Genotype-dependent effects of phosphorus supply on physiological and biochemical responses to Al-stress in cultivated and Tibetan wild barley

Aluminium (Al) toxicity and phosphorus (P) deficiency often co-exist in acidic soils and limit plant growth and crop production. To investigate the alleviating effects of different levels of phosphorus on Al stress, greenhouse hydroponic experiments were conducted using two contrasting Tibetan wild barley genotypes XZ16 and XZ61 of Al tolerant and sensitive, respectively, and Al tolerant cv. Dayton. The results showed that Al stress induced reduction in P accumulation in plants; and stem and leaf P concentrations of the three genotypes, except of XZ16 under HP + Al (100 µM Al with high level of 360 µM P) which was close to the control level. XZ16 recorded significantly higher P accumulation in plants, compared with XZ61 and Dayton, and P concentrations in leaves under Al stress, and in stems under NP + Al (100 µM Al with normal level of 180 µM P) and HP + Al. Meanwhile, H⁺-, Ca²⁺Mg²⁺-, and Total- ATPase activities in XZ16 and Dayton under Al stress were markedly higher than in XZ61. Normal or high level of P under Al stress could relieve Al stress as enhanced plant biomass, with increased photosystem II photochemistry (Fv/Fm) and P content, relative to the low level of 90 µM P. Compared with XZ61, addition of high P concentration for XZ16 significantly increased the values of Gs and Tr, with higher root GPX and H⁺-ATPase activities, and such nutrient elements as P, Mg and Ca in stems and leaves, and induced more malate secretion, but less MDA accumulation.