Dependence of mycorrhizal respiration on soil moisture, soil temperature and gross primary productivity in a dry grassland

Despite the growing recognition of arbuscular mycorrhizal fungi as key players in the carbon cycle, their independent contribution to soil respiration (R_s) under varying seasonal conditions is still not completely understood. Here, we explore how seasonal variation of soil moisture, soil temperature and gross primary productivity (GPP) influence mycorrhizal respiration (R_myc) in a temperate grassland.

Soil respiration components were separated using root exclusion method. Gas exchange measurements were performed by a chamber based automated R_s system and an eddy covariance flux tower in two consecutive years (2023 and 2024). Additional soil sampling and analyses were conducted for the estimation of mycorrhizal abundance (hyphal length, PLFA, NLFA).

The two complete study years were characterized by contrasting environmental conditions, which allowed us to monitor interannual differences. GPP exhibited strong seasonal variations reflecting vegetation phenology, with notable differences between the two years. R_s data varied largely in accordance with GPP. The partitioned soil respiration components followed the seasonal dynamics of plant activity, with peaks occurring in the growing season.

The overall sensitivity of R_myc to drivers differed according to the year effect. In 2023, GPP had a strong linear effect on R_myc, but soil temperature and soil moisture greatly influenced the strength of this relationship. On the other hand, in the dry year (2024), GPP had much smaller effect on R_myc and instead, soil temperature and soil moisture proved to be the main drivers.

In conclusion, based on data from the unbiased year, interannual variation in R_myc sensitivity arises mainly from changes in carbon supply rather than soil temperature and soil moisture. It is also clear that these relationships are co-dependent and greatly affect each other.