Leaf functional traits predict timing of nutrient resorption and carbon depletion in deciduous subarctic plants

Abstract

Abstract Resorption of key elements promotes their conservation in plants in nutrient‐poor ecosystems. In seasonal environments, the timing of resorption is expected to influence resorption efficiency and plant fitness due to the trade‐off between maximizing photosynthetic carbon gain by late resorption and minimizing frost risks and nutrient loss by early resorption. Here, we hypothesize that (1) these alternative strategies with respect to the timing of element resorption both occur among summergreen species; (2) deciduous woody plants favour delayed resorption while herbaceous species benefit from gradual, early onset resorption; (3) this pattern is part of a more general relationship in which species with conservative resource economic traits have more delayed resorption. We measured nitrogen (N), phosphorus (P) and carbon (C) contents of mature, senescing and senesced leaves of 22 predominant plant species across four types of ecosystems in a subarctic region. We then calculated timing of resorption as the Julian calendar day of 50% of element resorption (T50), and examined its relationship with plant functional types and leaf resource economic traits (leaf mass per area [LMA], leaf C, N and P contents). The timing of N resorption in subarctic plants ranged from day 213 to 254, while the timing of P resorption ranged from day 211 to 261 and of C from day 214 to 260 across species. On average, the resorption of N and P and depletion of C were 13, 12 and 19 days respectively earlier in herbaceous plants than in woody ones. For all the three elements, T50 of plants decreased significantly with increasing acquisitive economic traits. Synthesis: As hypothesized, we found that (1) both “steady‐and‐slow” and “late‐and‐fast” strategies of resorption timing co‐occurred in a subarctic flora; consistent with these two strategies, herbaceous plants resorbed nutrients and carbon earlier than deciduous woody species; (2) relevant functional traits representing resource conservation were positively and linearly related to the timing of nutrient resorption and carbon depletion. These findings for element resorption timing have important implications for functional changes in the vegetation composition of seasonal regions in response to temperature fluctuations in a changing climate.