施氮后蚯蚓对植物吸氮及微生物固氮的影响

为探讨尿素施用后蚯蚓对植物吸氮量及微生物固氮量的影响,通过盆栽试验,以威廉腔环蚓(Metaphire guillelmi)为试验材料,对比有、无蚯蚓作用下15N标记的尿素施入后植物氮素含量的差异及土壤微生物量的变化过程。结果表明:培养结束后对植物进行取样测定,发现不同处理间植株氮含量并无显著差异,但接种蚯蚓的处理增加了植株生物量,进而导致蚯蚓作用下的植株总吸氮量提高了约30.8%。从分配比例上看,接种蚯蚓显著增加了植物吸收土壤氮的比例,却显著降低了植物吸收肥料氮的比例。在整个试验过程中,两处理的全氮(TN)含量均无显著变化,但土壤中来源于肥料的氮却随着培养的进行逐渐降低,且接种蚯蚓使其下降速度更快。微生物生物量氮(M BN)先下降后上升,且接种蚯蚓处理的MBN含量在试验初期(第5d)与试验末期(第30d)较高,但MBN中固定的肥料氮含量始终低于不接种蚯蚓的对照处理。试验过程中,土壤可溶性有机氮(D ON)的含量先下降后上升,与MBN变化趋势一致。与对照处理相比,接种蚯蚓处理的铵态氮(N H4+-N)含量降低,硝态氮(N O-3-N)含量则差异不显著。综上,蚯蚓可通过调节微生物生物量形成氮素缓冲库,从而促进植株对土壤氮而非尿素氮的吸收。

Effects of earthworms on nitrogen uptake by lettuce and microbial nitrogen fixation after nitrogen application

In exploring the impact of the earthworm on nitrogen uptake by plants and microbial nitrogen fixation after urea application, a pot experiment was conducted to compare the difference in plant nitrogen content and explore the dynamic of soil microbial biomass between earthworm(Metaphire guillelmi)and non-earthworm treatments after ¹⁵N-labeled urea application. Results showed that there was no significant difference in plant nitrogen content among treatments, while earthworm presence increased the whole plant biomass, leading to an increase in total nitrogen uptake of about 30.8%. In terms of distribution ratio, earthworm presence significantly increased the proportion of soil nitrogen absorbed by the plant and reduced the proportion of applied urea nitrogen absorbed by the plant. There was no significant change in total nitrogen between earthworm presence and earthworm absence throughout the experiment, as nitrogen from fertilizer in the soil decreased gradually; however, the decrease in nitrogen was faster in the earthworm-treated soil. The microbial biomass nitrogen(MBN) content initially decreased and then increased, and high levels of MBN content were observed in earthworm treatments, especially at days 5 and 30. However, the content of fertilizer nitrogen in MBN was always lower than that in the control. Throughout the experiment, the content of soil dissolved organic nitrogen initially decreased and then increased, which was consistent with the trend for MBN. The content of ammonium nitrogen(NH₄⁺-N)in the earthworm treatment was lower than that in control treatment, while the content of nitrate nitrogen(NO₃^--N) was not significantly different. In conclusion, earthworms can promote growth and nitrogen uptake by plants by regulating microbial biomass to form a buffer pool, but this regulation mainly acts on native soil nitrogen rather than the newly applied urea nitrogen.