Comparing Measurement Approaches for Quantifying CO2 Flux from Downed Woody Debris with a Dynamic Chamber Method

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Mechanisms of carbon sequestration and stabilization by restoration of arable soils after abandonment: A chronosequence study on Phaeozems and Chernozems

Abandonment of croplands ongoing on 220 million ha worldwide contributes strongly to soil restoration by improvement of degraded properties and medium- and long-term carbon (C) sequestration in post-agricultural ecosystems. Two interrelated processes – decomposition and stabilization of soil organic carbon (SOC) – govern SOC dynamics and affect the C source or sink functions of former croplands. We investigated how the abandonment of arable soils affects (i) accumulation of SOC, its composition, stability, and turnover during the post-agricultural restoration of soils, and (ii) microbial activity parameters. A chronosequence study was carried in two bioclimatic zones of European Russia: deciduous forest (Luvic Phaeozems, PH-chronosequence) and dry steppe (Calcic Chernozems, CH-chronosequence). Each chronosequence included an arable soil, 3–4 soils abandoned at increasing time periods (up to 35 years), and natural soil: never cropped Phaeozem and completely restored Chernozem. We combined the results of nuclear magnetic resonance (NMR), thermal analysis including Differential Scanning Calorimetry and Derivative Thermogravimetry, long-term incubation for SOC mineralization, and microbiological activity (basal respiration and microbial C content). Degraded Phaeozems with low SOC amount had much higher relative increase in SOC content (134%) during the post-agricultural restoration compared to SOC-rich Chernozems (38%). SOC gains were recorded in all organic compound classes identified by NMR and thermal analysis, but the increase of recalcitrant SOC was more pronounced in the post-agricultural Chernozems than in the Phaeozems. The post-agricultural Chernozems were characterized by higher SOC aliphaticity and aromaticity than Phaeozems. Microbial activity and biodegradable SOC increased gradually during post-agricultural restoration. Being mostly a function of climate and vegetation, the soil type was the primary factor explaining the greatest portion (54–88%) of the total variance for most soil and microbial parameters. Concluding, despite SOC content increased in both Chernozems and Phaeozems during the post-agricultural restoration, the mechanisms of C sequestration and stabilization were dependent on climate, vegetation, and on the degradation intensity during the agricultural use. The accumulation of organic compounds was specific for virgin soils dominating in deciduous forest and steppes, and had direct consequences for microbial activities, C turnover and sequestration. © 2019 Elsevier B.V

Change in aggregate structure of various soil types during the succession of abandoned lands

A comparative analysis of the changes in the aggregate structure in various types of soils (Sod-podzolic, Gray forest, and Chernozems) during their postagrogenic evolution was carried out. The study plots included: sod-podzolic soils -plowland, laylands abandoned 8, 13, 35 years ago and a secondary forest (~100 years); gray forest soils -plowland, laylands abandoned 6,15 and 30 years ago and a secondary forest of 60 years; сhernozems-plowland and layland abandoned 10, 15, 26 and 81 years ago. The geobotanical studies have shown that the withdrawal of soils from agricultural use causes changes in species composition, increase of biodiversity, and a gradual recovery of climax communities, which are attributed for specific natural climatic zones. Along with vegetation succession, we observed the increase in the total carbon content in the upper part of the former arable layer (0-10 cm) in all studied soils. However, the trend becomes weaker from northern to southern climatic zones in the following sequence: Sod-podzolic soil > Gray forest soil >Chernozems ordinary. It was found that the content of macroaggregates increases authentically in the surface layers of all of the investigated soils from cropland to abandoned and forest soils during the self-restoration of Gray forest soils and Chernozems while the number of micro-aggregates, on the contrary, decreases. In all studied chronosequences, we observed the increase of the weighed mean diameter of the aggregates and the structure coefficients. The most pronounced changes in the aggregate structure were observed in the chronosequence, formed on Gray forest soils, while the weakest alterations were typical for the Sod-podzolic soils of the southern taiga