A non-destructive in vivo spectroscopic method for leaf chlorophyll (Chl) measurement was developed. Spectroscopic analyses of intact leaves of ageratum, petunia and salvia showed strong correlations between leaf light absorption at 723 nm and Chl-a contents. NH4+ increased Chl contents in both ageratum and petunia whereas NO3- increased Chl contents in salvia. Plants fed with NH4+ + NO3- also contained higher Chl. Chl-a/-b ratio in salvia was lowered by NO3-. Ageratum, petunia and salvia grown with either NH4+, NO3-, or NH4+ + NO3- were also examined for their light absorption characteristics. Light absorption at 705 nm by ageratum and petunia leaves was increased by NH4+ treatment. NH4+ is believed to have changed the structure of photosystem I in both ageratum and petunia but not in salvia. This result explain reasons for salvia's sensitivity to NH4+ fed as a sole N source.
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