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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. [ABSTRACT FROM AUTHOR]

The most important issues in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) management are the quantitative determination of stand density and the selection of appropriate density. Different stand density index models have advantages for special tree species, and this study aimed to estimate the carrying capacity of planted stands of Chinese fir and to select simple and reliable stand density indexes. Based on special experiment of different initial density, the maximum carrying capacity was estimated using Reineke’s self-thinning rule, Nilson’s sparsity theory, Beekhuis’s relative-spacing hypothesis, Zhang’s nutrient-competition rule, Curtis’s maximum stand basal area and Hui’s crowding degree based on mean tree distance. The restricted maximum likelihood method (REML) implemented with ‘nlme’ package in R software was used to refine the parameters of thinning age in Richard’s growth model. The results showed that stand density index models can describe the trends of stand density in response to tree growth: the higher the plantation initial density, the earlier age and stronger self-thinning capacity of stands. Reineke’s SDI and Zhang’s Z model are the most stable and suitable to estimate changes in the density of Chinese fir plantations, competition intensification, and the thinning age. The RD model can also be used, except at low Chinese fir densities. K, which can be affected by the mean crown width of trees, directly reflects the forest area of photosynthesis; this index is easy and simple to apply, but more research is needed to optimize the equation to evaluate whether a forest requires management and to determine the appropriate time for the first thinning and its intensity.

Tree mortality models are important tools for simulating forest dynamic processes, and logistic regression is widely used for modeling tree mortality. However, most of the mortality models that have been developed generally ignore the hierarchical structure. In this study, Bayesian logistic multilevel mortality models were developed with the independent variables of initial planting density, competition, site index, and climate factors in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations in southern China. The results showed that a Bayesian three-level model was best for describing tree mortality data with multiple sources of unobserved heterogeneity compared to fixed-effects and two-level models. The variance partition coefficient of tree mortality due to the tree level was much larger than that due to the plot level. The initial planting density and site index were positively correlated with mortality and symmetric competition was negatively correlated. For climate variables, the mortality probability decreased with the increasing mean annual temperature and previous summer mean temperature. By contrast, the mortality probability increased with the increasing previous winter mean minimum temperature and annual heat-moisture index. Identifying different sources of variation in tree mortality will help further our understanding of the factors that drive tree mortality during climate change. Key words: Bayesian logistic multilevel model, climate, initial planting density and competition, tree mortality, variance partition coefficient. Les modeles de mortalite des arbres sont des outils importants pour simuler les processus dynamiques de la foret, et la regression logistique est couramment utilisee pour modeliser la mortalite des arbres. Cependant, la plupart des modeles de mortalite qui ont ete mis au point ignorent generalement la structure hierarchique. Dans cette etude, des modeles de mortalite logistiques bayesiens multiniveaux ont ete mis au point pour des plantations d'araucaria de Chine (Cunninghamia lanceolata (Lamb.) Hook.) du sud de la Chine avec, comme variables independantes la densite initiale de la plantation, la competition, l'indice de qualite de station et des facteurs climatiques. Les resultats indiquent qu'un modele bayesien a trois niveaux etait le meilleur pour representer les donnees de mortalite des arbres ayant plusieurs sources d'heterogeneite non observees comparativement a des modeles a effets fixes et a deux niveaux. Le coefficient de repartition de la variance de la mortalite des arbres etait beaucoup plus grand a l'echelle de l'arbre qu'a l'echelle de la placette. La densite initiale de la plantation et l'indice de qualite de station etaient positivement correles a la mortalite alors que la competition symetrique y etait negativement correlee. Dans le cas des variables climatiques, la probabilite de mortalite diminuait avec la temperature annuelle moyenne et la temperature estivale moyenne de l'annee precedente. En revanche, la probabilite de mortalite augmentait avec la temperature minimale moyenne de l'hiver precedent et l'indice humidex annuel. L'identification de differentes sources de variation de la mortalite des arbres contribuera a ameliorer notre comprehension des facteurs qui determinent la mortalite des arbres pendant les changements climatiques. [Traduit par la Redaction] Mots-cles: modele logistique bayesien multiniveau, climat, densite initiale de la plantation et competition, mortalite des arbres, coefficient de repartition de la variance., Introduction Tree mortality, one of the main components of forest succession, is important for the maintenance of biological and structural diversity in forest ecosystems (Bigler and Bugmann 2003; Zhang et [...]

In plants, recent studies have revealed that N6-methyladenosine (m6A) methylation of mRNA has potential regulatory functions of this mRNA modification in many biological processes. m6A methyltransferase, m6A demethylase and m6A-binding proteins can cause differential phenotypes, indicating that m6A may have critical roles in the plant. In this study, we depicted the m6A map of sea buckthorn (Hippophae rhamnoides Linn.) transcriptome. Similar to A. thaliana, m6A sites of sea buckthorn transcriptome is significantly enriched around the stop codon and within 3ʹ-untranslated regions (3ʹUTR). Gene ontology analysis shows that the m6A modification genes are associated with metabolic biosynthesis. In addition, we identified 13,287 different m6A peaks (DMPs) between leaf under drought (TR) and control (CK) treatment. It reveals that m6A has a high level of conservation and has a positive correlation with mRNA abundance in plants. GO and KEGG enrichment results showed that DMP modification DEGs in TR were particularly associated with ABA biosynthesis. Interestingly, our results showed three m6A demethylase (HrALKBH10B, HrALKBH10C and HrALKBH10D) genes were significantly increased following drought stress, which indicated that it may contributed the decreased m6A levels. This exhaustive m6A map provides a basis and resource for the further functional study of mRNA m6A modification in abiotic stress. [ABSTRACT FROM AUTHOR]

Tree height–diameter allometry is crucial in regulating forest ecosystem structure and estimating biomass and carbon storage. Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) is the most widely planted tree species across subtropical China. Yet our understanding of how height–diameter allometry of Chinese fir relates to climate over different sites is limited. Remeasured data of 60 plots were used to explore height–diameter allometry of Chinese fir in relation to climate using a three-level NLME approach. The data consisted of five initial planting densities distributed in Fujian, Jiangxi, Guangxi and Sichuan provinces (sites) in subtropical China. Results showed that tree heights increased with increasing mean annual temperature (MAT) and mean warmest month temperature (MWMT) and decreased with increasing annual heat–moisture index (AHM) and summer mean maximum temperature (SMMT). The contribution of MAT to height–diameter allometry was larger than AHM, SMMT and MWMT, which suggested that temperature was a key climate factor that shapes height–diameter allometry of Chinese fir in subtropical China. Trees planted at a higher density level of 6667–10 000 trees ha−1 were slenderer than those planted at a lower density level of 1667–5000 trees ha−1. The scale of height–diameter allometry of Chinese fir nearly held constant in the four sites and was close to 0.5 predicted by the stress-similarity model. Our results will help further understanding of the climate sensitivity affecting the height–diameter allometry of Chinese fir plantations. [ABSTRACT FROM AUTHOR]