Plant and soil nitrogen in oligotrophic boreal forest habitats with varying moss depths: does exclusion of large grazers matter?

The boreal forest consists of drier sunlit and moister-shaded habitats with varying moss abundance. Mosses control vascular plant–soil interactions, yet they all can also be altered by grazers. We determined how 2 decades of reindeer (Rangifer tarandus) exclusion affect feather moss (Pleurozium schreberi) depth, and the accompanying soil N dynamics (total and dissolvable inorganic N, δ15N), plant foliar N, and stable isotopes (δ15N, δ13C) in two contrasting habitats of an oligotrophic Scots pine forest. The study species were pine seedling (Pinus sylvestris L.), bilberry (Vaccinium myrtillus L.), lingonberry (V. vitis-idaea L.), and feather moss. Moss carpet was deeper in shaded than sunlit habitats and increased with grazer exclusion. Humus N content increased in the shade as did humus δ15N, which also increased due to exclusion in the sunlit habitats. Exclusion increased inorganic N concentration in the mineral soil. These soil responses were correlated with moss depth. Foliar chemistry varied due to habitat depending on species identity. Pine seedlings showed higher foliar N content and lower foliar δ15N in the shaded than in the sunlit habitats, while bilberry had both higher foliar N and δ15N in the shade. Thus, foliar δ15N values of co-existing species diverged in the shade indicating enhanced N partitioning. We conclude that despite strong grazing-induced shifts in mosses and subtler shifts in soil N, the N dynamics of vascular vegetation remain unchanged. These indicate that plant–soil interactions are resistant to shifts in grazing intensity, a pattern that appears to be common across boreal oligotrophic forests.

The Moss Biomonitoring Method and Neutron Activation Analysis in Assessing Pollution by Trace Elements in Selected Polish National Parks

The concentrations of trace elements in feather moss Pleurozium schreberi (Brid.) Mitt. were used to indicate the relative levels of air pollution by trace elements in Polish national parks. Pleurozium schreberi was collected from nine national parks. The highest concentrations were recorded in the moss samples from the southern and most industrialised part of the country; the lowest from northern and north-eastern Poland. A comparison of data obtained from Polish national parks in the 1970s and 1990s showed a significant decrease in the concentrations of heavy metals. In the linear covariability estimation, the t quantile approach was used for multi-element comparison. A number of positive covariabilities were observed. This is a result of anthropogenic activity and the geochemical characteristics of the local environment, including crust composition to which soil composition is related. The statistical approach of t quantile to study common relationships between element concentrations can be used in the interpretation of biomonitoring research results in similar studies.

Early response of biological nitrogen fixation in a mature oak dominated forest to elevated atmospheric CO2 fumigation at BIFoR-FACE

<p>Elevated atmospheric carbon dioxide concentrations are stimulating photosynthesis and carbon sequestration. However, the extent of photosynthetic stimulation in forests under future climates is highly uncertain given that nutrient limitation in soils may constrain the CO<sub>2</sub> fertilization effect. The Birmingham Institute of Forest Research (BIFoR), University of Birmingham established the only global mature temperate deciduous forests Free Air Carbon Dioxide Enrichment (FACE) experiment to study the response of forests to future climates. Fumigation of the forest with ~550 ppm CO<sub>2</sub> started in 2017 and will continue until at least 2026. Soil nutrients cycling including nitrogen transformation in response to elevated atmospheric CO<sub>2</sub> (eCO<sub>2</sub>) fumigation is currently investigated to determine the role of nutrient availability in carbon capture by forests. In this paper, we show preliminary results of the response of asymbiotic biological nitrogen fixation (BNF) in soils and epiphytic bryophytes at BIFoR-FACE following a year of eCO<sub>2</sub> fumigation. It is hypothesized that the demand for available nitrogen by trees will increase under eCO<sub>2</sub> and that competition of roots and soil microbes for available nitrogen will enhance asymbiotic BNF to at least meet microbial metabolic nitrogen demands in the long run. Surface soils (0-5 cm) and epiphytic feather moss (Hypnum cupressiforme) growing on oak tree stems in the FACE site were  collected during the second year of eCO<sub>2</sub> fumigation for the quantification of BNF activity using the <sup>15</sup>N<sub>2</sub> assimilation methods (Saiz et al. 2019). Samples were incubated in 50 mL serum bottles under in situ conditions, followed by the analysis of soil and tissue samples for <sup>15</sup>N signature on an Isotope Ratio Mass Spectrometer for the quantification of BNF activity.</p><p>The BNF activity under eCO<sub>2</sub> were 369% higher than in soils under ambient atmospheric CO<sub>2</sub>. BNF rates associated with feather mosses (Hypnum cupressiforme) did not differ between the eCO<sub>2</sub> and control plots; however, rates under eCO<sub>2</sub> on average were 60% lower than in the control plots. Unlike soils, the moisture of feather mosses correlated significantly (R<sup>2</sup> = 51%) with BNF activity. Among nutrients in soil with implications for BNF activity, the concentrations of Mg, K, Co and Ni were significantly lower in soils under eCO<sub>2</sub> than in the control plots, while in feather moss tissues no differences were observed.  Our preliminary results show that eCO<sub>2</sub> fumigation primed asymbiotic BNF activity in soils. An enhancement of BNF together with the observation of a relatively low nutrient content under eCO<sub>2</sub> points to important changes in nitrogen cycling processes in the early years of CO<sub>2</sub> fumigation. Further detailed studies are underway to fully disentangle controls on nitrogen availability to trees under future climates.</p><p><strong> </strong></p><p><strong>Reference</strong></p><p>Saiz, E, Sgouridis, F, Drifjhout, F & Ullah, S. 2019. Biological nitrogen fixation in peatlands: comparison between acetylene reduction assay and <sup>15</sup>N<sub>2</sub> assimilation methods. Soil Biol. Biochem:131:157-165</p>

Fuel characteristics, loads and consumption in Scots pine forests of central Siberia

Forest fuel investigations in central and southern Siberian taiga of Scots pine forest stands dominated by lichen and feather moss ground vegetation cover revealed that total aboveground biomass varied from 13.1 to 21.0 kg/m2. Stand biomass was higher in plots in the southern taiga, while ground fuel loads were higher in the central taiga. We developed equations for fuel biomass (both aerial and ground) that could be applicable to similar pine forest sites of Central Siberia. Fuel loading variability found among plots is related to the impact and recovery time since the last wildfire and the mosaic distribution of living vegetation. Fuel consumption due to surface fires of low to high-intensities ranged from 0.95 to 3.08 kg/m2, that is, 18–74% from prefire values. The total amount of fuels available to burn in case of fire was up to 4.5–6.5 kg/m2. Moisture content of fuels (litter, lichen, feather moss) was related to weather conditions characterized by the Russian Fire Danger Index (PV-1) and FWI code of the Canadian Forest Fire Weather Index System. The data obtained provide a strong foundation for understanding and modeling fire behavior, emissions, and fire effects on ecosystem processes and carbon stocks and could be used to improve existing global and regional models that incorporate biomass and fuel characteristics.