| Magnolia wufengensis,a new species of the subgenus Magnolia in the Magnoliaceae family,which has extremely high ornamental value and scientific research value.However,the population of M.wufengensis has a narrow habitat,a sparse population and is in a critically endangered state.It is in urgent need of protection,introduction and cultivation,and expansion of suitable areas.At present,the suitable areas for the introduction of M.wufengensis are not clear and the limiting factors affecting the growth of M.wufengensis and the response to global warming are not understood.Therefore,in this research,the 1-year-old M.wufengensis seedlings cultivated in Wufeng,Hubei were used as the research material.They were introduced to three different climate experimental sites in Haidian(Beijing),Nanyang(Henan)and Dali(Yunnan)to carry out regional trials.The original place of Wufeng,Hubei,was used as a control experimental site,the M.wufengensis was compared with the major planted Magnolia species in each experimental site to explore the adaptability of M.wufengensis.At the same time,the four species distribution models of Maxent,GARP,Bioclim,and Domain were used to simulate the distribution of potential suitable areas for introduction of M.wufengensis in China under the current(1970-2000)climatic conditions.The optimal model was screened,and related parameters were optimized,fitness levels are divided,and the main environmental variables and thresholds that affect the distribution of M.wufengensis in China’s potential suitable areas were determined.Then,the optimal model selected was used to simulate the distribution of potential suitable areas for the introduction of M.wufengensis under different climate change scenarios(RCP2.6,RCP4.5,RCP6.0 and RCP8.5)in three periods(modern,2050s(2041-2060),and 2070s(2061-2080)).Finally,it is compared with the dominant environmental variables that affect the global distribution of M.denudata,M.biondii and M.liliflora,as well as global suitable areas for comparative analysis to evaluate the suitability of M.wufengensis and determine potential suitable areas for introduction.The mainly research results are as follows:(1)In the regional trials,it can be seen from the comparison of the environmental conditions of the three experimental sites that the Nanyang has the most similar environmental conditions to that of Wufeng,followed by Dali,and the difference in environmental conditions between Haidian and Wufeng is slightly larger,but they all can meet the growth needs of M.wufengensis.The M.wufengensis has good growth adaptability in the Nanyang and Dali experiment sites,the growth of seedling height reaches more than70%of Wufeng,the growth of ground diameter is higher than Wufeng,the ratio of height to diameter is less than Wufeng,and the crown width is not significant different from Wufeng,the survival rate of transplantation and retention rate reached more than 80%.The growth adaptability of the Haidian experiment was slightly weaker than that of Wufeng,and the growth of seedling height also reached more than 70%of Wufeng,the ground diameter growth was small,and he ratio of height to diameter was greater than Wufeng,the number of lateral branches,maximum lateral branch length and crown width were all below Wufeng,and the survival rate of transplantation and retention rate reached more than 70%.The overall evaluation of the heat resistance of M.wufengensis in Nanyang and Dali experimental sites is level II,the Haidian experimental site is level III,the overall evaluation of cold resistance is level I,and the comprehensive evaluation of resistance to diseases and insect pests is level II and above,and there were almost no serious pests and diseases.However,compared with the local M.denudate and M.biondii,the difference in stress resistance is not significant,and the morphological and physiological adaptability is slightly weaker,which also reflects that the M.wufengensis still needs many years of introduction and domestication.(2)Based on 49 distribution occurrences of M.wufengensis and 16 environmental variables,four species distribution models were used to simulate the distribution of M.wufengensis’s potential suitable areas for introduction in China.It shows that the potential suitable areas for M.wufengensis are mainly in the south of 40°N and east of 97°E in China.Through the AUC and Kappa values of the four models,it can be concluded that the AUC value simulated by the Maxent model is the highest,the consistency test Kappa value is the best,and the prediction performance is the best.The best parameter of the Maxent model to simulate the suitable area for the introduction of M.wufengensis is the feature combination LQ,and the regularization multiplier is 3.5.Under this parameter,the degree of model overfitting is lower,the complexity is obviously improved,and the model transfer ability is improved.(3)Through the Maxent model,the dominant environmental variables affecting the potentially suitable area for the introduction of M.wufengensis in China and the thresholds were the min temperature of the coldest month(-13.36～9.84°C),the mean temperature of the coldest quarter(-6.06～12.66°C),the annual mean temperature(≥4.49°C)and the elevation(0-2803.93 m).Under current climate conditions,the suitable area of M.wufengensis was classified into 4 levels.The high suitability area of M.wufengensis in China mainly include the Huanghuai Plain,the middle and lower reaches of the Yangtze River,and the northern part of the Jiangnan Hills,with a total area of 46.60×10~4 km~2(4.85%).The medium suitability areas include the North China Plain,most of the Jiangnan Hills,the northern parts of the Guangxi and Guangdong Hills,the eastern part of the Sichuan Basin,and the northeastern part of the Yunnan-Guizhou Plateau,with a total area of 122.82×10~4 km~2(12.79%).The low suitability areas include the southeastern part of the Sichuan Basin,the southern part of the Yunnan-Guizhou Plateau,south of the Guangdong and Guangzhou Hills,the Leizhou Peninsula,Hainan Island,the western part of Taiwan Island,the Shanxi-Hebei-Shandong mountainous hilly regions,the southern part of the Liaodong Peninsula,the southeastern part of the Loess Plateau and the southeastern part of the Qinghai-Tibet Plateau,with a total area of96.36×10~4 km~2(10.03%).The no suitability area includes the Northeast Plain,most of the Liaodong Peninsula,the northwestern part of the Loess Plateau,the northwestern part of the Qinghai-Tibet Plateau,Xinjiang and Inner Mongolia,with a total area of 694.83×10~4 km~2(72.33%).Under future climate change scenarios,the comparison of the current and future suitable areas for M.wufengensis revealed declines of approximately 4.53%-29.98%in high suitability areas and increases of approximately 6.45%-27.09%and 0.77%-21.86%in the’medium’,and’low’suitability areas,respectively,the centroids of M.wufengensis will migrate to high latitudes in the northeast.(4)The simulation results of the Maxent model show that the most important environmental variables(threshold)limiting the distribution of suitable areas for M.wufengensis in the world are the mean temperature of the coldest quarter(-6.75～14.31°C),mean diurnal range(≤14.29°C),min temperature of the coldest month(-13.73～10.77°C),mean temperature of the warmest quarter(≥12.93°C),precipitation of the wettest month(40.99～715.42 mm)and annual mean temperature(4.47～24.56°C).Under modern climatic conditions,the potential suitable areas of M.wufengensis in the world are mainly distributed in Asia,Europe,Africa and North America within the range of 20°～40°N in the Northern Hemisphere,and the western region of South America within the range of 35°～45°S,totaling about 490.89×10~4km~2,among which the total area of high,medium,and low suitability areas are 146.15×10~4km~2,119.88×10~4km~2,and224.87×10~4km~2.Under the future climate change scenarios,the potential suitable areas for the introduction of M.wufengensis in the world will continue to decrease,and the degree of fragmentation will increase.The highly s suitability areas for M.wufengensis will decrease overall by 8.37%-39.14%;medium suitability areas will decrease by 4.76%-16.39%;The low suitability area decreased by 6.65%-39.08%,and the centroids of the suitable area moved to the northeast as a whole.(5)The distribution of M.denudate,M.biondii,M.liliflora and M.wufengensis in the world suitable area is affected by the mean temperature of the coldest quarter,mean diurnal range,min temperature of the coldest month,mean temperature of the warmest quarter and annual mean temperature.The low temperature factor is the most important limiting factor.Under current climatic conditions,the distribution of suitable area of M.denudate,M.biondii and M.liliflora in the world is basically similar to that of M.wufengensis.Under future climate change scenarios,the global suitable areas of M.denudate,M.biondii and M.liliflora will be greatly reduced,and the trend of change is similar to that of M.wufengensis.Both M.denudate and M.liliflora migrate to the northeast,while M.biondii mainly moves to the southeast.Therefore,M.wufengensis can be introduced and cultivated globally with reference to the above Magnolia species.In summary,this study has shown that M.wufengensis has good adaptability in Haidian,Nanyang and Dali through regional trials.The Maxent model is the best model for 4 species distribution models to simulate the distribution of potential suitable areas for the introduction of M.wufengensis.There are some differences in the dominant factors affecting the distribution of M.wufengensis in China and the world suitable areas,but they all show the low temperature factor is the most important limiting factor.The model simulation results of the distribution of potential suitable areas for M.wufengensis are consistent with the results of regional trials.Future climate changes will have a significant impact on the distribution of suitable areas for M.wufengensis,some suitable areas will disappear,the degree of fragmentation will increase,and the whole suitable area will move to the northeast.The distribution of suitable area of M.denudate,M.biondii and M.liliflora in the world is basically similar to that of M.wufengensis.The results of this study can provide a theoretical basis for the effective protection and precise introduction and cultivation of Magnolia in China and the world. |
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