Nitrogen availability in the taiga forest ecosystem of northeastern Siberia

Abstract

The inorganic nitrogen (N) cycle and its dynamics in the soil were observed in the ecosystem at the Spasskaya Pad experimental forest near Yakutsk in northeastern Siberia in order to estimate the N availability for the larch (Larix cajanderi Mayr.) The soil pool of bulk N in the forest accounted for up to 866 g N m −2 (0-50 cm), whereas up to 1.7% (14.6 g N m −2 ) was potassium chloride (KCl)-extractable inorganic N. Ammonium was a dominant form of inorganic N. The size of the soil inorganic N pool fluctuated seasonally. It was small in the beginning of the summer and increased rapidly once the cumulative degree day of the soil temperature at 20 cm reached more than 300 (°C days), indicating that active N mineralization began at some point from the middle of July to the beginning of August. This soil pool of inorganic N that had accumulated at the end of the previous summer was consumed by the beginning of the next summer through microbial immobilization, which may have begun in September. Recycling of N in the soil was important because the input of inorganic N by deposition was very small (48 mg N m −2 year −1). A tracer 15 N experiment showed that larch did not uptake organic N in the form of amino acid (alanine); rather, it used ammonium and nitrate as N sources. The amount of available N for plants was assessed as water-extractable inorganic N in the soil solution that was transported to the rooting area by mass flow driven by plant transpiration, and it accounted for 1.9 × 10 3 (1.2 × 10 3 for trees) mg N m −2 during the growing season −1 (0-50 cm of the mineral soil layer in June, July, and August). Microorganisms in the soil are also expected to be competing for this available N. Our results show that despite a large amount of inorganic N production, N availability for plants is low as the soil pool of inorganic N is built up at the same rate as larch senescence.

Spatial variations in larch needle and soil δ15N at a forest–grassland boundary in northern Mongolia

“…Interpretations of Δδ 15 moisture conditions for plants [40], whereas the soil C/N as an indicator of the decomposition rate of soil organic matter [41]. Therefore, these parameters as well as the high NO3to NH4 + ratios at boundary sites in MM area (Table S1) with a previous study that showed the severe competition of available N between plant and soil microorganisms in taiga forest ecosystem [42].…”

“…Although there is not enough data to evaluate the N budget at our study sites, we assume that recycled N is the dominant flux compared with the input and loss fluxes in the plant-soil system. In taiga, the annual N demand of larch has been reported at 1,500 mg N m -2 yr -1 near at Tura in central Siberia [44], and 850 to 3,100 mg N m -2 yr -1 at Yakutsk in northeastern Siberia [42]. The estimated N loss as leaching (< 10mg N m -2 yr -1 ) at Tura [44] and N input as deposition (48 mg N m -2 yr -1 ) at Yakutsk [42] were much smaller than the N demand.…”

Wildfire effects on ecosystem nitrogen cycling in a Chinese boreal larch forest, revealed by &lt;sup&gt;15&lt;/sup&gt;N natural abundance

“…Therefore, δ 15 N could provide us a promising and comprehensive tool to detect the effect of wildfire on N cycling. Boreal forests are typical N limited ecosystems where N cycling is slow and a large proportion of total N capital is tied up in undecomposed organic matter (Hyodo et al, 2013;Metcalfe et al, 2013;Popova et al, 2013;Sah et al, 2006). This is consistent with low δ 15 N values of soil and plant (Hogberg, 1997).…”

“…Wildfire-induced nitrogen (N) cycling changes can greatly alter ecosystem structure and functions, such as species composition and biodiversity (Gallant et al, 2003), biogeochemical cycles and productivity (Boerner, 1982;Chorover et al, 1994;Woodmansee and Wallach, 1981), as N is likely to be the most essential element limiting plant growth in terrestrial ecosystems (Popova et al, 2013;Stark andHart, Biogeosciences Discuss., doi:10.5194/bg-2016-91, 2016 Manuscript under review for journal Biogeosciences Published: 4 April 2016 c Author(s) 2016. CC-BY 3.0 License.…”

Effects of Snow Manipulation on Larch Trees in the Taiga Forest Ecosystem in Northeastern Siberia

“…This may cuase nally an "increase (decrease) in forest production". Both soil moisture and soil nutrients are limiting factors for forest photosynthetic activity at the study site (Popova et al, 2013;Tei et al 2013).…”