Annual growth and primary production of sphagnum in raised bog Mukhrino (four-year observations: 2019-2022)

The linear growth and primary production of Sphagnum is an important parameter for estimation of carbon balance of peatland ecosystems, given large areas these landscapes cover in the Western Siberia. Sphagnum represents the largest pull of biomass in raised bogs, which in anoxic conditions becomes peat, storing the preserved sources of carbon. Primary production estimates of different Sphagnum species are well studied globally, different authors studied many parameters of growth and production in natural and experimental conditions. The main parameters defining the growth and primary production are: the species biology, humidity, nutrient balance and photosynthetic radiation. Regional monitoring of carbon balance requires local estimates of Sphagnum linear growth and production, registered for specific regional species for a number of years, covering temporal and spatial dynamics. This was the scope of the monitoring program, initiated in Mukhrino field station of Yugra State University in middle taiga zone of Western Siberia 4 years ago.

To cover biological, spatial and temporal variability of Sphagnum linear growth and productivity, a series of permanent plots was established in Mukhrino field station in October 2018. The plots were located along the boardwalks of the station to protect the surface of peatland during permanent monitoring. Eight species of Sphagnum were chosen, each species was measured in 2-3 plots to cover spatial variation, totaling in 27 plots. Each plot contains about 20 markers established to measure growth of a particular species in an exact location. Two types of markers were used for upright-growing (“wire brush”) and side-growing (“individual ring”) species of Sphagnum. The markers were attached at the end of vegetation season (October) and were measured a year after (the exact dates of measurements were 09.10.2019, 17.10.2020, 09.10.2021 и 13.09.2022). Additionally, a sample of Sphagnum carpet 1 dm³ was extracted from each plot on the date of measurements for estimation of Sphagnum productivity (to calculate the dry weight of 1-cm shoots per 1 dm², which is then multiplied by a mean annual increment on this plot). To estimate the parameters of linear growth and production, we measured the water level below the surface and described vegetation composition on each plot. Part of plots were established under experimental warming conditions using Open Top Chambers which raised temperature on 1.5˚C on average. Climatic parameters were measured using an automatic weather station in the near proximity to the plots.

Totally 1574 measurements of Sphagnum linear growth increment and 200 estimates of Sphagnum primary production were made during the four-years period.           The collected data were organized in a dataset using Darwin Core standard and published through Global Biodiversity Information Facility to be Findable, Accessible, Interoperable and Reusable by any researcher or project in this discipline. The analytical tools (R scripts) which were applied for the analyses of these data were published in GitHub and could be accessed and reproduced. Additionally, we made a literature database to integrate data of Sphagnum linear growth from published sources and compare our data with the previous results.

The following results were estimated during the study. The linear growth increment of eight species of Sphagnum varied from 1.6 to 3 (mean between species 2.1) cm per year. The species in ascending order of annual growth: S. divum (1.6 cm per year), S. fuscum (1.7), S. capillifolium (1.7), S. papillosum (1.9), S. jensenii (2.7), S. angustifolium (3), S. majus (4.5 cm per year). The annual primary production varied from 1.2 to 3.7 (mean between species 2.3) g/dm². The species in ascending order of annual primary production: S. divum (1.2 g/dm² per year), S. papillosum (2.1), S. fuscum (2.1), S. jensenii (2.2), S. angustifolium (2.2), S. balticum (2.3), S. capillifolium (2.5), S. majus (3.7). There are statistically significant differences in annual growth increments and primary production between some species, while others are the same. The specific year has significant influence on growth increment and primary production on average for Sphagnum species, but different species have positive or negative impact. There is statistically significant correlation between bog water level and growth increment for four species: two species with positive impact and two species with negative impact. When averaged for two habitats (treed bogs and Sphagnum lawns), the annual growth increments statistically differ, while the primary production is the same. There wasn’t statistical effect of raised temperature (Open Top Chambers) on Sphagnum linear growth.

We used literature data to compare our estimates of linear growth increment and primary production with other studies. The statistical analysis proved some difference for three species, but in general our data confirm the global trends.

The following conclusions could be used in modelling of carbon stock in regional models of raised bog ecosystems: 1) there is statistical difference between mean growth increment and primary production of different species of Sphagnum; 2) the specific year weather parameters influence growth and production, based on interannual variation; 3) the averaged linear growth estimates of two habitats (treed bogs and Sphagnum lawns) differ significantly, but there wasn’t statistical difference for primary production between habitats; 4) the linear growth of some species could be influenced by water level, negatively or positively for different species; 5) the mean estimates of species-specific linear growth increment and primary production coincide with literature-based information and could be used in modelling of regional scenarios of carbon cycle.