Tree Species and Stand Density: The Effects on Soil Organic Matter Contents, Decomposability and Susceptibility to Microbial Priming

Abstract

Forest stand density has been shown to have different, albeit small, effects on soil carbon. We hypothesized that the absence of a density effect on soil carbon (C) storage could be explained by a loss of old soil C. This replacement of old by fresh C could result in zero net C sequestration by soils but could also alter the quality of the soil organic matter. We used one afforestation experiment in Siberia, in which three tree species (spruce, larch and Scots pine) have been grown for the last 30 years at 18 levels of stand density, ranging originally from 500 to 125,000 stems per ha. We selected five density levels and studied the C and nitrogen (N) contents in mineral soils at 0–5 cm depth. The age of the soil C was measured under larch and spruce for three levels of density by radiocarbon (14C) dating. In all soil samples, we determined the stability of the soil organic matter (SOM) by assessing two indices: C decomposability (mineralization of C per unit of soil C) and primability (susceptibility of the SOM to microbial priming). The stand density affected the soil C and N contents differently depending on the tree species. Only under spruce did both the C and N contents increase with density; under larch and pine, the covariation was insignificant and N even tended to decline with a density increase. With the 14C data, we were able to show the strong dilution of old SOM by fresh C derived from the trees; the effect was stronger with a higher density. This provides the first evidence that a density increase increases the fractions of new C versus old C and this can happen without altering the total C contents such as under larch. Although the stand density altered the soil C and N contents only under spruce, it altered C decomposability under all tree species; with a density increase, the C decomposability declined under spruce but increased under larch and pine. This is relevant to predicting C losses from forest soils with different tree species and densities. Higher C losses would occur under larch and pine with higher densities but under spruce, a density increase would reduce the losses of C from the soil. Furthermore, although no significant covariation of stand density with C primability was detected, we first observed strong tree species effects on C primability. Twice as much C was lost from the soil under larch than under spruce or pine by an equal addition of C-glucose. This indicated that elevated C deposition from roots and exudates to the soil as predicted due to an elevated CO2 concentration would most strongly accelerate the soil C turnover and C losses under larch than under spruce and Scots pine. Overall, the tree species altered the susceptibility of the soil C to an elevated C input and the stand density had a strong effect on the decomposability of the SOM, which is an important parameter of C stability. The effect of stand density is, therefore, important to consider even if the stand density does not affect the total soil C.

Temporal changes in soil chemical compositions in acidified mountain forest soils of Czech Republic

“…Bradová et al (2015), who studied the same locality, reported that the beech forest was older than spruce, by approximately 80 years, and had larger canopy closure (87%) than spruce (40%). The higher density and age of the forest stands in the research area had typically larger basal area of trees, in which it enhanced SOC in the forest soil (Menyailo et al 2022). It was consistent with the finding of Yuan et al (2013) who found that SOC was stored higher under the old-growth forest trees.…”

Enhancing Forest Sustainability: A Comprehensive Exploration of Thinning Practices and their Effects on Soil Chemical and Biochemical Properties

“…Thinning, the strategic removal of a specific number of trees from a woodland to redirect tree growth toward fewer, more valuable stems, constitutes a pivotal silvicultural operation essential for effective forest ecosystem management [1]. This practice plays a crucial role in enhancing nutrient availability, productivity, biodiversity [2,3], and processes integral to the soil ecosystem [4]. Forest management practices, in general, exert a profound influence on key factors such as organic carbon storage and sequestration [5,6], nutrient concentrations [7], soil enzyme activities [8], soil biodiversity, and water retention [9,10].…”

Forest Soil Carbon and Climate Changes

“…The Issue includes 15 papers; based on the first author affiliation, the papers originate from Russia (7), China (3), Taiwan (2), Japan (1), South Korea (1) and Canada (1). Several papers were dealing with vegetation effects on soil organic matter [1][2][3][4][5]. Respiration as the second most important process of global carbon cycles was considered by researchers from several countries [5][6][7][8][9][10], including also research dealing with the temperature sensitivity of the respiration process [8,9].…”

“…Several papers were dealing with vegetation effects on soil organic matter [1][2][3][4][5]. Respiration as the second most important process of global carbon cycles was considered by researchers from several countries [5][6][7][8][9][10], including also research dealing with the temperature sensitivity of the respiration process [8,9]. Two papers concentrated on microbial metabolism in forest soils [5,11].…”

“…Respiration as the second most important process of global carbon cycles was considered by researchers from several countries [5][6][7][8][9][10], including also research dealing with the temperature sensitivity of the respiration process [8,9]. Two papers concentrated on microbial metabolism in forest soils [5,11]. Climate change [12] and forest fires [13] effects on peat formation were also reported.…”