Uptake of Boron and Silicon by Barley Genotypes with Differing Susceptibilities to Boron Toxicity

In long-term experiments with whole plants, boron uptake bybarley genotypes was linearly related to boron supply over arange of boron concentrations from normal to excessive. Thecomparative susceptibility of genotypes to boron toxicity wasreflected by the relative differences in boron uptake ratesover the entire range of boron supply. Root temperature over the range 5–25 °C markedly affectedplant growth but had no effect on the relative susceptibilityof genotypes to boron toxicity. Concentrations of boron in genotypeswere likewise unaffected by root temperature. Uptake of silicon differed greatly amongst genotypes and alsoreflected the relative susceptibility to boron toxicity andboron uptake. No competitive interaction was observed in theuptake of boron and silicon. The variation in boron accumulation, which governs susceptibilityto boron toxicity amongst barley genotypes, is the result ofdifferences in passive boron uptake via a mechanism which apparentlyalso governs silicon uptake. The nature of this mechanism isdiscussed in relation to the permeability of plant membranesto both boron and silicon. Hordeum vulgare L., barley, boron, toxicity, uptake, silicon, genotypic variation     

Functional Manganese Requirement and its use as a Critical Value for Diagnosis of Manganese Deficiency in Subterranean Clover (Trifolium subterraneum L. cv. Seaton Park)

The effects of manganese supply on plant growth and on photosynthesisand manganese concentrations in young leaves were examined inSeaton Park subterranean clover in three glasshouse water cultureexperiments. Plants werc grown initially with a copious supply of manganese,and transferred to solutions either with or without manganese.Sequential harvests were taken to determine the effects of developingmanganese deficiency on dry matter (DM) yield of whole plantsand selected characteristics [manganese, chlorophyll and photosyntheticoxygen evolution (POE)] of youngest open leaf blades (YOL).In addition, the deffect of leaf age and iron supply on POEwerc examined. Manganese concentrations and POE in YOL declined markedly andrapidly in plants transferred to solutions without manganese,while chlorophyll concentrations of YOL and plant DM yield respondedmore weakly and more slowly. As a result, a level of manganesedeficiency which depressed POE in young leaves by more than50 per cent had no effed on DM production. In youngleaves (YOL, YOL + 1, YOL–1), POE declined whentheir manganese concentrations were < 20 µg g^–1DM. Iron supply did not affect this rdationship. When learnwith < 20 µg Mn g^–1 DM were detached and incubatedfor 24 h in solutions containing high concentrations of manganese,their POE increased to normal rates; leaves with higher manganeseconcentrations did not respond. It is suggested that the valueof 20 µg Mn g^–1 DM is the functional manganese requirementfor POE in young subterranean clover leaves It is also suggestedthat this value may be used as a critical value for indicatingmanganese deficiency in subterranean clover. Functional nutrient requirements determined in this way by correlationof nutrient concentrations in young leaves with their biochemicalor physiological activities appear to offer more accurate andconsistent standards for use an critical values for diagnosisof plant nutrient status than do the critical values determinedin the usual way by correlation with plant dry weight. Trifolium subterraneum L. subterranean clover, manganese, functional requirements, deficiency diagnosis, nutrient requirements, critical values, photosynthetic oxygen evolution