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Significant increases in P demand by plants are likely to happen under elevated CO2 due to the stimulation of photosynthesis, and subsequent growth responses. Elevated CO2 alters P acquisition through changes in root morphology and increases in rooting depth. Moreover, the quantity and composition of root exudates are likely to change under elevated CO2, due to the changes in carbon fluxes along the glycolytic pathway and the tricarboxylic acid cycle. As a consequence, these root exudates may lead to P mobilization by the chelation of P from sparingly soluble P complexes, by the alteration of the biochemical environment and by changes to microbial activity in the rhizosphere. Future research on chemical, molecular, microbiological and physiological aspects is needed to improve understanding of how elevated CO2 might affect the use and acquisition of P by plants.

A rhizobox experiment was conducted to examine the P acquisition characteristics of cotton (Gossypium hirsutum L.), wheat (Triticum aestivum L.) and white lupin (Lupinus albus L.) under P-deficient conditions. We aimed to identify whether cotton is physiologically efficient at acquiring P through release of protons, phosphatases or carboxylates. Plants were pre-grown in the upper compartment of rhizoboxes filled with a sand and soil mixture to create a dense root mat against a 53 μm polyester mesh. For each species, two P treatments (0 and 20 mg P kg −1 ) were applied to the upper compartment in order to create P-deficient and P-sufficient plants. At harvest, the upper compartment with intact plants was used for collection of root exudates while the lower soil compartment was sliced into thin layers (1 mm) parallel to the rhizoplane.Noticeable carboxylates release was only detected for white lupin. All P-deficient plants showed a capacity to acidify their rhizosphere soil to a distance of 3 mm. The activity of acid phosphatase was significantly enhanced in the soil-root interfaces of P-stressed cotton and wheat. Under P-deficient conditions, the P depletion zone of cotton from the lower soil compartment was narrowest (<2 mm) among the species. Phosphorus fractionation of the rhizosphere soil showed that P utilized by cotton mainly come from NaHCO 3 -P i and NaOH-P o pools while wheat and white lupin markedly depleted NaHCO 3 -P i and HCl-P pools, and the depletion zone extended to 3 mm. Wheat also depleted NaOH-P o to a significant level irrespective of P supply. The study suggests that acquisition of soil P is enhanced through P mobilization by root exudates for white lupin, and possibly proton release and extensive roots for wheat under P deficiency. In contrast, the P acquisition of cotton was associated with increased activity of phosphatases in rhizosphere soil.

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Hydraulic lift can be a desirable characteristic for cotton growing in areas that experience frequent drying of the topsoil.

In floriculture, plant residues represent 90% of the total solid residues of the production process. It is important to look for alternatives of waste management, in order to be used;An alternative is composting. The objective of this investigation was to evaluate in 4 times with intervals of 11 weeks, the effect of the use of flower compost on some physical, chemical and biological properties of a soil cultivated with sunflower (Helianthus annuus) in greenhouse. The compost three types used: 100% from dianthus, 100% from sunflower and mixed residues (sunflower-dianthus), which were incorporated into the soil at doses of 8, 12 and 16 Kg / m2 and the control. The characterization and composition of the compost were determined and the chemical properties (pH, Effective Cation Exchange Capacity (CICE), Organic Carbon (CO), phosphorus, nitrogen and sulfur), physical (bulk density, structural stability, porosity and Moisture retention) and biological (Colony Forming Units (CFU) of phosphate solubilizing bacteria, nitrogen fixers and respiration) of the soil and for sunflower cultivation, production was quantified and quality grades were identified. In the results obtained in this investigation, dianthus, sunflower and mixed compost obtained a C / N ratio of 11.4; 13.1 and 11.7 respectively and without the presence of pathogens (Erwinia sp. And Pseudomonas sp.). In terms of physical properties, the apparent density decreased with respect to the initial value (1.14 g / cm3) of 17% and 25% in sunflower and dianthus at doses of 16 kg / m2 respectively. The porosity percentage increased with respect to the initial value (53.9%) of 8.1% and 10.5% in sunflower and mixed at doses of 16 kg / m2 respectively; while the structural stability and humidity retention did not present statistical differences with respect to the control. In chemical properties, the pH increased with respect to the initial value (6.7) by 0.62 and 0.69 in sunflower and dianthus at doses of 16 kg / m2 respectively. In the CICE, it increased with respect to the initial value (19.4 cmol / kg) 7.3 and 10.8 cmol / kg in sunflower and mixed at doses of 12 kg / m2 and 16 kg / m2 respectively. In CO it increased with respect to the initial value (2.44%) 2.33% in mixed at a dose of 16 kg / m2. In N, P and S there were no differences with respect to the control.In biological properties, respiration did not show statistical differences with respect to the control, in the CFU of phosphate-solubilizing bacteria, at time 4, the dose of 16 kg / m2 showed values of 3.5 X 106, 2.24 X 106, 2.29 X 106 CFU / g soil for mixed, dianthus and sunflower respectively, being greater than the control (0.64 X 106 CFU / g soil); In the CFU XII Efecto de la adición de compost de flores sobre algunas propiedades químicas, físicas y biológicas del suelo of nitrogen fixers, the highest values were recorded in dianthus the dose of 12 Kg / m2(1,189 x 107 CFU / g soil), sunflower the dose of 12 Kg / m2 (9,194 x 106 CFU / g soil), mixed the dose of 16 Kg / m2 (3,025 x 107 CFU / g soil) which...