基于稳定同位素的石漠化地区桑树根系水来源研究

Water absorption source analysis of mulberry roots based on stable isotopes in rocky desertification area

土壤水分亏缺是阻碍石漠化地区植被恢复重建的主要生态因子之一。然而,桑树(Morus alba L.)用于石漠化治理已取得良好效果,但其水分利用策略尚不清楚。该文基于氢、氧稳定同位素技术研究石漠化地区桑树根系在生长期内对不同深度土壤水分的利用程度,反映桑树根系在不同季节的吸水能力变化,揭示桑树生长期内水分利用策略。结果发现:桑树生长前期(春季,4-6月)降水中氢氧稳定同位素丰度较为偏正,比生长后期(秋季,9-11月)降水富集氢氧稳定同位素。土壤水氢氧稳定同位素随春季、秋季降雨的季节变化呈现下降趋势,并且受降雨、蒸发等影响,表现出不同的剖面垂直变化规律。桑树水与土壤水氢、氧稳定同位素变化相似,说明桑树生长所需的水分主要靠土壤水分提供。通过直观相关法和多元线性混合模型法判断出桑树在不同季节对土壤水分的吸收利用策略不同,其中春季先主要吸收10~30 cm土层水,随着降雨增多开始主要吸收利用50~60 cm深层水;进入秋季降雨量较大时亦是主要吸收利用50~60 cm的深层水,而降雨减少时转变为主要吸收利用0~10 cm的土壤水。研究可为桑树在石漠化治理中的应用提供依据。

Soil water deficit is the main obstacle factor of plant reconstruction in rocky desertification area of Southwest China.Mycorrhizal mulberry(Morus alba L.)can cope with the main ecological barriers during the seasonal drought in the rocky desertification area.However,it is unclear the water resource of mulberry.In this study,we studied the water use strategy of mulberry root in different seasons by hydrogen and oxygen stable isotope technique.The mulberry was grown in typical rocky desertification area in Qingshuipu town,Qixingguan district,Bijie city(105°35′02′′E,27°41′19′′N)in Guizhou Province.The precipitation was mainly concentrated in June-September.The mulberry was not irrigated.The annual growth of mulberry was in 2 seasons:from April to June and from September to November.The samples of rainfall water,soil and plant branch were collected from April to November of 2014.Soil was sampled at 0-60 cm depth with 10 cm as a sampling layer.The abundance of deuterium and oxygen stable isotope were measured.The correction analysis method was used to preliminarily evaluate water sources of mulberry.The contribution rate of water at each soil layer was also calculated.The results showed that in rainfall water,the abundance of deuterium from April to November averaged-25.9‰and the oxygen stable isotope abundance averaged-4.82‰.In spring from April to June,the abundance of deuterium and oxygen stable isotope in rainfall water averaged-0.24‰and-1.68‰,respectively.In autumn from September to November,the abundance of deuterium and oxygen stable isotope in rainfall water averaged-60.0‰and-8.17‰,respectively.In spring,the abundance of deuterium and oxygen stable isotope in soil water averaged-29.4‰and-4.77‰,respectively while the abundance of deuterium and oxygen stable isotope in xylem water averaged-33.2‰and-5.39‰,respectively.In autumn,the abundance of deuterium and oxygen stable isotope in soil water averaged-70.1‰and-9.27‰,respectively while the abundance of deuterium and oxygen stable isotope in xylem water averaged-55.7‰and-7.92‰,respectively.The abundance of both stable isotopes in soil water and xylem water were below that in the rainfall water and that of xylem water were between soil water and rainfall water.It indicated that the mulberry mainly used soil water.Both isotopes in rainwater were more enriched in the early stage of mulberry growth(spring,from April to June)than in the late growth stages(autumn,from September to November).With the seasonal variation of rainfall,the both isotopes of soil water showed a downward trend.According to rainfall water equations,the mulberry absorbed mainly soil water.Both isotopes had clear seasonal trend.In spring,the isotopes in soil water decreased with the increase of soil depth.In autumn,isotopes in soil water decreased then increased with soil depth.Based on the correlation method,the mulberry absorbed water from different soil depth.In spring,it absorbed water from soil below 20 cm while it absorbed water from soil 0-20 cm.In September,it also absorbed water from 50-60 cm soil layer.Based on results from the IsoSource software,in spring,mulberry mainly used soil water from soil layers of 10-30 to 50-60 cm.In autumn,it mainly used soil water from soil layers of 50-60 to 0-10 cm.In spring,the contribution rate was 69.1%by 10-30 cm in soil,31.8%and 66%by 50-60 cm layer in May and June,70.2%by 50-60 cm in September and 94.3%and 71.9%by 0-10 cm in October and November,respectively.The study will be helpful to mulberry manage and application in rocky desertification area.