Prediction of suitable tea growth area and analysis of germanium enrichment and transport characteristics in Chongqing based on MaxEnt model

【Objective】To predict the suitable areas for tea tree growth in Chongqing，and investigate the accumulation and translocation characteristics of germanium（Ge）in tea trees，which could provide reference for the production of high-quality and Ge-rich tea in Chongqing.【Method】Data on the distribution of 307 tea tree locations（including 295 artificially planted tea gardens and 12 ancient tea trees）and 19 environmental variables in Chongqing were collected. The MaxEnt model was used to classify the suitability levels of tea tree growth areas，and the contribution rate and replacement rate of each environmental variable were analyzed. The Jackknife method was employed to identify the main environmental variables affecting tea tree distribution. Young leaves，old leaves，branches and roots were collected from Nanchuan District，Chongqing. The germanium content was measured，and the accumulation coefficient and translocation coefficient were calculated to analyze the potential for germanium-rich tea production.【Result】All 19 environmental variables had an impact on the prediction of suitable tea tree growth areas in Chongqing，the lowest temperature in the coldest month owned the highest contribution rate，the seasonal variation in precipitation owned the highest replacement rate. The Jackknife detection indicated that the main environmental factors affecting the distribution of tea trees in Chongqing were annual average temperature，average temperature in the coldest quarter，the lowest temperature in the coldest month， average temperature in the wettest quarter，and the average temperature in the driest quarter. The tea tree suitable growth areas in Chongqing could be divided into 4 grades. Highly suitable areas and non-suitable areas were relatively small， while medium suitable areas and low suitable areas were larger. In Nanchuan District，most areas were classified as medium suitable areas，with a small part belonging to low suitable areas and non-suitable areas，and only a very small part belonging to highly suitable areas. In Nanchuan District，young leaves of ancient tea trees and young leaves，old leaves， branches，and roots of tea trees from artificially planted tea gardens were randomly collected. The measurements revealed that the germanium content in young leaves from the artificially planted tea gardens（0.0058 mg/kg on average）was higher than that from ancient tea trees（0.0047 mg/kg on average），and the germanium content in the old leaves from tea gardens（0.0119 mg/kg on average）was higher than that in the young leaves. The enrichment coefficient of germanium in tea trees was only 1.41，while the transport coefficients of germanium from the roots to the branches，from the roots to the old leaves，and from the roots to the young leaves were 0.32，0.30，0.14 respectively. Five artificial tea garden locations with relatively high soil germanium content in the suitable growth area of tea trees in Nanchuan District were selected to collect tea tree leaves for the determination of germanium content. The results showed that the germanium content in the old leaves of tea trees（0.0292-0.2840 mg/kg）was higher than that of randomly collected samples. Although tea plants had relatively weak ability to accumulate germanium，germanium-rich tea could be easily made from the old leaves of artificially planted tea gardens located in the suitable growth areas of tea trees and the distribution areas of germanium-rich soil.【Suggestion】Reasonably plan the tea planting areas in Chongqing，and develop tea tree cultivation in the highly suitable areas and medium suitable areas；fully utilize the germanium-rich soil resources to accelerate the production of germanium-rich tea.