Changes in Osmotic Adjustment and Antioxidant Enzyme in Maize (<i>Zea mays L.</i>) Root Exposed to K Deficiency

Potassium (K) deficiency damaged membrane stability through irregular reactive oxygen species (ROS) caused by K deficiency stress while osmotic adjustment and antioxidant capacities play an essential role in preventing plants from osmotic stress and oxidative damages. To investigate the difference of osmoprotectants and antioxidant enzyme activities in the root, two representative maize varieties, 90-21-3 (K-tolerant) and D937 (K-sensitive), were hydroponically cultivated under normal K (+K) and K deficiency (-K) treatments in Shenyang Agriculture University, China. The results showed that root accumulation, soluble protein in root of 90-21-3 and D937 were decreased under K deficiency stress, but the root to shoot ratio, proline, free amino acid, soluble sugar, reactive oxygen species (ROS) in root for both genotypes were increased. Compared with the root of D937, the root of 90-21-3 was able to swiftly accumulate more proline, free amino acid and soluble sugar in the root when encountering K deficiency. The antioxidant enzyme activity in the root of 90-21-3, including superoxide dismutase (SOD), and catalase (CAT), peroxidase (POD), were significantly increased to counter increased levels of O2·- and H2O2 under K deficiency stress. The presented results indicated that osmotic regulator and antioxidant enzyme were actively responded to K deficiency stress, 90-21-3 (K-tolerant maize) accumulated more osmoprotectants and enhanced the activity of antioxidant enzymes to degrade ROS, alleviating oxidative stress.

Effects of Different Nitrogen Applications on Soil Physical, Chemical Properties and Yield in Maize (<i>Zea mays</i>L.)

Application of nitrogen (N) fertilizer is one of the most important approaches on improving maize grain yield. However, as is known to all, overuse N fertilizer not only leads to decline of N use efficiency and maize yield, but also leads to potential risk to environment pollution. This experiment was conducted to determine the effects of N fertilizer applications with nine different treatments on soil physical-chemical characters and maize grain yield using hybrid variety Zhengdan 958 in 2011 and 2012. Results indicated that the soil bulk densities of T2 (CK) and T1 were the lowest compared to other treatments in 2011 and 2012, respectively, whereas the soil bulk density of T5 in 2011 and T3 in 2012 were higher than other treatments. The soil porosity and field capacity of T5 in 2011 and T3 in 2012 were lower than other treatments, but those of CK in 2011 and T1 in 2012 were higher than other treatments. The pH values of T3 to T7 were lower than other treatments. These results indicated that the soil bulk densities were increased, whereas the soil porosity, field capacity and values pH were decreased by N application at different stages. N application could increase the N contents of leaf and stem, whereas less or excess N application should not significant improve maize yield. Although the soil organic matter and total N contents of T3 were the highest in both 2011 and 2012, the yield of T4 is the highest in both 2011 and 2012. The application amount, period and times of N fertilizer were important to maize yield.

Effect of Potassium Deficiency on Root Growth and Nutrient Uptake in Maize (Zea mays L.)

Potassium (K) is an essential nutrient on the growth and development for maize (Zea Mays L.). And the developed root morphology and root activity have great significance to nutrient absorption and play an important role in the growth and development of plants. To explore the response to K-deficiency on root growth and nutrient absorption of maize, two inbred lines, 90-21-3 (Tolerance to K deficiency) and D937 (Sensitive to K deficiency) were carried out to investigate the root morphology, root activity, nutrient uptake and related traits. The results showed that K-deficiency inhibited the root growth of 90-21-3 and D937, but increased the ratio of root to shoot (R/S). The total length, root surface area, the root diameter and root volume of root system of 90-21-3 and D937 were significantly decreased by K deficiency, especially the fine root (0 - 0.4 mm) in root length and root surface area. In addition, the K concentration of root in the two lines was significantly decreased, but root activity was significantly improved, which promoted the absorption of the root system to Na+. Compared with D937, 90-21-3 was able to distribute more carbohydrates from shoot to the root system under K deficiency, alleviating the inhibition of root growth. The fine root system was the main part for absorption nutrient. The length and surface area of 90-12-3 were no difference, and significantly decreased by 12.90% and 17.65% in D937 after 5 d of K deficiency. As well, the root activity of 90-21-3 was significantly increased when encountered to K deficiency, which promoted the accumulation of Na+ and Ca2+ and regulated the osmotic stress. Therefore, it could be a responding mechanism for tolerance crop by maintaining large root system, increasing root activity and adjusting nutrient absorption to adapt to K deficiency.

Effects of Different Potassium Stress on Leaf Photosynthesis and Chlorophyll Fluorescence in Maize (Zea Mays L.) at Seedling Stage

Leaf early senescence caused by nutrition deficiency is one of the major limitation reasons in the world crop production. Potassium (K) is one of important nutrient elements in crop growth, which modifies dozens of enzyme activations and controls stomatal movement of photosynthesis. The yield and quality of maize (Zea Mays L.) have been limited due to K deficiency in plough layer soil. However, the mechanism of K deficiency tolerance is not fully understood in maize. In this study, two inbred lines, 099 (tolerance to potassium deficiency) and 835 (sensitive to potassium deficiency) were carried out to investigate the variations of chlorophyll content, photosynthetic and chlorophyll fluorescence parameters related with senescence under different K+ concentrations in maize at seedling stage. The results showed that the Chlorophyll a, b and (a + b) of 835 were significantly decreased under different K deficiency treatments, whereas those of 099 were remained normal. In addition, 099 showed a lower stomatal restriction and higher electronic transition capacity under different K deficiency treatments. The variations of F0, Fv/Fm, ΦPSⅡ, qP and NPQ in 835 were largely higher than those in 099. These results indicated that the inbred line 099 tolerance to K deficiency could keep chlorophyll content to maintain photosynthesis and to alleviate the injury of PSII under K deficiency condition. This study should contribute to explaining the physiological mechanism tolerance nutrition deficiency and improving breeding program in maize.

Assimilation of Doppler Radar Data with an Ensemble 3DEnVar Approach to Improve Convective Forecasting

An ensemble three-dimensional ensemble-variational(3DEnVar)data assimilation(E3DA)system was developed within the Weather Research and Forecasting model’s 3DVar framework to assimilate radar data to improve convective forecasting.In this system,ensemble perturbations are updated by an ensemble of 3DEnVar and the ensemble forecasts are used to generate the flow-dependent background error covariance.The performance of the E3DA system was first evaluated against one experiment without radar DA and one radar DA experiment with 3DVar,using a severe storm case over southeastern China on 5 June 2009.Results indicated that E3DA improved the quantitative forecast skills of reflectivity and precipitation,as well as their spatial distributions in terms of both intensity and coverage over 3DVar.The root-mean-square error of radial velocity from 3DVar was reduced by E3DA,with stronger low-level wind closer to observation.It was also found that E3DA improved the wind,temperature and water vapor mixing ratio,with the lowest errors at the surface and upper levels.3DVar showed moderate improvements in comparison with forecasts without radar DA.A diagnosis of the analysis revealed that E3DA increased vertical velocity,temperature,and humidity corresponding to the added reflectivity,while 3DVar failed to produce these adjustments,because of the lack of reasonable cross-variable correlations.The performance of E3DA was further verified using two convective cases over southern and southeastern China,and the reflectivity forecast skill was also improved over 3DVar.