Mycorrhizal fungi respiration dynamics in relation to gross primary production in a Hungarian dry grassland

Soil respiration (R_s) is a complex process including a wide range of soil biota and pathways of carbon cycling, all being under the control of various drivers. The most important biotic driver is the photosynthetic activity of the vegetation providing supply mainly for the autotrophic component of R_s: roots and their symbiotic partners. The objective of this study was to describe the time-lagged relationship between gross primary production (GPP) and the mycorrhizal R_s component in order to determine the amount of carbon derived from GPP appearing as mycorrhizal respiration (R_myc).

Measurements of R_s were conducted in three treatments - (i) undisturbed, root and arbuscular mycorrhizal fungi (AMF)-included (R_s), (ii) root-excluded (R_het+myc) and (iii) root- and AMF-excluded (R_het) plots - for three consecutive years in a Central-Hungarian dry sandy grassland. GPP data were derived from eddy-covariance measurements, while an automated system was used for continuous measurements of R_s. We analysed the relationship between R_myc and GPP by using cross-correlation and by fitting sine wave models on the diel datasets.

GPP was found to be the main driver of R_myc, responding with an average time lag of 18 h. The greatest lags were detected during periods characterized by minimal photosynthetic activity, while lags were the smallest during active periods.

Based on the seasonal changes in the delay, we concluded that GPP and soil temperature had simultaneous effects on the diel pattern of CO₂ emission of the different autotrophic components depending on the vegetation activity and environmental conditions.