Vanita Jain

Biomass production and nutritional levels of berseem (Trifolium alexandrium) grown under elevated CO2

There is little available information about the effect of elevated CO2 on the growth and mineral nutrients of fodder crops. To investigate the changes in vegetative biomass and nutrient concentration of berseem (Trifolium alexandrium L.), an important forage legume, was grown in ambient (360 μl l−1) as well as elevated (600 μl l−1) CO2 conditions from germination onwards in open top chambers. Elevated CO2 increased the leaf size, plant height and fresh and dry mass of shoots. There was more partitioning of photosynthates towards the growth of new branches than towards the growth of leaves. Leaf nitrogen, soluble proteins, calcium, iron and nitrate reductase (NR) activity decreased in elevated CO2 while leaf carbon and phosphorus contents increased. The results suggest that berseem grown in elevated CO2 throughout the crop season can produce more fodder in less time. The study concludes that elevated CO2 may increase the fodder production by 30–35% but will adversely affect the nutritional quality of the forage due to reduction in nitrogen, protein, calcium and iron concentration in leaves on a unit dry weight basis. On a unit area basis, however, there will be an increase in total nutrient content, including nitrogen, due to increased fodder biomass in elevated CO2.

Effects of elevated CO2 and nitrogen on wheat growth and photosynthesis

The effects of nitrogen [75 and 150 kg (N) ha−1] and elevated CO2 on growth, photosynthetic rate, contents of soluble leaf proteins and activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and nitrate reductase (NR) were studied on wheat (Triticum aestivum L. cv. HD-2285) grown in open top chambers under either ambient (AC) or elevated (EC) CO2 concentration (350 ± 50, 600 ± 50 μmol mol−1) and analyzed at 40, 60 and 90 d after sowing. Plants grown under EC showed greater photosynthetic rate and were taller and attained greater leaf area along with higher total plant dry mass at all growth stages than those grown under AC. Total soluble and Rubisco protein contents decreased under EC but the activation of Rubisco was higher at EC with higher N supply. Nitrogen increased the NR activity whereas EC reduced it. Thus, EC causes increased growth and PN ability per unit uptake of N in wheat plants, even if N is limiting.

Physiological and molecular alterations in plants exposed to high [CO2] under phosphorus stress

Atmospheric [CO2] has increased substantially in recent decades and will continue to do so, whereas the availability of phosphorus (P) is limited and unlikely to increase in the future. P is a non-renewable resource, and it is essential to every form of life. P is a key plant nutrient controlling the responsiveness of photosynthesis to [CO2]. Increases in [CO2] typically results in increased biomass through stimulation of net photosynthesis, and hence enhance the demand for P uptake. However, most soils contain low concentrations of available P. Therefore, low P is one of the major growth-limiting factors for plants in many agricultural and natural ecosystems. The adaptive responses of plants to [CO2] and P availability encompass alterations at morphological, physiological, biochemical and molecular levels. In general low P reduces growth, whereas high [CO2] enhances it particularly in C3 plants. Photosynthetic capacity is often enhanced under high [CO2] with sufficient P supply through modulation of enzyme activities involved in carbon fixation such as ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). However, high [CO2] with low P availability results in enhanced dry matter partitioning towards roots. Alterations in below-ground processes including root morphology, exudation and mycorrhizal association are influenced by [CO2] and P availability. Under high P availability, elevated [CO2] improves the uptake of P from soil. In contrast, under low P availability, high [CO2] mainly improves the efficiency with which plants produce biomass per unit P. At molecular level, the spatio-temporal regulation of genes involved in plant adaptation to low P and high [CO2] has been studied individually in various plant species. Genome-wide expression profiling of high [CO2] grown plants revealed hormonal regulation of biomass accumulation through complex transcriptional networks. Similarly, differential transcriptional regulatory networks are involved in P-limitation responses in plants. Analysis of expression patterns of some typical P-limitation induced genes under high [CO2] suggests that long-term exposure of plants to high [CO2] would have a tendency to stimulate similar transcriptional responses as observed under P-limitation. However, studies on the combined effect of high [CO2] and low P on gene expression are scarce. Such studies would provide insights into the development of P efficient crops in the context of anticipated increases in atmospheric [CO2].

Impact of CO2 enrichment and variable nitrogen supplies on composition and partitioning of essential nutrients of wheat

This study was conducted to determine effects of nitrogen supply (75 and 150 kg(N) ha−1) and CO2 enrichment on partitioning of macro and micro nutrients in wheat (Triticum aestivum L. cv. HD-2285). Plants were grown from seedling emergence to maturity inside open top chambers under ambient CO2 (CA, 350 ± 50 μmol mol−1) and elevated CO2 (CE, 600 ± 50 μmol mol−1). Leaves, stems and roots of the same physiological age were analyzed for carbon, nitrogen, calcium, copper, iron, zinc and manganese content at 40, 60 and 90 d after germination. C, Cu, Mn and Zn content was higher in the stem, leaves and roots on dry mass basis under CE than CA. However, N and Fe contents decreased in CE grown plants. Ca content was unaffected due to CE and variable N supplies.

Inhibition of nitrate uptake and assimilation in wheat seedlings grown under elevated CO2

Wheat (Triticum aestivum L.) cv PBW 343 was grown in Hoagland solution devoid of nitrogen (–N) under two CO2 levels viz. ambient (380 μLxa0L−1, AC) and elevated (600xa0±xa050 μLxa0L−1, EC) for 20xa0days in growth chambers. The rate of uptake, assimilation and accumulation of nitrate was compared. At lows nitrate concentration up to 0.5xa0mM, rate of nitrate uptake was higher in EC grown seedlings as compared to AC. Under non-limiting supply of external nitrate, the rate of uptake declined in EC grown seedlings. Nitrate reductase (NR) activity increased in EC grown seedlings at low external concentrations of nitrate. However, AC grown plants showed higher NR activity, but at very high concentrations of nitrate. EC grown plants showed low level of accumulation of nitrate in shoots under limited nitrate availability, indicating lower influx towards storage pool and more availability of nitrate in metabolic pool. Increasing nitrogen (N) fertilization therefore may not compensate for slower

Photosynthesis and nutrient composition of spinach and fenugreek grown under elevated carbon dioxide concentration

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Photosynthetic Characteristics in Two Wheat Genotypes as Affected by Nitrogen Nutrition

assimilationxa0rates under EC, as uptake and assimilation both decline under nitrate sufficient conditions. Effective management practices and changes in the pattern of fertigation may be required in response to rising atmospheric CO2 levels for wheat production.

Elevated CO2 Improves Growth and Phosphorus Utilization Efficiency in Cereal Species Under Sub-Optimal Phosphorus Supply

Study was done to compare the response of Triticum aestivum (hexaploid), Triticum durum (tetraploid) and Triticum monococcum (diploid) wheat species to the elevated CO2 using Free Air CO2 Enrichment (FACE) facility. It was demonstrated that the modern cultivar of wheat Triticum aestivum (hexaploid) was largely sink limited. It appeared to have less photosynthesis per unit leaf area than Triticum monococcum (diploid wheat). While leaf size, grain weight and amylase activity increased with the ploidy level from diploid to hexaploid wheat forms, the photosynthetic rate was reduced significantly. These wheat species responded differentially to the elevated CO2. The larger leaf area and greater seed weight and presence of 38 KDa protein band caused by elevated CO2 had additive effect in improving the productivity of hexaploid wheat by changing the source sink ratio. Whereas, such a source sink balance was not induced by elevated CO2 in diploid wheat. The increasing CO2 may present opportunities to breeders and possibly allow them to select for cultivars responsive to the elevated CO2 with better sink potential.