Physiological Mechanism Of Humic Acid Relieving Damage Of Drought Stress To Oat

Oat is a crop for both grain and forage,market demand increased year by year.Drought stress has become a major limiting factor in the increase in oat production due to its main planting in arid and semi-arid areas.Spraying Humic acid fertilizer(HA)water soluble fertilizer can improve crop resistance and yield and improve quality,but its mechanism is not clear.In this study,irrigated cultivars"Bai Yan 2"and dryland cultivars"Yanke 2"were used as materials.The effects of spraying HA on the photosynthesis and yield of oats were studied;and on the dry matter quality and leaf ultrastructure of oats was studied by pot experiment.The effects of HA on the osmotic regulation and endogenous hormones in oat leaves were studied under severe drought stress.We also examined the composition of leaf soluble sugar and the effect of spraying HA on the main sugar content.The effects of spraying HA and drought stress on gene expression were analyzed by RT-PCR.The main findings are as follows:1.Spraying HA can improve photosynthesis,aboveground dry matter quality and yield of oat under drought stress.After spraying HA,P_n of the leaf was significantly increased(P<0.05,the same below);and the ratio of P_n increased at the top of the leaf(the first leaf)was the largest;the rate of increase in leaf P_n was the highest at the heading stage.The average P_n increase ratio of Bai Yan 2 is greater than that of Yanke 2.Under the severe drought stress,the dry matter quality of the aboveground parts of 2 cultivars decreased significantly,and the decrease ratio of Yanke 2 was less than that of Baiyan 2.After spraying HA,the increase of Yanke 2 was less than that of Baiyan No.2.Under different drought stress treatments,the proportion of increace of dry matter on the ground of two cultivars was the largest when the HA was sprayed under severe drought stress.Spraying HA could significantly increase the yield of 2 varieties,and the proportion of Baiyan 2 was higher than that of Yanke 2.2.The damage of ultrastructure of mesophyll cells can be reduced after spraying HA under severe drought stress.Under the mild drought stress,the leaf epidermal cells were full,the stomata were slightly open,the chloroplast became round and the mitochondria were slightly expanded,and the structure had not obvious damage.Under the severe drought stress,the stomatal closure,the epidermal cells were shriveled,the larger cavity appeared in the chloroplast,the outer membrane of the mitochondria was disintegrated and the contents were outflow;Under the severe drought stress,the opening degree of stomata was not changed after spraying HA,but the epidermal cells were full and the damage degree of chloroplast and mitochondria was decreased.3.The content of osmotic regulators in oat leaves was significantly affected by spraying HA under severe drought stress.Compared with the normal water condition,the contents of Pro,soluble sugar,Put and Spm were significantly increased by 4.42 times,38.96%,85.90%and 68.18%respectively under severe drought stress,and the content of Spd significantly decreased by 38.97%.The contents of Pro,Spd and Spm were significantly increased by 7.53%,1.22 and 1.42 times,respectively,and the contents of Pro were significantly lower than those of non-sprayed HA under severe drought stress.Spd/Put and Spm/Put Were significantly increased,but the content of soluble sugar was not significantly changed.4.Under severe drought stress,the contents of sucrose and ribose were mainly affected by spraying HA.The 11 kinds of monosaccharides and the 5 kinds of oligosa-ccharides were detected in oat leaves.There was no significant difference between the levels of arabinose and glucose-6-phosphate.Through the analysis of principal component analysis,it was found that the main effect was the ribose and sucrose content after spraying HA under severe drought stress.Sucrose is the main component of soluble sugar.Under severe drought stress,sucrose content increased by 14.80%and ribose content increased by5.78%.The contents of sucrose and ribose were significantly decreased after spraying HA under severe drought stress.5.Spraying HA can reduce the content of endogenous senescence hormone in leaves under severe drought stress.The contents of ABA,JA and SA in the leaves were significantly increased and the content of growth hormone(IAA)was significantly decreased under severe drought stress.Under normal water condition,the contents of endogenous hormones were not significantly changed after spraying HA,but the contents of endogenous ABA,JA and SA were significantly decreased under severe drought stress.6.Spraying HA can induce the expression of NAC transcription factor family gene AsNAC1,jasmonic acid synthesis related gene(CL3266)and membrane protein gene(CL2689),all of which are drought stress response genes.