Exogenous Chemicals Used to Alleviate or Salvage Plants under Flooding/Waterlogging Stress: Their Biochemical Effects and Perspectives.

Plant flooding/waterlogging stress (FWS) can be a threat to food security worldwide due to climate change. To mitigate its potential devastation, numerous exogenous chemicals (ECs) have been used to demonstrate their effectiveness on alleviating FWS for the last 20 years. This review has summarized the most recent findings on use of various ECs as either nutrients or regulatory substances on crop plants under FWS and their roles involved in improving root respiration of seedlings, optimizing nutritional status, synthesizing osmotic regulators, enhancing the activity of antioxidant enzymes, adjusting phytohormone levels, maintaining photosynthetic systems, and activating flood-tolerance related gene expressions. The effect of ESs on alleviating plants under FWS proves to be beneficial and useful but rather limited unless they are applied on appropriate crops, at the right time, and with optimized methods. Further research should be focused on use of ESs in field settings and on their potential synergetic effect for more FWS tolerance.

Optimized management strategy increased grain yield, promoted nitrogen balance, and improved water productivity in winter wheat.

The increasing costs of agricultural production and environmental concerns reinforce the need to reduce resource inputs. Improvements in nitrogen (N) use efficiency (NUE) and water productivity (WP) are critical for sustainable agriculture. We aimed to optimize management strategy to increase wheat grain yield, promote N balance, and improve NUE and WP. A 3-year experiment was conducted with four integrated treatments: conventional practice treatment (CP); improvement of conventional practice treatment (ICP); high-yield management treatment (HY), which aimed for maximizing grain yield regardless of resource inputs cost; and integrated soil and crop system management treatment (ISM), which aimed for testing an optimal combination of sowing date, seeding rate, and fertilization and irrigation management. The average grain yield for ISM was 95.86% of that for HY and was 5.99% and 21.72% higher than that for ICP and CP, respectively. ISM promoted N balance as relatively higher aboveground N uptake, lower inorganic N residue, and lowest inorganic N loss. The average NUE for ISM was 4.15% lower than that for ICP and was remarkably higher than that for HY and CP by 26.36% and 52.37%, respectively. The increased soil water consumption under ISM was mainly due to its increased root length density. Along with a high level of grain yield, ISM obtained a relatively adequate water supply due to the effective use of soil water storage, thereby increasing the average WP by 3.63%-38.10% in comparison with other integrated management treatments. These results demonstrated that optimized management strategy (appropriately delaying sowing date, increasing seeding rate, and optimizing fertilization and irrigation management) used under ISM could promote N balance and improve WP while increasing grain yield and NUE in winter wheat. Therefore, ISM can be considered a recommendable management strategy in the target region.

[Responses of winter wheat tillers at different positions to low temperature stress at stem elongation stage and their freezing resistance evaluation].

Taking two winter wheat cultivars Ji' nan 17 and Shannong 8355 as test materials, this paper measured the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities and the malondialdehyde (MDA) and soluble protein contents in the functional leaves and sheaths of the tillers at different positions at stem elongation stage under low temperature stress, and then, the freezing resistance of the tillers was comprehensively evaluated by the methods of principal component analysis and cluster analysis. The results showed that under low temperature stress, the SOD, POD, and CAT activities in the functional leaves and sheaths of each tiller at stem elongation stage increased, but the MDA and soluble protein contents increased or decreased to some extent. By using principal component analysis and cluster analysis, the tillers of each cultivar were grouped into three kinds of freezing resistance type. For Ji' nan 17, the main stem, tiller I, and tiller II belonged to high freezing resistance type, the tiller III, tiller IV, and tiller I p belonged to medium freezing resistance type, and the tiller II p belonged to low freezing resistance type. For Shannong 8355, the main stem, tiller I, tiller II, and tiller III belonged to high freezing resistance type, the tiller IV and tiller I p belonged to medium freezing resistance type, and the tiller II p belonged to low freezing resistance type. It was concluded that the freezing resistance of the winter wheat tillers at different positions at stem elongation stage differed, with the lower position tillers being more resistant than the higher position tillers.

[Effects of planting density and spraying PP333 on winter wheat lodging-resistance and grain yield].

Taking two winter wheat varieties Gaocheng 8901 and Yannong 21 with different end-use qualities as test objects, a field experiment was conducted in the experimental farm of Shandong Agricultural University from 2008 to 2010, aimed to study the effects of different planting density and spraying PP333 on the basal stem morphological characteristics, snapping-resistance, lodging-resistant index, and grain yield. Gaocheng 8901 had higher lodging-resistance but lower grain yield than Yannong 21. Comparing with low planting density (180 x 10(4) basic seedlings per hm2), high planting density (240 x 10(4) basic seedlings per hm2) decreased the culm snapping-resistance and lodging-resistant index of the two varieties, especially Yannong 21. Spraying PP333 decreased the plant height and the basal internodes length, increased the snapping-resistance and lodging-resistant index, strengthened the lodging-resistance, and improved the spike number and grain yield. Correlation analysis showed that the second internode length, percentage of basal internodes (1 + 2) length to total internode length, and apparent lodging ratio were significantly negatively correlated with culm lodging resistant index. Therefore, to adopt an appropriate planting density combined with spraying PP333 could improve the lodging-resistance of winter wheat and its grain yield, being an important high-yielding cultivation technique for wheat production in sub-humid zone.