The scaling of respiratory metabolism with body mass is one of the most pervasive phenomena in biology. Using a single allometric equation to characterize empirical scaling relationships and to evaluate alternative hypotheses about mechanisms has been controversial. We developed a method to directly measure respiration of 271 whole plants, spanning nine orders of magnitude in body mass, from small seedlings to large trees, and from tropical to boreal ecosystems. Our measurements include the roots, which have often been ignored. Rather than a single power-law relationship, our data are fit by a biphasic, mixed-power function. The allometric exponent varies continuously from 1 in the smallest plants to 3/4 in larger saplings and trees. Therefore, our findings support the recent findings of Reich et al. [Reich PB, Tjoelker MG, Machado JL, Oleksyn J (2006) Universal scaling of respiratory metabolism, size, and nitrogen in plants. Nature 439:457–461] and West, Brown, and Enquist [West GB, Brown JH, Enquist BJ (1997) A general model for the origin of allometric scaling laws in biology.Science276:122 -126.]. The transition from linear to 3/4-power scaling may indicate fundamental physical and physiological constraints on the allocation of plant biomass between photosynthetic and nonphotosynthetic organs over the course of ontogenetic plant growth.

Permafrost exerts strong controls on forest development through nutrient availability. The key question of this study was to assess the effect of site conditions on macroelement concentration and stable isotope (δ¹³C and δ¹⁵N) dynamics during the growing season, and nutrient stoichiometry and resorption efficiency in the foliage of two common larch species in Siberia. Foliar nutrient (N, P and K) concentrations of larches grown on permafrost soils were exceptionally high in juvenile needles compared to those from a permafrost-free region (+50% and 130% for P and K), but were two-fold lower at needle maturation. Within permafrost terrain trees, sites with a warmer and deeper soil active layer had 15–60% greater nutrient concentrations and higher δ¹⁵N in their needles compared to shallower, colder soils. Larch of permafrost-free sites demonstrated an enrichment of foliage in ¹⁵N (+1.4% to +2.4‰) in comparison to permafrost terrain (−2.0% to −6.9‰). At all sites, foliar δ¹³C decreased from June to August, which very likely results from an increasing contribution of current photoassimilates to build foliar biomass. With senescence, nutrient concentrations in larch needles decreased significantly by 60–90%. This strong ability of larch to retain nutrients through resorption is the essential mechanism that maintains tree growth early in the growing season when soil remains frozen. The high resorptive efficiency found for K and P for larches established on permafrost suggests nutrient limitation of tree growth within the Central Siberian Plateau not only by N, as previously reported, but also by P and K. The increasing nutrient concentrations and a ¹⁵N enrichment of foliage towards warmer sites was paralleled by an up to 50-fold increase in biomass production, strongly suggesting that accelerated nutrient cycling with permafrost degradation contributes to an increased productivity of Siberian larch forests.

We examined and simulated the consequences of the degradation of the litter and the moss–lichen layer after fire impact, which could affect the seasonal temperature of the soil and the depth of the seasonally thawed layer (STL) in the permafrost zone. According to the analysis of satellite imagery for 2000 to 2019, the fire-disturbed area in the region of interest amounted to 20%. The main aims of the study included quantitative evaluation of the variation range of summer temperature anomalies at fire-damaged plots, summarizing the statistical norm of the STL depending on natural conditions, and numerical simulation of the response of the STL. Using Terra and Aqua/MODIS imagery, we analyzed surface temperature (in bands of λ = 10.780–11.280 and 11.770–12.270 μm) coupled with the normalized difference vegetation index (NDVI) for non-disturbed and fire-damaged sites under the same natural conditions of larch forests in Central Siberia. Heat transfer, freezing and thawing processes were numerically simulated for two extreme cases of soil conditions: dry soil and water-saturated soil. The model was also applied to soil with non-homogeneous water content. As input parameters, we used data on the properties of cryogenic soils collected in larch forests (Larix gmelinii) in the flat-mountainous taiga region of the Evenkia (Central Siberia). For post-fire plots, surface temperature anomalies observed during summer months remained significant for more than 15–20 years after fire impact, while the NDVI values were restored to the statistical norm within 7–10 years of the fire. According to the results of numerical simulation, the thickness of the STL could show a 30–50% increase compared to the statistical norm. In the first approximation, we showed the annual soil temperature dynamics at various depths in disturbed and non-disturbed plots.