Root Restriction as a Factor in Photosynthetic Acclimation of Cotton Seedlings Grown in Elevated Carbon Dioxide

Abstract

Interactive effects of root restriction and atmospheric CO2 enrichment on plant growth, photosynthetic capacity, and carbohydrate partitioning were studied in cotton seedlings (Gossypium hirsutum L.) grown for 28 days in three atmospheric CO2 partial pressures (270, 350, and Elevated atmospheric CO2 affects plant growth primarily by increasing net photosynthetic rates through an increase in CO2 partial pressure at the site of fixation in the chloroplast (26). Responses of plants to long-term exposure of elevated C02, however, are not well understood. Net photosynthesis of some species after long-term exposure (weeks, months) to elevated CO2 is often lower than net photosynthesis after short-term exposure (days, hours) (6,8,22,23,25,28,29 When photosynthesis was measured at 1000 ,ubar CO2 in Desmodium paniculatum after growth in 1000 Mbar CO2 for 3 to 7 weeks, rates were 33% lower relative to plants grown in 350 Mbar (29). After 3 weeks of growth in 680 Htbar C02, net photosynthetic rates of Eriophorum vaginatum measured at 680 ,ubar decreased 61% relative to plants grown at 340 pbar (25). Reduced photosynthetic capacity in elevated CO2 has been found in cotton growing in pots under nitrogenlimited conditions and under conditions of nonlimiting nitrogen (6, 28). On the other hand, cotton plants grown under field conditions at elevated CO2 maintained higher photosynthetic capacity compared to plants growing at ambient CO2 levels (2 1).It has been established that stomatal conductance of C3 plants typically decreases at elevated CO2 concentrations ( 14).Studies aimed at separating stomatal and biochemical limitations of photosynthesis, however, have concluded that stomatal closure was not responsible for reductions in photosynthetic rates of plants grown under long-term CO2 enrichment (6,8,30). Efforts to understand the physiological nature of the photosynthetic decline in plants exposed to long-term elevated CO2 have focused on chloroplast damage due to excessive carbohydrate accumulation (6, 29), on feedback inhibition associated with low utilization of photosynthate (6,8,22,23), and on changes in Rubisco activity (20,22,30). Starch often accumulates in chloroplasts in response to longterm elevated CO2 (3,6,29). This increase in nonstructural carbohydrate indicates that the plant cannot use photosynthate at the rate at which it is being produced and, when correlated with decreased net photosynthesis, reflects possible feedback effects on the photosynthetic process (1,11,15

Carbon allocation and water use in juvenile Douglas fir under elevated CO2

“…Our results clearly show that an initial growth stimulation can eventually be annulled by physiological or morphological adaptations. Cure & Acock (1986) argued that a strong sink strength is required for maintaining high photosynthetic activity at elevated CO2 and Thomas & Strain (1991) showed that a reduced photosynthetic capacity can be associated with a small rooting volume. Arp (1991) analyzed 14 observations and showed that a small rooting volume (pot size < 3-5 1) was probably responsible for photosynthetic acclimation under high CO^.…”

Global food insecurity. Treatment of major food crops with elevated carbon dioxide or ozone under large-scale fully open-air conditions suggests recent models may have overestimated future yields

“…Many of these studies, including some field studies, used plants grown in pots. Arp (1991) showed that rooting volume altered the response of plants to elevated [CO 2 ], and further experiments have reported a strong feedback when roots encounter a physical barrier (Masle et al 1990;Thomas & Strain 1991).…”

Responses of tree fine roots to temperature

“…Furthermore, soil temperature can affect photosynthesis, and as soil temperatures and photosynthesis increase together, changes in whole-plant source-sink relationships can occur (Lippu & Puttonen, 1991 ;Landhausser et al, 1996). For example, low soil temperatures can limit rates of enzymically driven root processes such as growth, nutrient uptake, and respiration, decreasing the demand for C and resulting in a negative feedback to photosynthesis through the accumulation of nonstructural carbohydrates in leaves (Thomas & Strain, 1991).…”