Seasonal CO2 source partitioning in thawing permafrost ecosystems: Contribution of winter processes to annual carbon cycling

北极的冬季漫长而寒冷，但适应寒冷的植物和土壤微生物被绝缘的雪层覆盖，继续呼吸二氧化碳（CO2），可占这些生态系统年二氧化碳排放量的20-50%。尽管冬季占了一年的大部分时间，但人们对冬季生态系统呼吸的机制知之甚少。高纬度生态系统受温度、光照和积雪覆盖的强烈季节性梯度支配。永久冻土，即至少连续两年处于或低于0°C的地面，对气候变化非常敏感。过去几十年的气候变暖导致了大范围的永久冻土融化，伴随而来的是植被从主要的浅根植物群落向深根植物群落的转变。然而，根系-土壤相互作用在冬季和永久冻土融化深度对生态系统呼吸的影响尚不清楚。此外，高纬度地区的气候变化速度是全球平均速度的两倍，大部分变化发生在冬季，积雪持续时间总体缩短，但雪深增加。气候变化、永久冻土融化和更深的根系系统预计会导致更高的生态系统呼吸，从而增加二氧化碳排放，但将生态系统呼吸划分为两个来源，即相对快速循环的植物源二氧化碳和较老的、缓慢循环的土壤有机碳，仍然是一个主要的研究挑战。然而，只有将这两个来源分离开来，才能使我们确定额外呼吸的二氧化碳的来源，从而帮助我们更好地了解永久冻土区融化在全球碳循环中的未来作用。我将把原位13c同位素标记研究与一个普通的花园实验结合起来：(1)确定驱动因素并量化冬季生态系统呼吸对瑞典北部多年冻土融化梯度的年碳循环的贡献，以及不同季节植物和土壤微生物呼吸对生态系统呼吸的相对贡献；(2)研究冬季永久冻土融化如何影响土壤根系动态。因此，该项目将为退化的受永久冻土影响的生态系统冬季过程的驱动因素提供新的见解，并且二氧化碳源的划分将有助于确定气候变化对受永久冻土影响的系统对变暖的北极大气二氧化碳的年汇强度的影响。在气候模式中，冬季过程和永久冻土过程目前都没有高统计置信度的表示。因此，迫切需要更好地了解这些独特生态系统中植物、土壤微生物和碳循环之间的季节性相互作用。

Winters in the Arctic are long and cold but cold-adapted plants and soil microorganisms, covered by insulating snow layers, continue to respire carbon dioxide (CO2), which can account for 20–50% to annual CO2 emissions from these ecosystems. And even though winter represents a major part of the year, the mechanisms of ecosystem respiration in winter are poorly understood.High-latitude ecosystems are governed by strong seasonal gradients in temperature, light and snow cover. Permafrost, i.e. ground that is at or below 0 °C for at least two consecutive years, is very sensitive to climatic change. Climate warming over the last decades resulted in wide-spread permafrost thaw with accompanying shifts in vegetation from primarily shallow-rooting plant communities to deep-rooting species. However, the effects of root-soil interactions on ecosystem respiration during winter and at depths where permafrost thaws remain unclear. Furthermore, the rate of climatic change in high-latitude regions has been twice the rate of the global average and most of the changes have been observed in winter, with an overall decrease in the duration of snow cover but an increase in snow depth. Climatic change, permafrost thaw, and deeper rooting systems are expected to result in higher ecosystem respiration and thus higher CO2 emissions but partitioning ecosystem respiration into its two sources, relatively fast cycling plant-derived CO2 and older, slow cycling soil organic carbon, remains a major research challenge. However, only the separation of these two sources will enable us to identify the origin of the additionally respired CO2 and thus help us to better understand the future role of thawing permafrost regions in the global carbon cycle.I will combine in situ 13C-isotopic labelling studies with a common garden experiment to (1) identify the drivers and quantify the contribution of winter ecosystem respiration to annual carbon cycling along a permafrost thaw gradient in northern Sweden as well as the relative contributions of plant- and soil microbial respiration to ecosystem respiration during different seasons and (2) examine how permafrost thaw affects soil-root dynamics in winter. This project will thus give new insights into the drivers of winter processes in degrading permafrost-affected ecosystems and the partitioning of CO2 sources will help to determine the effect of climatic change on the annual sink strength of permafrost-affected systems for atmospheric CO2 in a warming Arctic. Neither winter nor permafrost processes are currently represented in climate models with high statistical confidence. A better understanding of seasonal interactions between plants, soil microorganism, and carbon cycling in these unique ecosystems is therefore urgently needed.