Abstract
The role of soil microbial variables in shaping the temporal variability of soil respiration has been well acknowledged but is poorly understood, particularly under elevated nitrogen (N) deposition conditions. We measured soil respiration along with soil microbial properties during the early, middle, and late growing seasons in temperate grassland plots that had been treated with N additions of 0, 2, 4, 8, 16, or 32 g N m−2 yr−1 for 10 years. Representing the averages over three observation periods, total (Rs) and heterotrophic (Rh) respiration were highest with 4 g N m−2 yr−1, but autotrophic respiration (Ra) was highest with 8 to 16 g N m−2 yr−1. Also, the responses of Rh and Ra were unsynchronized considering the periods separately. N addition had no significant impact on the temperature sensitivity (Q10) for Rs but inhibited the Q10 for Rh. Significant interactions between observation period and N level occurred in soil respiration components, and the temporal variations in soil respiration components were mostly associated with changes in microbial biomass carbon (MBC) and phospholipid fatty acids (PLFAs). Further observation on soil organic carbon and root biomass is needed to reveal the long-term effect of N deposition on soil C sequestration.
Highlights
The role of soil microbial variables in shaping the temporal variability of soil respiration has been well acknowledged but is poorly understood, under elevated nitrogen (N) deposition conditions
Significant interactions between observation period and N level occurred in soil respiration components, and the temporal variations in soil respiration components were mostly associated with changes in microbial biomass carbon (MBC) and phospholipid fatty acids (PLFAs)
Soil autotrophic respiration (Ra) and heterotrophic respiration (Rh) have been found to be positively correlated with N addition with increased fine root biomass[4,5], increased litter input[6], and the priming effect resulting from the input of labile C substrates[7], while researchers have reported that soil respiration components are negatively correlated with N addition with reduced belowground C allocation, mycorrhizal hyphae[4], microbial biomass[8] and phenol oxidase concentration[9]
Summary
The role of soil microbial variables in shaping the temporal variability of soil respiration has been well acknowledged but is poorly understood, under elevated nitrogen (N) deposition conditions. N addition had no significant impact on the temperature sensitivity (Q10) for Rs but inhibited the Q10 for Rh. Significant interactions between observation period and N level occurred in soil respiration components, and the temporal variations in soil respiration components were mostly associated with changes in microbial biomass carbon (MBC) and phospholipid fatty acids (PLFAs). Soil autotrophic respiration (Ra) and heterotrophic respiration (Rh) have been found to be positively correlated with N addition with increased fine root biomass[4,5], increased litter input[6], and the priming effect resulting from the input of labile C substrates[7], while researchers have reported that soil respiration components are negatively correlated with N addition with reduced belowground C allocation, mycorrhizal hyphae[4], microbial biomass[8] and phenol oxidase concentration[9]. Previous studies have measured the respiration rate only between 08:00 and 11:00 hours during the day, and the experimental N addition gradients were insufficient[16,17]; actual or potential changes in soil respiration in response to N addition may have been misjudged
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