Response of nitrogen-fixing water fern Azolla biofertilization to rice crop

The water fern Azolla harbors nitrogen-fixing cyanobacterium Anabaena azollae as symbiont in its dorsal leaves and is known as potent N₂ fixer. Present investigation was carried out to study the influence of fresh Azolla when used as basal incorporation in soil and as dual cropped with rice variety Mahsoori separately and together with and without chemical nitrogen fertilizer in pots kept under net house conditions. Results showed that use of Azolla as basal or dual or basal plus dual influenced the rice crop positively where use of fern as basal plus dual was superior and served the nitrogen requirement of rice. There was marked increase in plant height, number of effective tillers, dry mass and nitrogen content of rice plants with the use of Azolla and N-fertilizers alone and other combinations. The use of Azolla also increased organic matter and potassium contents of the soil.

Microbial fixation of CO2 in water bodies and in drylands to combat climate change, soil loss and desertification

The growing concern for the increase of the global warming effects due to anthropogenic activities raises the challenge of finding novel technological approaches to stabilize CO2 emissions in the atmosphere and counteract impinging interconnected issues such as desertification and loss of biodiversity. Biological-CO2 mitigation, triggered through biological fixation, is considered a promising and eco-sustainable method, mostly owing to its downstream benefits that can be exploited. Microorganisms such as cyanobacteria, green algae and some autotrophic bacteria could potentially fix CO2 more efficiently than higher plants, due to their faster growth. Some examples of the potential of biological-CO2 mitigation are reported and discussed in this paper. In arid and semiarid environments, soil carbon sequestration (CO2 fixation) by cyanobacteria and biological soil crusts is considered an eco-friendly and natural process to increase soil C content and a viable pathway to soil restoration after one disturbance event. Another way for biological-CO2 mitigation intensively studied in the last few years is related to the possibility to perform carbon dioxide sequestration using microalgae, obtaining at the same time bioproducts of industrial interest. Another possibility under study is the exploitation of specific chemotrophic bacteria, such as Ralstonia eutropha (or picketii) and related organisms, for CO2 fixation coupled with the production chemicals such as polyhydroxyalkanoates (PHAs). In spite of the potential of these processes, multiple factors still have to be optimized for maximum rate of CO2 fixation by these microorganisms. The optimization of culture conditions, including the optimal concentration of CO2 in the provided gas, the use of metabolic engineering and of dual purpose systems for the treatment of wastewater and production of biofuels and high value products within a biorefinery concept, the design of photobioreactors in the case of phototrophs are some of the issues that, among others, have to be addressed and tested for cost-effective CO2 sequestration.

Phytostimulation and biofertilization in wheat by cyanobacteria

Cyanobacteria are commonly used for the phytostimulation and biofertilization of agriculture crops due to their nitrogen-fixing ability. However, the contribution by their phytohormones has been neglected. This study focuses on the screening of rhizospheric and free-living cyanobacteria for in vitro phytohormones production and growth stimulation in wheat. Selected isolates were shown to release cytokinin and indole-3-acetic acid (IAA) by using UPLC coupled with MS/MS via an electrospray interface. The maximum cytokinin and IAA concentration was 22.7 pmol mg(-1) ch-a and 38 pmol mg(-1) ch-a, respectively, in the culture medium of Chroococcidiopsis sp. Ck4 and Anabaena sp. Ck1. The growth of wheat inoculated with cyanobacterial strains was stimulated under axenic as well as field conditions. Seed germination, shoot length, tillering, number of lateral roots, spike length, and grain weight were significantly enhanced in inoculated plants. The maximum increase in grain weight (43%) was demonstrated in wheat plants inoculated with Chroococcidiopsis sp. Ck4 under natural conditions. Positive linear correlation of cyanobacterial cytokinin with shoot length (r = 0.608; P = 0.01), spike length (r = 0.682; P = 0.01), and grain weight (r = 0.0.869; P = 0.01) was recorded. Similarly, cyanobacterial IAA was correlated with the root growth parameters shoot length (r = 0.588; P = 0.01), spike length (r = 0.0.689; P = 0.01), and weight of seeds (r = 0.480; P = 0.05). The endogenous phytohormones pool of the plant was enhanced significantly as a result of the plant-cyanobacteria association in the rhizosphere. It was concluded that cyanobacterial phytohormones are a major tool for improved growth and yield in wheat.