Response to soil aluminium of two white clover (Trifolium repens L.) genotypes

Abstract

An aluminium (Al) tolerant genotype of white clover was compared with an Al susceptible genotype in artificial soil profiles in which exchangeable A1 increased with depth. The tolerant genotype had a greater proportion of its root mass deeper in the soil than the susceptible genotype. Nitrogenase activity showed a similar pattern. Shoot A1 concentration did not vary between the genotypes but root AI in the susceptible line was twice that in the tolerant genotype. Plant potassium content in the susceptible line was relatively less, probably in response to higher aluminium content.

Effect of different aluminium and phosphorus levels on aluminium-tolerant and aluminium-susceptible genotypes of white clover (Trifolium repensL.)

“…The data confirm previous experimental results in which greater shoot growth under Al stress was recorded in the AI-tolerant T77 (Caradus et al 1991) and extend the observation to root growth. As previously recorded (Crush & Caradus 1992), root/shoot ratios did not vary between the genotypes. T77 was leafier than the AI-susceptible S129 but no other morphological differences were observed.…”

“…The lower Zn concentration observed in the AI-tolerant T77 in the present experiment probably resulted from inhibition of zinc uptake by Ca and Mg rather than directly AI-related effects. In previous work with identicalsized plants of the two clover genotypes, shoot K concentrations were lower in S 129 than in T77 (Crush & Caradus 1992). This depression was assumed to result from maintenance of ionic balance under increased Al loading.…”

“…When the two genotypes were grown at a single P level in an artificial soil profile with Al increasing with depth, there was no genotypic variation in shoot Al concentration and S 129 had higher root Al concentrations (Crush & Caradus 1992). In the current experiment Al concentrations were again lower in shoots than in roots, which is normal for forage legumes (Macleod & Jackson 1965;Haynes & Ludecke 1981).…”

“…The soil used previously in the experimental programme (Wainui silt loam-a Typic Dystrochrept, Mackay et al 1990;Crush & Caradus 1992) was mixed with factorial combinations of H 3 P0 4 at 50, 100, 200, and 400 mg P/kg dry soil and AI 2 (S04h at 20,50, 150, and 250 mg Al/kg dry soil. All the treatments received 200 mg potassium (K)/ kg dry soil as K 2 S0 4 and 0.14 mg molybdenum (Mo )/kg dry soil as ammonium molybdate.…”

“…Selection for aluminium (AI) tolerance in white clover (Trifolium repens L.) (Caradus et al 1987;Mackay et al 1990;Caradus et al 1991) has produced genotypes able to grow roots deeper into AI-toxic soil and maintain lower root Al concentrations than genotypes identified as susceptible to Al (Crush & Caradus 1992). Phosphorus (P) deficiency symptoms occur as a result of white clover suffering from Al toxicity (Jarvis & Hatch 1987) and AI toxicity is ameliorated when P fertiliser is applied to clover (Davis 1981).…”