Elevated atmospheric partial pressure of CO2 and plant growth

Cotton plants were grown in late spring under full sunlight in glasshouses containing normal ambient partial pressure of CO₂ (32±2Pa) and enriched partial pressure of CO₂ (64±1.5Pa) and at four levels of nitrogen nutrition. Thirty-five days after planting, the total dry weights of high CO₂-grown plants were 2- to 3.5-fold greater than plants grown in normal ambient CO₂ partial pressure. Depending on nitrogen nutrition level, non-structural carbohydrate content (mainly starch) in the leaves of plants grown in normal CO₂ was between 4 and 37% of the total leaf dry weight compared to 39 to 52% in the leaves of high CO₂-grown plants. Specific leaf weight calculated using total dry weight was 1.6- to 2-fold greater than that based on structural dry weight. In high CO₂-grown plants the amount of non-structural carbohydrate translocated from the leaves at night was between 10 and 20% of the level at the end of the photoperiod. This suggests that the plant was unable to utilize all the carbohydrate it assimilated in elevated CO₂ atmosphere. While there was a 1.5-fold enhancement in the rate of CO₂ assimilation in plants grown in 64 Pa CO₂, there was, however, some evidence to suggest that the activities of other metabolic pathways in the plants were not stimulated to the same extent by the enriched CO₂ atmosphere. This resulted in massive accumulation of non-structural carbohydrate, particularly at low level of nitrogen nutrition.Abbreviations A rate of CO₂ assimilation - PPFD photosynthetic photo flux density - NAR net assimilation rate - pCO₂ partial pressure of CO₂ - RGR relative growth rate