The exchange of elements between plants and the soil in which they are growing creates reciprocal control of their element composition. Within plants, the growth rate hypothesis from ecological stoichiometry implies a strong coupling between C, N, and P. No similar theory exists for predicting relationships between elements in the soil or relationships between plants and the soil. We used a dataset of element concentrations in needles and humus of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) forests in Sweden to investigate the extent to which relationships between elements (C, N, P, S, K, Ca, Mg, Fe, Mn, Al) can be observed within and between plants and soils.We found element composition to be more strongly controlled in needles than in humus. Elements that are covalently bound were also more strongly controlled, with no apparent differences between macronutrients and micronutrients. With the exception of N/C, there were surprisingly few relationships between elements in needles and humus. We found no major differences between the two tree species studied, but investigations of additional forest types are needed for firm conclusions. More control over element composition was exercised with respect to N than C, particularly in needles, so it might be advantageous to express nutrient concentrations relative to N rather than on a dry weight or carbon basis. Variations in many ecosystem variables appeared to lack ecological significance and thus an important task is to identify the meaningful predictors.

Environmental conditions control physiological processes in plants and thus their growth. The predicted global warming is expected to accelerate tree growth. However, the growth response is a complex function of several processes with both direct and indirect effects. To analyse this problem we have used the nitrogen productivity, which is an aggregate parameter for tree growth. Data on needle dry matter, production, and nitrogen content in needles of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) from a wide range of climatic conditions were collected and needle nitrogen productivities, defined dry matter production of needles per unit of nitrogen in the needle biomass, were calculated. Our results show that the nitrogen productivity for spruce is insensitive to temperature. However, for pine, temperature affects both the magnitude of nitrogen productivity at low needle biomass and the response to self-shading but the temperature response is small at the high end of needle biomasses. For practical applications it may be sufficient to use a speciesspecific nitrogen productivity parameter that is independent of temperature. Because temperature affects tree growth also indirectly through soil processes, the effects of temperature change on tree growth and ecosystem carbon storage should mainly be derived from effects on nitrogen availability through changes in nitrogen mineralization. In addition, this paper summarises data on dry matter, production and nitrogen content of needles of conifer along a temperature gradient.

We quantified various terms in the N budget 12 years (pine) and 7 years (spruce) after the last N addition. In the pine ecosystem, large losses of added N occurred, whereas in the spruce ecosystem we recovered more N than could be accounted for by inputs. In the pine ecosystem, increases in N stocks were mainly in the soil, in contrast to the spruce ecosystem where trees accumulated most of the added N. There was no clear pattern in the interaction between acidification/liming and N deposition.