The sulfate-bearing strata on Mars must have recorded rich information of its aqueous history. However, the hydrated sulfates observed in the surface thin layer by remote sensing, especially widespread kieserite, are likely weathering products rather than pristine deposits. Here we report the results from mineralogical investigations and environmental monitoring on the sulfate-bearing Dalangtan Playa (an analog site with Mars-like environmental conditions in northern Tibetan Plateau) to examine the depositional and secondary processes of hydrated sulfates. The regional deposition characters of DLT Playa were described based on our mineralogical results. Widespread kieserite was identified in situ by portable laser Raman spectrometer on the weathered surface of the Mg-sulfates-rich section, which formed from the hexahydrite dehydration after exposed to the ambient conditions in six months covering the summer, and survived in the winter. During summer days, wind and sunlight may have facilitated the dehydration process, leading the formation of kieserite from dehydration. On the basis of the observed kieserite formation, the recorded local environment conditions, as well as previously reported phase diagrams for Mg-sulfates, we suggest that the current diurnal relative humidity-temperature circles at low latitudes of Mars favor the formation of kieserite through secondary processes.
Afforestation is an effective approach to rehabilitate degraded ecosystems, but often depletes deep soil moisture. Presently, it is not known how an afforestation‐induced decrease in moisture affects soil microbial community and functionality, hindering our ability to understand the sustainability of the rehabilitated ecosystems. To address this issue, we examined the impacts of 20 years of afforestation on soil bacterial community, co‐occurrence pattern, and functionalities along vertical profile (0–500 cm depth) in a semiarid region of China's Loess Plateau. We showed that the effects of afforestation with a deep‐rooted legume tree on cropland were greater in deep than that of in top layers, resulting in decreased bacterial beta diversity, more responsive bacterial taxa and functional groups, increased homogeneous selection, and decreased network robustness in deep soils (120–500 cm). Organic carbon and nitrogen decomposition rates and multifunctionality also significantly decreased by afforestation, and microbial carbon limitation significantly increased in deep soils. Moreover, changes in microbial community and functionality in deep layer was largely related to changes in soil moisture. Such negative impacts on deep soils should be fully considered for assessing afforestation's eco‐environment effects and for the sustainability of ecosystems because deep soils have important influence on forest ecosystems in semiarid and arid climates.
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