The effect of environmental conditions on the decomposition rate of cellulose in mountain soils

Abstract

Ecological studies rarely deal with the altitudinal aspect of the variability of the decomposition rate of dead organic matter. This phenomenon is of great importance in the formation of soil properties as it determines the characteristics of humus horizons and determines nutrient transformations and availability in ecosystems. Moreover research on the decomposition of organic matter is very important because an increased rate of C mineralization is expected in response to the predicted temperature rise. There is still relatively little data to help quantify the reduction of organic matter decomposition under mountain conditions (altitude gradient). Previous papers show a clear decrease in decomposition as altitude increases (tropical Andes and Appalachian Mts.) and soil scientists explain the large thickness and specific composition of the humus compounds of mountain soils by the slower rate of organic matter decomposition due to harsh climatic conditions and due to the specific high mountain vegetation. In recent years the issue has gained larger importance as several authors have connected the reduced rate of organic matter decomposition with the anthropogenous pollution of the soil environment by heavy metals and acid rain. Also particular investigations show a remarkable increase in heavy metal concentrations as altitudes rise (Alps and Tatra Mts.). The northern Carpathians, located in Central Europe, are distinctly exposed to pollution, although there are no significant signs of atmospheric pollution in this area. Therefore the aim of this paper is to determine the impact of environmental factors on the rate of cellulose decomposition in the mountain soils of the northern Carpathians. The main questions are: (1) Is it possible to distinguish the influence of climatic and edaphic factors in shaping the rate of cellulose decomposition? (2) There is a slower rate of cellulose decomposition due to harsh climatic conditions with altitude. Are there other factors which modify this simply-stated relationship? The research was carried out in four mountain ranges representing physiographically different Carpathian regions. Soil properties were analyzed using common methods. The properties of humus substances were calculated after the extraction and fractionation. The measurements of cellulose decomposition rates were conducted using the cellulose filters method (periods: 10, 20 weeks, and year). Among the environmental factors, those that can considerably influence the processes of cellulose decomposition in soil were chosen for the purpose of analysis. To evaluate their impact on the rate of cellulose decomposition, it was necessary to identify components by principal component analysis. The analysis was carried out on two components (PC1 and PC2) accounting for almost 82% of the variability. The properties of humus in the soils indicate their close relationship to environmental conditions as they change with altitude. This attempt to distinguish the influence of climatic and edaphic factors in shaping the rate of cellulose decomposition shows that the most important factor is the effect of altitude on overall environmental conditions (PC1). Separating the influence of particular conditions (i.e. climatic edaphic) is very difficult or impossible because they are closely connected. Their effect on specific humus horizons emphasizes the influence of harsh climatic conditions on the rate of cellulose decomposition. The relationship between a slower rate of cellulose decomposition and increasing altitude is not absolute. Within subalpine and alpine geoecological belts there is variation in the kind of feedback. Within the subalpine belt the feedback is negative. It is due to the fact that within that belt the ectohumus material originates from dwarf pine needles, which determines a relatively smaller rate of cellulose decomposition. Within the alpine belt the situation is opposite. Humus horizons here are determined by soft grass remnants and shape a relatively higher rate of cellulose decomposition (positive feedback). Both kinds of feedback occur under harsh climatic conditions.