Qiuying Zhang

Effect of soil type and soybean genotype on fungal community in soybean rhizosphere during reproductive growth stages

Fungal communities in soybean rhizosphere from reproductive growth stages R1 (beginning bloom) to R8 (full maturity) were studied based on the polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) banding patterns of partial rDNA internal transcribed spacer regions (ITS1) and sequencing methods. Pot experiment subjecting three soybean genotypes grown in two soils (Mollisol and Alfisol) indicated that the soil type was the major factor in shaping the fungal communities in the soybean rhizosphere. Field experiment was conducted in an Alfisol field with three soybean genotypes, and both pot and field experiments showed that rhizosphere fungal communities shifted with growth stages, and more diversity of communities was found in early reproductive growth stages than later stages. No major difference among fungal communities of three soybean genotypes was detected at individual growth stage. BLAST search of ITS sequence data generated from excised DGGE bands showed that fungi belonging to Ascomycetes and Basidiomycetes predominantly inhabited in the soybean rhizosphere. In addition, a few bands had low similarity with database sequences inferred that unknown fungal groups existed in soybean rhizosphere.

Responses of photosynthetic rates and yield/quality of main crops to irrigation and manure application in the black soil area of Northeast China

Soil nutrients and water have long been recognized as the main determining factors influencing agricultural productivity in rain-fed agriculture. Manure application and irrigation can increase crop yield when nutrients and water are deficient. Often effects of water and nutrients are closely related and can not be easily separated in actual production. Three years of experiment were conducted in northern part of black soil area of Northeast China to investigate the responses of photosynthetic rates and yield/quality of main crops, wheat (Triticum aestivum L.), maize (May zeas L.), soybean (Glycine max L. Merr.) to irrigation and manure application. Irrigation and manure application had no effects on photosynthetic patterns during reproductive development in crops, maximum photosynthetic rates were achieved by irrigation, and manure application maintained relatively higher photosynthetic rates after the peak. On average, higher photosynthetic rates with irrigation may contribute to higher yield in soybean but not in maize and wheat. Responses of crop yield and quality to manure application and irrigation varied in the crops. Soybean yield and quality was very sensitive to irrigation and manure application. The greater supply of nutrients with sufficient water, the higher the yield. However, the high-yield of soybean achieved was accompanied with a decline of seed protein content. Maize yield mainly depended on nutrients used not the water supply, irrigation resulted in higher water content in the seed of maize and lower grain protein content in wheat at harvest, which is detrimental to seed storage in maize and processing quality in wheat. In the northern part of black soil area in Northeast China, the management of manure is critical to improve crop production, the optimum management for maize and wheat production was to apply chemical fertilizer and manure without irrigation, but for soybean was to apply fertilizer and manure with irrigation.

Impact of Elevated CO2 on Seed Quality of Soybean at the Fresh Edible and Mature Stages

Although the effect of elevated CO2 (eCO2) on soybean yield has been well documented, few studies have addressed seed quality, particularly at the fresh edible (R6) and mature stages (R8). Under the current global scenario of increasing CO2 levels, this potentially threatens the nutritional content and quality of food crops. Using four soybean cultivars, we assessed the effects of eCO2 on the concentrations of crude protein, crude oil, and isoflavones and analyzed the changes in free amino acids, fatty acids, and mineral elements in seeds. At R6, eCO2 had no influence on soybean seed protein and oil concentrations. At R8, eCO2 significantly decreased seed protein concentration but increased seed oil concentration; it also significantly decreased total free amino acid concentration. However, at the same stage, the proportion of oleic acid (18:1) among fatty acids increased in response to eCO2 in the cultivars of Zhongke-maodou 2 (ZK-2) and Zhongke-maodou 3 (ZK-3), and a similar trend was found for linoleic acid (18:2) in Zhongke-maodou 1 (ZK-1) and Hei-maodou (HD). Total isoflavone concentrations increased significantly at both the R6 and R8 stages in response to eCO2. Compared with ambient CO2, the concentrations of K, Ca, Mg, P, and S increased significantly under eCO2 at R6, while the Fe concentration decreased significantly. The response of Zn and Mn concentrations to eCO2 varied among cultivars. At R8 and under eCO2, Mg, S, and Ca concentrations increased significantly, while Zn and Fe concentrations decreased significantly. These findings suggest that eCO2 is likely to benefit from the accumulation of seed fat and isoflavone but not from that of protein. In this study, the response of seed mineral nutrients to eCO2 varied between cultivars.

Key Components of Eating Quality and Their Dynamic Accumulation in Vege- table Soybean Varieties (Glycine max (L.) Merr.)

The eating quality and seed chemical compositions of 30 vegetable soybean cultivars (lines), as well as their correla- tions were analyzed. At the same time, main quality compositions and their roles for eating quality were investigated by path analysis, while the dynamic accumulation of each component was also studied with three cultivars differing in soluble sugar content. Results showed that the cumulative contribution of sucrose, fructose + glucose, raffinose, stachyose, protein, free amino acid and oil for eating quality was 67.8%. A significant positive correlation was found between eating quality score and sucrose content (0.864 ** ), while a significant negative correlation between eating quality score and protein content (-0.439 * ). The average content of raffinose and stachyose at fresh harvest stage was only 7.4% and 12.4% of that at mature stage respectively, which had much less negative impact on eating quality of vegetable soybean than field grain soybean. The optimum harvest time for fresh pods was at 42 days after flowering and could last for one week with highest sucrose content and lowest raffinose and stachyose contents. Besides, the average content of amino acids was higher and fructose + glucose contents were medium, and protein content was 3% less than that at mature stage. Postponing the harvest time deteriorated eating quality due to decreased content in sucrose and monosaccharide, increased content in fat and protein contents, as well as a dramatic increase in raffinose and stachyose contents.

Physiological aspects of wheat genotypes differing in protein content

The objectives of this study were to understand some physiological aspects including hormone activities and main enzyme activities in relation to the protein content of wheat and then to provide the theoretical basis for breeding and artificial regulation of yield and protein of wheat. In order to investigate their involvement in protein deposition, three wheat cultivars differing in yield and protein content were used in pot experiments. The results showed that there were some parallel relationships among hormone, enzyme and protein accumulation. IAA activities in higher-protein cultivars during grain filling were significantly higher than those of low-protein cultivars, and ABA activity was just opposite. Before reaching the peak, enzyme activities in higher-protein cultivars were higher in flag leaf but lower in grain.