«（落葉樹の根圏動態に対する高CO2とO3及び高窒素負荷の影響に関する研究） Wang Xiaona 王 晓娜 Division of ...»
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Study on the effects of elevated CO2, O3 and high nitrogen loading
on the rhizosphere dynamics of deciduous trees
Division of Environmental Resources
Graduate School of Agriculture
Doctor of Philosophy
Study on the effects of elevated CO2, O3 and high nitrogen loading on the rhizosphere dynamics of deciduous trees Name: Wang Xiaona
Approved, dissertation committee:
Committee chairperson: Professor Dr. Yuzo Sano Committee member: Professor Dr. Ryusuke Hatano Committee member: Associate professor Dr. Yutaka Tamai Committee member: Associate professor Dr. Toshihiro Watanabe Committee member: Associate professor Dr. Tatsuro Nakaji Committee member: Professor Dr. Heljä-Sisko Helmisaari
GRADUATE SCHOOL OF AGRICULTURE
I HEREBY RECOMMEND THAT THE DISSERTATION PREPARED UNDER MY
BE APPROVED AND ACCEPTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF AGRICULTURE
SUPERVISORProfessor Dr. Takayoshi Koike Hokkaido University Sapporo Japan
CHAPTER 1 GENERAL INTRODUCTION
1.1 CHANGING ENVIRONMENT
1.2 ROOT DYNAMICS UNDER CHANGING ENVIRONMENT
1.2.1 Fine root biomass under elevated CO2
1.2.2 Fine root biomass under elevated O3
1.2.3 Turnover of fine root
1.3 ECM SYMBIOSIS UNDER CHANGING ENVIRONMENT
1.3.1 Effect of elevated CO2 on ECM symbiosis
1.3.2 Effect of elevated O3 on ECM symbiosis
1.3.3 Specific symbiosis of ECM under elevated CO2
1.4 CHARACTERISTICS OF BIRCH AND LARCH
1.5 OBJECTIVE AND STRUCTURE OF STUDY
1.5.1 Hypothesis of the study
1.5.2 Structure of this study
CHAPTER 2 FINE ROOT DYNAMICS OF WHITE BIRCH UNDER ELEVATED CO2........25
2.2 MATERIALS AND METHODS
2.2.1 Study site and FACE system
2.2.2 Plant materials and soil type
2.2.3 Mini-rhizotron system
2.2.4 Root image analysis
2.2.5 Soil texture
2.2.6 Statistical analysis
2.3.1 Soil nutrient concentration
2.3.2 Live fine root length
2.3.3 Fine root production and mortality
2.3.4 Fine root longevity
CHAPTER 3 ECTOMYCORRHIZAL COLONIZATION AND GROWTH OF HYBRID LARCHF1 UNDER ELEVATED CO2 AND O3
3.2 MATERIALS AND METHODS
3.2.1 Experimental site and plant materials
3.2.2 CO2 and O3 treatment
3.2.3 ECM identification
3.2.4 Measurement of seedling growth and nutrient concentration.. 593.2.5 Measurement of the leaf gas exchange rate
3.2.6 Statistical analysis
3.3.1 ECM types colonizing F1
3.3.2 Extent of colonization and diversity of ECM
3.3.3 Abundance of ECM by species
3.3.4 Growth of seedlings and element concentrations
3.3.5 Gas exchange rate
CHAPTER 4 ECTOMYCORRHIZAL SYMBIOSIS OF THREE LARIX SPECIES WITHDIFFERENT N AND P LOADINGS
4.2 MATERIALS AND METHODS
4.2.1 Plants and soil materials
4.2.2 Nutrient treatments
4.2.3 Colonization rate and diversity of ECM
4.2.4 Plant growth and concentration of P in needles
4.2.5 Statistical analysis
4.3.1 Taxonomic identification
4.3.2 ECM colonization and species diversity
4.3.3 Species composition of ECM
4.3.4 Community structure of ECM species
4.3.5 Biomass of seedlings
4.3.6 Concentration of P in distal parts of seedlings
CHAPTER 5 GENERAL DISCUSSION
5. GENERAL DISCUSSION
5.1 ROOT DYNAMIC UNDER ELEVATED CO2
5.2 ECM SYMBIOSIS UNDER CHANGING ENVIRONMENT
ABSTRACT Recently, rapid economic growth, industrialization and urbanization have caused a series of environmental pollutions mainly due to tremendous energy consumption.
Subsequent increase in atmospheric carbon dioxide (CO2) concentration, nitrogen oxide deposition and tropospheric ozone (O3) are considered to incite environmental change, threatening forest ecosystems. In northeast Eurasia and Asia, birch and larch represent essential components as well as being promising species for afforestation.
Since northern Japan is mostly covered with volcanic ash and pumice soil, ectomycorrhizal (ECM) symbiosis is fundamental to sustain the growth of these trees.
This symbiotic relation directly affects rhizosphere activities, such as fine root development. In this study, I tried to elucidate the response of fine root dynamics, species richness of ECM fungi under elevated CO2 and O3 as well as high nitrogen loading, aiming to obtain basic information for future afforestation with birch and larch species under changing environments.
At elevated CO2 concentration, plants usually enhance the growth of aboveground parts and allocate more photosynthates to belowground. This allocation increases the respiration of both coarse and fine roots. Fine-root dynamics play an important role in carbon (C) cycling of belowground and influence C sequestration to the soil. In chapter 2, to investigate the effect of elevated CO2 on fine-root dynamic of Japanese white birch (Betula platyphylla var. japonica), I monitored their dynamics using the Free Air CO2 Enrichment (FACE) facility of Hokkaido University for three years (2011-2013). Elevated CO2 was maintained at 500 μmol/mol which simulating the situation around 2040 according to IPCC prediction, and currently the ambient air
contains 380-395 μmol/mol of CO2. Mini-rhizotron (MR) instrument was used: all MR tubes were set up with planting seedlings in 2010. The image scanning in the field started in 2011, one year later, to avoid the gap between tube and soil. Except for the CO2 treatment, I also applied two soil types, i.e., brown forest (BF) soil and volcanic ash (VA) soil, which is widely distributed in northern Japan. Live fine-root length (LRL), fine-root production (FRP), mortality (FRM) and root lifespan were analyzed after tracing images by the Win-Rhizotron software. LRL was estimated as the total length in each area unit. FRP (FRM) was calculated according to the annual length-based method. It equals to the annual length-based root production (mortality) to live root length. Fine root lifespan was determined by fine root longevity using the Kaplan-Meier survival function. LRL increased under elevated CO2 in the first year but showed no significant increase thereafter in BF soil. However, in VA soil, it decreased with CO2 enrichment for all three growing seasons. Independent of treatments and soils, turnover of FRP and FRM ranged from 0.25 to 1.69 yr-1. The turnover of both FRP and FRM was relatively lower under elevated CO2 in the first two years, and increased from the third growing season by elevated CO2 in both soils.
Elevated CO2 increased fine-root lifespan in BF soil during the first year and in VA soil during the three years. But the response of root longevity to elevated CO2 differed according to root diameter classes.
CO2 is the basic C source for photosynthesis related to plant growth, while O3 is a phytotoxic air pollutant of major concern for forest decline. In general, elevated CO2 decreases stomatal conductance, which may reduce harmful effect of O3 via stomatal function. How does this combination of CO2 and O3 effect growth of the underground parts of larch? For tree growth and fine root dynamics, ECM symbiosis is a vital issue.
In chapter 3, to clarify the combined effects of elevated CO2 and O3 on tree growth
and ECM symbiosis, I used the Open Top Chamber (OTC) system to estimate the response of hybrid larch (F1) (Larix. gmelinii var. japonica × L. kaempferi) for two years (2011 and 2012). Treatments consisted of i) charcoal-filtered ambient CO2 (almost no O3, 385 μmol/mol), ii) 60 nmol/mol O3, iii) high CO2 (600 μmol/mol), and iv) their combination. Elevated CO2 increased the ECM colonization rate but not the diversity of ECM types. Higher net photosynthetic rates at the growth CO2 level increased the biomass of underground parts and stems, which, in turn, increased the ECM colonization rate. Elevated O3 negatively affected the ECM colonization rate and more strongly, species abundance. The growth of F1 was restricted, and the biomass was reduced by O3. However, specific ECM species, such as Suillus grevillei was selected as the one of the capable species that flourishes under enhanced O3.
ECM efficiently absorbed Phosphorous (P) and other elements.
Moreover, the ECM symbioses with host plants greatly depend on C gain and allocation. Although N is an essential element for plant growth, the recent increase of N deposition surely brings an imbalance and is another critical factor of changing environment. N deposition usually increases tree growth, as it is an essential nutrient.
How does N deposition affect the ECM symbiosis with host plants, especially in relation to another important nutrient, such as P? In chapter 4, to estimate the ECM symbiosis under different levels of N deposition with P efficiency, I planted the seedlings of three larch species in pots and placed them outdoors in open air, i.e., Japanese larch (JL: Larix. kaempferi), Dahurian larch (DL: L. gmelinii var. japonica) and F1. Four nutrient levels were applied, using two levels of N (0 and 100 kg ha-1yr-1) and two levels of P (0 and 50 kg ha-1yr-1). After two years of nutrient application, seven types of ECM were identified to colonize the three larch species. The ECM colonization rate was reduced by 19.8 % for DL, and increased by 39.4 % for JL,
63.7 % for F1 in high N condition, respectively. P application positively affected the ECM colonization for the three larches. ECM diversity was not significantly affected by N or P treatment except DL. ECM community structure of JL significantly differed among the nutrient regimes, but this was not the case with DL or F1. Increasing N load obviously reduced P concentration in needles of the parents, but F1 was not affected.
In summary, elevated CO2 did not accelerate root turnover in infertile soil condition, especially at the beginning of CO2 enrichment. Root dynamics of birch seedlings indicated great activity in the third year, most possibly due to mycorrhizal symbiosis. Under elevated CO2 and O3, I selected F1 as the best ECM-colonized species, and found the ECM symbiosis extremely assisting seedling growth under external stress. Uptake of essential elements such as P via ECM symbiosis remained the same or accelerated under elevated O3 in F1. ECM community structure greatly changed, and ECM species belonging to genus Suillus predominated. Comparing the ECM symbiosis of F1 seedlings with its parents in terms of N and P treatment, F1 was considered to retain ECM diversity even when exposed to changes in the levels of N and P. In particular, under high N loading, P in the needle was reduced for DL and JL, but not affecting F1. This might be attributed to the specific ECM symbiosis between S. grevillei and F1, where the symbiotic relationship remained before and after the nutrient treatments.
From the view of larch afforestation, coping with P deficiency and/or infertile soil conditions is important for seedlings under changing environment, such as elevated CO2, O3 and N loading. The birch and F1 are promising species and is a good candidate for reforestation under such conditions. However, it requires the vital partner, i.e., ECM, especially at the seedling stage. In conclusion, for survival under
changing environment in future, it is necessary to develop the ECM inoculation method for seedlings.
Keywords: Elevated CO2, Ectomycorrhiza, Nitrogen deposition, Ozone, Root dynamic
1.1 Changing environment Forest ecosystems are threatened by changing environments due to recent anthropic activities (e.g. Karnosky et al. 2003a; Izuta 2006; Matyssek et al. 2013). This involves, increasing atmospheric CO2 (CO2) and tropospheric zone (O3) concentrations, nitrogen deposition have become the most phytotoxic air pollutants, which are critical factors of changing environment (e.g. Cubasch et al. 2001; Matyssek et al. 2012;
Koike et al. 2013).
The concentration of atmospheric CO2 is increasing continuously, due to intensive deforestation and the use of fossil fuels: in 2013 the concentration reached up to ≈ 400 μmol mol-1 (Meehl et al. 2007; Mauna-Loa HP). Moreover, according to modeling results from the last century, the ground surface O3 has been increasing sharply, and the pollution will extend to a larger region in Asia in the next decade (e.g.
Lelieveld and Dentener 2000), especially in East Asia (Akimoto 2003). Numerous studies attempted to investigate the effect of elevated CO2 and O3 on forest ecosystem.
For instance, Free Air CO2 Enrichment (FACE) and Open Top Chamber (OTC) systems were developed throughout the world (e.g. Klamer et al. 2002; Karnosky et al.
2003a; Lukac et al. 2003; King et al. 2005; Eguchi et al. 2005; Koike 2006; Norby and Zak 2011; Koike et al. 2013).