Gmj. Mohren et H. Ilvesniemi, MODELING EFFECTS OF SOIL ACIDIFICATION ON TREE GROWTH AND NUTRIENT STATUS, Ecological modelling, 83(1-2), 1995, pp. 263-272
Understanding the effects of soil acidification on tree growth require
s understanding the nutrient relations of trees and stands, notably th
e uptake of nutrients by the roots in relation to soil conditions. Alt
hough a substantial amount of research has been carried out on nutrien
t relationships, both on plant and stand scale, changes in nutrient up
take as a result of soil acidification are hard to predict. This poses
serious problems for attempts to model nutrient uptake by roots in re
lation to changes in soil chemistry induced by acidification and nitro
gen enrichment. Very detailed mechanistic models of root uptake have b
een developed, but the extrapolation of rhizosphere models developed u
nder controlled, laboratory conditions to field situations is cumberso
me. On the other hand, general models of nutrient dynamics very often
lack the sensitivity that is required to describe the reaction to grad
ually changing site conditions. This renders difficult the linkage bet
ween critical loads derived from soil criteria, and tree and stand rea
ctions such as allocation and growth. In the models applied to Selling
, most emphasis is on soil chemistry, with only few models accounting
for feedback mechanisms between soil conditions and tree growth. From
the model results presented during the workshop, it would appear that
nitrogen and magnesium are the key elements in Selling, but such concl
usion is biased as much the same assumption also underlies the guiding
concepts on which the models are based. From the models presented at
the workshop, no clear consensus emerged on the predictions of the con
sequences of changes in soil chemistry. At this stage, there seems to
be a clear need for additional experimental results on nutrient transp
ort in soil, on decomposition under changed soil conditions, and on nu
trient uptake in the case of competition between different ions. In ad
dition, more detailed information on the response of uptake kinetics a
nd biomass allocation in case of reduced nutrient supply, would improv
e deterministic models of nutrient relations of trees. From such exper
imental information, theoretical understanding can be derived, and per
spectives for generalization and modelling can be drawn.