Phosphorus recycling in photorespiration maintains high photosynthetic capacity in woody species

• Published in: Plant, cell and environment Vol. 38; no. 6; pp. 1142 - 1156
• Main Authors: ELLSWORTH, DAVID S., CROUS, KRISTINE Y., LAMBERS, HANS, COOKE, JULIA
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.06.2015
• Subjects: Carbon Dioxide - metabolism; low oxygen concentration; nitrogen; Models, Biological; Oxygen - metabolism; phosphate limitations; Phosphates - metabolism; Phosphates - physiology; phosphorus; Phosphorus - metabolism; Phosphorus - physiology; Photosynthesis - physiology; photosynthesis: carbon reactions; Plant Leaves - metabolism; Plant Leaves - physiology; sclerophyll trees; Trees - metabolism; Trees - physiology; photosynthesis: carbon reactions; sclerophyll trees; phosphate limitations; low oxygen concentration; nitrogen; phosphorus
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.12468

Leaf photosynthetic CO2 responses can provide insight into how major nutrients, such as phosphorus (P), constrain leaf CO2 assimilation rates (Anet). However, triose‐phosphate limitations are rarely employed in the classic photosynthesis model and it is uncertain as to what extent these limitations occur in field situations. In contrast to predictions from biochemical theory of photosynthesis, we found consistent evidence in the field of lower Anet in high [CO2] and low [O2] than at ambient [O2]. For 10 species of trees and shrubs across a range of soil P availability in Australia, none of them showed a positive response of Anet at saturating [CO2] (i.e. Amax) to 2 kPa O2. Three species showed >20% reductions in Amax in low [O2], a phenomenon potentially explained by orthophosphate (Pi) savings during photorespiration. These species, with largest photosynthetic capacity and Pi > 2 mmol P m−2, rely the most on additional Pi made available from photorespiration rather than species growing in P‐impoverished soils. The results suggest that rarely used adjustments to a biochemical photosynthesis model are useful for predicting Amax and give insight into the biochemical limitations of photosynthesis rates at a range of leaf P concentrations. Phosphate limitations to photosynthetic capacity are likely more common in the field than previously considered. Triose‐phosphate limitations to photosynthesis were described nearly 30 years ago with diagnostics revealed by CO2 exchange measurements in low O2 concentrations, yet are rarely measured or described for plants in the field. Nearly one‐third of the world's soils demonstrate elements of P‐limitation to plant productivity, and it is often believed that triose‐P limitations to net CO2 assimilation of leaves is greatest on P‐impoverished soils. Ellsworth et al. estimate triose‐P limitations to leaf net CO2 assimilation in the field in ten tree and shrub species across a range of Australian soils, and find evidence for triose‐P limitations to light‐ and CO2‐saturated photosynthetic capacity is relatively common. While triose‐P utilisation (Tp) limitations to photosynthesis are considered to be uncommon and are often ignored in photosynthetic model‐fitting, we have shown that Tp can be limiting in a wide range of species in the field and is revealed by low O2 gas exchange measurements.