Distribution of 35 Polycyclic Aromatic Hydrocarbons in Pine Needle Samples from Selected Locations in the Republic of Korea.

Polycyclic aromatic hydrocarbons (PAHs), dust, and wax were measured in pine needles, and PAHs were also measured in surface soil. Pearson correlation analysis was performed between the analytical values. The main compounds responsible for the increase in total PAHs were non-carcinogenic phenanthrene and fluoranthene. Therefore, the % content of carcinogenic PAHs decreased with a slope = -0.037 (r = 0.47, p < 0.01), as the total PAH concentration in pine needles increased. Correlations between individual PAHs in pine needles and surface soil were very high when only low-number ring PAHs (2R- and 3R-PAHs) were statistically analyzed and significant when only high-number ring PAHs were statistically analyzed. Low-number ring PAH mainly moves in the gas phase and diffuses into the wax layer, so it was found to be statistically significant with the wax content of pine needles. High-number ring PAHs showed a high correlation with the amount of dust in pine needles because they mainly attached to dust particles and accumulated on the surface of pine needles. The ratios of fluoranthene/pyrene and methylphenanthrene/phenanthrene for predicting the origin of atmospheric PAHs have also been proven valid for pine needles.

A novel seawater hydrothermal-deep eutectic solvent pretreatment enhances the production of fermentable sugars and tailored lignin nanospheres from Pinus massoniana.

Lignocellulose biorefinery depended on effective pretreatment strategies is of great significance for solving the current global crisis of ecosystem and energy security. This study proposes a novel approach combining seawater hydrothermal pretreatment (SHP) and microwave-assisted deep eutectic solvent (MD) pretreatment to achieve an effective fractionation of Pinus massoniana into high value-added products. The results indicated that complex ions (Mg2+, Ca2+, and Cl-) in natural seawater served as Lewis acids and dramatically promoted the depolymerization of mannose and xylan into oligosaccharides with 40.17 % and 75.43 % yields, respectively. Subsequent MD treatment realized a rapid and effective lignin fractionation (~90 %) while retaining cellulose. As a result, the integrated pretreatment yielded ~85 % of enzymatic glucose, indicating an eightfold increase compared with untreated pine. Because of the increased hydrophobicity induced by the formation of acyl groups during MD treatment, uniform lignin nanospheres were successfully recovered from the DES. It exhibited low dispersibility (PDI = 2.23), small molecular weight (1889 g/mol), and excellent oxidation resistance (RSI = 5.94), demonstrating promising applications in functional materials. The mechanism of lignin depolymerization was comprehensively elucidated via FTIR, 2D-HSQC NMR, and GPC analyses. Overall, this study provides a novel and environmentally friendly strategy for lignocellulose biorefinery and lignin valorization.

Impact of species composition on fire-induced stand damage in Spanish forests.

Mixed forests play a fundamental ecological role increasing biodiversity and providing ecosystem services; it has been suggested they have higher resilience and resistance against disturbances, particularly fire. Here, we compare tree mortality in post-fire mixed and pure stands in Spain, on 2,782 plots and 30,239 trees during the period 1986 to 2007. We show evidence that mixed stands can have higher post-fire mortality than pure stands, and specific mixtures of species with different fire-related strategies increase the stand's vulnerability to fire damage versus pure stands of either species, such is the case of Pinus halepensis-Pinus nigra mixtures. Mixtures of two species often had higher mortality than species growing in pure stands. Combinations of species with different fire-related strategies can both enhance or reduce forest resistance. The role and management of mixed forests should be reconsidered after these findings, in order to enhance forest resilience to fires.

Nitrogen addition changed soil fungal community structure and increased the biomass of functional fungi in Korean pine plantations in temperate northeast China.

Nitrogen (N) deposition is a global environmental issue that can have significant impacts on the community structure and function in ecosystems. Fungi play a key role in soil biogeochemical cycles and their community structures are tightly linked to the health and productivity of forest ecosystems. Based on high-throughput sequencing and ergosterol extraction, we examined the changes in community structure, composition, and biomass of soil ectomycorrhizal (ECM) and saprophytic (SAP) fungi in 0-10 cm soil layer after 8 years of continuous N addition and their driving factors in a temperate Korean pine plantation in northeast China. Our results showed that N addition increased fungal community richness, with the highest richness and Chao1 index under the low N treatment (LN: 20 kg N ha-1 yr-1). Based on the FUN Guild database, we found that the relative abundance of ECM and SAP fungi increased first and then decreased with increasing N deposition concentration. The molecular ecological network analysis showed that the interaction between ECM and SAP fungi was enhanced by N addition, and the interaction was mainly positive in the ECM fungal network. N addition increased fungal biomass, and the total fungal biomass (TFB) was the highest under the MN treatment (6.05 ± 0.3 mg g-1). Overall, we concluded that N addition changed soil biochemical parameters, increased fungal activity, and enhanced functional fungal interactions in the Korean pine plantation over an 8-year simulated N addition. We need to consider the effects of complex soil conditions on soil fungi and emphasize the importance of regulating soil fungal community structure and biomass for managing forest ecosystems. These findings could deepen our understanding of the effects of increased N deposition on soil fungi in temperate forests in northern China, which can provide the theoretical basis for reducing the effects of increased N deposition on forest soil.

Carbon stock projection for four major forest plantation species in Japan.

Carbon sequestration via afforestation and forest growth is effective for mitigating global warming. Accurate and robust information on forest growth characteristics by tree species, region, and large-scale land-use change is vital and future prediction of forest carbon stocks based on this information is of great significance. These predictions allow exploring forestry practices that maximize carbon sequestration by forests, including wood production. Forest inventories based on field measurements are considered the most accurate method for estimating forest carbon stocks. Japan's national forest inventories (NFIs) provide stand volumes for all Japanese forests, and estimates from direct field observations (m-NFIs) are the most reliable. Therefore, using the m-NFI from 2009 to 2013, we selected four major forest plantation species in Japan: Cryptomeria japonica, Chamaecyparis obtusa, Pinus spp., and Larix kaempferi and presented their forest age-carbon density function. We then estimated changes in forest carbon stocks from the past to the present using the functions. Next, we investigated the differences in the carbon sequestration potential of forests, including wood production, between five forestry practice scenarios with varying harvesting and afforestation rates, until 2061. Our results indicate that, for all four forest types, the estimates of growth rates and past forest carbon stocks in this study were higher than those considered until now. The predicted carbon sequestration from 2011 to 2061, assuming that 100 % of harvested carbon is retained for a long time, twice the rate of harvesting compared to the current rate, and a 100 % afforestation rate in harvested area, was three to four times higher than that in a scenario with no harvesting or replanting. Our results suggest that planted Japanese forests can exhibit a high carbon sequestration potential under the premise of active management, harvesting, afforestation, and prolonging the residence time of stored carbon in wood products with technology development.

Effects of four bolete species on ectomycorrhizae formation and development in Pinus thunbergii and Quercus acutissima.

BACKGROUND: Bolete cultivation is economically and ecologically valuable. Ectomycorrhizae are advantageous for plant development and productivity. This study investigated how boletes affect the formation of Pinus thunbergii and Quercus acutissima ectomycorrhizae using greenhouse-based mycorrhizal experiments, inoculating P. thunbergii and Q. acutissima with four species of boletes (Suillus bovinus, Suillus luteus, Suillus grevillei, and Retiboletus sinensis). RESULTS: Three months after inoculation, morphological and molecular analyses identified S. bovinus, S. luteus, S. grevillei and R. sinensis ectomycorrhizae formation on the roots of both tree species. The mycorrhizal infection rate ranged from 40 to 55%. The host plant species determined the mycorrhiza morphology, which was independent of the bolete species. Differences in plant growth, photosynthesis, and endogenous hormone secretion primarily correlated with the host plant species. Infection with all four bolete species significantly promoted the host plants' growth and photosynthesis rates; indole-3-acetic acid, zeatin, and gibberellic acid secretion increased, and the abscisic acid level significantly decreased. Indole-3-acetic acid was also detected in the fermentation broths of all bolete species. CONCLUSIONS: Inoculation with bolete and subsequent mycorrhizae formation significantly altered the morphology and hormone content in the host seedlings, indicating growth promotion. These findings have practical implications for culturing pine and oak tree species.

Functional Characterization of PmDXR, a Critical Rate-Limiting Enzyme, for Turpentine Biosynthesis in Masson Pine (Pinus massoniana Lamb.).

As one of the largest and most diverse classes of specialized metabolites in plants, terpenoids (oprenoid compounds, a type of bio-based material) are widely used in the fields of medicine and light chemical products. They are the most important secondary metabolites in coniferous species and play an important role in the defense system of conifers. Terpene synthesis can be promoted by regulating the expressions of terpene synthase genes, and the terpene biosynthesis pathway has basically been clarified in Pinus massoniana, in which there are multiple rate-limiting enzymes and the rate-limiting steps are difficult to determine, so the terpene synthase gene regulation mechanism has become a hot spot in research. Herein, we amplified a PmDXR gene (GenBank accession no. MK969119.1) of the MEP pathway (methyl-erythritol 4-phosphate) from Pinus massoniana. The DXR enzyme activity and chlorophyll a, chlorophyll b and carotenoid contents of overexpressed Arabidopsis showed positive regulation. The PmDXR gene promoter was a tissue-specific promoter and can respond to ABA, MeJA and GA stresses to drive the expression of the GUS reporter gene in N. benthamiana. The DXR enzyme was identified as a key rate-limiting enzyme in the MEP pathway and an effective target for terpene synthesis regulation in coniferous species, which can further lay the theoretical foundation for the molecularly assisted selection of high-yielding lipid germplasm of P. massoniana, as well as provide help in the pathogenesis of pine wood nematode disease.

UV blocking edible films based on corn starch/moringa gum incorporated with pine cone extract for sustainable food packaging.

Corn starch (CS) is a good alternative to synthetic polymers due to its sustainability; nevertheless, because of its weak tensile strength, the matrix requires another polymer. Therefore, 0.5 % (w/v) moringa gum (MG) was added. The purpose of this study was to assess how pine cone extract (PCE) affected the physiochemical and mechanical properties of corn starch and moringa gum (CS/MG) films and their use as UV-blocking composites. The findings suggest that the PCE improved the elongation at break from 3.27 % to 35.2 % while greatly reducing the tensile strength. The hydrogen bonding between CS/MG and PCE was visible in the FTIR spectra. The XRD graph indicated that the films were amorphous. In comparison to CS/MG films, PCE-incorporated edible films demonstrated significant UV-blocking ability indicating their potential as sustainable packaging material for light-sensitive food products.

Predicting the global potential distribution of Bursaphelenchus xylophilus using an ecological niche model: expansion trend and the main driving factors.

Bursaphelenchus xylophilus (Steiner&Buhrer) Nickle is a global quarantine pest that causes devastating mortality in pine species. The rapid and uncontrollable parasitic spread of this organism results in substantial economic losses to pine forests annually. In this study, we used the MaxEnt model and GIS software ArcGIS10.8 to predict the distribution of B. xylophilus based on collected distribution points and 19 environmental variables (with a correlation coefficient of|R| > 0.8) for the contemporary period (1970-2000), 2041-2060 (2050s), 2061-2080 (2070s), and 2081-2100 (2090s) under four shared socioeconomic pathways (SSPs). We conducted a comprehensive analysis of the key environmental factors affecting the geographical distribution of B. xylophilus and suitable distribution areas. Our results indicate that in current prediction maps B. xylophilus had potential suitable habitats in all continents except Antarctica, with East Asia being the region with the most highly suitable areas and the most serious epidemic area currently. Precipitation of the warmest quarter, temperature seasonality, precipitation of the wettest month, and maximum temperature of the warmest month were identified as key environmental variables that determine the distribution of B. xylophilus. Under future climatic conditions, the potential geographic distribution of B. xylophilus will expand relative to current conditions. In particular, under the SSP5-8.5 scenario in 2081-2100, suitable areas will expand to higher latitudes, and there will be significant changes in suitable areas in Europe, East Asia, and North America. These findings are crucial for future prevention and control management and monitoring.

Genome-wide identification and expression analysis of ARF gene family in embryonic development of Korean pine (Pinus koraiensis).

BACKGROUND: The Auxin Responsive Factor (ARF) family plays a crucial role in mediating auxin signal transduction and is vital for plant growth and development. However, the function of ARF genes in Korean pine (Pinus koraiensis), a conifer species of significant economic value, remains unclear. RESULTS: This study utilized the whole genome of Korean pine to conduct bioinformatics analysis, resulting in the identification of 13 ARF genes. A phylogenetic analysis revealed that these 13 PkorARF genes can be classified into 4 subfamilies, indicating the presence of conserved structural characteristics within each subfamily. Protein interaction prediction indicated that Pkor01G00962.1 and Pkor07G00704.1 may have a significant role in regulating plant growth and development as core components of the PkorARFs family. Additionally, the analysis of RNA-seq and RT-qPCR expression patterns suggested that PkorARF genes play a crucial role in the development process of Korean pine. CONCLUSION: Pkor01G00962.1 and Pkor07G00704.1, which are core genes of the PkorARFs family, play a potentially crucial role in regulating the fertilization and developmental process of Korean pine. This study provides a valuable reference for investigating the molecular mechanism of embryonic development in Korean pine and establishes a foundation for cultivating high-quality Korean pine.

Drought legacies in mixed Mediterranean forests: Analysing the effects of structural overshoot, functional traits and site factors.

Previous favorable climate conditions stimulate tree growth making some forests more vulnerable to hotter droughts. This so-called structural overshoot may contribute to forest dieback, but there is little evidence on its relative importance depending on site conditions and tree species because of limited field data. Here, we analyzed remote sensing (NDVI) and tree-ring width data to evaluate the impacts of the 2017 drought on canopy cover and growth in mixed Mediterranean forests (Fraxinus ornus, Quercus pubescens, Acer monspessulanum, Pinus pinaster) located in southern Italy. Legacy effects were assessed by calculating differences between observed and predicted basal area increment (BAI). Overall, the growth response of the study stands to the 2017 drought was contingent on site conditions and species characteristics. Most sites presented BAI and canopy cover reductions during the drought. Growth decline was followed by a quick recovery and positive legacy effects, particularly in the case of F. ornus. However, we found negative drought legacies in some species (e.g., Q. pubescens, A. monspessulanum) and sites. In those sites showing negative legacies, high growth rates prior to drought in response to previous wet winter-spring conditions may have predisposed trees to drought damage. Vice versa, the positive drought legacy found in some F. ornus site was linked to post-drought growth release due to Q. pubescens dieback and mortality. Therefore, we found evidences of structural drought overshoot, but it was restricted to specific sites and species. Our findings highlight the importance of considering site settings such as stand composition, pre-drought conditions and different tree species when studying structural overshoot. Droughts contribute to modify the composition and dynamics in mixed forests.

Green deserts, but not always: A global synthesis of native woody species regeneration under tropical tree monocultures.

Tree monocultures constitute an increasing fraction of the global tree cover and are the dominant tree-growing strategy of forest landscape restoration commitments. Their advantages to produce timber are well known, but their value for biodiversity is highly controversial and context dependent. Therefore, understanding whether, and in which conditions, they can harbor native species regeneration is crucial. Here, we conducted meta-analyses based on a global survey of the literature and on a database created with local, unpublished studies throughout Brazil to evaluate the regeneration potential of native species under tree monocultures and the way management influences this regeneration. Native woody species regeneration under tree monocultures harbors a substantial fraction of the diversity (on average 40% and 68% in the global and Brazilian surveys, respectively) and abundance (on average 25% and 60% in the global and Brazilian surveys, respectively) of regeneration observed in natural forests. Plantations with longer rotation lengths, composed of native tree species, and located adjacent to forest remnants harbor more species. Pine plantations harbor more native individuals than eucalypt plantations, and the abundance of regenerating trees is higher in sites with higher mean temperatures. Species-area curves revealed that the number of woody species under pine and eucalypt plantations in Brazil is 606 and 598 species, respectively, over an aggregated sampled area of ca. 12 ha. We highlight that the understory of tree monocultures can harbor a considerable diversity of regenerating native species at the landscape and regional scales, but this diversity strongly depends on management. Long-rotation length and favorable location are key factors for woody regeneration success under tropical tree monocultures. Therefore, tree monocultures can play a role in forest landscape restoration and conservation, but only if they are planned and managed for achieving this purpose.

Promotion of levoglucosan production from biomass pyrolysis by hydrogen peroxide pre-oxidation.

Due to the complexity of biomass structures, the conversion of raw biomass into value-added chemicals is challenging and often requires efficient pretreatment of the biomass. In this paper, a simple and green pre-oxidation method, which was conducted under the conditions of 2 wt% H2O2, 80 min, and 150 °C, was reported to significantly increase the production of levoglucosan (LG) from biomass pyrolysis. The result showed that the LG yield significantly increased from 2.3 wt% (without pre-oxidation) to 23.1 wt% when pine wood was employed as a sample for pyrolysis at 400 °C, resulting from the removal of hemicellulose fraction and the in-situ acid catalysis of lignin carboxyl groups formed during the pre-oxidation. When the conditions for pre-oxidation became harsher than the above, the LG yield reduced because the decomposition of cellulose fraction in biomass. The study supplies an effective method for utilization of biomass as chemicals.

Mixing of pine and arbuscular mycorrhizal tree species changed soil organic carbon storage by affecting soil microbial characteristics.

Pure and mixed pine forests are found all over the world. The mycorrhizal type affects soil microbial activity and carbon sequestration capacity in pure forests. However, the effects of mycorrhizal type on microbial characteristics and carbon sequestration capacity in pine mixed forests remain untested. Further, making it difficult to predict carbon storage of the conversion from pure pine forests to mixed forests at larger scales. Herein, a meta-analysis showed that the contents of soil microbial biomass, mineral-associated organic carbon, and soil organic carbon in pine mixed forests with introduced arbuscular mycorrhizal tree species (PMAM) increased by 26.41 %, 58.55 %, and 27.41 %, respectively, compared to pure pine forests, whereas those of pine mixed forests without arbuscular mycorrhizal tree species (PMEcM) remained unchanged. Furthermore, the effect size of microbial biomass, mineral-associated organic carbon and organic carbon contents in subsoil of PMAM are 56.48 %, 78.49 % and 43.05 %, respectively, which are higher than those in topsoil. The improvement of carbon sinks throughout the PMAM soil profile is positively correlated with increases in microbial biomass and mineral-associated organic carbon in subsoil, according to regression analysis and structural equation modelling. In summary, these results highlight that the positive effects of introducing arbuscular mycorrhizal tree species rather than ectomycorrhizal tree species into pure pine forests on soil microbial biomass and carbon sequestration. The positive link between microbial biomass, mineral-associated organic carbon, and soil organic carbon suggests an underlying mechanism for how soil microorganisms store carbon in pine mixed forests. Nevertheless, our findings also imply that the soil carbon pool of PMAM may be vulnerable under climate change. Based on the above findings, we propose that incorporating mycorrhizal type of tree species and soil thickness into mixed forests management and biodiversity conservation.

Height-diameter model of broad-leaved mixed forest based on species classification in Maoershan, Northeast China.

The complex stand structure and high species diversity of natural forests pose great challenges for analyzing stand growth and formulating reasonable plans for forest management. The height-diameter relationship is of great significance for predicting stand growth and formulating forest management measures. Based on survey data of 48 broad-leaved mixed forest plots in Maoershan, we classified 23 tree species into four groups based on species structure, growth characteristics and bionomics. We established a generalized model including stand, tree competition, species mixing and species diversity variables by reparameterization method, and a two-level mixed effect model of plot and tree species group. We tested the prediction ability of the model by leave-one-out cross-validation method. The results showed that the Ratkowsky (1990) model was the optimal basic model. The introduction of dominant height, basal area of trees larger than the object tree, basal area proportion of each species, and Shannon index could better explain the height-diameter relationship of broad-leaved mixed forest in Maoershan. The introduction of the mixed effect model of plot and tree species group could significantly improve the prediction accuracy of the model, with a Ra2 of 0.83. Under the same gradient of environmental factors, intolerant tree species exhibited higher tree heights than shade-tolerant tree species. In this study, we used the constructed tree height-diameter model to analyze the effects of species mixing and tree functional traits on tree height, which provided a theoretical basis for accurately predicting height of different tree species and analyzing the growth relationships in broadleaved mixed forests.

Effects of topography and stand spatial structure on the diameter at breast height growth of major pioneer tree species of natural broad-leaved mixed forests in Zhejiang Province, China.

Based on the continuous inventory data of forest resources in Zhejiang Province in 2019 and 2021, we used statistical methods such as polynomial regression to analyze the impacts of topography and forest spatial structure on average annual diameter at breast height (DBH) growth of main pioneer tree species in natural broad-leaved mixed forests. The results showed that DBH of Schima superba, Quercus glauca, Quercus fabri, Lithocarpus glaber, Castanopsis eyrei, and Castanopsis sclerophylla were between 5-50.8, 5-41.5, 5-50.8, 5-43.9, 5-55.5, and 5-46.1 cm, respectively. We classified all the trees into three classes based on DBH: small (6-12 cm), medium (12-14 cm), and large (>26 cm). The average annual DBH growth of S. superba and Q. glauca was the highest on semi-shady slope and shady slope, with increases of 2.9%-15.7% and 1.1%-41.2%, respectively. The average annual DBH growth of large-diameter S. superba, L. glaber, C. eyrei and C. sclerophylla decreased with the increase of slope, with a maximum decrease of 27.0% for S. superba, with no significant difference among small- and medium-diameter trees as a whole. The slope position did not affect the annual DBH growth of small-diameter trees, while that of medium- and large-diameter S. superba, Q. glauca, and large-diameter Q. fabri, L. glaber decreased with the change of slope position from downhill, mesoslope, uphill to ridge, with a maximum decrease of 28.1% for L. glabe, and the major-diameter C. eyrei was on the contrary. Appropriate increase in the mingling was beneficial to the average annual DBH growth of medium- and large-diameter trees. Moderate mixing was suitable for S. superba, while low degree mixing and moderate mixing was suitable for Q. glauca, Q. fabri and L. glaber, and intensive mixing was suitable for C. eyrei and C. sclerophylla. No significant difference was observed for minor-diameter trees under the mingling. The neighborhood comparison only had a significant effect on the average annual DBH growth of large-diameter Q. glauca, Q. fabri, and L. glaber, which was significantly higher under subdominance-moderation than moderation-inferiority. The average annual DBH growth in the study area was mainly affected by aspect and mixing degree.

Characteristics of pine wood nematode disease in Nankang District, Ganzhou, Jiangxi Province, China.

Pine wood nematode (PWN) disease is one of the major disasters in forests of southern China, causing substantial forest resources and ecological and economic losses. Based on field surveys and WFV image data from the GF-1 satellite, we constructed a spatial identification model of PWN disease with the random forest model to explore the relative influences of topography, human activities and stand factors on the occurrence of diseases and predict their spatial distribution. We then used the spatial autocorrelation analysis to assess the distribution characteristics of PWN disease at the regional scale. The results showed that the random forest model constructed in this study was effective in identifying pine nematode diseases (AUC value=0.99, overall accuracy=0.96). The norma-lized difference greenness index (NDGI), the distance to the highway, and normalized vegetation index (NDVI) were important factors in explaining the spatial variations of PWN disease occurrence. There was a positive spatial correlation in the occurrence of PWN disease (not randomly distributed but with obvious spatial aggregation characteristics). The high occurrence areas of pine wood nematode disease concentrated in Chitu Township, Zhufang Township and Shibatang Township, low occurrence areas concentrated in the vicinity of Rongjiang Street. The areas far away from the highway, low in elevation, and close to county roads were suffered to PWN disease. The results could serve the regional monitoring of pine nematode disease occurrence and provide practical guidance for PWN disease management.

[Influencing mechanism of stand age to the accumulation of microbial residue carbon in the Pinus masso-niana plantations]. / 林龄对马尾松人工林微生物残体碳积累的影响机制.

Clarifying the accumulation pattern of soil microbial residue carbon and its contribution to soil organic carbon (SOC) across stand age is helpful to understand the mechanism underlying soil carbon cycling. In this study, we analyzed the differences of amino sugar content, physicochemical properties and microbial composition in surface soil (0-10 cm) in young (6 a), middle-aged (13 a), near-mature (29 a), mature (38 a) and over-mature (57 a) Pinus massoniana plantations of subtropical China, quantified the microbial residue carbon content and its contribution to SOC, and discussed the mechanism. The results showed that SOC, total nitrogen, amorphous iron oxide and leucine aminopeptidase contents in the middle-aged plantation were significantly lower than those in the mature plantation. Soil pH and fungal/bacteria in young plantation were significantly higher than those in other age groups. Across the stand age gradient, the ranges of microbial, fungal and bacterial residue carbon were 7.52-14.63, 4.03-8.00 and 3.48-6.63 g·kg-1, respectively. The contents of all the residue carbon were significantly higher in the mature plantation than that of the middle-aged plantation, which were positively affected by soil total nitrogen content. The contribution of microbial, fungal, and bacterial residue carbon to SOC was 59.7%-72.3%, 33.4%-45.6%, and 24.3%-30.8%, respectively. The contribution of fungal residue carbon to SOC in young plantation was significantly higher than that in other age groups, and the contribution of bacterial residue carbon to SOC in middle-aged plantation was significantly higher than that in young and near-mature plantations, both of which were affected by soil inorganic nitrogen. Fungal residue carbon content was 1.2-1.7 times as that of bacterial residue carbon content, and dominated for the accumulation of microbial residue carbon. Results of the partial least squares model showed that stand age, soil environmental factors (such as leucine aminopeptidase, amorphous iron oxide, pH, and total nitrogen), bacterial residue carbon, fungal residue carbon and the contribution of bacterial residue carbon to SOC had total effects on the contribution of fungal residue carbon to SOC (-0.37, -1.16, 0.90, 1.09, and 0.83, respectively). In conclusion, stand age promoted the accumulation of microbial residue carbon but did not increase its contribution to SOC.

[Effects of mixed broadleaved tree species with pure Pinus massoniana plantation on soil microbial necromass carbon and organic carbon fractions]. / é©¬å°¾æ¾çº¯æž—æ··äº¤æ”¹é€ å¯¹åœŸå£¤å¾®ç”Ÿç‰©æ®‹ä½“ç¢³å’Œæœ‰æœºç¢³ç»„åˆ†çš„å½±å“.

Mixing native broadleaved tree species is a widely used method for renovating Pinus massoniana plantations. Soil microbial necromass carbon and organic carbon fractions are important parameters for evaluating the impacts of tree species mixing and soil organic carbon (SOC) stability. However, their responses to the mixing and renovation of P. massoniana plantation has not been understood yet. Here, we selected a pure P. massoniana plantation (PP) and a mixed P. massoniana and Castanopsis hystrix plantation, with ages of 16 (MP16) and 38 years (MP38), respectively, as the research objects. We quantified soil physical and chemical properties, microbial necromass carbon content, and organic carbon components at different soil layers to reveal whether and how the introduction of C. hystrix into P. massoniana plantation affected soil microbial necromass carbon and organic carbon components. The results showed that the mixed P. massoniana and C. hystrix plantation significantly reduced fungal necromass carbon content and the ratio of fungal/bacterial necromass carbon in the 0-20 cm and 20-40 cm soil layers. There were no significant differences in microbial necromass carbon contents, bacterial necromass carbon contents, and their contributions to SOC among the different plantations. The contribution of fungal necromass carbon to SOC was higher than that of bacterial necromass carbon in all plantation types. The contribution of soil mineral-associated organic carbon (MAOC) to SOC was higher than that of occluded particulate organic carbon (oPOC) and light-free particulate organic carbon (fPOC) for all plantation types. Mixing the precious broadleaved tree species (i.e., C. hystrix) with coniferous species (P. massoniana) significantly increased MAOC content and the contribution of MAOC, oPOC, and fPOC to SOC in the 0-20 cm and 20-40 cm soil layers. The MAOC of MP38 was significantly higher than that of PP in all soil layers and the MAOC of MP38 stands were significantly higher than MP16 stands in the 20-40 cm, 40-60 cm, and 60-100 cm soil layers, indicating that hybridization enhanced SOC stability and that the SOC of MP38 stands were more stable than MP16 stands. SOC and total nitrogen contents were the main environmental factors driving the changes in soil microbial necromass carbon, while soil total nitrogen and organically complexed Fe-Al oxides were the primary factors affecting organic carbon fraction. Therefore, SOC stability can be enhanced by introducing native broadleaved species, such as C. hystrix, during the management of the P. massoniana plantation.

Phytophthora pluvialis maintenance, spore production and detached needle assays.

Phytophthora pluvialis is an oomycete that primarily infects Pinus radiata and Pseudotsuga menziesii causing the destructive foliar disease red needle cast (RNC). Recent observations show that P. pluvialis can also infect western hemlock inducing resinous cankers. High-throughput and reproducible infection assays are integral to find key information on tree health and oomycete pathogenicity. In this protocol, we describe the propagation and spore induction of P. pluvialis, followed by detached needle assays for verification and quantification of virulence of P. pluvialis in P. radiata needles. These needle assays can be employed for high-throughput screening of tree needles with diverse genetic backgrounds. In downstream analysis, Quantitative PCR (qPCR) was utilized to assess relative gene expression, as exemplified by candidate RxLR effector protein PpR01. Additional techniques like RNA sequencing, metabolomics, and proteomics can be combined with needle assays and can offer comprehensive insights into P. pluvialis infection mechanisms.