![]() ![]() ![]() Despite the abundance of microbial nitrogen fixation, nitrogen is still a limiting resource, particularly for many plants without nitrogen-fixing symbionts. Free-living nitrogen-fixing bacteria (e.g., Azotobacter) also contribute to the nitrogen flux in the soil, as they are able to release useable nitrogen (nitrate or ammonia) into the soil. As a result, many plant species (e.g., legumes) form symbiotic associations with microorganisms that can fix atmospheric nitrogen that is then made accessible to the plant. ![]() However, nitrogen is often a limiting resource for primary producers and this deficit is due, in large part, to the inability of plants to directly utilize atmospheric nitrogen, and their subsequent reliance on microbial nitrogen fixation. ![]() Nitrogen exists in the soil in numerous forms, and these forms can be rapidly converted from inorganic to organic and vice versa. Root colonizing fungi are found in disparate fungal phylogenetic lineages, indicating possible convergent evolutionary strategies between taxa, evolution potentially driven by access to carbon-containing root exudates. They can infect a wide range of insect hosts and also form endophytic associations in which they transfer insect-derived nitrogen to the plant. These soil-inhabiting fungi form a remarkable symbiosis with certain plant species. Finally, a specialized group of endophytic, insect-pathogenic fungi (EIPF) provide host plants with insect-derived nitrogen. Secondly, numerous plants form associations with mycorrhizal fungi that can provide soluble nitrogen from the soil, some of which may be insect-derived nitrogen, obtained from decaying insects or insect frass. Insect carnivorous plants such as pitcher plants and sundews ( Nepenthaceae/ Sarraceniaceae and Drosera respectively) are able to obtain substantial amounts of nitrogen from the insects that they capture. First, we show specialized adaptations by carnivorous plants in low nitrogen habitats. In this review we show three specialized plant adaptations that allow for the recovery of insect nitrogen that is, plants gaining nitrogen from insects. A portion of this plant-associated nitrogen is then lost to insects through herbivory, and insects represent a nitrogen reservoir that is generally overlooked in nitrogen cycles. One of the best-known adaptations is that of plant symbiosis with nitrogen-fixing bacteria this is the major route by which nitrogen is incorporated into plant biomass. Many plants have evolved adaptations in order to survive in low nitrogen environments. ![]()
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