Publications

Introducing perennials to traditional cropland is an effective way to increase soil organic carbon (SOC) stocks, but the influence on soil inorganic carbon (SIC) stocks has yet to be understood. Alfalfa-grass-cropland (AGC) rotation involves the initial planting of alfalfa, which gradually degrades into a natural grassland over time, and is eventually reclaimed and converted back into cropland. The effects of AGC rotations with short, medium, and long periods of perennial growth (16, 22, and 27 years from alfalfa planting to natural grassland) on soil total C (SOC + SIC) stocks up to a depth of 2 m were investigated. The AGC rotation had opposite effects on organic and inorganic C stocks. SOC stocks increased with the duration of perennials due to raised soil nitrogen (N) stocks. SOC accumulation, however, was offset by decreasing the SIC stock with a prolonged duration of perennials attributed to soil acidification. Consequently, the soil total C stock increased by only 3 % during 22-year perennial growth, while minimal changes were observed for periods of 16 and 27 years. This study underscores the necessity for increased efforts for SIC management.

No abstract is provided for this article.

Agricultural land use profoundly alters soil carbon (C), nitrogen (N), and phosphorus (P) contents, impacting crop productivity, environmental quality, and soil C sequestration. However, how the soil C:N:P stoichiometry is affected by upland and paddy cropping over broad geographical scale remains largely unknown. The objective of this study is to examine the soil C:N:P stoichiometry in woodland (as control), agricultural upland and paddy from four climate zones (tropics, subtropics, warm temperate, and mid-temperate) across eastern China. 720 surface soil samples were collected from 240 sites with adjacent woodland, upland, and paddy at a depth of 0–15 cm. Total C, N, and P contents and their ratios were determined. Among climate zones, C and N contents and C:N ratios decreased in the order of mid-temperate > tropics > subtropics > warm temperate, whereas C:P and N:P ratios followed the order of subtropics > mid-temperate and tropics > warm-temperate. Compared to woodland, upland agriculture decreased the C content by 4.0–6.4 g kg−1, but increased P content by 0.2–0.5 g kg−1, resulting in the decreases of C:N, C:P, and N:P ratios by 1.4–5.1, 3.4–91.5, and 1.6–4.1, respectively. Hence, uplands are relatively limited by C and N but enriched with P, particularly in warm temperate zone. By contrast, the C, N, and P contents in paddy soils were all increased compared to woodland soils, but larger N and P increase leads to the decreases in C:N and C:P ratios. The higher P content, and consequently lower C:N:P ratios in both agricultural soils are the consequences of intensive fertilization. As a whole, the direction of soil C, N, and P contents and their stoichiometric ratios in response to agricultural use was similar in the four climate zones: P increased, but C:N:P ratios decreased. The more intensive agricultural practices and stronger biological and geochemical processes with higher temperature and precipitation in warmer and wetter zones lead to more pronounced differences of soil C, N, and P contents and their stoichiometric ratios among land-use types than those in cooler and drier climates.

Plants adjust root morphological and/or exudation traits in response to phosphorus (P) mobilization mediated by microorganisms. We hypothesized that straw application coupled with P fertilization would influence microbial P and then root nutrient-acquisition strategies related to crop growth. Root morphological (length and average diameter) and exudation traits (acid phosphatase and carboxylates) of Brassica chinensis, Solanum lycopersicum, Lactuca sativa, and Vigna unguiculata in response to microbial P dynamics were characterized in no-P and P-fertilized soil with/without straw addition. Straw addition increased the growth of fungi and bacteria, stimulating microbial P immobilization at day 24. The high microbial abundance was associated with four tested crops having short roots in straw-amended compared with no-straw soil at day 24. In straw-amended soil, B. chinensis and S. lycopersicum shifted toward root P-acquisition strategies based on fast elongation and strong carboxylate exudation from days 24 to 40. Such effective root P-acquisition strategies together with microbial P release increased shoot P content in S. lycopersicum in straw-amended compared with those without straw at day 40. Conversely, L. sativa and V. unguiculata produced short roots in response to the stable (or even increased) microbial P after straw addition till day 40. In straw-amended soil, high P application stimulated root elongation and carboxylate exudation in L. sativa and V. unguiculata, whereas carboxylate exudation by S. lycopersicum was decreased compared with the straw-amended but non-fertilized treatment at day 40. In summary, root P-acquisition strategies in response to microbial P differed among the tested crop species. Phosphorus fertilization needs to be highlighted when returning straw to enhance P-use efficiency in vegetable cropping systems.

Biochar plays an important role in soil carbon (C) sequestration, while the effectiveness of sequestration is mostly determined by microbial preferences to utilize the different biochar components (i.e. labile substances or fused aromatic backbone). Thus, it is important to investigate the responses of the bacterial community and specific taxa, and associated C metabolic functions to biochar labile C (i.e. easily mineralizable C) or aromatic backbone (i.e. persistent C). Here, we separated the biochar components into labile C and aromatic backbone, and used the 16S sequencing in conjunction with the addition of an internal standard to quantify the absolute copy number of various bacterial taxa. The aromatic backbone decreased microbial metabolic quotient by 47 %, incorporating more C into biomass and contributing to C sequestration rather than releasing it into the atmosphere, while the labile C caused the opposite trends. The bacterial generalists utilizing aromatic backbone and labile C were mainly from Oxalobacteraceae (Proteobacteria) and Sporosarcina (Firmicutes). The bacterial specialists responsive for aromatic backbone were from Myxococcaceae and Flavisolibacter, while those responsive to labile C were from Ktedonobacteraceae and Bradyrhizobiaceae. Microbial abundance of specialists responsive to labile C was 3.3 times larger than those responsive to aromatic backbone, indicating the preferences of labile C specialists for energy sources and aromatic C specialists for slow utilization of persistent C in versatile habitats. Our work revealed microbial strategies for utilization of organic substances of very contrast availability, and their contributions to soil C sequestration depending on biochar components.

The anaerobic oxidation of methane (AOM) removes most of the biologically produced methane (CH4) from marine ecosystems before it enters the atmosphere and thus mitigates greenhouse gas emissions. As compared to marine environments, surprisingly little is known about the role of AOM in terrestrial ecosystems. Particularly, how AOM controls the CH4 budget of paddy soils is unexplored, partly reflecting analytical difficulties in analyzing CH4 turnover. To date, the most commonly used method to study AOM in soils is in vitro incubation of microcosms with CH4 injection into the headspace with/without shaking of slurry. Shaking, however, introduces various errors and disturbances. Here we measured AOM in rice paddy soil using a new alternative approach that introduced 13C-labelled CH4 directly into soil slurry via a silicone tube without shaking. The results were compared to those obtained by the classical approaches (i.e., with and without tubes and/or shaking). In all batches, 13C enrichment of CO2 after 13CH4 injection clearly confirmed the occurrence of AOM in paddy soil. The cumulative AOM during 84 days reached 0.16–0.24 μg C g−1 dry soil without shaking, but it was 33–80% lower with shaking. Unexpectedly, the effect of silicone tubes on AOM was insignificant either with or without shaking, suggesting that the CH4 concentration in water (slurry) was not the main limiting factor for AOM. Without shaking, the controls without CH4 addition revealed a steady increase of CH4 in the headspace/tube, whereas the CH4 concentration in jars with shaking was constantly low during 59 days. This suggests that shaking inhibited methanogenesis. There was a strong linear correlation between the amount of CH4 oxidized and CH4 produced with shaking (R 2 = 0.91), whereas without shaking this relationship followed a power growth regression. Based on the current and reported AOM rates, rough upscale to paddy soils in China showed recycling of ca. 2.0 Tg C of CH4 each year, making AOM a crucial terrestrial CH4 sink.

In the last three decades there has been a major shift in China's agriculture with the conversion from cereal fields to vegetable production, however little is known about the impact of this land use change on labile soil carbon and microbial community structure. We conducted a study to characterize dissolved organic carbon (DOC) and soil microbial community by comparing greenhouse vegetable fields with contrasting management intensity and adjacent cereal fields (wheat–maize rotation) in Shouguang and Quzhou in North China. Compared with cereal fields, greenhouse vegetable cultivation increased soil organic carbon (SOC) and total nitrogen (TN), while it decreased the soil pH, particularly at the high-intensity site. The DOC concentration was significantly higher in greenhouse vegetable fields than in cereal fields, whereas DOC composition differed between greenhouse vegetable fields and cereal fields only at high management intensity. Chemical fractionation indicated that DOC from greenhouse vegetable fields with high management intensity was less decomposed than DOC from cereal fields, because the percentage of hydrophobic acid (HOA) as DOC was higher in vegetable fields. Vegetable production significantly changed the microbial community structure in comparison to cereal fields: high-intensity management increased total bacteria, G (+) bacteria and fungi, while low-intensity decreased fungi and increased bacteria-to-fungi ratio. The main factor affecting microbial community structure was soil pH in this study, accounting for 24% of the differences.

Quantifying changes in soil organic carbon (SOC) stocks within croplands across a broad spatiotemporal scale in response to anthropogenic and environmental factors offers valuable insights for sustainable agriculture aimed to improve soil health. Using a validated and widely used soil carbon model RothC, we simulated the SOC dynamics across intensive croplands in China that support ∼22 % of the global population using only 7 % of the global cropland area. The modelling results demonstrate that the optimized RothC effectively captures SOC dynamics measured across 29 long-term field trials during 40 years. Between 1980 and 2020, the average SOC at the top 30 cm in croplands increased from 40 Mg C ha−1 to 49 Mg C ha−1, resulting in a national carbon sequestration of 1100 Tg C, with an average carbon sequestration rate of 27 Tg C yr−1. The annual increase rate of SOC (relative to the SOC stock of the previous year), starting at <0.2 % yr−1 in the 1980s, reached around 0.4 % yr−1 in the 1990s and further rose to about 0.8 % yr−1 in the 2000s and 2010s. Notably, the eastern and southern regions, comprising about 40 % of the croplands, contributed about two-thirds of the national SOC gain. In northeast China, SOC slightly decreased from 58 Mg C ha−1 in 1980 to 57 Mg C ha−1 in 2020, resulting in a total decline of 28 Tg C. Increased organic C inputs, particularly from the straw return, was the crucial factor in SOC increase. Future strategies should focus on region-specific optimization of straw management. Specifically, in northeast China, increasing the proportion of straw returned to fields can prevent further SOC decline. In regions with SOC increase, such as the eastern and southern regions, diversified straw utilization (e.g., bioenergy production), could further mitigate greenhouse gas emissions.

Progressive conversion of tropical rainforests to agricultural monocultures in South East Asia increasingly affects landscape types such as riparian areas. The impacts of conversions on soil organic matter (SOM) vary with changing landforms. However, this was often not accounted for in previous studies where SOM in soils in riparian areas was combined with SOM from well-drained adjacent slopes. Because riparian areas have a high carbon (C) storage potential, our objectives were i) to assess their C stocks after conversion to rubber and oil palm plantations in Sumatra (Indonesia) and ii) to compare the impacts of land use conversion on C stocks between riparian and well-drained areas. Average soil C stock losses from the top 30 cm were about 14% and 4% following conversion of riparian forest to rubber and oil palm plantations, respectively, indicating a high resistance of C to mineralization. C losses from well-drained areas were twice as high as from riparian areas after the respective conversion. δ13C values from riparian areas showed clear heterogeneity down soil profiles that was explained i) by alternating oxic and anoxic conditions, leading to reduced SOM and litter decomposition in riparian areas and ii) by mineral sediments and organic matter deposition and accumulation by erosion from adjacent slopes covered by plantations. We conclude that riparian areas are more resilient in terms of soil C storage towards land-use change than well-drained areas because of sediment deposition and reduced oxygen availability. On this basis, we developed a conceptual model of the effects of land-use change and various ecotone characteristics on SOM mineralization in the top- and subsoil of riparian areas.

No abstract is provided for this article.

The aim of the study was to investigate the effects of post-agricultural soil development on the respiratory activity and thermal stability of accumulated organic matter. A post-agricultural chronosequence formed on Haplic Luvisols and including currently arable land, 7- and 25-year-old post-agricultural abandoned land and grassland was studied. Soils were studied using thermogravimetric analysis aimed to investigate pools of thermally labile, stable and persistent soil organic matter (SOM). Elemental analysis was used to determine organic carbon and total nitrogen in bulk soil and water extracts. Basal and substrate-induced respiration rates were determined by incubating soils and measuring the amount of CO 2 released. The content and pool of soil microbial carbon were calculated based on the measured substrate-induced respiration. Organic, dissolved and microbial carbon, total and dissolved nitrogen and basal respiration rates increased during the post-agricultural development of soils. The specific respiration of microbial biomass was lowest in arable soil and increased after its abandonment. The availability of soil carbon for microbial decomposition increased in abandoned soils compared to arable ones. The SOM was dominated by the thermally labile pool (54–68%). The size of the thermally stabile pool of SOM was 19–25%, persistent SOM was 13–21%. The accumulation rate of the thermally labile pool in the upper 30 cm of the soil, calculated for the 25-year period of the abandoned land use, was equal to 3.9 mg lab-SOM per year, stable –0.97 mg stab-SOM per year and persistent – 0.52 mg pers-SOM per year. As arable land was converted to abandoned, the proportion of the thermally labile pool in SOM increased. The post-agricultural increase in dissolved organic carbon was associated with the rise of the thermally labile pool of SOM, indicating the relationship between the availability of organic matter for microbial decomposition and its thermal stability.

The rapid development of biogas production will result in increased use of biogas residues as organic fertilizers. However, control of microbial activity by organic fertilizers remains a challenge for modern land use, especially with respect to mitigating greenhouse effects and increasing C sequestration in soil. To address this issue, we compared CO2 emissions, microbial growth and extracellular enzyme activities in agricultural soil amended with biogas residues (BGR) versus maize straw (MST). Over a 21 day incubation period, 6.4% of organic C added was mineralised and evolved as CO2 with BGR and 30% with MST. As shown by the substrate-induced growth respiration approach, BGR and MST significantly decreased the specific microbial growth rate (μ) and increased the microbial biomass C in the soil, indicating a clear shift in the microbial community to slower-growing microorganisms. Because of the reduced availability of C associated with the less labile C and more lignin in biogas residues, observed μ values and microbial biomass C were lower after BGR application than after MST application. After 21 days incubation, BGR had no effect on the activity of three extracellular enzymes: β-glucosidase and cellobiohydrolase, both of which are involved in cellulose decomposition; and xylanase, which is involved in hemicellulose decomposition. In contrast, MST significantly increased the activity of these three enzymes. The application of biogas residues in short-term experiment leads to a 34% increase in soil C content and slower C turnover as compared to common maize residues.