Under the influence of global change, precipitation amounts and extreme precipitation frequency during nongrowing seasons in mid -high latitude grasslands have been increasing. However, the ecological effects of nongrowing season precipitation in the desert steppe have long been overlooked due to an insufficient understanding of the correlative mechanisms linking non -growing season precipitation to plant growth. Therefore, a 3year non -growing season precipitation manipulation experiment was conducted to reveal the response of desert steppe plants to non -growing season precipitation changes. Our study indicates that, by influencing water budget and availability, non -growing season precipitation directly or indirectly impacted community structure, plant biomass allocation, and water -carbon utilization intensity. Adaptive strategies of communities and plants included: Dominant species enhanced their dominance in the community to adapt to non -growing season precipitation changes. Stipa krylovii exhibited different biomass allocation strategies in response to nongrowing season precipitation variations. Plants in the precipitation shading plots tended to allocate biomass to the roots, while those in the precipitation increase plots favored aboveground development. Persistent drought during the growing season intensified early insufficient development of plants in the precipitation shading plots. Upon entering the wet period, plants in the precipitation shading plots shifted into a compensatory growth mode with high water -carbon activity intensity, while those in the precipitation increase plots entered a moderate growth mode with relatively low water -carbon activity intensity. Additionally, our study found that the regulatory effects of non -growing season precipitation were more pronounced in the growing seasons with less precipitation in the early to middle stage. Moreover, increased non -growing season precipitation enhanced plant water use efficiency (WUE) and strengthened their resilience to drought conditions. Our study suggests that the ecological role of non -growing season precipitation may be further highlighted in the future climate change pattern. Given the worldwide increase in frequency of extreme precipitation events, particular vigilance should be paid to the underlying long-term adverse effects of severe droughts during the non -growing season. Our findings provide new insights and valuable experimental observational evidence for the climate change impact assessment and response in xerophytic grassland ecosystems.

How methane (CH4) fluxes from alpine peatlands, especially during freeze-thaw cycles, affect the global CH4 budget is poorly understood. The present research combined the eddy covariance method, incubation experiments and high-throughput sequencing to observe CH4 flux from an alpine fen during thawing-freezing periods over a period of four years. The response of CH4 production potential and methanogenic archaea to climate change was analyzed. We found a relatively high mean annual cumulative CH4 emission of 37.7 g CH4-C m(-2). The dominant contributor to CH4 emission was the thawing period: warmer, longer thawing periods contributed 69.1-88.6% to the annual CH4 budget. Non-thawing periods also contributed, with shorter frozen-thawing periods accounting for up to 18.5% and shorter thawing-freezing periods accounting for up to 8.8%. Over the course of a year, emission peaked in the peak growing season and at onset of thawing and freezing. In contrast, emission did not vary substantially during the frozen period. Daily mean emission was highest during the thawing period and lowest during the frozen period. Diurnal patterns of CH4 emission were similar among the four periods, with peaks ranging from 12:00 to 18:00 and the lowest emission around 00:00. Water table and temperature were the dominant factors controlling CH4 emissions during different thawing-freezing periods. Our results suggest that CH4 emission from peatland will change substantially as CH4 production, microbial composition, and patterns of thawing-freezing cycles change with global warming. Therefore, frequent monitoring of CH4 fluxes in more peatlands and in situ monitoring of methanogenesis and related microbes are needed to provide a clear picture of CH4 fluxes and the thawing-freezing processes that affect them.

Seasonal soil freeze-thaw events may enhance soil nitrogen transformation and thus stimulate nitrous oxide (N2O) emissions in cold regions. However, the mechanisms of soil N2O emission during the freeze-thaw cycling in the field remain unclear. We evaluated N2O emissions and soil biotic and abiotic factors in maize and paddy fields over 20 months in Northeast China, and the structural equation model (SEM) was used to determine which factors affected N2O production during non-growing season. Our results verified that the seasonal freeze-thaw cycles mitigated the available soil nitrogen and carbon limitation during spring thawing period, but simultaneously increased the gaseous N2O-N losses at the annual time scale under field condition. The N2O-N cumulative losses during the non-growing season amounted to 0.71 and 0.55 kg N ha(-1) for the paddy and maize fields, respectively, and contributed to 66 and 18% of the annual total. The highest emission rates (199.2-257.4 mu g m(-2) h(-1)) were observed during soil thawing for both fields, but we did not observe an emission peak during soil freezing in early winter. Although the pulses of N2O emission in spring were short-lived (18 d), it resulted in approximately 80% of the non-growing season N2O-N loss. The N2O burst during the spring thawing was triggered by the combined impact of high soil moisture, flush available nitrogen and carbon, and rapid recovery of microbial biomass. SEM analysis indicated that the soil moisture, available substrates including NH4+ and dissolved organic carbon (DOC), and microbial biomass nitrogen (MBN) explained 32, 36, 16 and 51% of the N2O flux variation, respectively, during the non-growing season. Our results suggested that N2O emission during the spring thawing make a vital contribution of the annual nitrogen budget, and the vast seasonally frozen and snow-covered croplands will have high potential to exert a positive feedback on climate change considering the sensitive response of nitrogen biogeochemical cycling to the freeze-thaw disturbance.

Rapid and extensive snowmelt occurred during 2 days in March 2013 at a low-Arctic study site in the ice-free part of southwest Greenland. Meteorology, snowmelt, and snow-property observations were used to identify the meteorological conditions associated with this episodic snowmelt event (ESE) occurring prior to the spring snowmelt season. In addition, outputs from the SnowModel snowpack-evolution tool were used to quantify the snow-related consequences of ESEs on ecosystem-relevant snow properties. We estimated a 50-80% meltwater loss of the pre-melt snowpack water content, a 40-100% loss of snow thermal resistance, and a 4-day earlier spring snowmelt snow-free date due to this March 2013 ESE. Furthermore, the accumulated meltwater loss from all ESEs in a hydrological year represented 25-52% of the annual precipitation and may potentially have advanced spring snowmelt by 6-12 days. Guided by the knowledge gained from the March 2013 ESE, we investigated the origin, past occurrences, frequency, and abundance of ESEs at spatial scales ranging from local (using 2008-2013 meteorological station data) to all of Greenland (using 1979-2013 atmospheric reanalysis data). The frequency of ESEs showed large interannual variation, and a maximum number of ESEs was found in southwest Greenland. The investigations suggested that ESEs are driven by foehn winds that are typical of coastal regions near the Greenland Ice Sheet margin. Therefore, ESEs are a common part of snow-cover dynamics in Greenland and, because of their substantial impact on ecosystem processes, they should be accounted for in snow-related ecosystem and climate-change studies.

In terrestrial high-latitude regions, observations indicate recent changes in snow cover, permafrost, and soil freeze-thaw transitions due to climate change. These modifications may result in temporal shifts in the growing season and the associated rates of terrestrial productivity. Changes in productivity will influence the ability of these ecosystems to sequester atmospheric CO2. We use the terrestrial ecosystem model (TEM), which simulates the soil thermal regime, in addition to terrestrial carbon (C), nitrogen and water dynamics, to explore these issues over the years 1960-2100 in extratropical regions (30-90 degrees N). Our model simulations show decreases in snow cover and permafrost stability from 1960 to 2100. Decreases in snow cover agree well with National Oceanic and Atmospheric Administration satellite observations collected between the years 1972 and 2000, with Pearson rank correlation coefficients between 0.58 and 0.65. Model analyses also indicate a trend towards an earlier thaw date of frozen soils and the onset of the growing season in the spring by approximately 2-4 days from 1988 to 2000. Between 1988 and 2000, satellite records yield a slightly stronger trend in thaw and the onset of the growing season, averaging between 5 and 8 days earlier. In both, the TEM simulations and satellite records, trends in day of freeze in the autumn are weaker, such that overall increases in growing season length are due primarily to earlier thaw. Although regions with the longest snow cover duration displayed the greatest increase in growing season length, these regions maintained smaller increases in productivity and heterotrophic respiration than those regions with shorter duration of snow cover and less of an increase in growing season length. Concurrent with increases in growing season length, we found a reduction in soil C and increases in vegetation C, with greatest losses of soil C occurring in those areas with more vegetation, but simulations also suggest that this trend could reverse in the future. Our results reveal noteworthy changes in snow, permafrost, growing season length, productivity, and net C uptake, indicating that prediction of terrestrial C dynamics from one decade to the next will require that large-scale models adequately take into account the corresponding changes in soil thermal regimes.