Baizhao Ren

Effects of waterlogging on the yield and growth of summer maize under field conditions

Ren, B., Zhang, J., Li, X., Fan, X., Dong, S., Liu, P. and Zhao, B. 2014. Effects of waterlogging on the yield and growth of summer maize under field conditions. Can. J. Plant Sci. 94: 23-31. A field experiment was performed to study the effects of waterlogging for different durations (3 and 6 d) on the yield and growth of summer maize at the three-leaf stage (V3), six-leaf stage (V6), and the 10th day after the tasseling stage (10VT). The results after 2 yr indicated that maize development and grain yield responses to waterlogging depended on both stress severity (intensity and duration) and different growth stage. Yield decreased significantly with an increased waterlogging duration during V3 and V6. The yields of maize hybrid Denghai 605 (DH605) in treatments V3-3, V3-6, V6-3, V6-6, 10VT-3, and 10VT-6 were 23, 32, 20, 24, 8, and 18% lower than those of the control (CK), respectively; Yields of Zhengdan 958 (ZD958) were lower by 21, 35, 15, 33, 7, and 12%, respectively. Waterlogging also affected the growth and development of summer maize. Ear characteristics (grains per ear and 1000-grain weight) and plant morphology (plant height, ear height, and leaf area index) decreased, whereas the bald tip length increased significantly. The maximum grain-filling rate decreased under waterlogging; furthermore, the dry matter accumulation decreased and dry matter distribution proportions of the stem and leaf increased. However, the distribution proportion of grain decreased. Maize was most susceptible to waterlogging damage at V3, followed by V6 and 10VT, with damage increasing with increasing waterlogging duration.

Responses of Nitrogen Metabolism, Uptake and Translocation of Maize to Waterlogging at Different Growth Stages

We performed a field experiment using the maize hybrids DengHai605 (DH605) and ZhengDan958 (ZD958) to study nitrogen uptake and translocation, key enzyme activities of nitrogen metabolism in response to waterlogging at the third leaf stage (V3), the sixth leaf stage (V6), and the 10th day after the tasseling stage (10VT). Results showed that N accumulation amount was significantly reduced after waterlogging, most greatly in the V3 waterlogging treatment (V3-W), with decreases of 41 and 37% in DH605 and ZD958, respectively. N accumulation in each organ and N allocation proportions in grains decreased significantly after waterlogging, whereas N allocation proportions increased in stem and leaf. The reduction in stem and leaf N accumulation after waterlogging was mainly caused by a decrease in dry matter accumulation, and a reduction in N translocation from stems and leaves to grains after waterlogging. Additionally, waterlogging decreased the activity of key N metabolism enzymes (nitrate reductase, glutamine, glutamate synthase, and glutamate dehydrogenase), and the most significant reduction in V3-W with a decrease of 59, 46, 35, and 26% for DH605, and 60, 53, 31, and 25 for ZD958, respectively. Waterlogging disrupted N metabolism, hindered N absorption and transportation, and decreased maize yield.

Effects of Waterlogging on Leaf Mesophyll Cell Ultrastructure and Photosynthetic Characteristics of Summer Maize

A field experiment was performed to study the effects of waterlogging on the leaf mesophyll cell ultrastructure, chlorophyll content, gas exchange parameters, chlorophyll fluorescence, and malondialdehyde (MDA) content of summer maize (Zea mays L.) hybrids Denghai605 (DH605) and Zhengdan958 (ZD958). The waterlogging treatments were implemented for different durations (3 and 6 days) at the third leaf stage (V3), the sixth leaf stage (V6), and the 10th day after the tasseling stage (10VT). Leaf area index (LAI), chlorophyll content, photosynthetic rate (Pn), and actual photochemical efficiency (ΦPSII) were reduced after waterlogging, indicating that waterlogging significantly decreased photosynthetic capacity. The chloroplast shapes changed from long and oval to elliptical or circular after waterlogging. In addition, the internal structures of chloroplasts were degenerated after waterlogging. After waterlogging for 6 d at V3, the number of grana and grana lamellae of the third expanded leaf in DH605 were decreased by 26.83% and 55.95%, respectively, compared to the control (CK). Those in ZD958 were reduced by 30.08% and 31.94%, respectively. Waterlogging increased MDA content in both hybrids, suggesting an impact of waterlogging on membrane integrity and thus membrane deterioration. Waterlogging also damaged the biological membrane structure and mitochondria. Our results indicated that the physiological reactions to waterlogging were closely related to lower LAI, chlorophyll content, and Pn and to the destruction of chloroplast ultrastructure. These negative effects resulted in the decrease of grain yield in response to waterlogging. Summer maize was the most susceptible to damage when waterlogging occurred at V3, followed by V6 and 10VT, with damage increasing in the wake of waterlogging duration increasing.

Response of Summer Maize Photosynthate Accumulation and Distribution to Shading Stress Assessed by Using 13CO2 Stable Isotope Tracer in the Field

Maize is one of the most important crops globally that provides food, feed, and bioenergy. However, shading stress threatens maize production. In this study, we investigated the effects of shading on photosynthate accumulation and distribution of summer maize in the field. Zhengdan958 (ZD958) and Denghai 605 (DH605) were used as experimental materials in a field experiment running from 2013 to 2015. Shading treatments were applied over different growth stages: from the tassel stage (VT) to physiological maturity (R6) (S1), from the six-leaf stage (V6) to VT (S2), and from emergence stage (VE) to R6 (S3). The effects of shading on plant photosynthesis, photosynthate accumulation and distribution, and yield were evaluated in comparison to ambient sunlight. Shading significantly decreased the leaf area, SPAD value, net photosynthetic rate, dry matter accumulation, and grain yield. During the 3-year experimental period, grain yields of ZD958 and DH605 were reduced by 83.4%, 34.2%, 53.1% and 79.3%, 24.2%, 57.6% as compared to the CK by treatments S3, S2, and S1, respectively. 13CO2 stable isotope tracing revealed that shading differentially affected the photosynthate transfer rate in different stages; photosynthates were transferred from top to bottom plant parts, in the order control > S2 > S1 > S3. We conclude that shading clearly disrupted photosynthate metabolism, and reduced the photosynthate accumulation in the grain, resulting in a yield reduction.

Regulations of 6-Benzyladenine (6-BA) on Leaf Ultrastructure and Photosynthetic Characteristics of Waterlogged Summer Maize

A field experiment was performed to study the effects of spraying exogenous 6-benzyladenine (6-BA) after waterlogging for 6 days at the third leaf stage on the leaf mesophyll cell ultrastructure, chlorophyll content, gas exchange parameters, chlorophyll fluorescence, and malondialdehyde (MDA) content of summer maize (Zea mays L.) hybrids Denghai605 (DH605) and Zhengdan958 (ZD958), to determine the photosynthetic mechanism for the regulation of 6-BA to waterlogged summer maize. Results showed that exogenous application of 6-BA effectively alleviated the adverse effects of waterlogging on photosynthetic characteristics by increasing leaf area index and chlorophyll content. Treatment with spraying exogenous 6-BA resulted in significant and substantial (in the range of 9–37%) increases of the net photosynthetic rate compared to waterlogging treatments. In addition, spraying 6-BA effectively alleviated the adverse effects of waterlogging on leaf ultrastructure by increasing the numbers of grana and grana lamella, decreasing MDA content, and improving membrane structure and chloroplast structure. Visibly, spraying exogenous 6-BA effectively alleviated the adverse effects of waterlogging on leaf ultrastructure of summer maize led to the improvement of photosynthetic performance, resulting in significant and substantial (around 20%) increases in grain yield compared to those of the waterlogging treatments.