Publications

Microbial necromass is a large and persistent component of soil organic carbon (SOC), especially under croplands. The effects of cropland management on microbial necromass accumulation and its contribution to SOC have been measured in individual studies but have not yet been summarized on the global scale. We conducted a meta‐analysis of 481‐paired measurements from cropland soils to examine the management effects on microbial necromass and identify the optimal conditions for its accumulation. Nitrogen fertilization increased total microbial necromass C by 12%, cover crops by 14%, no or reduced tillage (NT/RT) by 20%, manure by 21%, and straw amendment by 21%. Microbial necromass accumulation was independent of biochar addition. NT/RT and straw amendment increased fungal necromass and its contribution to SOC more than bacterial necromass. Manure increased bacterial necromass higher than fungal, leading to decreased ratio of fungal‐to‐bacterial necromass. Greater microbial necromass increases after straw amendments were common under semi‐arid and in cool climates in soils with pH <8, and were proportional to the amount of straw input. In contrast, NT/RT increased microbial necromass mainly under warm and humid climates. Manure application increased microbial necromass irrespective of soil properties and climate. Management effects were especially strong when applied during medium (3–10 years) to long (10+ years) periods to soils with larger initial SOC contents, but were absent in sandy soils. Close positive links between microbial biomass, necromass and SOC indicate the important role of stabilized microbial products for C accrual. Microbial necromass contribution to SOC increment (accumulation efficiency) under NT/RT, cover crops, manure and straw amendment ranged from 45% to 52%, which was 9%–16% larger than under N fertilization. In summary, long‐term cropland management increases SOC by enhancing microbial necromass accumulation, and optimizing microbial necromass accumulation and its contribution to SOC sequestration requires site‐specific management.

The dominance of sedges in Tibetan meadows is decreasing with the increasing abundance of grasses, mainly due to anthropogenic activities, nitrogen deposition, and climate warming. We investigated the effects of this vegetation shift on litter decomposition (in the field), mineralization to CO 2, and litter carbon (C) incorporation into microorganisms (under laboratory conditions) under sedges and grasses at community and species levels. Litter C incorporation into soil organic carbon (SOC) was estimated using 13 C labelling of the vegetation community. After one year of field incubation, a smaller proportion of shoot litter C was lost in sedges than in grasses at the species level and smaller proportions of root C were lost under sedges at community and species levels. Roots decomposed markedly slower than shoots across communities or species under sedges and grasses. Smaller proportions of the shoot and root C from sedges were incorporated into SOC than from grasses, and root C was less incorporated into the SOC than shoot C across communities. Over the 38‐day laboratory incubation, total microbial respiration and assimilation of litter C changed similarly to the C loss between litter types under the field condition. Across community and species levels, litter C loss in the field and incorporation of litter C into microorganisms under laboratory conditions all increased with initial phosphorus content in the litter and decreased with lignin content. Considering greater allocation of photosynthates belowground by sedges than grasses, we demonstrated that the ongoing replacement of sedges by grasses in the vast Tibetan alpine meadows is unfavorable for the maintenance of SOC storage.

Crop straw and it derived biochar are both promising to improve soil fertility and structure. However, the contribution of these amendments to mic

Climate warming threatens global food security by exacerbating pressures on degraded soils under intensive crop production. Conservation agriculture is promoted as a sustainable solution that improves soil health and sustains crop yields in a changing climate, but these benefits may be affected by long-term warming. Here, we investigate the effects of conservation agriculture compared to conventional agriculture on 17 soil properties, microbial diversity and crop yields, during eight-years' experimental warming. An overall positive effect of warming on soil health over time under conservation agriculture is characterized by linear increases in soil organic carbon and microbial biomass carbon. Warming-triggered shifts in microbial biomass carbon and fungal diversity (saprogen richness) are directly linked to a 9.3% increase in wheat yields over eight years, but only under conservation agriculture. Overall, conservation agriculture results in an average 21% increase in soil health and supports similar levels of crop production after long-term warming compared to conventional agriculture. Our work provides insights into the potential benefits of conservation agriculture for long-term sustainable food production because improved soil health improves resilience to the effects of climate warming.

No abstract is provided for this article.

The application of biodegradable film mulching (BFM) instead of non-biodegradable film mulching (NBFM) is a promising way to mitigate the negative impacts of residual film in agricultural mulching systems. But the effects of BFM on soil mineral nitrogen (N) are not known. To investigate the effects of BFM on N mineralization, nitrate (NO3 −) accumulation and leaching, and plant N uptake, we conducted two-year field experiment with five treatments: no-mulching (No-M), white non-biodegradable film mulching (White-NotBioM), black non-biodegradable film mulching (Black-NotBioM), white biodegradable film mulching (White-BioM), and black biodegradable film mulching (Black-BioM). The net N mineralization in NBFM was greater than that in BFM due to the disintegration of biodegradable films in the middle and late stages of maize growth, resulting in a decrease in soil water content under BFM. Higher net N mineralization caused a higher NO3 − accumulation in the topsoil (0–20 cm) under NBFM. The NO3 − accumulation in the topsoil in Black-NotBioM was 23–88% higher than that in Black-BioM; while in White-NotBioM it was 16–63% higher than that in White-BioM. After two years of cropping, the NO3 − accumulation in 100–180 cm (defined as N leaching in deep layers, NLD) in NBFM was 52–63% higher than that in BFM, implying that the higher NO3 − accumulation in the topsoil in NBFM caused more N leaching. The yields and plant N uptake were similar between NBFM and BFM, but BFM had higher N harvest index values. Compared with NBFM, BFM showed less NO3 − accumulation in the topsoil and less NLD, whereas yield, plant N uptake and net economic benefits were not reduced. Therefore, BFM, especially Black-BioM, could be an alternative to NBFM in maize production on the Loess Plateau. However, the higher N accumulation in root soil layer (0–100 cm) under Black-BioM should be accounted for in N fertilizer management.

The collapse of collective farming in Russia after 1990 and the subsequent economic crisis led to the abandonment of more than 45 million ha of arable lands (23% of the agricultural area). This was the most widespread and abrupt land use change in the 20th century in the northern hemisphere. The withdrawal of land area from cultivation led to several benefits including carbon (C) sequestration. Here, we provide a geographically complete and spatially detailed analysis of C sequestered in these abandoned lands. The average C accumulation rate in the upper 20 cm of mineral soil was 0.96 ± 0.08 Mg C ha(-1) yr(-1) for the first 20 years after abandonment and 0.19 ± 0.10 Mg C ha(-1) yr(-1) during the next 30 years of postagrogenic evolution and natural vegetation establishment. The amount of C sequestered over the period 1990-2009 accounts to 42.6 ± 3.8 Tg C per year. This C sequestration rate is equivalent to ca. 10% of the annual C sink in all Russian forests. Furthermore, it compensates all fire and postfire CO2 emissions in Russia and covers about 4% of the global CO2 release due to deforestation and other land use changes. Our assessment shows a significant mitigation of increasing atmospheric CO2 by prolonged C accumulation in Russian soils caused by collective farming collapse.

Forest restoration increases organic carbon (OC) sequestration mainly via the additional litter input and improvements in soil structure that result in biochemical and physical C stabilization over the short term. However, the pathways of long-term C stabilization in soil aggregates during forest succession are unclear. To characterize the long-term C fluxes, the aggregate-associated OC content and C flow pathways were examined over 160 years of secondary successional chronosequence from Lespedeza bicolor to Quercus liaotungensis. The contribution of plant-derived C (litter and fine root) to aggregate-associated OC was assessed using 13 C natural abundance. The proportion of macroaggregates was found to increase but microaggregates decreased along forest succession, and the macroaggregate-associated OC content increased from 4.6 to 28 g kg-1 soil during succession. The 13 C enrichment trend appeared in aggregate size classes: macroaggregates to silt and clay size classes. The maximum δ13 C was -23‰ in the silt and clay size classes in the pioneer weed stage in 20−30 cm soil depth. The C pathways followed the trend of macroaggregates to silt and clay size classes. The intensity of the C flow decreased in the topsoil (< 10 cm), but plant-derived C stocks within the aggregates increased during forest succession over the 160 years. Notably, compared to the contribution from aboveground litter, there was a greater contribution from fine root to the accumulation of OC within aggregates. The fine root and microbial biomasses were the important factors affecting fine root-derived C stocks in the aggregates. This analysis of natural δ13 C abundance provides detailed insights into long-term C stabilization pathways associated with soil aggregates during forest succession.

Microbiota within interconnected river-lake systems define cycles of carbon and nutrients, yet the mechanisms underlying the assembly of microbial communities during their transition from tributaries to lake remains to be deciphered. This study examined the communities of protists, fungi and bacteria in sediments of Qinghai Lake – a saline lake on the Tibetan Plateau, China – and its connected upstream freshwater tributaries, using high-throughput amplicon sequencing targeting the 18S, ITS2 and 16S rDNA regions. Our findings reveal divergent assembly mechanisms across microbial groups: communities of microeukaryotes (protists and fungi) in tributaries were predominantly shaped by stochastic processes (∼85% contribution), shifting to environmental selection dominance in the lake (∼55%). In contrast, bacterial community assembly in tributaries was primarily deterministic (∼60% environmental selection), shifting to stochastic dominance (∼70%) in the lake. Despite the differences, all groups exhibited congruent biogeographic patterns in terms of diversity and network complexity. The tributary-to-lake transition enhanced the complexity of microbial co-occurrence network but resulted in significant species loss, with α-diversity reduced by 56%–62%. β-diversity increased from tributaries to the estuary but decreased within the lake. Microbial α- and β-diversity correlated positively with sediment C: N ratio but negatively with total sediment C content. Notably, only 1% to 13% of microbial taxa in lake sediments originated from tributaries, suggesting alternative pathways that warrant further geological investigation. This study provides new insights into the convergent biogeographical patterns of diversity and network complexity, coupled with divergent assembly mechanisms, among protist, fungal, and bacterial communities along the river-Qinghai Lake sediment continuum.