Response of Potato to Phosphorous Nutrition and CO2 Enrichment.

Atmospheric CO₂ enrichment is known to positively influence potato yield and, in some cases, total dry matter production.  While various studies have indicated an interactive effect of CO₂ on nitrogen uptake and utilization in potato and other agronomically important crops, there has been little focus with respect to other nutrients.  Two seven-week studies were conducted in the summer of 2009 at USDA-ARS facilities in Beltsville, MD.  Both studies were conducted in six soil-plant-atmosphere research (SPAR) chambers that automatically measured whole plant gas exchange rates.  Twelve 16 liter pots were assigned to each chamber.  Nutrient treatments were applied to four pots per chamber and included three levels of phosphorous (P) supplied at 8 (high), 2 or 1 (medium), or 0 (low) grams of solid amendment (triple super-phosphate).  Additional fertilizer and water were provided via a micro-irrigation system.  Three SPAR chambers were maintained at a CO₂ concentration of 400 ppm (ambient), and another three at 800 ppm (elevated).  Five weeks into the season, all pots were re-arranged according to elevated or ambient CO₂ treatment so as to permit measurement of whole plant gas exchange rates among uniformly phosphorous treated plants.  Results from both studies were similar.  A significant interaction between CO₂ and P was observed only for stem dry mass and was largely a result of increased branching at the highest CO₂ and P treatments.  Total plant mass significantly increased with CO₂ enrichment, largely due to increased tuber number and size.  Total, leaf, stem, tuber, and stolon dry mass increased with P nutrition.  Leaf appearance and stem elongation rates were not influenced by CO₂, but the total number of leaves per plant at harvest increased with CO₂ and P nutrition, and plant height and individual leaf size also increased with P.  Individual leaf level photosynthesis and conductance were influenced by CO₂ and P level, and whole canopy gas exchange rates were influenced in a similar manner.  Data from these studies will be used to develop quantitative tools to help identify effective management strategies in response to climate change effects on agriculture.