Snow amounts and duration are susceptible to climate change and may significantly affect plant diversity and biomass in grassland ecosystems. Yet, the combined effects of grassland use (type and intensity) and snow depth on plant diversity and productivity remain poorly understood. We established two complementary field experiments to explore the mechanisms driving the effects of grassland use (type and intensity) and snow manipulation on plant diversity and productivity in the meadow steppe. An experiment on grassland use type and snow manipulation showed that lower snow cover in winter reduced soil moisture in the snowmelt period, significantly increased the abundance of ammonia-oxidizing archaea and ammonia-oxidizing bacteria, and initiated nitrification earlier, resulting in the loss of soil available nitrogen, and then reduced the aboveground biomass of early grasses. An experiment on grassland mowing intensity and snow manipulation showed that moderate mowing intensity can restrain the loss of grass biomass and soil nutrients and maintain grassland sustainability in winters with less snow. Stochasticity has played a more important role in plant community assembly in higher intensity of grassland use. Based on our results, we recommend that optimal defoliation height can restrain the loss of grass biomass and soil nutrients and maintain grassland sustainability in winters with less snow. This study has potential benefits for optimizing sustainable production and maintaining ecosystem function under winter snowfall changes in the future across large regions of arid and semiarid grasslands. (c) 2024 The Society for Range Management. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

AimsIn this study, we investigated the effects of reduced snow depth on plant phenology, productivity, nitrogen (N) cycling, and N use in canopy and understory vegetation. We hypothesized that decreased snow depth would hasten the timing of leaf flushing and N uptake in understory vegetation, increasing its N competitive advantage over canopy trees.ResultsSnow removal did not directly affect the phenology of either canopy or understory vegetation. Understory vegetation took up more N in the snow removal plots than in the control plots, particularly in the mid- to late-growing season. Leaf production and N uptake in canopy trees also did not differ between the control and snow removal plots, but N resorption efficiency in the snow removal plots (57.6%) was significantly higher than those in control plots (50.0%).ConclusionsIncreased N uptake by understory plants may induce N limitation in canopy trees, which in turn may cause canopy trees to increase their N use efficiency. Such competitive advantage of understory vegetation over canopy trees against snow reduction may affect N cycling via litter quality and quantity not only just after the growing season but also in subsequent seasons.

Recent global warming models project a significant change in winter climate over the next few decades. The decrease in snowpack in the winter will decrease the heat insulation function of the snowpack, resulting in increased soil freeze-thaw cycles. Here, we examined the impact of winter freeze-thaw cycles on year-round dissolved nitrogen (N) and carbon (C) dynamics and their relationship with dissolved organic matter and microbial biomass in soil by conducting an in situ experimental reduction in snowpack. We investigated dissolved inorganic N (NH4+ and NO3-), dissolved organic N (DON), dissolved organic carbon (DOC), inorganic N leaching, soil microbial biomass, and microbial activities (mineralization and nitrification) in the surface soil of a northern hardwood forest located in Japan. Experimental snowpack reduction significantly increased the number of soil freeze-thaw cycles and soil frost depth. The NH4+ content of the surface soil was significantly increased by the amplified soil freeze-thaw cycles due to decreased snowpack, while the soil NO3- content was unchanged or decreased slightly. The gravimetric soil moisture, DON and DOC contents in soil and soil microbial biomass significantly increased by the snowpack removal in winter. Our results suggest that the amplified freeze-thaw cycles in soil increase the availability of DON and DOC for soil microbes due to an increase in soil freezing. The increases in both DON and DOC in winter contributed to the enhanced growth of soil microbes, resulting in the increased availability of NH4+ in winter from net mineralization following an increase in soil freeze-thaw cycles. Our study clearly indicated that snow reduction significantly increased the availability of dissolved nitrogen and carbon during winter, caused by increased soil water content due to freeze-thaw cycles in winter.

Decomposition is a key process in carbon and nutrient cycling. However, little is known about its response to altered winter soil temperature regimes in boreal forests. Here, the impact of soil frost on cellulose decomposition over 1 yr and soil biotic activity (bait-lamina sticks) over winter, in spring, and in summer was investigated using a long-term (9-yr) snow-cover manipulation experiment in a boreal Picea abies forest. The experiment consisted of the treatments: snow removal, increased insulation, and ambient control. The snow removal treatment caused longer and deeper soil frost (minimum temperature - 8.6 degrees C versus - 1.4 degrees C) at 10 cm soil depth in comparison with control, while the increased insulation treatment resulted in nearly no soil frost during winter. Annual cellulose decomposition rates were reduced by 46% in the snow removal manipulation in comparison with control conditions. Increased insulation had no significant effect on decomposition. The decomposition was mainly driven by microorganisms, as no significant difference was observed for containers enclosed with a 44-mu m and a 1-mm mesh. Soil biotic activity was slightly increased by both the snow removal and the increased insulation treatment in comparison with control conditions over winter. However, this effect disappeared over spring and summer. We conclude that soil frost can have strong effects on decomposition in boreal ecosystems. Further studies should investigate to which degree the observed reduction in decomposition due to reduced snow cover in winter slows or even offsets the expected increase in decomposition rates with global warming.

Snow regimes affect biogeochemistry of boreal ecosystems and are altered by climate change. The effects on plant communities, however, are largely unexplored despite their influence on relevant processes. Here, the impact of snow cover on understory community composition and below-ground production in a boreal Picea abies forest was investigated using a long-term (8-year) snow cover manipulation experiment consisting of the treatments: snow removal, increased insulation (styrofoam pellets), and control. The snow removal treatment caused longer (118 vs. 57 days) and deeper soil frost (mean minimum temperature -5.5 vs. -2.2 degrees C) at 10 cm soil depth in comparison to control. Understory species composition was strongly altered by the snow cover manipulations; vegetation cover declined by more than 50% in the snow removal treatment. In particular, the dominant dwarf shrub Vaccinium myrtillus (-82%) and the most abundant mosses Pleurozium schreberi (-74%) and Dicranum scoparium (-60%) declined strongly. The C:N ratio in V. myrtillus leaves and plant available N in the soil indicated no altered nitrogen nutrition. Fine-root biomass in summer, however, was negatively affected by the reduced snow cover (-50%). Observed effects are attributed to direct frost damage of roots and/or shoots. Besides the obvious relevance of winter processes on plant ecology and distribution, we propose that shifts in the vegetation caused by frost damage may be an important driver of the reported alterations in biogeochemistry in response to altered snow cover. Understory plant performance clearly needs to be considered in the biogeochemistry of boreal systems in the face of climate change.

Current climate models are effective at projecting trends in mean winter temperature; however, other ecologically relevant parameters-such as snow cover and soil frost dynamics-are less well investigated. Changes in these parameters are expected to have strong ecological implications, especially in the temperate zone, where it is uncertain whether snow and soil frost will occur with regularity in the future. We explored trends in days with snow on the ground (snowdays), minimum soil temperature (MST), and number of soil freeze/thaw cycles (FTCs, i.e. changes in sign from negative to positive in any pair of consecutive soil temperature records at 5 cm depth) at 177 German weather stations for 1950-2000. Future trends were explored by statistical modelling based on climatic and topographic predictors. Snowdays decreased uniformly at a rate of 0.5 d yr(-1) in the recent past. This trend is projected to continue to a point where significant parts of Germany will no longer regularly experience snow cover. MST has increased, and is projected to do so in the future, mainly in southern Germany. FTCs have been decreasing uniformly in the recent past. No evidence for increased FTCs or decreased MST with decreasing insulation due to missing snow cover was found. FTCs are projected to decrease disproportionately in northeastern Germany, where past frequencies were higher. Ecological implications of the significant decrease in the occurrence and magnitude of the climate parameters studied include changes in nutrient cycling, productivity and survival of organisms over wintering at the soil surface. Ecological research is needed, as the effects of diminished winters on ecosystems are not well understood.