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University campuses usually have more trees and can provide various ecosystem services. However, there are few reports on tree ecosystem services of Chinese university campuses, especially in northern China. This study investigated the trees in the campus of Shenyang Institute of Technology and analyzed its ecological benefits and monetary value through i-Tree Streets. The campus trees contained a total of 5193 trees of 66 species, of which Catalpa ovata G. Don, Acer mono Maxim., Rhus typhina Nutt, and Salix babylonica L. accounted for 59.7% of the total number. The age structure of the trees in the campus was not ideal, with 71.5% of young trees, 24.0% of maturing trees, 4.5% of mature trees, and only 0.04% of old trees. The trees in the campus provided more energy saving benefits ($60,850, $11.7/tree), carbon reduction benefits ($34,318, $6.6/tree) and aesthetic benefits ($30,150, $5.8/tree). The benefits resulted from air pollutant removal ($12,889, $2.5/tree) and rainwater runoff interception ($15,534, $3.0/tree) were smaller. In addition, tree species with more maturing trees and mature trees (i.e., with larger diameter at breast height) and large leaf area in the campus contributed significantly to ecosystem services. Our results can provide suggestions and certain insights for Chinese campus greening managers in tree species selection and tree management.

In forest communities, conspecific density/distance dependence (CDD) is an important factor regulating diversity. It remains unknown how and the extent to which gap creation alters the mode and strength of CDD via changes in the relative importance of pathogens and mycorrhizae. Seeds of two hardwoods (i.e., Acer mono associated with arbuscular mycorrhizae [AM] and Quercus serrata associated with ectomycorrhizae [EM]) were sown reciprocally at four distances from the boundary between Acer- and Quercus-dominated forests towards forest interior in each of forest understories (FUs) and gaps. The causes of seed and seedling mortality, seedling growth and colonization of mycorrhizal fungi were investigated. In Acer, seed and seedling mortality were highest in Acer forests and gradually decreased towards the interior of Quercus forests in FU, mainly due to severe attack of soil pathogens, invertebrates, and leaf diseases. The reverse was true in gaps, due to reduction of damping-off damage caused by distance-dependent colonization of AM. In Quercus, most seeds and seedlings were eaten by vertebrates in FUs. The seedling mortality caused by leaf diseases was not high, even beneath conspecific forests with higher colonization of EM in gaps, suggesting a positive EM influence. In both species, seedling mass was greatest in conspecific forests and gradually decreased towards the interior of heterospecific forests in gaps, due to higher colonization of mycorrhizae near conspecifics. In conclusion, light conditions strongly altered the mode of CDD via changes in relative influence of pathogens and mycorrhizae, suggesting that gap creation may regulate species diversity via changes in the mode of CDD.

Acer pictum and Quercus acuta are native species recommended for restoration. To restore ecosystem functions and maintain natural ecosystems, it is suggested to deploy well-adapted and locally adapted plant material, and this notion is gaining interest. Studying how species change in response to climate change is an important part of forest restoration planning. Our method uses climate data to define the habitat range of species and to identify regions with relatively similar climates through Seed Transfer Zones (STZs). Potential habitat suitability changes of A. pictum and Q. acuta were identified under various environmental scenarios using seven climatic factors and five topographical factors. The MaxEnt algorithm was used to predict potential habitat suitability in current and future (1980–2100) climate change scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5). STZs are maps of areas with comparable climates and have been used to determine the climates of potentially habitable areas. This helps to minimize the maladaptation of seed movement within the same area. As a result, A. pictum growth increased along the southern coastal area and drainage was the paramount factor influencing A. pictum distribution. By checking the climate of regions with high habitability in STZs (Winter Minimum Temperature (WMT) 15–20 °F, Annual Heat: Moisture (AHM) 16–19 °C/m zone, WMT 20–25 °F, AHM 16–19 °C/m located in the zone), Q. acuta was shown to move northward with climate change centering on the southern coastal area. Additionally, Annual Precipitation (Bio12) was the most significant factor influencing Q. acuta distribution. In confirming the climate of areas with high habitability in STZs, we verified that habitat density was high in the WMT 10–15 °F, AHM 19–21 °C/m zone and WMT 20–25 °F, AHM 19–21 °C/m zone. This study establishes that the potential distributions of A. pictum and Q. acuta are affected by climate change. It supplies evidence for ecological restoration and sustainable development, and can formulate future conservation and management plans for economically valuable species.

Subcanopy tree species are an important component of temperate secondary forests. However, their biomass equations are rarely reported, which forms a “vertical gap” between canopy tree species and understory shrub species. In this study, we destructively sampled six common subcanopy species ( Syringa reticulate var. amurensis (Rupr.) Pringle, Padus racemosa (Lam.) Gilib., Acer ginnala Maxim., Malus baccata (Linn.) Borkh., Rhamnus davurica Pall., and Maackia amurensis Rupr. et Maxim.) to establish biomass equations in a temperate forest of Northeast China. The mixed-species and species-specific biomass allometric equations were well fitted against diameter at breast height (DBH). Adding tree height (H) as the second predictor increased the R 2 of the models compared with the DBH-only models by –1% to + 3%. The R 2 of DBH-only and DBH-H equations for the total biomass of mixed-species were 0.985 and 0.986, respectively. On average, the biomass allocation proportions for the six species were in the order of stem (45.5%) > branch (30.1%) > belowground (19.5%) > foliage (4.9%), with a mean root: shoot ratio of 0.24. Biomass allocation to each specific component differed among species, which affected the performance of the mixed-species model for particular biomass component. When estimating the biomass of subcanopy species using the equations for canopy species (e.g., Betula platyphylla Suk., Ulmus davidiana var. japonica (Rehd.) Nakai, and Acer mono Maxim.), the errors in individual biomass estimation increased with tree size (up to 68.8% at 30 cm DBH), and the errors in stand biomass estimation (up to 19.2%) increased with increasing percentage of basal area shared by subcanopy species. The errors caused by selecting such inappropriate models could be removed by multiplying adjustment factors, which were usually power functions of DBH for biomass components. These results provide methodological support for accurate biomass estimation in temperate China and useful guidelines for biomass estimation for subcanopy species in other regions, which can help to improve estimates of forest biomass and carbon stocks.

Acer L. species are well known as ornamental trees due to their colourful leaves in autumn season. Acer pictum subsp. mono (Maxim.) H. Ohashi (APM) and Acer tataricum subsp. ginnala (Maximowicz) Wesmael (ATG) form leaves with completely different colours in autumn, yellow and red, respectively. In response to this phenomenon, we investigated the metabolic regulation of APM and ATG in different seasons by combining metabolomics, ionomics, the antioxidant system and pigment content. The results showed that the process of senescence and discolouration exists in leaves of different Acer species, and the regulatory strategy shows species specificity. Compared with green leaves, the accumulation of primary metabolites in autumn leaves of APM was extensively depleted, chlorophyll content was decreased, and antioxidant enzymes and C6C3C6 type phenolic compounds synergistically enhanced the antioxidant capacity of plants to cope with senescence. Carotenoid content was raised, which together with phenolic compounds (chlorogenic acid, rutin) provides the leaves with a yellow colour. The response of chlorophyll and the antioxidant system in autumn leaves of ATG is consistent with that of APM, while sugar content increases. The increased anthocyanin content in autumn leaves of ATG explains the transition of leaves from green to the red colour, which may be accompanied by the combined effect of elements (Fe, Zn, Mn) and isoflavones. This study provides a reference for the study of colouration mechanism and seasonal adaptation in Acer L. species.

Key messageA negative productivity-diversity relationship was determined for biomass-dominant species at the community level. This study thus supports the hypothesis in which the effects of individual species on the productivity-diversity relationships at the community level are related to their biomass density, an important functional trait.ContextThe productivity-diversity relationships have been extensively studied in various forest ecosystems, but key mechanisms underlying the productivity-diversity relationships still remain controversial.AimsThe objective of this study is to explore the productivity-diversity relationships at the community level, and to investigate the roles of individual species in shaping the community-level relationships between productivity and diversity under different forest types.MethodsThe study was conducted in two fully stem-mapped temperate mixed forest plots in Northeastern China: a natural secondary forest plot, and an old-growth forest plot. An individual-based study framework was used to estimate the productivity-diversity relationships at both species and community levels. A homogeneous Thomas point process was used to evaluate the significance of productivity-diversity relationship deviating from the neutral.ResultsAt the species level, most of the studied species exhibit neutral productivity-diversity relationship in both forest plots. The percentage of species showing negative productivity-diversity relationship approaches linearly a peak value for very close neighborhoods (the secondary forest plot: r = 3 m, 38%; the old-growth forest plot: r = 4 m, 42%), and then decreases gradually with increasing spatial scale. Interestingly, only a few species displayed positive productivity-diversity relationship within their neighborhoods. Dominant species mainly exhibit negative productivity-diversity relationship while tree species with lower importance values exhibit neutral productivity-diversity relationship in both forests. At the community level, a consistent pattern of productivity-diversity relationship was observed in both forests, where tree productivity is significantly negatively associated with local species richness. Four biomass-dominant species (Juglans mandshurica Maxim., Acer mono Maxim.,Ulmus macrocarpa Hance and Acer mandshuricum Maxim.) determined a negative productivity-diversity relationship at the community level in the secondary forest plot, but only one species (Juglans mandshurica) in the old-growth forest plot.ConclusionThe productivity-diversity relationship is closely related to the dominance of individual species at the species level. Moreover, this analysis is the first to report the roles of biomass-dominant species in shaping the productivity-diversity relationship at the community level.

Royal jelly is a specific product secreted by honeybees, and has been sought after to maintain health because of its valuable bioactive substances, e.g., lipids and vitamins. The lipids in royal jelly come from the bee pollen consumed by honeybees, and different plant source of bee pollen affects the lipid composition of royal jelly. However, the effect of bee pollen consumption on the lipid composition of royal jelly remains unclear. Herein, we examined the influence of two factors on the lipid composition of royal jelly: first, two plant sources of bee pollen, i.e., Acer mono Maxim. (BP-Am) and Phellodendron amurense Rupr. (BP-Pa); secondly, different feeding times. Lipidomic analyses were conducted on the royal jelly produced by honeybees fed BP-Am or BP-Pa using ultra-high performance liquid chromatography (UPLC)-Q-Exactive Orbitrap mass spectrometry. The results showed that the phospholipid and fatty acid contents differed in royal jelly produced by honeybees fed BP-Am compared to those fed BP-Pa. There were also differences between timepoints, with many lipid compounds decreasing in abundance soon after single-pollen feeding began, slowly increasing over time, then decreasing again after 30 days of single-pollen feeding. The single bee pollen diet destroyed the nutritional balance of bee colonies and affected the development of hypopharyngeal and maxillary glands, resulting in differences in royal jelly quality. This study provides guidance for optimal selection of honeybee feed for the production of high-quality royal jelly.

The management of stand structure and the protection of species diversity are crucial to forest ecosystem service functions. Changbai Mountain is one of the three major forest regions in Northeast China, and understanding the characteristics of stand structure and the allometric relationship between stand structure variables and the correlation between stand factors and species diversity is the basis for achieving effective forest management and ecological function improvement. In this study, the typical deciduous broad-leaved mixed forest and coniferous and broad-leaved mixed forest of the Longwan Nature Reserve in the Changbai Mountain were taken as the research objects, and the stand structure and diversity were investigated in detail. Allometric growth equations were established using the breast height diameter (DBH), tree height, and crown width of the main dominant species. Pearson correlation analysis was conducted on the stand structure and diversity of the forest community. The experimental results showed that young forests with small diameters and small individuals were the main part of the stands. Optimal allometric growth models of the main tree species (Acer mandshuricum, Ulmus davidiana var. japonica, Juglans mandshurica, Acer mono, and Tilia amurensis) were 0.807D0.646, 0608D0.381H0.390, 0.502D0.533H0.295, 0.795D0.540H0.157, and 0.541D0.484H0.301, respectively, with R2 values ranging between 0.6 and 0.8, indicating a good fit for the models. Furthermore, tree density, crown width, and DBH were the main factors affecting tree diversity. The research results will provide theoretical support for the efficient management of forest stand structure and diversity conservation in the Longwan Reserve.

Reducing greenhouse gas emissions is one of the major challenges in combating global warming. Carbon, including in the form of carbon dioxide (CO 2 ), is considered an essential greenhouse gas under human control to demonstrate success in emission reductions. However, many carbon stock quantifications in forest ecosystems still rely on the estimated 50% carbon content instead of more precise species-, tissue- and site-specific values. Thus, this study aimed to thoroughly measure and analyze the carbon content and variability using the 14 major tree species in Northeast China. Over 600 trees were destructively sampled from three different major mountainous regions (i.e., the Changbai, Daxing’an, and Xiaoxing’an mountains), and the carbon contents of each species were precisely measured to the sub-tissue level. Carbon contents varied significantly between species, with foliage carbon mostly found to be the highest, while root carbon contents were the lowest. Average carbon contents can be ranked as: Ulmus laciniata (43.4%) <  Phellodendron amurense (43.5%) <  Acer mono (43.8%) <  Tilia amurensis (44.2%) <  Populus davidiana (44.5%) <  Fraxinus mandshurica (44.7%) <  Juglans mandshurica (44.9%) <  Quercus mongolica (45.3%) <  Betulla davurica (45.8%) <  Betulla platyphylla (46.7%) <  Picea koreansis (46.9%) <  Larix gmelinii (47.4%) <  Pinus koreansis (48.3%) <  Abies nephrolepis (48.3%). Carbon contents were higher in conifers (47.7%) compared to broadleaf species (44.9%). In addition, both tree tissues and growing sites also had a significant effect on carbon content. At the sub-tissue level, only stem’s sub-tissues (i.e., bark, heartwood, and sapwood) carbon contents showed significant variations. The results suggest that bark should be separated from other stem sub-tissues and considered separately when determining carbon stocks. This research contributes to improving estimates of terrestrial carbon quantifications, and in particular, the values obtained can be used in China’s National Forest Inventory.

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