亚热带湿润区樟树吸水的土层来源及研究方法对比

Study on Water Uptake Layers of the Cinnamomum camphora and Comparison of the Methods of Water Uptake in Subtropical Humid Region

以长沙地区针阔混交林内的樟树为对象,基于2017年3月至2019年9月降水、土壤水和樟树茎杆水稳定同位素观测数据,利用直接比较法、水线法(δ^2 H和δ^18 O的线性关系)、Iso-Source模型和MixSIR模型,分析了樟树吸收水分的土层来源的季节变化,并比较4种方法的优缺点,旨在为植物水分利用来源研究提供新思路。结果表明:在判别樟树吸收水分的土层来源中,4种方法的判别结果基本一致。观测期内,樟树吸水层位存在明显季节变化。在2017年3^-6月、2017年10月至2018年6月、2018年10月至2019年6月的湿润期,樟树分别主要利用0-20,0-40,0-20 cm土层的土壤水。在2017年、2018年、2019年的干旱期(7-9月),樟树分别主要利用20-60,0-60,60-100 cm土层的土壤水。在各层土壤水稳定同位素组成不存在明显差异时,水线法可很好地揭示樟树吸收水分的土层来源,而其他方法均无法判别樟树吸水层位。Iso-Source模型分别基于δ^2 H和δ^18 O计算得到的樟树主要吸水层位及其利用比例均存在一定差异,相比之下,MixSIR模型分别根据δ^2 H和δ^18 O计算得到的樟树主要吸水层位基本一致,且利用比例较接近。综上,在植物水分利用来源的定性判别中,适宜将直接比较法和水线法相结合进行分析;而在植物水分利用来源的定量研究中,MixSIR模型较Iso-Source模型更优。

The typical plant species Cinnamomum camphora in the Needle-broad leaf mixed forest in Changsha was used as research object.Based on the stable isotopic composition of precipitation,bulk soil water,and twig xylem water from March 2017 to September 2019,the seasonal variations of water uptake layers of C.camphora was analyzed by the graphical inference,water-line inference,Iso-Source model and MixSIR model.In addition,the advantages and disadvantages of four methods in determining plant water use are compared,in order to provide new perspectives for the following analysis of plant water use.The results show that:four methods of determining the water uptake layers of C.camphora are basically identical.Pronounced seasonal variation of water use of C.camphora is observed during the observation period.During the wet period consisting of March to June 2017,October 2017 to June 2018 and October 2018 to June 2019,C.camphora mainly uses the soil water at 0-20,0-40 and 0-20 cm depth,respectively.During the dry periods(July to September)in 2017,2018 and 2019,C.camphora mostly uptakes the soil water at 20-60,0-60 and 60-100 cm depth,respectively.If there is no obvious difference of the stable isotopic composition of soil water at each depth,the water-line inference could determine the water uptake layers of C.camphora other than others.The main water uptake layers and utilization ratios of C.camphora calculated by Iso-Source model based on different isotopic composition are both different,however,calculated by the MixSIR model based on different isotopic composition are both largely identical.In conclusion,it is appropriate to combine graphical inference and water-line inference in the qualitative analysis of plant water use,and MixSIR model is more reliable than Iso-Source model in the quantitative research of plant water use.