Tue, Aug 03, 2021:On Demand
Background/Question/Methods
Root and mycorrhizal inputs to the soil system represent a dominant control on microbial activity and ultimately the fate of soil organic carbon (C). Due to the plastic and ephemeral nature of the fine root -mycorrhizal system, there exists the capacity for rapid plastic response to ecosystem change, with consequences for soil C allocation belowground due to shifts in C inputs from root-derived sources. The goal of this study was to determine how belowground C inputs, specifically from fine roots and mycorrhizal fungi, change in response to soil warming and N addition. Soil samples were collected from the Soil Warming x Nitrogen Addition Study at the Harvard Forests Long-term Ecological Research (LTER) site where replicate (n = 6) plots have been warmed (+5◦C above ambient soil temperature), fertilized (50 kg N m-2 yr-1 ) or both (warmed+N) for 15 years . Absorptive and transport fine roots were separated from the soil samples and assessed for biomass and mycorrhizal colonization. Soil C stocks were also measured.
Results/Conclusions Chronic warming decreased absorptive fine root biomass by only 16% but increased the ratio of absorptive to transport fine roots by 159% compared to the control treatment. Nitrogen (N) addition decreased absorptive root biomass by 28% but maintained similar levels of transport fine roots relative to the control. Soil warming + N addition decreased absorptive roots by 58%. Heat and N addition alone resulted in a 54% and 88% reduction in ECM colonization, respectively. Soil warming + N addition had no effect on ectomycorrhizal (ECM) colonization rates. Soil C stocks in the warmed alone and warmed+N plots were significantly reduced, while there was no effect of N addition. The results illuminate the tradeoffs that exists within the fine root system across the spectrum of soil warming and N addition. Soil warming maintains absorptive root tissues at the costs of transport fine roots and mycorrhizal associations, while roots in the warmed+N plots invest more heavily in mycorrhizal associations. The study highlights the need to integrate mycorrhizal metrics in determining the effect of ecosystem change on fine root systems and C allocation belowground.
Results/Conclusions Chronic warming decreased absorptive fine root biomass by only 16% but increased the ratio of absorptive to transport fine roots by 159% compared to the control treatment. Nitrogen (N) addition decreased absorptive root biomass by 28% but maintained similar levels of transport fine roots relative to the control. Soil warming + N addition decreased absorptive roots by 58%. Heat and N addition alone resulted in a 54% and 88% reduction in ECM colonization, respectively. Soil warming + N addition had no effect on ectomycorrhizal (ECM) colonization rates. Soil C stocks in the warmed alone and warmed+N plots were significantly reduced, while there was no effect of N addition. The results illuminate the tradeoffs that exists within the fine root system across the spectrum of soil warming and N addition. Soil warming maintains absorptive root tissues at the costs of transport fine roots and mycorrhizal associations, while roots in the warmed+N plots invest more heavily in mycorrhizal associations. The study highlights the need to integrate mycorrhizal metrics in determining the effect of ecosystem change on fine root systems and C allocation belowground.