Priming effects in the rhizosphere and root detritusphere of two wet-grassland graminoids

Aims: The rhizosphere and root detritusphere are hotspots of microbial activity, where root-derived inputs induce intensive priming effects (PE) on soil organic carbon (SOC) decomposition. These conditions for induced PE differ between rhizosphere and detritusphere and are modified by plant traits. Methods: Continuous labelling with 13C-depleted CO2 allowed for the partitioning of plant and soil C sources of CO2 efflux and the investigation of the PE in the rhizosphere and detritusphere of slow-growing conservative Carex acuta and fast-growing acquisitive Glyceria maxima. Results: Glyceria allocated more C into the soil, induced higher microbial activity and a larger portion of active microorganisms, and depleted mineral N stronger than Carex. Its rhizosphere PE was 2.5 times stronger than that of Carex. Root residues (detritusphere) induced negative PE at the early stage of decomposition (1–9 months). The depletion of available organic substances in the detritusphere of more easily decomposable Glyceria roots resulted in positive PE after 3 months. The PE in the detritusphere of N-poorer Carex roots was more intensive but started after 9 months. Conclusions: The rhizosphere PE was positive and stronger than the detritusphere PE, which switched from initially negative to positive PE after depletion of available substances during few months. More productive species with faster N-uptake and higher belowground C input (here Glyceria) induce larger rhizosphere PE than slower-growing species (here Carex). The N-rich Glyceria roots decompose faster than N-poor roots of Carex and, consequently, have a lower impact on SOC dynamics and induced a smaller positive detritusphere PE. Graphic abstract: [Figure not available: see fulltext.

Priming effects in the rhizosphere and root detritusphere of two wet-grassland graminoids

Aims: The rhizosphere and root detritusphere are hotspots of microbial activity, where root-derived inputs induce intensive priming effects (PE) on soil organic carbon (SOC) decomposition. These conditions for induced PE differ between rhizosphere and detritusphere and are modified by plant traits. Methods: Continuous labelling with 13C-depleted CO2 allowed for the partitioning of plant and soil C sources of CO2 efflux and the investigation of the PE in the rhizosphere and detritusphere of slow-growing conservative Carex acuta and fast-growing acquisitive Glyceria maxima. Results: Glyceria allocated more C into the soil, induced higher microbial activity and a larger portion of active microorganisms, and depleted mineral N stronger than Carex. Its rhizosphere PE was 2.5 times stronger than that of Carex. Root residues (detritusphere) induced negative PE at the early stage of decomposition (1–9 months). The depletion of available organic substances in the detritusphere of more easily decomposable Glyceria roots resulted in positive PE after 3 months. The PE in the detritusphere of N-poorer Carex roots was more intensive but started after 9 months. Conclusions: The rhizosphere PE was positive and stronger than the detritusphere PE, which switched from initially negative to positive PE after depletion of available substances during few months. More productive species with faster N-uptake and higher belowground C input (here Glyceria) induce larger rhizosphere PE than slower-growing species (here Carex). The N-rich Glyceria roots decompose faster than N-poor roots of Carex and, consequently, have a lower impact on SOC dynamics and induced a smaller positive detritusphere PE. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG

Short term effects of experimental eutrophication on carbon and nitrogen cycling in two types of wet grassland

Plant biomass production, soil chemical and microbial parameters, microbial processes of C and N cycle and gases emissions were studied in soils at two types of grasslands (wet meadows). Both sites are situated in the Czech Republic: (1) a nutrient poor sedge meadow on organic soil (Z) and (2) a mesotrophic sedge-sweet grass meadow on mineral soil (H). Eutrophication was simulated by the application of NPK fertilizer to selected permanent plots in 2006 and 2007 in amounts of 9 kg N + 4 kg P ha-1 year-1 (low dose) and 45 kg N + 20 kg P ha- year- (high dose). After two years of fertilizer application, we observed an increase in net aboveground plant production (about 9–12 kg ha-1 year- ) connected with an increase in shoot:root ratio in fertilized plots of both sites, with more pronounced changes in oligotrophic sedge meadow. Total CO2 efflux from the ecosystem measured in situ was significantly higher at fertilized plots as well as increase in total soil respiration in case of sedge meadow, but we found no significant effect of fertilization on CO2 efflux from the system at mesotrophic site. Surprisingly, other parameters, like soil microbial biomass C and N content, the rates of respiration, denitrification, nitrification, nitrogen mineralization and nitrogen assimilation were not affected by fertilization. In conclusion, an interesting finding is that despite non significant impact on aboveground component there were significant responses in belowground part which suggest that belowground processes may be suitable early warning signals. Peaty oligotrophic soil seems to be more sensitive to nutrient addition than mineral soil. However, final effect of fertilization on ecosystem C balance stays unknown and longer study is necessary to draw explicit conclusion

Soil microbial biomass, activity and community composition along altitudinal gradients in the High Arctic (Billefjorden, Svalbard)

The unique and fragile High Arctic ecosystems are vulnerable to global climate warming. The elucidation of factors driving microbial distribution and activity in arctic soils is essential for a comprehensive understanding of ecosystem functioning and its response to environmental change. The goals of this study were to investigate microbial biomass and activity, microbial community structure (MCS), and their environmental controls in soils along three elevational transects in the coastal mountains of Billefjorden, central Svalbard. Soils from four different altitudes (25, 275, 525 and 765 m above sea level) were analyzed for a suite of characteristics including temperature regimes, organic matter content, base cation availability, moisture, pH, potential respiration, and microbial biomass and community structure using phospholipid fatty acids (PLFAs). We observed significant spatial heterogeneity of edaphic properties among transects, resulting in transect-specific effects of altitude on most soil parameters. We did not observe any clear elevation pattern in microbial biomass, and microbial activity revealed contrasting elevational patterns between transects. We found relatively large horizontal variability in MCS (i.e., between sites of corresponding elevation in different transects), mainly due to differences in the composition of bacterial PLFAs, but also a systematic altitudinal shift in MCS related to different habitat preferences of fungi and bacteria, which resulted in high fungi-to-bacteria ratios at the most elevated sites. The biological soil crusts on these most elevated, unvegetated sites can host microbial assemblages of a size and activity comparable to those of the arctic tundra ecosystem. The key environmental factors determining horizontal and vertical changes in soil microbial properties were soil pH, organic carbon content, soil moisture and Mg2+ availability

A plant–microbe interaction framework explaining nutrient effects on primary production

In most terrestrial ecosystems, plant growth is limited by nitrogen and phosphorus. Adding either nutrient to soil usually affects primary production, but their effects can be positive or negative. Here we provide a general stoichiometric framework for interpreting these contrasting effects. First, we identify nitrogen and phosphorus limitations on plants and soil microorganisms using their respective nitrogen to phosphorus critical ratios. Second, we use these ratios to show how soil microorganisms mediate the response of primary production to limiting and non-limiting nutrient addition along a wide gradient of soil nutrient availability. Using a meta-analysis of 51 factorial nitrogen–phosphorus fertilization experiments conducted across multiple ecosystems, we demonstrate that the response of primary production to nitrogen and phosphorus additions is accurately predicted by our stoichiometric framework. The only pattern that could not be predicted by our original framework suggests that nitrogen has not only a structural function in growing organisms, but also a key role in promoting plant and microbial nutrient acquisition. We conclude that this stoichiometric framework offers the most parsimonious way to interpret contrasting and, until now, unresolved responses of primary production to nutrient addition in terrestrial ecosystems