Do plants need root based nutrients if there's enough in the water column?

Tom Barr

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In an interesting study by Rattray et al (1991, Aquat Bot 40:225-237). Lagarosiphon major and Myriohyllum triphyllum were planted in situ in either oligo(low nutrients) or eutrophic(high) sediments in an oligotrophic or eutrophic New Zealand lake. Growth of both plants was 2-fold greater in the oligotrophic lake on the eutrophic sediment, and tissue P was 2-fold more (sediment provided the P which in the natural oligotrophic lake was limiting). In contrast in the eutrophic lake sediment made no difference to growth (plants got enough from the water) which is what I've suggested for many years but...........this is for these species plant species, some plants species(there are over 300 plant species commonly kept, but perhaps only 30 have been looked at in much detail) may have different requirements and practical matters such as how to maintain 2ppm of NH4 in the water column without algae.


Cedergreen and Madsen(Tom Madsen, Nina Cedergreen Freshwater Biology(2002) 47, 283-291 ) showed a similar case in nutrient rich waste streams, even going so far as to cut the roots off of the plants and found that they had no decline in growth rates.

Regards,
Tom Barr