Interdependence of Nitrogen Nutrition and Photosynthesis in Pisum sativum L

Abstract

Physiological responses to infection by strains of Rhizobium leguminosarum which differed in their capacity to reduce N2 were determined in 26-day-old pea plants (Pisum sadvum L. cv. Alaska) grown under uniform environmental conditions in the absence of combined N. The highest N2 reduction rates, calculated from H2 evolution and C2H2-dependent C2H4 production measurements, were approximately 6-fold greater than the lowest. Higher N2 fixation rates were associated with greater CO2 exchange rates (R2 = 0.92) and carboxylation efficiency (R2 = 0.99). Increases in the apparent relative efficiency of N2 fixation II-(H2 evolved in air/C2H2 reduced)l (acteroid efficiency) were associated with increases in whole-plant N2 fixation efficiency (N2/CO2 reduction ratio) (R2 = 0.95). Whole-plant dry weight and total N content were related by regression analysis (R2 = 0.98); both parameters were enhanced by increased N2 fixation in a manner analogous to previously reported increases caused by greater external applications of NH4'. These data reveal that photosynthetic parameters in genetically uniform host plants grown under identical environmental conditions are affected by N2 fixation characteristics of the rhizobial symbiont. The measured efficiencies of micro-and macrosymbiont are directly related under uniform environments.Dependence of N2 fixation on photosynthetic products is a concept supported by data of numerous investigations (3,4,6,10). It is axiomatic that the capacity of the photosynthetic apparatus to provide required photosynthate for all plant functions including N2 fixation is controlled to a large extent by the availability of reduced N. Previous work has shown that photosynthesis in 26-day-old Alaska peas (Pisum sativum L.) is strongly influenced by availability of reduced nitrogen, whether it is supplied exogenously or by the Rhizobium symbiosis (2). The present study was begun to determine whether photosynthesis in a genetically uniform host legume grown under controlled conditions could be altered by providing Rhizobium strains which differed in their capacity to reduce N2. photosynthesis, N2 fixation; and N content measurements were made as described previously (2), with the following exceptions. All plants were grown in the absence of combined N, and treatments consisted of eight single plant replications inoculated with Rhizobium leguminosarum strains TA 101 (obtained originally from J. J. Child, N.R.C. Saskatoon, Sask.), 175G 10, 128C53, 92A2, or 92FI (obtained originally from J. C. Burton, The Nitragin Co., Milwaukee). Nitrogen content, N2 fixation, RE3 (9), CER, CE, and C2H2 reduction data were evaluated by Duncan's multiple range test (5) to determine if significant differences existed in plants inoculated with different strains. The relationships of N2 fixation to CER, N2 fixation to CE, N2 fixation to N content, N content to dry weight, and RE to N2/CO2 fLxation ratio were evaluated by linear and nonlinear regression analyses. Data points were fitted with curves corresponding to the func...

Interactions between Nitrogen Fixation, Mycorrhizal Colonization, and Host-Plant Growth in the Phaseolus-Rhizobium-Glomus Symbiosis

“…Thus, within the concept of the two opposing processes (21) stimulation due to enhanced P uptake no longer occurred, whereas competition for carbohydrates determined host growth response. Although compensatory CO2 fixation by the host plant in response to increased carbohydrate requirements by microsymbionts have been noted in the past (4,23), the conclusion that the host will meet higher demand by increased production (25) has not been verified by the results of this experiment, perhaps due to limitations on photosynthesis caused by suboptimal light conditions. Low levels of light intensity have been shown to depress nodulation (10) and VAM fungal development (17).…”

Variation in Nitrogenase and Hydrogenase Activity of Alaska Pea Root Nodules

“…Energy lost to H2 production probably was minimized in strains 128C53 and 92F 1 by hydrogenase activity. These strains also had relatively low rates of total H2 production and high rates of C2H2 reduction (Table I) (3). Dixon (9) demonstrated that different species of host plants induced various levels of uptake hydrogenase activity in Rhizobium bacteroids.…”

“…The present experiments were performed to separate the effects of ontogeny and growth irradiance on nitrogenase and hydrogenase activity in Rhizobium leguminosarum 128C53. In addition, other strains of this bacterial species were examined for hydrogenase and nitrogenase activity in vivo to determine the mechanisms underlying different N2 reduction rates which alter photosynthetic efficiency (3). MATERIALS to control diffusion of gas through the needle.…”

Establishing symbiotic nitrogen fixation in cereals and other non-legume crops: The Greener Nitrogen Revolution

“…Indeed, even with the cost to the plant of reduced photosynthate by as much as 14% [87], rhizobia have been demonstrated to increase the rate of photosynthesis and other associated measures in common bean (intercellular CO 2 concentration and the transpiration rate) [70], peas [88] and soybean [87]. Rhizobial colonization of the non-legume crop rice increased photosynthetic rate, stomatal conductance, transpiration velocity, water utilization efficiency and flag leaf area.…”