A new perspective on structural characterisation and immunomodulatory activity of arabinogalactan in Larix kaempferi from Qinling Mountains

In this study, crude polysaccharide (LAG-C) and homogeneous arabinogalactan (LAG-W) were isolated from Qinling Larix kaempferi of Shaanxi Province. Bioactivity assays showed that LAG-W and LAG-C enhanced the phagocytic ability, NO secretion, acid phosphatase activity, and cytokine production (IL-6, IL-1β, and TNF-α) of RAW264.7 macrophages. Notably, LAG-W exhibited a significantly stronger immunomodulatory effect than LAG-C. The primary structure of LAG-W was characterised by chemical methods (monosaccharide composition, methylation analysis, and alkali treatment) and spectroscopic techniques (gas chromatography-mass spectrometry, high-performance liquid chromatography-mass spectrometry, and 1D/2D nuclear magnetic resonance). LAG-W was identified as a 22.08 kilodaltons (kDa) neutral polysaccharide composed of arabinose and galactose at a 1:7.5 molar ratio. Its backbone consisted of repeated →3)-β-Galp-(1→ residues. Side chains, connected at the O-6 position, were mainly composed of T-β-Galp-(1→ and T-β-Galp-(1→6)-β-Galp-(1→ residues. And it also contained small amounts of T-β-Arap-(1→, T-α-Araf-(1→6)-β-Galp-(1→6)-β-Galp-(1→, and T-α-Araf-(1→3)-α-Araf-(1→6)-β-Galp-(1→ residues. By structurally and functionally characterising L. kaempferi polysaccharides, this study opens the way for the valorisation of this species.

Phylogeny and expression patterns of ERF genes that are potential reproductive inducers in hybrid larch

BACKGROUND

Larch is an important component of northern forests and a major cultivated tree species in restoration of forest cover using improved seed material. In recent years, the continuous low seed production has severely affected the production of improved variety seedlings and natural regeneration. However, research on the reproductive growth of gymnosperms is extremely scarce.

RESULTS

In this study, based on differential transcriptome analysis of two asexual reproductive phases, namely high-yield and low-yield, we further screened 5 ERF family genes that may affect the reproductive development of larch. We analyzed their genetic relationships and predicted their physicochemical properties. The expression patterns of these genes were analyzed in different tissues, developmental stages, hormone treatments, and environmental conditions in hybrid larch.

CONCLUSION

The results showed that all 5 genes were induced by low temperature and ABA, and their expression patterns in different tissues suggested a suppressive role in the development of female cones in larch. Among them, LkoERF3-like1 and LkoERF071 may be involved in the flowering age pathway. This study enriches the scarce research on reproductive development in gymnosperms and provides a theoretical basis and research direction for regulating the reproductive development of larch in seed orchards.

pollination and germination

The involvement of Ca2+ ions in angiosperms sexual processes is well established, while in gymnosperms, such knowledge remains limited and is still a topic of discussion. In this study, we focused on Larix decidua, using Alizarin-red S staining and the pyroantimonate method to examine the tissue and subcellular distribution of free and loosely bound Ca2+ ions at different stages of the male gametophyte's development and its interaction with the ovule. Our findings show that in larch, both the germination of pollen grains and the growth of pollen tubes occur in an environment rich in Ca2+. These ions play a crucial role in the adhesion of the pollen grain to the stigmatic tip and its subsequent movement to the micropylar canal. There is a significant presence of free and loosely bound Ca2+ ions in both the fluid of the micropylar canal and the extracellular matrix of the nucellus. As the pollen tube extends through the nucellus, we observed a notable accumulation of Ca2+ ions just above the entry to the mature archegonium, a region likely crucial for the male gametophyte's directional growth. Meanwhile, the localized presence of free and loosely bound Ca2+ ions within the egg cell cytoplasm may inhibit the pollen tubes growth and rupture, playing an important role in fertilization.

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.

Higher latewood to earlywood ratio increases resistance of radial growth to severe droughts in larch

As drought has caused great losses of tree growth across the world, the mechanism of how trees adapt to drought has been extensively investigated. However, how trees change their late- to earlywood ratio (LER) to adapt to severe drought events remains poorly understood. We used a network of Larix principis-rupprechtii earlywood and latewood width data from 1979 to 2018, covering most of the distribution of planted larch across North China, to investigate how latewood proportion affected trees' resistance to drought. The interactions among LER, minimum temperature, vapor pressure deficit (VPD), growing season length, and their contributions to drought resistant (Rt) were estimated using structural equation models. The results show a significant increase in LER of the juvenile wood throughout the first 15 growth rings after which it stabilizes. The LER decreased significantly with elevation for the juvenile wood. March-May temperature and VPD were the main determinant in the LER of mature wood. The sensitivity of radial growth to droughts was positively changed with LER when LER was below 0.50, but negatively changed with LER when LER is above 0.50. We confirmed that high LER increases resistance of tree growth to severe droughts in L. principis-rupprechtii. Our results highlight that a higher proportion of latewood is formed in dry years, and this high drought sensitivity of LER in turn led to an increased resistance to drought. This combination of reduced radial growth during dry years, while the latewood proportion remains increases maybe an adaptive strategy of larch trees to cope with severe droughts.

plantations in northeast China

Planted forests play a crucial role in addressing global climate change and are also valued globally for their numerous ecosystem services. Therefore, it is essential to understand how biotic and abiotic factors affect the carbon sequestration potential. This study focuses on quantifying the effects of 26 different variables on the carbon sequestration potential of Larix spp. plantations in northeast China, utilizing the random forest algorithm (RF). To eliminate the age-related tendency of stand carbon stock, a novel carbon sequestration index (CSI) was defined, which measures the ratio of actual to predicted stand carbon stocks for a stand at a specific age. The results indicated that the developed RF model explained approximately 64.75 % of the variations of CSI. Among the four categories of variables analyzed, stand variables (35.73 %) contributed significantly more than terrain variables (3.31 %), soil variables (3.68 %), and climate variables (9.06 %). The partial dependence analysis revealed that the Larix spp. plantations had a potential maximum carbon stock of approximately 73.34 t·ha-1. This potential was associated with certain attributes, including a stand mean diameter of 15 cm, a stand density of 1700 trees·ha-1, a stand basal area of 30 m2·ha-1, and a crown density of 0.7, respectively. These findings provide insightful information for plantation management to improve stand carbon stocks in northeast China with attempting to mitigate climate change.

Host-specific growth responses of Larix kaempferi and Quercus acutissima to Asian gypsy moth defoliation in central Korea

As the risk of gypsy moth outbreaks that have detrimental effects on forest ecosystem in the Northern Hemisphere increase due to climate change, a quantitative evaluation of the impact of gypsy moth defoliation is needed to support the adaptive forest management. To evaluate the host-specific impact of gypsy moth defoliation, radial growth and annual carbon accumulation were compared for one severely defoliated (Larix kaempferi (Lamb.) Carrière) and one moderate defoliated (Quercus acutissima Carruth.) host, in defoliated and non-defoliated site using tree-ring analysis. Finally, the resilience indices of radial growth variables were calculated to assess the ability of sampled trees to withstand defoliation. Gypsy moth defoliation mainly decreased latewood width and caused reduction in annual carbon absorption more than 40% for both tree species. However, L. kaempferi, showed the reduced growth until the year following defoliation, while Q. acutissima, showed no lagged growth depression and rapid growth recover. The findings show how each species reacts differently to gypsy moth defoliation and highlight the need of managing forests in a way that takes resilient tree species into account.

Transitional responses of tree growth to climate warming at the southernmost margin of high latitudinal permafrost distribution

The marked increase in temperature warming and permafrost degradation has raised apprehensions about the fate of forests of boreal forests in permafrost regions. However, the impact of climate on tree growth is not limited to direct effects but also involves complex interactions with permafrost. The degradation of permafrost poses a threat to forest growth that has received insufficient attention thus far, after analyzing the impact of permafrost degradation and climate on Dahurican larch (Larix gmelinii) growth from six forest sites with two maximum active layer thickness (ALT) classifications (more and less than tree root length) across the southern margin of the permafrost region. We found that accompanying the continued degradation of permafrost, tree growth was inhibited (slope = -0.67, p < 0.05) by the degradation of permafrost and the growth-climate relationship was shifted from positive to negative at maximum ALT less than tree root length sites. However, the growth rate of trees significantly accelerated (slope = 5.46, p < 0.05) at maximum ALT more than tree root length sites. Path analysis indicated that tree growth did not benefit from temperature warming and more stress could be caused by waterlogging due to permafrost degradation at maximum ALT less than tree root length sites, however, enhanced tree growth primarily by reducing the physical spatial constraints and root layer additional water source with permafrost degradation at maximum ALT more than tree root length sites. It also implies that the matchiness between tree root and maximum active layer depth is critical to the effect of permafrost degradation on tree growth. The transitional response to climate warming and the opposite trend of tree growth at two ALT classification sites suggest that future tree growth responds to the different stages of permafrost degradation differently. Our study provides a new insight on permafrost degradation impact on tree growth.

Contrasting growth responses to drought in three tree species widely distributed in northern China

Tree species-specific responses to drought are urgently needed for assessing the impacts of current climate change on forest ecosystems. Here, we characterized the resistance, recovery, resilience, and growth recovery periods in response to different drought events based on tree-ring width index data (>30 years) for three tree species widely distributed in northern China, among which larch (Larix principis-rupprechtii Mayr) and Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) are two major species used for afforestation, and birch (Betula platyphylla Suk.) is one of the most common natural tree species. Despite no significant effects of mild drought on tree growth, severe drought events significantly reduced the growth of all species, with contrasting species-specific responses. Larch trees had the lowest resistance and resilience among the three species, and Mongolian pine trees were more resistant but had a longer recovery period than birch trees. The drought responses varied with tree size. Large Mongolian pine and birch trees were more resistant but large larch trees were much more vulnerable than small trees during severe droughts. Smaller birch trees had higher resilience to severe droughts. Our study shows species-specific differences in drought responses and suggests that drought responses are tree-size dependent and drought-intensity associated, which further provides a guidance for selecting optimal cultivated tree species and designing forest managements in this region.

H2O2 Significantly Affects Larix kaempferi × Larix olgensis Somatic Embryogenesis

Larch is widely distributed throughout the world and is an important species for timber supply and the extraction of industrial raw materials. In recent years, the hybrid breeding of Larix kaempferi and Larix olgensis has shown obvious heterosis in quick-growth, stress resistance and wood properties. However, its growth and development cycle is too long to meet general production needs. In order to shorten the breeding cycle, we have for the first time successfully established and optimized a somatic embryogenesis system for Larix kaempferi × Larix olgensis. We found that the highest rate of embryonal-suspensor mass (ESM) induction was observed when late cotyledonary embryos were used as explants. The induced ESMs were subjected to stable proliferation, after which abscisic acid (ABA) and polyethylene glycol (PEG) were added to successfully induce somatic embryos. Treatment with PEG and ABA was of great importance to somatic embryo formation and complemented each other's effect. ABA assisted embryo growth, whereas PEG facilitated the formation of proembryo-like structures. On top of this, we studied in more detail the relationship between redox homeostasis and the efficiency of somatic embryogenesis (frequency of ESM induction). During subculture, we observed the gradual formation of three distinct types of ESM. The Type I ESM is readily able to form somatic embryos. In contrast to type I, the type III ESM suffers from severe browning, contains a higher level of hydrogen peroxide (H2O2) and demonstrates a decreased ability to form somatic embryos. External treatment with H2O2 decreased the somatic embryogenesis efficiency of Type I and type III ESMs, or the higher the exogenous H2O2 content, the lower the resulting somatic embryogenesis efficiency. We found that treatment with the H2O2 scavenger DMTU (dimethylthiourea) could significantly increase the somatic embryogenesis efficiency of the type III ESM, as a result of a decline in endogenous H2O2 content. Overall, these findings have contributed to setting up a successful somatic embryogenesis system for larch production.

Anatomical and morphological changes in Pinus sylvestris and Larix sibirica needles under impact of emissions from a large aluminum enterprise

Species-specific anatomical and morphological characteristics of Pinus sylvestris and Larix sibirica needles were studied at different levels of tree stand pollution by aluminum smelter emissions. The anatomical characteristics of the needle were studied using light microscopy. The level of tree stand pollution was determined using the cluster analysis outcomes of the pollutant elements content (fluorine, sulfur, and heavy metals) in the needles. Four levels of tree stand pollution were separated: low, moderate, high, and critical, as well as background tree stand in unpolluted areas. It was found that the state of tree phytomass deteriorated with increasing levels of pollution (from low to critical): pine crown defoliation increased to 85%, and larch defoliation increased to 65%. The life span of pine needles was reduced to 2-3 years, with a background value of 6-7 years. The change of morphological parameters was more pronounced in P. sylvestris: the weight and length of the 2-year-old shoot decreased by 2.7-3.1 times compared to the background values; the weight of needles on the shoot and the number of needle pairs on the shoot-by 1.9-2.1 times. The length of the needle and shoot and the number of L. sibirica brachyblasts decreased by 1.8-1.9 times. The anatomical parameters of the needle also changed to a greater extent in P. sylvestris. Up to the high level of tree pollution, we observed a decrease in the cross-sectional area of the needle, central cylinder, vascular bundle, area and thickness of mesophyll, number and diameter of resin ducts by 18-66% compared to background values. At the critical pollution level, when the content of pollutant elements in pine needles reached maximum values, the anatomical parameters of the remaining few green needles were close to background values. In our opinion, this may be due to the activation of mechanisms aimed at maintaining the viability of trees. A reduction in thickness and area of assimilation tissue in the L. sibirica needle was detected only at the critical pollution level. An upward trend in these parameters was found at low, medium, and high pollution levels of tree stand, which may indicate an adaptive nature. The results suggested that at a similar pollution level of trees, the greatest amount of negative anatomical and morphological changes were recorded in pine needles, which indicates a greater sensitivity of this species to technogenic emissions.

to environmental stress caused by tailings waste highly contaminated by trace elements

The seedlings of some tree species can successfully develop in areas polluted by heavy metals. Research on such species is important in order to explore the possibility of introducing tree species for the permanent biological stabilization and reclamation of post-flotation tailings, especially after the final recycling of trace metals, but where concentrations remain much higher than in natural soils. To better understand the adaptation and reaction of Betula pendula Roth., Pinus sylvestris L., and Larix decidua Mill. seedlings to heavy metals pollution caused by tailings waste highly contaminated by trace elements: 1) the relationships between the concentration of heavy metals in the soil substrate, the efficiency of heavy metal ions accumulation in plant organs, and the biometric parameters of the seedlings; and 2) the threshold content of heavy metals in the roots above which the plant physiological response is triggered was determined. We assume that there are certain limit concentrations of heavy metals in the soil and fine roots, which depend on the tree species and beyond which the plant responds strongly to stressThe obtained results showed that Betula is a suitable species for the phytostabilization of post-flotation tailings due to its rapid growth rate and production of root biomass. The accumulation of metals in Betula roots was found to be much greater than in Pinus and Larix. Despite the high concentrations of heavy metals in the prepared substrates, there was only a slight transfer of these elements to the aboveground parts of the plant. At high soil concentrations, the heavy metals adversely affected the cellular and physiological processes of plants. In plants growing in such conditions, the activity of the antioxidant system depended both on the species and organ of the plant, as well as on the type and metal concentration.

UAV Photogrammetry for Estimating Stand Parameters of an Old Japanese Larch Plantation Using Different Filtering Methods at Two Flight Altitudes

Old plantations are iconic sites, and estimating stand parameters is crucial for valuation and management. This study aimed to estimate stand parameters of a 115-year-old Japanese larch (Larix kaempferi (Lamb.) Carrière) plantation at the University of Tokyo Hokkaido Forest (UTHF) in central Hokkaido, northern Japan, using unmanned aerial vehicle (UAV) photogrammetry. High-resolution RGB imagery was collected using a DJI Matrice 300 real-time kinematic (RTK) at altitudes of 80 and 120 m. Structure from motion (SfM) technology was applied to generate 3D point clouds and orthomosaics. We used different filtering methods, search radii, and window sizes for individual tree detection (ITD), and tree height (TH) and crown area (CA) were estimated from a canopy height model (CHM). Additionally, a freely available shiny R package (SRP) and manually digitalized CA were used. A multiple linear regression (MLR) model was used to estimate the diameter at breast height (DBH), stem volume (V), and carbon stock (CST). Higher accuracy was obtained for ITD (F-score: 0.8-0.87) and TH (R2: 0.76-0.77; RMSE: 1.45-1.55 m) than for other stand parameters. Overall, the flying altitude of the UAV and selected filtering methods influenced the success of stand parameter estimation in old-aged plantations, with the UAV at 80 m generating more accurate results for ITD, CA, and DBH, while the UAV at 120 m produced higher accuracy for TH, V, and CST with Gaussian and mean filtering.

Seasonal occurrence of bark and woodboring Coleoptera in stands of Pinus densiflora (Pinales: Pinaceae) and Larix kaempferi (Pinales: Pinaceae) and monitoring method using multifunnel traps baited with pine volatiles

This study investigated the seasonal occurrence of bark and woodboring Coleoptera in Pinus densiflora (Pinales: Pinaceae), and Larix kaempferi (Pinales: Pinaceae) stands using multifunnel traps baited with pine volatiles in Korea. The number and species of bark and woodboring beetles caught in traps baited with ethanol, α-pinene, and ethanol+α-pinene were compared to determine the effective attractants. In addition, the effects of other pine volatiles, such as (-)-β-pinene, β-caryophyllene, (±)-limonene, β-myrcene, and 3-carene, were investigated. A total of 13,134 woodboring beetles from 150 species were collected from pine and larch stands from 2019 to 2020. Tomicus minor (Hartig) (Coleoptera: Curculionidae) adults were more attracted to traps baited with α-pinene, whereas Xyleborinus saxesenii (Ratzeburg) (Coleoptera: Curculionidae), Cyclorhipidion pelliculosum (Eichhoff) (Coleoptera: Curculionidae), and Phloeosinus pulchellus (Blandford) (Coleoptera: Curculionidae) adults were more attracted to traps baited with ethanol. Hylurgops interstitialis (Chapuis) (Coleoptera: Curculionidae), Shirahoshizo genus group, Rhagium inquisitor (Linne) (Coleoptera: Cerambycidae), and Rhadinomerus maebarai (Voss & Chûjô) (Coleoptera: Curculionidae) were more frequently attracted to traps baited with ethanol+α-pinene than to traps baited with other attractants. The addition of 3-carene to ethanol+α-pinene enhanced the capture of H. interstitialis, R. inquisitor, and Hylobius (Callirus) haroldi (Faust) (Coleoptera: Curculionidae).

Diversity and negative effect of PM0.3-10.0 adsorbed by needles of urban trees in Irkutsk, Russia

The study was performed in natural forests preserved within the Boreal zone city, Irkutsk, Russia. Test sites were selected in the forests in different districts of the city, where samples of Scots pine (Pinus sylvestris L.) and Siberian larch (Larix sibirica Ledeb.) needles were taken to study the adsorption on their surface of aerosol particles of different sizes, in microns: PM0.3, PM0.5, PM1, PM2.5, PM5, PM10. Scanning electron microscopy was used to obtain high-resolution photographs (magnification 800- × 2000, × 16,000) and aerosol particles (particulate matter-PM) were shown to be intensively adsorbed by the surface of needles, with both size and shape of the particles characterized by a wide variety. Pine needles can be covered with particles of solid aerosol by 50-75%, stomata are often completely blocked. Larch needles often show areas, which are completely covered with aerosol particles, there are often found stomata deformed by the penetration of PMx. X-ray spectral microanalysis showed differences in the chemical composition of adsorbed PMx, the particles can be metallic if metals predominate in their composition, carbonaceous-in case of carbon predominance-or polyelemental if the composition is complex and includes significant quantities of other elements besides metals and carbon (calcium, magnesium, potassium, sodium, sulfur, chlorine, fluorine). Since the particles contain a large proportion of technogenic pollutants, accumulation by the needles of some widespread pollutants was investigated. A direct correlation of a highly significant level between the concentration of PMx in the air and the accumulation of many heavy metals in pine and larch needles, as well as sulfur, fluorine, and chlorine, has been revealed, which indicates a high cleaning capacity of urban forests. At the same time, the negative impact of PMx particles on the vital status of trees is great, which shows in intense disturbance of the parameters of photosynthesis and transpiration, leading to a significant decrease in the growth characteristics of trees and reduction in the photosynthetic volume of the crowns. We consider that the results obtained are instrumental in developing an approach to improvement of urban forests status and creating a comfortable urban environment for the population.

Distribution characteristics of mercury concentration and estimation of mercury pools in different age groups of Larix gmelinii forests of Daxing'an Mountain

Forests are important sinks of atmospheric mercury. Quantifying mercury pools in forest ecosystem tissues are essential for understanding the global mercury cycle. To reveal the characteristics of Hg concentration and Hg pool distribution in natural forests at different ages, samples from the vegetation layer, organic horizons, coarse wood debris, and mineral soil layers were collected in young forest, middle forest, near-mature forest, and mature forest of Larix gmelinii forests at the Daxing'an Mountain. The results showed that there were differences in the absorption and accumulation of Hg by different tree species and tissues. In Larix gmelinii, the concentration of Hg followed the order of bark > branch > leaf > root > core, whereas in Betula platyphylla, the order was bark > leaf > branch > root > core. The mercury concentration in the organic horizons increased gradually with the decomposition process. There were no obvious regular patterns in the mercury concentrations of each tissue in different age groups Larix gmelinii forests. Furthermore, total biomass mercury pools (overstory, shrub layer, herb layer, moss layer, and coarse woody debris （CWD）) in the young, middle, near-mature, and mature forests of Larix gmelinii forests at Daxing'an Mountain were estimated to be 99.0 μg m-2，207 μg m-2，207 μg m-2 and 194 μg m-2, respectively. On ecosystem scale, total mercury pools were 16.9 mg m-2 (young), 27.5 mg m-2 (middle), 17.0 mg m-2 (near-mature), and 11.8 mg m-2(mature). The mineral soil mercury pool accounts for 94.0%-98.1% of the total ecosystem mercury pool, and its mercury pool proportion gradually decreased with the increase in forest age. These obtained results are quite valuable for further assessing the role of forest ecosystems in the atmospheric mercury cycle and estimating potential mercury emissions from biomass burning during forest wildfires.

Tree rings as historical archives of atmospheric mercury: A critical review

Historical concentrations of atmospheric mercury (Hg) are uncertain, as monitoring only began a few decades ago. Tree rings can serve as historical archives of Hg, providing centennial trends. The vast majority of tree-ring Hg studies have been published in the last decade, demonstrating the growing use of tree rings for Hg dendrochemistry. Thus, there is a need for a systematic review on current knowledge of tree rings as archives of atmospheric Hg. In this review, the predominant pathways of Hg uptake to tree rings are discussed, including the initial Hg uptake from the surrounding environment, fixation, and subsequent translocation. Foliar uptake of Hg was found to be the most important uptake route for Hg in tree rings, the root and bark route being negligible. Our summary of the suitability of different tree species indicates that radial translocation is the biggest limiting factor for Hg dendrochemistry, shifting and blurring historical Hg trends. Based on the review findings, Picea (spruce) and Larix (larch) are the most promising genera for Hg dendrochemistry. Additionally, the use of tree-ring Hg archives in combination with other co-located archives, namely lake sediments, peat, and ice, is suggested as it enhances the viability of observed tree-ring historical Hg trends. Finally, we propose future directions and recommendations for research using tree-ring Hg, including sampling protocols, experimental designs, and tree selection.

Construction of universal equations for knot attributes of three coniferous species

We constructed base model, dummy variable model, and mixture model with three variables including knot diameter, loose knot length, and sound knot length with three typical coniferous species, Pinus koraiensis, Larix olgensis, and Pinus sylvestris var. mongolica, from the Linkou Forestry Bureau and Mengjiagang forest farm in Heilongjiang Province in 2020. We analyzed the differences in knot properties among different tree species and simplified the modeling work. Firstly, we collected relevant knot property data through the sectioning method based on relevant literature, transformation of the model form and substitution of related variables to conduct a base model. We transformed the species into dummy variables as qualitative factors, and introduced the dummy variable model of the relevant attributes into the base model. We introduced the random effects of sample trees and sample plots when constructing the mixture model. By comparing evaluation indicators, such as Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC), the mixture model with the best fitting effect was selected. We selected the optimal universal equation by comparing the fitting accuracy of the base model, dummy variable model and mixture model. The fitting accuracy of the dummy variable model and mixture model was higher than that of the basic model. The evaluation indicators (AIC and BIC) showed that the mixture model had a better fitting effect on knot properties than the dummy variable model. In the model comparison results, R2 of mixture models for sound knot length, the loose knot length, and knot diameter increased by 13.2%, 84.8% and 40.3%, respectively. The predictive accuracy of the three base models for different tree species' knot attributes was above 90%, and both the prediction accuracy of the dummy variable model and mixture model were above 94%, indicating that the constructed models could well predict knot-related properties. From the perspective of tree species, the sound knot length, knot diameter, and loose knot length was in order of P. sylvestris var. mongolica > P. koraiensis > L. olgensis. Fitted results of the dummy variable model and the mixture model were superior to the basic model, with higher accuracy.

Comparative analysis of microbial community structure in different times of Panax ginseng Rhizosphere microbiome and soil properties under larch forest

BACKGROUND

Panax ginseng cultivated under the forest is popular because its shape and effective ingredients are similar to wild ginseng. The growth of P. ginseng in the larch forest is generally better than in the broad-leaved forest, and the incidence rate of diseases is low. Therefore, the selection of forest species is one of the basic factors in the successful cropping of P. ginseng.

METHODS

Illumina HiSeq high-throughput sequencing was used to analyze the 16S rRNA/ITS gene sequence of P. ginseng rhizosphere soil under larch forest to study the rhizosphere microbiome's diversity and community composition structure.

RESULTS

The species classification and richness of rhizosphere bacterial and fungal communities in the same-aged P. ginseng were similar. Consistent with the soil system of commonly cultivated crops, Proteobacteria, Actinobacteriota, Acidobacteriota, Verrucomicrobiota, Chloroflexi, and Basidiomycota, Ascomycota were the dominant phylum of bacteria and fungi, respectively. Compared with the soil without planting P. ginseng, the diversity of microorganisms and community structure of continuous planting for 2 years, 5 years, and 18 years of P. ginseng rhizosphere soil had little change. The accumulation levels of Ilyonectria, Fusarium, Gibberella, and Cylindrocarpon were not significantly increased with planting P. ginseng and the increased age of cropping P. ginseng.

CONCLUSIONS

The results of this study showed that the soil function of the larch forest was good, which provided a theoretical basis for the land selection and soil improvement of cultivating P. ginseng under the larch forest.

Height-diameter models of regenerated saplings of Larix gmelinii based on dummy variable and quantile regression

Based on data collected from 2054 saplings of Larix gmelinii forest in 55 fixed plots in 2018-2019 in Cuigang Forestry Station, Daxing'anling area, we classified the stand density index (SDI) into four classes, i.e., Class Ⅰ (SDI1<1863 plants·hm-2), Class Ⅱ (1863 plants·hm-2≤SDI2<2155 plants·hm-2), Class Ⅲ (2155 plants·hm-2≤SDI3<2459 plants·hm-2) and Class Ⅳ (SDI4≥2459 plants·hm-2) by using the quartile method. We constructed a dummy variable model and quantile regression model for the height-breast diameter of saplings of L. gmelinii with dummy variable method introduced SDI. The results showed that among the five selected representative non-linear tree height curve models, the Richards model fitted the best, with Ra2, RMSE and MAE of 0.7637, 0.8250 m and 0.5696 m. The dummy variable model including the SDI constructed based on the Richards model showed a 1.3% increase in Ra2 compared with the base model, while RMSE, MAE, and AIC decreased by 2.1%, 1.5%, and 11.2%, respectively. When the quantile τ was 0.5, Ra2 of quantile regression model was the maximum, and RMSE, MAE, AIC was the minimum, being 0.7612, 0.8294 m, 0.5657 m, and -767.19, respectively. Compared with SDI1, sapling height in SDI2-SDI4 was increased by 5.6%, 5.6%, and 11.3%, suggesting reasonable that regulation of stand density was conducive to increase the height growth of saplings in regeneration.

Compatibility predictive model for regeneration quantities of Larix gmelinii natural forest in Daxing'anling Mountains, China

The natural regeneration grade is an important foundation for formulating forest management measures. Traditional studies have only considered the regeneration quantities predictive model of the total stand or dominant tree species, but the consistency among the prediction results of different tree species and the total regeneration quantities of stand is not solved. That is, the regeneration prediction results at the stand level are not equal to the sum of the predicted results of all tree species. To address this, on the basis of the traditional counting model, we attempted to construct a compatibility predictive model for regeneration quantities of different tree species within the stand, which would provide a theoretical basis for the rational management and decision-making of natural forest. Based on the survey data from 96 standard plots of Cuigang Forest Farm, Xinlin Forest Farm, and Zhuangzhi Forest Farm in Daxing'an Mountains, we selected 30 basic indices from five aspects of site factor, soil factor, stand factor, tree diversity and stand spatial structure, and used Poisson model and negative binomial model as the basic models to construct the regeneration prediction models of Larix gmelinii, Betula platyphylla and other tree species. By comparing the accuracy and fitting effect of the two traditional counting models, we selected the optimal model and used the seemingly unrelated regressions to further construct the compatibility predictive model for regeneration quantities of different tree species. Poisson model was the best one for the regeneration of L. gmelinii, B. platyphylla, and other tree species. The test index RMSE of the compatibility predictive model for regeneration quantities of L. gmelinii, B. platyphylla, other tree species and total stand regeneration quantities were 388, 413, 504, and 871 trees·hm-2, respectively. The adjusted R2 was 0.389, 0.421, 0.488, and 0.407, respectively. The most influential variables for regeneration quantities of L. gmelinii, B. platyphylla and other tree species were Pielou evenness index of DBH (25.2%), herbal coverage (34.6%) and organic matter in B layer (23.2%). In this study, the compatibility predictive model system for regeneration quantities satisfied the additive logic among L. gmelinii, B. platyphylla, other tree species, and total stands, and provided a basis for accurately estimating natural regeneration.

Potential factors promoting the natural regeneration of Larix principis-rupprechtii in North China

Natural regeneration plays an important role in species diversity and evolution. Exploring the causes of variation in regeneration dynamics can provide key insights into the factors affecting regeneration. However, the relationship between the regeneration of Larix principis-rupprechtii and environmental factors in North China has remained unexplored. In this study, 14 plots were established based on the three extents of regenerated plant numbers in Shanxi Province. Redundancy analysis determined that environmental factors (topography, stand structure, soil property, and litter) affected natural regeneration. Structural equation modeling identified the most important direct and indirect factors that affected L. principis-rupprechtii natural regeneration. Litter thickness, canopy density, and adult tree diameter at breast height were positively correlated with natural regeneration. Aspect and total nitrogen volume were negatively associated with natural regeneration. Additionally, there was no significant correlation between natural regeneration and other environmental factors (altitude, slope, adult tree height, stand density, soil water content, SOC, total P, available N, available P, or soil enzyme). Further artificial intervention measures should be considered to promote plantation regeneration. These findings provide an effective basis for future forest restorations and sustainable management.

Effect of gap size on the regeneration in Larix principis-rupprechtii plantation

We conducted a survey on seedlings (height <1 m) and saplings (height ≥1 m, diameter at breast height <5 cm) in 20 gaps of Larix principis-rupprechtii plantations on Guandi Mountains, Shanxi to analyze regene-ration density, growth indicators, and spatial distribution of L. principis-rupprechtii seedlings and saplings under four gap sizes (<60 m2, 60-120 m2, 120-180 m2, and ≥180 m2). The results showed that growth indicators (ground diameter, height) of seedlings and saplings and regeneration density of seedlings were highest in small gaps (14-60 m2). The sapling regeneration density was highest in medium gaps (60-120 m2), and sapling density exceeded seedling density in each size category. L. principis-rupprechtii seedlings and saplings exhibited favorable regeneration in small and medium gaps, while large gaps (120-180 m2) and extra-large gaps (≥180 m2) were unfavorable for L. principis-rupprechtii regeneration. L. principis-rupprechtii seedlings and saplings were mainly distributed within the canopy projection area and along the edge of canopy gap area. Controlling gap size within the range of 14-120 m2 through artificial interventions, such as planting and thinning, could promote the regeneration of L. principis-rupprechtii.

Provenance variation of root C, N, P, and K stoichiometric characteristics under different diameter classes of Larix gmelinii

For exploring the difference of root stoichiometric characteristics among diameter classes and provenances, we examined the contents and stoichiometric ratios of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) in three diameter classes of roots (0-1, 1-2 and 2-5 mm, respectively) of 39-year-old Larix gmelinii grown in a common garden. The results showed that root element contents and their stoichiometric ratios had significant difference among three diameter classes of roots. C content, C:N, C:P, C:K were the lowest, and N, P, K contents, N:P, and N:K were the highest in 0-1 mm diameter class roots. Compared with the 1-2 and 2-5 mm diameter class roots, 0-1 mm diameter class roots had different seasonal dynamics, which might be caused by the fact that 0-1 mm diameter class roots are absorptive roots and the other diameter class roots are transport roots. There was no provenance difference in C content among all diameter class roots, while significant provenance differences were found in N, K contents, C:N, and C:K in 0-1 mm diameter class roots, and great provenance differences for in P content, C:P, N:P, and N:K in 0-1 and 1-2 mm diameter class roots. N content, K content, C:P, N:P, and N:K in 0-1 mm diameter class roots had positive correlation with the aridity index of seed-source sites, while the P content, C:N and C:K had negative correlations. The stoichiometric characteristics were related with the diameter (or function) of roots, and had significant provenance differences in 0-1 mm (absorptive root) and 1-2 mm diameter class roots, which might be attributed to their genotypic adaptation to the environment of seed-source sites.

Differences in ecological resilience of radial growth between Larix principis-rupprechtii and Picea meyeri after drought

To understand the responses of radial growth to climatic factors and the differences in ecological resilience to drought between a heliophilous species Larix principis-rupprechtii and a shade species Picea meyeri in mixed forests, we developed the tree-ring width chronologies of L. principis-rupprechtii and P. meyeri in three mixed forests based on the samples collected from Toudaogou of Saihanba in Hebei, Ningwu County and Kelan County in Shanxi Province. We analyzed the correlation between climatic factors and various chronologies and examined the differences in resistance (Rc), recovery (Rt), and resilience (Rs) of L. principis-rupprechtii and P. meyeri in response to drought stress. The results showed that the radial growth of L. principis-rupprechtii and P. meyeri was negatively correlated with the mean and maximum air temperature from May to July in three mixed forests, and was positively correlated with the Palmer drought index (PDSI) from May to September. Radial growth decline in trees due to drought stress was significantly different between the two species among the three sites, indicating different physiological and ecological regulation strategies. The resistance of P. meyeri was stronger than that of L. principis-rupprechtii at the three study sites, with stronger resilience and resilient elasticity of L. principis-rupprechtii than P. meyeri. As a result, P. meyeri exhibited greater drought resistance than L. principis-rupprechtii. Under global warming condition, L. principis-rupprechtii might be at greater risk of growth decline than P. meyeri in this region.

Trade-offs between leaf stoichiometric characteristics and photosynthetic traits of Larix gmelinii and its differences among provenances

Variations and trade-offs between leaf stoichiometric characteristics and photosynthetic traits are indicative of ecological adaptation strategies of plants and their responses to environment changes. In a common garden of Maoershan, we measured leaf stoichiometric characteristics (carbon content (C), nitrogen content (N), phosphorus content (P), C/N, C/P, N/P) and photosynthetic traits (maximum net photosynthetic rate (Amax), maximum electron transport rate (Jmax), maximum carboxylation rate (Vmax)) of Larix gmelinii from 17 geographical provenances. We examined the provenance differences in stoichiometric characteristics and photosynthetic traits, and analyzed their trade-offs and influencing factors. The results showed leaf stoichiometric characteristics and photosynthetic traits significantly differed among provenances. The climatic factors of seed-source sites explained 54.8% and 67.2% of the variation in stoichiometric characteristics and photosynthetic traits, respectively. Aridity index (AI) of seed-source sites was positively correlated with C, N, P, Amax, Jmax, Vmax, but negatively with C/N, C/P, and N/P. Results of redundancy analysis showed that stoichiometric characteristics accounted for 75.0% of the variation in photosynthetic traits. Amax, Jmax, Vmax were positively correlated with C, N, P, and negatively correlated with C/N, C/P, N/P. The provenance differences in stoichiometric characteristics, photosynthetic traits, and their synergistic relationship suggested the long-term adaptation of trees to the climate of seed-source sites. These findings were of great significance for understanding ecological adaptation strategies of trees in response to climate change.

Precision medicine in laryngeal cancer: protocol of the laryngeal cancer cohort (LARCH)

INTRODUCTION

Laryngeal cancer disproportionately affects socioeconomically disadvantaged patients. Treatment can render a patient nil by mouth or in need of a permanent tracheostomy. In the past 30 years, survival has remained at best static and at worst it has declined. Currently, there is no method of prognosticating how a patient will respond to treatment.The LARyngeal Cancer coHort (LARCH) aims to establish how survival and quality-of-life outcomes compare between surgery and (chemo)radiotherapy in early and advanced laryngeal cancer and how the presenting features of laryngeal cancer influence oncological, functional and quality-of-life outcome.

METHODS AND ANALYSIS

This study is the first enhanced laryngeal cancer disease cohort. In the initial phase, we aim to deliver a prospective cohort study of 150 patients in 8 centres over a 3-year period.Patient, tumour, quality-of-life and laryngeal functional data will be collected from patients with squamous cell carcinoma of the larynx at baseline, 6, 12 and 24 months. Multiple logistic regression analyses will be used to quantify locoregional control and identify factors associated with control overall and by treatment modality and identify factors associated with quality of life overall and by treatment modality.

ETHICS AND DISSEMINATION

Most interventions take place as part of routine care, with LARCH providing a mechanism for recording this data centrally. When successfully recruiting in the North of England, we plan to roll out LARCH nationwide; in the future, LARCH can be used as a trial platform in the disease. The results will be submitted for publication in high-impact international peer-reviewed journals and presented to scientific meetings. Access to the anonymised LARCH dataset by other researchers will be publicised and promoted.

TRIAL REGISTRATION NUMBER

ISRCTN27819867.

Tree-ring anatomy of Pinus cembra trees opens new avenues for climate reconstructions in the European Alps

Tree rings form the backbone of high-resolution palaeoclimatology and represent one of the most frequently used proxy to reconstruct climate variability of the Common Era. In the European Alps, reconstructions were often based on tree-ring width (TRW) and maximum latewood density (MXD) series, with a focus on European larch. By contrast, only a very limited number of dendroclimatic studies exists for long-lived, multi-centennial Pinus cembra, despite the widespread occurrence of the species at treeline sites across the European Alps. This lack of reconstructions can be ascribed to the difficulties encountered in past studies in extracting a robust climate signal from TRW and MXD chronologies. In this study, we tested various wood anatomical parameters from P. cembra as proxies for the reconstruction of past air temperatures. To this end, we measured anatomical cell parameters and TRW of old-growth trees from the God da Tamangur forest stand, known for being the highest pure, and continuous P. cembra forest in Europe. We demonstrate that several wood anatomical parameters allow robust reconstruction of past temperature variability at annual to multidecadal timescales. Best results are obtained with maximum latewood radial cell wall thickness (CWTrad) measured at 40 μm radial band width. Over the 1920-2017 period, the CWTrad chronology explains 62 % and >80 % of interannual and decadal variability of air temperatures during a time window corresponding roughly with the growing season. These values exceed those found in past work on P. cembra and even exceed the values reported for MXD chronologies built with L. decidua and hitherto considered the gold standard for dendroclimatic reconstructions in the European Alps. The wood anatomical analysis of P. cembra records therefore unveils a dormant potential and opens new avenues for a species that has been considered unsuitable for climate reconstructions so far.

Transplanting larch trees into warmer areas increases the photosynthesis and its temperature sensitivity

To investigate the effects of climate warming on photosynthesis, Dahurian larch (Larix gmelinii Rupr.) trees from four sites (spanning ~ 5.5° in latitude and ~4 °C of warming) within the geographic range in China were transplanted into a common garden close to the warmer border in 2004. Throughout the growing season of 2018, the CO2- and temperature-response curves of the photosynthesis in the common garden and at the original sites were measured. It was discovered that warming treatment considerably increased the maximum net photosynthetic rate (Amax) by 23.4-35.3% depending on the sites, signifying that warming upregulated Amax with respect to the degree of warming. At 25 °C, warming enhanced the maximum Rubisco carboxylation rate (Vcmax), maximum electron transport rate (Jmax), and mass-based leaf nitrogen concentration (Nmass). The climate warming effect (CWE) on Amax was positively associated with the CWEs on Vcmax, Jmax and Nmass, which indicated that warming promoted Amax primarily via increasing carboxylation and photosynthetic electron transport rates and leaf nitrogen supply. The CWE in optimal photosynthetic temperature (Topt) was significant for the trees from the northern sites rather than the southern sites; however, the effect vanished for the trees transplanted to the common garden; this implied that Topt exhibited limited local thermal acclimation. Nevertheless, warming narrowed the temperature-response curve, the effect of which was positively associated with the warming magnitude. These findings implied that trees transplanted into warmer areas changed the photosynthetic optimum temperature and sensitivity. In summary, our results deepen the understanding of the underlying mechanisms of intraspecific responses of photosynthesis to temperature changes, including which of the modeling would improve the prediction of tree growth and forest carbon cycling under climate warming.

Activity of low-molecular weight components of Larix sibirica antioxidant system under exposure to technogenic pollution

Changes in the antioxidant protection system of Larix sibirica Ledeb at different pollution levels caused by emissions from a large aluminum smelter (BrAS) have been studied. We revealed that the content of peroxide (H₂O₂) in the needles is a reliable marker of oxidative stress in the trees under pollution. The crucial role of non-enzymatic components, in particular, proline, phenolic compounds, ascorbic acid, glutathione, in reducing the level of free radicals in the needles cells was found. Proline concentration in the needles significantly rises with the increase in pollution levels from low to high. Under critical level pollution, it decreases by 40% compared to the background. The total content of ascorbic acid (ASC) in the needles of polluted trees varies slightly; however, there are significant changes in its various forms. With an increase in pollution to a high level, the content of the reduced form of ASC in the needles increases by 1.5-2.9 times compared to the background content. At a critical level of pollution, the total level of ascorbic acid and its reduced form falls, the content of the oxidized form reaches minimum values. The total content of phenolic compounds in the needles increased by 50-55%, concentration of flavonoids by 1.5-1.8 times, catechins by 1.9-2.5 times, proanthocyanidins by 45% compared to the background level under low, moderate, high pollution, whereas under critical pollution their content decreased. The absolute concentration of the reduced form glutathione in the needles falls by 1.9-3.0 times, the oxidized form increases by 1.5-2.0 times compared to the background. The ratio of reduced glutathione to oxidized glutathione decreased, especially during critical pollution. The data obtained show significant activation of Siberian larch biochemical protection at low, moderate and high levels of pollution by the aluminum smelter emissions. At a critical levels of contamination, a significant depletion of the pool of low-molecular antioxidants was observed.

Reduced diurnal temperature range mitigates drought impacts on larch tree growth in North China

Forests are facing climate changes such as warmer temperatures, accelerated snowmelt, increased drought, as well as changing diurnal temperature ranges (DTR) and cloud cover regimes. How tree growth is influenced by the changes in daily to monthly temperatures and its associations with droughts has been extensively investigated, however, few studies have focused on how changes in sub-daily temperatures i.e., DTR, influence tree growth during drought events. Here, we used a network of Larix principis-rupprechtii tree-ring data from 1989 to 2018, covering most of the distribution of planted larch across North China, to investigate how DTR, cloud cover and their interactions influence the relationship between drought stress and tree growth. DTR showed a negative correlation with larch growth in 95 % of sites (r_mean = -0.30, significant in 42 % of sites). Cloud cover was positively correlated with growth in 87 % of sites (r_mean = 0.13, significant in 5 % of sites). Enhanced tree growth was found at lower DTR in the absence of severe drought. Our findings highlight that in the absence of severe droughts, reduced DTR benefits tree growth, while increased cloud cover tended to benefit tree growth only during severe drought periods. Given how DTR influences drought impacts on tree growth, net tree growth was found to be larger in regions with smaller DTR.

Phytochemical and biological studies on rare and endangered plants endemic to China. Part XXV. Structurally diverse triterpenoids and diterpenoids from two endangered Pinaceae plants endemic to the Chinese Qinling Mountains and their bioactivities

A joint phytochemical investigation on the MeOH extracts of the twigs and needles of two endangered Pinaceae plants endemic to the Chinese Qinling Mountains, Picea neoveitchii (an evergreen spruce) and Larix potaninii var. chinensis (a deciduous larch), led to the isolation and characterization of 34 and 24 structurally diverse terpenoids, respectively. Among them, seven are previously undescribed, including a picane-type [i.e., 14(13 → 12)abeo-12αH-serratane] (neoveitchin A) and a serratane-type (neoveitchin B) triterpenoids, and an abietane-type (neoveitchin C) as well as four labdane-type (potalarxins A-D) diterpenoids. Their structures and absolute configurations were established by extensive spectroscopic methods and/or X-ray diffraction analyses. All isolates were evaluated for their inhibitory activities against the human protein tyrosine phosphatase 1B (PTP1B). Serrat-14-en-3α,21β-diol, betulinic acid, 3β-hydroxy-11-ursen-13(28)-olide, ursolic acid, and oleanolic acid were found to have considerable inhibitory effects against PTP1B, with IC₅₀ values ranging from 1.1 to 18.1 μM. The interactions of the bioactive triterpenoids with PTP1B were thereafter performed by employing molecular docking studies. In addition, 7-oxo-dehydroabietic acid (an abietane-type diterpenoid) and mangiferonic acid (a cycloartane-type triterpenoid) inhibited acetyl-coenzyme A carboxylase 1 (ACC1), with IC₅₀ values of 3.4 and 6.6 μM, respectively.

[Simulation of carbon sequestration and timber production in Larix olgensis plantation based on CO2FIX model]

Based on datasets from plot survey and bibliographic of Larix olgensis plantations in Maoer Mountain, the CO₂FIX model was used to quantitatively simulate the effects of different rotations (30, 40, 50, 60 years), site indices (12, 16, 20 m), and initial densities (2500, 3333, 4444 trees·hm^-2) on the stand level carbon flows among different carbon pools (i.e., biomass carbon pool, soil carbon pool, and product carbon pool). The results showed that the CO₂FIX model had high reliability for simulating the processes of L. olgensis plantation, with the average relative errors of stand biomass and volume between analog and measured values being 6.4% and 3.7%. Under the baseline conditions of initial density of 3333 trees·hm^-2, site index of 16 m and rotation of 40 years, the carbon stock of total and sub-pool of L. olgensis plantation changed periodically with rotation. The total stand carbon stock and volume for L. olgensis plantation increased with the extension of rotation, the improvement of site index, and the increase of initial density. The stand carbon stock and volume would be increased by 12.2% and 31.2%, 36.7% and 67.8%, respectively, when the reference rotation was correspondingly extended by 10 and 20 years. However, if the reference rotation was shortened by 10 years, stand carbon stock and volume would be correspondingly decreased by 20.9% and 40.4%, respectively. When the initial density was set as 3333 and 4444 trees·hm^-2, stand carbon stock and volume were increased by 27.8% and 50.9%, 27.4% and 49.1%, respectively. When the site index was under the range of 12 to 20 m, stand carbon stock and volume could be increased by 36.0% and 40.3%, 39.3% and 44.2%, respectively, with each increase of 4 m in site index. During one rotation, 271.57 t C per hectare could be fixed into L. olgensis plantation. At the end round of the rotation, 27.47 and 56.75 t C were transferred to soil and wood product carbon pools. Therefore, when the site condition was good, the management model with a higher initial density (4444 trees·hm^-2) and longer rotation (60 years) would be more beneficial to maximizing the carbon sink and timber benefits of L. olgensis plantation.

[Natural regeneration of Larix principis-rupprechtii plantations with different densities and its influencing factors]

In this study, we analyzed the natural regeneration of Larix principis-rupprechtii pure plantations with stand densities of 128, 240, 320, 400, 480, 560, 640 and 720 trees·hm^-2 in the Guandi Mountains and its influencing factors. The results showed that the regeneration index first increased and then decreased with the increases of stand density, and that the regeneration performance of stand with medium density (400-560 trees·hm^-2) was significantly better than other stands. Light conditions, herbaceous plants and litter of the understory had a dual effect on the regeneration of L. principis-rupprechtii. Excessive light, herbaceous plant cover or over-thick litter was not instrumental to the regeneration. Soil organic matter promoted stand regeneration by providing soft soil texture, adequate water content, low phosphorus but high nitrogen. The effects of the examined factors on the regeneration index were as follows: soil water content (0.798) &gt; total nitrogen (0.621) &gt; litter thickness (-0.597) &gt; soil porosity (0.504) &gt; soil organic matter (0.493) &gt; total phosphorus (-0.404) &gt; transmitted total light (-0.274) &gt; herbaceous plants cover (-0.021). In the plantation management, stand density could be controlled at about 480 trees·hm^-2 by thinning or replanting, while litter could be cleared properly to improve soil condition and to promote natural regeneration of L. principis-rupprechtii.

[Classification of forest types in Cuigang Forest Farm based on time series data of Landsat 8]

To explore the practical role of enhanced vegetation index (EVI) time series data in improving the accuracy of forest type recognition could promote the deep application of optical remote sensing data in forest resources investigation and monitoring. With Cuigang Forest Farm of Xinlin Forestry Bureau in Daxing'anling as the object, we constructed six classification schemes, using random forest algorithm with spectral feature, texture feature and EVI time series feature. The data sources were 20-view Landsat 8 OLI time series data from 2014 to 2018, 56 fixed plots data from 2017-2019, and the 2016 Class II survey data. Our aims were to realize the classification of forest types in Cuigang Forest Farm and to evaluate the accuracy of different classification schemes. The results showed the EVI values of Larix gmelinii forest, Betula platyphylla forest, coniferous-broadleaved mixed forest, coniferous mixed forest and broadleaved mixed forest were significantly different in non-growing seasons (36-111 days and 287-367 days), with the EVI value of mixed conifer forest being significantly higher, and that of mixed broadleaf forest being always lower than the other four forest types. In the early growing season (111-143 days), the EVI value of B. platyphylla forest were higher than L. gmelinii forest, which could effectively distinguish the two forests. Among the six classification schemes, spectral feature, texture feature, and EVI time series feature had the highest classification accuracy, with a Kappa of 0.82 and a classification accuracy of 86.1%. The comparison results showed that the overall accuracy of adding vegetation index time series feature was improved by 14.3% compared with that of spectral feature. The random forest algorithm with combined spectral, texture and EVI time series features could effectively classify forest stand types in Cuigang Forest Farm, with good recognition accuracy and confidence.

Tree growth is connected with distribution and warming-induced degradation of permafrost in southern Siberia

Hemiboreal and boreal forests growing at the southern margin of the permafrost distribution are vulnerable to climate warming. However, how climate warming threatens the growth of dominant tree species that are distributed on permafrost remains to be determined, particularly in synchrony with warming-induced permafrost degradation. Tree growth in the permafrost region of southern Siberia was hypothesized to be highly sensitive to temperature increasing and warming-induced permafrost degradation. To test this hypothesis, we sampled the tree ring width of 535 trees of dominant species, larch (including Larix gmelinii and L. sibirica) and white birch (Betula platyphylla), in ten hemiboreal to boreal forest plots within different permafrost zones. The relationships between the tree ring basal area index (BAI) and temperature, precipitation, and the Palmer drought severity index (PDSI) were compared among plots located in two permafrost zones. In the isolated permafrost zone, white birch grows better than larch and is not drought-stressed (p < .05). We suggest that the deep-rooted white birch benefits from the water from thawing permafrost, while the growth of the shallow-rooted larch is stressed by drought. In the sporadic discontinuous permafrost zone, both white birch and larch benefited from permafrost melting, but the sensitivity of larch growth to PDSI is still significant (p < .05), indicating drought is still an important climatic factor limiting the growth of larch. Our results imply that the permafrost degradation caused by climate warming affects tree growth by creating the root layer additional water source. In the future, it is necessary to focus on monitoring permafrost degradation to better predict forest dynamics at the southern margin of the permafrost distribution.

[Structure and dynamics of co-dominant species in different succession stages of natural forests in Daxing'an Mountains, China]

Affected by the disturbance of forest fire and logging, the primary forest in Daxing'an Mountains gradually degenerates into secondary forest. In this study, we established 16 plots in each of three typical forests, including natural Betula platyphylla pure forest (pioneer stage), natural B. platyphylla and Larix gmelinii mixed forest (transition stage) and natural L. gmelinii pure forest (top stage). The methods of population age and tree height structure, static life table, survival analysis, dynamic index and time series prediction were used to quantitatively analyze the dynamics of dominant species (B. platyphylla and L. gmelinii) and all the arbors, aiming to provide scientific basis for the restoration and development of natural L. gmelinii forest. The results showed that the abundance of young co-dominant species and total arbors in each stage was large, and that all population had strong self-renewal potential. With the progress of succession, the abundance of B. platyphylla in each age class gradually decreased, whereas that of L. gmelinii gradually increased. The mortality and disappearance rates of total arbors and B. platyphylla in the transition stage and L. gmelinii in the pioneer stage gradually increased with the increases of age class, and the survival curve was Deevey-Ⅰ type. The survival analysis results showed that the population was stable in the early stage, increased in the middle stage, and declined in the later stage. In other stages, the mortality rates fluctuated slightly, the survival curves were Deevey-Ⅱ type, and the population increased in the early stage, declined in the middle stage, and stable in the later stage. The co-dominant species and total arbors were growing in the three succession stages, among which B. platyphylla in the pioneer stage, L. gmelinii and total arbors in the top stage showed the lowest sensitivity to the environment. The results of time series prediction showed that the co-dominant species and total arbors in each stage would increase in the future. During forest succession, it was necessary to strengthen the protection of seedlings and young trees, thin the forest with large coverage, and take appropriate measures to ensure population renewal.

Alleviates cisplatin-induced acute intestinal injury in vitro and in vivo through IRE1α/JNK axis mediated apoptotic signaling pathways

Many dietary polysaccharides have been shown to protect against various harmful external stimuli by protecting the integrity of the intestinal barrier. Arabinogalactan (AG) is a high molecular weight polysaccharide composed of arabinose and galactose, which has good immunomodulatory, antioxidant and intestinal conditioning activities. Gastrointestinal injury caused by cisplatin (CP) is an inevitable damage during CP chemotherapy. This research explored the ameliorative effect of AG on cisplatin-induced intestinal toxicity and its possible molecular targets and mechanisms. The results showed that AG (200, 400 mg/kg) could significantly reverse the intestinal histopathological changes and oxidative stress injury caused by CP. Meantime, AG could target the IRE1α/JNK axis to inhibit the expression of apoptosis-related proteins and block the apoptotic cascade, thus reducing intestinal damage. In vitro, AG (10, 20, and 40 μg/mL) could regulate the IRE1α/JNK axis, inhibit apoptosis, and restore the antioxidant defense system damaged by CP to play a protective role in the intestine. In addition, 4-phenylbutyrate (4-PBA), a specific inhibitor of endoplasmic reticulum stress, was used to verify that AG also affected protein expression levels by regulating the IRE1α/JNK pathway-mediated endoplasmic reticulum stress signaling pathway, thereby alleviating CP-induced gastrointestinal dysfunction. Therefore, AG may be a potential drug to prevent CP-induced intestinal damage.

[Cell characteristics of Larix principis-rupprechtii on the edge of different stand types]

To analyze the effects of forest edge on radial growth and cell characteristics in different stand types of Larix principis-rupprechtii, we investigated the differences on radial growth, cell size and numbers between edge trees and inner trees of L. principis-rupprechtii in pure L. principis-rupprechtii forests and mixed forests of L. principis-rupprechtii and Betula platyphylla in Saihanba mechanical forest farm, China. The results showed that radial growth of the edge trees was significantly faster than that of the inner trees in pure forests, with the total ring width, earlywood width and latewood width of edge trees being 48.9%, 58.9% and 29.6% higher than those of inner trees, respectively. However, there was no difference in radial growth between edge trees and inner trees in mixed forest. The total number of earlywood cells, the number of large cells and small cells in earlywood of edge trees were increased by 63.3%, 55.6% and 70.0%, while the total number of latewood cells, the number of large cells and small cells in latewood of edge trees were increased by 35.4%, 37.5% and 28.5% compared with those of inner trees. There was no significant difference in the cell sizes between edge trees and inner trees. The cell numbers of earlywood and latewood of edge trees were not significantly different from those of inner trees in mixed forest, but the cell size in the earlywood of edge trees was 50.0% larger than those of inner trees in mixed forest. The sizes of the largest cells, the smallest cells, the large cells and the small cells in the earlywood of edge trees were increased by 28.6%, 33.3%, 16.6% and 25.0% compared with those of inner trees, respectively. The fast growth of edge trees and slow growth of inner trees in the pure forests could be effectively alleviated by cultivating mixed forests.

[Analysis of carbon concentration and allometric growth model of carbon content for Larix olgensis]

Forest carbon storage accounts for about 45% of terrestrial carbon storage. Accurate assessment of forest carbon storage is of great significance to the scientific management and planning of forests. Based on the data of 77 sampling Larix olgensis trees from Mengjiagang, Shangzhi Maoershan, Xiaojiu Forest Farm and Dongjing, Lin-kou Forestry Bureaus of Jiamusi, Heilongjiang Province from 2015 to 2018, we analyzed the partition of carbon content and variation of carbon concentration for five tree components (i.e., wood, bark, branch, leaf, and root). The mono-element and dual-element additive models of carbon content for each component of L. olgensis were deve-loped. The nonlinear seemly unrelated regression was used to estimate the parameters in the additive models, while the jackknife resampling technique was used to verify and evaluate the developed models. The results showed that the weighted mean carbon concentration of each component differed significantly, branches (49.3%) > bark (48.7%) > foliage (48.5%) > wood (48.2%) > root (47.1%). The aboveground and belowground carbon content accounted for about 80% and 20% of the total carbon content, respectively. The adjusted coefficient of determination (R_a²) of additive models of carbon content was greater than 0.89, the mean absolute error was less than 4.1 kg, and the mean absolute error percentage for most models was less than 30%. Adding tree height in the additive models of carbon content could significantly improve model fitting performance and predicting precision. The additive models of carbon content of total, aboveground, wood and bark were better than that of carbon content of branch, foliage, root and crown.

[Effects of mixing proportions on carbon storage and allocation in mixed plantation of Larix olgensis and Fraxinus mandshurica]

In this study, four types of mixed Larix olgensis and Fraxinus mandshurica plantations were selected according to the rows-mixing proportions (type Ⅰ: 5:3, type Ⅱ: 6:4, type Ⅲ: 5:5, type Ⅳ: 1:1). The see-mingly unrelated biomass models of L. olgensis and F. mandshurica were developed for obtaining biomass values, and the difference and composition of carbon storage in each forest layer and ecosystem were analyzed. The results showed that carbon storage of arbor layer in different stand types was 39.86-50.12 t·hm^-2, the carbon storage of arbor layer inⅠ, Ⅱ and Ⅳ was significantly higher than that in type Ⅲ. The carbon storage of understory was 0.10-0.30 t·hm^-2, with that in type Ⅱ being significantly higher than other types. Carbon storage of litter layer was 4.43-6.96 t·hm^-2, with type Ⅱ and Ⅲ being significantly higher than those of the other types. In the soil layer, carbon storage was 34.97-54.66 t·hm^-2. The carbon storage of soil layer in type Ⅱ was significantly greater than those in the other types. At the whole ecosystem level, carbon storage of type Ⅰ-Ⅳ was 90.43, 108.27, 85.83 and 89.92 t·hm^-2, respectively. Type Ⅱ had significantly greater carbon storage than the other types. The arbor layer and soil layer were the major carbon pools in the ecosystem, which accounted for 43.3%-55.7% and 38.7%-50.5% of the total, respectively. Our results suggested that mixing by six rows of L. olgensis and four rows of F. mandshurica was better for future planting.

Antimicrobial Activity and Wound-Healing Capacity of Birch, Beech and Larch Bark Extracts

Bark is a major by-product of woodworking industries. The contents of several wood species are known to harbor antimicrobial, antiviral, anti-inflammatory and wound-healing capacities. The aim of this work was to identify beneficial properties of Austrian larch, birch and beech bark extracts for their potential usage as additives or active ingredients in dermatological applications. Bacterial agar diffusion assay and resazurin-based broth microdilution assay were used to evaluate anti-bacterial activity. To gain more insight into the cellular response to bark extracts, viability-, scratch-assays and ELISAs were performed. Birch and beech extracts showed strong antimicrobial activities against Gram-positive bacteria, including Cutibacterium acnes, Staphylococcus epidermidis and MRSA. Wound closure was enhanced with birch and beech extracts as compared to controls in the scratch-assays. Whereas beneficial properties of birch bark components have previously been described, the similar effects of beech extracts are novel. The combined positive effect on wound-healing and antimicrobial activity has great potential for the treatment of various skin diseases, including acne in future dermal applications.

[Comparison of artificial neural network with compatible biomass model for predicting aboveground biomass of individual tree]

Forest biomass is an important index in forest development planning and forest resource monitoring. In order to provide a more efficient and low-biased method for estimating individual tree biomass, we introduced artificial neural network here. We used the data of aboveground biomass of 101 Larix olgensis trees harvested from the Dongzhelenghe Forest Farm in Heilongjiang Province to develop four aggregation model systems (AMS), based on different combination of the variables (diameter at breast height, tree height, crown width). The weighted functions were used to eliminate heteroscedasticity. Then, we trained artificial neural network (ANN) biomass model based on the optimal combination. The models were tested by the leave-one-out cross-validation method to compare the accuracy of the two biomass estimation methods. The results showed that biomass model based on only one variable, diameter at breast height, could accurately estimate the biomass of L. olgensis. Adding two indices, tree height and crown width, could improve the fitting performance of models, with AMS4 performing the best among the four addictive model systems. The biomass models developed by the two methods both could estimate biomass at tree level accurately, with the coefficient of determination (R²) of each component was higher than 0.87. Compared with the AMS4, R² of leaf biomass model was about 0.05 higher, and that of other organs were also about 0.01 higher in artificial neural network model system. In addition, the root mean square error (RMSE) and other indicators were also significantly smaller. For example, the RMSE of tree stem and aboveground biomass were smaller by 2.135 kg and 3.908 kg, respectively. The model's validation statistics mean relative error (MRE) performed better. In general, ANN was a flexible and reliable biomass estimation method, which was worthy consideration when predicting tree component biomass or aboveground biomass.

Warming and elevated CO2 alter tamarack C fluxes, growth and mortality: evidence for heat stress-related C starvation in the absence of water stress

Climate warming is increasing the frequency of climate-induced tree mortality events. While drought combined with heat is considered the primary cause of this mortality, little is known about whether moderately high temperatures alone can induce mortality, or whether rising CO2 would prevent mortality at high growth temperatures. We grew tamarack (Larix laricina) under ambient (400 p.p.m.) and elevated (750 p.p.m.) CO2 concentrations combined with ambient, ambient +4 °C and ambient +8 °C growth temperatures to investigate whether high growth temperatures lead to carbon (C) limitations and mortality. Growth at +8 °C led to 40% mortality in the ambient CO2 (8TAC) treatment, but no mortality in the elevated CO2 treatment. Thermal acclimation of respiration led to similar leaf C balances across the warming treatments, despite a lack of photosynthetic acclimation. Photosynthesis was stimulated under elevated CO2, increasing seedling growth, but not leaf C concentrations. However, growth and foliar C concentrations were lowest in the +8 °C treatments, even with elevated CO2. Dying 8TAC seedlings had lower needle C concentrations and lower ratios of photosynthesis to respiration than healthy 8TAC seedlings, indicating that C limitations were likely the cause of seedling mortality under high growth temperatures.

A 168-year temperature recording based on tree rings and latitude differences in temperature changes in northeast China

A ring-width series was developed from Dahurian larch (Larix gmelinii) in the northeastern forest area of Inner Mongolia, China. By analyzing the relationships between tree-ring data and climate records, an August-September mean maximum temperature (T₈₉) series during 1845 and 2012 was reconstructed based on a simple linear regression equation. This reconstructed series explained 40.9% variance of the observed temperature from 1959 to 2012. The reconstructed T₈₉ series was consistent with the historical disaster events caused by extreme climate (e.g., flood, frost disaster, and cold damage). Besides, the temperature comparisons showed that the year in which the warm months (April-September) in northeast China began to warm up has latitude differences. It started with a gradual delay from north to south, starting 1980 in the south region, after 1950 AD in the central region and after 1940 in the north region. Our study can enrich high-resolution temperature series in Northeast China and help clarify the characteristic of recent warming in northeast China.

Seasonal dynamics of manganese accumulation in European larch (Larix decidua Mill.), silver birch (Betula pendula Roth), and bilberry (Vaccinium myrtillus L.) over 10 years of monitoring

Leaves of European larch, silver birch, and bilberry were sampled 5-7 times per growing season in 2010-2019 in a locality near the city of Litvínov in the Krušné Hory Mts. (Ore Mts.) near the Czech/German border. The locality is characterised by a large amount of plant-available Mn because of acidic soils in the study area. All three investigated plants at the studied site acquired manganese concentrations close to the definition of hyperaccumulation (ca. 10,000 mg kg^-1). This paper presents the most detailed collection of plant material for the characterisation of seasonal dynamics of Mn concentrations in the foliage of the three studied plants under field conditions and compares this information with that in published studies. Time (day in the year or day in the growing season) and cumulative precipitation anomalies were major and minor variables, respectively, explaining Mn dynamics in leaves, while temperature and insolation anomalies were not significant. The three investigated species showed plant-specific Mn acquisition rates in the growing season and specific effects of precipitation. Seasonal dynamics must be considered if plant leaves are used for environmental monitoring.

Growth variations of Dahurian larch plantations across northeast China: Understanding the effects of temperature and precipitation

Climate change is affecting the growth and distribution of trees in the Chinese boreal forest. Such changes in China, the southern terminus of the extensive Eurasian boreal forests, reflect on the changes that could occur further north under a warming climate. Most studies have found that tree growth increases with increasing temperature and precipitation in boreal forests, but there is little observational evidence of the climate thresholds that might slow these growth rates at the more extreme temperatures which are predicted to occur under future global warming. Here, we examine growth responses of this dominant boreal tree species (Larix gmelinii) to climate based on the data from plantation sample plots across a broad region (40° 51'-52° 58'N, 118° 12'E-133° 42'E) in northeast China. From statistically significant fits to quadratic equations, temperature and precipitation are the important climatic factors determining tree growth in L. gmelinii plantations at two age classes (<10 year and 10-30 year-old stands). The maximum rates of tree height and diameter at breast height (DBH) were about 0.53 m/year and 0.46 cm/year at <10 year stands, and about 0.63 m/year and 0.60 cm/year at 10-30 year stands, respectively. For stands with the highest values of mean annual increment (MAI), the corresponding optimal mean annual temperature (MAT_opt) focused between 0.66 °C and 1.57 °C. The optimal mean annual precipitation (MAP_opt) between 663 mm and 708 mm produced the maximal growth increments. With mean annual temperature of -2.4 °C and precipitation of 470 mm averaged over 1954-2005 in Chinese boreal forest region as baseline, we conservatively estimated that trees in Chinese boreal forest appear to have higher growth potentials with the maximum temperature increase of 3.6 °C and precipitation increase of 40%.

[Effects of tree species interaction, stand density, and tree size on the productivity of Larix principis-rupprechtii]

Pure and mixed larch (Larix pricipis-rupprechtii) and birch (Betula platyphylla) plantations in Saihanba area were selected as test objects, with two stand density (200-340 and 880-1100 trees·hm^-2) of each stand type. Based on tree size-stratified sampling approach, a total of 668 tree core samples were collected. A linear mixed model was used to analyze the effects of tree species interaction, stand density, and tree size on larch productivity. Results showed that basal area increment of larch was affected by competition, diameter at breast height, tree age, and neighborhood density to different degrees. Overyielding of larch was mainly due to the positive effect of birch on larch growth in the mixed plantation with higher stand density. For mixed plantation with lower stand density, the productivity of those two species was lower than that pure plantation because of a lack of species interaction. Intraspecific competition was the main factor influencing larch productivity. Larch productivity was positively affected by tree size, with the magnitude of tree size effect varying with stand density and species composition. Suitable enhancement of stand density and selection of birch as the mixing tree species could improve productivity of larch.

Extraction of branch factors and model construction for Larix plantation using terrestrial laser scanning (TLS)

Forest parameters could be estimated without damage using terrestrial laser scanning (TLS). In this study, 1266 sets of branch parameters, including branch height, branch chord length, branch length, branch angle, branch diameter and the branch arc height, of 26 Larix trees were extracted based on TLS using point cloud processing software in the way of human-computer interaction. The average of extracted maximum relative height of the branches was 0.83. The accuracy of the extracted branch attributes followed the order of branch height > branch chord length > branch length > branchdiameter (with the branch diameter >20 mm) > branch arc height. After dividing the crown into four parts, it proved that the density of the branches increased while the extraction ratio and precision of branches decreased with the increase of crown height. Due to the low accuracy of branch diameter extraction, we developed a base diameter prediction model using the branch chord length, the height of branch, diameter at breast height and tree height as independent variables. The measured, extracted and model predicted values of different base diameter were compared, and discovered that accuracy of model prediction was greater than that of extraction by TLS. For timber production, the most worthy wood was the middle and lower section of the tree. The method could accurately extract tree height, diameter at breast height (DBH) and the branch attributes with the relative branch height of less than 0.8, providing the parameters that are necessary to develop a wood quality model.

Unexpected greening in a boreal permafrost peatland undergoing forest loss is partially attributable to tree species turnover

Time series of vegetation indices derived from satellite imagery are useful in measuring vegetation response to climate warming in remote northern regions. These indices show that productivity is generally declining in the boreal forest, but it is unclear which components of boreal vegetation are driving these trends. We aimed to compare trends in the normalized difference vegetation index (NDVI) to forest growth and demographic data taken from a 10 ha mapped plot located in a spruce-dominated boreal peatland. We used microcores to quantify recent growth trends and tree census data to characterize mortality and recruitment rates of the three dominant tree species. We then compared spatial patterns in growth and demography to patterns in Landsat-derived maximum NDVI trends (1984-2019) in 78 pixels that fell within the plot. We found that NDVI trends were predominantly positive (i.e., "greening") in spite of the ongoing loss of black spruce (the dominant species; 80% of stems) from the plot. The magnitude of these trends correlated positively with black spruce growth trends, but was also governed to a large extent by tree mortality and recruitment. Greening trends were weaker (lower slope) in areas with high larch mortality, and high turnover of spruce and birch, but stronger (higher slope) in areas with high larch recruitment. Larch dominance is currently low (~11% of stems), but it is increasing in abundance as permafrost thaw progresses and will likely have a substantial influence on future NDVI trends. Our results emphasize that NDVI trends in boreal peatlands can be positive even when the forest as a whole is in decline, and that the magnitude of trends can be strongly influenced by the demographics of uncommon species.