The Role of Proteins in the Nitrogen Nutrition of Ectomycorrhizal Plants

Abstract

SUMMARY f !The ability of mycorrhizal (M) and non-mycorrhizal (NM) plants of Pinus contorta (Dougl. ex Loud) to utilize protein as a nitrogen source was examined. Mycorrhizas were synthesized with the fungal symbionts PaxiUus involutus, Rhizopogon roseolus, Suillus bovinus and Pisoiithus tinctorius. The plants were grown under aseptic conditions and provided with nitrogen in the form of either protein or ammonium.Dry weight yields of plants infected with P. involutus, R. roseolus and S. bovinus were significantly higher than those of NM plants when grown on protein as the N source. In these associations yields of M plants on protein were similar to those obtained on ammonium-N. Non-mycorrhizal plants had little ability to use protein N and the same was true of plants infected with P. tinctorius.Plants in those associations which provided a yield increase also contained larger quantities of N. Calculations show that in all tbese cases some of tbe increases of N content arise through utilization of protein.The implications of the results are discussed in relation to the nitrogen nutrition of the plant and to the pattern of N mobilization in soil. It is proposed that the ability of mycorrhizal associations to utilize protein N will lead not only to an increased supply of N to the plant but also to more effective competition with the decomposer population and to an overall tightening of the nitrogen cycle.

A comparison of the extracellular enzyme activities of two ectomycorrhizal and a leaf‐saprotrophic basidiomycete colonizing beech leaf litter

“…Extracellular protease activin-has been demonstrated in an ericoid and in a few ectomycorrhizal fungi (Leake & Read, 1990;Zhu et al, 1994). Indirect evidence of ectomycorrhizal protease production was also obtained in the experiments of Ahuzinadah, Finlay & Read (1986) and Ahuzinadah & Read (1986).…”

Translocation of 32P between interacting mycelia of a wood‐decomposing fungus and ectomycorrhizal fungi in microcosm systems

“…As the transfer in the other direction was very slow, there was a net capture of P by the mycorrhizal fungi. Abuzinadah et al (1986) emphasized the importance of microbial biomass as a major source of organic N for mycorrhizal plants. The same idea is presented by Leake & Read (1997), who point out that, since microbial biomass is more easily degradable than most plant litter, the rapid turnover of the microbial nutrient pool could make it a more important source of organic nutrients than plant litter, despite the much larger size of the total plant litter nutrient pool.…”

Effects of liming on the uptake of organic and inorganic nitrogen by mycorrhizal (Paxillus involutus) and non‐mycorrhizal Pinus sylvestris plants

“…The proteolytic capability of P. involutus in pure culture is strongly influenced by pH. However the pH optimum varies substantially according to substrate (Abuzinadah & Read, 1986 a;Bending & Read, 1995). The uptake of amino acids by the P. involutus strain used in the present study was shown to be strongly influenced by pH (Chalot et al, 1995).…”

“…It is also possible that P. involutus accumulates N in the mycelium under some circumstances. It has been observed that Pinus contorta and Betula pendula plants inoculated with P. involutus can show lower uptake of NH^""" than non-mycorrhizal plants, a phenomenon which was not found with some other ectomycorrhizal fungi (Abuzinadah et al, 1986;Abuzinadah & Read, 1989a, b). These authors proposed that P. involutus might accumulate N in the mycelium.…”

“…Mycorrhizal fungi are also able to utilize soluble proteins and amino acids as a N-source (Abuzinadah & Read, 1986 a), and it has been shown that mycorrhizal plants of Betula pendula, Picea mariana, Pinus contorta. Eucalyptus grandis and E. maculata grown axenically can take up N from soluble proteins, while they are unable to do so when non-mycorrhizal (Abuzinadah, Finlay & Read, 1986;Abuzinadah & Read, 1986Z>;Abuzinadah & Read, 1989a, b\ Finlay, Frostegard & * To whom correspondence should he addressed. Sonnerfeldt, 1992;Turnbull, Goodall & Stewart, 1995).…”