Effect Of Difference Between Day And Night Temperature On Low Molecular Weight Organic Acid Secretion Of Tomato Roots And Nutrition Uptake

The difference between day and night temperature (DIF) is a major environmental factor affecting crop growth. In order to study the appropriate DIF to promote the growth of the tomato, and to clarify its mechanism, an artificial controlled pot trial was conducted to investigate the effect of DIF conditions on crop performance. A fixed daily temperature of 25? and five DIF treatments (-12, -6, 0, 6 and 12?) were used to grow tomato in a climate chamber in different growth stage(seedlings stage, flowering stage, fruit setting stage and mature stage). Root/shoot ratio, leaf maximum photosynthetic rate (Pmax), root activity, concentrations of low molecular weight organic acids (LMWOAs) secreted by tomato (Lycopersicon esculentum Mill.), soil available nitrogen (N), phosphorus (P) and potassium (K) and their uptake by tomato were measured. Finally, correlation analysis (CA) and principal component analysis (PCA) were used to clarify the relationship between all indexes, in order to analyze the effect of DIFs on low molecular weight organic acid secretion of tomato root and nutrition uptake. The main results are as follows:The growth performance was the best under 6? DIF, i.e., Pmax, dry matter and root shoot ratio were increased significantly. However, this tendency was inhibited when the DIF was up to 12?. Whereas the negative DIFs significantly decreased tomato Pmax, dry matter and root shoot ratio, and the reduction was enhanced with the decrease of DIF.In the whole growth period, tomato root activity was the highest in fruit setting stage. 6? DIF significantly increased root activity by 33.4%, which was the highest increasing rate among all DIFs. Whereas the negative DIFs significantly inhibited root activity by 4.3-24.2%, and the reduction was enhanced with the decrease of DIF.The types and concentrations of LMWOAs secreted by tomato root were various in different DIFs, the positive DIFs mainly increased the secretion of oxalic acid,formic acid, malonic acid, lactic acid and acetic acid. While the negative DIFs mainly increased the secretion of propionic acid, malic acid and citric acid. Oxalic acid was the main LMWOA secreted by tomato roots.The positive DIFs significantly decreased soil pH, and promoted the release of soil available N, P and K, 6? DIF represented the highest increasing rate. Due to this, N, P and K uptake by tomato tissues were significantly increased under 6? DIF.The negative DIFs had no obvious impact on soil available N, P and K,but reduced the N, P and K concentration in tomato tissues.CA and PCA analysis revealed that, a significant positive correlation relationship was occurred between every two variables in LMWOAs, root activity,root shoot ratio, Pmax, soil available N, P and K, and N, P and K concentration in plant. And PCA analysis showed that 0?, -6? and-12? DIF were harmful to all indexes.Above all,the positive DIFs, especially for 6? DIF, might increase photosynthetic product by promoting tomato photosynthesis, which was beneficial to LMWOAs secretion, then soil available N, P and K would be activated, finally promoted N, P and K uptake by tomato and enhanced tomato growth.