Nitrogen forms affect root structure and water uptake in the hybrid poplar

The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and water uptake of two hybrid poplar (Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a link between form (architecture) and function (water uptake)

NITREX project - Gårdsjøn. Status report for 1988-1990

At the NITREX site at Gårdsjøn, Sweden, nitrogen deposition will be experimentally increased to an entire forested catchment to study the potential for nitrogen saturation. Investigations include regular sampling of precipitation, thoughfall and runoff and compilation of input-output beugets. Short-term experiments of toxicity of the runoff water to fish are also underway. Studies of vegetation and soils are centered around three vegetation types characteristic of the catchments. Plots have been selected on the basis of soil and vegetation maps of the three catchments. Regular measurements include (1) volume and chemical composition of soil solution, (2) soil temperature, (3) chemical composition of needles, (4) amount and chemical composition of litterfall, and (5) soil moisture. In addition studies of mineralization, fine roots, and mycorrhiza are being conducted. Nitrogen addition will begin in April 1991. The NITREX data from Gårdsjøn will be combined with similar data from the other NITREX sites throughout Europe

Gårdsjön Status Report for 1991-1992: The first Year of Treatment

Nitrogen addition weekly to catchment G2 at Gårdsjön began April 1991. During the first year of treatment a total of 230 meq/m²yr NH4No3 was added in 33 mm of water plus 90 meq/m²/yr deposited in 631 mm throughfall. Runoff contained significantly higher concentrations of No3 (but not NH4) beginning in November 1991. No respons was seen during the growing season. None of the other components and processes (soil solution, mineralization, fine-roots, mycorrhiza and vegetation) studied as part of NITREX showed significant response during the first year of treatment

Nitrex project - Gårdsjöen, Status report for 1990-91

At the NITREX site at Gårdsjön, Sweden, ambient nitrogen deposition of 90 meg m² yr 1 will be experimentally increased by 286 meg m² yr 1 to an entire forested catchment G2 to study the potential for nitrogen saturation. Investigations include mearsurements of catchment inputs and outputs, as well as studies of vegetation, soil, mycorrhiza, fine roots and fish response. Results from the pre-treatment period 1990-91 show acidic runoff and soil solution with high concentrations of inorganic aluminium. Concentrations of nitrate and ammonium are very low, indicating no nitrogen satuation. The trees are slightly-to-moderately defoliated, and the needles are discolored. The nutrient contents of needles indicate that no elements are in the deficiency or the toxin range. The mycorrhiza of the root mat at the forest floor are generally 100 % alive and healthy. At catchment G2 nitrogen addition began April 1991.NMF/NAVF, SN