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Search for projects with tag "nitrogen deposition"

Low and high nitrogen deposition rates in northern coniferous forests have different impacts on aboveground litter production, soil respiration, and soil carbon stocks

PI: Benjamin Forsmark

Nitrogen (N) deposition can change the carbon (C) sink of northern coniferous forests by changing the balance between net primary production and soil respiration. We used a field experiment in an N poor Pinus sylvestris forest where five levels of N (0, 3, 6, 12, 50 kg N ha-1 yr-1, n = 6) had been added annually for 12-13 years to investigate how litter C inputs and soil respiration, divided into its autotrophic and heterotrophic sources, respond to different rates of N input, and its subsequent effect on soil C storage. The highest N addition rate (50 kg N ha-1 yr-1) stimulated soil C accumulation in the organic layer by 22.3 kg C kg-1 N added, increased litter inputs by 46 %, and decreased soil respiration per mass unit of soil C by 31.2 %, mainly by decreasing autotrophic respiration. Lower N addition rates (≤12 kg N ha-1 yr-1) had no effect on litter inputs or soil respiration. These results support previous studies reporting on increased litter inputs coupled to impeded soil C mineralization, contributing to enhancing the soil C sink when N is supplied at high rates, but add observations for lower N addition rates more realistic for N deposition. In doing so, we show that litter production in N poor northern coniferous forests can be relatively unresponsive to low N deposition levels, that stimulation of microbial activity at low N additions are unlikely to reduce the soil C sink, and that high levels of N deposition enhance the soil C sink by increasing litter inputs and decreasing soil respiration.

carbon budgetnitrogen depositionsoil respiration

Nitrogen deposition and soil phosphorus

PI: Benjamin Forsmark

Does long-term nitrogen deposition lead to increased microbial mining for phosphorus in organic and mineral soils, and what is the consequence for the soil carbon sink? This project use the long-term nitrogen addition experiment at Svartberget and ingrowth cores with needle litter, humus, and mineral soil with and without elevated phosphorus content. Substrates were collected in a phosphorus addition experiment in the Tönnersjöheden research forest in Halland.

nitrogen depositionsoilphosphorus

Nitrogen deposition and soil microbiology

PI: Benjamin Forsmark

This project made an inventory of the soil microbial communities in the organic layer of the D (n=6) and E (n=6) plots at the Svartberget nitrogen addition experiment in 2016, after 20 years of annual N addition at 12.5 and 50 kg N ha-1 yr-1. We used PLFA profiling and fungal DNA sequencing to study shifts in the microbial community structure, and used enzyme assays to study the impact of nitrogen on the soil metabolism targeting key components of soil organic matter and litter, including cellulose and hemicellulose, organic nitrogen in peptides and microbial necromass, phosphates, and lignin.

soil microbiologynitrogen depositionfungal communities

Nitrogen deposition and tree carbon allocation

PI: Benjamin Forsmark

Nitrogen deposition can enhance above ground carbon sequestration, but most of the carbon in boreal forest soils are stored in soils. A higher above ground growth enables a higher input of above ground litter to soils, potentially increasing soil carbon stocks. However, a large flux of carbon is entering soils through roots, where it is used to produce and maintain root biomass, as well as exported into microbial biomass such as ectomycorrhiza. Root and microbial biomass production and turnover is an important source of soil carbon, but labile carbon in the root zone is also driving decomposition processes. In this project, we use the Åheden long-term low to high N addition rate experiment to study the consequence of different rates of N input on the soil C balance. We combine above ground flux measurements including the input of above ground litter and output of CO2 by respiration, and below ground measurements on fine-root and ectomycorrhizal fungal biomass production to understand how different rates of nitrogen addition influence the amount, form, and location of carbon inputs to soils, with the overall goal to understand how N deposition influence the boreal forest carbon sink.

nitrogen depositionlitterectomycorrhiza