天山林区雪岭云杉和异果小檗夏季水分来源

天山雪岭云杉针叶林内乔灌木水分利用模式尚不明确,水分利用动态缺乏定量分析。本研究对雪岭云杉和伴生灌木异果小檗茎杆木质部水及各潜在水源的氢氧稳定同位素组成进行测定,运用IsoSource模型定量分析两树种夏季对各潜在水源的相对利用比例。结果表明: 7月,土壤含水量充足时,雪岭云杉和异果小檗主要吸收利用60 cm以上土壤水,相对利用比例分别为73.8%和63.2%。8月,土壤含水量相对较低时,雪岭云杉水分来源保持稳定,对60 cm以上土壤水的相对利用比例为69.5%;异果小檗则转换至利用更深层的水源,对0～20 cm浅层土壤水的相对利用比例降至14.3%,主要吸收利用中层(20～60 cm)和深层(60～100 cm)土壤水,相对利用比例为67.7%。9月,随着0～20 cm浅层土壤含水量升高,两树种恢复对浅层土壤水的吸收利用,相对利用比例达95.0%。综上,雪岭云杉表现出典型的浅根系特征,其吸收利用的水源主要来自浅层土壤水;异果小檗则能够在0～100 cm的土壤各层吸收利用水分,同时随土壤含水量的变化灵活转换其水源,从而应对环境水分变异。

Water sources of Picea schrenkiana and Berberis heteropoda in the Tianshan Mountains in summer

Water use patterns of trees and shrubs in the Picea schrenkiana coniferous forest remain unclear, due to a lack of quantitative analysis on water use dynamics. In this study, the xylem water hydrogen and oxygen stable isotope compositions of P. schrenkiana and the companion shrub species Berberis heteropoda were measured to detect their water sources. The IsoSource model was used to analyze the relative contribution of each potential water source for both species during summer. The results showed that during July, P. schrenkiana and B. heterocarpa mainly extracted water from the 0-60 cm soil layer due to the relatively sufficient soil water content, with the relative contributions being 73.8% and 63.2% for the two species, respectively. In August, with the decreases in soil water content, water source of P. schrenkiana remained stable, and the relative contribution of soil water above 60 cm was 69.5%. In contrast, B. heterocarpa reverted to water source from deeper soil layer, with the relative contribution of shallow soil (0-20 cm) water decreasing to 14.3% and that of middle (20-60 cm) to deep (60-100 cm) soil water increased to 67.7%. In September, with the increases of water content in the shallow soil layer, both species extracted water from shallow soil layers, with the relative contribution reaching to 95.0%. In summary, P. schren-kiana exhibited typical shallow root characteristics, while B. heterocarpa extracted water from the 0-100 cm soil profile and could flexibly change its water source corresponding to changes in soil water content to cope with changing environmental water condition.