基于贝叶斯模型MixSIAR的不同水同位素输入方法对苹果园吸水特征分析结果的影响

doi:10.17521/cjpe.2021.0472

摘要/Abstract

摘要：

准确量化浅、中、深3层土壤水源对植物根系吸水的贡献是明确植物水分利用策略的前提。为探究同位素混合模型MixSIAR中不同水同位素输入方法对预估植物水分来源的影响, 该研究于2019年5-9月在陕西长武塬区对7年和18年苹果园共进行5次土壤和植物木质部取样, 测定对应样品水同位素比值(δ²H、δ¹⁸O)和土壤含水量, 并分别利用基于单同位素(²H、¹⁸O)、双同位素(²H & ¹⁸O)和经木质部氢同位素校正后双同位素(²H(+8.1) & ¹⁸O)输入的MixSIAR模型计算了根区不同土层(0-0.4、0.4-2、>2 m根系深度)土壤水对苹果(Malus pumila)树根系吸水的贡献率。结果表明: 与²H单同位素方法相比, 利用¹⁸O单同位素方法得到的2 m以下深层土壤水的贡献率更低, 而表层(0-0.4 m)土壤水的贡献率更高, 且更接近于²H(+8.1) & ¹⁸O同位素方法。与²H & ¹⁸O双同位素方法相比, 利用²H(+8.1) & ¹⁸O方法得到的表层土壤水的贡献率在表层土壤水同位素值富集时较高, 在表层土壤水同位素值贫化时较低。苹果树木质部氢同位素校正后更靠近于土壤水同位素所在的蒸发线, 因而相比于²H和²H & ¹⁸O, ¹⁸O和²H(+8.1) & ¹⁸O分析方法更符合根系吸水过程同位素质量守恒定律。与7年苹果园相比, 18年苹果园浅层(0-2 m)土壤水的季节性变异更大, 对表层土壤水的依赖更强。对于7年和18年苹果园, 深层土壤水对其根系吸水贡献率的年平均值为19%和23%, 两者无显著性差异。综上, 建议今后在利用水稳定同位素研究植物水分来源时要进一步明确不同水同位素输入方法对植物水源划分分析结果的影响。

关键词: 氢稳定同位素, 氧稳定同位素, MixSIAR, 木质部氢同位素校正, 长武塬区, 苹果园

Abstract:

Aims Accurately quantifying the contribution of shallow, middle and deep soil water sources to the root water uptake is the prerequisite for understanding water uptake strategy of plants. This paper evaluates the effects of different water isotopes input methods on plant water sources analysis results in Bayesian mixing model MixSIAR.

Methods Soil and plant xylem samples were taken five times from May to September in 2019 in two apple (Malus pumila) orchards at 7- and 18-year age in Changwu Tableland of Shaanxi Province. Soil water contents and isotope ratios (δ²H and δ¹⁸O) were measured, and the different input methods of single isotope (²H and ¹⁸O), dual isotopes (²H & ¹⁸O) and xylem hydrogen corrected dual isotopes (²H(+8.1) & ¹⁸O) coupled with MixSIAR model were used to estimate the contribution ratio of different soil layers (0-0.4, 0.4-2, >2 m root depth) to orchards root water uptake.

Important findings The results showed that compared to the ²H isotope method, the contribution from soil layer below 2 m was lower and that from the surface 0-0.4 m was higher using the ¹⁸O isotope method, which was close to the ²H(+8.1) & ¹⁸O isotope method. Compared with ²H & ¹⁸O dual isotopes method, the contribution ratio from surface 0-0.4 m soil layer was higher using the ²H(+8.1) & ¹⁸O method when the surface soil water isotope was enriched, and that was lower when the surface soil water isotope was depleted. The corrected apple xylem hydrogen isotopes were closer to the evaporation line of soil water isotopes, thus the analysis methods of ¹⁸O and ²H(+8.1) & ¹⁸O accorded more with the isotope mass balance during root water uptake than ²H and ²H & ¹⁸O methods. Soil water contents in 0-2 m in 18 years old apple orchard showed greater seasonal variation than that in 7 years old apple orchard, and are more dependent on 0-0.4 m surface soil water. For the root water uptakes in 7- and 18-year apple orchard, the yearly-averaged contributions of deep soil water were 19% and 23%, respectively, showing no significant difference. We suggest that more attention should be drawn on the influence of different isotope input methods when using water stable isotopes to estimate plant water sources contribution in future studies.

Key words: stable hydrogen isotope, stable oxygen isotope, MixSIAR, xylem hydrogen isotope correction, Changwu Tableland, apple orchard

路晨曦, 徐漫, 石学瑾, 赵成, 陶泽, 李敏, 司炳成. 基于贝叶斯模型MixSIAR的不同水同位素输入方法对苹果园吸水特征分析结果的影响. 植物生态学报, 2023, 47(2): 238-248. DOI: 10.17521/cjpe.2021.0472

LU Chen-Xi, XU Man, SHI Xue-Jin, ZHAO Cheng, TAO Ze, LI Min, SI Bing-Cheng. Effects of different water isotope input methods based on Bayesian model MixSIAR on water uptake characteristic analysis results in apple orchards. Chinese Journal of Plant Ecology, 2023, 47(2): 238-248. DOI: 10.17521/cjpe.2021.0472

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链接本文: https://www.plant-ecology.com/CN/10.17521/cjpe.2021.0472

https://www.plant-ecology.com/CN/Y2023/V47/I2/238

图/表 6

图1 长武样地采样期间降水量(P)及其降水同位素比值(δ2H、δ18O)分布。A中灰色箭头表示采样时间。

Fig. 1 Precipitation (P) and the precipitation isotope ratio (δ2H, δ18O) distribution during the sampling periods in Changwu. In A, the gray arrows represent the sampling time.

图2 长武7年(A)、18年(B)苹果园细根根长密度剖面分布。

Fig. 2 Profile distribution of fine root length density in 7- (A) and 18-year (B) apple orchards in Changwu.

图3 长武7年(A)、18年(B)苹果园不同采样时期土壤含水量剖面分布。

Fig. 3 Profile distribution of soil water contents in 7- (A) and 18-year (B) apple orchards at different sampling periods in Changwu.

图4 长武7年(A)、18年(B)苹果园不同土层土壤平均含水量季节变化(平均值±标准差)。7年、18年苹果园根系深度分别为8和21 m, 因此取样深度分别到8和21 m。

Fig. 4 Seasonal variations of average soil water contents in different soil layers in 7- (A) and 18-year (B) apple orchards (mean ± SD) in Changwu. The root depths of the 7- and 18-year apple orchards were 8 and 21 m, respectively, therefore the sampling depths were 8 and 21 m, respectively.

图5 长武7年(A)、18年(B)苹果园各取样时期不同土层土壤水和木质部水同位素比值分布(平均值±标准差)。LMWL, 当地大气降水线(δ2H = 6.98δ18O + 2.34)。δ2H, 氢稳定同位素比值; δ18O, 氧稳定同位素比值。

Fig. 5 Distribution of soil water isotope ratios in different soil layers and xylem water isotope ratios in 7- (A) and 18-year (B) apple orchards at different sampling dates in Changwu (mean ± SD). LMWL, the local meteoric water line (δ2H = 6.98δ18O + 2.34). δ2H, stable hydrogen isotope ratio; δ18O, stable oxygen isotope ratio.

图6 不同水同位素输入方法分析不同时期不同土层土壤水对长武7年(A)、18年(B)苹果园根系吸水的贡献率(平均值±标准差)。I, 单同位素(2H); II, 单同位素(18O); III, 双同位素(2H & 18O); IV, 木质部同位素校正后双同位素(2H(+8.1) & 18O)。

Fig. 6 Different water isotope input methods analyzing soil water contribution for 7- (A) and 18-year (B) apple orchards root water uptake in Changwu (mean ± SD). I, single isotope (2H); II, single isotope (18O); III, dual isotopes (2H & 18O); IV, dual isotopes (2H(+8.1) & 18O).

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