Nutrient cycling and limitation in soils of higher latitude ecosystems

磷(P)和氮(N)常常限制或共同限制陆地生态系统中植物的生长。许多研究表明，这两种养分在土壤发育过程中的有效性是不同的。在土壤发育的早期阶段，植物的生长大多受到N的限制，而在较老的土壤上，植物的生长变得越来越受P的限制。加拿大的大多数土壤在地质时间尺度上都相对年轻，因为它们是在大约12,000年前的最后一次冰川之后发育起来的。出于这个原因，人们通常认为加拿大大多数生态系统中的植物生长是受N限制的。化石燃料的燃烧和氮肥的挥发大大增加了北半球大气中氮的沉积。因此，加拿大的许多自然生态系统可能已经从主要的N限制转变为P限制或P共同限制，其后果未知，并可能对初级生产力、植物和微生物群落结构、二氧化碳的净生态系统交换以及生态系统的稳定性和弹性产生影响。因此，我的研究计划旨在阐明N供应的变化如何影响高纬度非农业生态系统土壤中P的生物地球化学循环和有效性。将进行实验室和现场实验，以回答从分子到生态系统规模的研究问题。野外实验将在森林和湿地生态系统中进行，特别是在昆士兰圣希莱尔山的温带落叶和针叶林，在安大略省梅尔布莱的营养丰富的沼泽，以及在安大略省实验湖地区的北方森林。增加氮素供应对这些生态系统土壤中磷的生物有效性的影响将通过测量酶活性、化探土壤磷库浓度的变化以及对营养贫瘠的有机土壤的大气磷输入的量化来研究。将特别侧重于使用磷酸盐中的氧同位素来追踪环境P循环中的源、汇和生物地球化学过程。如有必要，将开发新的实验室方法来处理高有机含量土壤中的磷循环的具体问题，例如泥炭地土壤和北方森林土壤。总之，这项研究计划将对加拿大和其他地方陆地生态系统中P和N的循环、限制和通量提供新的基本见解，因为这些生态系统正在适应人为影响和全球变化。

Phosphorus (P) and nitrogen (N) often limit or co-limit plant growth in terrestrial ecosystems. Many studies have suggested that the availability of these two nutrients differs during soil development. While plant growth during early stages of soil development is mostly N-limited, it becomes increasingly P-limited on older soils. Most soils in Canada are relatively young on a geological timescale, because they have developed since the last glaciation approximately 12,000 years ago. For this reason, it is generally assumed that plant growth in most Canadian ecosystems is N-limited. The combustion of fossil fuels and the volatilization of N-fertilizers have substantially increased the atmospheric deposition of N in the northern hemisphere. Many natural ecosystems in Canada might therefore have shifted from being primarily N-limited to being P-limited or P co-limited, with unknown consequences to for primary productivity, plant and microbial community structures, net ecosystem exchange of CO2 and ecosystem stability and resilience. My research program therefore aims to elucidate how a changing supply of N affects the biogeochemical cycling and availability of P in soils of non-agricultural ecosystems in higher latitudes. Both laboratory and field experiments will be carried out to answer research questions ranging from the molecular to the ecosystem scale. Field experiments will be conducted in forest and wetland ecosystems, specifically in a temperate mixed deciduous and coniferous forest on Mont Saint Hilaire, QC, in an ombrotrophic bog in Mer Bleue, ON, and in a boreal forest in the Experimental Lakes Area, ON. The effect of increasing supply of N on the bioavailability of P in soils of these ecosystems will be investigated by measuring enzyme activities, changes in concentration of geochemical soil P-pools and by quantifying atmospheric P inputs to nutrient poor organic soils. A special focus will be on the use of oxygen isotopes in phosphates to trace sources, sinks and biogeochemical processes in the environmental P-cycle. If necessary, new laboratory methods will be developed to address specific questions dealing with P-cycling in soils with high organic content, for example peatland soils and boreal forest soils. In summary, this research program will give new and fundamental insights into the cycling, limitation and fluxes of P and N in terrestrial ecosystems in Canada and elsewhere, as these ecosystems adapt to anthropogenic impacts and global change.