Quantitative Effects of Phosphorus on Maize Canopy Photosynthesis and Biomass

The objective of this study was to quantify the response of maize ( Zea mays L.) canopy photosynthesis, development and biomass to P under controlled conditions. Maize was grown in Soil‐Plant‐Atmosphere Research (SPAR) chambers in Beltsville, MD, with four levels of P (0 [L], 0.01 [Ml], 0.05 [M2], and 0.2 [H] mmol P L −1 ) and three levels of N (2, 5, and 12 mmol L −1 ). Five destructive harvests for biomass were taken. There was no significant N effect, so only the P effects were analyzed, and chambers were pooled over P treatments. Maximum net canopy carbon assimilation in the two lowest P rates was 0.4 g C plant −1 d −1 . Carbon assimilation for the M2 rate was half that of the control (1.3 vs. 2.5 g C plant −1 d −1 ). End of season biomass was decreased relative to the control by 57% in M2 and 79% in L and M1. Leaf appearance rate and area decreased with increasing P deficiency. Differences in tissue P concentrations varied over a narrow range in the P deficiency treatments, suggesting that continued availability of P to maintain growth was important. Decreases in biomass were due to P‐deficiency‐related decreases in leaf growth and photosynthetic rate. Light interception in the low P treatments was near 90%, suggesting that decreases in photosynthesis and leaf growth were due to P effects on metabolic factors rather than reduction in light interception.