Densiflora Seedlings Research Articles

Photosynthetic responses of Larix kaempferi and Pinus densiflora seedlings are affected by summer extreme heat rather than by extreme precipitation

The frequency and intensity of summer extreme climate events are increasing over time, and have a substantial negative effect on plants, which may be evident in their impact on photosynthesis. Here, we examined the photosynthetic responses of Larix kaempferi and Pinus densiflora seedlings to extreme heat (+ 3 °C and + 6 °C), drought, and heavy rainfall by conducting an open-field multifactor experiment. Leaf gas exchange in L. kaempferi showed a decreasing trend under increasing temperature, showing a reduction in the stomatal conductance, transpiration rate, and net photosynthetic rate by 135.2%, 102.3%, and 24.8%, respectively, in the + 6 °C treatment compared to those in the control. In contrast, P. densiflora exhibited a peak function in the stomatal conductance and transpiration rate under + 3 °C treatment. Furthermore, both species exhibited increased total chlorophyll contents under extreme heat conditions. However, extreme precipitation had no marked effect on photosynthetic activities, given the overall favorable water availability for plants. These results indicate that while extreme heat generally reduces photosynthesis by triggering stomatal closure under high vapor pressure deficit, plants employ diverse stomatal strategies in response to increasing temperature, which vary among species. Our findings contribute to the understanding of mechanisms underlying the photosynthetic responses of conifer seedlings to summer extreme climate events.

Waterlogging Hardening Effect on Transplant Stress Tolerance in Pinus densiflora

Waterlogging induces oxidative damage by accumulation of reactive oxygen species due to stomatal closure. Plants alter their physiological and molecular mechanisms to reduce and adapt to oxidative stress. This mechanism of adaptation to stress, known as hardening, can support future stress tolerance. Pinus densiflora seedlings were grown under waterlogging treatment for three years and then transplanted to another site to identify the waterlogging hardening effect on transplanting. Transcriptome analysis was conducted before and after transplanting, and physiological factors were measured after transplanting. After transplanting, wounding stress is the main cause of transplant stress, and 13 genes related to phenylpropanoid were upregulated for the recovery of wounded roots in waterlogged hardened seedlings. The leaf starch and soluble sugar content of the waterlogged hardened seedlings were 50.3% and 40.5% lower due to the formation of cell walls. However, auxin-related genes were downregulated in waterlogging hardened seedlings, resulting in a lower tendency for height growth in hardened waterlogged seedlings. Waterlogging hardening mitigated transplant stress by wounding more than non-hardening, whereas waterlogging hardening may negatively affect seedling height. Our study provides evidence for the hardening effect of long-term waterlogging on transplanted P. densiflora seedlings.

Miscanthus sinensis contributes to the survival of Pinus densiflora seedlings at a mining site via providing a possible functional endophyte and maintaining symbiotic relationship between P. densiflora and endophytes from high soil temperature stress.

At a sedimentary site in an old mine site, Miscanthus sinensis formed patches, where Pinus densiflora seedlings could grow better compared with those outside the patches, indicating that M. sinensis would improve P. densiflora seedling establishment. The purpose of this study was to understand the mechanisms by which M. sinensis facilitates the survival of P. densiflora seedlings by considering the soil properties, heavy metal tolerance, and root endophytes in P. densiflora seedlings at the sedimentary site. The sedimentary site, which is a bare ground, contained high concentrations of Fe, indicating that plants should be exposed to Fe and high soil temperature stresses. Measurement of soil temperature revealed that M. sinensis suppressed sharp increases and alternation of soil temperature, resulting in reducing high soil temperature stress in P. densiflora seedlings. To adapt to the Fe stress environment, P. densiflora outside and inside the patches produced Fe detoxicants, including catechin, condensed tannin, and malic acid. Ceratobasidium bicorne and Aquapteridospora sp. were commonly isolated from P. densiflora seedlings outside and inside the patches as root endophytes, which might enhance Fe tolerance in the seedlings. Aquapteridospora sp., which is considered as a dark-septate endophyte (DSE), was also isolated from the roots of M. sinensis, suggesting that M. sinensis might play a source of a root endophyte to P. densiflora seedlings. Ceratobasidium bicorne could be classified into root endophytes showing symbiosis and weak pathogenicity to host plants. Therefore, high soil temperature stress would weaken P. densiflora seedlings, causing root endophytic C. bicorne to appear pathogenic. We suggested that P. densiflora could adapt to the Fe stress environment via producing Fe detoxicants, and M. sinensis would facilitate the establishment of P. densiflora seedlings in the sedimentary site by providing a DSE, Aquapteridospora sp., and maintaining symbiosis of C. bicorne from high soil temperature stress.

Ectomycorrhizal fungi, two species of Laccaria, differentially block the migration and accumulation of cadmium and copper in Pinus densiflora

The root tips of host plant species can establish ectomycorrhizae with their fungal partners, thereby altering the responses of the host plants to heavy metal (HM) toxicity. Here, two species of Laccaria, L. bicolor and L. japonica, were investigated in symbiosis with Pinus densiflora to study their potential for promotion of phytoremediation of HM-contaminated soils in pot experiments. The results showed that L. japonica had significantly higher dry biomass than L. bicolor in mycelia grown on modified Melin-Norkrans medium containing elevated levels of cadmium (Cd) or copper (Cu). Meanwhile, the accumulations of Cd or Cu in L. bicolor mycelia were much higher than that in L. japonica at the same level of Cd or Cu. Therefore, L. japonica displayed a stronger tolerance to HM toxicity than L. bicolor in situ. Compared with non-mycorrhizal P. densiflora seedlings, inoculation with two Laccaria species significantly increased the growth of P. densiflora seedlings in absence or presence of HM. The mantle of host roots blocked the uptake and migration of HM, which led to the decrease of Cd and Cu accumulation in the P. densiflora shoots and roots, except for the root Cd accumulation of L. bicolor-mycorrhizal plants when 25 mg kg−1 Cd exposure. Furthermore, HM distribution in mycelia showed Cd and Cu are mainly retained in the cell walls of mycelia. These results provide strong evidence that the two species of Laccaria in this system may have different strategies to assist host tree against HM toxicity.

Exploring fine-scale assembly of ectomycorrhizal fungal communities through phylogenetic and spatial distribution analyses.

Ectomycorrhizal fungi (EMF) form symbiotic relationship with the roots of host plants. EMF communities are composed of highly diverse species; however, how they are assembled has been a long-standing question. In this study, we investigated from a phylogenetic perspective how EMF communities assemble on Pinus densiflora seedlings at different spatial scales (i.e., seedling scale and root tip scale). P. densiflora seedlings were collected from different habitats (i.e., disturbed areas and mature forests), and their EMF communities were investigated by morphotype sequencing and next-generation sequencing (NGS). To infer assembly mechanisms, phylogenetic relatedness within the community (i.e., phylogenetic structure) was estimated and spatial distribution of EMF root tips was analyzed. The EMF communities on pine seedlings were largely different between the two habitats. Phylogenetically restricted lineages (Amphinema, /suillus-rhizopogon) were abundant in the disturbed areas, whereas species from diverse lineages were abundant in the mature forests (Russula, Sebacina, /tomentella-thelephora, etc.). In the disturbed areas, phylogenetically similar EMF species were aggregated at the seedling scale, suggesting that disturbance acts as a powerful abiotic filter. However, phylogenetically similar species were spatially segregated from each other at the root tip scale, indicating limiting similarity. In the mature forest seedlings, no distinct phylogenetic signals were detected at both seedling and root tip scale. Collectively, our results suggest that limiting similarity may be an important assembly mechanism at the root tip scale and that assembly mechanisms can vary across habitats and spatial scales.

Estimation of the most suitable nitrogen concentration for sporocarp formation in Laccaria japonica colonizing Pinus densiflora seedlings through in vitro mycelial culture.

Many ectomycorrhizal (ECM) fungi produce commercially valuable edible sporocarps. However, the effects of nitrogen (N) application on ECM fungal sporocarp formation remain poorly understood. In this study, we investigated the effect of application of various N concentrations (0, 5, 25, 50, 100, and 200mg/L) on the growth of Laccaria japonica mycelia in vitro for 1month. The results showed that L. japonica mycelial biomass was highest in the 50mg/L treatment and was significantly inhibited at N concentrations higher than 200mg/L. Next, we investigated the effects of N application on mycorrhizal colonization and sporocarp formation in L. japonica colonizing Pinus densiflora seedlings in pots. The seedlings were watered with nutrient solutions containing 0, 5, 25, 50, or 100mgN/L. The biomass, photosynthetic rate, and mycorrhizal colonization rates of the seedlings were measured at 45days (first appearance of primordia), 65days (sporocarp appearance on the substrate surface), and 4months after seedlings were transplanted. The numbers of primordia and sporocarps were recorded during the experimental period. Total carbon (C) and N content were determined in seedlings at 4months after transplantation, and in L. japonica sporocarps. Both mycelial growth and sporocarp production reached their maximum at an N application concentration of 50mg/L, suggesting that the most suitable N concentration for ECM fungal sporocarp formation can easily be estimated in vitro during mycelial growth. This finding may help determine the most suitable N conditions for increasing edible ECM fungus sporocarp production in natural forests.

Systemic Acquired Resistance-Mediated Control of Pine Wilt Disease by Foliar Application With Methyl Salicylate.

Pine wilt disease (PWD), caused by the pinewood nematode, is the most destructive disease in pine forest ecosystems worldwide. Extensive research has been done on PWD, but effective disease management is yet to be devised. Generally, plants can resist pathogen attack via a combination of constitutive and inducible defenses. Systemic acquired resistance (SAR) is an inducible defense that occurs by the localized infection of pathogens or treatment with elicitors. To manage PWD by SAR in pine trees, we tested previously known 12 SAR elicitors. Among them, methyl salicylate (MeSA) was found to induce resistance against PWD in Pinus densiflora seedlings. In addition, the foliar applications of the dispersible concentrate-type formulation of MeSA (MeSA 20 DC) and the emulsifiable concentrate-type formulation of MeSA (MeSA 20 EC) resulted in significantly reduced PWD in pine seedlings. In the field test using 10-year-old P. densiflora trees, MeSA 20 DC showed a 60% decrease in the development of PWD. Also, MeSA 20 EC gave the best results when applied at 0.1 mM concentration 2 and 1 weeks before pinewood nematode (PWN) inoculation in pine seedlings. qRT-PCR analysis confirmed that MeSA induced the expression of defense-related genes, indicating that MeSA can inhibit and delay the migration and reproduction of PWN in pine seedlings by modulating gene expression. These results suggest that foliar application of MeSA could reduce PWD incidence by inducing resistance and provide an economically feasible alternative to trunk-injection agents for PWD management.

Differential water-use and growth responses of Pinus densiflora and Larix kaempferi seedlings to microclimate manipulation

Our study assessed how physiological traits and the growth of seedlings of Pinus densiflora and Larix kaempferi, representative coniferous species of Korea, are affected by warming and precipitation manipulation. A warming and precipitation manipulation experiment was conducted with 1- and 2-year-old seedlings using infrared heaters, transparent panels, and an irrigation system. Plant physiological activities were monitored using a portable photosynthesis measurement system, and seedling growth was investigated by measuring the dry weight of harvested biomass. P. densiflora, an isohydric species, showed an overall decrease in physiological activities under the warming treatment in the first (germination) year. In particular, stomatal conductance decreased to prevent excessive water loss, with minimal decreases in photosynthetic activity, and increased the water-use efficiency in the first year. L. kaempferi, an anisohydric species, maintained stomatal conductance under the warming treatment. Both species maintained physiological activities with their distinct responses to heat in the second year, while the seasonal variation pattern changed in 2-year-old P. densiflora seedlings. The dry weight of L. kaempferi seedlings increased under warming; however, it decreased by warming combined with increased precipitation. These results can enhance the understanding of seedling responses to microclimate manipulation according to the different water-use by species and seedling age. Under the future climate change, these responses should be accounted for in management of seedlings in nurseries or newly afforested areas.

Effect of Neutralizing Treatments Using a Waste-lime and Oyster Mix on the Growth of Pinus densiflora Seedlings and Herbaceous Vegetation in the Acid Soil of an Abandoned Metal Mine

Effect of Neutralizing Treatments Using a Waste-lime and Oyster Mix on the Growth of Pinus densiflora Seedlings and Herbaceous Vegetation in the Acid Soil of an Abandoned Metal Mine

Ectomycorrhizal Fungi Associated with Pinus densiflora Seedlings under Flooding Stress

Flooding is an environmental stress for plants that not only limits aeration and nutrient acquisition, but also disturbs underground plant-associated fungal communities. Despite frequent flooding, red pine (Pinus densiflora) seedlings thrive in streamside environments. However, whether the compatible ectomycorrhizal fungi (EMF) of red pine are affected by natural flooding is unclear. As EMF are vital symbionts for the development of many trees and allow them to overcome various environmental stresses, in this study, the EMF species associated with red pine seedlings in a streamside environment in Korea were investigated after flooding. The EMF species in 47 seedlings collected from the streamside site were identified by observing their different morphotypes using internal transcribed spacer sequence analysis, and a total of 10 EMF species were identified. The EMF species diversity was lower than that in samples collected from a nearby forest analyzed as a control. The dominant EMF species of streamside seedlings included Amphinema spp., Rhizopogon luteolus, Suillus luteus, and Thelephora terrestris. This study could serve as a basis for investigating the mechanisms by which advantageous EMF aid plant development under flooding stress.

Mycorrhizal synthesis, morpho-anatomical characterization of mycorrhizae, and evaluation of mycorrhiza-forming ability of Hydnum albidum-like species using monokaryotic and dikaryotic cultures.

Despite the economic and ecological importance of Hydnum species, in vitro synthesis of ectomycorrhizae of this genus has not been reported due to difficulties in establishing pure cultures. We inoculated pure cultures of 12 monokaryotic and 3 dikaryotic mycelial strains of an undescribed Hydnum albidum-like species on roots of axenic Pinus densiflora seedlings to synthesize ectomycorrhizae and to evaluate their mycorrhiza-forming ability. Six months after inoculation, both monokaryotic and dikaryotic strains formed ectomycorrhizae with Hartig net hyphae at the root cortex. Monokaryotic and dikaryotic strains exhibited similar morpho-anatomical characteristics of ectomycorrhizae, with the exception for clamped septa of emanating and outer mantle hyphae in the latter. Between monokaryotic and descendant dikaryotic strains, there were no significant differences in number of mycorrhizae in pine seedlings, whereas monokaryotic strains showed a greater total number of root tips and lower colonization rates than the descendant dikaryotic strains. These results indicate that both monokaryotic and dikaryotic mycelia of the H. albidum-like species can form mycorrhizae under axenic condition, and that can be applied toward the cultivation of hedgehog mushrooms.

Successional Change of the Fungal Microbiome Pine Seedling Roots Inoculated With Tricholoma matsutake.

The pine mushroom (Tricholoma matsutake; Agaricales, Tricholomataceae) is an ectomycorrhizal fungus that produces a commercially valuable, edible mushrooms. Attempts to artificially cultivate T. matsutake has so far been unsuccessful. One method used to induce T. matsutake to produce fruiting bodies of in the wild is shiro (mycelial aggregations of T. matsutake) transplantation. In vitro ectomycorrhization of T. matsutake with seedlings of Pinus densiflora has been successful, but field trials showed limited production of fruiting bodies. Few studies have been done to test what happens after transplantation in the wild, whether T. matsutake persists on the pine seedling roots or gets replaced by other fungi. Here, we investigated the composition and the interaction of the root fungal microbiome of P. densiflora seedlings inoculated with T. matsutake over a 3 year period after field transplantation, using high-throughput sequencing. We found a decline of T. matsutake colonization on pine roots and succession of mycorrhizal fungi as P. densiflora seedlings grew. Early on, roots were colonized by fast-growing, saprotrophic Ascomycota, then later replaced by early stage ectomycorrhiza such as Wilcoxina. At the end, more competitive Suillus species dominated the host roots. Most of the major OTUs had negative or neutral correlation with T. matsutake, but several saprotrophic/plant pathogenic/mycoparasitic species in genera Fusarium, Oidiodendron, and Trichoderma had positive correlation with T. matsutake. Four keystone species were identified during succession; two species (Fusarium oxysporum, and F. trincintum) had a positive correlation with T. matsutake, while the other two had a negative correlation (Suillus granulatus, Cylindrocarpon pauciseptatum). These findings have important implications for further studies on the artificial cultivation of T. matsutake.

Effects of heavy metal pollution on germination and early seedling growth in native and invasive Spartina cordgrasses

Seed germination and seedling establishment are the stages most sensitive to abiotic stress in the plant life cycle. We analyzed the effects of copper, zinc and nickel on seed germination and early seedling growth of native Spartina maritima and invasive S. densiflora from polluted and non-polluted estuaries. Germination percentages for either species were not affected by any metal at any tested concentration (up to 2000 μM). However, the increase in metal concentration had negative effects on S. densiflora seedlings. The primary effect was on radicle development, representing initial seedling emergence. Spartina densiflora seedlings emerging from seeds from Tinto Estuary, characterized by high bioavailable metal loads, showed higher tolerance to metals than those from less polluted Odiel and Piedras Estuaries. Comparing our results to metal concentrations in the field, we expect S. densiflora seedling development would be negatively impacted in the most metal-polluted areas in Odiel and Tinto Estuaries.

Effects on Pinus densiflora Seedlings as Affected by Different Container Growth Conditions.

The purpose of this study was to determine the effects that different container conditions have on Pinus densiflora seedling growth. Under greenhouse cultivation, there were no statistical differences observed in plant height and the number of branches; however, significant differences in root collar diameter and root status were observed. In control container growth conditions, the roots grew in an abnormal spiral shape, while in negative phototropism container growth conditions the roots grew in a vertical shape. In outdoor cultivation, seedlings in various container growth conditions showed significant differences. The seedlings that were grown in negative phototropism container growth conditions showed the greatest increases in height, number of branches, root collar diameter, and root growth. This study determined that seedling roots in negative phototropism container growth conditions grew vertically, thus displaying successful rooting when they were transplanted outdoors. This resulted in favorable measurements in height, number of branches, root collar diameter, and root growth.

Bioactive properties of streptomyces may affect the dominance of Tricholoma matsutake in shiro

Tricholoma matsutake is known to be the dominant fungal species in matsutake fruitbody neighboring (shiro) soil. To understand the mechanisms behind matsutake dominance, we studied the bacterial communities in matsutake dominant shiro soil and non-shiro soil, isolated the strains of Streptomyces from matsutake mycorrhizal root tips both from shiro soil and from the Pinus densiflora seedlings cultivated in shiro soil. Further, we investigated three Streptomyces spp. for their ability to inhibit fungal growth and Pinus densiflora seedling root elongation as well as two strains for their antifungal and antioxidative properties.Our results showed that Actinobacteria was the most abundant phylum in shiro soil. However, the differences in the Actinobacterial community composition (phylum or order level) between shiro and non-shiro soils were not significant, as indicated by PERMANOVA analyses. A genus belonging to Actinobacteria, Streptomyces, was present on the matsutake mycorrhizas, although in minority. The two antifungal assays revealed that the broths of three Streptomyces spp. had either inhibitory, neutral or promoting effects on the growth of different forest soil fungi as well as on the root elongation of the seedlings. The extracts of two strains, including one isolated from the P. densiflora seedlings, inhibited the growth of either pathogenic or ectomycorrhizal fungi. The effect depended on the medium used to cultivate the strains, but not the solvent used for the extraction. Two Streptomyces spp. showed antioxidant activity in one out of three assays used, in a ferric reducing antioxidant power assay. The observed properties seem to have several functions in matsutake shiro soil and they may contribute to the protection of the shiro area for T. matsutake dominance.

Effects of imidazole-4-carboxamide and 2-azahypoxanthine on the growth and ectomycorrhizal colonization of Pinus densiflora seedlings inoculated with Tricholoma matsutake

Imidazole-4-carboxamide (ICA) and 2-azahypoxanthine (AHX) obtained from Lepista sordida inhibit and promote the growth of herbaceous plants, respectively. In this study, we examined the effects of these compounds on the growth and ectomycorrhizal (EM) colonization of Pinus densiflora seedlings inoculated with Tricholoma matsutake that forms EM associations with pines. The EM colonization by T . matsutake was observed on the root systems of P . densiflora seedlings treated with and without ICA and AHX. The growth of both non-EM and EM P . densiflora seedlings was inhibited by ICA, regardless of the EM colonization. In contrast, AHX promoted the growth of non-EM P . densiflora seedlings, but not of EM seedlings, suggesting that EM colonization interferes with the effect of AHX on P . densiflora growth. • Imidazole-4-carboxamide (ICA) and 2-azahypoxanthine (AHX) are bioactive compounds. • Tricholoma matsutake – Pinus densiflora ectomycorrhizal (EM) seedlings were tested. • Growth of both non-EM and EM P. densiflora seedlings was inhibited by ICA. • Growth of non-EM P. densiflora was promoted by AHX; EM seedlings were unaffected. • EM colonization interfered with the growth promotion of AHX on P. densiflora.

실외 실험적 온난화 및 강수 조절 하에서 토양 수분과 소나무 묘목의 생리 및 생장 반응 간의 관계

We investigated the changes in soil water and physiological and growth responses of Pinus densiflora seedlings under open‐field experimental warming and precipitation manipulation. In April 2013, we planted 2‐year‐old P. densiflora seedlings at 2 temperature levels (control, +3°C warmed) × 3 precipitation levels (control, ‐30% decreased, +30% increased) × 3 replicates (n=18). Soil water content (SWC), net photosynthetic rate (PSUBn/SUB), stomatal conductance (gSUBs/SUB), transpiration rate (E), intrinsic water use efficiency (iWUE), and total chlorophyll content (Tchl.) were measured in April, May, July, and August 2015, and the growth rate was calculated for April 2015‐March 2016. SWC significantly decreased by warming and precipitation manipulation. The rate of change in SWC was 12.17% under warming, but 5.13% and 6.53% under decreased and increased precipitation, respectively. PSUBn/SUB, gSUBs/SUB, and E decreased significantly by 17.09%, 18.25%, and 16.76% under warming, while only E changed by ‐5.29% and 20.28% under decreased and increased precipitation, respectively. There were no significant changes in iWUE or Tchl. by warming or precipitation manipulation. SWC was correlated with PSUBn/SUB, gSUBs/SUB, and E in April and May, and Pn in July, but was not correlated with any physiological properties in August. Seedling growth rates of root collar diameter and height were not changed despite the decrease in PSUBn/SUB related to warming. In this study, the effect of warming on physiological responses was greater than that of precipitation manipulation, and PSUBn/SUB decreased due to stomatal closure induced by soil water reduction under warming. These responses changed with seasonal environmental changes.

Abnormal Shoot Responses of Pinus densiflora Seedlings to Open-field Experimental Warming and Precipitation Manipulation

This study was conducted to investigate abnormal shoot responses in Pinus densiflora seedlings to open-field warming and precipitation manipulation. In May 2017, 18 plots (2 temperature levels × 3 precipitation levels × 3 replicates) were constructed and 90 seedlings of 1-year-old P. densiflora were planted in each plot. The temperature in the temperature warming (TW) plots was set to 3℃ higher than that in the temperature control (TC) plots, and precipitation was set to decrease (PD) or increase (PI) by 40% compared to the precipitation control (PC) plots. The manipulation experiment started in June, 2017. The abnormal shoot occurrence rates in September and November, 2017; seedling number in each needle length growth stage in September, 2017; and length of abnormal shoots in November, 2017 were measured. Warming significantly increased the occurrence rate and developed the needle length growth stage of abnormal shoots in P. densiflora seedlings, whereas precipitation and interaction effects between the two treatments were not significant. The mean occurrence rates in September and November were 86.17 ± 11.80% and 90.78 ± 7.92% in the TW plots and 58.59 ± 16.13% and 64.80 ± 14.71% in the TC plots, respectively. Thus, the abnormal conditions derived from increased temperature stimulated the occurrence of abnormal shoots. Warming also elongated the needle length of the abnormal shoots, which might affect future photosynthesis. However, there was no significant difference in abnormal shoot length under warming and precipitation manipulation. Thus, warming stimulated the occurrence and needle development of abnormal shoots in P. densiflora seedlings, which could lead to the inhibition of subsequent growth by the use of reserved nutrients and degradation of seedling quality.

Species specific physiological responses of Pinus densiflora and Larix kaempferi seedlings to open-field experimental warming and precipitation manipulation

Physiological responses of 1-year-old Pinus densiflora and Larix kaempferi seedlings were measured under open-field warming and precipitation manipulation. Air temperature of warming plots was 3 °C higher, while precipitation manipulation plots received ±40% of the precipitation than control plots. Seedlings were planted in May, and temperature and precipitation were manipulated from June 2017. Total chlorophyll content (Chlt), net photosynthetic rate (Pn), transpiration rate (E), and stomatal conductance (gs) were measured between July and September 2017. For P. densiflora and L. kaempferi, Chlt increased by 11.75% and 11.64%, and Pn decreased by 9.14% and 2.17% under warming, respectively. E and gs were lower under warming in P. densiflora, but higher in L. kaempferi. The lower Pn in P. densiflora resulted from stomatal closure, while that of L. kaempferi resulted from reduced vitality. Lower precipitation increased Chlt and Pn by 11.64% and 2.66% for P. densiflora, and by 6.40% and 4.32% for L. kaempferi, respectively. Conversely, higher precipitation decreased Pn of P. densiflora by 5.72%, and decreased Chlt and Pn of L. kaempferi by 8.24% and 4.55%, respectively. These results can be attributed to concentrated precipitation. In this study, two species responded differently even when they were exposed to the same environmental conditions, and this was due to the species-specific mechanisms to water stress derived from the high temperature.

Influence of Ectomycorrhizal Colonization on Cesium Uptake by Pinus densiflora Seedlings

Radionuclides were deposited at forest areas in eastern parts of Japan following the Fukushima Daiichi Nuclear Power Plant incident in March 2011. Ectomycorrhizal (EM) fungi have important effects on radiocaesium dynamics in forest ecosystems. We examined the effect of colonization by the EM fungus Astraeus hygrometricus on the uptake of cesium (Cs) and potassium (K) by Pinus densiflora seedlings. Pine seedlings exhibited enhanced growth after the EM formation due to the colonization by A. hygrometricus. Additionally, the shoot Cs concentration increased after the EM formation when Cs was not added to the medium. This suggests that A. hygrometricus might be able to solubilize Cs fixed to soil particles. Moreover, the shoot K concentration increased significantly after the EM formation when Cs was added. However, there were no significant differences in the root K concentration between EM and non-EM seedlings. These results suggest that different mechanisms control the transfer of Cs and K from the root to the shoot of pine seedlings.