Boron Toxicity in Barley Genotypes: Effects of Pattern and Timing of Boron Application

Boron (B) toxicity has been found to be a common nutritional disorder in dry areas, where excessive B tends to accumulate in the subsoil. However, in many of the pot experiments on B toxicity, excess B was mixed uniformly in soil or added from the soil surface, a method that does not detect the subsoil B effect. The objective of this plastic‐house experiment was to study the effects of different patterns and timings of B application on the development of B toxicity (BT) symptoms, tissue B concentrations, and growth and yield of barley. A three‐factor factorial design with three patterns of B application, three timings of B application, and two barley lines was used. A moderately BT‐tolerant barley line from the cross ‘Arar/Arabic Aswad’ (abbreviated as AA) and the moderately BT‐susceptible variety ‘Harmal’ were compared. Each pot consisted of two sections of 20‐cm‐tall PVC pipe. The second section was watered to field capacity and joined to the bottom of the top section on 25 January (tillering; roots reached the bottom of top section), 15 February (stem elongation), and 20 March (flag leaf emerged for ‘Harmal’; booting stage for AA). The three patterns of B application were (1) no B added (?/?), (2) B added to the bottom section only (?/+), and (3) B added to both sections (+/+). The addition of 50 mg B/kg soil increased the hot‐water‐soluble B level from 0.7 to 21 mg kg^?1. Interaction between pattern of B application and timing of B application had significant effects on BT symptom scores and straw B concentrations but not on grain yield. Grain yield of the +/+ treatment was much less than that of ?/+, which in turn was less than ?/?, but different timings of joining of the pot sections did not have a significant effect on grain yield. Relative to ?/?, the percentage of grain yield reduction (8%) sustained by AA when grown in ?/+ was less than half of the reduction (18%) suffered by ‘Harmal.’ In conclusion, subjecting plants to high‐B soils from germination to maturity exaggerates the effects of B on rainfed crops in the field. High subsoil B levels can cause significant yield reduction even when roots reach it as late as the boot stage, suggesting the need to screen/breed and grow BT‐tolerant cultivars. The use of subsectioned pots introduced in this study is an effective way to simulate BT in the field.     

Significant Nitrogen by Sulfur Interactions Occurred for Canola Grain Production and Oil Concentration in Grain on Sandy Soils in the Mediterranean-Type Climate of Southwestern Australia

The nitrogen (N) by sulfur (S) interaction for canola (Brassica napus L.) grain production and oil concentration in grain has been quantified in temperate climates, but it is not known if these results also apply to sandy soils common in the Mediterranean-type climate of southwestern Australia where canola is now a major crop. Seventeen field experiments were undertaken with canola in the region during 1994 to 2005 in which 4 rates of both N (0–138 kg N/ha) and S (0–34 kg S/ha) were applied. Significant grain yield responses to applied N occurred in all experiments and the responses increased as more S was applied. Grain yield responses to applied S only occurred when N was applied and tended to increase as more N was applied. When no S was applied the two largest rates of N applied, 69 and 138 kg N/ha, induced S deficiency reducing grain yields. The oil concentration in grain tended to decrease as more N was applied and increased as more S was applied, particularly when the two largest rates of N were applied. Consequently significant N × S interactions were obtained in all experiments for grain production and in 15 experiments for oil concentration in grain.     

外源水杨酸对锰污染红壤中玉米的生长与抗氧化酶活性的调节作用

采用盆栽实验方法研究了外源水杨酸（SA）对锰污染红壤中玉米的生长、脂质过氧化程度、活性氧水平以及抗氧化酶活性的影响。结果表明,过量锰明显降低玉米植株干重,显著提高了茎叶和根中锰的含量。SA促进锰胁迫下玉米的生长,但对植株中锰的含量与分布无影响。过量锰处理下,玉米叶片超氧阴离子（O.2-）和过氧化氢积累显著增加,脂质过氧化、电解质渗透率和脯氨酸含量显著升高;而SA和过量锰复合处理下,这些指标则显著降低。过量锰诱导超氧化物歧化酶（SOD,EC1.15.1.1）、过氧化物酶（POD,EC1.11.1.7）活性升高,抑制过氧化氢酶（CAT,EC1.11.1.6）和抗坏血酸过氧化物酶（APX,1.11.1.11）活性;SA处理促进锰胁迫下SOD和POD活性进一步升高,减小CAT和APX活性下降的程度。这些结果提示,SA调节抗氧化酶活性,保护组织细胞免遭氧化损伤,是SA缓解过量锰对玉米毒害作用的重要生理原因。