Kinetics of amino acid uptake by ectomycorrhizal roots

Abstract

It is well established that ectomycorrhizal fungi can use amino acids as nitrogen and carbon sources, but data on the kinetic properties of amino acid uptake systems of ectomycorrhizal systems are scarce. Using 14 C-labelled compounds we have determined the kinetics of uptake of amino acids by excised ectomycorrhizal roots for a range of distinct mycorrhizal types from three tree species, beech, spruce, and pine. All mycorrhizal types examined took up amino acids via high-affinity transport systems (K M values ranging from 19 to 233 mmol m -3 ). A comparative analysis of kinetic parameters for uptake of amino acids and the ammonium analogue methylammonium showed that ectomycorrhizal roots have similar or even higher affinities (lower K M values) for the amino acids, indicating that absorption of these organic forms of nitrogen (N) can contribute significantly to total N uptake by ectomycorrhizal plants. Analysis of amino acid uptake by ectomycorrhizal roots collected along a European north/south gradient of increasing mineral N pollution from northern Sweden to south Germany revealed no obvious trend in the uptake capabilities for amino acids by ectomycorrhizal roots in relation to the location of the sampling site on this gradient. Rather, the fungal species forming a particular morphotype was the factor determining uptake kinetics. It can therefore be deduced that the species composition of the fungal community will contribute significantly to the functional diversity of a population of mycorrhizal roots.

Effects of heavy metals on nitrogen uptake by Paxillus involutus and mycorrhizal birch seedlings

“…Organic nitrogen is the predominant form of N in most temperate soils [47,48] and often accounts for more than 95% of the total N [47]. Our results indicate that absorption of organic forms of N can contribute signi¢cantly to total N uptake by ectomycorrhizal plants and are in agreement with those from Wallenda and Read [26] who reported, in a comparative analysis of the kinetics parameters for uptake of amino acids and ammonium, that ectomycorrhizal roots have similar or even higher a¤nities for the amino acids. Indeed, non-mycorrhizal plants rarely take up amino acids because their roots are at a spatial disadvantage in competition with microorganisms, a wide range of which use such compounds, both as N and energy sources.…”

“…Ammonium transport in Paxillus involutus was found to be dependent on the electrochemical H -gradient [25]. In a comparative analysis of the kinetic parameters for uptake of amino acids and ammonium Wallenda and Read [26] reported that ectomycorrhizal roots have similar or even higher a¤nities for amino acids, indicating that absorption of organic N forms can contribute signi¢cantly to total N uptake by ectomycorrhizal plants. Transport of amino acids was investigated in the mycorrhizal fungi P. involutus [27] and Amanita muscaria [28], which demonstrated their ability to take up a variety of amino acids, as do mycorrhizal plants [23,26].…”

“…In a comparative analysis of the kinetic parameters for uptake of amino acids and ammonium Wallenda and Read [26] reported that ectomycorrhizal roots have similar or even higher a¤nities for amino acids, indicating that absorption of organic N forms can contribute signi¢cantly to total N uptake by ectomycorrhizal plants. Transport of amino acids was investigated in the mycorrhizal fungi P. involutus [27] and Amanita muscaria [28], which demonstrated their ability to take up a variety of amino acids, as do mycorrhizal plants [23,26]. Since the uptake processes for organic and inorganic N sources operate quite di¡er-ently [23,25,29], di¡erent responses between mineral N uptake and organic N uptake could be expected under metal stress.…”

Significance of organic nitrogen acquisition for dominant plant species in an alpine meadow on the Tibet plateau, China

“…The amount of C uptake by each plant species from the organic N source derived from the added algae was calculated using added activity (Alg activity , DPM) and C content (C added , mg C m )2 ) of algae and the total activity (S activity , DPM) of each sample on a dry weight basis per collar (Wallenda and Read 1999).…”

The unexpected versatility of plants: organic nitrogen use and availability in terrestrial ecosystems

“…While the role of ericoid and ectomycorrhizae in transferring ON to plants is well established (Read 1991;Marschner and Dell 1994;Chalot and Brun 1998), the relative contributions of mycorrhizal and non-mycorrhizal roots is still an open question for many ecosystems. Ecto-and ericoid mycorrhizae improve the surface area (Rousseau et al 1994) and affinity (Chalot et al 1996;Wallenda and Read 1999) of plant roots for ON, and many of the plant species studied are unable to grow on ON sources without their mycorrhizal symbiont (Stribley and Read 1980;Bajwa and Read 1985;Abuzinadah and Read 1989;Finlay et al 1992;Turnbull et al 1995). However, because many nonmycorrhizal roots can also take up amino acids with high affinity, it is sometimes difficult to quantify the contribution of mycorrhizal versus non-mycorrhizal uptake of amino acid N. Microcosm and field experiments that measure competitive abilities of plants for labeled amino acids generally cannot distinguish between plant and mycorrhizal uptake of amino acid N Lipson and Monson 1998;Lipson et al 1999a).…”