Abstract: With solution culture experiment,this paper studied the effects of two potassium supply levels on the root exudates content and its dynamics of two grain amaranth genotypes (potassium-enrichment K12 and ordinary M9),and the activation of root exudates on soil mineral potassium.The results showed that the root exudation rates of soluble sugar,amino acids and organic acids of these two genotypes were decreased with increasing potassium supply level,which was higher in K12 than in M9.The root exudation capability of the two genotypes was similar under normal potassium supply level,while that of K12 was significant higher than M9 under low potassium supply level.Organic acid was the main root exudate under two potassium supply levels,which was several decuples or hundreds times as much as that of soluble sugar and amino acids.Compared with those at the fortieth day,the exudation rates of soluble sugar,amino acids and organic acids at the fiftieth day decreased rapidly in M9,while decreased slowly in K12.At three growth phases,the contents of soluble sugar,amino acid and organic acid were higher in the root exudate of K12 than in that of M9,and the difference of the two genotypes became significant with time extended.The content of organic acid in root exudate was accounted for >93% in the two genotypes at three growth phases.Soil available potassium content after treated by the root exudates of grain amaranth was higher than that treated by pure water.Under low potassium stress,the content of soil available potassium treated by the root exudates of K12 was higher than that treated by those of M9.

Key words: landscape pattern, remote sensing, urban landscape, Guangdong-Hong Kong-Macao Greater Bay Area., impervious surface