Abstract:To assess the impact of thinning intensity on soil nutrient release characteristics, the Daling Mountain Forest Farm in Dongguan City, Guangdong Province was selected as the study area. Soil carbon (C), nitrogen (N), and phosphorus (P) contents, as well as the extracellular enzyme activities related to N and P nutrient acquisition, were measured in 13- to 17-year-old Acacia mangium and Eucalyptus urophylla plantations that had undergone near-natural transformation (thinning + planting native tree species) under three thinning intensities (no thinning, 30% thinning, and 60%–70% thinning). The results showed that compared with the unthinned plots, the available N and P contents in the thinned plots of A. mangium increased by an average of 28% and 71%, respectively, and those in the thinned plots of E. urophylla increased by an average of 21% and 33%, respectively. The activities of soil C, N, and P acquisition enzymes in both thinned plots decreased to varying degrees. By comparing the stoichiometric ratios and vector characteristics of ecological enzymes under the two thinning intensities, it was indicated that thinning could effectively alleviate the C limitation required for nutrient transformation, but excessive thinning might further lead to soil N limitation. It was suggested that moderate thinning (30%) could balance the release of N and P nutrients in the soil and the improvement of vegetation diversity in both plantations, and should be the optimal choice for thinning intensity in the near-natural transformation of these two forest types.

Abstract:Fourteen long-term fixed monitoring plots were established in the Chenhedong Provincial Nature Reserve in Conghua, Guangdong Province to explore the community structure characteristics of woody plants in this area. The results showed that a total of 23777 woody plants with a diameter at breast height (DBH) ≥1.0 cm were recorded in the plots, of which 185 were unidentified and the rest belonged to 289 species in 121 genera and 55 families. Among the plant composition, there were 8 dominant families, accounting for 14.54% of the total number of families; 14 dominant genera, accounting for 11.57% of the total number of genera; and 25 species with an importance value ≥1.00%, accounting for 8.65% of the total number of species. The distribution types of plant families included 7 types and 8 variants, with tropical distribution being the most dominant, accounting for 62.50% of the total number of dominant families; the distribution types of plant genera included 12 types and 10 variants, with tropical distribution being the most dominant, accounting for 78.57% of the total number of dominant genera. The number of common, occasional and rare species in the plots were 120, 107 and 62 respectively, accounting for 41.52%, 37.02% and 21.45% of the total number of species. The average DBH of all individuals in the plots was 5.33 cm, and the average tree height was 5.85 m. The diameter and height class structures were both in an inverted “J” shape, indicating a good community regeneration and a stable growth process. This study enhanced the understanding of the structural characteristics of the evergreen broad-leaved forest ecosystem in the South China subtropical region, and also provided a basis for the management, protection strategies and ecological restoration of the nature reserve.

Abstract:To explore the characteristics of plant communities and soil erosion resistance under different vegetation types in the Huangfu Basin, the community characteristics of mosses and herbaceous plants of different vegetation types in the Huangfu Basin were investigated, including 20-year artificial oil pine forest, 20-year artificial pine and poplar mixed forest, 40-year artificial oil pine forest, 40-year artificial poplar forest, artificial caragana shrub forest, degraded grassland and bare land. The soil erosion resistance from 13 indicators was comprehensively evaluated by using principal component analysis. The results showed that the α diversity of mosses was the highest under 40-year artificial oil pine forest; the species richness and evenness of herbaceous plants were the greatest under 40-year artificial poplar forest. The surface roughness, saturated hydraulic conductivity, soil organic matter content, total carbon and total nitrogen content, and bulk density of artificial tree forest, artificial caragana shrub forest and degraded grassland were higher than those of bare land, while the average weight diameter, pH and erodibility K factor were lower than those of bare land; the particle size was mainly concentrated in 10-250 µm; the soil cohesion of artificial tree forests was higher than that of bare land. The principal component analysis indicated that soil total nitrogen, soil total carbon, organic matter, silt content and surface roughness were important indicators for evaluating soil erosion resistance; the comprehensive soil erosion resistance of 40-year artificial oil pine forest was the highest, and that of artificial caragana shrub forest was the lowest.

Abstract:To understand the response and adaptation mechanisms of forest plants to drought, the minimum leaf conductance (g_min) of 26 Magnoliaceae species (16 evergreen and 10 deciduous) in a common garden was measured. The results showed that the g_min of evergreen species [6.5 mmol/(m²·s)] was significantly lower than that of deciduous species [11.6 mmol/(m²·s)], and g_min was generally significantly negatively correlated with leaf cuticle thickness, but not significantly correlated with stomatal size, density, and stomatal index. The g_min decreased with the increase of mean annual temperature (MAT) of the species distribution area, but was not significantly correlated with mean annual precipitation (MAP). However, in evergreen species, the g_min decreased significantly with the decrease of MAP in distribution area, indicating that reducing g_min was an adaptation strategy to drought adopted by evergreen species (but not deciduous species). In addition, evergreen species had thicker cuticles, which explained the lower g_min. There was significant interspecific variability in g_minof Magnoliaceae species, and it was mainly regulated by cuticle characteristics rather than stomatal characteristics. These would provide a new perspective for revealing the drought adaptation mechanisms of plants.

Abstract:To explore the hydraulic coordination mechanism between leaflets and petioles of ferns, the pressure-volume curves of leaflets of five fern species (Cyclosorus interruptus, Diplazium donianum, Nephrolepis cordifolia, Psilotum nudum and Pteris vittata) were measured, and the correlations between the morphological structures of leaflets and petioles and their hydraulic functions were analyzed. The results showed that the hydraulic efficiency [theoretical water conductivity of leaflets (K_leaf) and theoretical water conductivity of petioles (K_th)] and the hydraulic safety [water potential at the loss of turgor pressure (Ψ_tlp)] of Pteris vittata were higher than those of other species. The pinnae of D. donianum exhibited the highest water storage capacity [absolute water capacity (C_T) and saturated water content (SWC)], but its safety was the lowest. Diplazium donianum had the most dense and smaller stomata and the highest minimum leaf surface conductance (g_min), while Psilotum nudum had the most sparse and larger stomata. The maximum theoretical stomatal conductance (g_s,max) of Pteris vittata was higher than that of other species. The supply and consumption of water by petioles and leaflets of ferns were coordinated. The water supply function of petioles was significantly correlated with the stomatal traits. Higher K_th was accompanied by smaller and denser stomatal distribution and larger g_s,max. In addition, g_s,max was significantly positively correlated with the area of xylem in petiole) (P<0.05), and g_min is significantly positively correlated with SWC (P<0.05). The hydraulic efficiency was coordinated with hydraulic safety in pinnae (P<0.01), meaning that pinnae with higher K_leaf have more negative Ψ_tlp. This revealed the hydraulic coordination mechanism between pinnae and petioles of ferns, indicating that ferns achieve a dynamic balance between water transport efficiency and transpiration demand through structural-functional coordination. This adaptive strategy might enhance their adaptability to the environment.

Abstract:To explore the physiological response mechanism of Michelia macclurei seeds under different storage temperatures and conditions, the viability, germination rate, moisture content, physiological and biochemical indicators were determined. The results showed that with the extension of storage time, the viability, germination rate, protein content, and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and amylase (AMY) of the seeds all showed a downward trend; the contents of soluble sugar and malondialdehyde (MDA) first increased and then decreased, and the MDA content after storage was always significantly higher than that before storage. The moisture content of seeds stored at 4 ℃, –20 ℃ and –196 ℃ showed a trend of first decreasing and then increasing; among them, the seeds stored at 4 ℃ and –196 ℃ had higher viability, germination rate, soluble sugar and protein content, as well as SOD, POD, CAT and AMY activities. In addition, retaining the pseudocarp significantly increased the viability and germination rate of the seeds. The germination rate and viability were significantly or extremely significantly correlated with contents of moisture, soluble sugar, protein and MDA, as well as activities of SOD, POD, CAT and AMY. Storage temperature, storage duration and the removal of pseudocarp all had significant effects on the physiological and biochemical indicators of M. macclurei seeds. Therefore, in the actual storage process, low temperature (such as 4 ℃ or –196 ℃) combined with pseudocarp protection could be adopted to maintain the physiological activity of M. macclurei seeds to the greatest extent and extend their storage life.

Abstract:Ochroma lagopus, an important fast-growing tropical timber tree species, has been successfully introduced and cultivated in the tropical regions of southwest China. However, the region’s distinct tropical monsoon climate, characterized by a pronounced seasonal drought lasting half a year, poses significant challenges to growth and large-scale industrial production of O. lagopus. To reveal the response mechanism of O. lagopus seedlings to drought, gradient water stress treatments were set up. The key photosynthetic parameters, such as net photosynthetic rate (P_n), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), transpiration rate (T_r), and water use efficiency (WUE) were measured. Growth indicators, such as plant height and basal diameter, as well as biomass allocation characteristics, such as dry weight and proportion of roots, stems, and leaves were monitored. The effects of drought stress on the photosynthetic physiology and growth characteristics of O. lagopus seedlings were systematically studied. The results showed that drought stress significantly inhibited the plant height, ground diameter and biomass accumulation of O. lagopus seedlings. Under mild drought stress, P_n, g_s and C_i decreased simultaneously, indicating that stomatal limitation was the main cause of photosynthetic inhibition. The significant reduction in biomass under mild to moderate drought was mainly due to the insufficient supply of carbon assimilates caused by restricted photosynthesis. At the same time, the increase in WUE helped maintain the balance between water conservation and carbon assimilation under drought conditions. Therefore, in the field cultivation of O. lagopus, providing appropriate water supply through water-saving irrigation techniques such as drip irrigation during the dry season to maintain soil moisture at 80% to 85% of field capacity can significantly improve the photosynthetic efficiency and biomass accumulation capacity of O. lagopus, thereby achieving the purpose of optimizing the cultivation management of O. lagopus and increasing wood volume.

Abstract:To screen the optimal fertilizer formula for pot cultivation of Rhododendron hybrid ‘Carnation’, a three-factor three-level L9(3⁴) orthogonal test design was adopted to systematically investigate the effects of different nitrogen (N), phosphorus (P), and potassium (K) ratios on plant growth and physiological characteristics. The test factors included urea (N≥46%, set at 0.5, 1.0, and 1.5 g/pot, represented by N₁, N₂, and N₃ respectively), superphosphate (P₂O₅≥12%, set at 0.8, 1.6, and 2.4 g/pot, represented by P₁, P₂, and P₃ respectively), and potassium sulfate (K₂O≥52%, set at 1.0, 2.0, and 3.0 g/pot, represented by K₁, K₂, and K₃ respectively). The results showed that treatment M5 (N₂P₂K₂) significantly promoted plant height growth and flower quantity, while treatment M6 (N₂P₃K₁) was most conducive to stem diameter thickening. The application amounts of P and K fertilizers had significant effects on the accumulation of aboveground, underground, and total biomass. Treatment M9 had the highest chlorophyll content; treatment M5 had the optimal soluble sugar content; treatment M7 (N₃P₁K₂) had the highest soluble protein content; in terms of antioxidant enzyme activity, treatment N₁P₂K₁ had the highest superoxide dismutase activity, and treatment N₃P₁K₁ had the highest peroxidase content; treatment M7 had the lowest malondialdehyde content. Based on the comprehensive evaluation by principal component analysis, the comprehensive score ranking of each treatment was M5>M4>M6>M1>M2>M7>M8>M3>M9>CK (control). Among them, the optimal treatment M5 was most effective in promoting the growth, enhancing physiological activity, and increasing flowering of ‘Carnation’. This provides a theoretical basis for the optimization of efficient cultivation and propagation techniques for ‘Carnation’.

Abstract:To understand the root response mechanism of Capsicum annuum under continuous cropping obstacles, three types of media, namely substrate soil (CSS), rotation soil (CRS) and continuous cropping soil (CCS), were used to pot the peppers. The root systems were collected when they entered the fruiting period for omics research to analyze the specific components of flavonoids and the information of their synthase genes in the root systems of peppers. The results showed that a total of 31 flavonoids were detected in the root systems of peppers in the three types of media. Compared with CSS, the contents of six flavonoids, namely pelargonidin 3-O-caffeoyl-β- d-glucoside, cyanidin 3-O-glucosides (2 types), delphinidin 3-O-β-d-glucoside, neohesperidin, quercetin 3-O-β-d- glucosyl-β-d-glucoside, were significantly increased in the two cultivation conditions of CRS and CCS, while only one flavonoid, malvidin-3-rutinoside-5-glucoside, was significantly decreased (by 82.37% and 91.29%, respectively). The synthesis of flavonoids involves 202 enzyme genes, among which the families with more genes mainly include cytochrome P450 (15) and UDP glycosyltransferase (14). Compared with CSS, the expression of main synthase genes of these flavonoids in CRS and CCS were significantly different, including 23 flavonoid synthase genes, 3 anthocyanin synthase genes, 7 isoflavone synthase genes, and 5 flavone and flavonol synthase genes. Among them, the expression of UDP glycosyltransferase genes in anthocyanin synthesis metabolism (1) and flavone and flavonol synthesis metabolism (3) were significantly increased on CCS cultivation (by 150.00%, 161.45%, 92.77% and 773.50%, respectively). Therefore, continuous cropping and other adverse stress could significantly increase the content of most flavonoids in the root systems of peppers, and the up and down regulation trends of their synthase genes were not obvious.

Abstract:The farnesol dehydrogenase gene (ClFLDH) of Curcuma longa is a key rate-limiting enzyme in the terpene compound synthesis pathway. To explore the improvement of terpene compound production in C. longa, the cDNA sequence of ClFLDH was obtained through homologous cloning. The open reading frame (ORF) of ClFLDH was 855 bp, encoding 295 amino acids. Bioinformatics analysis indicated that the relative molecular mass of ClFLDH protein was 31 kDa, with an isoelectric point of 6.79, and it was a liposoluble, hydrophobic and neutral protein. The pCE32a-FLDH prokaryotic expression vector was constructed and expressed in Escherichia coli DH5α. The SDS-PAGE electrophoresis results of the recombinant strain showed that the size of the target protein was 37 kDa. GC-MS analysis indicated that the ClFLDH protein might catalyze 3,5-dimethoxyphenol to generate [1,2-a]pyrazine-1,4-dione, 6H-3-(benzyl)-pyrrole. These would provide a new perspective for in-depth understanding of the regulatory mechanism of curcuminoid terpene synthesis and lay a foundation for increasing the production of curcuminoid terpene compounds through genetic engineering.

Abstract:Eucalyptus spp., as an important fast-growing economic tree species in southern China, plays a significant role in forestry production. However, with the large-scale use of single clone and the continuous expansion of plantation area, the risk of biotic and abiotic stress faced by Eucalyptus has significantly increased. Endoplasmic reticulum (ER) stress is an important organelle stress response mechanism formed during the evolution of eukaryotes, which plays a key role in maintaining protein homeostasis within cells and resisting adverse environments. The EgrUTr1 gene was successfully cloned from E. grandis. The full-length coding sequence (CDS) of EgrUTr1 is 1 023 bp encoding a putative transmembrane protein of 340 amino acids. Subcellular localization analysis confirmed that EgrUTr1 was located in ER. EgrUTr1 was expressed in all tissues of E. grandis, and its expression was significantly upregulated under the induction of ER stress inducers dithiothreitol (DTT) and tunicamycin (TM). Heterologous expression of EgrUTr1 in the model plant Arabidopsis thaliana significantly enhanced the plant resistance to TM stress, indicating that EgrUTr1 might be involved in the ER stress response pathway and play an important regulatory role in the process of plants responding to ER stress. These would provide important clues for further understanding the molecular mechanism of ER stress response in E. grandis.

Abstract:Jasminum elongatum is a climbing shrub, usually grows in the evergreen broad-leaved forests and forest edges in south China. In order to understand the sexual system and reproductive characters of J. elongatum, the distylous floral morphology, pollen-ovule ratios, ancillary floral characters, inter- and intra-morph incompatibility were studied. The results showed that there are significant differences between L- and S-morph in style length, stigma and anther heights, corolla tube diameter, and corolla tube length. The flower of J. elongatum showed pollen dimorphism in terms of size and ornamentation, and stigmatic dimorphism in terms of size and shape. After artificial pollination, the inter-type cross-pollination between long-styled and short-styled flowers grew normally, and the pollen tubes could enter the ovary after pollination 8 hours. However, self-pollination and intra-type cross-pollination showed incompatibility. The pollen tubes were inhibited on the surface of the S-morph stigma and in the middle of L-morph stigma respectively, and the pollen tubes were deformed and swollen with callose accumulation at the tip. Therefore, the flower of J. elongatum was atypical dimorphic style in morphology and had a strict heteromorphic self-incompatibility system.