Effects of labile soil carbon on nutrient partitioning between an arctic graminoid and microbes |
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Authors: | Inger K Schmidt Anders Michelsen Sven Jonasson |
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Institution: | Botanical Institute, Department of Plant Ecology, University of Copenhagen, ?ster Farimagsgade 2D, DK-1353 Copenhagen K, Denmark Fax: +45 35 32 23 21; e-mail: IngerKS@bot.ku.dk, DK
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Abstract: | We measured partitioning of N and P uptake between soil microorganisms and potted Festuca vivipara in soil from a subarctic heath in response to factorial addition of three levels of labile carbon (glucose) combined with
two levels of inorganic N and P. The glucose was added to either non-sterilized or sterilized (autoclaved) soils in quantities
which were within the range of reported, naturally occurring amounts of C released periodically from the plant canopy. The
aims were, firstly, to examine whether the glucose stimulated microbial nutrient uptake to the extent of reducing plant nutrient
uptake. This is expected in nutrient-deficient soils if microbes and plants compete for the same nutrients. Secondly, we wanted
to test our earlier␣interpretation that growth reduction observed in graminoids after addition of leaf extracts could be caused
directly by labile carbon addition, rather than by phytotoxins in the extracts. Addition of high amounts of N did not affect
the microbial N pool, whereas high amounts of added P significantly increased the microbial P pool, indicating a luxury P
uptake in the microbes. Both plant N and in particular P uptake increased strongly in response to soil sterilization and to
addition of extra N or P. The increased␣uptake led to enhanced plant growth when both elements were applied in high amounts,
but only led to increased tissue concentrations without growth responses when the nutrients were added separately. Glucose
had strong and contrasting effects on plant and microbial N and P uptake. Microbial N and P uptake increased, soil inorganic
N and P concentrations were reduced and plant N and P uptake declined when glucose was added. The responses were dose-dependent
within the range of 0–450 μg C g−1 soil added to the non-sterilized soil. The opposite responses of plants and microbes showed that plant acquisition of limiting
nutrients is dependent on release of nutrients from the soil microbes, which is under strong regulation by the availability
and microbial uptake of labile C. Hence, we conclude, firstly, that the microbial populations can compete efficiently with
plants for nutrients to an extent of affecting plant growth when the microbial access to labile carbon is high in nutrient
deficient soils. We also conclude that reduced growth of plants after addition of leaf extracts to soil can be caused by carbon-induced
shifts in nutrient partitioning between plants and microbes, and not necessarily by phytotoxins added with the extracts as
suggested by some experiments.
Received: 15 February 1997 / Accepted: 12 July 1997 |
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Keywords: | Arctic soil Allelopathy Microbial immobilization Plant-microbe interactions Soil labile carbon |
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