Maintaining genetic diversity among generations in seed orchards is an important management goal because it lays a foundation for the generation process of seed orchards and the formulation of breeding plans. Meanwhile, clonal seed orchards play a pivotal role in supplying genetically improved seeds for afforestation, but the dynamics of genetic diversity and structure across multiple generations and geographic regions remain poorly understood. This study aimed to investigate genetic variation patterns across generations and geographic genetic differences in Chinese fir seed orchards using microsatellite markers. We analyzed genetic diversity, population structure, and co-ancestry of nine Chinese fir seed orchards, with three generations each in Hunan, Fujian, and Zhejiang provinces (representing central and marginal production regions, respectively). Results showed genetic diversity of the seed orchards remained relatively high (mean Ho = 0.553, He = 0.657) and exhibited distinct geographic variations with generational advancement, reflecting differences in parental selection strategies. Genetic diversity in Hunan (HN) first increased (HN2 > HN1) then slightly decreased (HN3 < HN2), while Fujian (FJ) showed a trend of initial decline followed by recovery (FJ1 > FJ3 > FJ2), and Zhejiang (ZJ) exhibited a gradual decrease (ZJ1 > ZJ2 > ZJ3). Geographic differences were evident, with diversity levels ordered ZJ > FJ > HN. Genetic differentiation among populations was low (Fst = 0.007 – 0.043), with 97.81 % of variance attributed to within-population variation. The population structure of the Hunan seed orchard was different from those of the Fujian and Zhejiang orchards, the population structure of Zhejiang’s advanced-generation seed orchards risked genetic convergence. All seed orchard populations had mixed branches, which shows the complex relationships among the population genotypes. There was a moderate degree of genetic homology (56 %) among the seed orchard resources, and the genetic relationship between generations in seed orchards in the same region became closer as generations improved. Population genetic analysis will greatly promote the molecular breeding of Chinese fir.

Chinese fir plantations are a major component of China’s forest carbon sink, and their mitigation value depends not only on total biomass but also on how carbon is allocated among stems, crowns, and roots at the tree level. Carbon allocation responds to competition and resource availability, proxied by stand structure (initial planting density and dominance classes) and environmental conditions (site index and climate). Yet how planting density, site index, and climate are associated with allocation variation across dominance classes remains poorly quantified, limiting density- and site-adaptive management for carbon sequestration. We used long-term density experiments at three subtropical sites (Sichuan, Guangxi, and Fujian), comprising 45 plots and five initial planting densities (1,667 to 10,000 trees ha-1). Trees were classified into four dominance classes, organ biomass and carbon were estimated with region-specific additive equations, and the effects of planting density, site index, climatic moisture deficit, and dominance class were evaluated with dominance-class regressions and linear mixed-effects models. From dominant to suppressed trees, the stem biomass fraction increased from 73.1% to 76.8%, whereas branch and root fractions decreased from 6.6% to 4.8% and from 15.0% to 13.1%, respectively. Higher site index was associated with greater stem allocation (+0.33 to +0.59 percentage points per meter) and lower leaf allocation (−0.28 to −0.44 percentage points per meter), whereas stronger competition (indexed by planting density and stand density index) was associated with higher stem but lower branch, leaf, and root allocation. Responses to climatic moisture deficit were dominance-dependent: dominant trees maintained relatively stable root allocation, whereas suppressed trees shifted carbon toward stems and away from roots. These results indicate that competitive structure was more closely associated with estimated carbon-allocation patterns than any single environmental gradient, and that limiting severe suppression and protecting root allocation through density management may help sustain the size and resilience of plantation carbon stocks.

The growing demand for wood products and ecosystem services in Chinese fir plantations has led to longer rotation ages and density control practices, raising concerns about their impact on soil fertility. This study assessed soil fertility of Chinese fir plantations in Fujian, Jiangxi, and Sichuan Provinces using the Nemerow index. The effects of stand age and initial planting density on soil fertility were analyzed using statistical models. In Fujian and Jiangxi, soil fertility was significantly higher at 11 and 30 years than at 5 and 25 years, while in Sichuan, it was higher at 25 and 30 years than at 5 and 11 years. In Fujian, soil fertility was higher at 6667 trees ha⁻2 than at 1667 trees ha⁻2. No significant differences were observed in Jiangxi, while in Sichuan, soil fertility at 6667 trees ha⁻2 was significantly higher than at 5000 and 1667 trees ha⁻2, and soil fertility at 10,000 trees ha⁻2 exceeded that at 1667 trees ha⁻2. Soil fertility typically increased with stand age, especially in Fujian and Sichuan. Soil fertility also increased with initial planting density, especially in Jiangxi and Sichuan. A structural equation model (SEM) explained 88% of the variance in soil fertility, with stand age directly affecting soil fertility and soil organic matter mediating the effects of stand age and planting density. These findings suggest that adjusting rotation age and planting density could help improve soil fertility, offering practical implications for sustainable forest management in Chinese fir plantations.

The response of tree growth to ongoing climate change has significant implications for sustainable forest management. An analysis of 10-year diameter at breast height, height, individual stem volume, and volume per hectare was conducted for 43 populations of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) grown in 32 common gardens across southern China. Population-specific performance under contemporary and future climate conditions was examined using response function and transfer projection. Findings indicated that mean temperature in the coldest month was the most influential variable in predicting population growth-related traits. Adaptation lags were more pronounced in populations at the climatic margins compared to core populations. On average, provenances from cooler climates benefited from long southward transfers (3.9-4.0 degrees C warmer), while warm-origin provenances responded favorably to shorter northward transfers (2.7-3.0 degrees C cooler). Calculated transfer limits were substantial, indicating populations could tolerate significant climatic shifts before experiencing a decline below 90 % of the local seed source's growth. The moderate climate model (SSP119) predicted minimal declines, whereas the extreme scenario (SSP585) projected significant growth reductions in southern populations. Other nonmarginal populations in near-optimal climates were also expected to be negatively affected, whereas most northern populations were projected to benefit from climate warming. These findings indicate that the response of Chinese fir to climate variation varies according to genetic differences between populations. These valuable insights are essential for the strategic selection of seed sources in reforestation initiatives.

The site index (SI), an important indicator of forest health, has been well-documented due to its impact on tree growth. Soil microorganisms, as decomposers that control nutrient cycling in forest ecosystems, usually respond significantly to changes in site index. However, most of the existing studies have focused on the direct effects of SI on tree growth, while the response mechanism of the microbial community network and its function has rarely been explored. In view of this, this study investigated the co-occurrence network and function of soil microbial communities under different site index (SI-14.96, SI-15.70, and SI-16.90) and soil depths (0-20 cm, 20-40 cm, and 40-60 cm) within a mixed Chinese fir plantation. The increase of site index significantly improved the soil physical and chemical properties of the Chinese fir plantation, including total phosphorus, total nitrogen, exchangeable magnesium, and soil water content. Dominant bacterial communities included Acidobacteria, Chloroflexi, and Proteobacteria, while Ascomycota and Basidiomycota dominated the fungal community. The variation in bacterial community structure was mainly driven by soil depth (R 2 = 37.33%), while the fungal community structure was influenced primarily by the site index (R 2 = 20.80%). Soil phosphorus, organic carbon, and soil water content drove microbial community variation. In the relatively high site index, the topological properties of the bacterial and fungal co-occurrence network, including nodes, edges, and the average clustering coefficient, reached the highest, showing the highest network complexity, and the keystone taxa were more abundant in the surface soil. Functional annotation analysis further indicated that bacterial functions related to nitrogen cycling and arbuscular mycorrhizal fungi were both significantly highest at SI-16.90. In general, a relatively high site index (SI-16.90) for Chinese fir plantations can improve the complexity of the soil microbial network, enhance the abundance of keystone taxa, and optimize the nitrogen cycle and the function of arbuscular mycorrhizal fungi. These findings are of great significance to the shaping of soil microbial diversity and ecological functions and provide a practical basis for improving soil ecology with a high site index in forest management.

This study investigated the effects of planting density and site index on stand attributes and soil nutrients in mature Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] plantations across Fujian and Sichuan Provinces, elucidating the pathways through which these factors influence standing volume (SV). The results showed that (1) planting density significantly affected stand variables, with average diameter at breast height (ADBH) decreasing and SV initially increasing and then declining with higher density. The number of mortality plants (NMP) and actual stand density (ASD) both increased significantly with higher density. Average tree height (ATH) and dominant height (DH) responses varied by region, with ATH decreasing in Sichuan and DH decreasing in Fujian with higher density. (2) Planting density affected soil nutrients differently in the two provinces, with soil total potassium (TK) increasing in Fujian and phosphorus decreasing in Sichuan. (3) Site index was positively correlated with ATH and ADBH but negatively correlated with ASD and NMP. Its relationship with soil nutrients was province-specific: in Fujian, site index was negatively correlated with total phosphorus (TP) and positively correlated with TK and soil pH, while in Sichuan it was only positively correlated with TK. (4) Structural equation modeling revealed different regulatory pathways: in Fujian, planting density influenced SV through both ASD and soil nutrients, while in Sichuan it affected only through ASD. This study highlights the region-specific interactions between planting density, site index, stand structure, and soil nutrients, providing a foundation for optimized plantation management.

Reanalysis of historical provenance trial data yields critical knowledge that can enhance climate change adaptation. The universal response functions (URFs) were developed for 205 populations of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) growing at 32 planting sites in subtropical China. Tree growths were modeled for contemporary climate and then projected using data from three climate models for the periods 2011-2040, 2041-2070, and 2071-2100, under three scenarios of trajectories of greenhouse gas concentrations (SSP119, SSP245, SSP585). Mean coldest month temperature (MCMT) of provenance and test site explained 33.8-41.8 % of population variation in regressions that were statistically significant. However, growth performance was mainly related to MCMT at test site and, to a lesser degree, to MCMT at seed origin, indicating a pronounced environmental response of Chinese fir populations. There was a clear indication of a climatic optimum in central regions, and the growth of Chinese fir is expected to be limited at sites with the MCMT of more than approximately 8 degrees C under climate warming. The URFs' explicit predictions indicated that populations from northern regions exhibited a moderate increase in growth, while for southern populations, a marked reduction in growth will be observed. Under severe global warming (SSP585), local populations at the southern margins might face extirpation. Assisted migration could help most populations take advantage of potential growth opportunities in warmer climates. As an important tree species in subtropical plantations, the lessons learnt from Chinese fir will help to avoid potential maladaptation of forests to future climates.

IntroductionActinorhizal symbioses are gaining attention due to the importance of symbiotic nitrogen fixation in sustainable agriculture. Sea buckthorn (Hippophae L.) is an important actinorhizal plant, yet research on the microbial community and nitrogen cycling in its nodules is limited. In addition, the influence of environmental differences on the microbial community of sea buckthorn nodules and whether there is a single nitrogen-fixing actinomycete species in the nodules are still unknown.MethodsWe investigated the diversity, community composition, network associations and nitrogen cycling pathways of the microbial communities in the root nodule (RN), nodule surface soil (NS), and bulk soil (BS) of Mongolian sea buckthorn distributed under three distinct ecological conditions in northern China using 16S rRNA gene and metagenomic sequencing. Combined with the data of environmental factors, the effects of environmental differences on different sample types were analyzed. ResultsThe results showed that plants exerted a clear selective filtering effect on microbiota, resulting in a significant reduction in microbial community diversity and network complexity from BS to NS to RN. Proteobacteria was the most abundant phylum in the microbiomes of BS and NS. While RN was primarily dominated by Actinobacteria, with Frankia sp. EAN1pec serving as the most dominant species. Correlation analysis indicated that the host determined the microbial community composition in RN, independent of the ecological and geographical environmental changes of the sea buckthorn plantations. Nitrogen cycle pathway analyses showed that RN microbial community primarily functions in nitrogen fixation, and Frankia sp. EAN1pec was a major contributor to nitrogen fixation genes in RN.DiscussionThis study provides valuable insights into the effects of eco-geographical environment on the microbial communities of sea buckthorn RN. These findings further prove that the nodulation specificity and stability of sea buckthorn root and Frankia sp. EAN1pec may be the result of their long-term co-evolution.

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) is the most widely distributed conifer species in the subtropical region of southern China. Due to its ecological and economic significance, accurate prediction of growth of Chinese fir plantations is crucial for forest management and industrial timber production. In this study, we employed a physiologically process-based model (3-PG) to simulate the growth dynamic of Chinese fir plantations under various initial planting densities in southern China. Calibration and validation results indicated that the model outputs have strong correlations with the observed data (R2 > 0.79, p < 0.01), except foliage biomass and root biomass. Self-thinning will occur earlier at higher initial planting densities, and stand DBH and height will increase dramatically afterwards. Sensitivity analysis further revealed that the FR (soil fertility rating), alphaCx and gammaN1 parameters were highly sensitive in the 3-PG model (p < 0.01), while their sensitivity was influenced by stand age and initial density variations. This study confirmed that the parameter-specific optimized 3-PG model could accurately predict the growth process of Chinese fir plantations under different densities. It will provide a scientific reference for regional-scale management of Chinese fir plantations.

The growth of timber assortment is related to site conditions and forest management measures. To our knowledge, however, the effects and relative importance of these factors on the growth of different timber assortments of Chinese fir have not yet been explored. Based on data from long-term fixed observation plots in the northwest of the Chinese fir distribution zone, we examined the effects of planting density and the site index on the timber assortment structure of Chinese fir. Furthermore, we quantified the relative importance of stand factors (age, planting density, stand density index, number of living trees, Gini coefficient, and site index) in determining the growth of various timber assortments. The results showed that the wood yield of all timber assortment types increased as the site quality improved. The outturn and outturn rate of large- and medium-diameter timber were negatively correlated with the planting density. Before the age of 22, planting density had a negative impact on total timber yield and small-diameter timber outturn. After 22 years, planting density had a positive impact on total timber yield and small-diameter timber outturn. SDI (stand density index), age, and SD (stand density) were the most important factors influencing total timber yield and small-diameter timber. The relative importance of age to large-diameter timber was the greatest, followed by SI (site index) and SD. The effects of age, SD, SI, and PD (planting density) on the medium-diameter timber were greater than those of SDI and Gini coefficient. The results indicate small- and medium-diameter timber as the primary target timber assortment types to be cultivated in the study area, while large-diameter timber cannot be effectively produced under the current site conditions. Our findings provide valuable insights for the management of Chinese fir plantations and the directed cultivation of target timber assortments in the northwest of the Chinese fir distribution zone.

Biomass and carbon allocation among plant organs are influenced by the individual tree's development and climate conditions. Chinese fir forests play an important role in the carbon cycle and climate change mitigation in China. Understanding how forest age, tree size, and climate factors affect biomass and carbon allocation in Chinese fir forests is crucial to fully utilize the carbon sequestration potential. We analyzed the response of Chinese fir biomass allocation fractions (BAFs) and carbon stock allocation fractions (CAFs) to forest age, tree size, and climate factors, utilizing field survey data on biomass of 93 trees in Fujian, Sichuan, Guangxi, and Jiangxi provinces and carbon storage of 40 trees in Fujian, Sichuan, and Guangxi provinces in China. Our results showed that BAFs depend on individual development. In young and middle-aged forests, BAFs were unaffected by diameter at breast height (DBH), whereas branch and root biomass fractions displayed a significant positive correlation with DBH, and stem biomass fraction displayed a negative correlation with DBH in mature forests. Carbon concentration exhibited substantial variation among distinct components and regions. Overall, the carbon concentration of each organ ranked as Guangxi > Sichuan > Fujian. BAFs of dominant trees are almost independent of climatic factors, while suppressed trees will alter their strategies for biomass allocation in response to climate change. Stem biomass fraction exhibited a significant positive correlation with maximum growing season temperature, mean summer temperature, and maximum summer temperature, whereas leaf biomass fraction showed the opposite trend. Under future climate warming, Chinese fir will allocate more biomass to the stem, at the expense of leaf biomass. These findings support the idea that biomass allocation patterns serve as adaptive patterns to address fluctuations in internal and external conditions. The interaction between climate factors and tree size shows promise for predicting trends in forest biomass and carbon accumulation in the context of future climate change.

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is one of China's most important tree species, and possible adverse factors affecting its growth and physiology is of particular concern for climate change adaptation. In this context, growth performance (BAI: basal area increment and MAXD: maximum density), climate sensitivity, and the relative contributions of climatic and physiological determinants to growth were evaluated across the 30 Chinese fir provenances using a combination of dendroclimatology and carbon isotope analysis (delta 13C). Over the past 27 years, intrinsic water-use efficiency (iWUE) increased significantly by 12.71-33.56 %, while radial growth decreased (-63.38 % to -88.93 %). Strong growth decreases reflected increasing water stress due to climate warming, which was not offset by greater iWUE. A similar trend was observed in the theoretical gas exchange scenario as a response to increasing Ca as stomata opened and Ci increased proportionally to Ca. This study identified temperature and relative humidity as determinants of growth and physiology. However, meteorological factors (temperature, relative humidity, and sunshine hours) contributed much less to growth than physiological factors (iWUE). Variation in performance and climate sensitivity among populations significantly correlated with the mean annual temperature of the seed source origin. In general, seed sources from warmer and more humid climates in the center region grew faster and had higher iWUE. Provenances from drier climates had slower growth, higher wood density, and higher carbon isotope discrimination (Delta 13C) compared to those from wetter climate conditions. Compared to provenances from cooler regions, the seed sources from warmer climates were less sensitive to temperature but more sensitive to sunshine hours for BAI and MAXD. These results contribute to a better understanding of the climate sensitivity and physiological responses of the Chinese fir provenances to long-term changing climate.

Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] is a critical timber tree species for its fast growth and high yield in southern China and is widely planted in subtropical regions of the country. However, the management of Chinese fir in the form of a monoculture plantation is not conducive to the maintenance of soil fertility and improvements in forest productivity. The establishment of mixed conifer-broad-leaved forests through near-natural transformation is developing into a promising method of forest cultivation for replacing large pure coniferous plantations. Bacteria and fungi are an important part of the soil microbiota and are involved in the soil nutrient cycle. Therefore, this study investigated the response of soil bacterial and fungal communities to the introduction of broad-leaved trees in three types of Chinese fir plantations [Cunninghamia lanceolata monoculture plantation (CMP), C. lanceolata-Castanopsis hystrix Hook. f. & Thomson ex A. DC.-Michelia hedyosperma Law. mixed plantation (CCM), and C. lanceolata-Castanopsis fissa (Champ. ex Benth.) Rehder & E.H.Wilson-Erythrophleum fordii Oliv. mixed plantation (CCE)] located in Guangxi Province, China. And the effect of soil layers (0-20, 20-40, and 40-60 cm soil depths) on the soil microbial communities was further analyzed. The results suggested that tree species mixing significantly affected bacterial and fungal communities, but soil depth only significantly affected bacterial communities (P < 0.01). The relative abundance of Basidiomycetes in CCE (53.91-78.76 %) was significantly higher than that in pure forest (P < 0.05). Bacteria exhibited more complex and multilinked networks in the mixed stands, particularly for the CCE plantation. Mixed planting patterns significantly enhanced bacterial nitrogen fixation and the presence of symbiotic fungi. Redundancy analysis (RDA) and correlation analyses indicated that the microbial community structure was strongly affected by soil environmental factors, with bacteria affected mainly by available phosphorous (AP) and fungi affected mainly by soil enzyme activity and total potassium (TK). In summary, the introduction of broad-leaved species (especially C. fissa and E. fordii) had a significant impact on the soil microbial community, increasing the relative abundance of bacterial nitrogen fixation and symbiotic fungi and generating a complex microbial network. We suggest that changes in AP, TK, and fungal communities should be considered in the near-natural transformation of Chinese fir or soil fertility maintenance and sustainable management to maintain soil fertility.

Near-natural forest management is an important way to change the soil fertility decline and productivity reduction of pure Chinese fir plantations. At present, many detailed studies have been carried out on the impact of near-natural forest management on Chinese fir plantations at home and abroad.

沙棘(Hippophae rhamnoides)叶片黄酮提取与应用潜力巨大.基于12个选 自中国沙棘亚种、蒙古沙棘亚种及2个亚种间杂交种的优良沙棘无性系在内蒙古磴口与黑龙江绥棱2个试点的测试,分析了沙棘叶片黄酮含量变异的品种效应与气候区效应.研究发现:沙棘叶片黄酮含量变化范围达278.9～3 727.2 mg/100 g,远高于沙棘果实黄酮含量;沙棘叶片黄酮含量在不同品种间差异十分明显,槲皮素是沙棘总黄酮的主要成分,但品种间亦表现出明显差异,沙棘叶片高黄酮新品种选育前景广阔;沙棘叶片黄酮含量在干旱区高于湿润区,干旱胁迫有利于沙棘叶片黄酮的积累.

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is one of the most important tree species for afforestation in China. First-, second-, and third-generation seed orchards of Chinese fir have been established successively, and rich germplasms have been accumulated in the process of genetic improvement. It is necessary to build a core collection of germplasms from Chinese fir seed orchards. In this work, we constructed core collections representing the genetic diversity of Chinese fir seed orchard resources based on SSR data. A total of 607 seed orchard materials from three generations were used to determine the best sampling method and intensity by comparing and analyzing nine methods for constructing core collections. Core Hunter’s multi-strategy optimizes allele coverage and the distance criterion under a 30% sampling intensity (weight: A–NE, 0.7; CV, 0.3 and E–NE, 0.5; CV, 0.5), which is superior to other strategies and was selected as the best method. The two core collections (A–NE&CV73, E–NE&CV55) constructed contained all the alleles of the whole collection and effectively limited the homology in the core collections; each core collection contained 182 accessions. Our findings could contribute greatly towards improving the management of genetic resources in Chinese fir seed orchards and provide elite materials for future studies.

'中棘4号'是以蒙古沙棘(Hippophae rhamnoides subsp.mongolica)亚种优良引进品种'乌兰格木'及中国沙棘(Hippophae rhamnoides subsp.sinensis)亚种优良无性系'丰宁'分别为母本和父本杂交选育得到的沙棘新品种.生态适应性强,株高可达4.5 m.果实呈黄色,近圆形,百果质量36.6 g,盛果期平均单株产量4.8 kg以上,少刺,2年生结果枝每10 cm枝段棘刺数2～3个.适宜中国北纬35°～45°干旱半干旱区域种植.

Stand density control coupled with site control is a key technique for cultivating large-diameter timber of Chi -nese fir trees, whose yield can be effectively increased by the optimal density and site management mode employed. This study aimed to evaluate the dynamic changes in timber assortment structure under differing initial planting densities and site quality based on growth data of a 41-year trial of Chinese fir plantations. Our results showed that the total timber yield and both large-diameter timber outturn and the outturn rate all increased with better site quality under the same initial planting density. Further, the outturn peak as well as outturn rate peak for both medium-and small-diameter timber was reached sooner with improved site quality. For the same site class, a lower initial planting density augmented the total timber outturn rate, and also resulted in less time required for the total timber outturn rate to reach a constant or maximum value. Finally, the total timber outturn rate of all density plots tended to be nearly identical. Using a high planting density increased the outturn of small-diameter timber, whose outturn peak was delayed in the denser plots. The bolstering effect of low density upon the growth of large-diameter timber was enhanced by higher site quality, with density-induced differences in large-diameter timber more pronounced; conversely, that promoting effect weakened under poor site quality conditions. The interaction between planting density and site index significantly influenced the growth of any timber assortment of Chinese fir in the early stage following its formation. Notably, the significant effect of site index on large-diameter timber lasted longer than that of other timber assortments. The optimal site conditions for cultivating large-diameter timber trees of Chinese fir consist of a site class >= 20 with a planting density limited to no more than 1667 trees/ha, whose stand rotation period should not exceed 26 years, so as to maximize the output of large-diameter timber yield. Our empirical findings will be helpful for the construction of an optimal cultivation mode for the density, site, and rotation age of large-diameter timber in Chinese fir plantations.

[目的]探讨初植密度对不同产区杉木人工林优势高生长全过程的影响规律和发生程度,揭示杉木人工林优势高生长的初植密度效应及其对立地质量指示性的有效范围,为杉木人工林优势高生长评价及密度有效调控提供科学依据.[方法]以杉木中带东区(江西分宜)和中带中区(四川纳溪)共 30块长期定位观测的杉木密度试验林样地(林龄范围为 2～30年生)为研究对象,分析杉木人工林在不同产区和不同林分生长发育阶段下优势高对初植密度的响应规律.[结果]林分优势高与初植密度呈负相关关系,即初植密度越小,优势高越大.在林分生长发育前期,不同初植密度林分优势高生长轨迹几乎重合,初植密度影响较小,随林龄增长,不同初植密度间林分优势高生长差异呈增大趋势,至成熟龄期,林分优势高受初植密度的影响因产区而异,在中带东区影响仍很明显,在中带中区影响逐渐减弱.优势高年均生长量和连年生长量与初植密度呈负相关关系,且初植密度越大,其峰值越小,峰值出现时间越早.同一林龄下,与中带中区相比,立地条件整体更优的中带东区林分优势高生长受初植密度作用产生的分化程度相对更大.中带东区试点在5年生以后,中带中区试点在10～19年生期间,在低、中初植密度范围(1 667～3 333株·hm-2)或高初植密度范围(6 667～10 000株·hm-2)内,林分优势高生长不受初植密度显著影响,当初植密度达到或超过 5 000株·hm-2 后,其与相对低的初植密度(1 667～3 333株·hm-2)林分相比,林分优势高生长则受初植密度的显著制约.[结论]初植密度不同,林分优势高生长过程明显不同.在一定初植密度级差范围内,初植密度对林分优势高生长没有显著影响,超过一定级差时则高、低初植密度间林分优势高生长具有显著差异.标准年龄 20年生时,中带东区试点差异显著的密度组合中,优势高差值最大达 2.46 m,超过一个立地指数级,此时用优势高指示立地质量缺乏一定准确性.预估立地指数时,对初植密度高于5 000株·hm-2 的林分需要修正密度的影响.

Seed orchards represent the link between forest breeding and conifer production forests, and their mating patterns determine the genetic quality of seed orchard crops to a large extent. We genotyped the parental clones and their open pollination offspring in the third-generation seed orchard of Chinese fir using microsatellite markers and observed the synchronization of florescence in the seed orchard to understand the genetic diversity and mating structure of the seed orchard population. Genetic coancestry among parental clones was detected in the third generation seed orchard of Chinese fir, and the genetic diversity of the open-pollinated offspring was slightly higher than that of the parental clones. The external pollen contamination rate ranged from 10.1% to 33.7%, 80% of the offspring were produced by 44% of the parental clones in the orchard, and no evidence of selfing was found. We found that 68.1% of the effective pollination occurred within 50 m, and 19.9% of the effective pollination occurred in the nearest neighbors. We also found that successful mating requires about 30% of florescence overlap between males and females, and there was a significant positive correlation between male reproductive energy and male parental contribution. Our results provide a valuable reference for the management and design of advanced generation seed orchards.