THE RELATIONSHIP BETWEEN SPECIES DIVERSITY AND NITROGEN CYCLING IN PASTURE

生物多样性的研究不仅对群落生态学有重要意义，而且对应用生态学也有重要意义。我们想知道生物多样性程度是否影响牧草氮循环效率。许多科学家认为生物多样性与生产有着密切的关系。如果生物多样性与产量之间存在正相关关系，则高生物多样性的生态系统具有较高的母体循环能力，如氮循环能力。然后从管理对生物多样性的影响、生物多样性与氮循环的关系两个方面对草地生物多样性进行了探讨。通过对各牧场植物和土壤蜱类的取样，测定了植物和土壤蜱类的物种多样性。以牛奶、肥料和饲料籽粒中的氮含量计算氮损失，分析其对环境的影响。为了测量牛尿氮对牧草生产的回收效率，我们在另一个实验中使用了15N标记的尿液。低投入牧草的植物多样性高于高投入牧草。植物蜱和土壤蜱的多样性之间存在着密切的关系。单位牧场产奶量的成本效益分析结果表明，存在产奶量的最优投入。许多奶农将达到最佳点，这意味着牛奶生产效率高。在这20年间，氮素损失从80%以上下降到50%。单位牧场产奶量效率与生物多样性呈正相关。我们用15n标记法估计牛尿氮对草生长的回收率为21.6% ~ 39.4%。

The study of bio-diversity is very important for not only community ecology but also applied ecology. We want to know whether degree of bio-diversity affects efficiency of nitrogen recycling in a pasture or not. Many scientists said that there are close relationship between bio-diversity and production. If there are positive relationships between bio-diversity and production then the ecosystem of high bio-diversity have high ability of maternal recycling such as nitrogen recycling.Then we tried to the roll of bio-diversity in pasture by two aspects such as effects of management on bio-diversity, relation between bio-diversity and nitrogen recycling.Species diversities of plant and soil tick were measured by sampling data from each pasture. Nitrogen losses were calculated by nitrogen amount in milk, fertilizer and feed grains for environmental impact. To measure the efficiency of nitrogen recovery from cattle urine to grass production we used 15N marked urine in another experiment.The plant diversities of low-input pastures were higher than high-input pastures. There is strong relationship between plant and soil tick diversity. Results of Cost-benefit analysis for milk production per unit pasture show the presence of optimal-input for milk production. Many farmers will arrive to optimal point that means high efficiency of milk production. The nitrogen losses were decreased from over 80% to 50% during these 20 years.There is a positive relationship between efficiency of milk production per unit pasture and bio-diversity.We estimated the recovery % of nitrogen from cattle urine to grass growth using 15N-marker method ranged 21.6% to 39.4%.