Not really a black and white answer to your question but...
IMHO, any "gray" answer would be highly species dependent,
Most CP's need a combination of root and insect nutrition
There are many papers on the subject of CP root/insect nutrition... jstor is an excellent resource
Butch, those are basically the conclusions of the Adamec paper, however he cites lack of data in many cases. This is a 13 year old paper after all.
I've noticed unpublished studies cited in other papers. It's difficult to obtain copies of these without be acquainted with the author.
Let's see how your plants are doing a year or two down the road. Long term results on hydroponics is lacking.
Just on my own observation with Dionaea the plants I've grown in pure peat moss develop massive root systems - a mat forms on the bottom of the pot - vs those grown in the usual 50/50 sand/peat moss mix or even live Sphagnum. Yet very little difference in growth of the plant and rhizomes themselves. So substrate in itself may make a difference in root growth for this species. I've started using much less sand in my mixes from now on.
Grand Hotel... always the same. People come, people go. Nothing ever happens.
Oh I totally agree, my main point is that it is not an either/or situation...but in most cases both are inter-related with nutrition from insects usually being the regulation variable. For optimum health, both variables must be met.
Adamec did a good follow up in 2002 for New Phytologist
"Leaf absorption of mineral nutrients in carnivorous plants
stimulates root nutrient uptake"
Basically restating that root uptake was directly proportional to leaf/trap uptake...
Later in 2005, we have
The roots of carnivorous plants
Wolfram Adlassnig1, Marianne Peroutka1, Hans Lambers2 & Irene K. Lichtscheidl1,3
1Institute of Ecology and Conservation Biology, University of Vienna, Althanstrasse 14, 1090 Vienna,
Austria. 2School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of
Western Australia, Crawley WA 6009, Australia. 3Corresponding author*
Received 30 April 2004. Accepted in revised form 31 August 2004
"....Some carnivorous plants appear to have a
limited capacity for nutrient absorption from the
soil, and therefore depend on animals to a
greater extent: Utricularia gibba (Pringsheim and
Pringsheim, 1967) can survive on an inorganic
medium, but grows very slowly. Better growth
occurs, when beef extract, peptone, glucose and
acetate are added to the medium. The same is
the case with Dionaea muscipula on a nutrientrich
soil: without animals plants produce no new
roots, only few flowers, no fertile seeds, and die
(Roberts and Oosting, 1958). Therefore, in the
natural habitat of Dionea, only 8–25% of the
total N comes from the soil. The greatest
amounts are found in dense vegetation, where
the traps work less effectively (Schulze et al.,
2001). The closely related Aldrovanda vesiculosa
is able to survive without animal prey, but shows
only poor growth (Adamec, 2000).
The amount of nutrients obtained from either
prey or from the soil seems to vary substantially.
Sarracenia leucophylla can get 60 times more ions
from the prey than from the soil (Gibson,
1983b). Nepenthes mirabilis gets about 60% of its
N from insect prey, whereas in Cephalotus it is
only 30% (Schulze et al., 1997). In Drosera
rotundifolia about 50% of the total N is of animal
origin (Millett et al., 2003), and in D. hilaris
68% (Anderson and Midgley, 2003). The protocarnivorous
Roridula gorgonias, which needs
symbiotic hemipterans for digestion, even up to
70% of N comes from animals (Anderson and
For another group of plants, applied mineral
nutrients (i.e. fertilizers) can be fatal: Sarracenia
alata, for instance, grows on soil containing sufficient
concentrations of N, P and K; it is, however,
very sensitive to fertilizer additions, and
dies when growing in such nutrient-enriched
areas (Eleuterius and Jones, 1969).
Nutrition can also influence the morphology
of some carnivorous plants, and the size
and number of their traps. In some species of
Sarracenia (Ellison and Gotelli, 2002) and of Nepenthes
(Smythies, 1963) more, and more efficient
pitchers are produced on a nutrient-poor medium.
On a richer medium the leaf bases become
flattened and hence more suitable for photosynthesis,
whereas the pitchers are reduced.
Another interesting observation is that plants
may take up only some specific nutrients through
the roots, whereas others come through the
leaves from the prey. This is the case for some
Australian Drosera species that grow in habitats
subjected to fires. The soil in this habitat in general
is very poor, but enriched in K after a fire.
Drosera is thought to take up the K+ by its
roots, and the other nutrients from insects
(Dixon and Pate, 1978; Pate and Dixon, 1978),
but this effect has not been quantified. Nepenthes
pervillei sends its roots into rock cliffs where the
cyanobacterium Lyngbia (Oscillatoriaceae) grows.
Lyngbia fixes atmospheric dinitrogen, which is
suggested to be absorbed by the roots, whereas
other nutrients may come from animals that are
caught in the few functioning traps (Juniper
et al., 1989)."