Soil organic matter mineralization rate and metal contamination of the main soil types in central part of Yamal region (West Siberia, Russia)

Soils have a defining role in global carbon cycling, having one of the largest dynamic stocks of C on earth—3300 Pg of C are stored in soils, which is three-times the amount stored in the atmosphere and more than the terrestrial land plants. An important control on soil organic matter (SOM) quantities is the mineralization rate. It is well recognized that the rate and extent of SOM mineralization is affected by climatic factors and mineral-organic matter associations. What remained elusive is to what extent constraints on microbial metabolism induced by the respiratory pathway, and specifically the electron acceptor in respiration, control overall rates of carbon mineralization in soils. Therefore, physical factors limiting oxygen diffusion such as soil texture and aggregate size (soil structure) may therefore be central controls on C mineralization rates. The goal of our research was therefore to determine if variations in microbial metabolic rates induced by anaerobic microsites in soils are a major control on SOM mineralization rates and thus storage. We performed a combination of laboratory experiments and field investigations will be performed to fulfill our research objectives. We used laboratory studies to examine fundamental factors of respiratory constraints (i.e., electron acceptor) on organic matter mineralization rates. We ground our laboratory studies with both manipulation of field samples and in-field measurements. Selection of the field sites is guided by variation in soil texture and structure while having (other environmental/soil factors constant. Our laboratory studies defined redox gradients and variations in microbial metabolism operating at the aggregate-scale (cm-scale) within soils using a novel constructed diffusion reactor. We further examined micro-scale variation in terminal electron accepting processes and resulting C mineralization rates within re-packed soils. A major outcome of our research is the ability to quantitatively place the importance of aggregate-based heterogeneity in microbial redox processes and the resulting lack of oxygen on the rate of carbon mineralization. Collectively, our research shows that anaerobic microsites are prevalent in soils and are important regulators of soil carbon persistence, shifting microbial metabolism to less efficient anaerobic respiration and selectively protecting otherwise bioavailable, reduced organic compounds such as lipids and waxes from decomposition. Further, shifting from anaerobic to aerobic conditions leads to a 10-fold increase in volume-specific mineralization rate, illustrating the sensitivity of anaerobically protected carbon to disturbance. Vulnerability of anaerobically protected carbon to future climate or land use change thus constitutes a yet unrecognized soil carbon-climate feedback that should be incorporated into terrestrial ecosystem models.

Influence mechanisms of long-term fertilizations on the mineralization of organic matter in Ultisol

Priming effects (PE) on soil organic matter (SOM) mineralization depend strongly on the type of carbon substrates added. It is crucial to understand the PE induced by various carbon substrates for predicting SOM dynamics and soil-atmosphere carbon feedback. We conducted a meta-analysis of 8015 observations from 283 articles to evaluate how carbon substrates (plant residues, root exudates, biochar, and degradable microplastics) regulate the mineralization of SOM through PE. Results demonstrated that all these types of carbon substrates increased SOM mineralization, which induced a positive PE. Plant residues induced the highest average PE, followed by root exudates, biochar, and degradable microplastics. Compared to soils without carbon substrate inputs, the rate of SOM mineralization increased by 113% in soil with cellulose-rich non-woody residues, whereas it increased by only 25% in soil with lignin-rich woody residues. The mineralization of SOM increased by organic acids (151%) was greatest in root exudates, followed by monosaccharides (60%) and polysaccharides (12%). The strong mineralization induced by organic acids was probably related to the release of more mineral nutrients by reducing soil pH. The PE on SOM mineralization by woody biochar with high aromatic carbon content (48%) was greater than that of non-woody biochar with high alkyl carbon content (43%). Microplastics with rapidly degradable polyhydroxyalkanoates induced more SOM mineralization (258%) than polybutylene succinate (61%) and polybutylene adipate-co-terephthalate (21%). The SOM priming was positively correlated with soil clay and incubation moisture, and negatively correlated with soil organic carbon, total nitrogen, soil C:N ratio, dissolved organic carbon, microbial biomass carbon, carbon input rate, incubation temperature, and soil depth. These results show that the positive PE is ubiquitous in soil ecosystems; its magnitude is linked intrinsically to the physicochemical characteristics and source of exogenous carbon substrate.

Is there a linear relationship between priming effect intensity and the amount of organic matter input?

Effects of biotic and abiotic factors on soil organic matter mineralization: Experiments and structural modeling analysis

Modeling Soil Organic Matter Dynamics Under Intensive Cropping Systems on the Huang-Huai-Hai Plain of China

Incorporating straw into soils is an effective and cost-efficient method for sequestering organic carbon (C) and enhancing soil quality. However, the interactive effects of soil moisture and temperature on soil organic matter (SOM) mineralization have remained unclear in the presence of plant residues. We assessed the impacts of 13C-labeled maize (Zea mays) straw on SOM mineralization in two soils with contrasting soil C content (3.0 % and 6.8 %) under two moisture levels (45 % or 65 % water holding capacity (WHC)) and two temperatures (12 °C or 22 °C) through an experimental incubation. In the absence of straw addition, CO2 production at 22 °C was 2–3 times more than at 12 °C, and was 31–40 % higher at 65 % WHC than at 45 % WHC in both soils. Soil temperature and moisture interactively affected straw decomposition. After a 66-day incubation, approximately 7–11 % of straw was decomposed to CO2, contributing 44–67 % to the total CO2 production. Straw addition increased SOM mineralization across all temperature and moisture levels, resulting in a positive priming effect (PE). The highest PE was observed at 45 % WHC and 22℃ in both soils. The temperature sensitivity (Q10 value) of native SOM mineralization decreased with straw addition due to higher quality SOM (i.e., higher the basal microbial respiration rate per unit organic C at 0 °C and DOC/SOC) compared with control (no straw addition). The Q10 values of SOM and straw decomposition was higher at 65 % WHC compared to 45 % WHC, indicating that drought conditions have potential to dampen effects of temperature on the decomposition. We also discovered a positive correlation between Q10 and activation energy and a negative correlation with soil C quality, providing support for the C quality temperature hypothesis. In summary, our findings contribute to advancing our understanding of how soil C dynamics respond to exogenous C inputs under environment change.

The possibility that N fertilizer increases soil organic matter (SOM) mineralization and, as a result, reduces SOM stocks has led to a great debate about the long-term sustainability of maize-based agroecosystems as well as the best method to estimate fertilizer N use efficiency (FNUE). Much of this debate is because synthetic N fertilizer can positively or negatively affect SOM mineralization via several direct and indirect pathways. Here, we test a series of hypotheses to determine the direction, magnitude, and mechanism of N fertilizer effect on SOM mineralization and discuss the implications for methods to estimate FNUE. We measured the effect of synthetic N fertilizer on SOM mineralization via gross ammonification at two long-term experiments in central and southern Iowa, USA with replicated plots of continuous maize that received one of three “historical” N fertilizer rates (zero, moderate or high) from 1999 to 2014. In 2015, prior to our measurements, we split the historical N fertilizer rate plots into two subplots that received either the site-specific agronomic optimum N rate or zero N fertilizer. At the onset of rapid maize N uptake, N fertilizer reduced gross ammonification by 13–21% (2–5 kg NH4-N ha−1 d−1). A companion laboratory experiment rejected the hypothesis that differences in net primary productivity between fertilized and unfertilized treatments explained the negative effect of N fertilizer on SOM mineralization. Moreover, the NH4+ pool size was negatively correlated with the gross ammonification rate (r2 = 0.85, p < 0.001). Thus, we conclude that NH4+-N fertilizer had a direct suppressive effect on SOM mineralization. These results demonstrate that the direct effect of N fertilizer on microbial activity can exceed the indirect effects of N fertilizer via large changes in NPP that alter organic matter inputs, soil temperature and moisture content. The magnitude of this effect and specificity to NH4+-N has significant implications for fertilizer management as well as the measurement and modeling of agroecosystem N dynamics including FNUE.

The relationships among microbial parameters and the rate of organic matter mineralization in forest soils, as influenced by forest type

Priming of soil organic matter mineralisation is intrinsically insensitive to temperature

Effects of nitrogen addition on soil organic carbon mineralization after maize stalk addition

Effects of soil organic matter composition on unfrozen water content and heterotrophic CO 2 production of frozen soils

Mineralization of native soil organic matter is not regulated by the size, activity or composition of the soil microbial biomass—a new perspective

Column experiments containing an aquifer sand were subjected to static and oscillating water tables to investigate the impact of natural fluctuations and rainfall infiltration on the groundwater bacterial community just below the phreatic surface, and its association with the geochemistry. Once the columns were established, the continuously saturated zone was anoxic in all three columns. The rate of soil organic matter (SOM) mineralization was higher when the water table varied cyclically than when it was static due to the greater availability of NO3− and SO42−. Natural fluctuations in the water table resulted in a similar NO3− concentration to that observed with a static water table but the cyclic wetting of the intermittently saturated zone resulted in a higher SO42− concentration. Rainfall infiltration induced cyclic water‐table variations resulted in a higher NO3− concentration than those in the other two columns, and a SO42− concentration intermediate between those columns. As rainwater infiltration resulted in slow downward displacement of the groundwater, it is inferred that NO3− and SO42− were being mobilized from the vadose zone. NO3− was mainly released by SOM mineralization (which was enhanced by the infiltration of oxygenated rainwater), but the larger amount of SO42− release required a second mechanism (possibly desorption). Different groundwater bacterial communities evolved from initially similar populations due to the different groundwater histories.

In arable soils, the topsoil and subsoil are commonly mixed in the operation of deep tillage. It is not yet clear whether the influence of crop straw on soil organic matter (SOM) mineralization of the mixed soil (from the topsoil and subsoil) is different from that of solely the topsoil or subsoil. We conducted a 120‐d incubation experiment with the addition of 13 C‐labeled maize ( Zea mays L.) straw to study SOM mineralization and straw decomposition in the topsoil (0–15 cm), subsoil (15–30 cm), and their mixture (0–30 cm). Straw addition promoted SOM mineralization and thus induced a positive priming effect. The mineralization of SOM in topsoil with straw addition was 122% higher than in subsoil, and 45% higher than in mixed soil. After the 120‐d incubation, 12–16% of straw C was mineralized as CO 2 , contributing approximately 50–70% to the total CO 2 production. Furthermore, straw C was also incorporated into SOM fractions, with 34, 7, and 59% in the light fraction, particulate organic C (coarse and fine), and mineral‐associated organic C (MAOC) in topsoil, respectively. The SOM mineralization and priming were greater in the topsoil with higher dissolved organic C and NO 3 –N throughout the incubation. Despite more straw C retained in MAOC in topsoil, the significant decrease in total MAOC with straw addition indicated that SOM turnover induced by fresh C application was probably faster in topsoil than the subsoil and mixed soil. Our findings indicated that both subsoil and mixed soil tended to sequester C with straw addition, whereas topsoil C turnover was faster than subsoil in the presence of straw addition.