EliseGallois/Above_v_Below_Phenology: rootpheno_2025

The below-ground growing season often extends beyond the above-ground growing season in tundra ecosystems and as the climate warms, shifts in growing seasons are expected. However, we do not yet know to what extent, when and where asynchrony in above- and below-ground phenology occurs and whether variation is driven by local vegetation communities or spatial variation in microclimate. Here, we combined above- and below-ground plant phenology metrics to compare the relative timings and magnitudes of leaf and fine-root growth and senescence across microclimates and plant communities at five sites across the Arctic and alpine tundra biome. We observed asynchronous growth between above- and below-ground plant tissue, with the below-ground season extending up to 74% (~56 days) beyond the onset of above-ground leaf senescence. Plant community type, rather than microclimate, was a key factor controlling the timing, productivity, and growth rates of fine roots, with graminoid roots exhibiting a distinct ‘pulse’ of growth later into the growing season than shrub roots. Our findings indicate the potential of vegetation change to influence below-ground carbon storage as the climate warms and roots remain active in unfrozen soils for longer. Taken together, our findings of increased root growth in soils that remain thawed later into the growing season, in combination with ongoing tundra vegetation change including increased shrub and graminoid abundance, indicate increased below-ground productivity and altered carbon cycling in the tundra biome.苔原（tundra）生态系统的地下生长季通常长于地上生长季；随着气候变暖，生长季预计将发生改变。然而，目前我们尚不明确地上与地下物候学（phenology）的异步性会在何种程度、何时何地出现，也不清楚其差异是由本地植被群落还是微气候（microclimate）的空间变异所驱动。 本研究整合了地上与地下植物物候学指标，对北极-高山苔原生物群区（biome）5个样点中不同微气候与植物群落条件下，叶片与细根（fine root）的生长、衰老的相对时序与强度展开对比分析。 本研究观测到植物地上与地下组织的生长存在异步性：地下生长季可比地上叶片衰老启动时间最长多出74%（约56天）。 调控细根生长时序、生产力与生长速率的关键因素为植物群落类型，而非微气候；相较于灌木根系，禾草类（graminoid）根系的生长“脉冲”现象会持续至生长季更晚的阶段。 本研究结果表明，随着气候变暖、根系在未冻结土壤中的活跃时间延长，植被变化可能会对地下碳储量（carbon storage）产生影响。 综合来看，本研究发现生长季后期仍处于解冻状态的土壤中根系生长有所提升，结合苔原植被正在发生的变化（如灌木与禾草类植物丰度增加），表明苔原生物群区的地下生产力有所提升，且碳循环（carbon cycling）模式已发生改变。