Impacts of Logging-Associated Compaction on Forest Soils: A Meta-Analysis

Soil compaction associated with mechanized wood harvesting can long-lastingly disturb forest soils, ecosystem function, and productivity. Sustainable forest management requires precise and deep knowledge of logging operation impacts on forest soils, which can be attained by meta-analysis studies covering representative forest datasets. We performed a meta-analysis on the impact of logging-associated compaction on forest soils microbial biomass carbon (MBC), bulk density, total porosity, and saturated hydraulic conductivity (Ksat) affected by two management factors (machine weight and passage frequency), two soil factors (texture and depth), and the time passed since the compaction event. Compaction significantly decreased soil MBC by −29.5% only in subsoils (>30 cm). Overall, compaction increased soil bulk density by 8.9% and reduced total porosity and Ksat by −10.1 and −40.2%, respectively. The most striking finding of this meta-analysis is that the greatest disturbance to soil bulk density, total porosity, and Ksat occurs after very frequent (>20) machine passages. This contradicts the existing claims that most damage to forest soils happens after a few machine passages. Furthermore, the analyzed physical variables did not recover to the normal level within a period of 3–6 years. Thus, altering these physical properties can disturb forest ecosystem function and productivity, because they play important roles in water and air supply as well as in biogeochemical cycling in forest ecosystems. To minimize the impact, we recommend the selection of suitable logging machines and decreasing the frequency of machine passages as well as logging out of rainy seasons especially in clayey soils. It is also very important to minimize total skid trail coverage for sustainable forest management

Keeping thinning-derived deadwood logs on forest floor improves soil organic carbon, microbial biomass, and enzyme activity in a temperate spruce forest

Deadwood is a key component of forest ecosystems, but there is limited information on how it influences forest soils. Moreover, studies on the effect of thinning-derived deadwood logs on forest soil properties are lacking. This study aimed to investigate the impact of thinning-derived deadwood logs on the soil chemical and microbial properties of a managed spruce forest on a loamy sand Podzol in Bavaria, Germany, after about 15 years. Deadwood increased the soil organic carbon contents by 59% and 56% at 0–4 cm and 8–12 cm depths, respectively. Under deadwood, the soil dissolved organic carbon and carbon to nitrogen ratio increased by 66% and 15% at 0–4 cm depth and by 55% and 28% at 8–12 cm depth, respectively. Deadwood also induced 71% and 92% higher microbial biomass carbon, 106% and 125% higher microbial biomass nitrogen, and 136% and 44% higher β-glucosidase activity in the soil at 0–4 cm and 8–12 cm depths, respectively. Many of the measured variables significantly correlated with soil organic carbon suggesting that deadwood modified the soil biochemical processes by altering soil carbon storage. Our results indicate the potential of thinned spruce deadwood logs to sequester carbon and improve the fertility of Podzol soils. This could be associated with the slow decay rate of spruce deadwood logs and low biological activity of Podzols that promote the accumulation of soil carbon. We propose that leaving thinning-derived deadwood on the forest floor can support soil and forest sustainability as well as carbon sequestration

Spatio-temporal pattern of root exudation and enzyme activities in the rhizosphere

This thesis aims at studying the role of root hairs, benzoxazinoids, soil texture and drought on the spatio-temporal pattern of root exudates and enzyme activities in the rhizosphere of maize. The rhizosphere processes of soil organic matter decomposition and phosphorus mobilization were studied using non-destructive 2-D imaging methods. Thus, zymography, phosphor imaging, neutron radiography, planar optodes and diffusive gradients in thin films (DGT) we applied to visualize enzyme activity, 14C exudates, soil water, pH values and dissolved nutrients, respectively. The obtained images were then analyzed for colocalization of the measured parameters. In addition, soil samples were taken locally to measure enzyme kinetics and to conduct microbiome analysis using DNA sequencing. This multi-imaging approach coupled with co-localization analyses was applied for the first time in the laboratory in rhizobox experiments and in the field using root windows. Root hairs enraged enzymatic rhizosphere extent of three-weeks-old maize grown in the rhizoboxes, but had no effect at late growth stage under field conditions. Under drought, root hairs widen the rhizosphere to ensure better nutrient mining and water uptake. Soil texture play an important role on phosphorus mobilization processes. Despite more intensive processes detected in sand, a higher soil organic matter and better physico-chamical properties in loam combined with the presence of root hairs provide better plant phosphorus nutrition.Benzoxazinoids are secreted by roots to defend against pathogenic fungi, but may suppressed the activities of beneficial microorganisms. Plant breeding towards increasing the content of benzoxazinoids and the presence of root hairs is a promising tool for better plant protection and improving nutrients acquisition, especially under drought and on sandy soils