Activation of potassium released from soil by root-secreted organic acids in different varieties of tobacco (Nicotiana tabacum).

Organic acids secreted from the roots of plants play important roles in nutrient acquisition and metal detoxification; however, the precise underlying mechanisms of these processes remain poorly understood. In the present study we examined the content of organic acids exuded from roots and the effects of these organic acids on the activation of slowly available potassium (K) at different K levels, including normal K supply and K-deficient conditions. In addition, the study system also comprised a high-K tobacco variety (ND202) and two common ones (K326 and NC89). Our results showed that high-K varieties exhibited significantly higher contents of organic acids in its root exudates and available K in both rhizosphere and non-rhizosphere soils than the other varieties. This research also suggested that a cyclic process in which soil was acidified after being complexed by organic acids was involved in the release of slowly available K, and that this process primarily depended on the soil pH at high organic acids concentrations, but the complexation of organic ligands became dominant at low concentrations. In conclusion, tobacco roots secrete organic acids to increase available K content and improve the utilisation rate of soil K. High-K varieties probably enhance slowly available K activation by secreting relatively high amounts of organic acids, thus leading to more available K in soil for absorption by plants.

[Difference of potassium absorption characters and mechanism of tobacco in genotypes].

Tabacco (Nicotiana tabacum) has a relatively high requirement for potassium (K). The difference in root characteristics and ability to release K from minerals of flue-cured tobacco in four genotypes ND202, NC628, G28 and NC628 x ND202 were analyzed. The results showed that the more available K released from minerals by roots, the more K would be accumulated by plants. ND202, which was K-enriched genotype, had well developed root system and was easily influenced by K content in the environment. Compared with ND202, NC628 significantly enhanced the effectiveness of K in substrate by releasing K from minerals, though the ability to absorb K was weak. Moreover, the hybrid of NC628 x ND202 had a higher ability to release K and to tolerate low-level K than maternal parent. It was higher in dry matter accumulation and K enrichment than male parent. So hybridization had the utility value in high-K variety cultivation. These results provided evidence that parents should have the ability to enhance available K from soil besides the high combining ability for breeding the high-K variety.

[Nitrogen uptake and allocation characteristics of flue-cured tobacco in Nanxiong tobacco-planting area of Guangdong Province].

By the method of field in situ culture and 15N isotopic tracer technique, and taking flue-cured tobacco (Nicotiana tobacum) cultivar K326 as test material, a field experiment was conducted in the Nanxiong tobacco-planting area of Guangdong Province to study the characteristics of soil nitrogen (N) mineralization, the patterns of N accumulation and allocation in tobacco plants, and the allocation of plant-absorbed fertilizer N applied in current growth season. In the study area, the amount of soil mineralized N increased with tobacco growth, peaked at 75 days after transplanting, and decreased thereafter. The soil mineralized N at each tobacco growth stage was significantly higher in the control than in the N fertilization treatment. The N accumulation in tobacco plant organs was in the order of leaf > stalk > root. Tobacco plants mainly absorbed fertilizer N at rosette stage and topping stage, and mainly absorbed soil N at mature stage. The absorbed N in tobacco whole growth period was mainly derived from soil N, and the absorbed soil N and its proportion to the total absorbed N increased evidently with extending growth stage and ascending leaf position. The fertilizer N use efficiency per plant and the residual rate and loss rate of applied fertilizer N were 30. 8%, 32. 3% , and 36. 9% , respectively. In the study area, soil N mineralization rate was relatively high, and soil N had greater effects on the quality of upper tobacco leaves. Under the application rate of 150 kg N x hm(-2), the residual amount and loss amount of applied fertilizer N were relatively high.

[Effects of nitrogen fertilization on leaf senescence, photosynthetic characteristics, yield, and quality of different flue-cured tobacco varieties].

Taking three flue-cured tobacco (Nicotiana tabacum L.) varieties Y5, Y7, and NC89 as test objects, this paper studied the effects of nitrogen fertilization on their leaf senescence, photosynthetic characteristics, yield, and quality. Increasing nitrogen supply increased the leaf superoxide dismutase (SOD) activity, chlorophyll content, and photosynthetic performance, and decreased the leaf malondialdehyde (MDA) content significantly. Accordingly, the leaf senescence was delayed. Compared with Y5 and NC89, variety Y7 had higher leaf MDA content and lower leaf SOD activity, chlorophyll content, and photosynthetic performance, and thus, its leaves senesced faster. High quality tobacco leaves with higher average price, gross value, superior leaves percentage, and reasonable chemical constituents were harvested under the application of 45 kg N x hm(-2), compared with applying 60 and 75 kg N x hm(-2). It was suggested that different flue-cured tobacco varieties had obvious differences in their leaf senescence physiological characteristics, and nitrogen fertilization played important roles in regulating their leaf senescence, yield, and quality. Appropriate nitrogen fertilization could improve the quality of tobacco leaves, and achieve higher economic benefits.

[Effects of different planting patterns on the senescence characteristics of flue-cured tobacco roots and leaves].

With flue-cured tobacco (Nicotiana tabacum) cultivar K326 as test material, a field experiment was conducted at Nanxiong area of Guangdong Province in 2008 to study the effects of four planting patterns, i.e., single-row ridge + film mulching at early stage, single-row ridge + film mulching at early and late stages, double-row concave ridge + film mulching at early stage, and double-row concave ridge + film mulching at early and late stages, on the senescence characteristics of its roots and leaves, and the economic traits of its leaves. Comparing with other three planting patterns, double-row concave ridge + film Aulching at early and late stages promoted the root growth of test cultivar during its whole growth period, with the root vigor increased significantly. Meanwhile, the leaf chlorophyll content and protective enzymes (SOD and POD) activities were higher, and the MDA content was lower. The leaf yield, output value, average price, and the proportion of superior leaves were also higher. Double-row concave ridge + film mulching at early and late stages alleviated the senescence characteristics of roots and leaves, and improved the economic traits of flue-cured tobacco leaves, being the efficient planting pattern to product high-quality flue-cured tobacco leaves in Nanxiong tobacco-growing area of Guangdong Province.