Phosphorus alleviates aluminum-induced inhibition of growth and photosynthesis in Citrus grandis seedlings.

Limited data are available on the effects of phosphorus (P) and aluminum (Al) interactions on Citrus spp. growth and photosynthesis. Sour pummelo (Citrus grandis) seedlings were irrigated for 18 weeks with nutrient solution containing 50, 100, 250 and 500 microM KH(2)PO(4)x 0 and 1.2 mM AlCl(3). 6H(2)O. Thereafter, P and Al in roots, stems and leaves, and leaf chlorophyll (Chl), CO(2) assimilation, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Chl a fluorescence (OJIP) transients were measured. Under Al stress, P increased root Al, but decreased stem and leaf Al. Shoot growth is more sensitive to Al than root growth, CO(2) assimilation and OJIP transients. Al decreased CO(2) assimilation, Rubisco activity and Chl content, whereas it increased or did not affect intercellular CO(2) concentration. Al affected CO(2) assimilation more than Rubisco and Chl under 250 and 500 microM P. Al decreased root, stem and leaf P, leaf maximum quantum yield of primary photochemistry (F(v)/F(m)) and total performance index (PI(tot,abs)), but increased leaf minimum fluorescence (F(o)), relative variable fluorescence at K- and I-steps. P could alleviate Al-induced increase or decrease for all these parameters. We conclude that P alleviated Al-induced inhibition of growth and impairment of the whole photosynthetic electron transport chain from photosystem II (PSII) donor side up to the reduction of end acceptors of photosystem I (PSI), thus preventing photosynthesis inhibition through increasing Al immobilization in roots and P level in roots and shoots. Al-induced impairment of the whole photosynthetic electron transport chain may be associated with growth inhibition.