Temporal patterns of carbon flow from grassland vegetation to soil microorganisms measured using 13C-labelling and signature fatty acids

Abstract

Purpose We investigated how the C flow from plants to microorganisms varies throughout the year in a temperate grassland. Additionally, we investigated how the C flow relates to saprotrophic activity and vegetation changes. Methods In situ stable isotope pulse labelling (13CO2) was employed to estimate the flow of recently plant-derived C to soil microorganisms by using signature fatty acids. Bacterial and fungal growth was estimated using radio-labelling in laboratory incubations. Results The C flow from plants to arbuscular mycorrhizal (AM) fungi peaked during the warmer parts of the year, but saprotrophic microorganisms showed little temporal variation in C flow. Also saprotrophic fungi received considerable amounts of C from plants throughout the year. Bacterial and fungal growth showed temporal variation with a growth peak in August for both. This suggests a shift in the C source from mainly rhizosphere C in colder parts of the year, to older C-sources in warmer parts of the year (August). Conclusion We conclude that AM fungi, saprotrophic fungi and bacteria differ in the amount of recently-fixed C they receive from plants throughout the year. Hence, temporal patterns need to be considered to understand ecosystem functioning. The studied plant community included winter annuals, which potentially maintain a high C flow to saprotrophic fungi during the cold season.

Above- and below-ground responses to grazing in alpine grasslands: insights from carbon allocation and dynamic in plant-soil-microbe system

“…Reference source not found.). This finding was supported by Birgander and Olsson (2021), who reported that the PLFA-13 C content in soil organic matter derived from saprophytic fungi was approximately six times higher than that derived from bacteria, indicating the superior ability of saprophytic fungi to acquire plant-derived C. Regarding grazing intensity, the value PLFA-13 C in SAP under HG was apparently higher than under MG and NG on the 60 th sampling day (Fig. 2B), probably driven by substantial root mortality caused by HG, which in turn triggered a significant proliferation of rhizosphere saprophytic fungi.…”

“…Previous studies revealed that when considering the combination of PLFA relative abundance and 13 C enrichment ( 13 CCr), 13 CCr enabled better quantified the activity of soil microbes (Paterson et al, 2009;Balasooriya et al, 2013;Balasooriya et al, 2014;Balasooriya et al, 2016). Although the most previous studies had been proved that there were temporal patterns of rhizodeposit-C assimilating microbial communities in temperate ecosystems (Birgander and Olsson, 2021), in natural wetland (Balasooriya et al, 2013) and also in tropical paddy fields (Balasooriya et al, 2016), our studies found that different variations in soil microbial groups in alpine grassland (Fig. 3).…”

“…The methods for extracted lipids were based on Balasooriya et al (2014). The procedures for detection and analysis of PLFA and PLFA-13 C were based on Frostegård et al (1993) and Birgander and Olsson (2021). Additionally, we classified the soil microbial PLFAs into five functional groups depending on the number of carbons, the number of double bonds, and the position of the configuration: arbuscular mycorrhizal fungi (AMF), saprotrophic fungi (SAP), actinomycetes (Act), gram-positive bacteria (Gram (+)), and gramnegative bacteria (Gram (-)), based on Tang et al (2021).…”

“…2B), probably driven by substantial root mortality caused by HG, which in turn triggered a significant proliferation of rhizosphere saprophytic fungi. Meanwhile, a potential association exists between the PLFA indicator of saprophytic fungi and its commonality among ascomycetes and basidiomycetes (Birgander and Olsson, 2021). Unlike AMF and SAP, bacteria [Act and Gram (+)] exhibited persistent fluctuations in response to MG and HG (Fig.…”

“…Consequently, grazing activities directly or indirectly impact the rhizosphere deposition process of microorganisms by altering the partitioning of photosynthetic C in roots through the intake of the above-ground portion of plants (Zhang et al, 2022;Zhao et al, 2022). However, the effects of grazing activity on the short-term C cycling linkages between the plants above-ground portion and microorganisms participating in the rhizosphere are often overlooked in many experiments, primarily due to the rapid response of microorganisms to rhizosphere deposition (Birgander and Olsson, 2021).…”