Abstract
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.
Highlights
Boreal forest ecosystems store large amounts of carbon (C) in their biomass and soils and changes in their C stocks might have large impacts on atmospheric CO2 concentrations [1].In this context, vast larch forests across Siberia may play an important role in C sequestrationForests 2018, 9, 314; doi:10.3390/f9060314 www.mdpi.com/journal/forestsForests 2018, 9, 314 given the unique characteristics of Larix spp. [2], including its broad geographic distribution [3,4], high photosynthetic capacity [5,6,7], and high stand biomass under favorable conditions [2,8]
Stand productivity increased with active layer depth and reached the greatest values at the permafrost-free site
Our study along a gradient in the permafrost regime in Central Siberia showed that the nutritional status of larch trees strongly improved with a deepening of the active layer
Summary
Boreal forest ecosystems store large amounts of carbon (C) in their biomass and soils and changes in their C stocks might have large impacts on atmospheric CO2 concentrations [1].In this context, vast larch forests across Siberia may play an important role in C sequestrationForests 2018, 9, 314; doi:10.3390/f9060314 www.mdpi.com/journal/forestsForests 2018, 9, 314 given the unique characteristics of Larix spp. [2], including its broad geographic distribution [3,4], high photosynthetic capacity [5,6,7], and high stand biomass under favorable conditions [2,8]. Boreal forest ecosystems store large amounts of carbon (C) in their biomass and soils and changes in their C stocks might have large impacts on atmospheric CO2 concentrations [1] In this context, vast larch forests across Siberia may play an important role in C sequestration. Larix species in continental Siberia are generally exposed to a water deficit [6,7,10,12], they typically show the highest photoassimilation rates among coniferous tree species when climatic conditions are favorable, on a yearly basis, and on a daily basis, which allows them to compensate for the short growing period [6]. Such a strategy is associated with greater water conductance, much higher transpiration water losses [6], and lower water use efficiency (WUE)
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