Interaction of temperature and CO2 enrichment on soybean : Photosynthesis and seed yield

Seed yield and photosynthetic responses of soybean (Gtycine mnx L. Met. ,Ransom') were studied in growth chambers at day/night temperatures of 18/12,22/16, and 26/20'C and atmospheric CO, concentrations of 350, 6i5 and 1000 pL L-1. No seeds were produced at 18/12°C within any of the CO2 concentrations. Numbers of pods and seeds increased with increasing temperature and CO2 levels. Carbon dioxide enrichment increased seed yield of soybean grown at moderately cool temperatures. This increase was associated with an increase in net photosynthetic rate. Leaf photosynthesis in response to CO2 enrichment increased more at 22/16°C than at 26/20°C. Increases in, temperature and CO2 levels enhanced total growth of plants but hastened senescence of leaves. The extended photosynthetic capacity at cool temperatures did not result in allocating more dry matter to developing pods. CO2 enrichment at 26/20°C resulted in greater seed yield increases than CO2 enrichment at lower temperatures

The response of Plantago major ssp pleiosperma to elevated CO2 is modulated by the formation of secondary shoots

The effect of elevated CO2 on the relative growth rate (RGR) of Plantago major ssp. pleiosperma was studied during the vegetative stage, in relation to plant development, by growing plants at 350 mu l l(-1) or at 700 mu l l(-1) CO2 in non-limiting nutrient solution with nitrate. To minimize interference by the accumulation of non-structural carbohydrates in the interpretation of results, RGR was expressed on a f. wt basis (RGR(FW)), as were all plant weight ratios. Stimulation of the RGR(FW) Of the whole plant by elevated CO2 was transient, and did not last longer than 8 d. At the same time a transient increase in root weight ratio (RWR) was observed. In order to investigate whether the transient effect of elevated CO2 on RGR(FW) was size-dependent, the data were plotted versus total f. wt (log(e) transformed). The transient period of stimulation of RGR(FW) and of RWR by elevated CO2 was still found, but in both CO2 treatments RGR(FW) decreased after a certain plant size had been reached. This size coincided with the stage at which secondary shoots started to develop, and was reached earlier in plants grown at elevated CO2. The RGR of these secondary shoots (RGR(see)) was Still increased when the period of whole plant stimulation of RGR(FW) had ended, indicating that the development of these new sinks took priority over a continuation of the stimulation of RWR. It is hypothesized that in this Plantago subspecies the response of the RGR(FW) of the whole plants to elevated CO2 is modulated by the formation of secondary shoots. Apparently, partitioning of the extra soluble carbohydrates at elevated CO2 to this tissue takes precedence over partitioning to the roots. resulting in a cessation of stimulation of plant RGR(FW) by elevated CO2.info:eu-repo/semantics/publishedVersio

Effects of Two Species of VA Mycorrhizal Fungi on Drought Tolerance of Winter Wheat

Roots and soils from western Nebraska fields of native and planted grasslands, and winter wheat of varied fallow-wheat cultivation duration, were evaluated for vesicular-arbuscular (VA) mycorrhizal root infection and spore numbers and types. Increased cultivation decreased percentage mycorrhizal infection in wheat and reduced spore numbers of Glomus fasciculatus, the dominant VA mycorrhizal fungus in these soils. Spore numbers of other VA mycorrhizal fungi did not change significantly with cultivation although mean numbers of G. mosseae increased with continued wheat production. Water relations and growth were determined for greenhouse-grown non-mycorrhizal, G. fasciculatus-infected, and G. mosseae-infected wheat in wet and dry soils. Stomatal conductances were higher in mycorrhizal than in non-mycorrhizal plants in both wet and dry treatments. Stomatal closure in mycorrhizal plants occurred at lower leaf water potentials (ψ1) and after greater desiccation than in non-mycorrhizal plants, but some leaves of G. masseae-infected plants showed no stomatal response to drought and continued to transpire at ψ1 as low as -4◦1 MPa. Leaf osmotic adjustment was greater for G. fasciculatus-infected plants. Non-mycorrhizal and G. fasciculatus-infected plants had equal dry wts in both wet and dry conditions. Infection by G. fasciculatus appeared to increase wheat drought tolerance while infection by G. mosseae did not

Yield responses of wild C3 and C4 crop progenitors to sub-ambient CO2 : A test for the role of CO2 limitation in the origin of agriculture.

Limitation of plant productivity by the low partial pressure of atmospheric CO2 (Ca ) experienced during the last glacial period is hypothesised to have been an important constraint on the origins of agriculture. In support of this hypothesis, previous work has shown that glacial Ca limits vegetative growth in the wild progenitors of both C3 and C4 founder crops. Here we present data showing that glacial Ca also reduces grain yield in both crop types. We grew four wild progenitors of C3 (einkorn wheat and barley) and C4 crops (foxtail and broomcorn millets) at glacial and post-glacial Ca , measuring grain yield, and the morphological and physiological components contributing to these yield changes. The C3 species showed a significant increase in unthreshed grain yield of ~50% with the increase in Ca , which matched the stimulation of photosynthesis, suggesting that increases in photosynthesis are directly translated into yield at sub-ambient levels of Ca . Increased yield was controlled by a higher rate of tillering, leading to a larger number of tillers bearing fertile spikes, and increases in seed number and size. The C4 species showed smaller, but significant, increases in grain yield of 10-15%, arising from larger seed numbers and sizes. Photosynthesis was enhanced by Ca in only one C4 species and the effect diminished during development, suggesting that an indirect mechanism mediated by plant water relations could also be playing a role in the yield increase. Interestingly, the C4 species at glacial Ca showed some evidence that photosynthetic capacity was upregulated to enhance carbon capture. Development under glacial Ca also impacted negatively on the subsequent germination and viability of seeds. These results suggest that the grain production of both C3 and C4 crop progenitors was limited by the atmospheric conditions of the last glacial period, with important implications for the origins of agriculture. This article is protected by copyright. All rights reserved