Effects of Water Stress on Photosynthesis and Carbon Partitioning in Soybean (Glycine max [L.] Merr.) Plants Grown in the Field at Different CO₂ Levels

Abstract

The effects of water stress and CO2 enrichment on photosynthesis, assimilate export, and sucrose-P synthase activity were examined in field grown soybean plants. In general, leaves of plants grown in C02-enriched atmospheres (300 microliters per liter above unenriched control, which was 349 ± 12 microliters per liter between 0500 and 1900 hours EST over the entire season) had higher carbon exchange rates (CER) weight accumulation of leaves during the light period (28), provides an estimate of the rate of photosynthetic sucrose formation in situ. When CER is restricted (e.g. low irradiance), export rate can be maintained by mobilization of reserves (9-11). One of the principal determinants of export rate is leaf sucrose concentration (7,9,23), which is a function of both CER and the partitioning of carbon among end products.The enzyme SPS may be involved in the regulation of carbon partitioning in leaves in two different ways (14). SPS is activated by glucose-6-P and inhibited by Pi (6), and the concentration of these metabolites changes as a function of CER (26). Thus, metabolic regulation of SPS may coordinate the rate of sucrose formation in the cytosol with the rate of C-assimilation in the chloroplast when CERs are low. However, when CER is high (light-saturated), sucrose formation may be limited by the maximum activity of SPS (12,13,24,25). Consequently, short-term CO2 enrichment of soybean plants did not result in increased rates of export even though CER was increased (14).In addition to using CO2 enrichment as a system to study carbon partitioning (14) and the interaction between C and N metabolism (8), the long-term effects of CO2 supply are also of interest because global CO2 is increasing (16). In particular, plant growth is often enhanced by CO2 enrichment, but the effects are not necessarily related to sustained increases in CER (20). Rather, increased water use efficiency may also be involved (16,20).The present study was conducted to obtain more information on the interactions between CO2 enrichment and plant water stress, both of which are known to affect carbohydrate concentrations in leaves (1,4,5,17,18). Specific objectives were to determine the long-term effects of CO2 enrichment on (a) CER and photosynthate partitioning and (b) SPS activity in leaves of nonstressed versus water-stressed plants. The study was conducted over a 2-week period when plants were in early podfill. The plants were grown in the field from emergence at ambient CO2 or with CO2 enrichment (300 ppm above ambient). The stressed plants had been subjected continuously to cycles ofstress, and measurements were conducted during two drying cycles. MATERIALS AND METHODSSeeds of soybean (Glycine max [L.] Merr. cv 'Bragg') were planted on June 6, 1983 on an Appling-Cecil3 association soil.

Field study of the effects of excess copper on wheat photosynthesis and productivity

“…Productivity and stomatal conductance in the field-grown ore wheats decreased with a resultant reduction in transpiration and total water loss. Our results are in good agreement with those from other field studies in different environments (Huber et al 1984;Idso et al 1987;Lawlor and Mitchell 1991).…”

Source-sink relationships in two soybean cultivars with indeterminate growth under water deficit

“…However, the observed reduction of Ai in plants submitted to water deficit was attributed to a decrease in Y L (Figures 2a,b; 6a,b), as reported by other authors (Bunce 1982;Egli and Bruening, 2004;Liu et al 2004a,b;Ribas-Carbo et al 2005). It is known that low Y L increases the stomatal resistance, which in turn reduces the CO 2 uptake, thereby affecting leaf photosynthesis by the diffusive process (Huber et al 1984). Therefore, the low grain-yield found in T2 and T3 plants can be attributed to the photosynthesis reduction per unit of leaf area and photosynthesis on the canopy scale in response to the LA reduction (Figures 3b,e; 6a,b).…”

Evaluation of certain rainfed food and oil seed crops for their response to elevated CO₂ at vegetative stage

“…This shows that the response of leaf weight was relatively higher than the expansion of the leaves and thereby leaves are thicker under elevated CO 2 . Huber et al (1984) concluded that the increase in specific leaf mass (leaf weight/leaf area) was presumably due mostly to the increase in starch content but the leaves of soybean are also thicker under enhanced CO 2 condition, due to the increase in palisade cells, which was not observed in maize (Thomas andHarvey 1983, Lawlor andMitchell 1991).…”