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Abstract The rapid A‐Ciresponse (RACiR) technique alleviates limitations of measuring photosynthetic capacity by reducing the time needed to determine the maximum carboxylation rate (Vcmax) and electron transport rate (Jmax) in leaves. Photosynthetic capacity and its relationships with leaf development are important for understanding ecological and agricultural productivity; however, our current understanding is incomplete. Here, we show that RACiR can be used in previous generation gas exchange systems (i.e., the LI‐6400) and apply this method to rapidly investigate developmental gradients of photosynthetic capacity in poplar. We compared RACiR‐determined Vcmaxand Jmaxas well as respiration and stomatal conductance (gs) across four stages of leaf expansion inPopulus deltoidesand the poplar hybrid 717‐1B4 (Populus tremula × Populus alba). These physiological data were paired with leaf traits including nitrogen concentration, chlorophyll concentrations, and specific leaf area. Several traits displayed developmental trends that differed between the poplar species, demonstrating the utility of RACiR approaches to rapidly generate accurate measures of photosynthetic capacity. By using both new and old machines, we have shown how more investigators will be able to incorporate measurements of important photosynthetic traits in future studies and further our understanding of relationships between development and leaf‐level physiology.
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Rising CO 2 and warming reduce global canopy demand for nitrogen
Summary Nitrogen (N) limitation has been considered as a constraint on terrestrial carbon uptake in response to rising CO2and climate change. By extension, it has been suggested that declining carboxylation capacity (Vcmax) and leaf N content in enhanced‐CO2experiments and satellite records signify increasing N limitation of primary production. We predictedVcmaxusing the coordination hypothesis and estimated changes in leaf‐level photosynthetic N for 1982–2016 assuming proportionality with leaf‐levelVcmaxat 25°C. The whole‐canopy photosynthetic N was derived using satellite‐based leaf area index (LAI) data and an empirical extinction coefficient forVcmax, and converted to annual N demand using estimated leaf turnover times. The predicted spatial pattern ofVcmaxshares key features with an independent reconstruction from remotely sensed leaf chlorophyll content. Predicted leaf photosynthetic N declined by 0.27% yr−1, while observed leaf (total) N declined by 0.2–0.25% yr−1. Predicted global canopy N (and N demand) declined from 1996 onwards, despite increasing LAI. Leaf‐level responses to rising CO2, and to a lesser extent temperature, may have reduced the canopy requirement for N by more than rising LAI has increased it. This finding provides an alternative explanation for declining leaf N that does not depend on increasing N limitation.
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- Award ID(s):
- 2045968
- PAR ID:
- 10445069
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 235
- Issue:
- 5
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 1692-1700
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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