To investigate the growth, physiological and photosynthetic responses of Cyclobalanopsis glauca seedlings to light variation and phosphorus-potassium addition, aiming to screen treatment groups suitable for regulating Cyclobalanopsis glauca seedlings under different phosphorus-potassium nutrient and light conditions, and to provide scientific basis for the cultivation of high-quality seedlings of Cyclobalanopsis glauca.

A three-factor pot experiment was conducted using one-year-old Cyclobalanopsis glauca seedlings as the research subjects, with 2 light levels (55% natural light, full light), 4 phosphorus levels (0, 2.4, 4.8, 7.2 g/plant), and 3 potassium levels (0, 1.6, 3.2 g/plant). The growth (seedling height, root collar diameter, root biomass, stem biomass, leaf biomass, and total biomass), physiological indicators: catalase activity (CAT), peroxidase activity (POD), soluble sugar content (SS), soluble protein content (SP), and malondialdehyde content (MDA), and photosynthetic gas exchange parameters Net photosynthetic rate (P_n), Stomatal conductance (G_s), and Intercellular CO₂ concentration (C_i) of the seedlings under each treatment were measured. The best treatment combination was selected through a comprehensive analysis of three-factor variance, correlation analysis, seedling quality index evaluation, and fuzzy function analysis.

Under appropriate phosphorus and potassium addition, the full light treatment significantly increased root collar diameter, root biomass, stem biomass, leaf biomass, total biomass, peroxidase activity, catalase activity, soluble sugar content, soluble protein content, G_s, and C_i compared to the shading treatment. Among different phosphorus content levels, seedling height, root collar diameter, root biomass, stem biomass, leaf biomass, total biomass, catalase activity, peroxidase activity, soluble sugar content, P_n, and G_s showed a trend of first increasing and then decreasing with the increase in phosphorus content, with the maximum values typically occurring at the P2 (2.4 g/plant) and P3 (4.8 g/plant) levels. The SP content decreased first and then increased with increasing phosphorus content, while MDA content decreased. Among different potassium content t, seedling height, root biomass, stem biomass, leaf biomass, total biomass, SS content, P_n, and G_s showed a trend of first increasing and then decreasing with increasing potassium content, with the maximum values typically occurring at the K2 (1.6 g/plant) level, while POD activity, CAT activity, and SP content showed a trend of first decreasing and then increasing.

Through comprehensive analysis, the LP2K2 (full light, phosphorus 2.4 g/plant, potassium 1.6 g/plant) treatment group exhibited the best performance in terms of growth, photosynthetic efficiency, antioxidant enzyme activity, and other indicators for Cyclobalanopsis glauca seedlings.

Phoebe hui is a rare wood species in China and belongs to the national second-class protected species. The simulation of regional changes in the suitable physiology of P. hui since the middle of Holocene, the investigation of its response to historical climate change, and the prediction of its future geographical distribution pattern can provide a reference for the formulation of resource conservation strategies and afforestation regionalization of P. hui.

Based on the existing geographic distribution data and climatic factors, the R language Kuenm package was invoked to adjust and optimize the feature combination (FC) and regularization multiplier (RM) of MaxEnt prediction model for modeling. The main climatic factors affecting the distribution of P. hui were tested and evaluated by the contribution rate of climatic factors and cutting method. The reliability and accuracy of the model results were evaluated by the area under the receiver operating characteristic curve (AUC) of the model output. Based on the output results of MaxEnt and ArcGIS software, the geographical distribution of the suitable areas from the middle Holocene to the future (2050s, 2070s, 2090s) under different climate scenarios (SSP2-4.5, SSP5-8.5) was obtained to analyze the migration trend of its distribution center in the future.

Model optimization results showed that when RM=0.7 and FC=QH, MaxEnt model complexity and overfitting degree were low, and model prediction accuracy was high. The AUC of the receiver operating characteristic curve is 0.984±0.005, which indicates that the prediction result is good. Based on the contribution rate of climatic factors and the assessment results of the knife cutting method, Annual precipitation (contribution rate=42.1%), Precipitation of Coldest Quarter (contribution rate=15.7%), Precipitation of Warmest Quarter (contribution rate=9.9%), Mean Temperature of Warmest Quarter, Temperature Seasonality (contribution rate=7.6%), Min Temperature of Coldest Month (contribution rate=7.3%) and Mean Diurnal Range Mean of monthly (contribution rate=6.1%) were the dominant limiting factors for the geographical distribution of P. hui. The prediction results of the model showed that P. hui was mainly distributed in southwest China and a few areas in central and South China from the middle of Holocene to the present, and the overall suitable area showed a decreasing trend. In the future, the habitat area of P. hui will continue to decrease, and the distribution center will gradually migrate to the north, only in Wulong District and Nanchuan District of Chongqing, as well as in the junction area between Chongqing and southwest Hubei, Yunnan and southwest Guizhou, there will be small areas of high habitat.

The optimized MaxEnt model can accurately predict the potential geographical distribution area of P. hui, which is mainly restricted by precipitation and temperature climate factors, and the precipitation factor plays a leading role. Since the middle of the Holocene, the suitable distribution area of P. hui has been decreasing and fragmentizing, especially under the high emission concentration of greenhouse gases in the future. The distribution center tends to migrate from low latitude to high latitude, and the population extinction risk is high. The results of this study can provide theoretical reference for exploring the mechanism of response to climate change, and explore the future suitable growth areas according to the distribution change and migration trend of P. hui maximus to reduce the extinction risk.

Cunninghamia lanceolata is one of the most important fast-growing timber species in southern China. Long-period management of Cunninghamia lanceolata is a new management mode that takes into account the high-value large-diameter timber production and long-period maintenance of soil strength. This paper investigates the effects of different densities on the growth and soil of long-period management of Cunninghamia lanceolata forests, in order to determine the reasonable management density of long-period management of Cunninghamia lanceolata plantation forests, and to provide a basis for sustainable management of Cunninghamia lanceolata plantation forests.

A 40-year-old fir plantation forest in Lanshan County, Yongzhou City, Hunan Province, which had been logged at 30 years of age, was used as the study object, and four densities were set at the time of inter-harvesting (A: 750 plants/hm², B: 825 plants/hm², C: 900 plants/hm², and D: 1 050 plants/hm²), to analyze the effects of densities on the growth of the forest stand and the physicochemical properties of the soil through the investigation of the sample plots and the testing of the soil samples.

The average DBH, tree height, number of large diameter timber plants and stock volume of fir forests all showed a tendency of increasing and then decreasing with increasing stand density, and were highest at density B. The soil nutrients were affected by the density of fir forests, and the soil nutrients were affected by the density of Cunninghamia lanceolata forests. Soil nutrients were significantly affected by changes in stand density, showing a trend of increasing and then decreasing with increasing density, mostly reaching a maximum at density B. Soil nutrients in the 40-60 cm soil layer were more closely related to the growth of cedar. The average diameter at breast height was positively correlated with soil nitrogen and potassium; the total accumulation was positively correlated with phosphorus content, and the number of large-diameter Cunninghamia lanceolata plants and accumulation were both positively correlated with soil nitrogen and potassium. The diversity index and OTU number of the soil bacterial community increased with increasing density, and the diversity index and OTU number of the fungal community decreased. The effect of total phosphorus content on the community structure of fungi was significant, and the effect of total potassium content on the community structure of fungi was highly significant.

It can be summarized that density B (825 plants/hm²) is the most suitable density for long-period large-diameter timber management in Cunninghamia lanceolata forests. Long-period management of Cunninghamia lanceolata is conducive to the cultivation of large-diameter timber and the maintenance of good bacterial community structure, which promotes the accumulation of soil organic matter and nutrients, and is conducive to the sustainable management and stable development of Cunninghamia lanceolata forests.