Relationships between tree and soil properties in Picea abies and Pinus sylvestris forests in Sweden

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 data set 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 macro- 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

Fungerar kretsloppen om vi använder mera biobränslen?

• Biobränslen kan i praktiken betraktas som koldioxidneutrala. • Vid uttag av biobränslen bör blad och barr lämnas kvar för att minska näringsförlusterna. • Återföring av vedaska krävs förmodligen för omfattande utnyttjande av biobränslen från skog. • Upprätthållandet av kretsloppen för viktiga grundämnen är inte vad som kommer att sätta gränserna för hur mycket biobränslen som kan utnyttjas. Det är andra faktorer såsom upprätthållande av biodiversitet, landskapsbild, risk för näringsläckage samt ekonomi

Temperature sensitivity of soil respiration rates enhanced by microbial community response

Soils store about four times as much carbon as plant biomass(1), and soil microbial respiration releases about 60 petagrams of carbon per year to the atmosphere as carbon dioxide(2). Short-term experiments have shown that soil microbial respiration increases exponentially with temperature(3). This information has been incorporated into soil carbon and Earth-system models, which suggest that warming-induced increases in carbon dioxide release from soils represent an important positive feedback loop that could influence twenty-first-century climate change(4). The magnitude of this feedback remains uncertain, however, not least because the response of soil microbial communities to changing temperatures has the potential to either decrease(5-7) or increase(8,9) warming-induced carbon losses substantially. Here we collect soils from different ecosystems along a climate gradient from the Arctic to the Amazon and investigate how microbial community-level responses control the temperature sensitivity of soil respiration. We find that the microbial community-level response more often enhances than reduces the mid-to long-term (90 days) temperature sensitivity of respiration. Furthermore, the strongest enhancing responses were observed in soils with high carbon-to-nitrogen ratios and in soils from cold climatic regions. After 90 days, microbial community responses increased the temperature sensitivity of respiration in high-latitude soils by a factor of 1.4 compared to the instantaneous temperature response. This suggests that the substantial carbon stores in Arctic and boreal soils could be more vulnerable to climate warming than currently predicted.Output Type: Lette

Quality or decomposer efficiency - which is most important for the temperature response of litter decomposition?

Effects of temperature history on litter decomposition was evaluated with the Q-model calibrated to a needle litter incubation experiment and using the GLUE modelling framework. The needle litter incubation was a full factorial design with initial and final temperatures 5, 15 and 25oC. Samples going to a different second temperature were moved when approximately 12% carbon had respired. We used four variations of the Q-model; the combination of one or two initial litter quality values and fixed or temperature-dependent decomposer efficiency. The model was calibrated to the constant temperature subset of the data. Evaluated against the subset containing temperature shifts, gave good results, except just after the change in temperature where the model predicted less than measured. Using one or two initial litter quality values and fixed decomposer efficiency had little effect on litter quality and respiration during the final incubation temperature. When the decomposer efficiency was allowed to vary with temperature, the best predictions had decomposer efficiency values that decreased between 5 to 15oC and did not change between 15 and 25oC. Having flexible decomposer efficiency resulted in substantial differences in litter quality between the three temperatures at the end of the initial incubation. This resulted in that samples at the same final temperature, subjected to different initial temperatures, decomposed at significantly different rates. The result suggests that it might be important to consider other factors than the variation in temperature sensitivity with quality when evaluating effects of temperature changes on soil organic matter stability

Temperature sensitivity of nitrogen productivity for Scots pine and Norway spruce

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 needle nitrogen productivity, which is an aggregate parameter for production of new foliage. 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 as 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 biomass. For practical applications it may be sufficient to use a speciesspecific nitrogen productivity that is independent of temperature. Because temperature affects tree growth indirectly as well as 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 conifers along a temperature gradient

Temperature sensitivity of nitrogen productivity

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. To circumvent this problem we have used the nitrogen productivity (dry matter production per unit of nitrogen in the plant), which is an aggregate parameter. Data on needle dry matter, production, and nitrogen content in needles of Scots pine (Pinus sylvestris) from a wide range of climatic conditions were collected from which needle nitrogen productivities were calculated. Our results show that nitrogen productivity is rather insensitive to temperature. As a consequence, 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 mineralisation

Multi-Dimensional Plant Element Stoichiometry-Looking Beyond Carbon, Nitrogen, and Phosphorus

Nutrient elements are important for plant growth. Element stoichiometry considers the balance between different nutrients and how this balance is affected by the environment. So far, focus of plant stoichiometry has mainly been on the three elements carbon (C), nitrogen (N), and phosphorus (P), but many additional elements are essential for proper plant growth. Our overall aim is to test the scaling relations of various additional elements (K, Ca, Mg, S, Cu, Zn, Fe, Mn), by using ten data sets from a range of plant functional types and environmental conditions. To simultaneously handle more than one element, we define a stoichiometric niche volume as the volume of an abstract multidimensional shape in n dimensions, with the n sides of this shape defined by the plant properties in question, here their element concentrations. Thus, a stoichiometric niche volume is here defined as the product of element concentrations. The volumes of N and P (V-NP) are used as the basis, and we investigate how the volume of other elements (V-Oth) scales with respect to V-NP, with the intention to explore if the concentrations of other elements increase faster (scaling exponent > 1) or slower (<1) than the concentrations of N and P. For example, scaling exponents >1 suggest that favorable conditions for plant growth, i.e., environments rich in N and P, may require proportionally higher uptake of other essential elements than poor conditions. We show that the scaling exponent is rather insensitive to environmental conditions or plant species, and ranges from 0.900 to 2.479 (average 1.58) in nine out of ten data sets. For single elements, Mg has the smallest scaling exponent (0.031) and Mn the largest (2.147). Comparison between laboratory determined stoichiometric relations and field observations suggest that element uptake in field conditions often exceeds the minimal physiological requirements. The results provide evidence for the view that the scaling relations previously reported for N and P can be extended to other elements; and that N and P are the driving elements in plant stoichiometric relations. The stoichiometric niche volumes defined here could be used to predict plant performances in different environments

Monte-carlo study of motions for a flexible macromolecule in the presence of fixed obstacles

We study the brownian motion of a chain with N points (20 ≤ N ≤ 140) moving on a two dimensional hexagonal lattice. Certain points on the lattice (« obstacles ») cannot be crossed by the chain. We find a rather good convergence for the correlation function of the end-to-end vector, suggesting that the renewal time for chain conformation Tr is proportional to N2.8. On the other hand, for the self diffusion coefficient, the convergence is not very fast, and prohibitive calculational times would be required to obtain a reliable exponent