Scale-dependent effects of plant and animal functional characteristics on nutrient cycling in pastures

点击翻译按钮获取中文摘要

Both in low-input managed pastures and in natural ecosystems grazed by large herbivores, nutrients excreted in dung and urine of the grazing animals play an important part in the nutrient cycle. These nutrient flows involve spatial concentration and spatial separation of the main mineral nutrients at the scale of the excreta patch. Animal and plant functional characteristics influence the grain size and degree of this spatial heterogeneity, as well as the patch-scale responses of vegetation and grazing animal biomass intake to the nutrient input through excreta. While ecological research has strongly focused on large-scale effects of herbivory in terms of speed and stoichiometry of nutrient cycling, agricultural research has mostly regarded excreta-patch effects on a small scale and detached from the large-scale systems in which they occur. Plant and animal functional characteristics have important effects on nutrient cycling at the excreta-patch scale that have not yet been explicitly addressed in either ecological or agricultural research. The project intends to combine approaches and concepts from both ecological and agricultural research about herbivory effects on nutrient cycling. It will investigate how the effect of animal excreta on above-ground nutrient flows and on plant biomass nutrient stoichiometry is influenced by plant functional groups and grazing animal functional characteristics.The study system will be a long-term unfertilized grazing experiment with two experimental factors: sward type (diverse and grass-dominated) and grazing animal species (cattle and sheep, differing in body size, excreta patch size and grazing selectivity). Data will be gathered on three levels: paddock-scale and patch-scale data in the grazed system and patch-scale data under simulated grazing. At the paddock scale, biomass productivity and nutrient concentrations (nitrogen, phosphorus and potassium), biomass and mineral nutrient ingestion by the grazing animals and nutrient excretion in dung and urine will be quantified, and will be used to up-scale excreta patch effects to the paddock scale. At the patch scale, dung, urine and unaffected control patches will be marked in the grazed pasture to assess plant and herbivory responses to excreta patches. A cutting experiment with simulated dung and urine patches will be used to validate these data under controlled conditions and to extend observation period and measured parameters beyond the programme feasible under grazing. Process parameters such as defoliation interval and defoliation severity will be chosen to simulate those of the grazed study system.The project is expected to advance the basic knowledge about large-herbivore effects on nutrient cycling by addressing the small-scale heterogeneity of the quantitatively important nutrient flows through herbivore excreta and the functional characteristics of plants and herbivores that are process-relevant at this scale.