东北森林两种典型阔叶树种子和幼苗对15N同位素的富集响应

以东北森林两种典型的阔叶树种风力传播种子——花曲柳和色木槭种子为研究对象,通过室内¹⁵N尿素浸泡试验和温室盆栽试验,设置4个浓度(0、0.05、0.1和0.2 g·L^-1)、3个浸泡时间(4、8和12 d)与4个叶期(2、4、6和8叶)处理,研究种子浸泡浓度、浸泡时间和幼苗叶期对种子和幼苗¹⁵N富集的影响.结果表明: 浸泡浓度和浸泡时间对两树种种子δ¹⁵N值均有显著的正反馈作用,高浓度和长时间(0.2 g·L^-1+12 d)更有利于种子¹⁵N总量的富集,花曲柳和色木槭种子¹⁵N同位素最大富集倍数的浸泡浓度和浸泡时间组合分别为0.1 g·L^-1+(4、8 d)和0.05 g·L^-1+(4、8 d);δ¹⁵N值稀释率随幼苗株高的增加先急剧减少(2~6叶)后趋于稳定,幼苗从8叶开始叶片¹⁵N总量降低,表明6叶幼苗更适合追踪幼苗的来源;幼苗叶片δ¹⁵N值与种子浸泡浓度、浸泡时间和种子的δ¹⁵N值呈显著正相关.花曲柳和色木槭种子及幼苗均能成功富集到¹⁵N信号,采用0.1 g·L^-1+8 d+6叶组合最适合追踪花曲柳和色木槭种子和幼苗.

Accumulation responses of seeds and seedlings to 15N isotope for two typical broadleaved trees in Northeast China.

Two typical broadleaved trees (i.e., Fraxinus rhynchophylla and Acer mono) with wind-dispersed seeds in Northeast China were selected in this study. A method of ¹⁵N isotope labeling was used to explore the accumulation responses of seeds and seedlings to ¹⁵N-urea soaking concentration (0, 0.05, 0.1 and 0.2 g·L^-1), soaking time (4, 8 and 12 days) and leaf stage (2, 4, 6, and 8 leaves). The results showed that ¹⁵N-urea soaking concentration and soaking time had significantly positive effects on δ¹⁵N values of seeds, i.e., higher ¹⁵N-urea concentration and longer period of soaking (0.2 g·L^-1+12 d) were contributed to more ¹⁵N accumulation of seeds. The maximum multiples of ¹⁵N accumulation in F. rhynchophylla seeds and A. mono seeds were observed in 0.1 g·L^-1+ (4 d, 8 d) and 0.05 g·L^-1+ (4 d, 8 d), respectively. The loss rate of δ¹⁵N values decreased markedly from 2 leaves to 6 leaves and then kept relatively stable with the increasing seedling height, and the total δ¹⁵N values of seedlings started to decline at the stage of 8 leaves. These results suggested that seedlings with 6 leaves were more suitable for tracking seedling source. The δ¹⁵N values in leaves of seedlings were significantly positively correlated with ¹⁵N-urea concentration level, soaking time and δ¹⁵N values of seeds. Overall, the accumulation of ¹⁵N-urea could be found in seeds and seedlings of F. rhynchophylla and A. mono. The combination of ¹⁵N-urea concentration (0.1 g·L^-1), soaking time (8 d) and leaf stage (6 leaves) was the most suitable for tracking the seeds and seedlings of these two broadleaved trees.