Mongolica Var Research Articles

Common‐garden study of introgression at loci associated with traits adaptive to coastal environment from Quercus dentata into Quercus mongolica var. crispula

AbstractAdaptive introgression, which can provide genetic diversity resulting in the expansion to novel habitats and the creation of different ecotypes, has been proposed in oaks (genus Quercus). In northern Japan, Quercus mongolica var. crispula (Qc) is common in inland habitats, and Quercus dentata (Qd) occurs in coastal habitats. At the northern distributional limit of Qd, Quercus × angustilepidota (Qa), a hybrid taxon between Qc and Qd, occurs in coastal habitats. These taxa, Qc, Qa, and Qd, were transplanted to inland and coastal common gardens (sites). Genotypes at 27 495 loci, phenotypes of eight leaf and shoot traits, and the size of 30‐year‐old trees were measured for 224 individuals in both sites. Genotypic variation revealed a hybrid zone between Qc and Qd, including both northern‐edge Qd admixed with Qc and coastal Qa backcrossed to Qc. Phenotypes of Qa trees were intermediate between those of Qc and Qd trees. The size of Qa and Qd trees was smaller than that of Qc trees in the inland site but was larger in the coastal site, suggesting adaptation of Qa and Qd to coastal environment. Local ancestry was estimated from phased genotypes of admixed trees using reference genotypes of 47 Qc and 25 Qd trees, indicating heterogeneous ancestry along chromosomes. Admixture mapping of local ancestry detected loci significantly associated with a leaf trait, which were located in an introgressed genomic region with genes related to stress response. Further studies are necessary to elucidate the genetic basis of adaptive introgression resulting in Qd‐like phenotypes of Qa.

Broad-leaved and mixed cooltemperate forests from the class Fagetea crenatae Miyawaki, Ohba et Murase 1964 on Kunashir Island (the Kurils archipelago)

This study presents the classification and description of three new associations of cool-temperate zonal forests of the vegetation class Fagetea crenatae Miyawaki, Ohba et Murase 1964 on Kunashir and Hokkaido islands. The Filipendulo camtschaticae–Aceretum mayrii ass. nov. encompasses broad-leaved forests in eutrophic moist ecotopes dominated by Acer mono subsp. mayrii. The Abieti sachalinensis–Quercetum crispulae ass. nov. represents zonal mixed forests dominated by Quercus mongolica var. crispula with an admixture of coniferous tree species Abies sachalinensis, Taxus cuspidata, and Picea jezoensis (the latter only on Kunashir Island, in forests of the subass. piceetosum jezoensis). The Hydrangeo paniculatae–Quercetum crispulae ass. nov. includes secondary species-poor forests dominated by Q. mongolica var. crispula, Betula ermanii, or B. pendula subsp. mandshurica. All associations feature a dense understory of dwarf bamboo species Sasa spp., with the densest tickets found in Hydrangeo paniculatae–Quercetum crispulae forests. We also validated the union Carpino cordatae–Quercion crispulae Takeda, Uemura et Nakanishi ex Korznikov, Dzizyurova et Petrenko all. nov. which represents the zonal cool-temperate broad-leaved and mixed forests in Hokkaido, Sakhalin, Iturup and Kunashir. Broad-leaved forests of Kunashir exhibit lower species diversity compared to Hokkaido, missing typical temperate tree species such as Acer palmatum, Carpinus cordata, and Tilia japonica.

Ecophysiological difference in co-existing beech and oak saplings grown in different soil types under a free-air ozone exposure system

ABSTRACT To know effects of elevated ozone (eO3) response to beech (Fagus crenata) and oak (Quercus mongolica var. crispula) saplings, focusing on shoot elongation and leaf nutrient characteristics, beech and oak were grown in a free-air ozone-enrichment system (concentration: 35 ppb (aO3) vs. 75 ppb (eO3)) for two years under different soils (volcanic ash soil vs. brown forest soil). This treatment resulted in lower O3 tolerance in beech than in oak. The ratio of 2nd shoot flush showed a characteristic response to eO3 fumigation in beech and oak. For beech, the ratio was less than 0.5, while for oak, it ranged between 0.4 and 0.6. There was no difference in the photosynthetic rate of oak, although the photosynthetic rate of beech was slightly lower under elevated O3. Principal component analysis provided a good summary of the traits of beech and oak in response to O3 enrichment and soil combination, with O3-enriched beech characterized by higher Ca and lower N, P, K and A max in the 1st component and lower Mg and Mn in the 2nd component. O3 -treated oak in O3-enriched brown forest soils was characterized by high N, P, K and A max, while the influence of the 2nd component was small. Increased soil acidification will increase soil Mn and Al concentrations and may reduce the photosynthetic activity of beech saplings in eO3.

Composition of Organic Carbon-Based Compounds in the Stem Wood of Quercus mongolica Seedlings Grown Under Elevated CO2 and/or O3 Concentrations

In this study, we examined the composition of organic constituents of stem woody tissue together with tree growth in Quercus mongolica var. grosseserrata Blume seedlings raised under controlled CO2 and/or O3 concentrations in a Free-Air Concentration Enrichment system. After exposure to ambient air (control), elevated CO2 concentration (550 μmol mol–1 CO2), elevated O3 concentration (double that of the control), and a combination of elevated CO2 and O3 concentrations during a growing season, we measured the diameter and length of stem, and biomass of sampled seedlings and quantified the lignin, extractive, and holocellulose contents of the woody tissue of current-year stems. We confirmed that the growth of seedlings was enhanced under an elevated CO2 concentration condition. In line with this, the extractive content was lower in woody tissue formed under an elevated CO2 concentration than that formed under ambient air, whereas holocellulose content showed an inverse pattern. Elevated O3 concentration itself did not change the organic constituents of the woody tissue, but it reduced the influence of an elevated CO2 concentration. We thus assume that Q. mongolica formed woody tissue with a low extractive content under the high CO2 concentration condition, although this response was possibly mitigated by an elevated O3 concentration. Extractives contains antimicrobial components such as tannins, flavonoids, quinones, and terpenoids. The decrease in extractives within the widely distributed Q. mongolica in East Asia may have a non-negligible impact on C cycling in the future earth with high atmospheric CO2 concentration.

Species-Specific Nitrogen Resorption Efficiency in Quercus mongolica and Acer mono in Response to Elevated CO2 and Soil N Deficiency

To test the effects of elevated CO2 and soil N deficiency on N resorption efficiency (NRE) from senescing leaves in two non-N2-fixing deciduous broadleaved tree species, Japanese oak (Quercus mongolica var. grosseserrata Blume) and Painted maple (Acer mono Maxim. var. glabrum (Lév. Et Van’t.) Hara), potted seedlings were grown in a natural daylight phytotron with either ambient or elevated CO2 conditions (36 Pa and 72 Pa CO2) and with two levels of N (52.5 and 5.25 mg N pot−1 week−1 for high N and low N, respectively). We examined the N content (Nmass) of mature and senescent leaves, as well as photosynthesis and the growth of plants, and calculated both the mass-based NRE (NREmass) and leaf area-based NRE (NREarea). In both species, the Nmass of mature leaves decreased with high CO2 and low N, whereas the leaf mass per area (LMA) increased under elevated CO2, regardless of N treatments. In Q. mongolica, both the maximum rate of carboxylation (Vcmax) and the maximum electron transport rate (Jmax) were reduced by elevated CO2 and low N, but Vcmax exhibited an interactive effect of N and CO2 treatments. However, in A. mono, both the Vcmax and Jmax decreased under elevated CO2, regardless of N treatments. The partitioning of N for the photosynthetic function within leaves was also significantly decreased by elevated CO2 in both species and increased under low N in A. mono. The Nmass of senesced leaves decreased under low N in both species and exhibited an increase (Q. mongolica) or no effect (A. mono) by elevated CO2. The NREarea of Q. mongolica was affected by CO2 and N treatments, with a decrease under elevated CO2 compared to ambient CO2 and under low N compared to high N. The NREarea of A. mono was also affected by CO2 and N treatments and decreased under elevated CO2; however, unlike in the case of Q. mongolica, it increased under low N. We speculate that these interspecific differences in the responses of leaf N allocation, indicated by the photosynthetic (Vcmax and Jmax) and morphological (LMA) responses to elevated CO2, may have affected the NRE during defoliation under high CO2 and soil N-deficient conditions.

Different population size change and migration histories created genetic diversity of three oaks in Tokai region, central Japan.

To understand genetic diversity in focal species, it is important to consider the possibility of speciation with gene flow, especially in species with porous genomes such as oaks. We studied genetic diversity and structure in three oaks, Quercus mongolica var. mongolicoides (QM), Q. mongolica var. crispula (QC) and Q. serrata (QS), growing in the Tokai region, central Japan. QM is semi-endemic to the region while the others are common taxa. We also conducted demographic modeling to infer their population size change and migration histories using an approximate Bayesian computation (ABC) approach. The three taxa showed distinct genetic structures but there was genetic admixture among the taxa, especially between QM and QC. ABC analysis of population size change revealed that the population size of QM was stable during and after the last glacial period, while QC and QS showed population expansion after the last glacial maximum. ABC analysis of population divergence and migration revealed that continuous gene flow between QM and QC after their divergence was supported, while between QM and QS, and between QC and QS, secondary contact after sufficient isolation was supported. These historical migration patterns among the three taxa indicate that QM and QC are currently in the early stage or gray zone of speciation, whereas speciation of the other two taxon pairs is considered to have almost been established. Observed gene flow patterns and strength between QM and QC, and between QM and QS, were explained by both flowering patterns and historical distributions, but those between QC and QS were not.

Seed transfer across geographic regions in different climates leads to reduced tree growth and genetic admixture in Quercus mongolica var. crispula

Seed transfer may affect not only the performance of trees growing from transferred seeds but also the reproduction of the trees and the performance of their progeny. We investigated Quercus mongolica var. crispula trees transplanted from multiple provenances and their seedlings naturally regenerated in northeastern and southwestern test sites in Japan. The test sites and provenances were grouped into seven regions based on their geographic and climatic profiles. We defined the local population as trees from provenances in a region of either test site and the foreign population as trees from provenances in the other regions. Tree size was larger in the local population than in the foreign population in both test sites. We estimated foreign population ancestry from the allele frequencies in the local and foreign populations in each test site using microsatellite genotypes. We discriminated the local and foreign populations using foreign population ancestry although genetic differentiation between these populations were relatively low (0.022 ≤ FST ≤ 0.034). Different frequency distributions of foreign population ancestry between transplanted trees and regenerated seedlings indicated crossing between the local and foreign populations. Tree size decreased as foreign population ancestry increased in both test sites. Seedling mass increased in the northeastern test site but decreased in the southwestern test site as foreign population ancestry increased, indicating larger mass of seedlings with genetic properties of southwestern provenances. The findings suggest that seed transfer between regions results in reduced performance of trees growing from transferred seeds and admixed progeny of trees from local and foreign regions.

Impact Assessment of Ozone Absorbed through Stomata on Photosynthetic Carbon Dioxide Uptake by Japanese Deciduous Forest Trees: Implications for Ozone Mitigation Policies

Photosynthesis by trees is expected to contribute to preventing climate change including global warming. However, the current levels of tropospheric ozone (O3) reduce the uptake of photosynthetic carbon dioxide (CO2) by forest trees in Japan, which is a concern. Furthermore, it is unknown how much O3 should be reduced to prevent plants’ O3-induced damage. The objective of the present study was to assess the negative effects of the current levels of O3 absorbed via stomata and the impact of its mitigation on the CO2 uptake by trees in Japanese forests. Impact assessment, targeted in 2011–2015, was performed for four deciduous broad-leaved trees: Fagus crenata, Quercus serrata, Q. mongolica var. crispula, and Betula platyphylla var. japonica. The assessment was based on species-specific cumulative stomatal O3 uptake (COU) and species-specific responses of annual photosynthetic CO2 uptake to COU. Annual COU differed between the four trees; the average COU of F. crenata, Q. serrata, Q. mongolica var. crispula, and B. platyphylla var. japonica across Japan was 41.7, 26.5, 33.0, and 29.1 mmol m−2, respectively, and the reductions in CO2 uptake by the four trees were 14.0%, 10.6%, 8.6%, and 15.4%, respectively. Further analysis revealed that reducing the atmospheric O3 concentration by approximately 28%, 20%, 17%, and 49% decreased the O3-induced reductions in photosynthetic CO2 uptake to 5% in F. crenata, Q. serrata, Q. mongolica var. crispula, and B. platyphylla var. japonica, respectively. In the near future, implementing mitigation measures for the O3 damage in plants is expected to enhance the photosynthetic capacity of Japanese forest tree species.

Succession of litter-decomposing microbial organisms in deciduous birch and oak forests, northern Japan

Biological litter decomposition and the litter-associated microbial organisms were monitored for three years to characterize litter decomposition in early and late successional stages. Two forests were used for the investigation: pioneer a forest dominated by birch (Betula platyphylla var. japonica) and a climax forest by oak (Quercus mongolica var. grosseserrata) in the cool-temperate region of northern Japan. Three types of litter were used: birch, oak and mixed litter. The litter decomposition was effective during the first year but 50% of the original litter remained even after three years. Carbon-to-nitrogen ratios in the litter decreased largely in the first year and became stable thereafter. The litter decomposition rates were not different among the litter types and between the forests. The temporal changes in phospholipid fatty acids (PLFAs) showed that fungal biomass reached its peak in the first year and the bacterial biomass increased steadily until the end of the experiment. The concentrations of fungal PLFAs in the litter did not differ between the litter types but were lower in the oak forest. The litter decomposition was performed mostly by fungi, in particular in the early stages, while bacterial decomposition depended on the litter types and/or the forest types. Gram-negative bacteria reached their peak of PLFAs in the second year while gram-positive bacteria PLFAs increased gradually during the three years. Therefore, the succession of microorganisms in the litter occurred from fungi to bacteria and from gram-negative bacteria to gram-positive bacteria in the two forests. Unlike in the case of coniferous or monotonic forests, the effects of forests and litter types on litter decomposition for the first year were weak. The forest types on litter decomposition appeared only for the long-term litter decomposition. The successional changes of microorganisms occurred from fungi to bacteria for long-term litter decomposition processes with increasing N concentration in the litter.

Environment-dependent introgression from Quercus dentata to a coastal ecotype of Quercus mongolica var. crispula in northern Japan.

Summary Introgression from one species in a specific environment to another may facilitate colonization of the environment by the recipient species. However, such environment‐dependent introgression has been clarified in limited plant taxa.In northern Japan, there are two interfertile oak species: Quercus dentata (Qd) in coastal areas and Q. mongolica var. crispula (Qc) in inland areas. However, at higher latitudes where Qd is rare, a coastal Qc ecotype with Qd‐like traits is distributed in the coastal areas. We distinguished inland Qc, coastal Qc, and coastal Qd populations based on genome‐wide genotypes and multitrait phenotypes and verified introgression from coastal Qd to coastal Qc using reduced library sequencing.Genotypes and phenotypes differed among the populations, and coastal Qc was intermediate between inland Qc and coastal Qd. The ABBA–BABA test showed introgression from coastal Qd to coastal Qc. In coastal Qc, we found various stages of introgression after the first generation of backcross but detected no genomic regions where introgression was enhanced.Overall, we show evidence for introgression from a coastal species to an ecotype of an inland species, which has colonized the coastal environment. It remains unclear whether introgressed alleles are selected in the coastal environment.

Evaluation of O3 Effects on Cumulative Photosynthetic CO2 Uptake in Seedlings of Four Japanese Deciduous Broad-Leaved Forest Tree Species Based on Stomatal O3 Uptake

The current level of tropospheric ozone (O3) is expected to reduce the net primary production of forest trees. Here, we evaluated the negative effects of O3 on the photosynthetic CO2 uptake of Japanese forest trees species based on their cumulative stomatal O3 uptake, defined as the phytotoxic O3 dose (POD). Seedlings of four representative Japanese deciduous broad-leaved forest tree species (Fagus crenata, Quercus serrata, Quercus mongolica var. crispula and Betula platyphylla var. japonica) were exposed to different O3 concentrations in open-top chambers for two growing seasons. The photosynthesis–light response curves (A-light curves) and stomatal conductance were measured to estimate the leaf-level cumulative photosynthetic CO2 uptake (ΣPn_est) and POD, respectively. The whole-plant-level ΣPn_est were highly correlated with the whole-plant dry mass increments over the two growing seasons. Because whole-plant growth is largely determined by the amount of leaf area per plant and net photosynthetic rate per leaf area, this result suggests that leaf-level ΣPn_est, which was estimated from the monthly A-light curves and hourly PPFD, could reflect the cumulative photosynthetic CO2 uptake of the seedlings per unit leaf area. Although the O3-induced reductions in the leaf-level ΣPn_est were well explained by POD in all four tree species, species-specific responses of leaf-level ΣPn_est to POD were observed. In addition, the flux threshold appropriate for the linear regression of the responses of relative leaf-level ΣPn_est to POD was also species-specific. Therefore, species-specific responses of cumulative photosynthetic CO2 uptake to POD could be used to accurately evaluate O3 impact on the net primary production of deciduous broad-leaved trees.

Light Energy Partitioning under Various Environmental Stresses Combined with Elevated CO2 in Three Deciduous Broadleaf Tree Species in Japan

Understanding plant response to excessive light energy not consumed by photosynthesis under various environmental stresses, would be important for maintaining biosphere sustainability. Based on previous studies regarding nitrogen (N) limitation, drought in Japanese white birch (Betula platyphylla var. japonica), and elevated O3 in Japanese oak (Quercus mongolica var. crispula) and Konara oak (Q. serrata) under future-coming elevated CO2 concentrations, we newly analyze the fate of absorbed light energy by a leaf, partitioning into photochemical processes, including photosynthesis, photorespiration and regulated and non-regulated, non-photochemical quenchings. No significant increases in the rate of non-regulated non-photochemical quenching (JNO) were observed in plants grown under N limitation, drought and elevated O3 in ambient or elevated CO2. This suggests that the risk of photodamage caused by excessive light energy was not increased by environmental stresses reducing photosynthesis, irrespective of CO2 concentrations. The rate of regulated non-photochemical quenching (JNPQ), which contributes to regulating photoprotective thermal dissipation, could well compensate decreases in the photosynthetic electron transport rate through photosystem II (JPSII) under various environmental stresses, since JNPQ+JPSII was constant across the treatment combinations. It is noteworthy that even decreases in JNO were observed under N limitation and elevated O3, irrespective of CO2 conditions, which may denote a preconditioning-mode adaptive response for protection against further stress. Such an adaptive response may not fully compensate for the negative effects of lethal stress, but may be critical for coping with non-lethal stress and regulating homeostasis. Regarding the three deciduous broadleaf tree species, elevated CO2 appears not to influence the plant responses to environmental stresses from the viewpoint of susceptibility to photodamage.

Phylogeography and conservation genetics of the endangered Tugarinovia mongolica (Asteraceae) from Inner Mongolia, Northwest China.

Tugarinovia (Family Asteraceae) is a monotypic genus. It’s sole species, Tugarinovia mongolica Iljin, is distributed in the northern part of Inner Mongolia, with one additional variety, Tugarinovia mongolica var ovatifolia, which is distributed in the southern part of Inner Mongolia. The species has a limited geographical range and declining populations. To understand the phylogeographic structure of T. mongolica, we sequenced two chloroplast DNA regions (psbA-trnH and psbK-psbI) from 219 individuals of 16 populations, and investigated the genetic variation and phylogeographic patterns of T. mongolica. The results identified a total of 17 (H1-H17) chloroplast haplotypes. There were no haplotypes shared between the northern (T. mongolica) and southern groups (T. mongolica var. ovatifolia), and they formed two distinct lineages. The regional split was also supported by AMOVA and BEAST analyses. AMOVA showed the main variation that occurred between the two geographic groups. The time of divergence of the two groups can be dated to the early Pleistocene epoch, when climate fluctuations most likely resulted in the allopatric divergence of T. mongolica. The formation of the desert blocked genetic flow and enhanced the divergence of the northern and southern groups. Our results indicate that the genetic differences between T. mongolica and T. mongolica var. ovatifolia are consistent with previously proposed morphological differences. We speculate that the dry, cold climate and the expansion of the desert during the Quaternary resulted in the currently observed distribution of extant populations of T. mongolica. In the northern group, the populations Chuanjinsumu, Wuliji and Yingen displayed the highest genetic diversity and should be given priority protection. The southern group showed a higher genetic drift (FST = 1, GST = 1), and the inbreeding load (HS = 0) required protection for each population. Our results propose that the protection of T. mongolica should be implemented through in situ and ex situ conservation practices to increase the effective population size and genetic diversity.

An admixture of Quercus dentata in the coastal ecotype of Q. mongolica var. crispula in northern Hokkaido and genetic and environmental effects on their traits.

In northern Japan, coastal oak forests consist of Quercus dentata (Qd) on the coastal side and Q. mongolica var. crispula (Qc) on the inland side. In the forests of northern Hokkaido, Qd is rare, and a coastal ecotype of Qc with some Qd-like traits grows on the coastal side. To reveal the genetic background of this ecotype, nuclear microsatellite genotypes in closely related oak taxa were obtained from the Eurasian continent, Sakhalin, and Hokkaido. The clustering of these genotypes suggests an admixture of Qd in the coastal ecotype of Qc. Next, we evaluated the effects of admixture and coastal stress on the leaf and shoot traits of Qc and Qd along coastal-inland gradients in northern Hokkaido. The admixture of Qd in Qc was quantified by the Qd ancestry proportions. Coastal stress causes bud mortality in the upper parts of shoots and was quantified by the survival patterns of buds in shoots. The genetic and environmental effects on the traits at Qd-abundant and Qd-rare sites were estimated using linear mixed models. The genetic effect was detected in all traits. Both genetic and environmental effects were detected in most traits. Some traits differed between Qd-abundant and Qd-rare sites in addition to these effects, indicating more Qd-like traits at Qd-rare sites. The findings suggest that an admixture of Qd characterizes the genetic background of the coastal ecotype of Qc and that not only the coastal stress but also the genetic background is responsible for the leaf and shoot traits of Qc and Qd in northern Hokkaido.

Unveiling the origin of Quercus serrata subsp. mongolicoides found in Honshu, Japan, by using genetic and morphological analyses

AbstractQuercus mongolica is a tree found in temperate deciduous forests in east Asia. In Japan, Q. mongolica var. crispula is commonly found; moreover, an oak whose morphology is similar to that of Q. mongolica var. mongolica of the Asian continent has been found in certain areas of Honshu and Hokkaido. Recently, the oak found in Honshu was described as Q. serrata subsp. mongolicoides (QSM). However, genetic comparison between this oak and Q. mongolica var. mongolica of the Asian continent has not been performed; the origin of QSM is thus unknown. Therefore, we aimed to determine the origin of QSM by conducting nuclear microsatellite (nSSR), chloroplast DNA (cpDNA) and leaf morphology analyses for the three taxa, as well as other congeners. The cpDNA variation overlapped among the three taxa, suggesting low discrimination ability for these taxa. Although morphological congruency was found between QSM and Q. mongolica var. mongolica, results of nSSR analyses showed that QSM contained a genetic admixture of Q. mongolica var. mongolica of the Asian continent and Q. mongolica var. crispula of Japan, bolstering an admixture hypothesis. The nSSR and cpDNA analyses suggested that Q. mongolica var. crispula can be the progenitor of Q. mongolica var. mongolica and harbors the ancestral cpDNA haplotypes. Therefore, we concluded that QSM might have been created by an admixture that likely occurred within Japan between Q. mongolica var. crispula and putative relict Q. mongolica var. mongolica, which might have diverged in or around Japan from Q. mongolica var. crispula during the late Pleistocene.

Ozone-induced stomatal sluggishness changes stomatal parameters of Jarvis-type model in white birch and deciduous oak.

Stomatal ozone flux is closely related to ozone injury to plants. Jarvis-type multiplicative model has been recommended for estimating stomatal ozone flux in forest trees. Ozone can change stomatal conductance by both stomatal closure and less efficient stomatal control (stomatal sluggishness). However, current Jarvis-type models do not account for these ozone effects on stomatal conductance in forest trees. We examined seasonal course of stomatal conductance in two common deciduous tree species native to northern Japan (white birch: Betula platyphylla var. japonica; deciduous oak: Quercus mongolica var. crispula) grown under free-air ozone exposure. We innovatively considered stomatal sluggishness in the Jarvis-type model using a simple parameter, s, relating to cumulative ozone uptake (defined as POD: phytotoxic ozone dose). We found that ozone decreased stomatal conductance of white birch leaves after full expansion (-28%). However, such a reduction of stomatal conductance by ozone fell in late summer (-10%). At the same time, ozone reduced stomatal sensitivity of white birch to VPD and increased stomatal conductance under low light conditions. In contrast, in deciduous oak, ozone did not clearly change the model parameters. The consideration of both ozone-induced stomatal closure and stomatal sluggishness improved the model performance to estimate stomatal conductance and to explain the dose-response relationship on ozone-induced decline of photosynthesis of white birch. Our results indicate that ozone effects on stomatal conductance (i.e. stomatal closure and stomatal sluggishness) are crucial for modelling studies to determine stomatal response in deciduous trees, especially in species sensitive to ozone.

A practical approach to estimate diffusional leakages of leaf chamber of open gas exchange systems using intact leaves.

We propose a novel approach to determine the coefficient of CO2 diffusional leakage (k_CO2 ) in the chamber of a portable open gas exchange system (Li-6400, Li-Cor Inc., NE, USA) using intact leaves. Assuming that dark respiration rate (Rn ) is constant at various CO2 concentrations, at least in a short term, k_CO2 should be the value that makes the leak-corrected Rn constant. We used 2 representative tree species native to northern Japan, Japanese white birch (Betula platyphylla var. japonica) and Japanese oak (Quercus mongolica var. crispula), to determine k_CO2 , by measuring Rn at various CO2 concentrations. Irrespective of the species, k_CO2 estimated by the present approach was well correlated with the diffusional leak coefficient (k_flow ) estimated by the generally used approach that utilizes CO2 concentrations inside and outside the chamber based on thermally killed leaves at various flow rates. Furthermore, the present approach does not require the ambient CO2 concentration outside the chamber (Ca ) if Ca in the laboratory is stable, which provides a feasible way to correct the photosynthetic rate, taking diffusional leakage into account.

ブナ・ミズナラの開芽・開葉に与える晩霜の影響

ブナ・ミズナラの開芽・開葉に与える晩霜の影響

Leaf stoichiometry of deciduous tree species in different soils exposed to free-air O3 enrichment over two growing seasons

The effects of elevated O3 in different soil conditions on foliar elements stoichiometry were investigated in 3 native tree species with a free-air enrichment system in northern Japan over two growing seasons. Essential elements (Mg, K, Ca, Mn, Fe, Ni, P, N) and two non-essential elements (Cr, Al) were analyzed in leaf samples obtained from 6 different treatments of O3 and soils at 5 collection times from 2014 to 2015. In this study, relationships among the foliar elements within each species were investigated and negative correlations between foliar N and the metal elements were observed in birch (Betula platyphylla var. japonica). From the differences of foliar contents as well as their retranslocation rate, beech (Fagus crenata) with determinate shoot growth pattern were rather more sensitive to O3 stress on foliar contents, meanwhile oak (Quercus mongolica var. crispula) was possibly susceptible to O3 on dynamics of immobile elements. Soil nutrients have distinct impacts on retranslocation rate of K, Fe, and P. Principal component analysis revealed that Mn and K can become indices in assessing the O3 and soil effects in both short and long term monitoring of the growth of these tree species. Our findings are essential in further comprehension to nutrient conservation mechanism in the nutrient dynamics of cool-temperate forests.

Retranslocation of foliar nutrients of deciduous tree seedlings in different soil condition under free-air O3 enrichment

Retranslocation is the amount of an element that is depleted from old plant components and is provided for new growth. Leaf senescence is usually accelerated at elevated O3 (eO3), and leaf shedding is influenced by soil nutrient availability (and acidification). In this study, we focused on the net retranslocation and allocation dynamics of foliar nutrients (N, P, Mg, K, Ca, Mn, Fe and Al) to investigate the effect of eO3 on birch (Betula platyphylla var. japonica), oak (Quercus mongolica var. crispula), and beech (Fagus crenata) seedlings grown in different soil conditions. Seedlings of the 3 species were planted in a free-air O3 enrichment system under 3 soil types (brown forest soil, serpentine soil, volcanic ash soil) for one growing season. All tree species were grown with 3 replications per each plot at elevated O3 (about 80 ppb) and ambient condition (O3 ranging 25-35 ppb). Leaf samples were taken from the top part of seedlings during the growing season in mid-September, and senescing leaves were sampled in mid-November. Both were collected for chemical composition analysis. Retranslocation rate of P was markedly increased by eO3 in birch and significantly differed among soil types in oak seedlings, while was constant across treatments in beech seedlings. Retranslocation of N in oak seedlings was significantly affected by soil type. Retranslocation of other elements was most sensitive to both eO3 and soil type in beech seedlings. The influence of differential growth patterns among species in modulating the physiological response of seedlings to high levels of ozone and different soil conditions are discussed.