| The growth and development of plants and their distribution depend on the external environment,of which climate change has the strongest impact on plant distribution.The potential geographical distribution of Zizyphus jujuba was predicted by using niche model,and the spatial change of Zizyphus jujuba in China under the background of climate change was estimated,so as to provide a scientific basis for the development of Zizyphus jujuba industry to cope with climate and environmental changes.Based on R language and GIS,121 distribution points of Zizyphus jujuba were selected through field investigation and herbarium,etc.Using34 environmental factors including climate,soil and terrain,the ENMeval package in R language was used to adjust the default parameters of the MaxEnt model.The potential geographical distribution of Zizyphus jujuba in different periods was analyzed by using the optimized MaxEnt model.Person correlation analysis and VIF variance expansion factor were used to screen out the required factors to participate in the modeling,and the Jackknife method was used to statistically analyze the dominant environmental factors in the suitable habitats.The main results of the study show that:(Ⅰ)The results of ENMeval optimization showed that when the feature combination is linear,quadratic and hinge,and the regulation multiplier is 3.5,the complexity and over-fitting of the MaxEnt model were the lowest.The AUC of the working characteristic curve analysis method of the subjects was 0.946,which indicates that the prediction model has high reliability and excellent accuracy.(Ⅱ)The results of the jackknife test showed that the annual mean temperature,the mean temperature of wettest quarter,the precipitation of wettest month,the precipitation seasonality,the elevation,and the top soil base saturation are the main environmental factors affecting the distribution of Zizyphus jujuba.The total contribution rate of these six environmental factors is as high as 79.5%,and the total replacement important value of these six environmental factors is 79.4%.Among them,the most significant factors are climate factors.The contribution rate of climate factors is the highest,followed by topographic factors,and the influence of soil factors is the lowest.(Ⅲ)Based on the MaxEnt niche model,the potential geographical distribution of Chinese Zizyphus jujuba were divided.The area of the most suitable area of Zizyphus jujuba is653490.9km~2,and the area of suitable area is 793432.9km~2.The suitable area with a suitable grade greater than 0.29 is called the total suitable area,which is 1446924km~2.The total suitable area accounts for 15.0%of China’s total area.The distribution range of Zizyphus jujuba suitable areas in China is concentrated in(104.3°E～124.2°E,29.8°N～45.6°N),mainly distributed in Shanxi,Ningxia,Inner Mongolia,Shanxi,Henan,Hebei,Beijing,Tianjin,Liaoning,Shandong,Sichuan and other regions.The most suitable areas for Zizyphus jujuba are in the continental regions of warm temperate zone and middle temperate zone.The forest vegetation in these areas is mainly deciduous broad-leaved forest with dry climate.(Ⅳ)The degree of climate anomaly and the most dissimilar environmental variables in the current suitable regions in different periods of Zizyphus jujube were analyzed,and the key regional and geographic changes that cause environmental anomalies under climate change were explored.It is concluded that the degree of climate anomaly in the historical period ranges from large to small is the Last Inter Glacial>Last Glacial Maximum>Mid Holocene.Under future climate change,the RCP2.6-2050s climate scenario will have the highest multivariate similarity value and the lowest climate anomaly;and the RCP8.5-2070s climate scenario will have the lowest multivariate similarity value and the highest climate anomaly.From the last interglacial period to the 2070s,the most dissimilar variables were dominated by precipitation at first and gradually changed to temperature as the climate changed,which was the key factor that caused the geographical distribution of Zizyphus jujuba.(Ⅴ)The potential distribution of Zizyphus jujuba from the Last Inter Glacial to Last Glacial Maximum,the mid Holocene,the current,and the 2050s and 2070s was predicted to reveal the migration route of Zizyphus jujuba population,and the fluctuation of the distribution of Zizyphus jujuba was fully proved to be related to global climate change.(Ⅵ)Comparing the potential suitable areas for Zizyphus jujuba in China in different periods,the results show that during the Last Inter Glacial,Zizyphus jujuba has experienced extensive population expansion,but in the Last Glacial Maximum and the mid of the Holocene,the suitable area for Zizyphus jujuba has shrunk to higher latitude area.In future climate scenarios,as climate warming intensifies,suitable habitats will shift to higher latitudes,while habitats at lower latitudes will become fewer.Global warming will change the distribution pattern of for Zizyphus jujuba in China.The area of the jujube growth area will change to varying degrees.By 2050s and 2070s,the area of Zizyphus jujuba growth area will increase to a certain extent.The response under the RCP4.5 and RCP8.5 scenarios is sensitive and shows an increasing trend.Compared with the other two scenarios,the increasing trend is smaller under the RCP2.6 scenario.The total area of the suitable growth area of Zizyphus jujuba increased.The expansion area of the growth area was mainly in the middle and high latitudes,and the decreased area was mainly in the low latitudes.Under the three climatic scenarios of 2050s and 2070s,the center of mass migration routes are all migrating to high latitudes,and climate warming will make the suitable habitats of Zizyphus jujube in China migrate to high latitudes as a whole. |
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