It's cold and raining and I have too much time on my hands so here.....
http://www.falw.vu.nl/nl/Images/11 - heijden_tcm19-29530.pdf
One part.......
Perhaps the most important route by which free-living
microbes influence plant nutrient availability, and hence
plant productivity, is via processes of nutrient mineraliza-
tion, whereby soil microbes break down soluble and
insoluble organic matter and convert it into inorganic, plant
available forms. Most soil N (some 96–98%) is contained in
dead organic matter as complex insoluble polymers such as
proteins, nucleic acids and chitin, and these polymers are
broken down into dissolved organic N (DON) by extra-
cellular enzymes that are produced by soil microbes
(Schimel & Bennett 2004). This DON, which can constitute
a significant portion of the total soluble N pool, is either
absorbed by free-living soil microbes, or it is mineralized by
the microbial biomass (under conditions when microbial
growth is C limited), thereby liberating inorganic-N into the
soil environment. Alternatively, plants might take up DON
directly from soil, in the form of amino acids, thereby
by-passing the microbial mineralization step. This was
shown to be the case in many ecosystems, but especially in
those that are strongly N limited, such as in arctic This growing awareness of the ability
of plants to use organic N and compete with soil microbes
for N has led to a radical rethink of terrestrial N cycling and
especially the processes that control N availability to plants
(Schimel & Bennett 2004)
http://www.falw.vu.nl/nl/Images/11 - heijden_tcm19-29530.pdf
One part.......
Perhaps the most important route by which free-living
microbes influence plant nutrient availability, and hence
plant productivity, is via processes of nutrient mineraliza-
tion, whereby soil microbes break down soluble and
insoluble organic matter and convert it into inorganic, plant
available forms. Most soil N (some 96–98%) is contained in
dead organic matter as complex insoluble polymers such as
proteins, nucleic acids and chitin, and these polymers are
broken down into dissolved organic N (DON) by extra-
cellular enzymes that are produced by soil microbes
(Schimel & Bennett 2004). This DON, which can constitute
a significant portion of the total soluble N pool, is either
absorbed by free-living soil microbes, or it is mineralized by
the microbial biomass (under conditions when microbial
growth is C limited), thereby liberating inorganic-N into the
soil environment. Alternatively, plants might take up DON
directly from soil, in the form of amino acids, thereby
by-passing the microbial mineralization step. This was
shown to be the case in many ecosystems, but especially in
those that are strongly N limited, such as in arctic This growing awareness of the ability
of plants to use organic N and compete with soil microbes
for N has led to a radical rethink of terrestrial N cycling and
especially the processes that control N availability to plants
(Schimel & Bennett 2004)