Contrasting synchrony in root and leaf phenology across multiple sub‐Arctic plant communities

Abstract

Summary Roots account for > 50% of net primary production in many ecosystems and are widely accepted as playing a fundamental role in ecosystem carbon and nutrient cycling. Despite this, the timing and controls of root production and the relationships between root and leaf phenology are still poorly understood in many plant communities, making it challenging to elucidate broad scale patterns and to predict ecosystem responses to a changing climate. Here, we investigate and compare the extent of synchrony of community‐level fine root and leaf production in 10 widespread sub‐Arctic plant communities, including deciduous forest, evergreen shrub, deciduous shrub and sedge‐dominated communities. We show that across contrasting plant communities, timing of leaf production does not vary substantially, but there are considerable differences in timing of root production between woody plant‐ and sedge‐dominated vegetation. In sedge communities, root production occurs early in the growing season, soon after the peak of leaf production, whereas in woody plant communities, leaf and root production are highly asynchronous, with the majority of root production occurring late in the growing season. Seasonal dynamics of root growth were not consistently correlated with soil temperature, suggesting that differences in timing of production relate to inherent differences between plant functional types. This raises important questions as to the drivers of root production, the functional reasons underlying these contrasting plant strategies, as well as the consequences for microbial communities and nutrient cycling of such contrasting timing of carbon inputs to soil. Synthesis. We demonstrate that major differences exist in the synchrony of temporal dynamics of leaf and root production between woody plant and sedge‐dominated sub‐Arctic vegetation. The substantially greater asynchrony in root and leaf production in woody plants compared with sedges suggests that vegetation change associated with climate warming will result in significant shifts in timing of carbon fluxes to soil, and highlights the need for separate leaf and root components in ecosystem carbon and nutrient cycle models.