At high elevations, tree saplings and shrubs are usually protected by mid-winter snow cover, although climate change is expected to extend the snow-free (SF) period. Exposure to winter drought, freeze-thaw events and freezing temperatures will therefore increase, inducing damages to the hydraulic system and to living cells, resulting in reduced growth and increased mortality. A snow removal experiment was carried out at 1700 m. above sea level on saplings of five different species (Acer pseudoplatanus, Juniperus communis, Larix decidua, Picea abies and Sorbus aucuparia). Stem diameter was continuously monitored and compared with spring hydraulic conductivity (PLCspring), living cell mortality (PLDspring), nonstructural carbohydrates (NSCs), growth and survival rates. Under SF conditions, saplings had higher PLCspring and higher PLDspring, and thus experienced greater winter dehydration, resulting in lower growth compared with snow-covered saplings. Summer mortality was strongly correlated with PLCspring and PLDspring. These two key ecophysiological parameters predicted the risk of mortality in all species, whereas only PLDspring reduced growth. By monitoring stem diameter during winter, we have defined indices to quantify resistance and recovery of woody plants under increased frost pressure. Recovery strategies such as resprouting or embolism repair were critical for survival, highlighting the potential vulnerability of saplings to climate change at high elevations.

High latitude regions are experiencing considerable winter climate change, and reduced snowpack will likely affect soil microbial communities and their function, ultimately altering microbial-mediated biogeochemical cycles. However, the current knowledge on the responses of soil microorganisms to snow cover changes in permafrost ecosystems remains limited. Here, we conducted a 2-year (six periods) snow manipulation experi-ment comprising ambient snow and snow removal treatments with three replications of each treatment to explore the immediate and legacy effects of snow removal on soil bacterial community and enzyme activity in secondary Betala platyphylla forests in the permafrost region of the Daxing'an Mountains. Generally, bacterial community diversity was not particularly sensitive to the snow removal. Seasonal fluctuations in the relative abundance of dominated bacterial taxa were observed, but snow removal merely exerted a significant impact on the bacterial community structure during the snow melting period and early vegetation growing season within two consecutive years, with a reduction in the relative abundance of Chloroflexi and an increase in the relative abundance of Actinobacteria, and no evidence of cross-season legacy effects was found. Moreover, snow removal significantly altered the soil enzyme activities in the snow stabilization period and snow melting period, with an increase in soil acid phosphatase (ACP) activity of snow melting period and a decrease in polyphenol oxidase (PPO) activity of snow stabilization period as well as beta-glucosidase (BG) activity of snow stabilization period and snow melting period, but this effect did not persist into the vegetation growing periods. The seasonal variations in bacterial community and enzyme activity were mostly driven by changes in soil nutrient availability. Overall, our results suggest that soil bacterial communities have rather high resilience and rapid adaptability to snow cover changes in the forest ecosystems in the cold region of the Daxing'an Mountains.

The continuing warming of the climate system is reducing snow cover depth and duration worldwide. Changes in snow cover can significantly affect the soil microclimate and the functioning of many terrestrial ecosystems across latitudinal and elevational gradients. Yet, a quantitative assessment of the effects of snow cover change on soil physicochemical and biotic properties at large or regional scales is lacking. Here, we synthesized data of 3286 observations from 99 publications of snow manipulation studies to evaluate the effects of snow removal, addition, and compaction on soil physicochemical and biotic properties in winter and in the following growing season across (sub)arctic, boreal, temperate, and alpine regions. We found that (1) snow removal significantly reduced soil temperature by 2.2 and 0.9 degrees C in winter and in the growing season, respectively, while snow addition increased soil temperature in winter by 2.7 degrees C but only by 0.4 degrees C in the following growing season whereas snow compaction had no effect; (2) snow removal had limited effects on soil properties in winter but significantly affected soil moisture, pH, and carbon (C) and nitrogen (N) dynamics in the growing season; (3) snow addition had significant effects on soil properties both in winter (e.g., increases in soil moisture, soil C and N dynamics, phosphorus availability, and microbial biomass C and N) and in the growing season (e.g., increases in mineral N, microbial biomass C and N, and enzyme activities); and (4) the effects of snow manipulation on soil properties were regulated by moderator variables such as ecosystem type, snow depth, latitude, elevation, climate, and experimental duration. Overall, our results highlight the importance of snow cover-induced warmer microclimate in regulating soil physicochemical and biotic properties at regional scales. These findings are important for predicting and managing changes in snow-covered ecosystems under future climate change scenarios.