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In Arctic soils, warming accelerates decomposition of organic matter and increases emission of greenhouse gases (GHGs), contributing to a positive feedback to climate change. Although microorganisms play a key role in the processes between decomposition of organic matter and GHGs emission, the effects of warming on temporal responses of microbial activity are still elusive. In this study, treatments of warming and precipitation were conducted from 2012 to 2018 in Cambridge Bay, Canada. Soils of organic and mineral layers were collected monthly from June to September in 2018 and analyzed for extracellular enzyme activities and bacterial community structures. The activity of hydrolases was the highest in June and decreased thereafter over summer in both organic and mineral layers. Bacterial community structures changed gradually over summer, and the responses were distinct depending on soil layers and environmental factors; water content and soil temperature affected the shift of bacterial community structures in both layers, whereas bacterial abundance, dissolved organic carbon, and inorganic nitrogen did so in the organic layer only. The activity of hydrolases and bacterial community structures did not differ significantly among treatments but among months. Our results demonstrate that temporal variations may control extracellular enzyme activities and microbial community structure rather than the small effect of warming over a long period in high Arctic soil. Although the effects of the treatments on microbial activity were minor, our study provides insight that microbial activity may increase due to an increase in carbon availability, if the growing season is prolonged in the Arctic., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Arid ecosystems constitute 41% of land's surface and play an important role in global carbon cycle. In particular, biological soil crusts (BSC) are known to be a hotspot of carbon fixation as well as mineralization in arid ecosystems. However, little information is available on carbon decomposition and microbes in BSC and key controlling variables for microbial activities in arid ecosystems. The current study, carried out in South Mediterranean arid ecosystem, aimed to evaluate the effects of intact and removed cyanobacteria/lichen crusts on soil properties, soil enzyme activities, and microbial abundances (bacteria and fungi). We compared five different treatments (bare soil, soil with intact cyanobacteria, soil with cyanobacteria removed, soil with intact lichens, and soil with lichens removed) in four different soil layers (0-5, 5-10, 10-15, and 15-20 cm). Regardless of soil treatments, activities of hydrolases and water content increased with increasing soil depth. The presence of lichens increased significantly hydrolase activities, which appeared to be associated with greater organic matter, nitrogen, and water contents. However, phenol oxidase was mainly controlled by pH and oxygen availability. Neither fungal nor bacterial abundance exhibited a significant correlation with enzyme activities suggesting that soil enzyme activities are mainly controlled by edaphic and environmental conditions rather than source microbes. Interestingly, the presence of lichens reduced the abundance of bacteria of which mechanism is still to be investigated.

High and fluctuating salinity is characteristic for coastal salt marshes, which strongly affect the physiology of halophytes consequently resulting in changes in stable isotope distribution. The natural abundance of stable isotopes (δ 13 C and δ 15 N) of the halophyte plant Salicornia brachiata and physico-chemical characteristics of soils were analysed in order to investigate the relationship of stable isotope distribution in different populations in a growing period in the coastal area of Gujarat, India. Aboveground and belowground biomass of S. brachiata was collected from six different populations at five times (September 2014, November 2014, January 2015, March 2015 and May 2015). The δ 13 C values in aboveground (-30.8 to -23.6 ‰, average: -26.6 ± 0.4 ‰) and belowground biomass (-30.0 to -23.1 ‰, average: -26.3 ± 0.4 ‰) were similar. The δ 13 C values were positively correlated with soil salinity and Na concentration, and negatively correlated with soil mineral nitrogen. The δ 15 N values of aboveground (6.7-16.1 ‰, average: 9.6 ± 0.4 ‰) were comparatively higher than belowground biomass (5.4-13.2 ‰, average: 7.8 ± 0.3 ‰). The δ 15 N values were negatively correlated with soil available P. We conclude that the variation in δ 13 C values of S. brachiata was possibly caused by soil salinity (associated Na content) and N limitation which demonstrates the potential of δ 13 C as an indicator of stress in plants.