学位論文審査の要旨 
 
博士の専攻分野の名称  博士（農学）  氏 名 Cong SHI 
審査担当者 主査 特任教授 小池 孝良 
      副査 教授   波多野隆介 
      副査 准教授  渡部 敏裕 
      副査   准教授  中村 誠宏（北方生物圏フィールド科学センタ－） 
副査 教授   Grantz A. David 
（カルフォルニア大学リバーサイド校 , USA） 
学位論文題名 
Physiological and stoichiometry study on foliar nutrients and defensive characteristics of representative 
deciduous broad-leaved tree species in northern Japan under environmental changes  
（変動環境における北日本の落葉広葉樹の葉成分と防御特性に関する生理的・化学量論的研究） 
 
This thesis consists of total 164 pages including 14 Figures, 17 Tables, and 6 chapters, with 3 
references.  
Introduction 
Global environment has been dramatically changing due to human activities, especially elevated 
atmospheric carbon dioxide (CO2), ozone (O3), and nitrogen (N) as a precursor for O3. Atmospheric 
CO2 has been globally increasing and promotes plant growth via photosynthetic enhancement for an 
extent. At the same time, ground-level O3 has also been continuously increasing especially in Asia. 
Elevated O3 can accelerate foliar senescence and negatively affect the vigor and health of forests. 
Moreover, soil conditions (e.g. nutrient availability) also affect the physiological function of both 
nutrient retranslocation and plant defense. 
As representatives of deciduous broad-leaved tree species native to northern Japan, Japanese white 
birch (Bp: Betula platyphylla var. japonica Hara), Siebold’s beech (Fc: Fagus crenata Blume), 
Mizunara oak (Qm: Quercus mongolica Fisch. ex Ledeb. var. crispula (Blume) Ohashi) and Konara oak 
(Qs: Quercus serrata Murray) are applied to this study. Specific O3 sensitivity has been estimated in 
sequence of beech, birch and oak, with determinate, indeterminate and semi-determinate shoot growth 
pattern, respectively. 
To assess the responses of the above species on various environmental changes, three researches 
have been carried out with a free-air enrichment system to simulate forest ecosystems.  
1. Foliar nutrients composition of oak species to elevated O3 accompanied with elevated CO2 
    Oaks are regarded as O3 stress tolerant species among 18 woody plants tested in Japan while Qm is 
considered to be more tolerant to O3 compared to Qs. At eCO2, stomatal conductance is low, which 
results in suppression of O3 absorption via stomata. As eCO2 may have combined effects with eO3 on 
growth and photosynthetic capabilities of the two oak species, I investigated foliar nutrients 
composition (Ca, K, K, Mg, Mn, N, P) as well as the foliar carbohydrates (starch and sugar) amount of 
2-year-old oak seedlings (Qm and Qs) exposed to eCO2 and/or eO3 with a free-air enrichment system. 
From the results of element concentration, it was found that N and Mg may have the potential to be 
 
 
major indicators in assessing the effects of O3 on two oaks. I also found that Qs may have a higher 
ability of recovering from O3 damages and likely become more tolerant to eO3 than Qm under eCO2 
independent of sugar and starch concentration.  
2. Foliar element concentrations, the retranslocation and seasonal changes of three species to 
elevated O3 under three different soils  
This study consists with two chapters (Chapter 3 and 4). Retranslocation is the amount of an 
element that is depleted from aged plant components and is provided for new growth. As leaf 
senescence is usually accelerated at eO3 and leaf shedding is also influenced by soil nutrient availability 
(and acidification), 2 year-old (as of 2014) seedlings of Bp, Fc, and Qm were planted in a free-air O3 
enrichment system under three different soil types (brown forest: B, volcanic ash: V, and serpentine: S).  
In chapter 3, I focused on the net retranslocation of foliar elements (N, P, K, Ca, Fe, Mg, Mn and 
Al) to discuss potential effects of eO3 on seedlings in relation to different soil conditions via 
retranslocation traits. I also found that the retranslocation rate of P was increased by eO3 in Bp and by 
soil treatment in Qm; but constant across treatments in Fc. Retranslocation of N was affected by soil in 
Qm. Retranslocation of other elements was most sensitive to both eO3 and soil in Fc.  
In chapter 4, in addition to above elements, I added foliar Ni and Cr to further estimate the effects 
of eO3 alone and together with different soils over two growing seasons. I investigated on physiological 
understanding of stoichiometry of foliar elements as well as relationships among the foliar elements 
within each species. I found Fc with a determinate shoot growth pattern, was relatively more sensitive 
to O3 stress on foliar contents, but Qm was possibly susceptible to eO3 concerning dynamics of 
immobile elements. Principal component analysis revealed that K and Mn can become indicators in 
assessing O3 and soil effects in both short and long term growth monitoring of these tree species.  
3. Foliar defense characteristics of three species to elevated O3 under two different soils 
    As leaf defense depends on both genotype and environmental conditions, I investigated the leaf 
chemical defense traits by analyzing the C/N ratio and amount of defensive compounds (lignin, total 
phenolics and condensed tannin) in response to eO3 under B and V soils for Bp, Fc and Qm species. In 
this study, foliar defensive traits were affected by eO3 for Bp; N and C/N were influenced by soils but 
defensive chemicals were by eO3 for Fc; Qm as a tolerant species, was able to survive under various 
environmental changes. 
    In conclusion, my results provide evidences that physiological explanation on stoichiometry of 
foliar elements and their dynamic variation as well as foliar defensive traits are varied upon 
environmental changes for each species and they are also species specific. Although Qm is regarded as 
an O3 tolerant species, after making comparisons among species, it can be susceptible to O3 concerning 
dynamics of immobile elements. My findings are essential in further comprehension to nutrient 
ecophysiological mechanism in the nutrient dynamics of cool-temperate forests of Japan and will be of 
help for the investigation of species adaption to environmental changes, which will be utilized on 
developing appropriate strategies of afforestation in the future. 
  Therefore, we acknowledge that the author is qualified to be granted the Degree of Doctor of 
Philosophy in Agriculture from Hokkaido University.