Effects of Nitrogen and Phosphorus Fertilization on Soil pH-Plant Productivity Relationships in Upland Grasslands of Northern Greece

The potential role of soil pH in modulating plant productivity was assessed on the basis of dry mass, harvested in the form of 0.25 m(2) quadrats, in two low-productivity upland grasslands of northern Greece subjected to annual factorial nitrogen (N) and phosphorus (P) fertilization (15 g N M(-2) year(-1) and 10 g P m(-2) year(-1)) over a minimum period of 3 years. It was hypothesized that under these particular conditions, a positive relationship would exist between soil pH and plant productivity and, further, that N or P fertilizer application of a nutrient limited system, would result in a weakening of this positive relationship. A significant positive relationship was confirmed between soil pH and plant productivity in one of the two study areas and a positive trend in the other. Moreover; plant productivity increase, following fertilization, appeared to have a detrimental effect on the soil pH-plant productivity relationship. Findings support the original hypotheses and strengthen the idea that plant diversity-mediated soil pH-plant productivity relationships are a result of the more intense plant speciation that occurred under the more typical soil conditions of higher pH in temperate as opposed to tropical regions.