二氧化碳倍增对植物叶片^(15)N自然丰度的影响

Effect of Carbon Dioxide Enrichment on^(15)N Natural Abundance of Leaves

大气CO_(2)浓度上升通常会提高植物生产力并伴随叶片氮含量的下降。然而大气CO_(2)如何影响叶片^(15)N丰度及其相关机理还不清楚。以小麦和向日葵为实验材料,测定了两个CO_(2)浓度(410与820μmol•mol^(-1))处理下叶片的氮同位比值(δ^(15)N)和氮含量。结果表明:小麦和向日葵叶片氮含量随CO_(2)浓度升高呈下降趋势,然而δ^(15)N对CO_(2)浓度倍增的响应存在差异。在高CO_(2)浓度处理下小麦叶片δ^(15)N显著下降6.5‰,而向日葵叶片δ^(15)N小幅上升2.1‰,且叶片和地上部生物量显著增加。基于此,小麦的氮营养特征符合氮同化受限假说,而向日葵符合稀释效应假说。小麦叶片δ^(15)N随叶龄或者细胞年龄的增加而显著下降,因此在利用^(15)N来研究植物氮代谢时需要区分叶龄的影响。整合分析结果表明,CO_(2)浓度升高导致非豆科C_(3)植物的δ^(15)N显著下降达0.3‰,与小麦的研究结果相符。综上所述,限制硝态氮同化是CO_(2)影响植物氮代谢和^(15)N丰度的重要机制。

Plant productivity is enhanced by elevated atmospheric CO_(2)concentration,but N content of leaf is reduced.How atmospheric CO_(2)affects leaf^(15)N composition and the related mechanisms remain unclear.δ^(15)N and N content of wheat and sunflower leaves were determined under two CO_(2)concentration(410 and 820μmol•mol^(-1))treatments.The results show that the N content of both species decreases with elevated CO_(2)concentration,but the response ofδ^(15)N to CO_(2)enrichment is different between wheat and sunflower.Under high CO_(2)concentration treatment,δ^(15)N of wheat leaves decreases significantly by 6.5‰,whileδ^(15)N of sunflower leaves increases slightly by 2.1‰,accompanied by a significant increase in leaf mass and aboveground biomass.Therefore,N nutrition characteristics of wheat are consistent with N assimilation limitation hypothesis,while the response of sunflower is consistent with dilution effect hypothesis.δ^(15)N in wheat leaves decreases significantly with leaf aging and cell aging.Therefore,when usingδ^(15)N to infer environmental impacts on plant N metabolism,it is necessary to account for the leaf age effect.The results of meta-analysis show thatδ^(15)N of non-legume C_(3)plants decreases significantly by 0.3‰under elevated CO_(2)concentration,in line with our results on wheat plants.The study shows that the inhibited N assimilation is an important mechanism related to the CO_(2)effect on N metabolism and^(15)N content of plants.