Aims Seed germination is affected by both provenance and habitat conditions (light, temperature, etc.). Then natural regeneration capacity of Korean pine (Pinus koraiensis) is determined by its seed germination, which is the key to restore the broadleaved Korean pine forest—a regional climax community. This study aimed to reveal the effects of light and temperature on seed germination of Korean pine with different provenances.

Methods Germinations of the P. koraiensisseeds produced in the year were investigated in both field and lab from three provenances in China (i.e. Qingyuan, Liaoning Province; Changbai Mountain, Jilin Province; and Yichun, Heilongjiang Province). Specifically, for field survey, seed germination data were obtained from both forest canopy gap and forest understory in different seasons. While for lab experiment, the seed germination in growth chamber were recorded under three light intensities (i.e. 200, 20 and 0 μmol·m^-2·s^-1, L200, L20 and L0 hereafter) and two temperature conditions (i.e. 25 and 15 °C).

Important findings Results showed that no seeds germinated in spring (May) under natural conditions. In comparison, the seed germination percentages (GP) from three provenances were relatively low ranging from 1.8% in understory to 33.7% in canopy gaps in summer (July) and autumn (September). However, we found that the GP were significantly higher in the canopy gap than in the understory in summer. Besides, lab experiments showed that the GP were relatively high (ranged from 32% to 77%) for spring and summer seeds under suitable light and temperature conditions (L200, 25/15 °C) in growth chamber, but the GP were very low for autumn seeds (<2%). At 25 °C condition, the GP and germination values (GV) were significantly higher under L200 than those under L20 and L0 conditions for all the three provenances. At 15 °C condition, the response of GP and GV was consistent with that of 25 °C for seeds from Qingyuan, while the GP and GV were the highest under L0 and L20 conditions for seeds from Changbai Mountain and Yichun, respectively. Under all light intensities, GP and GV from three provenances were all higher under 25 °C than those under 15 °C. In conclusion, temperature is essential for seed germination of P. koraiensis, and the seeds from Changbai Mountain and Yichun might require higher accumulated temperature to break dormancy. Moreover, light helps promote seed germination at relatively high temperature condition (25 °C). However, the impacts of light and temperature were provenance-dependent. More specifically, the light impacts on germination were reduced at lower temperature conditions for seeds collected from Changbai Mountain and Yichun. Our study indicated that the poor regeneration of Korean pine natural forests might attribute to the unsuitable light and temperature conditions for seed germination.

Aims Current research on the maintenance mechanisms of forest biodiversity mainly focuses on the stage of examining the abundance of aboveground organisms. However, many gaps remain in our knowledge of interactions between species and on whether the underground fungi affect the maintenance of biodiversity. This study explores the role of soil fungi in maintenance of biodiversity and the relationship between plant-soil feedbacks and plant growth. We selected four tree species in a broadleaved Korean pine forest in Northeast China, and used controlled seedling planting experiments to test the Janzen-Connell hypothesis.

Methods Experimental treatments included fungicide application and controlled seedling planting of four tree species (Pinus koraiensis, Fraxinus mandshurica, Phellodendron amurenseand Tilia amurensis) in Jiaohe forest farm, Jilin Province. Biotic and specific feedbacks were assessed using the fungicide treatment and the control seedling planting of different tree species. Soil fungal diversity was determined by high-throughput sequencing method and tested for differences among different treatments. The relationships of the two feedback types with tree species, functional types of fungi and soil were analyzed by variance partitioning analysis (VPA).

Important findings Fungicide treatment did not significantly affect the biotic feedback, and seedling biomass in conspecific soil did not show significant distance dependence. The specific feedbacks were not significantly improved by presence of different tree species. In addition, VPA showed that the most important factor affecting plant-soil feedbacks was inherent species characteristics, with the influence of soil and fungi varying with the feedback type. This study identified the factors influencing plant-soil feedbacks in mixed forest of temperate zone, and demonstrated the variability of Janzen-Connell hypothesis with temperate forest tree species, laying a foundation for better understanding the interactions between species and the underlying regulation mechanisms.

Aims Forest ecosystem changes with time in response to environmental fluctuations and disturbances, and the research on its stability and influence mechanism is conducive to maintaining ecosystem services. The temperate coniferous and broadleaved mixed forest is an important component of the global forest ecosystem. Therefore, we aimed to investigate the influence of overyielding, stand structure, species asynchrony and dominant species stability on the community stability of a temperate natural coniferous and broadleaved mixed forest and to clarify its main influence mechanism.

Methods In this study, species richness, coefficient of variation of diameter at breast height (DBH), species asynchrony, and dominant species stability were used as independent variables, and community biomass stability, mean biomass and standard deviation of biomass were set as dependent variables, respectively. In this case, three structural equation models were constructed to quantify the relative size of the direct and indirect effects among all variables.

Important findings (1) The structural equation model provides a good fit for the data and accounts for 40.6% of the community biomass stability changes. (2) Species richness was significantly negatively correlated with mean biomass and standard deviation of biomass, with the path coefficients -0.103 and -0.061, respectively. (3) The coefficient of variation of DBH was significantly negatively correlated with the community biomass stability and mean biomass, and the path coefficients were -0.123 and -0.097, respectively. (4) Species asynchrony was significantly positively correlated with the community biomass stability, mean biomass and standard deviation of biomass, and the path coefficients were 0.055, 0.085 and 0.055, respectively. (5) Dominant species stability was significantly positively correlated with the community biomass stability and mean biomass, with the path coefficients 0.623 and 0.085, respectively. And it has a significant negative correlation with the standard deviation of biomass, with the path coefficient -0.68. The results showed that although species asynchrony and stand structure both have significant effects on the community's biomass stability in the temperate coniferous and broadleaved mixed forest, but the dominant species stability is the main factor that directly affects the community biomass stability.

Aims Harvesting is an important way to adjust stand structure. Trees in different forest strata have different responses to harvesting intensity. Traditionally, qualitative or simple quantitative methods (e.g., with equal distance of tree height) were used to identify the vertical layers of the forest, and the impact of harvesting on each layer were analyzed subsequently. However, these methods of specification ignore the differences in tree growth between different tree species and different developmental stages within the same layer.

Methods Four permanent plots were established in a broadleaved Korean pine forest in Jiaohe, Jilin Province, ranging in harvesting intensities from low (17.3% of basal area removed), medium (34.7%) to high (51.9%), together with an unharvested control plot. Tree growth rates were documented 2, 4 and 7 years after harvesting. According to the position of an individual tree in the forest layer, as well as its development stages, we aggregated all individuals into three cohorts: mature canopy trees (I), immature canopy trees (II), and understory species of any size (III). Tree diameter growth of each cohort were compared during different recovery periods.

Important findings The average relative growth rate (RGR) of diameter at breast height (DBH) for cohort II (0.033 cm·cm^-1·a^-1) was significantly higher than that of cohort I (0.016 cm·cm^-1·a^-1) and II (0.018 cm·cm^-1·a^-1). Overall, harvesting promoted the DBH growth of most canopy dominant tress (I and II). In particular, RGR of cohort II increased progressively with increasing harvesting intensity, while only the greatest harvesting intensity showed a significant positive effect on RGR of cohort I. In contrast, rare species showed weak responses to harvesting treatment. It should be noted that there was a response lag of tree growth to harvesting: no detectable difference in RGR was found between control and harvested plots within the first two years after harvesting, whereas the positive effect of harvesting on RGR began to appear 2-4 years after harvesting and continued during the subsequent monitoring period. The RGR of each cohort decreased with the increase of initial DBH. Moreover, the slopes of initial DBH-RGR relationship increased with harvesting intensity, suggesting that smaller trees benefited more from reduced competition. Our results may provide scientific basis for a more accurate monitoring of the post-harvesting forest dynamics, and would be helpful to future sustainable management of temperate mixed forests.

Aims A particular set of species that have the potential to inhabit a local community but are locally absent is called dark diversity. Our aim was to investigate the impacts of plant characteristics and environmental factors on the dark diversity in a broadleaved Korean pine (Pinus koraiensis) forest.

Methods The study was conducted based on survey data of a 9-hm² broadleaved Korean pine forest in the Liangshui National Nature Reserve of Heilongjiang Province. We estimated the dark diversity probability of main species by using the Beals index. The correlations between the shade tolerance index, importance value and dark diversity probability were evaluated, and the effects of life form and shade tolerance on dark diversity probability were analyzed at the individual level. The correlations between community completeness and environmental factors, and community completeness and species diversity were investigated at the plot level.

Important findings The results showed that: (1) Average dark diversity probability for these species in this plot was 77.79%. For arbors, Juglans mandshurica had the highest dark diversity probability of 97.21%; however, for shrubs, the dark diversity probability of Viburnum opulus subsp. calvescens and Rhamnus davuricawere the highest, at 98.01%. (2) The dark diversity probability was negatively correlated with the importance value. However, the shade tolerance index was positively correlated with the importance value. (3) There was no significant difference in the dark diversity probability between arbors and shrubs, but the dark diversity probability of shade-intolerant species was significantly higher than that of shade-tolerant species. (4) Slope and convexity were both significantly positively correlated with community completeness. Soil organic matter, soil available potassium, soil bulk density, mass moisture content, soil pH, soil available nitrogen, and soil total nitrogen were not significantly related to community completeness; however, soil available phosphorus, soil total phosphorus and volumetric moisture content were all significantly negatively correlated with community completeness. The correlations between the species diversity indices and community completeness were significantly positive. In short, the dark diversity probability of shade-intolerant species and rare species in the broadleaved Korean pine forest was relatively high. Slope, convexity, soil available phosphorus, soil total phosphorus and volumetric moisture content were the main environmental factors that significantly influenced community completeness. The higher the community completeness was, the higher the species diversity of the community.

Aims To provide a theoretical basis for the protection and restoration of broadleaved Korean pine forest in Changbai Mountain area, the population age structure and quantitative dynamics of Pinus koraiensis were investigated.

Methods We used field data to form the static life table, estimate the population quantitative indexes, and to fit the survival and mortality curves for identifying the population characteristics of P. koraiensis. We also used the survival functions and spectral analysis to explore its population age structure and to reveal natural regeneration processes and as well as future developmental trend.

Important findings Based on the distribution of diameter, the population of P. koraiensis could be sorted into 14 age classes and combined into four subpopulations, i.e., juvenile (I-III), middle-age (IV-VI), adult (VII-X) and old (XI-XIV) stages. By contrast, the number of individuals in population was higher in stages of young and adult and lower in middle and old stages. However, the survival curve of population was close to Deevey-III type, reflecting that the high mortality occurred in juvenile stage. In addition, external random interference was crucial for whole population dynamics. With and without such interference, the population of P. koraiensis become the constant type (V′_pi was close to 0) and increasing type (V_pi > 0), respectively. Moreover, the survival function analysis showed that the number of individuals of this species was dramatically decreased in early stage, and then relatively stable in middle-age stage and declined again in late stage. Furthermore, spectral analysis for this population indicated that the pattern of natural regeneration exhibited periodic fluctuation along successional process. With population development, the number of young and middle-aged individuals would gradually decrease while the number of adult and old individuals would gradually increase. High mortality of young individuals, limitation of resources, and physiological aging of old trees seem likely to be the important factors that drove population dynamics in this species. We thus suggest that improving habitat condition from silvicultural way may enhance seedling or sapling survival rate and promote their growth, which may benefit the recovery of population for P. koraiensis in this area.

Aims Understanding the trade-offs between leaf functional traits has long been a hot topic in ecological research.

Methods In a broadleaved Korean pine (Pinus koraiensis) forest and a spruce-fir valley forest in the Liangshui National Nature Reserve, Heilongjiang Province, we measured 5 leaf economic traits and 4 leaf defense traits for seedlings of 8 tree species and 11 shrub species, to evaluate trait variation across species life forms and forest types, as well as trait correlations.

Important findings There was no significant difference in leaf traits between the seedlings of trees and shrubs. The total phenolic content and tannin content of plants in the spruce-fir valley forest were significantly higher than those in broadleaved Korean pine forest. Compared with broadleaved Korean pine forest, the spruce-fir valley forest has lower under-canopy light intensity but higher air and soil moisture, which is more conducive to the aggregation of natural enemies. This stronger biological interaction may in turn drives seedlings to invest more on their defense traits in spruce-fir forest. Leaf chlorophyll content was positively correlated with specific leaf area, leaf nitrogen and phosphorus content. Leaf nitrogen content was positively correlated with leaf phosphorus content. Moreover, there was a significant and positive correlation between leaf defense traits. Leaf chlorophyll and nitrogen content were negatively correlated with total phenolic content, tannin content and content of flavonoids. This suggests the existence of a trade-off between leaf carbon economics and defense. The seedlings of trees and shrubs had similar carbon economics strategies. The results of this study have implications for predicting forest dynamics and community composition based on leaf functional traits.

Aims The lamina and petiole of a leaf are closely related in structure and function, of which the variation and correlation are important for understanding the strategies of biomass allocation at the leaf level.

Methods In this study, we sampled Betula platyphylla, Tilia amurensisand Acer pictum subsp. mono in a broadleaved Korean pine (Pinus koraiensis) forest in Northeast China and explored effects of species, tree size and canopy position on variations in and correlations between lamina and petiole traits. For each species, we selected 10 trees for small (diameter at breast height (DBH): 1-6 cm), intermediate (DBH: 15-20 cm), and large sizes (DBH: 35-45 cm), respectively. For the large-sized trees, we took canopy position into account. We measured lamina area (LA), lamina dry mass (LDM), petiole length (PL), and petiole dry mass (PDM).

Important findings (1) The four traits significantly varied with species and tree size. PL and PDM of the small trees were significantly lower than those of large trees for the three species. LDM of the small trees was significantly less than that of the large trees for T. amurensis and A. pictum subsp. mono, while LA of the small trees was significantly greater than that of the large trees for B. platyphyllaand T. amurensis. For the large trees, the effect of canopy position on the variations in the four traits was species-depended. (2) There was a significant allometric scaling relationship between the lamina and petiole traits for all the three species. The regression slopes ranked as T. amurensis > B. platyphylla> A. pictum subsp. mono; the slopes for B. platyphyllaranked as small size > large size > intermediate size, while the slopes for the large-sized trees were the greatest among different tree sizes for T. amurensisand A. pictum subsp. mono. Canopy position had no significant effect on the regression slope for the large-sized trees. These results showed that species and tree size significantly influenced the variations in and correlations between the lamina and petiole traits for the three temperate tree species, while canopy position had little effect for the large-sized trees.

Aims At leaf level, trade-offs between petiole (supporting structure) and lamina (assimilation structure) are influenced by several factors. Here, we aim to provide insight into the growth features and life history strategies of plants by exploring the trade-offs between petiole and lamina traits for different functional plants in Northeast China.

Methods We measured leaf traits in three life-form plants (tree, shrub, herb) of a broadleaved Korean pine (Pinus koraiensis) forest in Xiao Hinggan Mountains, China. The least significant difference method was used to compare the variation of leaf traits among the three life forms. Trade-offs between lamina and petiole traits were estimated by using standardized major axis method for the three groups, in terms of their life form, leaf type, and shade tolerance.

Important findings Significant allometric scaling relationships were found between lamina traits and petiole dry mass in all life forms, leaf types and different shade tolerant tree species, with slopes significantly departing from 1.0. As petiole dry mass increased, the lamina fresh mass and lamina dry mass of trees increased more significant than shrubs and herbs, but tree petioles can support the smallest leaf area for a given petiole dry mass. The regression slope of lamina area-petiole dry mass for simple-leaved species was significantly greater than that of compound-leaved species, but the regression slope of lamina fresh mass-petiole dry mass was opposite, and simple-leaved species had greater lamina dry mass at a given petiole dry mass than compound-leaved species. Shade tolerant tree species were observed to have larger lamina area and greater lamina fresh mass at a given petiole dry mass than shade intolerant tree species. Moreover, the slope of petiole biomass allocation ratio (petiole dry mass/leaf dry mass)-lamina trait was greater than 0 for shade intolerant tree species and less than 0 for shade tolerant tree species. Our results suggested trade-offs exist between leaf properties (leaf area, leaf fresh mass, leaf dry mass) and petiole traits (petiole dry mass), which can be varied for plants with different life form, leaf type, and shade tolerance, thus to some extent, revealed the growth features and life history strategies of different functional plants.

Aims Compound-leaved plants commonly grow better than simple-leaved plants, but it is unknown about how leaflet growing position influences leaflet trait variations and its correlations in compound leaves. Our aim was to address this question with a model tree species Fraxinus mandshurica.

Methods Fraxinus mandshurica, a typical compound-leaved tree in northeastern China, was selected as a focal plant species. We measured leaflet thickness (LT), leaflet area (LA), leaflet dry matter content (LDMC), specific leaflet area (SLA), leaflet nitrogen content (LNC), and leaflet phosphorus content (LPC) across leaflet growing position in the compound leaves of F. mandshurica.We analyzed its leaflet trait variations with leaflet growing position and examined if leaflet growing position significantly affected leaflet traits using the least significant difference (LSD) method. Similarly, we analyzed the relationships among leaflet traits and examined if leaflet growing position significantly affected these relationships using the standardized major axis (SMA) method.

Important findings (1) LT, LA, LDMC and LNC decreased with leaflet growing position (from the tip to the base of a compound leaf), but SLA and LPC increased with leaflet growing position. LT and LA were significantly variable with leaflet growing position. (2) Within a compound leaf, there was an isometric relationship between SLA and LNC or between LDMC and LT. However, LA showed an allometric relationship with LT, SLA and LPC; LDMC show an allometric relationship with SLA, LNC and LPC; LPC showed an allometric relationship with LT. (3) Leaflet growing position had significant effects on the relationships of LA with LT, SLA, and LPC. The greatest slopes between LT and LA and between SLA and LA occurred at the third leaflet growing position (the middle of a compound leaf). The smallest values of absolute slopes between LT and LA and between LPC and LA appeared at the sixth leaflet growing position (the base of a compound leaf). The results suggest that leaflet traits in the compound leaves of F. mandshurica could change with leaflet growing position, and most of trait relationships might be allometric. To a certain extent, the growth relationships among leaflet traits could vary with leaflet growing position.

Aims Temperate forest tree species adopt different strategies in storing and utilizing non-structural carbohydrates (NSC). Trunk is the main storage pool of NSC. However, the radial variation and interspecific difference of trunk NSC are still unclear, and how wood porous group—non-porous wood (gymnosperms), diffuse-porous wood and ring-porous wood (both are angiosperms)—influences NSC concentrations of trunks is still uncertain. The objective of this study was to explore the variation of trunk NSC concentrations of major tree species in temperate forests with wood porosity and trunk tissues.

Methods We selected 32 tree species in a broadleaved and Pinus koraiensis mixed forest in Muling City, Heilongjiang Province. Bark, sapwood, and heartwood of stem at the breast height were collected to analyze the variation of NSC concentrations with wood porosity and tissue.

Important findings (1) Tree species, tissue and wood porosity significantly affected the NSC concentration of trunk. The interspecific variation of concentrations of soluble sugars, starch, total NSC and sugar/starch in the three tissues was large, with the lowest coefficient of variation of 37% (total NSC concentration in bark) and the highest of 101% (starch concentration in heartwood). Tissue, species and their interactions significantly affected trunk NSC concentration. (2) The concentrations of soluble sugar, starch and total NSC decreased with the increasing radial depth. The concentration of soluble sugars and sugar/starch in bark of non-porous species was significantly higher than those of diffuse-porous and ring-porous species. The concentration of starch and total NSC in sapwood was in the order of ring-porous > diffuse-porous > non diffuse-porous wood species. (3) The ratio of soluble sugars, starch and total NSC concentrations in sapwood to in heartwood was about 1 for non-porous wood species, which was significantly lower than those for diffuse-porous and ring-porous wood species, and the correlation of the starch concentration between sapwood and heartwood of non-porous wood was more significant than that of the other two wood-porous types, indicating that the functional differentiation between sapwood and heartwood was clearer for angiosperms than for gymnosperms. These results revealed that wood porosity influenced storage strategy of NSC in trunks of temperate tree species, and it was necessary to distinguish trunk tissues in the study of the whole-tree NSC storage and the ecophysiological function of trees.