«（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 ...»
affected by elevated CO2, but elevated CO2 altered the relative abundances of particular ECM taxa colonizing fine roots, and increased prevalence of unique ECM species. Finally, a greater ECM community dissimilarity was found among individual P. taeda plots (Parrent et al. 2006). On the other hand, the response of the mycorrhizal community to elevated CO2 varies among tree species. For instance, Lukac et al.
(2003), who investigated three Populus species in FACE system, stated that the rate of ECM colonization increased only in P. alba species.
Besides elevated CO2, microhabitat characteristics also have effects on colonization of ECM at lava flow of Mt. Oshima-Koma, Hokkaido (Akasaka et al.
2007). After estimating Japanese larch seedlings from three microhabitats in three elevation zones, the results showed that the highest ECM colonization rate was in the most shaded micro-habitat in Larix understory than the other two (bare-ground and patch community of Salix reinii). Another factor is the N concentration. In a loblolly pine forests, increase of net N mineralization rate was negatively correlated with ECM fungi richness. ECM community composition and structure will change, but the diversity will be maintained with N loading for larch species (unpublished data).
High soil N concentrations can also negatively affect ECM diversity (Parrent et al.
The extra-matrical mycelia (EMM) of ECM make up a large proportion of the microbial diversity and biomass in forest soils. Thus, their response to elevated CO2 can affect plant nutrient acquisition and carbon movement through forests. So, for extra-radical mycelium study under elevated CO2, Parrent and Vilgalys (2007) and Godbold et al. (2006) used in-growth bags to assess the response of the extra-radical mycelium. One more study, related with the effects of CO2 and N fertilization on EMM biomass and community structure in forest plots of P. taeda, was conducted by
Parrent et al. (2007): they used sand-filled mesh bags buried in the field, and they found no increase of biomass at elevated CO2 plots relative to control plots. However, after the analysis of phospholipid fatty acid (PLFA) and DNA sequencing, they found thelephoroid and athelioid taxa were both frequent and abundant as EMM and thelephoroid richness was extremely high. This shows the presence of ECM specific symbiosis under certain conditions. How will this specific symbiosis perform under elevated CO2 (Fig.1.2)?
Figure 1.2 Relation between carbon allocation to belowground of a host tree, and the ectomycorrhizal symbiosis under elevated CO2 and O3.
Arrows shows the carbon driver of different factors (Solid line denotes enhancing factor and dashed line denotes the limiting factors) (Wang XN original) 1.3.2 Effect of elevated O3 on ECM symbiosis It is well known that elevated O3 reduces carbon assimilation and alters the allocation of photosynthates to below-ground (Grantz and Farrar 2000, King et al. 2005). O3 exposure may slow the specific rate of inorganic N uptake by roots (Haberer et al.
2007), and decrease the standing biomass of fine root and sporocarp production of
fungi (Kasurinen et al. 2005; Andrew and Lilleskov 2009).
The effect of high levels of O3 on mycorrhizas is not consistent. Some studies have found that high O3 limits carbon allocation to roots and this is expected to decrease mycorrhizal colonization and alter species-host compatibility (Edwards and Kelly 1992; Smith and Read 1997). Other short-term studies have reported the enhancement of mycorrhizal short-root formations under O3 exposure (Rantanen et al.
1994; Kasurinen et al. 1999). Furthermore, no effect on mycorrhizae was reported (Kainulainen et al. 2000).
It seems that the effects of elevated O3 on ECM symbiosis vary according to treatment period. However, there are still limited reports of long-term treatment on O3 fumigation on forests (Karnosky et al. 2003b; Matyssek et al. 2013). Therefore, this weak point should be taken into account for the next step in research.
1.3.3 Specific symbiosis of ECM under elevated CO2 Differences in the effectiveness of ECM for improving tree growth and tree nutrition are often species specific (Bruns et al. 2002), or even strain specific (Dell et al. 1994;
Agerer 2001). The majority of trees form symbioses with a plethora of fungi species, while some of the latter favor specificity and interact with only one host plant (Krause and Kothe 2006). The reason for this is considered to be that plants can control mycorrhizal colonization by controlling carbon allocation to short or fine roots according to the efficiency of the symbionts (Hoeksema and Kummel 2003). Thus, fungi with low carbohydrate requirements are often favored as symbionts in forest nurseries. Another possible explanation is ascribing this diverse symbiosis to ECM functional diversity.
Unfortunately reports on ECM functional diversity are still limited (Wang et al.
2015). Brearley and Scholes (2005) found ECM fungi isolated from mineral soils of tropical rain forests and are less able to utilize organic sources of nitrogen than mineral sources. For functional diversity of ECM, much more pertinent experiments are urgently required to further understand the response of ECM symbiosis related to changing environments.
1.4 Characteristics of Birch and Larch White birch (Betula platyphylla var. japonica) is one of the typical pioneer tree species (e.g. Koike 1995). It widely distributed and is well acclimated in several environmental conditions, its distribution range covers from central Honshu to Far Eastern Asia (including Siberia) (Mao et al. 2010; Shi et al. 2010; Zyryanova et al.
2010). Moreover, this species exists under various conditions, and also has a strong tendency to form a pure stand. White birch is well used in several regions of Hokkaido (Terazawa 2005) as well as in Russia (Zyryanova et al. 2010). They are restricted to distribute in the special habitat, among the marshy edaphic and have shrub habit (the former grows at the special soil originated from peridotite, the latter mainly distributes in wetlands in the eastern Hokkaido).
Larches are considered to be promising species for afforestation and woody resources because of fast growth and high specific gravity of stem (Ryu et al. 2009).
They are common components in the northern hemisphere, ranging from China to Japan, Siberian, European and North America and are recognized to be a major carbon sink.
Japanese larch (Larix kaempferi) is a native larch species in central, and partly
found in Mt. Manokami, northern Honshu, Japan and was transplanted to Hokkaido Island for timber use. As Dahurian larch (L. gmelinii) is found as fossil currently in Hokkaido (Koike et al. 2000), this species and its variety were introduced from most of the temperate forests, such as Siberia, Northeastern China to Hokkaido Island(Kelliher et al. 1997; Wang et al. 2008). Since Japanese larch has good tolerance to cold moist climate and grows rapidly (Matyssek and Schulze 1987a; b;
1988), they were introduced from Honshu mountains areas to northern Japan for reforestation or rehabilitation of bare ground. Due to their high production rate for timber, they were intensively used to reforestation in northern Japan. A variety of Dahurian larch (L. gmelinii var. japonica) is introduced to Hokkaido with the intention of using it as a breeding material for afforestation. It original distribution area is the Kurile Islands. Besides the fast growth and high yield, it is tolerant to infertile soil. Therefore it has a strong capacity of carbon sink.
Hybrid larch F1 (Larix gmelinii var. japonica × L. kaempferi) was bred from crossing female Dahurian larch (L. gmelinii var. japonica.) with a pollen parent of Japanese larch (L. kaempferi). The hybrid larch F1 has more suitable characteristics to the boreal region (Koike et al. 2000; Kuromaru 2008; Ryu et al. 2009). For example, it has much better tolerance to the shoot blight disease, grazing by the Red back vole and deer, and the damage caused by wind and snow. More amazing characteristics and utilities of hybrid larch F1 are under research (Ryu et al. 2009; Kita et al. 2009).
Although both birch and larch have similar growth traits, such as, light demanding and preference to fertile soil habitat, they can survive in severe environment regions (Mao et al. 2010). Both species are dominant components of boreal forests, and it is vital to evaluate their response to changing environment. To obtain experience for reforesting and contributing trees to adapt to the environment
stresses is an important strategy.
1.5 Objective and structure of study Recently, CO2 concentration in the atmosphere has been reported to increase year by year. Though CO2 is one of the essential components for photosynthesis, along with the increasing tropospheric O3 concentration and N deposition, the net primary production of forest ecosystems is affected. Our understanding of belowground responses to elevated O3 and CO2 as well as N deposition is still not enough due to several limitations (Andersen 2003; Kasurinen et al. 2005).
1.5.1 Hypothesis of the study In this study, I aim to investigate the effects of elevated CO2 and O3, N deposition on deciduous trees (species of birch and larch) in northern Japan.
My questions mainly focus to address (Fig. 1.1):
1) How do the root dynamics change under elevated CO2, especially in infertile soil condition?
2) What is effect of elevated CO2 and/or O3 on plant growth and ECM symbiosis?
3) What is the ECM community structure response to different N and P levels?
1.5.2 Structure of this study To reveal these questions (1.5.1 questions 1~3), I made three experiments as shown in Fig.1.3. All target plants are light demanding species with high specific gravity, and
are promising tree species for making plantations and re-vegetating open lands and degraded areas in East Asia (Zhang et al. 2000; Mao et al. 2010). The detail effects and their interaction impact of various environmental factors are presented in Fig. 1.4.
At first, I monitored seasonal changes of fine root of Japanese white birch as a model plant grown in volcanic ash and brown forest soil under elevated CO2 using the free air CO2 enrichment (FACE). I tried to apply the mini-rhizotoron developed by Nakaji et al (2008) to obtain the essential role of the dynamics of fine root of young fast growing tree species at enhanced CO2 concentration estimated at 2040 by IPCC.
interaction, especially ectomycorrhizal (ECM) colonization (Chapter 1). Overall, I tried to clarify the performance of colonization rate and species richness of ECM in larch species under different environmental stresses. According to the previous report (Yamakawa 2012), the number of ECM species colonized with Japanese is limited, although its species amount increases with tree size. The infection of ECM with larch is smaller compared with mountain birch (Wang et al. 2012) and white birch (Araki et al. 2013).
In Chapter 2, I found the essential role of dynamics of fine root in different soil types at elevated CO2 in relation to the colonization of ECM. To reduce the variation of ECM colonization with individual levels, I also studied using a clonal plant, i.e.
Hybrid larch F1 as host plant. I focused on symbiotic relationships between ECM and F1 grown under elevated CO2 and/or O3 grown in brown forest soil (Chapter 3). Then I examined combination effects of high N and Phosphorous loading on ECM colonization and growth of hybrid larch F1 and its parent larch (Dahurian larch and Japanese larch) grown in immature volcanic ash soils (Chapter 4). Based on my findings, I propose specific traits of ECM on larch as a host plant when grown under various environmental stresses to sustain growth (Chapter 5).
Figure 1.4 Impact scale and interaction effect of different environmental factors.
Note: solid arrow denotes the effects of elevated CO2, dashed arrow denotes the combined effects of elevated CO2 and O3; The different size of shape boxes symbolize influences strength, and overlap of different ellipses indicates the their interaction effects.
2.1 INTRODUCTION The atmospheric carbon dioxide (CO2) concentration has risen to nearly 30% since the century, resulting from large increases in fossil fuel burning and deforestation (Meehl et al. 2007). The impacts of elevated CO2 on forest trees and forest ecosystems is currently of great interest, including exchange of energy and materials among soil, aboveground biomass, and the atmosphere (Lal 2005).
The average enhancement of photosynthesis for trees exposed to elevated CO2 (300 ppm) has been about 60% (Norby et al. 1999). However, the responses vary considerably between species (Naumburg et al. 2001), by position in the crown (Takeuchi et al. 2001), by nitrogen (N) fertility level (Watanabe et al. 2008), by season (Noormets et al. 2001 b), and by co-occurring pollutant concentrations (Noormets et al. 2001a). It is far less certain tree growth and productivity under elevated CO2. Furthermore, not only the aboveground related to photosynthesis activity, the belowground parts linked with aboveground also required major attention (Scarascia-Mugnozza et al. 2001). Thus, root systems particularly the fine root dynamics should be highlighted in order to thoroughly understand the nutrient cycling under elevated CO2.
Fine roots were classified generally as ≤ 2 mm in diameter based on the definition proposed by Pregitzer et al. (2002). Although fine roots contribute less than 2% of tree biomass in forest ecosystem (Brunner and Godbold 2007), from 33 to 67% of the annual net primary productivity (NPP) in forest ecosystems derives from fine roots (Gill and Jackson 2000). Importantly, despite the small biomass of fine roots relative to aboveground tissues in forest ecosystems, large amounts of carbon (C) and N cycle annually through fine roots, which grow, die, and decompose very rapidly and
have high N concentrations (Hendrick and Pregitzer 1992; Ruess et al. 2003).