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2000

Sammendrag

The nutrient cycling model (NuCM) is a stand level model that depicts the cycling of N, P, K, Ca, Mg, and S on daily, weekly or monthly time scales. NuCM has been applied to several forest ecosystems (ponderosa pine, red spruce, beech, eastern deciduous, loblolly pine, slash pine, Scots pine, and Norway spruce) to simulate the effects of changing atmospheric deposition, harvesting, species change, precipitation quantity, increased temperature, elevated CO2, and liming. In some cases (e.g., harvesting, liming), the model output has matched field data quite well; however, it cannot be known whether the model does so because it accurately portrays nutrient cycling processes or simply because of chance. In other cases, NuCM simulations have either failed to match field data (as in the case of the observed chromatographic response of soil solution cations to a nitrate pulse in a beech forest) or produced results that are counterintuitive but as yet untested (as in the case where increased N translocation caused increased leaching). In that the primary purpose of these simulations has been heuristic rather than predictive, the simulation outputs that are either inconsistent with field data or counter-intuitive are of greatest interest. This review of NuCM applications led to the conclusion that the model has been more successful in matching decadal-scale changes in nutrient pools and soils and less successful in capturing intra-annual variations in soil solution chemistry. The NuCM model, like all models, can use improvements and these have been suggested; however, the model as it is has provided valuable insights into nutrient cycling in forest ecosystems, including the potential for short-term soil change and the great importance of nutrient translocation in N cycling.

Sammendrag

We have studied how callus cultures from two clones of Norway spruce influence the growth of two pathogens, Ceratocystis polonica and Heterobasidion annosum, when co-cultivated in vitro. In field experiments, trees of clone 409 were susceptible to both fungi, whereas clone 589 was less affected. Callus was cultured on medium containing cytokinins (benzylaminopurine, kinetin) and with or without auxin (2,4-dichlorphenoxy acetic acid). For co-cultivation with fungus, one piece of callus was placed towards the edge of each Petri dish. One and 14 days after inoculation with callus the dishes were co-inoculated with the fungus. Both clones strongly stimulated the initial growth of both fungi. Clone 589 inhibited the growth of both fungi when the fungi were inoculated one day after the callus. When the callus was cultured on medium without auxin for 14 days before co-inoculation clone 589 strongly inhibited the growth of both fungi, whereas clone 409 inhibited H. annosum only.