论文部分内容阅读
Abstract Different concentrations of sodium selenite and sodium selenate were applied to leaves and roots of longan ( Dimocarpus longan Lour.) to study the absorption and transfer characteristics of exogenous selenium in longan, and the effects of nitrogen and phosphorus fertilizers on the absorption of selenium in longan were discussed. This study provides a theoretical basis and reference for the research and influence on the absorption and transfer mechanism of selenium in longan and the production of selenium-enriched longan.
Key words Longan; Selenium; Concentration; Effect
Received: March 5, 2020Accepted: April 29, 2020
Supported by Guangxi Science and Technology Program Project of China (GuiKe-AA17202037, GuiKe-AD19245169, GuiKe-AD18281072); Yulin Science and Technology Project (YuShi KeNeng 20194301, 2019CXPT00A4).
Wei HUANG (1990-), female, P. R. China, lecturer, PhD, devoted to research about crop nutrition enhancement.
*Corresponding author. E-mail: 363583837@qq.com.
Selenium is a necessary micronutrient element for humans and animals. Selenium deficiency in the human body can cause many diseases. Guangxi is rich in selenium-rich soil resources, and longan ( Dimocarpus longan Lour.) is one of the important economic fruit trees in Guangxi. However, there are few reports on the absorption and transfer characteristics of exogenous selenium in longan. In this study, the absorption and transfer of exogenous selenium in longan and its effects were summarized.
Response to Foliar Application of Selenium in Longan
Effect of foliar selenium application on longan plant biomass
With the increase of sodium selenite concentration, the aboveground and underground biomass of longan first increased and then decreased. When the foliar spray concentration was 25 mg/L , the dry weights of the aboveground and underground parts both reached their maximum values, respectively, 1.551 and 0.849 g, which were 14.46% and 16.46% higher than the control check (CK), respectively, and the difference between the aboveground part and the CK reached a significant level. When the foliar spray concentration reached 100 mg/L, the dry weights of the aboveground and underground parts of longan seedlings decreased, and the dry weight of the aboveground part decreased by 8.86%, which reached a significant level. It shows that sodium selenite has a concentration threshold for longan plant growth, and exceeding this threshold leads to an inhibitory effect on plant growth. The biomass of the aboveground and underground parts of longan increased first and then decreased with the increase of sodium selenate concentration［1］. The biomass of aboveground and aboveground parts reached their maximums when the concentration of sodium selenium was 10 and 25 mg/L, respectively, which significantly increased by 27.36% and 67.86%, respectively, compared with the CK. With further increase of sodium selenate, the growth of longan seedlings was severely inhibited, and some plants leaves withered and fell off, suggesting that the biological effectiveness of sodium selenate is narrower［2］, and its toxic effect is stronger than sodium selenite.
Effect of foliar application of selenium on selenium content in longan
After 50 d of treatment with different concentrations of selenium, the selenium content in the longan seedlings increased linearly with the increase of selenium concentration. According to the coefficients of the fitted linear equations, the absorption rate of sodium selenate by longan is 1.687 7, while that of sodium selenite was 3.742 7 , which was 2.22 times of the value of sodium selenate［3］, indicating that under the same selenium concentration, longan absorbed sodium selenate faster than sodium selenite. The T test of different selenium concentration treatments on longan seedlings showed that when Cse ≤10 mg/L, sodium selenite and sodium selenate showed a significant difference, and when Cse >10 mg/L, the sodium selenate treatment accumulated more selenium in longan than the sodium selenite treatment at a significant level of 0.01, indicating that sodium selenite and sodium selenate have a significant difference in selenium enrichment in longan at a low selenium concentration, and there is a very significant difference between sodium selenate and sodium selenite at a higher concentration.
With the increase of sodium selenite concentration, the selenium contents in the aboveground and underground parts of longan showed a very significant linear increasing trend. For the selenium enrichment in the aboveground part, at low selenium concentrations (<10 mg/L), the differences between the treatments of different concentrations were not significant, and when the selenium concentration≥10 mg/L, the differences between the treatments of different concentrations reached a significant or extremely significant level, while the underground part showed differences between the treatments of different concentrations in selenium absorption reaching a significant level when the selenium concentration>25 mg/L, suggesting that the transfer rate of selenium in plants is slow when foliar spraying of sodium selenite is adopted［4］. When sodium selenite was applied on the leaves, as the concentration increased, the transfer coefficient increased and was all less than 1, indicating that when sodium selenite is applied on the leaves, selenium mainly accumulates in the aboveground part. With the sodium selenate concentration increasing, the selenium contents in the aboveground and underground parts of longan showed a very significant linear increasing trend. For the selenium enrichment in the aboveground part, at low selenium concentrations (<10 mg/L), the differences between the treatments of different concentrations were not significant, and when the selenium concentration≥10 mg/L, the differences between different concentration treatments reached a significant or extremely significant level, while the underground part showed differences between the treatments of different concentrations in selenium absorption reaching a significant level when the selenium concentration>25 mg/L, suggesting that the transfer rate of selenium in plants is slow when foliar spraying of sodium selenate is adopted. When foliar application of sodium selenate was performed, with the concentration increasing, the transfer coefficient increased and was all less than 1, indicating that when sodium selenate is applied on the leaves, selenium mainly accumulates in the aboveground part. Effects of foliar selenium application on the dynamic changes of selenium absorption and accumulation in longan
With the extension of time after the treatment with sodium selenite, the selenium contents in the aboveground and underground parts of longan seedlings were on the increase, and the daily average selenium enrichment gradually decreased. The average daily selenium enrichment was 4.53 μg/kg from 0 to 7 d after treatment and 1.38 μg/kg at 50 d of treatment, with a difference of 3.28 times therebetween, showing that the absorption efficiency of sodium selenite applied on the leaves by longan gradually decreased［5］. Comparing the transfer coefficients at different time after treatment, it was found that the transfer coefficient of sodium selenite to longan seedlings gradually decreased with time, but the TF values were all larger than 1, indicating that after foliar spraying of sodium selenite, selenium is mainly concentrated in the aboveground part, and with time, the transfer capacity tends to decline.
The increasing trend of selenium content in longan by the sodium selenate treatment was consistent with that by the sodium selenite treatment. The daily average selenium enrichment amount from 0 to 7 d after the treatment was 2.86 μg/kg, which was 1.58 times less than that in the sodium selenite treatment, indicating that longan absorbs sodium selenite faster［6］. The transfer coefficient of sodium selenate showed a decreasing trend, but the TF values were all larger than 1, indicating that selenium is mainly concentrated in the aboveground part after sodium selenate is applied.
Previous studies have shown that there are significant differences in the distribution of selenium content in plants under the supply of selenium of different valences and different selenium application methods［7］. Sodium selenite has a poor transferability from the roots to the aboveground part, so it mainly accumulates in the roots or the tree trunk, while sodium selenate has a strong transferability from the roots to the aboveground part, and mainly accumulates in the leaves. However, when sprayed on the leaves, sodium selenite is more transferable than sodium selenate, and more selenium is transferred to the roots through the application of sodium selenite.
When selenium was applied on the leaves, the selenium content of longan was mainly distributed in the aboveground part, and the transferability of sodium selenite was greater than that of sodium selenate. When selenium was applied to the root system, the accumulation of selenium in the underground part was significantly greater than that in the aboveground part when the plants were treated with different concentrations of sodium selenite. However, when the plants were treated with sodium selenate, the transfer coefficient was in the range of 0.74-1.29, and the accumulation of selenium in the aboveground and underground parts was not much different. The above-mentioned differences are mainly related to the difference in absorption and transfer of sodium selenate and sodium selenite by plants. After plants absorb sodium selenite, it needs to be converted into selenium methionine (SeMet), selenium cystine (SeCys) and other forms of selenium to be transported out. And SeMet and SeCys are mainly stored in the roots, and only a small amount of Se (IV) can be detected in xylem. Response to Root Selenium Application in Longan
Effect of selenium application on root biomass of longan plants
The treatment with different concentrations of sodium selenite had no significant effect on the aboveground and underground parts of longan seedlings, but compared with the CK, 6 and 10 mg/kg sodium selenite increased and decreased the underground biomass by 22.62% and 19.35%, respectively, indicating that sodium selenite has a concentration threshold for longan plant growth, and exceeding this threshold leads to inhibition on plant growth.
The aboveground and underground biomass of longan increased first and then decreased with the increase of sodium selenate concentration. When the concentration of sodium selenate was 6 mg/kg, the aboveground and belowground biomass reached maximum values, which significantly increased by 23.11% and 41.46% compared with the CK, but when the concentration was increased to 10 mg/kg, the growth of longan seedlings was severely inhibited, and some plant leaves withered and fell off［8］, showing that the biological effectiveness of sodium selenium is narrower, and its toxic effect is stronger than sodium selenite.
Effect of root selenium application on the selenium content of longan seedlings
After 50 d of treatment with different concentrations of selenium, the selenium content in longan seedlings showed a very significant linear increase with the increase of selenium concentration. The T test on the selenium content in longan seedlings under different concentration treatments showed that there was no significant difference between sodium selenite and sodium selenate when Cse ≤2 mg/kg; sodium selenate significantly promoted the absorption of selenium in longan compared with the sodium selenite treatment when Cse =4 mg/kg; and whenCse >4 mg/kg, the treatment of sodium selenate extremely significantly promoted the absorption of selenium in longan compared with the sodium selenite treatment, indicating that at very low selenium concentrations, sodium selenite and sodium selenate have no significant difference on selenium enrichment in longan, and there is a significant or very significant difference between sodium selenate and sodium selenite in the absorption of selenium in longan at higher concentrations.
When sodium selenite was applied to the root system, the selenium content in the aboveground and underground parts gradually accumulated with the increase of selenium concentration. When the concentration of sodium selenite reached 10 mg/kg, the selenium content in the aboveground and underground part of Longan reached the highest values, at 18.90 and 63.73 μg/kg, respectively, which were significantly different from the selenium treatment with a concentration≤6 mg/kg. When sodium selenate was applied to the root system, the selenium content in the aboveground and underground parts increased obviously with the increase of selenium concentration. When the concentration of sodium selenate was 10 mg/kg, the selenium content in the aboveground and underground parts reached the highest values, at 177.56 and 137.88 μg/kg, respectively, the former one of which had a significant difference from the selenium treatment with a concentration≤8 mg/kg, and the later one was significantly different from the selenium treatment with a concentration≤6 mg/kg. When sodium selenite was applied, the transfer coefficients of longan seedlings were all less than 1 and there were no significant differences between the treatments of different concentrations, indicating that the selenium content is mainly accumulated in the underground part when sodium selenite is applied to the root system. With the increase of sodium selenate concentration, the transfer coefficient of longan seedlings gradually increased, and when the selenium concentration≥4 mg/kg, the transfer coefficients were all greater than 1, indicating that when sodium selenate is applied, the ability of selenium to transfer from the roots to the aboveground part is strong, and the selenium content is mainly distributed in the aboveground part of the plant［9］.
Effect of root selenium application on dynamic changes of selenium absorption and accumulation in longan
With the extension of time after the sodium selenite treatment, the selenium content in the aboveground and underground parts of longan seedlings showed an increasing trend, and the daily average selenium enrichment showed a trend of increasing first and then decreasing, with a peak of 3.24 μg/kg at 7-15 d of the treatment, indicating that the absorption of selenium by longan after the selenium application in the root system changes from fast to slow. Comparing the transfer coefficients at different time after the treatment, the transfer coefficients of selenium in longan seedlings with the sodium selenite treatment were all less than 1, indicating that selenium is mainly distributed in the roots after sodium selenite application.
The change trend of selenium content in longan plants after sodium selenate application was consistent with that of the sodium selenite treatment. The peak appeared from 7 to 15 d after the treatment. The average daily selenium content was 9.43 μg/kg, which was 2.9 times that of the sodium selenite treatment. It suggests that Longan absorbs sodium selenate faster. The transfer coefficient of sodium selenate gradually increased. After 15 d of treatment, the TF values were all greater than 1, indicating that selenium is mainly distributed in the aboveground part after sodium selenate is applied.
Effects of nitrogen and selenium application on longan growth
When the phosphate fertilizer factor was fixed, the selenium content of longan plants gradually increased with the increase of nitrogen application, and the differences were extremely significant, indicating that there were very significant differences in selenium content of longan between different nitrogen application rates. When the nitrogen fertilizer factor was fixed, the selenium content of longan plants increased first and then decreased gradually, but compared with the CK, all phosphorus application treatments increased the selenium content of longan plants［10］, indicating that phosphorus fertilizer promotes the sodium selenite absorption by longan plants. However, at higher phosphorus concentrations, phosphorus and selenium have a competitive relationship, which is unfavorable for plants to absorb selenium. After two-factor analysis of variance of nitrogen application and phosphorus application on the selenium content of longan seedlings, the differences were found to be extremely significant, indicating that there are very significant differences in selenium content of longan between different phosphorus application rates. In the interaction of nitrogen and phosphorus, F =1.94, P =0.090 1 , the difference was not significant, indicating that the effects of nitrogen fertilizer and phosphorus fertilizer on the absorption of selenium in longan are independent of each other, that is, the significance of difference between the levels of nitrogen application will not vary with the change in the amount of phosphorus application.
Wei HUANG et al. Absorption and Transfer of Exogenous Selenium in Longan ( Dimocarpus longan Lour.) and Its Effect
References
［1］ BAO QL. Study on selenium content of soil and crop product and selenium-rich products development prospect of Qinzhou［D］. Nanning: Guangxi University, 2016. (in Chinese)
［2］ CAI XL. Absorption and transfer of exogenous selenium in Longan and its effect on the storage of fruits staying on trees［D］. Nanning: Guangxi University , 2017. (in Chinese)
［3］ WANG SM. Spraying selenium-containing foliar fertilizer significantly improves pear fruit quality［J］. China Fruit News, 2019, 36(12): 50. (in Chinese)
［4］ ZHOU YM. Effects of soil total selenium and exogenous selenium on tree nutrition and fruit quality in different longan orchards［D］. Nanning: Guangxi University, 2018. (in Chinese)
［5］ YANG SJ, YANG XR, ZHANG HX. Experiments of foliar application of selenium fertilizer on the yield and selenium content of red dates［J］. forest Science And Technology, 2018(10): 65-66. (in Chinese)
［6］ PAN JC, XU SL, ZHOU YM, et al. Effects of foliar spraying of sodium selenite on longan tree nutrition and fruit quality［J］. Chinese Journal of Tropical Agriculture, 2019, 39(4): 1-7. (in Chinese)
［7］ WANG XF, LUO Z, WANG YN, et al. Effect of foliar spraying of different forms of selenium on strawberry absorption and translocation of selenium［J］. Journal of Agricultural Resources and Environment, 2016(4): 334-339. (in Chinese)
［8］ SHI CL, YE X, ZHU LH, et al. Effects of selenium application on fruit quality and total selenium content of dragon fruit［J］. Jiangxi Agriculture, 2019(22): 36-37. (in Chinese)
［9］ SU XW, LIU XQ, WEI AH, et al. Preliminary study on the application effect of selenium fertilizer on longan and litchi［J］. China Agricultural Information, 2013(17): 113. (in Chinese)
［10］ WU DD, WU YY, HUANG YC, et al. Effects of different selenium fertilizer types on selenium content and quality of Lingfeng grape［J］. South China Fruits, 2018, 47(4): 132-134. (in Chinese)
Editor: Yingzhi GUANGProofreader: Xinxiu ZHU
Key words Longan; Selenium; Concentration; Effect
Received: March 5, 2020Accepted: April 29, 2020
Supported by Guangxi Science and Technology Program Project of China (GuiKe-AA17202037, GuiKe-AD19245169, GuiKe-AD18281072); Yulin Science and Technology Project (YuShi KeNeng 20194301, 2019CXPT00A4).
Wei HUANG (1990-), female, P. R. China, lecturer, PhD, devoted to research about crop nutrition enhancement.
*Corresponding author. E-mail: 363583837@qq.com.
Selenium is a necessary micronutrient element for humans and animals. Selenium deficiency in the human body can cause many diseases. Guangxi is rich in selenium-rich soil resources, and longan ( Dimocarpus longan Lour.) is one of the important economic fruit trees in Guangxi. However, there are few reports on the absorption and transfer characteristics of exogenous selenium in longan. In this study, the absorption and transfer of exogenous selenium in longan and its effects were summarized.
Response to Foliar Application of Selenium in Longan
Effect of foliar selenium application on longan plant biomass
With the increase of sodium selenite concentration, the aboveground and underground biomass of longan first increased and then decreased. When the foliar spray concentration was 25 mg/L , the dry weights of the aboveground and underground parts both reached their maximum values, respectively, 1.551 and 0.849 g, which were 14.46% and 16.46% higher than the control check (CK), respectively, and the difference between the aboveground part and the CK reached a significant level. When the foliar spray concentration reached 100 mg/L, the dry weights of the aboveground and underground parts of longan seedlings decreased, and the dry weight of the aboveground part decreased by 8.86%, which reached a significant level. It shows that sodium selenite has a concentration threshold for longan plant growth, and exceeding this threshold leads to an inhibitory effect on plant growth. The biomass of the aboveground and underground parts of longan increased first and then decreased with the increase of sodium selenate concentration［1］. The biomass of aboveground and aboveground parts reached their maximums when the concentration of sodium selenium was 10 and 25 mg/L, respectively, which significantly increased by 27.36% and 67.86%, respectively, compared with the CK. With further increase of sodium selenate, the growth of longan seedlings was severely inhibited, and some plants leaves withered and fell off, suggesting that the biological effectiveness of sodium selenate is narrower［2］, and its toxic effect is stronger than sodium selenite.
Effect of foliar application of selenium on selenium content in longan
After 50 d of treatment with different concentrations of selenium, the selenium content in the longan seedlings increased linearly with the increase of selenium concentration. According to the coefficients of the fitted linear equations, the absorption rate of sodium selenate by longan is 1.687 7, while that of sodium selenite was 3.742 7 , which was 2.22 times of the value of sodium selenate［3］, indicating that under the same selenium concentration, longan absorbed sodium selenate faster than sodium selenite. The T test of different selenium concentration treatments on longan seedlings showed that when Cse ≤10 mg/L, sodium selenite and sodium selenate showed a significant difference, and when Cse >10 mg/L, the sodium selenate treatment accumulated more selenium in longan than the sodium selenite treatment at a significant level of 0.01, indicating that sodium selenite and sodium selenate have a significant difference in selenium enrichment in longan at a low selenium concentration, and there is a very significant difference between sodium selenate and sodium selenite at a higher concentration.
With the increase of sodium selenite concentration, the selenium contents in the aboveground and underground parts of longan showed a very significant linear increasing trend. For the selenium enrichment in the aboveground part, at low selenium concentrations (<10 mg/L), the differences between the treatments of different concentrations were not significant, and when the selenium concentration≥10 mg/L, the differences between the treatments of different concentrations reached a significant or extremely significant level, while the underground part showed differences between the treatments of different concentrations in selenium absorption reaching a significant level when the selenium concentration>25 mg/L, suggesting that the transfer rate of selenium in plants is slow when foliar spraying of sodium selenite is adopted［4］. When sodium selenite was applied on the leaves, as the concentration increased, the transfer coefficient increased and was all less than 1, indicating that when sodium selenite is applied on the leaves, selenium mainly accumulates in the aboveground part. With the sodium selenate concentration increasing, the selenium contents in the aboveground and underground parts of longan showed a very significant linear increasing trend. For the selenium enrichment in the aboveground part, at low selenium concentrations (<10 mg/L), the differences between the treatments of different concentrations were not significant, and when the selenium concentration≥10 mg/L, the differences between different concentration treatments reached a significant or extremely significant level, while the underground part showed differences between the treatments of different concentrations in selenium absorption reaching a significant level when the selenium concentration>25 mg/L, suggesting that the transfer rate of selenium in plants is slow when foliar spraying of sodium selenate is adopted. When foliar application of sodium selenate was performed, with the concentration increasing, the transfer coefficient increased and was all less than 1, indicating that when sodium selenate is applied on the leaves, selenium mainly accumulates in the aboveground part. Effects of foliar selenium application on the dynamic changes of selenium absorption and accumulation in longan
With the extension of time after the treatment with sodium selenite, the selenium contents in the aboveground and underground parts of longan seedlings were on the increase, and the daily average selenium enrichment gradually decreased. The average daily selenium enrichment was 4.53 μg/kg from 0 to 7 d after treatment and 1.38 μg/kg at 50 d of treatment, with a difference of 3.28 times therebetween, showing that the absorption efficiency of sodium selenite applied on the leaves by longan gradually decreased［5］. Comparing the transfer coefficients at different time after treatment, it was found that the transfer coefficient of sodium selenite to longan seedlings gradually decreased with time, but the TF values were all larger than 1, indicating that after foliar spraying of sodium selenite, selenium is mainly concentrated in the aboveground part, and with time, the transfer capacity tends to decline.
The increasing trend of selenium content in longan by the sodium selenate treatment was consistent with that by the sodium selenite treatment. The daily average selenium enrichment amount from 0 to 7 d after the treatment was 2.86 μg/kg, which was 1.58 times less than that in the sodium selenite treatment, indicating that longan absorbs sodium selenite faster［6］. The transfer coefficient of sodium selenate showed a decreasing trend, but the TF values were all larger than 1, indicating that selenium is mainly concentrated in the aboveground part after sodium selenate is applied.
Previous studies have shown that there are significant differences in the distribution of selenium content in plants under the supply of selenium of different valences and different selenium application methods［7］. Sodium selenite has a poor transferability from the roots to the aboveground part, so it mainly accumulates in the roots or the tree trunk, while sodium selenate has a strong transferability from the roots to the aboveground part, and mainly accumulates in the leaves. However, when sprayed on the leaves, sodium selenite is more transferable than sodium selenate, and more selenium is transferred to the roots through the application of sodium selenite.
When selenium was applied on the leaves, the selenium content of longan was mainly distributed in the aboveground part, and the transferability of sodium selenite was greater than that of sodium selenate. When selenium was applied to the root system, the accumulation of selenium in the underground part was significantly greater than that in the aboveground part when the plants were treated with different concentrations of sodium selenite. However, when the plants were treated with sodium selenate, the transfer coefficient was in the range of 0.74-1.29, and the accumulation of selenium in the aboveground and underground parts was not much different. The above-mentioned differences are mainly related to the difference in absorption and transfer of sodium selenate and sodium selenite by plants. After plants absorb sodium selenite, it needs to be converted into selenium methionine (SeMet), selenium cystine (SeCys) and other forms of selenium to be transported out. And SeMet and SeCys are mainly stored in the roots, and only a small amount of Se (IV) can be detected in xylem. Response to Root Selenium Application in Longan
Effect of selenium application on root biomass of longan plants
The treatment with different concentrations of sodium selenite had no significant effect on the aboveground and underground parts of longan seedlings, but compared with the CK, 6 and 10 mg/kg sodium selenite increased and decreased the underground biomass by 22.62% and 19.35%, respectively, indicating that sodium selenite has a concentration threshold for longan plant growth, and exceeding this threshold leads to inhibition on plant growth.
The aboveground and underground biomass of longan increased first and then decreased with the increase of sodium selenate concentration. When the concentration of sodium selenate was 6 mg/kg, the aboveground and belowground biomass reached maximum values, which significantly increased by 23.11% and 41.46% compared with the CK, but when the concentration was increased to 10 mg/kg, the growth of longan seedlings was severely inhibited, and some plant leaves withered and fell off［8］, showing that the biological effectiveness of sodium selenium is narrower, and its toxic effect is stronger than sodium selenite.
Effect of root selenium application on the selenium content of longan seedlings
After 50 d of treatment with different concentrations of selenium, the selenium content in longan seedlings showed a very significant linear increase with the increase of selenium concentration. The T test on the selenium content in longan seedlings under different concentration treatments showed that there was no significant difference between sodium selenite and sodium selenate when Cse ≤2 mg/kg; sodium selenate significantly promoted the absorption of selenium in longan compared with the sodium selenite treatment when Cse =4 mg/kg; and whenCse >4 mg/kg, the treatment of sodium selenate extremely significantly promoted the absorption of selenium in longan compared with the sodium selenite treatment, indicating that at very low selenium concentrations, sodium selenite and sodium selenate have no significant difference on selenium enrichment in longan, and there is a significant or very significant difference between sodium selenate and sodium selenite in the absorption of selenium in longan at higher concentrations.
When sodium selenite was applied to the root system, the selenium content in the aboveground and underground parts gradually accumulated with the increase of selenium concentration. When the concentration of sodium selenite reached 10 mg/kg, the selenium content in the aboveground and underground part of Longan reached the highest values, at 18.90 and 63.73 μg/kg, respectively, which were significantly different from the selenium treatment with a concentration≤6 mg/kg. When sodium selenate was applied to the root system, the selenium content in the aboveground and underground parts increased obviously with the increase of selenium concentration. When the concentration of sodium selenate was 10 mg/kg, the selenium content in the aboveground and underground parts reached the highest values, at 177.56 and 137.88 μg/kg, respectively, the former one of which had a significant difference from the selenium treatment with a concentration≤8 mg/kg, and the later one was significantly different from the selenium treatment with a concentration≤6 mg/kg. When sodium selenite was applied, the transfer coefficients of longan seedlings were all less than 1 and there were no significant differences between the treatments of different concentrations, indicating that the selenium content is mainly accumulated in the underground part when sodium selenite is applied to the root system. With the increase of sodium selenate concentration, the transfer coefficient of longan seedlings gradually increased, and when the selenium concentration≥4 mg/kg, the transfer coefficients were all greater than 1, indicating that when sodium selenate is applied, the ability of selenium to transfer from the roots to the aboveground part is strong, and the selenium content is mainly distributed in the aboveground part of the plant［9］.
Effect of root selenium application on dynamic changes of selenium absorption and accumulation in longan
With the extension of time after the sodium selenite treatment, the selenium content in the aboveground and underground parts of longan seedlings showed an increasing trend, and the daily average selenium enrichment showed a trend of increasing first and then decreasing, with a peak of 3.24 μg/kg at 7-15 d of the treatment, indicating that the absorption of selenium by longan after the selenium application in the root system changes from fast to slow. Comparing the transfer coefficients at different time after the treatment, the transfer coefficients of selenium in longan seedlings with the sodium selenite treatment were all less than 1, indicating that selenium is mainly distributed in the roots after sodium selenite application.
The change trend of selenium content in longan plants after sodium selenate application was consistent with that of the sodium selenite treatment. The peak appeared from 7 to 15 d after the treatment. The average daily selenium content was 9.43 μg/kg, which was 2.9 times that of the sodium selenite treatment. It suggests that Longan absorbs sodium selenate faster. The transfer coefficient of sodium selenate gradually increased. After 15 d of treatment, the TF values were all greater than 1, indicating that selenium is mainly distributed in the aboveground part after sodium selenate is applied.
Effects of nitrogen and selenium application on longan growth
When the phosphate fertilizer factor was fixed, the selenium content of longan plants gradually increased with the increase of nitrogen application, and the differences were extremely significant, indicating that there were very significant differences in selenium content of longan between different nitrogen application rates. When the nitrogen fertilizer factor was fixed, the selenium content of longan plants increased first and then decreased gradually, but compared with the CK, all phosphorus application treatments increased the selenium content of longan plants［10］, indicating that phosphorus fertilizer promotes the sodium selenite absorption by longan plants. However, at higher phosphorus concentrations, phosphorus and selenium have a competitive relationship, which is unfavorable for plants to absorb selenium. After two-factor analysis of variance of nitrogen application and phosphorus application on the selenium content of longan seedlings, the differences were found to be extremely significant, indicating that there are very significant differences in selenium content of longan between different phosphorus application rates. In the interaction of nitrogen and phosphorus, F =1.94, P =0.090 1 , the difference was not significant, indicating that the effects of nitrogen fertilizer and phosphorus fertilizer on the absorption of selenium in longan are independent of each other, that is, the significance of difference between the levels of nitrogen application will not vary with the change in the amount of phosphorus application.
Wei HUANG et al. Absorption and Transfer of Exogenous Selenium in Longan ( Dimocarpus longan Lour.) and Its Effect
References
［1］ BAO QL. Study on selenium content of soil and crop product and selenium-rich products development prospect of Qinzhou［D］. Nanning: Guangxi University, 2016. (in Chinese)
［2］ CAI XL. Absorption and transfer of exogenous selenium in Longan and its effect on the storage of fruits staying on trees［D］. Nanning: Guangxi University , 2017. (in Chinese)
［3］ WANG SM. Spraying selenium-containing foliar fertilizer significantly improves pear fruit quality［J］. China Fruit News, 2019, 36(12): 50. (in Chinese)
［4］ ZHOU YM. Effects of soil total selenium and exogenous selenium on tree nutrition and fruit quality in different longan orchards［D］. Nanning: Guangxi University, 2018. (in Chinese)
［5］ YANG SJ, YANG XR, ZHANG HX. Experiments of foliar application of selenium fertilizer on the yield and selenium content of red dates［J］. forest Science And Technology, 2018(10): 65-66. (in Chinese)
［6］ PAN JC, XU SL, ZHOU YM, et al. Effects of foliar spraying of sodium selenite on longan tree nutrition and fruit quality［J］. Chinese Journal of Tropical Agriculture, 2019, 39(4): 1-7. (in Chinese)
［7］ WANG XF, LUO Z, WANG YN, et al. Effect of foliar spraying of different forms of selenium on strawberry absorption and translocation of selenium［J］. Journal of Agricultural Resources and Environment, 2016(4): 334-339. (in Chinese)
［8］ SHI CL, YE X, ZHU LH, et al. Effects of selenium application on fruit quality and total selenium content of dragon fruit［J］. Jiangxi Agriculture, 2019(22): 36-37. (in Chinese)
［9］ SU XW, LIU XQ, WEI AH, et al. Preliminary study on the application effect of selenium fertilizer on longan and litchi［J］. China Agricultural Information, 2013(17): 113. (in Chinese)
［10］ WU DD, WU YY, HUANG YC, et al. Effects of different selenium fertilizer types on selenium content and quality of Lingfeng grape［J］. South China Fruits, 2018, 47(4): 132-134. (in Chinese)
Editor: Yingzhi GUANGProofreader: Xinxiu ZHU