Towards moss-dominated biocrust effects on soil temperature across seasons in drylands: Insight from continuous measurements of soil thermal properties and solar radiation

• Biocrusts increase heat capacity by 2% in wet term but decrease it by 6% in dry term. • Moss crusts increase soil moisture by 500% due to their higher water-holding capacity. • Biocrusts reduce soil heat flux by 20%, verifying their effects on thermal properties. • Biocrusts decrease surface albedo by 32% and increase net solar radiation by 30% • Higher soil moisture and lower surface albedo are keys to raise biocrust temperature. Globally widespread, biocrusts form a “living skin” on most dryland soils, helping govern fundamental ecosystem functions, particularly water and heat balances in drylands. Nevertheless, the underlying mechanisms of biocrust effects on topsoil thermal properties and temperature ( T ) are still unclear. In this study, we continuously measured thermal properties of moss-dominated biocrusts and bare soil (aeolian sand) at 1 cm depth by utilizing heat pulse probes for one year on the Chinese Loess Plateau. The surface soil water content ( θ ), net all-wave radiation ( J n ), surface albedo ( α ), heat flux ( G ), and other properties were further measured to analyze their connections with soil thermal properties. Our results indicated that biocrusts decreased ( F ≥ 1.91, P ≤ 0.031) heat capacity ( C ), thermal conductivity ( λ ), and thermal diffusivity ( κ ) by 1.6% (1.36 vs. 1.38 MJ m −3 K −1 ), 11.6% (0.62 vs. 0.69 W m −1 K −1 ), and 8.7% (0.62 vs. 0.69 × 10 −7 m 2 s −1 ) on average, respectively, in contrast to bare soil. Moreover, biocrusts variously regulated soil thermal properties in dry and wet seasons owing to the influences of rainfall events and θ . As compared with bare soil, the C , λ , and κ of biocrusts in dry season (Nov.–Apr.) were decreased by 5.7%, 19.0%, and 12.2%, respectively; while only the C was increased by 2.2% by biocrusts in wet season, but the λ and κ of biocrusts were similar to that of bare soil. Furthermore, biocrusts increased θ both in dry (by 5.0 times) and wet (by 3.5 times) seasons as compared with bare soil. Especially, biocrusts decreased α by 32.1% (0.19 vs. 0.28) and G (at 8 cm depth) by 20.0% (0.8 vs. 1.0 W m −2 s −1 ), and increased J n by 30.1% (73.0 vs. 56.1 W m −2 ) in comparison to bare soil. Lastly, combining with the higher θ and lower α as well as the lower soil thermal properties, biocrusts greatly increased T by 1.7 ℃ (up to 4.5 °C; P < 0.001) on average. In conclusion, moss-dominated biocrusts have great regulating effects on surface soil thermal properties and T , and these effects are mostly attributed to their lower bulk density and α but higher porosity and water-holding capacity, which further change surface θ and T regimes and play a vital role in soil water and heat balances as well as other critical processes in drylands.