Effect Of Drought Stress On Soybean Biological Drought-resistance Indexes, Yield And Quality

To estimate the effects of drought stress on soybean yield, quality and biological drought-resistance indexes in the northeast, from 2011 to 2013, soybean quality traits (such as amino acids, protein, fat and fatty acid), yield characters, physiologic and biochemical index, and mineral metabolism indexes were examined under such conditions:using PEG6000 nutrient solution to simulate drought stress at different stage, including the seedling stage, flowering and pod-setting stage and seed-filling stage, respectively. This study will help to elucidate the resistance mechanism of drought resistant varieties and sensitive cultivars. The results were as following:Drought stress could cause membrane lipid peroxidation and rising MDA contents, but did improving osmoregulation substances (such as free proline, soluble sugar, and so on) contents, antioxidant enzymes activity enhancing. The analysis showed that in osmoregulation substances, particularly free proline played a more important role than antioxidant enzymes in improving drought tolerance, while in antioxidant enzymes, SOD had the best activity, followed by CAT and POD.Accumulation dynamics of soybean plant dry matter conformed to Logistic curve, which the chi-square test had proved that Logistic equations were applicable. Drought stress was mainly decreased dry matter accumulation rate, average and maximum growth rate, so dry matter accumulation and biological yield were reduced. There was a good correlations between economic output with Logistic equations coefficients of leaves and roots, while was independent with equation parameters of petioles and stems, which predicted that economic yield mainly affected by leaves and roots. Drought stress decreased assimilation products, reduced absorption capacity of roots, grain leaf ratio significantly declined, the materials accumulated in non harvested organs in maturation period.Although there was closely relationship between material output rate and yield and quality, because drought stress influenced the ability to transport materials in vegetative organs, so it made material output rate decreased in all parts of soybean. Also, drought stress was mainly influenced matter export of the leaf and root And there was a close relationship between the material output rate of leaf and economic yield, but had a good relationship between petiole output rate with quality.Drought stress affected absorption and distribution of mineral element, which there was close relations between N, P, K metabolism and yield and quality, followed by Mg and Ca. Besides, because of drought stress, absorption of mineral elements was decreased, nutrients transport capacity of petiole and stem was declined, and amassing mineral elements were retained in the straw in mature period, leading to loss of the efficiency. The impact of drought stress on absorption of five mineral elements was N> P and K> Mg> Ca, and that on transportation inside plant was K> P=N> Mg> Ca. So the drought stress mainly hampered mineral elements output in leaves, then petioles and stems, and finally, the foot.Drought stress could make flower and pod abscission, increase shriveled pods number, decrease hundred grain weight, number of seeds and pods per plant, and decrease the economic and biological yield. With increase of drought stress, the economic and biological yield decreased continuously, which were negative correlated with each other. Under drought stress, the number of seeds and pods per plant of Hefeng 47 was significantly decreased, while hundred grain weight of Kenfeng 16 was apparently reduced. Drought stress at seeding stage mainly affected hundred grain weight, while if at flowering and pod-setting period and seed-filling stage, it mainly affected the pod number and grain number.Drought stress seriously affected the soybean quality, which the content of protein, fat and the total content of protein and fat was increased, and majority of amino acid of soybean seeds was decreased significantly, but the ratio of EAA/NEAA had not changed. Except that the oleic acid in Kenfeng 16 and linoleic acid in Hefeng 47 had some increase, the most of fatty acid content were either reduced slightly or unchanged under drought stress.The mineral nutrition in soybean seeds was less affected by drought stress at seedling stage, while drought stress at reproductive growth stage could increase the content of phosphorus and magnesium, reduce calcium content.From drought index, the effect of drought stress on yield was greater than those of quality.Hefeng 47 had stronger drought resistance than Kenfeng 16, because that effect of equal stress intensity was more serious on yield and quality of Kenfeng 16 than Hefeng 47. There was the greater influence on dry matter accumulation, material output rate of nutrient organs, grain leaf ratio, absorption and transport of mineral elements of Kenfeng 16 than those of Hefeng 47 under same conditions. Correlation analysis showed that physiological and biochemical process, dry matter accumulation, transportation and distribution, grain leaf ratio and mineral element metabolism were main factors affecting the yield and quality.Under same drought stress, effects during seed filling stage were most serious on yield, quality, dry matter accumulation and output, grain leaf ratio, and absorption and transportation of mineral elements, followed by flowering and podding stage, seedling stage with minimal impact. It showed that seed filling stage was a critical period for water requirement of soybean, which the stage was very sensitive to drought.The analysis of relation between many parameters and drought stress showed that slight drought could affect those parameters to low level in seed filling stage, while no further reduction with stress intensity increasing, but those parameters was approximately linear or quadratic curve relationship to the drought stress during flower and pod stage and seedling stage.