Cyanobacterial- and moss-forming biocrusts consistently decrease the temperature sensitivity of microbial respiration along a continental precipitation gradient

Biocrusts are prevalent and participate in many soil organic carbon (C) processes in drylands. The predicted increase in aridity will expand the biocrust cover and significantly impact soil organic C dynamics. However, how biocrusts change soil organic C decomposition and what factors drive the effect in response to climate warming remains largely unknown at a continental scale. We measured microbial respiration and its temperature sensitivity (Q(10)) in bare soil lacking biocrusts and two universal biocrusted soils (cyanobacterial- and moss-crusted soil) from 43 sites across a precipitation gradient from 39 to 443 mm to evaluate the relative effects of biocrusts on Q(10) and the driving forces in northern China's dryland. Microbial respiration increased and Q(10) decreased with increasing precipitation in bare soil, cyanobacterial- and moss-crusted soil. Biocrusts positively affected microbial respiration, with a more substantial magnitude by moss crusts than cyanobacterial crusts. Biocrusts negatively impacted Q(10), and the magnitudes were similar between moss and cyanobacterial crusts. Most importantly, the relative effects of biocrusts on microbial respiration and Q(10) increased with decreasing precipitation. The positive effects of biocrusts on soil organic C content and microbial biomass carbon were positively correlated with the level of increased microbial respiration. Contrastingly, the magnitude of reduced Q(10) was attributed to the biocrusts' positive effects on soil organic C quality and adverse effects on the ratio of fungal to bacterial PLFAs (F:B). Our study provides strong evidence that biocrusts decrease the temperature sensitivity of microbial respiration in northern China's dryland. This result suggests that the predicted expanding biocrust cover is crucial for maintaining the soil organic C stability by buffering the positive impacts of climate warming on soil organic C decomposition in drylands. Read the free Plain Language Summary for this article on the Journal blog.

Automated summary

Biocrusts play a significant role in soil organic carbon processes in drylands, and the predicted increase in aridity will impact soil organic carbon dynamics. In this study, microbial respiration and its temperature sensitivity were measured in bare soil and two types of biocrusted soils in northern China's dryland. The results showed that biocrusts positively influenced microbial respiration and had a negative impact on the temperature sensitivity, which increased with decreasing precipitation. These findings highlight the importance of expanding biocrust cover in maintaining soil organic carbon stability in response to climate warming.