Abiotic Parameters and Pedogenesis as Controlling Factors for Soil C and N Cycling Along an Elevational Gradient in a Subalpine Larch Forest (NW Italy)

Emanuele Pintaldi,Michele Eugenio D’Amico,Michele Freppaz,Davide Viglietti,Andrea Magnani

doi:10.3390/f10080614

Abstract

Mountain regions are vulnerable to climate change but information about the climate sensitivity of seasonally snow-covered, subalpine ecosystems is still lacking. We investigated the impact of climatic conditions and pedogenesis on the C and N cycling along an elevation gradient under a Larch forest in the northwest (NW) Italian Alps. The environmental gradient that occurs over short distances makes elevation a good proxy for understanding the response of forest soils and nutrient cycling to different climatic conditions. Subalpine forests are located in a sensitive elevation range—the prospected changes in winter precipitation (i.e., shift of snowfalls to higher altitude, reduction of snow cover duration, etc.) could determine strong effects on soil nitrogen and carbon cycling. The work was performed in the western Italian Alps (Long-Term Ecological Research- LTER site Mont Mars, Fontainemore, Aosta Valley Region). Three sites, characterized by similar bedrock lithology and predominance of Larix decidua Mill., were selected along an elevation gradient (1550–1900 m above sea level-a.s.l.). To investigate the effects on soil properties and soil solution C and N forms of changing abiotic factors (e.g., snow cover duration, number of soil freeze/thaw cycles, intensity and duration of soil freezing, etc.) along the elevation gradient, soil profiles were opened in each site and topsoils and soil solutions were periodically collected from 2015 to 2016. The results indicated that the coldest and highest soil (well-developed Podzol) showed the highest content of extractable C and N forms (N-NH4+, DON, DOC, Cmicr) compared to lower-elevation Cambisols. The soil solution C and N forms (except N-NO3−) did not show significant differences among the sites. Independently from elevation, the duration of soil freezing, soil volumetric water content, and snow cover duration (in order of importance) were the main abiotic factors driving soil C and N forms, revealing how little changes in these parameters could considerably influence C and N cycling under this subalpine forest stand.

Highlights

It is a matter of fact that the mean surface air temperature has increased by about 1 ◦ C in the last century, and a further increase, which will probably exceed 1.5 ◦ C, is expected by the end of the21st century [1]
(I) we evaluated whether differences in soil type and pedogenesis occurred along the altitudinal gradient and their interaction with C and N dynamics; (II) we investigated whether differences in topsoil and soil solution C and N forms concentration occurred along the altitudinal gradient, evaluating their mutual interaction, proving a direct connection between soil and soil solution systems; (III) independently from elevation, we investigated which were, among the investigated variables, the main abiotic drivers influencing the soil C and N cycling in this forest ecosystem
Our results showed that duration of soil freezing (DSF) had the strongest impact on the C and N forms: the longer the DSF, the higher the total amount of N-NH4 +, Dissolved organic nitrogen (DON), dissolved organic carbon (DOC), and Cmicr that were measured in the topsoil in the snow-free season, as indicated by the positive relation (Table 5)

Summary

Introduction

It is a matter of fact that the mean surface air temperature has increased by about 1 ◦ C in the last century, and a further increase, which will probably exceed 1.5 ◦ C, is expected by the end of the21st century [1]. Climate change over the century will affect soil temperatures in seasonally snow-covered northern temperate forests in opposed directions across seasons, with warmer soils in the growing season and reduced snowpack leading to colder soils with greater frequency of freeze-thaw cycles in winter [3,4]. In order to obtain possible responses to the expected warming on soil carbon and nitrogen cycling, biogeochemical properties might be analyzed and used as short-term indicators due to their great sensitivity, even to slight environmental modifications [5], such as changes in pedoclimatic factors. Soil moisture and temperature are known to be of paramount importance, affecting microorganisms and nutrient cycling in forests soil [6] and in higher alpine tundra soils [7]. The presence of a thick snowpack strongly influences soil temperature and moisture, especially during the snowmelt period [8,9]

Results

Discussion

Conclusion