To investigate the effects of different nitrogen applications on the growth and leaf nutrient uptake of Ochroma lagopus plantations,one-and a-half-year-old O.lagopus trees were used as experimental materials.Five treatments set up:0(N0),50 kg·hm-2 urea(N1),100 kg·hm-2 urea(N2),50 kg·hm-2 slow-release nitrogen fertilizer(PCU1),and 100 kg·hm-2 slow-release nitrogen fertilizer(PCU2);tree height,diameter at breast height(DBH),and leaf carbon(C),nitrogen(N),phosphorus(P),chlorophyll,and non-structural carbohydrates(NSC)contents were measured.The results were as follows:(1)Compared with the N0 treatment,tree height,DBH,chlorophyll a,chlorophyll b,and chlorophyll(a+b)contents were significantly increased by 28.66％,50.72％,50.17％,50.71％,and 50.25％,respectively,under the N2 fertilization treatment(P＜0.05).(2)Compared with the N0 treatment,leaf N content significantly increased by 60.16％(P＜0.05)under the N2 fertilization treatment;P content showed a decreasing trend.Under the N0 treatment,leaf N/P＜14,indicating that O.lagopus growth was limited by N element.After nitrogen addition,N/P＞14,indicating that nitrogen fertilization altered the N-element limitation on O.lagopus growth.(3)Compared with the N0 treatment,leaf soluble sugar and NSC contents were significantly increased by 78.98％and 52.49％,respectively,under the N2 fertilization treatment(P＜0.05).(4)Under urea application,the leaf soluble sugar content showed significant positive correlations with N content,C/P,and N/P,and a significant negative correlation with P content;under slow-release fertilizer application,the leaf starch content showed a significant negative correlation with P content and a significant positive correlation with N/P;under nitrogen application,the leaf soluble sugar and starch contents showed significant positive correlations with N content and N/P.(5)The phenotypic plasticity indices for leaf N,N/P,C/P,soluble sugar content,and soluble sugar/starch were all relatively high.The cumulative variance contribution rates of principal component 1(PC1)and principal component 2(PC2)were 66.3％.In summary,nitrogen addition significantly promotes the growth of O.lagopus and leaf nutrient absorption,with the N2 fertilization treatment yielding the best results;nitrogen addition alleviates the limiting effect of nitrogen on O.lagopus growth;O.lagopus promotes growth by increasing chlorophyll content,improving leaf utilization efficiency of nitrogen and phosphorus,and thereby altering the distribution of leaf soluble sugar and starch contents.
The Xisha Islands are a group of tropical coral islands in the northwest of the South China Sea. In these islands, the natural environment is unique and harsh, the biodiversity is low, and the ecosystem is extremely fragile. Threat from pernicious plants is one of the important factors for vegetation degradation in the Xisha Islands. It is necessary to investigate the pernicious plant species and their distribution, and the extent of harm in the Xisha Islands. In this research, field investigation on the 24 islands with vegetation in the Xisha Islands was conducted, and the species composition, distribution, growth characteristics and hazard degree of pernicious plants were comprehensively investigated and analyzed in combination with relevant literature and evaluation system. The results were as follows:(1)There were 26 species of pernicious plants belonging to 20 genera and 10 families in the Xisha Islands, of which the number of plant species belonging to four families of Asteraceae, Fabaceae, Verbenaceae and Lauraceae, accounted for 53.8% of the total number species of pernicious plants.(2)According to their growth, distribution, and hazard degree, pernicious plants could be classified into three hazard levels. The Level 1 of pernicious plants included Cassytha filiformis, Chromolaena odorata, Wollastonia biflora, Leucaena leucocephala, Bidens pilosa and Tridax procumbens, mainly distributed in Yongxing Dao, Dong Dao, Chenhang Dao, and Shanhu Dao.(3)The severity of pernicious plants was closely related to the total number of plant species and area of the island. The life form of pernicious plants in the Xisha Islands was mainly terrestrial herbs, accounting for 57.7%. The pernicious plants mainly came from the Americas, with a similar proportion of natural spread, unintentional introduction, intentional introduction sources. Based on the above results, it is suggested to conduct long-term monitoring of pernicious plants in the Xisha Islands, and formulate scientific prevention and control strategies for pernicious plants that have caused serious harm, including strengthening inspection and quarantine, physical removal, chemical control, alternative control, and publicity and education, etc. The research results provide important basic data, scientific and technological support for the protection, health and sustainable development of the vegetation and ecosystems in the Xisha Islands.
To study the correlation between endogenous hormone content and physiological and biochemical characteristics and somatic embryogenic capacity for different cell lines of Pinus elliottii,seven cell lines induced by immature seeds of P.elliottii were used as materials.The phenotype and cellular structure were observed,and the contents of endogenous hormones,soluble protein,soluble sugar,starch and antioxidant enzyme activities were determined,followed by the maturation culture of five selected cell lines.In order to explore the characteristic index values that affect the embryogenic capacity of cell lines,so as to identify the embryogenic capacity of cell lines with strong embryogenic capacity in the early stage,and provide technical reference for optimizing the somatic embryogenesis and improving the somatic embryo induction rate of P.elliottii.Data analysis involved analysis of variance(ANOVA),Duncan multiple range test,and pearson correlation analysis.The results were as follows:(1)Different cell lines differed in cytological observation,among which the V30 cell line had obvious and more embryonal-suspensor mass(ESM),indicating the V30 line was a strong embryonic line.(2)The endogenous hormone content was significantly and different among cell lines,with a significant positive correlation among abscisic acid(ABA),trans-zeatin riboside(ZR)and cell lines,a significant negative correlation among indoleacetic acid(IAA)content and cell lines,no significant difference among gibberellic acid(GA3)and no significant correlation among GA3 and cell lines.(3)The soluble protein content,soluble sugar content,starch content,peroxidase(POD),superoxide dismutase(SOD),and catalase(CAT)activity were significantly different among cell lines,but showed no obvious correlation with the embryogenic ability of cell lines.(4)Based on the embryogenesis of the cell line and the number of mature embryos,the V30 cell line had a high somatic embryogenesis potential.In conclusion,the somatic embryogenic capacity of the P.elliottii cell line is significantly correlated with the endogenous hormone content,which can provide reference for improving the embryogenic capacity of cell lines and optimizing the maturation conditions of somatic embryos by regulating hormone levels,and also offers technical reference for optimizing somatic embryogenesis and improving the somatic embryo induction rate in P.elliottii.
To explore the community niche characteristics,interspecific relationships and community stability of secondary tropical rainforest in the main stream of the Nandu River,and to reveal its community structure,succession status and trend,21 main species in the tree and shrub layer of the community were studied.Niche width,niche similarity and niche overlap were used to analyze niche characteristics.Spearman coefficient,chi-square(x2)statistic,association coefficient and matching coefficient were used to analyze the interspecific association relationship of the community.The stability of the community was determined by the improved M.Godron stability measurement method.The results were as follows:(1)Heptapleurum heptaphyllum had the highest importance value,and Aporosa dioica had the largest niche width.The total niche similarity and overlap among these main species were generally low,among which Machilus chinensis-Eurya nitida had the highest niche similarity and overlap index(0.69 and 0.87,respectively).(2)The overall association of the main species was a significant positive association,but the significant rate of association test between species pairs was 3.81％.(3)The intersection point of the fitted curve with line segment y=100-x was(39.80,60.20),and the Euclidean distance from the stable point(20,80)was 28.00,which indicates that the community of the secondary tropical rainforest along the main stream of the Nandu River is unstable.In conclusion,the secondary tropical rainforest of the main stream of the Nandu River is in the key stage of transition from pre-successional to mid-successional.In order to maintain and enhance the stability of the community of the secondary tropical rainforest,we should take measures to close hillsides to facilitate for afforestation and reduce human disturbance.The study provides the data basis for promoting the protection and restoration of secondary tropical rainforests and enhancing the stability of watershed ecosystems.
Litter is an important part of forest productivity,and its productivity and stoichiometric ratio(high N and low C∶N,C∶P and N∶P,which facilitate litter decomposition)are vital in regulating soil carbon dynamics through decomposition rate modulation and nutrient release optimization.Although mixed-species plantations are known to significantly alter litter production and soil carbon sequestration compared with monocultures,but how these mixing effects change across different stand age stages remains poorly understood.The objective of this study was four pure Pinus massoniana plantation with different stand ages(25,36,46 and 63 years old)and their corresponding mixed plantations with Castanopsis hystrix.We measured litter production,litter stoichiometric ratio,and soil carbon storage to assess how mixing broad-leaved tree species with pure Pinus massoniana affects these factors across different stand ages.The results were as follows:(1)Tree species mixing significantly increased litter production in mature forests(36 years old).The positive mixing effect on litter production mainly existed in near-mature forests(25 years old)and mature forests(36 years old).Consequently,the litter N content gradually increased with increasing stand age,whereas the P content firstly increased and then decreased.Except for the mature forest(46 years old),mixed plantations had lower C∶N than pure plantations.In over-mature forests(63 years old),we observed maximal mixing effects on litter N content and N∶P but minimal effects on C∶N.(2)Mixing also promoted an increase in soil carbon storage for most stand ages,particularly in the 0-60 cm soil layer.We also observed that the over-mature forest exhibited maximal mixing effect values in each soil layer.(3)Spearman's correlation analysis showed strong association between mixing-influenced soil carbon storage variations and litter C,N,C∶N and N∶P.Thus,introducing Castanopsis hystrix into pure Pinus massoniana plantations can effectively increase litter production and quality,thereby increasing soil carbon storage and promoting nutrient cycling.Moderately extending the management cycle of mixed plantations is beneficial for maximizing their ecosystem functions.
