Assessing soil C stock and C to N ratio of soil organic matter under mixed pine-beech forests at different scales

Abstract

Healthy soils are the second C sink on Earth, and this sink could last for hundreds or even thousands of years as stable soil organic matter (SOM). Forest soils, in particular, have the potential to store significant amounts of C, however, the amount of C sequestered and the carbon-to-nitrogen (C/N) ratio of soil organic matter (SOM) depend on the vegetation influencing the soil. In the last decades, mixed stands have aroused great interest among the scientific community, but it is still necessary to intensify research on its effect on soils and their C storage capacity. In this study, we assess soil C sequestration potential in soil and litter of mixed and pure stands of Scots pine and beech (Pinus sylvestris–Fagus sylvatica). Three triplets (9 forest plots), two located in Southern Poland and one in Southern Germany were studied. A total of 40 circular subplots of 5 m radius were selected within the triplets, covering a wide range of species mixture, and soil and litter were sampled. Data were analyzed at two scales (plot-level and microsite-level) to determine which option is more appropriate when studying the mixing effect on SOM. Cstock in forest floor ranged between 2.5 and 11.1 Mg C ha−1 and in mineral soil between 39.6 and 337.8 Mg ha−1. According to our findings, the percentage of species mixture primarily impacted the forest floor rather than the mineral soil. On the forest floor, stands with 25–50% pine in the mixture were found to have a C/N ratio between 20 and 30, which indicates an equilibrium state between mineralization and immobilization. In the mineral soil, total organic C was the only variable affected by mixture percentage (p < 0.1). Finally, microsite-level scale proved to be the most appropriate when studying tree stand composition effect on SOM, as the plot-level scale diluted or masked some effects.

Quality and quantity of topsoil organic matter in monospecific and mixed pine forests: role of overstory and understory vegetation

“…Therefore, composite samples as in Cools et al (2014) may hide understory effects such as those demonstrated in Rodríguez et al (2009) The different topsoil organic matter described at the stand level (previously reported by López-Marcos et al, 2018) and at a smaller spatial scale (just described here) could be linked to various trends in tree density and basal area at both spatial scales (López-Marcos et al, 2021c). The impact of different mixing percentages of stands on soil organic matter also in uences, as reported by Getino-Álvarez et al (2023). This is because, as suggested by Yeste et al (2021), not only litterfall production but also root systems and secretions may play a crucial role.…”

“…On the other side, the C/N ratio, a proxy of the lower quality of organic matter (Yeste et al 2021;Getino-Álvarez et al 2023) increased towards the negative end of PC2, meaning that the highest organic matter quality is found in the subplots towards the positive end of PC2. bD over the PC2 is likely to be an indirect effect of the change of the soil's physical properties associated with the formation of aggregates during organic matter decomposition (Prescott and Vesterdal 2021) and, therefore, provides here similar information as C/N.…”

“…However, further research is needed. Therefore, a ne-scale approach is welcome here to assess the relationship among understory, overstory, and topsoil as other authors considered (López-Marcos et al 2021a; Osei et al 2021;Getino-Álvarez et al 2023). Indeed, mixed forests can be considered a network of local interactions of individuals of different species (Vandermeer 1989;Michalet et al 2015), and consequently, the mixture response should be the result of aggregated ne-scale variations in neighbourhood interactions (López-Marcos et al 2021).…”

Microbial transformation of soil organic matter under varying agricultural management systems in Ukraine

“…It is known that the decomposition of the siderate biomass, rich in carbohydrates and proteins, occurs much faster than straw, which has a higher content of aromatic compounds of phenolic nature in its composition and a wide C:N ratio ( Getino-Álvarez et al, 2023 ). The presence of straw in combination with siderates has a notable effect: it retards the decomposition of the green siderate mass, leading to favourable conditions for humus accumulation.…”

“…A similar situation was observed in greyzemic phaeozems, where the combined application of wheat straw with cover crops, manure, and mineral fertilisers increased the activity of CO 2 release by 39.8-48.1%. 10.3389/fmicb.2023.1287701 It is known that the decomposition of the siderate biomass, rich in carbohydrates and proteins, occurs much faster than straw, which has a higher content of aromatic compounds of phenolic nature in its composition and a wide C:N ratio (Getino-Álvarez et al, 2023). The presence of straw in combination with siderates has a notable effect: it retards the decomposition of the green siderate mass, leading to favourable conditions for humus accumulation.…”