| CDs are a new type of zero-dimensional carbon nanomaterials.Once discovered,they have attracted people's great interest.The CDs are notably advantageous in their good biocompatibility,robust chemical inertness,low cytotoxicity and high light stability.CDs have broad application prospects in bioimaging,sensing and catalysis.Currently,the research about nano-carbon materials on crops can be divided into two categories: one is to focus on the impact of various nano-carbon materials on crop physiology and toxicology;the other is to focus on the efffect of nano-carbon materials in agricultural fertilization.Currently,studying on biological effect of CDs is still very limited.In this research,yeast powder was used as a raw material to synthesize nitrogen-doped carbon quantum dots,and three common vegetables,Italian lettuce,Lactuca sativa L and cucumber were used as test materials.In plant factory,the effects of different concentrations N-doped CDs on the growth,quality,antioxidant capacity,photosynthetic pigments of Italian lettuce,Lactuca sativa L and cucumber seedlings were studied.Control group does not add carbon dots,three low-concentration carbon treatments were set up in the experiment: T1 = 5 mg/L,T2 = 25 mg/L and T3 = 50 mg/L;The two high-concentration treatments were H1 = 500 mg/L and H2 = 1000 mg/L.The main results are as follows:1.Different concentrations of nitrogen-doped CDs have different effects on the physiological and biochemical characteristics of Italian lettuce and Lactuca sativa L.(1)With the concentration increasing of nitrogen-doped CDs treatments,the fresh and dry weight of Italian lettuce and Lactuca sativa L showed the trend of increasing firstly and then decreasing.Under 25 mg/L CDs treatment,the dry and fresh weight of shoots and roots of lettuce and Lactuca sativa L reached the maximum.The fresh weight of lettuce's shoots and roots increased by 33.18% and 42.39% respectively than CK;The shoots and roots fresh weight of Lactuca sativa L increased by 28.10% and 26.38% respectively,and under higher concentration CDs(500 and 1000 mg/L),the growth of lettuce and Lactuca sativa L was significantly inhibited.(2)The treatment of nitrogen-doped CDs improved the soluble sugar content,soluble protein content and the root vitality of Italian lettuce and Lactuca sativa L,and reduced nitrate content in leaves significantly.The soluble sugar content of Italian lettuce was highest at 5 mg/L CDs,and the root vitality of Italian lettuce was highest under at 50 mg/L CDs.The soluble protein content of lettuce was highest under at 25mg/L CDs,the antioxidant capacity of Italian lettuce was significantly enhanced than CK.The soluble sugar content,soluble protein content and root vitality of Italian lettuce and Lactuca sativa L were all optimal under 25 mg/L CDs treatment.The CDs treatment have no significant effect on the antioxidant capacity of Lactuca sativa L.(3)Under 25 mg/L nitrogen-doped CDs treatment,the content of photosynthetic pigments of Italian lettuce and Lactuca sativa L was the highest,and promotting the photosynthetic rate of plants.With nitrogen-doped CDs treating can increase the stomatal conductance of Italian lettuce and Lactuca sativa L,increasing the intercellular CO2 concentration,promoting the transpiration rate and the growth and metabolism of Italian lettuce and Lactuca sativa L.Under the treatment of 5 mg/L and 25 mg/L nitrogen-doped CDs,the photosynthetic quantum efficiency,apparent electron transport efficiency,and photochemical activity of lettuce were significantly increased than CK.(4)Compared with CK,the phosphorus content of lettuce's shoots was decreased under nitrogen-doped CDs treatment,and iron and zinc of lettuce's shoots was enhanced than CK.With the concentration increasing of CDs,the accumulation of nutrients of lettuce could be promoted,and the accumulation of total nitrogen,total phosphorus,total potassium,calcium,magnesium,iron and zinc in the shoot were increased.Under 25mg/L nitrogen-doped CDs streatment,the total nitrogen,total phosphorus,total potassium,and magnesium accumulation in lettuce's shoot was the highest;Under the 50 mg/L CDs treatment,the accumulation of calcium,iron,and zinc in the lettuce's shoot was highest.2.Different concentrations of nitrogen-doped CDs have different effects on the physiological and biochemical characteristics of cucumber seedlings.(1)Compared with CK,cucumber seedlings were treated with T1(5 mg/L),T2(25 mg/L),and T3(50 mg/L),strong seedling index 1 increased by 35.64%,23.45%,and 15.76% respectively.The biomass,stem diameter,plant height,leaf area,and strong seedling index of cucumber seedlings treated with T1 were the highest.(2)Within a certain range,the concentration increasing of nitrogen-doped CDs is beneficial for enhancing the soluble sugar,soluble protein contents and root vitality of cucumber seedlings.Under T1 treatment,the soluble sugar,soluble protein and root activity of cucumber seedling reached the maximum.(3)Compared with CK,T1 treatment of cucumber seedlings chlorophyll a,chlorophyll b,total chlorophyll content were increased 18.22%,22.55%,and 19.21% respectively.The contents of chlorophyll a,total chlorophyll,and carotenoids in T3 treatment were lower than CK.The vitality of POD enzyme and CAT enzyme in cucumber seedlings showed a trend of increasing firstly and then decreasing,and the vitality reached the maximum at T1 treatment,indicating that suitable concentration of nitrogen-doped CDs treatment could increase the antioxidant capacity of cucumber seedlings.In summary,under the treatment of 25 mg/L nitrogen-doped CDs,the growth and quality of Italian lettuce and Lactuca sativa L are optimal.With the treatment of 25 mg/L nitrogen-doped CDs,strong seedling index,physiological quality and antioxidant enzyme activities of cucumber seedlings were best.Therefore,carbon quantum dots have potential applications in promoting crop growth,this study has a reference value for expanding the application of carbon quantum dots in agriculture. |
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