Climatic and pedoclimatic factors driving C and N dynamics in soil and surface water in the alpine tundra (NW-Italian Alps)

Michele Freppaz,Raffaella Balestrini,Davide Viglietti,Nicola Colombo,Michele Lonati

doi:10.3897/natureconservation.34.30737

Abstract

In alpine tundra the interannual and seasonal variability of C and N forms in soil and lake water during the short snow-free season could be significant and related to climatic and pedoclimatic variables. The hypothesis that not only the climatic and pedoclimatic parameters recorded during the summer season but also the ones measured during the previous snow-covered season could contribute to explaining the C and N dynamics in soil and surface water was tested along 10 snow-free seasons in 3 sites in the alpine tundra in the north-western Italian Alps (LTER site Istituto Mosso). Among the considered parameters, the snow cover duration (SCD) exerted a primary control on soil N-NH4+, DOC, Cmicr, Nmicr and DOC:DON ratio, with an inverse relationship. A long SCD might cause the consumption of all the subnival substrata by the soil microorganisms, determining a C starvation during the subsequent snow-free season. An opposite trend was observed for the lake water, where a longer SCD corresponded to a higher content of inorganic N forms. Among the pedoclimatic indices, the number of soil freeze/thaw cycles (FTC) recorded during the snow-covered season had a positive relation with most of soil C and N forms and N-NO3− in lake water. Only the soil DON showed an inverse pattern, and this result is consistent with the hypothesis that FTC released soil DON, subsequently decomposed and mineralized. Only N-NO3− had a significant intraseasonal variability, reaching the highest values in September both in soil and water, revealing a significant slowdown of the contribution of soil N immobilization processes.

Highlights

The alpine tundra is a high-mountain environment located above the tree-line, which occurs across a wide range of latitudes and landscapes with common properties such as: a short growing season, extended periods with air temperature below freezing, and long periods with snow-covered soils (Edwards et al 2007, Knowles et al 2015)
The mean annual air temperature measured at the Automatic Weather Station (AWS) in the time-span 2008–2017 was -2.3 °C, with mean daily values ranging from a minimum of -21.1 °C (16 January 2017) to a maximum of +12.4 °C (24 August 2016) (Fig. 2a)
In the LTER site Istituto Mosso the C and N forms analyzed in soil and water for a decade showed a significant interannual variability, while a seasonal change was observed only for N-NO3– both in soil and water lake, with the greatest values recorded in early fall, probably due to the slowdown of biological-mediated processes of N immobilization

Summary

Introduction

The alpine tundra is a high-mountain environment located above the tree-line, which occurs across a wide range of latitudes and landscapes with common properties such as: a short growing season, extended periods with air temperature below freezing, and long periods with snow-covered soils (Edwards et al 2007, Knowles et al 2015). Direct control involves the effects of snow cover on winter soil temperature by insulating soil from air temperature and/or on summer soil moisture. Indirect control involves the effects of snow cover variations on growing-season length and soil nutrients dynamics (Edwards et al 2007). The climatic and pedoclimatic conditions recorded during the growing season (e.g. soil temperature and moisture) can strongly affect the soil nutrient cycling, and those of the previous winter season (e.g. snow cover duration, number of soil freeze/thaw cycles)

Methods

Results

Discussion

Conclusion