| With the great advancement of China’s economy and people’s increasing emphasis on their own health,the demand for vegetables and off-season vegetables is increasing.In recent years,China’s facility vegetable industry has developed rapidly and has now become the largest producer in the world.However,compared with developed countries,China’s facility vegetable technology is still in a backward state.As an important measure to increase the yield of greenhouse vegetables,CO2 fertilization can increase the crop yield by 30%on average,and the increase in leafy yield is more significant.The application of CO2 fertilization aims to overcome the phenomenon that the photosynthetic efficiency is reduced due to the lack of CO2 in the relatively closed greenhouse under the off-season cultivation.As CO2 fertilization was practiced more widely,more and more researches were done about it and some problems were revealed.In order to solve the problem of the lack of mineral elements in CO2 fertilization conditions and the imbalance of carbon and nitrogen,phosphorus and other mineral elements in plants,the most convenient and effective method is to apply additional mineral fertilizer.However,what is the ratio of added mineral fertilizers to the CO2 fertilization and whether there are interactive effects on vegetable growth have been rarely studied.In three open-top chambers,the effects of different combinations of atmospheric CO2 concentration([CO2]),nitrogen(N)and phosphorus(P)levels on cucumber were studied by the nutrient solution culture method,in terms of root morphological traits,micronutrients concentrations and root exudates.The results showed that:(1)Under the condition of P deficiency(P1),the total root length and total root surface area increased with the increase of N level,whereas a decrease in P levels caused an increase in total root length and total root surface area at the same N level and[CO2].(2)The N concentrations in all parts of cucumber increased with the increase of N level,and the N concentration in N3 treatment was significantly higher than that in N1 and N2.The increase of P level also promoted the N concentrations in cucumber.The concentrations of P in all parts of plants increased with the P supply increasing.Under the condition of N deficiency(N1),the concentration of P in each part increased.Elevated[CO2]reduced N and P concentrations in specific parts of cucumber plants.The total root length and total root surface area of cucumber increased with the[CO2]increasing.The concentration of calcium(Ca)in the roots of cucumber decreased significantly with the increase of[CO2],whereas higher N and P levels significantly increased its concentration.There were apparent interactions between the[CO2]and P level,N level and P level,and within these three factors on Ca concentration in the roots of cucumber.The rise of N level and P level also significantly increased the concentration of Ca in cucumber leaves and the concentration of magnesium(Mg)in stems,and there was a significant interaction between N and P levels.(3)The abundance of sugars,organic acids and amino acids in root exudation were different from each group.For sugars,both elevating[CO2]and increasing N supply greatly increased their amounts.For organic acids and amino acids,their amounts were increased only when the N supply increasing,whereas the effect of[CO2]was not significant.In general,the increase of[CO2]can promote the growth of cucumber roots and the amount of sugar in root exudates,but it will reduce the concentrations of mineral elements such as N,P,Ca and Mg in some parts of cucumber.However,the increase of N and P levels can promote the absorption of mineral nutrients in roots and the amount of root exudation by enhancing the growth and vitality of cucumber,thereby alleviating the risk of a decrease in mineral elements concentrations due to the elevated[CO2].This suggests us that application of the suitable amount and the matched proportion of mineral elements are quite necessary while CO2 fertilization is conducted to the greenhouse vegetables. |
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