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Understanding carbon (C) and nitrogen (N) sequestration in diversified cropping systems provides a pivotal insight for soil health management. Here, the soil was sampled from an ongoing field experiment (five years) with three cropping systems: i) winter wheat/summer maize, ii) winter wheat/summer maize-early soybean, and iii) fallow. We evaluated C and N stocks in aggregates for topsoil (0–20 cm) and subsoil (20–40 cm) depending on cropping systems by comparison of three aggregate fractionation methods (dry, optimal-moisture, and wet sieving). Although the fertilizer application rate for wheat/maize was twice as much as for wheat/maize-soybean, this resulted in similar C and N stocks in the topsoil. The N stock, however, was 13% higher under wheat/maize-soybean than under wheat/maize in the subsoil due to N2 fixation by soybean. The C and N stocks decreased by 22% and 12% under fallow compared to wheat/maize in the topsoil. The wheat/maize-soybean cropping system increased soil aggregates size when estimated by dry and optimal-moisture fractionations. The aggregate size distribution shifted from the dominance of large (> 2 mm) toward small macroaggregates (0.25–2 mm) with increasing moisture used by fractionation due to the low stability of large macroaggregates. Thus, the combination of dry and optimal-moisture sieving is the preferred method to characterize aggregate stability. Overall, diversified cropping systems increase soil aggregation and stability, thus have great potential to enhance soil C and N stocks.

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Since the late 1950s, governmental rangeland policies have changed the grazing management on the Tibetan Plateau (TP). Increasing grazing pressure and, since the 1980s, the privatization and fencing of pastures near villages has led to land degradation, whereas remote pastures have recovered from stronger overgrazing. To clarify the effect of moderate grazing on the carbon (C) cycle of the TP, we investigated differences in below-ground C stocks and C allocation using in situ 13 CO2 pulse labeling of (i) a montane Kobresia winter pasture of yaks, with moderate grazing regime and (ii) a 7-year-old grazing exclosure plot, both in 3440 m asl. Twenty-seven days after the labeling, 13 C incorporated into shoots did not differ between the grazed (43% of recovered 13 C) and ungrazed (38%) plots. In the grazed plots, however, less C was lost by shoot respiration (17% vs. 42%), and more was translocated below-ground (40% vs. 20%). Within the below-ground pools, <2% of 13 C was incorporated into living root tissue of both land use types. In the grazed plots about twice the amount of 13 C remained in soil (18%) and was mineralized to CO2 (20%) as compared to the ungrazed plots (soil 10%; CO2 9%). Despite the higher contribution of root-derived C to CO2 efflux, total CO2 efflux did not differ between the two land use types. C stocks in the soil layers 0–5 and 5–15 cm under grazed grassland were significantly larger than in the ungrazed grassland. However, C stocks below 15 cm were not affected after 7 years without grazing. We conclude that the larger below-ground C allocation of plants, the larger amount of recently assimilated C remaining in the soil, and less soil organic matter-derived CO2 efflux create a positive effect of moderate grazing on soil C input and C sequestration.

The applicability of DNA-based analysis of soil microbial biomass was proven under conditions when the common approaches – chloroform fumigation-extraction (CFE) and substrate-induced respiration (SIR) – are restricted. These restrictions include certain soil properties typical for arid areas (alkaline or carbonaceous soils) or limitation by sample preparation (frozen samples). To prove the suitability and correspondence of the methods, microbial biomass was determined by CFE, SIR and by DNA quantification in slightly alkaline Chernozem and strongly alkaline Calcisol of semi-arid climate under contrasting land use. Quantification of double-stranded DNA (dsDNA) revealed an excellent agreement (R2 = 0.96) with SIR-based microbial biomass (SIR-Cmic) for soils with pH lower than 8. DNA- and CFE-based microbial biomass (CFE-Cmic) correlated well (R2 = 0.97) for all studied soils. The conversion factors from dsDNA to SIR-Cmic of 5.1 and to CFE-Cmic of 4.4 were obtained. In alkaline soils (pH > 8), microbial biomass measured by SIR was strongly underestimated because of CO2 retention in soil solution due to high pH and CO3 2− exchange with carbonates. Thus, the dsDNA quantification provides a simple and durable approach for microbial biomass analysis as alternative for SIR and CFE and can be successfully used in alkaline or calcareous semi-arid soils.

Coastal wetlands are key players in mitigating global climate change by sequestering soil organic matter. Soil organic matter consists of less stable particulate organic matter (POM) and more stable mineral-associated organic matter (MAOM). The distribution and drivers of MAOM and POM in coastal wetlands have received little attention, despite the processes and mechanisms differ from that in the upland soils. We explored the distribution of POM and MAOM, their contributions to SOM, and the controlling factors along a salinity gradient in an estuarine wetland. In the estuarine wetland, POM C and N were influenced by soil depth and vegetation type, whereas MAOM C and N were influenced only by vegetation type. In the estuarine wetland, SOM was predominantly in the form of MAOM (> 70 %) and increased with salinity (70 %–76 %), leading to long-term C sequestration. Both POM and MAOM increased with SOM, and the increase rate of POM was higher than that of MAOM. Aboveground plant biomass decreased with increasing salinity, resulted in a decrease in POM C (46 %–81 %) and N (52 %–82 %) pools. As the mineral amount and activity, and microbial biomass decreased, the MAOM C (2.5 %–64 %) and N pool (8.6 %–59 %) decreased with salinity. When evaluating POM, the most influential factors were microbial biomass carbon (MBC) and dissolved organic carbon (DOC). Key parameters, including MBC, DOC, soil salinity, soil water content, aboveground plant biomass, mineral content and activity, and bulk density, were identified as influencing factors for both MAOM abundance. Soil water content not only directly controlled MAOM, but together with salinity also indirectly regulated POM and MAOM by controlling microbial biomass and aboveground plant biomass. Our findings have important implications for improving the accumulation and increased stability of soil organic matter in coastal wetlands, considering the global sea level rise and increased frequency of inundation.

This dataset is composed of soil layer thickness, bulk density, soil organic carbon density, basal mirobial respiration, cumulative priming effect and relative priming effect across 24 sampling permafrost sites on the Tibetan Plateau. Besides, it also includes CO2 emission rate and δ13C values of individual samples with three replicates for 9 times' measurments during the 60-day incubation.

Understanding microbial community succession is key to uncover the mechanisms driving variation in soil fertility under rice cultivation. To evaluate microbial community divergence along paddy soils after 9, 15 and 25 years of cultivation with and without intensive fertilization, 16S rRNA gene high throughput sequencing and network co-occurrence analysis were used. Except for the initial barren soil, three different fertilization treatments were applied to rice planted soil: control (CK, without fertilization), NPK (N + P + K), and NPKM (NPK plus manure). Fertilization increased the difference of microbial species abundance between rice paddy soil and the initial barren soil reflecting higher C input by roots under fertilization. The bacterial communities after 9 and 15 years of rice cultivation clustered together and differed from those in barren soil and after 25 years of rice cultivation. Oligotrophic bacterial groups in the fertilized soil were gradually substituted with copiotrophic microorganisms during rice cultivation. The redundancy analysis indicated that the divergence in the microbial community structure during rice cultivation increased with soil organic C and total N. The network co-occurrence analysis showed that microbial network in NPKM soil contained the largest ratio of positive to negative links, whereas the CK network contained the smallest. Hence, fertilization and its duration control the distribution of keystone species and the nature of the links established between them.

Soil organic carbon (SOC) and its labile fractions are strong determinants of chemical, physical, and biological properties, and soil quality. Thus, a 15-y