分类： 生物学 >> 植物学 >> 植物学研究、实验与植物演化、发展 提交时间： 2016-05-31
摘要： Grassland agriculture is experiencing a number of threats including declining profitability and loss of area to other land uses including expansion of the built environment as well as from cropland and forestry. The use of grassland as a natural resource either in terms of existing vegetation and land cover or planting of new species for bioenergy and other nonfood applications presents an opportunity, and potential solution, to maintain the broader ecosystem services that perennial grasslands provide as well as to improve the options for grassland farmers and their communities. This paper brings together different grass or grassland-based studies and considers them as part of a continuum of strategies that, when also combined with improvements in grassland production systems,will improve the overall efficiency of grasslands as an important natural resource and enable a greater area to be managed, replanted or conserved. These diversification options relate to those most likely to be available to farmers and land owners in the marginally economic or uneconomic grasslands of middle to northern Europe and specifically in the UK. Grasslands represent the predominant global land use and so these strategies are likely to be relevant to other areas although the grass species used may vary. The options covered include the use of biomass derived from the management of grasses in the urban and semi urban environment, semi-natural grassland systems as part of ecosystem management, pasture in addition to livestock production, and the planting and cropping of dedicated energy grasses. The adoption of such approaches would not only increase income from economically marginal grasslands, but would also mitigate greenhouse gas emissions from livestock production and help fund conservation of these valuable grassland ecosystems and landscapes, which is increasingly becoming a challenge.
分类： 生物学 >> 植物学 >> 植物生态学和植物地理学 提交时间： 2016-05-04
Jon P. McCalmont
Astley Hastings
Niall P. McNamara
Goetz M. Richter
Paul Robson
Iain S. Donnison
John Clifton-Brown
摘要： Planting the perennial biomass crop Miscanthus in the UK could offset 213Mtoileq.yr1, contributing up to 10% of current energy use. Policymakers need assurance that upscaling Miscanthus production can be performed sustainably without negatively impacting essential food production or the wider environment. This study reviews a large body of Miscanthus relevant literature into concise summary statements. Perennial Miscanthus has energy output/input ratios 10 times higher (47.32.2) than annual crops used for energy (4.70.2 to 5.50.2), and the total carbon cost of energy production (1.12gCO2-Ceq.MJ1) is 2030 times lower than fossil fuels. Planting on former arable land generally increases soil organic carbon (SOC) with Miscanthus sequestering 0.72.2MgC4-Cha1yr1. Cultivation on grassland can cause a disturbance loss of SOC which is likely to be recovered during the lifetime of the crop and is potentially mitigated by fossil fuel offset. N2O emissions can be five times lower under unfertilized Miscanthus than annual crops and up to 100 times lower than intensive pasture. Nitrogen fertilizer is generally unnecessary except in low fertility soils. Herbicide is essential during the establishment years after which natural weed suppression by shading is sufficient. Pesticides are unnecessary. Water-use efficiency is high (e.g. 5.59.2gaerial DM (kgH2O)1, but high biomass productivity means increased water demand compared to cereal crops. The perennial nature and belowground biomass improves soil structure, increases water-holding capacity (up by 100150mm), and reduces run-off and erosion. Overwinter ripening increases landscape structural resources for wildlife. Reduced management intensity promotes earthworm diversity and abundance although poor litter palatability may reduce individual biomass. Chemical leaching into field boundaries is lower than comparable agriculture, improving soil and water habitat quality.
分类： 生物学 >> 植物学 >> 植物生态学和植物地理学 提交时间： 2016-05-04
摘要： A 6-ha field at Aberystwyth, UK, was converted in 2012 from semi-improved grassland to Miscanthus x giganteus for biomass production; results from transition to the end of the first 3years are presented here. An eddy covariance sensor mast was established from year one with a second mast added from year two, improving coverage and providing replicated measurements of CO2 exchange between the ecosystem and atmosphere. Using a simple mass balance approach, above-ground and below-ground biomass production are combined with partitioned CO2 fluxes to estimate short-term carbon deltas across individual years. Years one and two both ended with the site as a net source of carbon following cultivation disturbances, cumulative NEE by the end of year two was 138.5716.91gCm2. The site became a cumulative net sink for carbon by the end of June in the third growing season and remained so for the rest of that year; NEE by the end of year three was 616.52 39.39gCm2. Carbon gains were primarily found in biomass pools, and SOC losses were limited to years one (1.43MgCha1yr1) and two (3.75MgCha1yr1). Year three saw recoupment of soil carbon at 0.74MgCha1yr1 with a further estimate of 0.78MgCha1 incorporated through litter inputs over the 3years, suggesting a net loss of SOC at 3.7Mgha1 from a 0- to 30-cm baseline of 78.613.28Mgha1, down 4.7%. Assuming this sequestration rate as a minimum would suggest replacement of cultivation losses of SOC by year 8 of a potential 15- to 20-year crop. Potential coal replacement per hectare of harvest over the three-year study would offset 68Mg of carbon emission, more than double the SOC losses.
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