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.