不同氮磷水平下不同土层中紫花苜蓿细根周转特征

为探讨不同氮磷配施条件下紫花苜蓿细根周转及不同土层分布动态特征，分析苜蓿细根周转各指标之间的关系。采用双因素随机区组设计进行田间试验，设置4个施磷水平［0（P₀）、50（P₁）、100（P₂）和150 kg·hm^-2（P₃）］和两个氮水平［0（N₀）和120 kg·hm^-2（N₁）］，共计8个处理，通过微根管根系监测0~60 cm的土层细根周转特征。结果表明：在相同施氮条件下，随着施磷量的增加，紫花苜蓿细根总现存量、细根表面积密度、细根生产量和死亡量呈先增加后降低的趋势，在P₂条件下达到最大值，且P₁、P₂处理显著大于P₀处理（P<0.05），在相同施磷条件下，N₁处理显著大于N₀处理。在不同土层中，在相同施氮条件下，随着施磷量的增加，苜蓿细根现存量在0~30 cm土层中呈先增加后降低的趋势，在0~15 cm土层中，P₂处理苜蓿细根现存量显著高于其他处理（P<0.05）。不同处理下，苜蓿细根现存量主要集中在15~30 cm土层。在相同施氮条件下，随施磷量的增加，苜蓿细根周转率呈先降低后增加的趋势。细根周转率受细根现存量与细根死亡动态变化的影响较大。细根死亡量与周转率拟合的相关系数最大，拟合效果最好。综上所述，当施磷（P₂O₅）量为100 kg·hm^-2、施氮（N）量为120 kg·hm^-2时，能够显著增加苜蓿细根的现存量和根表面积密度，进而促进苜蓿根系周转和生长。

Fine root turnover of alfalfa in different soil horizons under different nitrogen and phosphorus levels

This research explored the dynamics of fine root turnover and distribution in different soil horizons of alfalfa （Medicago sativa） under different nitrogen and phosphorus application conditions in a field experiment with a two-factor randomized block design in which the relationships between the indexes of fine root turnover were analyzed. Four phosphorus application levels ［0 （P₀）， 50 （P₁）， 100 （P₂） and 150 kg·ha^-1 P₂O₅ equivalent （P₃）］ and two nitrogen application levels ［0 （N₀） and 120 kg·ha^-1 （N₁）］ were included in a total of 8 treatments. The turnover characteristics of fine roots in 0-60 cm soil horizon were monitored through minirhizotron. It was found that： 1） With the same rate of N application， alfalfa standing biomass， root surface area density， and fine root production and death rate were typically maximized at P₁ or P₂， with values for P₂ significantly greater than those for P₀ （P<0.05）. 2） With the rate of P application， values for the N₁ treatment were significantly greater than those for the N₀ treatment （P<0.05）. In different soil horizons， under the same nitrogen application conditions， alfalfa fine root mass in the 0-30 cm soil horizon initially increased and then decreased with successive rises in the rate of P application. In the 0-15 cm soil horizon， alfalfa fine root mass in treatment P₂ was significantly higher than that in other treatments （P<0.05）. In the different treatments， alfalfa fine roots were mainly found in the 15-30 cm soil horizon. Under the same nitrogen application rate， the fine root turnover of alfalfa initially decreased and then increased with successive increases in phosphorus application rate. Among the measured parameters， the fitting effect was best and the correlation coefficient was greatest between fine root death and root turnover. In conclusion， optimal of root mass and root surface area density of alfalfa fine roots were observed in the treatment combination N₁P₂， and this management regime is recommended for the promotion of root turnover and growth in alfalfa.