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This report aims to identify and discuss in detail the various ways that nettle can be utilised as a conservation tool by reviewing and evaluating existing literature on this subject. The common stinging nettle (Urtica dioica L.) (nettle) is a nitrophilous ruderal species, distributed across Europe from the Arctic fringe to the Mediterranean up to an altitude of 2500m, frequently colonising highly disturbed and nutrient enriched ground. Sympodial growth of rhizomes and stolons with nodal rooting and aerial shoots reaching ~1.5m when mature with post-anthesis nodal branching. Unifoliate, coarsely serrated, lanceolate, acuminate leaves covered by hairs and stinging trichomes on both the adaxial and abaxial surfaces with a net-like vascular system typical of dicotyledons. Trichomes are silica tubes with a bulbous tip which fractures under pressure leaving a sharp needle-like point. The base of the trichomes contain toxins including formic acid, histamine and acetycholine which cause irritation, swelling and redness to skin. Dioica comes from the Latin word 'dioecious' which translates as 'two houses' and is thought to refer to the presence of single sex plants. Male plants have four patent, densely clustered inflorescences per node, containing fours stamens which leptokurtically release pollen upon anthesis. Female plants also have four inflorescences per node but these are more pendent than male plants and the flowers contain a single pistel and achene. Both pollen and seeds can be dispersed by wind although seeds have a hairy calyx which allows transportation by mammalian vectors. Nettle seeds need direct sunlight to initiate germination which accounts for their association with disturbed ground. Nettle demonstrates a high level of phenotypic plasticity and varies greatly in height, leaf size and shape and trichome density. Herbivory by mammals increases the density of stinging trichomes which effectively deters most mammalian herbivores. However invertebrate herbivores appear to be unaffected by the trichomes and herbivory by them appears to have no effect on trichome density.
Nettle has historically been cultivated for fibre, medicinal and culinary use and is currently making a comeback in scientific research with a potential contribution to HIV treatment, GM crops and sustainable fibre composites.
Evaluation and critical appraisal of the literature (750).
Nettle provides shelter and food for a range of invertebrates including many specialist species which are more or less confined to nettles such as Apion urticarium. The abundance of invertebrate prey species found on nettle boosts predatory invertebrate populations which organic gardeners and farmers find beneficial in controlling pest species such as aphids.
The level of invertebrate fauna associated with nettle provides good foraging for insectivorous birds and due to the abundance of fruits on female nettle plants also provide a good source of seeds for granivorous birds.
Stands of nettle have good buffering qualities due to its high uptake of nutrients, particularly nitrate, from the soil.
However, nettle in some nutrient rich areas can also have a negative effect on biodiversity due to its competitive ability. Where nutrients allow, nettle can quickly establish into thick monospecific stands.
One solution to the competitive advantage of nettles is to harvest them. Many farmers currently mow nettles, particularly where they impinge upon public rights of way, and leave the cuttings in place which results in the nutrients being returned to the soil. By removing the cuttings the nutrient content of the soil will drop which could when used as a conservation tool aid the removal of nutrients from sensitive areas or help with restoration of areas damaged by agricultural applications of fertiliser such as wildflower/hay meadows.
An added benefit of harvesting nettle is the possibility of utilising the crop as a source of biofuel, medicinal extract for use on a range of species (apiary), [DNA extract for GM crops attributing anti-fungal properties to crop plants thus reducing the need for fungicides], a green compost or as a compost extract.
Compost extracts show high potential to increase crop yields by increasing nitrate uptake by plants which also has the added benefit of reducing eutrophication due to less leaching from the soil and could also reduce reliance of synthetic fertilisers derived from fossil fuels.
Literature gap, hypothesis and proposal (250).
There has been some successful research into the use of compost extracts as a supplement to fertiliser that has shown yields can be increased. Some studies go on to suggest that nutrient leaching leading to eutrophication can also be curtailed and the application of fertiliser with its associated cost reduced. However most studies have failed to detail the contents of the compost and although some have identified the nutrient content of the extract none have considered manipulating the ingredients in order to increase this. Therefore it would be advantageous to test the hypothesis that a compost extract supplement from a species with high nitrate content, such as nettle, can when combined with 80% application of conventional fertiliser increase yields beyond those of crops with a maximum application of conventional fertiliser.
To test this hypothesis it is suggested that a greenhouse test be carried out to compare untreated wheat (control) with wheat treated with the maximum dose of conventional fertiliser and wheat treated with 80% of the maximum dose of conventional fertiliser supplemented with nettle compost extract. Growth rates (sward height per day), number and weight of grains, root length and dry weight and total dry weight of all biomass will all be measured and compared to ascertain the effects of the treatment upon the subjects. The three separate treatments need to be housed, but isolated, within the same greenhouse/poly tunnel to ensure consistency of abiotic factors and replication (number of pots), substrate and water availability should all be standardised.
If carefully managed nettle can aid conservation through direct and indirect effects on ecosystems. However, due to anthropogenically-enhanced soil nutrient content in many areas nettles can, without intervention, reduce biodiversity as a result of its competitive adavantage. Possible conservation tool use: sponge to mop up excessive soil nutrients / buffer zone between agricultural land and sensitive areas / renewable source of biofuel / sustainable organic medicine (apiary) / nitrate rich green compost / compost extract.