、SOD、POD和CAT活性均随着土壤水提液浓度升高而升高，T₃处理与CK相比，SOD活性增长56.77%，差异显著；POD活性增加96.28%，差异极显著。综上可知，发病咖啡植株根际土水提液中存在自毒物质，破坏咖啡幼苗根系结构、抑制根系生长发育。

Effects of Aqueous Extracts from Continuous Cropping Rhizosphere Soil of Coffee on Development of Seedling Roots

Coffee with rich nutritional value and high economic value is one of the three major beverages in the world, and is deeply welcome by consumers all over the world. Coffee is an important perennial cash crop in hot areas, and the long-term continuous cropping of which has produced serious continuous cropping obstacles, which has become a serious problem affecting the income of coffee farmers and restricting the sustainable development of the industry. Therefore, it needs to be solved urgently. In order to clarify the mechanism of coffee continuous cropping obstacle and provide scientific and experimental basis for overcoming it, the rhizosphere soil of diseased coffee plants was collected, and the indoor pot experiment was carried out to study the response of root growth and development of coffee seedlings to four concentrations of which water extracts (0, 0.50, 1.00 and 2.00 g/mL, recorded as CK, T₁, T₂ and T₃, respectively) in this study. The rhizosphere soil aqueous extracts of diseased coffee plants caused the epidermal cells of coffee seedlings to become smaller and arranged more closely. With the increase of its concentration, the root cell wall and intimal system were gradually destroyed and formed a cavity. The lignification degree of primary xylem cells increased gradually as well. Root fresh weight, dry weight, total root length, root volume, root tip number, total root surface area and root activity decreased with the rhizosphere soil aqueous extracts of diseased coffee plants. Compared with CK, those from T₂ decreased to a significant different level (P<0.05), and those from T₃ decreased to a very significant different level (P<0.01). The lignin content and relative conductivity of roots increased gradually with the rhizosphere soil aqueous extracts. Compared with CK, the lignin content of T₁ increased by 29.53%, reaching a significant different level, and the lignin of T₂ and T₃ increased by 42.38% and 66.52% respectively, reaching a very significant different level. The root relative conductivity of T₂ and T₃ increased by 34.40% and 58.30%, respectively. With the aqueous extracts concentration rising up, the soluble protein content of roots increased, 61.75% higher of T₂ than that of CK. Although subsequently the amount decreased, but which was significantly different according to the data recorded before. MDA content, and the activities of SOD, POD and CAT increased with the increase of the aqueous extracts concentration. Compared with CK, the activity of SOD in T₃ increased by 56.77%, reaching a significant different level, POD activity increased by 96.28%, reaching a very significant different level. In conclusion, there are autotoxic substances in the aqueous extract of rhizosphere soil of diseased coffee plants, which destroy the root structure of coffee seedlings and affect the growth and development of roots.