Morphological and Biochemical Responses of Some Promising Tea Genotypes to Aluminum-induced Soil Acidification

The present study aimed to assess both soil and tea plant responses to acidification induced by aluminum (Al). In this way, the effects of four levels of soil acidification by aluminum sulfate were examined (A1=0, A2=500, A3=1000, A4=2000 mg kg-1 soil) on five promising tea genotypes (G1=100, G2=440, G3=444, G4=591 and G5=703). The genotypes were originally from Lahijan Tea Research Center and were tested on split plots in a randomized complete block design with three replications. A breakpoint of 250 mg kg-1 of exchangeable Al was identified as critical for the severe release of Al into the soil solution. Both soluble and exchangeable fractions of soil Al showed strong power regression relationships with soil pH measured in water as well as 1M KCl solution. The genotype with the highest yield (G3) experienced a significantly greater decline in fresh yield following treatments with Al, compared with the genotype having low yield (G4) (22% vs. 6%, on average). Acidification adversely affected all morphological parameters but no significant impacts were detected on selected biochemical parameters (i.e. caffeine, total polyphenols, and chlorophyll index). Leaf Al concentration, followed by shoot weight and leaf thickness showed significant relationships (p<0.01) with soluble and exchangeable fractions of Al in the soil. The highest and the lowest leaf Al concentrations were obtained in G4 (837 mg kg-1 DM, on average) and in G3 (623 mg kg-1 DM, on average), respectively. Based on all morphological traits, the most tolerant genotype to soil acidification was G4, which is a low-yield tea with a relatively high Al accumulation affinity.