Diurnal variation of oxygen isotope ratio and quantitative partitioning of evapotranspiration in Larix gmelinii forest in Da Hinggan Ling of Nei Mongol, China

doi:10.17521/cjpe.2025.0072

Abstract

Abstract:

Aims To comprehensively investigate the dynamics of atmospheric water vapor concentration, water vapor isotopes, and evapotranspiration components in the forest ecosystem of the Da Hinggan Ling across different plant growing seasons and at a diurnal scale.

Methods This study conducted high-frequency monitoring of water vapor concentrations and isotopes at different heights using a stable water vapor isotope analyzer, while also determining the oxygen stable isotope ratio (δ¹⁸O) of plants and soil using vacuum extraction and a liquid water isotope analyzer. Additionally, evapotranspiration components in the Larix gmelinii forest were partitioned and compared across different periods by applying Isotope Steady-State (ISS) and Non-Steady-State (NSS) theories.

Important findings During the vigorous growing period of Larix gmelinii (July-August), atmospheric water vapor concentration and isotopic enrichment were elevated, whereas depletion occurred during the leaf-fall period. Diurnal variations exhibited a complex “V” shaped cycle with high-low-high fluctuations. On the diurnal scale, the δ¹⁸O of soil evaporation vapor ranged from -27.15‰ to -18.31‰, while that of ecosystem evapotranspiration vapor varied between -15.48‰ and -8.05‰, both demonstrating unimodal trends. Under ISS conditions, the δ¹⁸O of plant transpiration vapor spanned -10.83‰ to -5.31‰, contrasting with -12.21‰ to -6.63‰ under NSS conditions. Minimal divergence between ISS and NSS estimates occurred during 13:00-17:00, where transpiration contributions showed closest alignment. Overall, the transpiration contribution to evapotranspiration was 69.48%-85.08% (ISS) and 76.38%-91.05% (NSS), indicating substantially lower soil evaporation compared to vegetation transpiration, with plant transpiration dominating the forest ecosystem’s evapotranspiration.

Key words: stable isotope, vapor, Larix gmelini, evapotranspiration, non-steady-state assumption

LI Jia-Ze, JIA De-Bin, HAO Yu-Sheng, HAO Shuai, SHANG Zi-Qin, JI Ming-Yu. Diurnal variation of oxygen isotope ratio and quantitative partitioning of evapotranspiration in Larix gmelinii forest in Da Hinggan Ling of Nei Mongol, China[J]. Chin J Plant Ecol, 2026, 50(4): 959-970.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2025.0072

https://www.plant-ecology.com/EN/Y2026/V50/I4/959

Figures/Tables 10

References 37

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日期 Date	时间 Time	δ_s (‰)	δ_v (‰)	δ_E(‰)	日期 Date	时间 Time	δ_s (‰)	δ_v (‰)	δ_E(‰)
2022-07-15	6:00-8:00	-9.90	-18.64	-20.76	2022-09-15	6:00-8:00	-11.69	-21.82	-22.91
	8:00-10:00	-8.56	-17.37	-18.96		8:00-10:00	-11.03	-20.21	-21.92
	10:00-12:00	-8.30	-16.52	-18.55		10:00-12:00	-10.72	-20.21	-21.39
	12:00-14:00	-8.25	-16.81	-18.31		12:00-14:00	-10.06	-19.56	-20.59
	14:00-16:00	-9.08	-16.74	-19.22		14:00-16:00	-10.65	-19.74	-21.03
	16:00-18:00	-9.84	-16.82	-20.29		16:00-18:00	-11.33	-20.37	-21.83
	18:00-20:00	-10.44	-17.35	-21.14		18:00-20:00	-12.01	-20.86	-23.00
2022-08-15	6:00-8:00	-9.27	-17.89	-21.01	2022-10-15	6:00-8:00	-14.39	-24.54	-26.76
	8:00-10:00	-8.88	-16.36	-19.71		8:00-10:00	-13.81	-24.60	-26.14
	10:00-12:00	-8.41	-16.44	-18.79		10:00-12:00	-13.25	-23.81	-25.50
	12:00-14:00	-8.17	-16.06	-18.48		12:00-14:00	-13.54	-23.11	-25.78
	14:00-16:00	-8.33	-16.17	-18.57		14:00-16:00	-13.86	-22.92	-26.16
	16:00-18:00	-8.86	-18.00	-19.51		16:00-18:00	-14.09	-23.66	-26.48
	18:00-20:00	-9.51	-17.90	-20.54		18:00-20:00	-14.60	-24.19	-27.15

日期 Date	时间 Time	δ_s (‰)	δ_v (‰)	δ_E(‰)	日期 Date	时间 Time	δ_s (‰)	δ_v (‰)	δ_E(‰)
2022-07-15	6:00-8:00	-9.90	-18.64	-20.76	2022-09-15	6:00-8:00	-11.69	-21.82	-22.91
	8:00-10:00	-8.56	-17.37	-18.96		8:00-10:00	-11.03	-20.21	-21.92
	10:00-12:00	-8.30	-16.52	-18.55		10:00-12:00	-10.72	-20.21	-21.39
	12:00-14:00	-8.25	-16.81	-18.31		12:00-14:00	-10.06	-19.56	-20.59
	14:00-16:00	-9.08	-16.74	-19.22		14:00-16:00	-10.65	-19.74	-21.03
	16:00-18:00	-9.84	-16.82	-20.29		16:00-18:00	-11.33	-20.37	-21.83
	18:00-20:00	-10.44	-17.35	-21.14		18:00-20:00	-12.01	-20.86	-23.00
2022-08-15	6:00-8:00	-9.27	-17.89	-21.01	2022-10-15	6:00-8:00	-14.39	-24.54	-26.76
	8:00-10:00	-8.88	-16.36	-19.71		8:00-10:00	-13.81	-24.60	-26.14
	10:00-12:00	-8.41	-16.44	-18.79		10:00-12:00	-13.25	-23.81	-25.50
	12:00-14:00	-8.17	-16.06	-18.48		12:00-14:00	-13.54	-23.11	-25.78
	14:00-16:00	-8.33	-16.17	-18.57		14:00-16:00	-13.86	-22.92	-26.16
	16:00-18:00	-8.86	-18.00	-19.51		16:00-18:00	-14.09	-23.66	-26.48
	18:00-20:00	-9.51	-17.90	-20.54		18:00-20:00	-14.60	-24.19	-27.15

日期 Date	时间 Time	δ_ET (‰)	δ_T-NSS (‰)	δ_T-ISS(‰)	日期 Date	时间 Time	δ_ET (‰)	δ_T-NSS (‰)	δ_T-ISS(‰)
2022-07-15	6:00-8:00	-9.88	-8.24	-5.69	2022-09-15	6:00-8:00	-13.27	-11.13	-9.03
	8:00-10:00	-9.55	-7.33	-6.08		8:00-10:00	-12.43	-10.30	-8.58
	10:00-12:00	-8.74	-7.31	-5.31		10:00-12:00	-11.21	-9.74	-7.87
	12:00-14:00	-8.06	-6.63	-5.69		12:00-14:00	-10.28	-8.81	-7.90
	14:00-16:00	-8.22	-6.94	-5.83		14:00-16:00	-10.85	-9.36	-8.35
	16:00-18:00	-9.00	-6.95	-5.90		16:00-18:00	-11.73	-9.64	-8.73
	18:00-20:00	-9.63	-6.95	-6.25		18:00-20:00	-13.22	-10.75	-9.25
2022-08-15	6:00-8:00	-10.99	-8.98	-7.81	2022-10-15	6:00-8:00	-15.48	-11.99	-10.53
	8:00-10:00	-10.01	-8.36	-7.10		8:00-10:00	-13.72	-10.47	-9.04
	10:00-12:00	-8.90	-7.59	-6.38		10:00-12:00	-12.60	-10.08	-8.92
	12:00-14:00	-8.05	-7.02	-6.03		12:00-14:00	-11.17	-9.20	-8.32
	14:00-16:00	-8.71	-7.56	-6.47		14:00-16:00	-11.21	-9.44	-8.59
	16:00-18:00	-9.58	-7.90	-6.82		16:00-18:00	-12.93	-10.21	-9.14
	18:00-20:00	-10.17	-8.36	-7.08		18:00-20:00	-15.29	-12.21	-10.83

日期 Date	时间 Time	δ_ET (‰)	δ_T-NSS (‰)	δ_T-ISS(‰)	日期 Date	时间 Time	δ_ET (‰)	δ_T-NSS (‰)	δ_T-ISS(‰)
2022-07-15	6:00-8:00	-9.88	-8.24	-5.69	2022-09-15	6:00-8:00	-13.27	-11.13	-9.03
	8:00-10:00	-9.55	-7.33	-6.08		8:00-10:00	-12.43	-10.30	-8.58
	10:00-12:00	-8.74	-7.31	-5.31		10:00-12:00	-11.21	-9.74	-7.87
	12:00-14:00	-8.06	-6.63	-5.69		12:00-14:00	-10.28	-8.81	-7.90
	14:00-16:00	-8.22	-6.94	-5.83		14:00-16:00	-10.85	-9.36	-8.35
	16:00-18:00	-9.00	-6.95	-5.90		16:00-18:00	-11.73	-9.64	-8.73
	18:00-20:00	-9.63	-6.95	-6.25		18:00-20:00	-13.22	-10.75	-9.25
2022-08-15	6:00-8:00	-10.99	-8.98	-7.81	2022-10-15	6:00-8:00	-15.48	-11.99	-10.53
	8:00-10:00	-10.01	-8.36	-7.10		8:00-10:00	-13.72	-10.47	-9.04
	10:00-12:00	-8.90	-7.59	-6.38		10:00-12:00	-12.60	-10.08	-8.92
	12:00-14:00	-8.05	-7.02	-6.03		12:00-14:00	-11.17	-9.20	-8.32
	14:00-16:00	-8.71	-7.56	-6.47		14:00-16:00	-11.21	-9.44	-8.59
	16:00-18:00	-9.58	-7.90	-6.82		16:00-18:00	-12.93	-10.21	-9.14
	18:00-20:00	-10.17	-8.36	-7.08		18:00-20:00	-15.29	-12.21	-10.83