积雪变化对地下生态系统影响的研究进展

Research progress on effects of snow cover change on belowground ecosystem

在气候变化背景下,全球积雪厚度、积雪密度和雪水当量发生着一系列变化,并进一步影响陆地生态系统的水热状况、生物地球化学循环过程以及生态系统的结构与功能。本文综述了北半球积雪变化(雪深、积雪覆盖日数)的现状,积雪生态研究方法及其优缺点,积雪与生态系统相互作用,以及积雪变化对主要陆地生态系统类型(草地、灌丛和森林)地下过程(养分周转、土壤动物和微生物、根系生长)的影响及其机制。研究发现:(1)雪深在40~70 cm时对土壤的保温作用最显著;(2)积雪增加通过加速土壤碳氮循环过程引起碳氮损失,尤其显著发生在相对湿润的生境中,相对干旱的生境中变化不显著;(3)在草地生态系统中,土壤有效磷含量对积雪增加的响应程度受生态系统自身干湿条件调控,即湿润的生境有效磷增加,干旱的生境有效磷降低;(4)积雪增加促进了草地生态系统植物表层根系的生长,积雪减少对植物根系生长的影响程度取决于消极影响(根系损伤和死亡)和积极影响(土壤养分有效性增加)之间的动态平衡;(5)相对于草地生态系统和森林生态系统植物根系生长而言,灌丛生态系统植物根系生长对积雪变化的响应更稳定。本文还提出了现有研究中存在的不足和未来发展趋势。

Under climate change,snow depths,snow density and snow water equivalent on global scale are undergoing numbers of changes,which further affect the hydrothermal status,biogeochemical cycle process,and structure and function of terrestrial ecosystems.The present paper reviews the current results of snow cover changes including snow depths,periods of snow cover in the Northern Hemisphere,ecologically experimental methods to simulate snow change and their pros and cons,the interaction between snow and ecosystem,and the effects of snow changes on soil nutrient turnover,soil fauna and microorganisms,root biomass and functional traits in three major terrestrial ecosystem types(grassland,shrub and forest)and their mechanisms.Thus,the main conclusions we have are:snow has the most significant warming effects in the depth of between 40 and 70 cm.The higher albedo under no snow or depth less than 40 cm may significantly reduce heat reaching the ground surface,thus soil temperature obviously decreased,and even the frequency and depth of soil freezing and thawing in winter are increased so to compensate for the huge heat loss.When the snow depth is greater than 70 cm,the latent heat of snow melting causes surface heat loss,which reduces soil temperature and weakens the heat preservation effect of snow.Increased snow cover leads carbon and nitrogen loss by accelerating soil carbon and nitrogen cycling,especially in humid habitats,but this is not the case in arid habitats.Snow reduction mainly affects root mortality,microbial activity,soil organic matter accumulation,nitrification and denitrification processes by acting on soil freeze-thaw cycles,thereby affecting soil nutrient turnover.In the grassland ecosystem,the response of soil available phosphorus content to the increase of snow cover is regulated by the ecosystem water conditions,that is,the available phosphorus increases in the humid habitat and decreases in the arid habitats.The increase of snow cover promotes the growth of plant roots in grassland ecosystem by improving the nutrient availability and water availability of shallow soil and changing the root morphological characteristics.The impact of reduced snow cover on plant root growth in ecosystems depends on the dynamic balance between negative effects(root damage and death)and positive effects(increased soil nutrient availability).Compared with grassland and forest ecosystem,the response of plant root growth to snow cover change in shrub ecosystem was more stable.We also summarize the shortcomings and future trends in the study of effects of snow cover on belowground ecosystems.First of all,the response of phosphorus to snow cover increase is different from that of carbon and nitrogen,and it affects the coupling mechanism of soil carbon,nitrogen and phosphorus through influencing the decomposition rate of organic matter,which is very important for underground ecosystems.In the future,more attention should be paid to the response of soil phosphorus cycle and carbon,nitrogen and phosphorus coupling under snow cover change in different ecosystem environments.Secondly,at present,in the northern hemisphere,the effects of snow cover on root morphology and stoichiometric characteristics of plants in different ecosystems are not comprehensive.Further research on the response of root biomass,morphological characteristics and stoichiometric characteristics to snow cover changes in different ecosystems is still needed.Finally,to reveal the response mechanism of belowground processes in different ecosystems to snow cover changes,it is necessary to carry out more extensive and longer-term continuous field positioning observations and multi-factor comprehensive control experiments.