Why is azolla considered a natural fertilizer

The dry matter is also a source of feed for ruminants, poultry, pigs, and fish. So, Azolla is an organic or alternative source of feed for animals. Azolla can be mixed with other items to make high-quality chicken and duck feed to the relief of organic farmers.

The filamentous blue-green algae, Azolla harbor Anabaena azollae , a nitrogen-fixing Cyanobacteria under the dorsal leaves. By a special a mechanism they are able to carry out photosynthesis and release oxygen. Azolla and Cyanobacteria in symbiosis reduce atmospheric nitrogen for availability by the higher plants.

It is a fast-growing water plant which for ages has been known to act as biofertilizer and green manure in the field of rice crop by fixing nitrogen of air. In addition to using azolla as a biofertilizer, they think it could be a starting material for the production of biofuels. All while helping to clean waste water. Channels: Close.

What is azolla? That it grows in both brackish and fresh water is only one of its unique traits. Challenges Although azolla has long been used as a biofertilizer in rice paddies in China, it has been a traditional, almost coincidental co-crop, not viewed as having commercial potential. To Prapas, the answer may lie with animal and human waste.

Prapas and Reardon are pursuing funding to continue this research. Azolla is a nitrogen-fixing plant. Because flooded habitat is good for it, it is grown in lowland rice fields. It fixes atmospheric nitrogen at a rate faster than the Legume-Rhizobium symbiotic interaction under good field conditions.

It increases nitrogen mineralization in waterlogged soil when used as green manure. It improves the effectiveness of N fertilizers by reducing NH3 volatilization losses through its influence on floodwater pH, which leads to the conservation of urea-N in the system. The use of biofertilisers is quite important while practising the concepts of integrated plant nutrient management and organic farming.

Besides several microorganisms such as algae and various inorganic compound fixing bacteria, Azolla is also used as a biofertilizer in temperate as well as tropical rice-growing areas. Azolla has been in use widely in countries like China and Vietnam for centuries but it is of a recent introduction in India. Presently there are several Azolla species that are under cultivation in India e.

The information gathered on the bacterium-plant symbiosis will also help us to understand another agriculturally and environmentally important plant-fungus symbiotic system— mycorrhizae, as the two systems seem to have involved the same set of plant genes Fifth, Azolla is one of the few heterosporous pteridophyte lineages, the others being Isoetes-Selaginella , Marsileaceae, and Salviniaceae Heterospory is an intermediate condition between homospory and seed-pollen in the evolution of reproductive dispersal units in land plants.

The seed is an extremely important plant structure that provides nutrition for human and animals. As of yet, there have been only a few studies initiated to investigate evolution of the seed from a genomic perspective Because none of the heterosporous pteridophyte taxa except Azolla has any economic application, they are unlikely to be subjected to intensive studies like most model organisms. Azolla would be the only plant, if its genome is sequenced, that can provide a comparative perspective for understanding evolution of heterospory and seed.

Finally, because Azolla has been used in agricultural production and environmental pollution control for quite some time, a relatively large body of literature is already in existence, particularly on its physiology and ecology 2. Its small size, fast growth, and easy culturing should make it fairly easy to grow in laboratories. All these factors should make it easy to popularize Azolla as a model organism. What should be the goals for extensive investigations of Azolla , especially the large-scale genomic studies?

First, a number of constraints that currently limit the use of Azolla as a biofertilizer can be relaxed or removed, so that it can be used on a larger scale in a wide variety of environmental conditions. In the summer of tropics the water fern cannot propagate fast enough to keep in pace with the growth of rice plants.

Likewise, in temperate regions application of Azolla is hampered due to the low temperature. Another problem often encountered in Azolla application is its phosphor P requirement, as the water fern can derive nitrogen from the cyanobacterial symbiont. A fairly minimal work on mutagenesis, selection, and breeding of Azolla and their symbionts has resulted in significant improvement of both these traits. The third area where improvement can be made to increase the use of Azolla in rice cultivation is its propagation.

The current practice is that Azolla is raised in a nursery field or a pond, where the water fern mostly reproduces by asexual reproduction, and is then transported to rice fields 2. There is a fair amount of labor involved in harvesting, transporting, and dispersing the water fern in this practice.

If sexual reproduction can be used to propagate Azolla , only a few handfuls of spores need to be thrown into the field and the resulting labor cost can be greatly reduced 3. Yet, this method is still not available for large-scale agricultural production. For these three major bottleneck factors, a completely sequenced Azolla genome and a large number of ensuing studies can surely improve our understanding of physiology particularly temperature sensitivity and phosphor requirement and reproductive biology of the water fern, and thus increase our ability to genetically engineer strains that can grow in different environmental conditions and be propagated by spores.

Hence, it can be predicted that Azolla will be used more commonly in agricultural production and bioremediation. The kind of extensive and intensive studies as usually applied to model organisms on Azolla is also likely to greatly enhance our understanding on the symbiotic relationship of the water fern with N 2 -fixing cyanobacteria.

Given the paucity of N 2 -fixing plant-bacterium symbioses that have ever evolved in land plants see above for cyanobacteria; ref. Therefore, it will be more efficient to study, improve, and make use of the naturally occurring systems like those of Azolla-Anabaena and legumes-rhizobia in order to solve the nitrogen supply problem for agricultural production. The fact that no monocot has any symbiotic association with N 2 -fixing bacteria further highlights the potential difficulty to genetically engineer a cereal-bacterium N 2 -fixing system.

Thus, Azolla-Anabaena symbiosis will likely remain as the only choice for supplying the fields with nitrogen in a self-renewable and environmentally sustainable way for rice and rice-wheat growing countries.

It is of a pragmatic necessity, not just an intellectual curiosity, to understand and improve this system. Initiating an Azolla genome-sequencing project will itself provide an essential amount of basic genomic information about this organism, opening a way for its future research. More importantly, the project will make the Azolla-Anabaena system more attractive to many experimental biologists for intensive studies of both the plant and bacterium, which have not been as well studied as the legumes and rhizobia.

Historically, designation of an organism as a model naturally leads to intensive characterization of every aspect of the organism. An increased understanding of symbiotic relationships between plants and bacteria or fungi, as can be obtained from studies of Azolla-Anabaena , legumes-rhizobia, and plant-mycorrhizae, will provide the much-needed knowledge to help formulate environmentally sustainable policies and practices in agricultural production.

The last major goal of making Azolla a model organism for genomic studies is to gather information from the species that represent a major and intermediate step in plant evolution so that comparative analyses can be conducted to shed light on many aspects of the nuclear genome evolution in green plants. One such aspect concerns genome size.

The plant nuclear genome seems to have increased steadily in size at every major step of phyletic evolution, e. This increase may have been achieved through polyploidization 36 , as a gradually lengthened sporophyte diploid generation in the life cycle provides an opportunity for manifesting the evolutionary advantage of multiple copies of the same or similar genes.

Along this major trend, occasional dramatic genome size expansion e. Such phenomena have been seen in the sequenced genomes of human 24 and fission yeast The Mb Azolla genome is smaller than most pteridophyte genomes 38 , but significantly larger than those of Arabidopsis 4 and rice 5. Comparisons between the two angiosperm genomes have yielded several interesting insights into possible mechanisms of the genome size variation in plants. First, plant genomes are organized in such a way that the transposon-derived repetitive sequences are scattered between gene-islands where the plant genes are clustered; thus, the increase of genome size due to transposon expansion is largely intergenic 5.

Second, the rice genome has twice as many genes as predicted for the Arabidopsis genome, indicating that an ancient genome duplication event had happened after the split of monocot and eudicot plants. Surprisingly, the extra set of genes in the rice genome lacks homologs in any other known genomes sequenced so far but is definitely transcribed; some genes are expressed at high levels in rice tissues 5. Third, the average size of the rice genes is larger than that of the Arabidopsis , attributable mainly to the gradual intron size increase not due to transposon insertions over the evolutionary time scale.

Our preliminary analysis has shown that the difference is extendable between the genes of monocot and eudicot plants in general, regardless of the actual genome sizes.

Such a maneuver in DNA composition suggests that evolutionary forces, such as mutation and selection at the DNA sequence level, are working on the genes constantly. Taken together, Azolla should have fewer genes than the two sequenced angiosperms, as it has not evolved many features of the latter two, e.

It may have lineage-specific transposons that are propagating or deteriorating to affect the genome size. However, we will not know the answer with certainty until the Azolla genome is fully sequenced. Another aspect regarding genome evolution involves gene content.

A few studies that have examined evolution of multigene families in land plants show that the copy number increases steadily from charophytes to angiosperms, e. It is not known whether the gene copy number increases via individual gene duplication, chromosome segmental duplication, or polyploidization.

If the last two mechanisms are responsible for evolution of the multigene families, the next question is to what extent the synteny has been maintained. Comparisons among three flowering plants, Arabidopsis , tomato, and soybean show that there are major syntenic blocks conserved on the chromosomes after duplication It is tempting to ask how far back during land plant evolution this kind of large-scale syntenic relationships was maintained, and what kind of evolutionary forces were behind the maintenance.

It has been known for a long time that most eukaryotic genomes, especially those of high plants and animals, are packed with highly and moderately repetitive DNAs from DNA denaturation and renaturation Cot curve plotting studies. Now whole genome sequence analyses have confirmed this aspect of genome organization. At least one quarter of the rice genome is of recognizable transposons in origin 5 , whereas for a large genome like that of human, transposons account for about half of the genome What are the evolutionary and functional roles of this massive amount of transposon sequences in the genome?

It has been suggested that they are involved in origins and functions of centromeres Further, they are responsible for chromosome rearrangements Hence, these seemingly useless DNAs, as judged by geneticists in the traditional sense of coding capacity for phenotype, are actually fundamental forces in maintaining faithful inheritance of the information in the genome from generation to generation, and at the same time breaking up syntenic relationships among loci after replicated chromosomes are partitioned into daughter species and generating genetic diversity via recombination and independent assortment.

Similarly, introns have been dubbed molecular parasites, but now we know that they play an extremely important role in eukaryotes to generate protein diversity by making alternative splicing possible in animal genomes, such as the human genome It has been suggested that plants may not use much of the cellular alternative splicing machinery to the same extent as animals 5 , but this conclusion is drawn from comparisons of two small, perhaps atypical plant genomes Arabidopsis and rice, see Table1 with the large human genome.

These are just a few clues seen from a very small sample of diversity of life that has been subjected to whole genome sequencing and analysis. It would be ideal to see if the validity and generality of the conclusions drawn from these studies can be extended to all life when a larger diversity of representative organisms is investigated.

Thus, a plant like Azolla makes an ideal candidate for future genome sequencing projects to help us understand the evolution of the nuclear genome in plants. In a broader perspective, as we turn over more rocks sequenced genomes , we will certainly see more surprises new insights into genome biology and evolution! The Azolla genome most likely will be sequenced through a whole genome shotgun approach due to the genome size and the readiness of sequence-assembly software tools.

It can be carried out in two phases, a genome survey sequencing phase and a gene-map construction phase. In the first phase of the project, sequencing reads or sequencing traces, usually about bp in average length of a low coverage 0. An adequate amount of expressed sequence tags ESTs or cDNAs say, representing over 10, unique genes from different tissues or developmental stages to provide enough sample diversity of the plant should also be sequenced. In order to localize genes on chromosomes, some large-insert clone libraries, such as those of bacterial artificial chromosomes BACs and cosmids, should be constructed concurrently for subsequent physical mapping.

In the second phase of the project, significant sequence coverage should be achieved, usually in a range of X of the genome equivalents.