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Description of the project objectives (
SLAvONIC aims to fill the gap in understanding of the combined effects of S and N deposition on altering C and N cycling in forest soils. In particular, the project will examine whether there has been a shift in the relative balance of ecosystem N and C accumulation, versus ecosystem losses in either (dissolved) organic or (dissolved or gaseous) inorganic forms. A set of replicated acidity/N availability manipulation experiments in broad leave (beech forest) and conifer (spruce forest) sites will be undertaken in an area of formerly high S/N deposition (northern part of the Czech Republic) over the time period of 4 years. SLAvONIC will address the following objectives:
1) To quantify the effect of acidity/N availability changes on the amount of C and N lost from the ecosystem via organic (DOC, DON - dissolved organic nitrogen) and inorganic (NO3, CO2) pathways, in two major forest types.
2) To measure how acidity/N availability affects a range of key internal N and C transformations; decomposition of SOM, net nitrogen mineralisation and nitrification.
3) To use the results to support the development of a model of C and N cycling which, unlike most existing models, fully incorporates the effects of changing acidity, and this model will be used to predict future change in ecosystem carbon and nitrogen balances.
A description of the work performed since the beginning of the project
Immediately after SLAvONIC project started in August 2013, experimental plots have been established in two nearby forests (spruce and beech). In total 32 plots were located - representing four replicates for each treatment (S, N, S+N and Control). Within each plot, soil solution samplers were installed – minimum of four for forest floor soil solution (Rhizon type) and one in 30cm depth in the mineral soil (vacuum lyzimeterPrenart). Within each forest type, installation of probes for soil temperature, soil moisture, air temperature and air moisture were performed. To assess the amount and quality of litter production, five litter collectors at each site were installed. To perform regular soil respiration measurements, within each plot four collars were installed – all together 128 collars (64 in each forest type).
Soil waters have been sampled in three to four weekly intervals and analyzed for : pH, DOC, DON, Ca, Mg, Na, K, Al, NH4, NO3, Cl and SO4. Litter collectors were collected every two month and the litter analyzed for C and N content. Soil respiration has been measured by two methods. Every month (from April till November – snow free period) all 128 soil collars are measured with dark survey chamber (LiCor). Every two months continuous measurements of soil respiration is performed using LiCor long-term chambers – within each plot one long-term chamber is placed. All together 16 chambers continuously measure soil respiration for 48 hours in each forest site. Thus, temporal resolution (day vs. night) is obtained. LiCor system is expensive equipment, thus students (Michal and Martin) and technician (Oldřich) involved in the SLAvONIC overnight in the field for five days, irrespective to the current weather conditions.
Since April 2014 regular application of treatments (Control, S, N and combined S+N) has been conducting at each forest site in four replicates. Application consists of monthly addition of S (50 kgS/ha/year), N (50 kgN/ha/year), both S+N (50+50kg S+N/ha/year) and Control (just rain water).
In March 2015, litterbag experiment has been established. In contrary to the project proposal instead of using on site litter we decided to follow recommended procedure by Utrech University using tea bags (
Rhizon type lyzimeter for colleting forest floor soil solution. /
Prenart type lyzimeter for colleting mineral soil solution.
Soil/air temperature and moisture sensors and litterfall collector. /
Soil respiration measurements with LiCor long-term chambers. All together 16 long-term chambers are used for soil respiration assessment.
Bulding the roof for rain water collection. Rain water is used for monthly addition of treatments by water cans. Every month approximately 300 l of rain water is needed at each forest site.
A description of the main results achieved so far
Before spring 2014 all plots were measured for all chemical parameters to assess differences across individual plots (sampling between May and July 2013 supported by the Czech Geological Survey). Immediate effects of treatments on soil solution chemistry have been observed since application started in April 2014.pH of soil water in O horizon decreased in both forests (spruce, beech), primarily as a consequence of S application. Due to the acidity constrains on DOC leaching, as proposed in the project, DOC concentration was reduced as well. Despite substantial N fertilizing, only minor and mostly non significant effect on NO3 leaching has been observed after 1st year of soil manipulation. However, higher overall NO3 leaching was measured in beech forest compared to spruce. No effects of soil treatments were detected in deeper mineral soil waters, suggesting effective retention of chemicals in top soil layers.
Soil respiration measurements revealed tight relation between CO2 soil efflux and soil temperature. Surprisingly the dependence of in situ soil respiration on soil temperature was similar in both forests – despite rather different litter quality (needles vs. leaves). Despite immediate acid treatments on dissolved organic carbon (DOC) leaching limited treatment effect on soil respiration was detected. However, up-to-date results (July 2015, not shown) have shown reduction of soil respiration under acid treatments, which is in accordance with hypothesis postulated in project proposal.
Forest floor soil solution chemistry (pH, DOC and NO3) under different treatment in spruce (left column) and beech (right column) forests. Treatment application started in April 2014.Soil respirationunder different treatments (started April 2014) in spruce (left) and beech (right) forests. Soil moisture and temperature are shown as well.
Soil respiration and soil temperature relationship in spruce (left) and beech (right) forests.
The expected final results and their potential impact and use
In the middle of the project all (three) general objectives were addressed. SLAvONIC results were also used to address the 3rd objective of the project – modelling work. Updated version of MAGIC model (see Oulehle et al., 2015) was satisfactorily applied to model seasonal behaviour of N retention at four European catchments. As such, prediction of future C and N balance can be done on catchment scale. Furthermore, MAGIC model can be used to assess climate change impacts on C and N balance.
There is a great deal of national and international legislation relating to atmospheric pollution, conservation and biodiversity across Europe. The SLAvONIC work has been presented onJoint Expert Group on Dynamic Modelling under the Working Group on Effects (WGE) – body under the UN Convention on Long-Range Transboundary Air Pollution.
We hope that in the second half of the project, more progressive soil respiration decline will be measured as a consequence of acid and N treatments. Afterwards, science based estimation of anthropogenic acidification and eutrophication impacts on carbon and nitrogen balance in temperate forests can be postulated.
Within the SLAvONIC project, two students and one technician were deeply involved. SLAvONIC team has got additional science support from the Czech Science Foundation. As a consequence, colleagues from the University of South Bohemia joint the project and established additional research focused on microbial activity within the soil environment. As such, SLAvONIC was extended far beyond we hoped by submitting the proposal in 2013. However, in 2015/2016 we expect PhD student of prof. Evans from Centre of Ecology and Hydrology to collect samples from our plots. We hope that our project results can be then compared with similar project taking place in Wales (UK).