Incident radiation and the allocation of nitrogen within Arctic plant canopies: implications for predicting gross primary productivity

• Published in: Global Change Biology
• Main Authors: Street, L.E., Shaver, G.R., Rastetter, E.B., van Wijk, M.T., Kaye, B.A., Williams, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: air-temperature; c-3 plants; carbon-exchange; co2 flux; economics spectrum; leaf-area index; leaves; photosynthesis; tundra; vegetation; Arctic; Tundra
• Online Access: https://research.wur.nl/en/publications/incident-radiation-and-the-allocation-of-nitrogen-within-arctic-p; https://doi.org/10.1111/j.1365-2486.2012.02754.x

Arctic vegetation is characterized by high spatial variability in plant functional type (PFT) composition and gross primary productivity (P). Despite this variability, the two main drivers of P in sub-Arctic tundra are leaf area index (LT) and total foliar nitrogen (NT). LT and NT have been shown to be tightly coupled across PFTs in sub-Arctic tundra vegetation, which simplifies up-scaling by allowing quantification of the main drivers of P from remotely sensed LT. Our objective was to test the LT–NT relationship across multiple Arctic latitudes and to assess LT as a predictor of P for the pan-Arctic. Including PFT-specific parameters in models of LT–NT coupling provided only incremental improvements in model fit, but significant improvements were gained from including site-specific parameters. The degree of curvature in the LT–NT relationship, controlled by a fitted canopy nitrogen extinction co-efficient, was negatively related to average levels of diffuse radiation at a site. This is consistent with theoretical predictions of more uniform vertical canopy N distributions under diffuse light conditions. Higher latitude sites had higher average leaf N content by mass (NM), and we show for the first time that LT–NT coupling is achieved across latitudes via canopy-scale trade-offs between NM and leaf mass per unit leaf area (LM). Site-specific parameters provided small but significant improvements in models of P based on LT and moss cover. Our results suggest that differences in LT–NT coupling between sites could be used to improve pan-Arctic models of P and we provide unique evidence that prevailing radiation conditions can significantly affect N allocation over regional scales