Comparison of water use patterns among tree species using water stable isotopes in Mt. Baekwoon = 물 안정동위원소를 이용한 백운산 지역 수종의 수분 이용 경향 비교

다국어 초록 (Multilingual Abstract)

This study explored plant-soil-water interactions within forest ecosystems, employing stable isotopes of water (δ2H and δ18O) as tracers to understand the impact of different extraction and analysis methods on data interpretation. It comprised three key experiments. Firstly, soil water was analyzed using isotope ratio mass spectrometry (IRMS) and cavity ring-down spectroscopy (CRDS), which revealed notable differences in isotopic compositions. Secondly, isotopes in xylem water from nine tree species were examined using cryogenic vacuum distillation (CVD) with variable heating times. It was found that prolonged heating led to enriched isotopic values, indicating that over three hours of heating were required to achieve consistent results. Lastly, a comparison of isotopic compositions derived from three extraction methods—Pressure chamber (PC), an induction module (IM), and CVD—demonstrated that the PC and IM methods yielded more enriched isotopic compositions compared to CVD, particularly in δ2H.
In the second part of the study, a new correction method for xylem water extracted by cryogenic vacuum distillation (CVD) was introduced and assessed. This involved comparing four distinct methods designed to correct isotopic offsets in xylem water extracted from its soil water sources. These correction methods were applied to xylem water samples from P. densiflora, C. laxiflora, and Q. acutissima. It was consistently observed that the uncorrected xylem water samples displayed more depleted isotope values (δ2H and δ18O) compared to both soil water and corrected xylem water. Notably, the corrected xylem water showed significantly enriched δ2H values, underscoring the importance of correction for accurate isotopic measurement and interpretation. Among the evaluated correction methods, Method 1, which utilized the relationship between δ2H and δ18O values in CVD and Pressure Chamber (PC) extractions, was found to be the most effective. This conclusion was based on its low bias, Root Mean Square Error (RMSE), and Akaike Information Criterion (AIC).
In the third part, the isotopic composition (δ2H and δ18O) of soil and xylem water was investigated to estimate the water use patterns of six tree species across three different study sites. The broadleaved site displayed a higher usage of water from deeper soil layers compared to the coniferous and mixed sites, suggesting an adaptation in broadleaved species to more efficiently utilize water from deeper sources. P. densiflora, in particular, showed variable water use tendencies, dependent on the environmental conditions of its habitat, highlighting the species' adaptability to different habitat conditions. During the drought year of 2017, an increase in the utilization of water from deeper soil layers was observed across the majority of the species, aligning with the expected adaptation to limited water availability. Interestingly, this reliance on deeper water sources persisted into 2018, a year marked by abundant rainfall.

국문 초록 (Abstract)

본 연구는 물 안정동위원소(δ2H 와 δ18O)를 이용하여 산림생태계에서 식물-토양-물의 상호 작용을 조사하였다. 첫번째
연구에서는 세 가지 실험이 진행되었다. 첫번째 실험에서는 동위원소 질량 분석기(Isotope Ratio Mass Spectrometry)와 공동 광자 감쇠 분광기(Cavity Ring-down Spectroscopy)를 사용하여 토양수의 산소와 수소 안정동위원소비를 분석하였다. 두 장비간 유의한 차이는 있었으나 그 차이는 매우 적었다.
두번재 실험에서는 초저온 진공 증류를 이용하여 서로 다른 가열 시간이 9 수종의 수액 (xylem water) 내 안정동위원소비에 미치는 영향을 분석하였다. 가열 시간에 따라 동위원소비는 변화하였으며, 일관된 결과를 얻기 위해 세시간 이상 가열 할 필요가 있었다. 세번째 실험에서는 세가지 방법(프레셔챔버, 인덕션 모듈, 초저온 진공 증류 시스템)을 이용하여 수액 내 동위원소비를 비교하였다. 그 결과 초저온 진공 증류 시스템으로 추출한 수액의안정동위원소비가 다른 두 방법으로 추출한 수액에 비해 작았다.
두번째 연구에서는 초저온 진공 증류 시스템으로 추출한 수액에 대한 새로운 보정 방법을 소개하였다. 이 연구에서는
새로운 보정 방법을 포함한 총 네가지 보정 방법을 소나무, 서어나무, 신갈나무의 수액에 적용하여 평가하였다. 보정되지 않은 수액의 동위위원소비(δ2H 및 δ18O)는 보정된 수액의 동위원소비에 비해 현저히 낮은 값을 보였다. 보정 방법 중
CVD와 PC의 관계성을 이용한 보정 방법이 가장 좋은 보정 방법으로 평가되었다.
마지막 연구에서는 서로 다른 세 임분(침엽수림, 혼효림, 활엽수림)에 서식하고 있는 여섯 수종의 물 이용 경향을 조사했다. 다섯 깊이(10, 30, 50 100, 120cm)의 토양수와 여섯 수종의 수액을 분석하여 MixSIAR 모델을 이용하여 수종별 물 사용 깊이를 추정하였다. 활엽수림은 침엽수림과 혼효림에 비해 깊은 토심의 물 사용량이 더 많았으며, 각 수종별 계절에 따른 물 사용 전략이 달랐다. 소나무는 서식지 환경 조건에 따라 다양한 물 사용 경향을 보였다. 강수량이 적었던 2017년, 대부분의 수종들은 깊은 곳의 물 사용량이 증가했으며, 강수량이 풍부했던 2018년에도 비슷한 경향을 보였다.

목차 (Table of Contents)

• Abstract ⅰ
• List of Tables ⅶi
• List of Figures x
• Chapter 1. Introduction 1
• 1.1. Research background 1
• 1.2. Research objectives 7
• Chapter 2. Site description 10
• 2.1. Study sites 10
• 2.2. Study species 13
• 2.3. Meteorological conditions 14
• 2.4. Soil properties 17
• Chapter 3. Comparison analysis of water isotopic compositions: evaluating isotope analyzer for soil water and extraction method for
• xylem water 22
• 3.1. Introduction 22
• 3.2. Materials and methods 26
• 3.2.1. Study sites 26
• 3.2.2. Soil water collection 26
• 3.2.3. Branch sample collection 30
• 3.2.4. Xylem water extraction 34
• 3.2.5. Isotope analysis 37
• 3.2.6. Data analysis 40
• 3.3. Results 41
• 3.3.1. Differences in stable istope ratios between IRMS and CRDS 41
• 3.3.2. Differences in stable istope ratios among extraction times 44
• 3.3.3. Differences in stable istope ratios among extraction methods 47
• 3.4. Discussion 52
• 3.4.1. Effects of soil properties on the differences between IRMS and CRDS 52
• 3.4.2. Effects of Extraction Time on Stable Isotope Ratios 54
• 3.4.3. Effects of Stem Water Extraction Method on Stable Isotope Ratios 56
• 3.5. Summary 60
• Chapter 4. Correction methods for estimating water use patterns of three species using water stable isotope 62
• 4.1. Introduction 62
• 4.2. Materials and methods 68
• 4.2.1. Study sites . 68
• 4.2.2. Soil and xylem water extraction 69
• 4.2.3. Isotope analysis 70
• 4.2.4. Correction methods 71
• 4.2.5. Statistical analysis 74
• 4.3. Results 76
• 4.3.1. Isotopic composition of soil and xylem water 76
• 4.3.2. Evaluation of correction methods 80
• 4.3.3. Seasonal variation in isotopic composition of soil and xylem water correction method 81
• 4.4. Discussion 84
• 4.4.1. Isotopic offsets of xylem water 84
• 4.4.2. Correction methods for identification of plant water sources 85
• 4.4.3. Seasonal variation in isotopic composition of soil and xylem water 88
• 4.5. Summary 92
• Chapter 5. Estimation of water use patterns of tree species at Mt. Baekwoon 94
• 5.1. Introduction 94
• 5.2. Materials and methods 97
• 5.2.1. Study sites 97
• 5.2.2. Sample collection 98
• 5.2.3. Isotope analysis 99
• 5.2.4. Xylem water correction 100
• 5.2.5. Statistical analysis 101
• 5.3. Results 102
• 5.3.1. Isotopic composition of soil water at different soil depth 102
• 5.3.2. Isotopic composition of xylem water 109
• 5.3.3. Variation in the proportion of tree water uptake 111
• 5.4. Discussion 117
• 5.4.1. Species-specific water use patterns to drought 117
• 5.4.2. Effects of co-existing species on water use pattern 118
• 5.4.3. Effects of soil water profiles along the mountainous slope on water use pattern 120
• 5.5. Summary 123
• Chapter 6. Conclusion 125
• Bibliography 130
• Abstract in Korean 152