Nitrogen Storage in Alpine Plants

本研究验证了高山植物在冬季储存氮是一种重要的适应性假设。高山环境具有生长季节短，土壤温度低，氮有效度低的特点。通过使用在一个生长季节储存的氮，植物可以在下一个春天开始生长，即使土壤太冷，它们无法从土壤中获得氮。这可能使它们能够最大限度地利用高山生长季节短的优势，在霜冻的危险变得很大之前迅速开花和结籽。研究人员将确定植物何时利用氮生长，以及何时能够从土壤中吸收氮。如果他们发现植物在春天获得氮之前就开始生长，那么这个假设就会得到支持。然而，确定植物什么时候能真正利用氮是一项复杂的任务。氮的有效性取决于土壤中矿物氮的数量，氮的添加速度（来自雨或雪，或来自旧植物物质的分解）以及植物与土壤微生物获得氮的相对能力。因此，土壤中氮离子浓度的年度格局，分解产生这些离子的速度，必须确定植物和土壤微生物吸收这些氮的相对能力。这项研究之所以重要，有几个原因。首先，对高寒环境下植物氮素分配和植物-养分关系有较深入的认识。在决定植物最终生存能力的过程中，植物分配资源的方式与它从环境中获得的资源数量一样重要。其次，这项研究将解决一个重要的一般性问题：“微生物在多大程度上与高等植物争夺氮？”人们越来越认识到，这种竞争可能对植物的营养状况产生强有力的影响。这些问题具有实际意义。例如，对高山植物氮储存的了解可能有助于了解温带地区果树越冬时发生的情况。通过了解土壤温度如何影响高山地区的氮循环，科学家们可能能够深入了解氮肥在寒冷农业系统中的命运，从而实现更有效地利用肥料和减少氮肥对地下水的污染。最后，硝酸盐反硝化成一氧化二氮（一种温室气体）受到本研究中测试的许多土壤参数的影响。这些结果可能有助于预测极地变暖对北极温室气体排放的影响。

This study tests the hypothesis that storing nitrogen over winter is an important adaptation in alpine plants. The alpine environment is characterized by: 1) a short growing season, (2) low soil temperatures, and 3) low nitrogen (N) availability. By using N that is stored during one growing season plants can begin growth in the following spring, even though soils are too cold for them to acquire N from the soil. This may allow them to take maximum advantage of the short alpine growth season and to quickly flower and set seed before the danger of frost becomes great. The investigators will determine when plants are using nitrogen for growth, and when plants are able to take nitrogen from the soil. If they find that plants start growing before they can acquire N in the spring, the hypothesis will be supported. However, determining when N is actually available to plants is a complicated task. Nitrogen availability is determined by the amount of mineral N in the soil, the rate at which this N is added (from rain or snow, or from decomposition of old plant matter) and the relative ability of plants versus soil microbes to acquire this N. Therefore, the annual pattern of N ion concentration in the soil, the rate of production of these ions from decomposition, and the relative ability of plants and soil microbes to assimilate this nitrogen must be determined. The study is significant for several reasons. First, it will advance basic understanding of plant N allocation and plant- nutrient relations in the alpine environment. The manner in which a plant allocates its resources can be as important as the quantity of resources it garners from the environment in determining a plant's ultimate ability to survive. Second, the study will address the important general question "to what extent do microorganisms compete for nitrogen with higher plants?" Awareness is growing that such competition can have a potent affect on plant nutrient status. These questions have practical implications. For example, an understanding of N storage in alpine plants may provide insight into what happens when fruit trees overwinter in temperate areas. By learning how soil temperature affects N cycling in the alpine, scientists may be able to provide insight into the fate of N fertilizer in cold agricultural systems with a goal of more efficient use of fertilizer and reduced ground water pollution by nitrogen fertilizers. Finally, denitrification of nitrate into nitrous oxide (a greenhouse gas) is affected by many of the soil parameters tested in this study. These results could be useful in predicting the effect of polar warming on greenhouse gas emissions from the arctic.