ATP as Phosphorus and Nitrogen Source for Nutrient Uptake by Fagus sylvatica and Populus x canescens Roots

The present study elucidated whether roots of temperate forest trees can take up organic phosphorus in the form of ATP. Detached non-mycorrhizal roots of beech (Fagus sylvatica) and gray poplar (Populus x canescens) were exposed under controlled conditions to ³³P-ATP and/or ¹³C/¹⁵N labeled ATP in the presence and absence of the acid phosphatase inhibitor MoO₄ ^2-. Accumulation of the respective label in the roots was used to calculate ³³P, ¹³C and ¹⁵N uptake rates in ATP equivalents for comparison reason. The present data shown that a significant part of ATP was cleaved outside the roots before phosphate (P_i) was taken up. Furthermore, nucleotide uptake seems more reasonable after cleavage of at least one P_i unit as ADP, AMP and/or as the nucleoside adenosine. Similar results were obtained when still attached mycorrhizal roots of adult beech trees and their natural regeneration of two forest stands were exposed to ATP in the presence or absence of MoO₄ ^2-. Cleavage of P_i from ATP by enzymes commonly present in the rhizosphere, such as extracellular acid phosphatases, ecto-apyrase and/or nucleotidases, prior ADP/AMP/adenosine uptake is highly probable but depended on the soil type and the pH of the soil solution. Although uptake of ATP/ADP/AMP cannot be excluded, uptake of the nucleoside adenosine without breakdown into its constituents ribose and adenine is highly evident. Based on the ³³P, ¹³C, and ¹⁵N uptake rates calculated as equivalents of ATP the 'pro and contra' for the uptake of nucleotides and nucleosides is discussed. Short Summary Roots take up phosphorus from ATP as P_i after cleavage but might also take up ADP and/or AMP by yet unknown nucleotide transporter(s) because at least the nucleoside adenosine as N source is taken up without cleavage into its constituents ribose and adenine.