关键词: 青杨, 扦插苗, 多倍体, 覆膜滴肥

Abstract:

【Objective】 Effects of exponential fertilization (EF) and conventional fertilization (CF) with film mulching and drip irrigation on the aboveground growth, root morphology, biomass allocation and photosynthesis of one-year-old Populus cathayana seedlings were investigated in this study to shorten the growth cycle of seedlings under the conditions of improving the quality of P. cathayana polyploidy seedlings and provide a theoretical basis for water and fertilizer management of P. cathayana cutting seedlings of different ploidy types. 【Method】 A nitrogen fertilization experiment was conducted with one-year-old diploid, triploid and tetraploid P. cathayana cutting seedlings under drip irrigation with plastic film mulching. Further,three treatments with film mulching and drip irrigation were applied: exponential fertilization (8.01 g per seedling, EF), constant fertilization (7.98 g per seedling, CF), and non-fertilization (CK). We fertilized one-year-old P. cathayana seedlings every 15 days from the end of May by drip irrigation facilities, and seven times in the whole seedling growth period. During the experimental period, the height and base diameter of the seedlings were measured before each fertilization, and the data were used to plot the growth curve. Photosynthesis was measured during the period of vigorous growth, including chlorophyll content, net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), and transpiration rate (T_r). When these P. cathayana seedlings were harvested, roots were separated from the plants for scanning and calculating their morphological indices, namely, root length, diameter, surface area, volume and tips. After drying, the biomass of the roots, stems and leaves of each cutting seedling was determined.【Result】 By the end of the growing season, CF promoted the growth of P. cathayana one-year-old cutting seedlings more significantly than EF did, and the seedling height and ground diameter were significantly increased by 27.80% and 13.81%, respectively (P < 0.05). The biomass of P. cathayana one-year-old cutting seedlings with polyploid (the triploid and tetraploid seedlings) under CF treatment increased significantly; the biomass of roots, stems and leaves of seedlings treated with CF was significantly higher than that of CK by 102.25%, 191.02% and 102.90%, respectively (P < 0.05); and the biomass of roots of tetraploid P. cathayana cuttings was the highest at 25.73 g. The root length, diameter, surface area, volume and tips of polyploid seedlings under CF treatment was 182.60%, 32.97%, 122.02%, 119.48% and 178.25% higher than those of CK, respectively (P < 0.05), and those with different ploidy types were in the order triploid > tetraploid > diploid. Chlorophyll content and photosynthetic yield per stem of polyploid seedlings under CF treatment were 14.66% and 38.79% greater than those of CK, respectively (P < 0.05), and the order of those with different ploidy types was tetraploid > triploid > diploid. The G_s of P. cathayana one-year-old cutting seedlings under CF treatment were lower than those of EF but maintained a high C_i. The G_s of the polyploid seedlings of both EF and CF were higher than those of diploid seedlings, indicating that polyploid P. cathayana one-year-old cutting seedlings could maintain a high photosynthetic physiological process while reducing water transpiration. 【Conclusion】 Constant fertilization regimes under film mulching and drip irrigation effectively promoted the growth of P. cathayana one-year-old cutting seedlings, and no significant difference between triploid and tetraploid seedlings was observed.

Key words: Populus cathayana, cutting seedlings, polyploid, fertilizer under film mulching and drip irrigation