Water scarcity in semi-arid regions intensifies interspecific competition in intercropping systems, thereby constraining agricultural productivity. Although film mulching effectively conserves soil moisture in monoculture systems, its potential to enhance intercropping performance under water-limited conditions remains unclear. This study evaluated whether film mulching could improve soil moisture and thereby enhance photosynthetic performance, ultimately increasing the productivity of maize-soybean intercropping in semi-arid Northwest China. A two-year field experiment compared film-mulched maize-soybean intercropping (FM) with nonmulched intercropping (NM), maize sole cropping (MS), and soybean sole cropping (SS). Soil water content (SWC), crop photosynthetic characteristics, aboveground biomass accumulation (AGB), system productivity, and economic performance were comprehensively assessed. Film mulching increased SWC by 8.12-46.37% in maize strips and 12.47-35.82% in soybean strips relative to NM, predominantly in the 0-30 cm layer. This improvement elevated net photosynthetic rates by 21.09-37.33% and subsequently increased aboveground biomass across both crops at reproductive stages. Consequently, FM substantially improved crop yield and water productivity over NM, achieving land equivalent ratios of 1.30-1.50. Despite 13.80% higher production costs, FM increased total revenue by 39.08-50.16% over NM, resulting in substantially greater economic profit. Path analysis confirmed that film mulching alleviated interspecific water competition by improving soil moisture. The enhanced water availability promoted photosynthetic capacity in both crops, ultimately leading to higher economic returns compared with non-mulched intercropping. These findings support integrating film mulching with strip intercropping as a viable strategy for sustainable agricultural intensification in water-scarce drylands.

Underground coal mining disrupts surface stability, depletes soil organic carbon (SOC) stocks through persistent alterations in topography and hydrological regimes, and adversely affects soil microbial diversity and ecological functioning. Biological soil crusts (biocrusts) play critical roles in soil stabilization, SOC sequestration, and microbial nutrient transformations in coal-mining areas. However, the mechanisms by which different mining disturbance gradients regulate organic carbon composition and stability, microbial metabolic processes, and nutrient limitations within biocrusts remain poorly understood. In this study, we investigated biocrust organic carbon fractions and microbial resource characteristics across coal mining subsidence areas by applying an organic carbon stability index and ecoenzymatic stoichiometry model to evaluate the effects of mining disturbance gradients (unmined, active mining, and 1-2 year mined-out) and vegetation types (herbaceous and shrub) on biocrust properties and microbial resource limitation. Biocrust cover ranged from 26.4 to 40.8%, with the highest moss cover occurring in herbaceous vegetation in unmined areas, whereas cyanobacterial biocrusts were most abundant under shrub vegetation in unmined areas. Compared with unmined sites, active mining and 1-2 year mined-out areas exhibited significantly lower recalcitrant organic carbon (ROC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) in biocrusts. Active mining markedly reduced biocrust nutrient availability, organic carbon stability, microbial enzyme activities related to carbon (C), nitrogen (N), and phosphorus (P) acquisition, and microbial carbon use efficiency (CUE). Vector analysis of extracellular enzyme activities indicated that moss biocrusts were primarily P-limited. In contrast, cyanobacterial biocrusts were predominantly N-limited, with nutrient limitations most pronounced in active mining and 1-2 year mined-out areas. Moreover, microbial carbon limitation was significantly greater in the moss biocrusts than in the cyanobacterial biocrusts. Partial least squares path modeling further demonstrated that coal mining influences microbial CUE, primarily by altering metabolic limitations and organic carbon stability, with microbial carbon limitation exerting the strongest negative total effect on CUE. Overall, these findings elucidated the key mechanisms governing the stability of biocrust organic carbon and the microbial metabolic constraints under mining disturbance, providing a scientific basis for ecological protection and restoration in arid and semi-arid mining regions.

Soil respiration (Rs), driven by microbial activity, varied with mulching practices, but the microbial mechanisms behind these differences remain unclear. To address this knowledge gap, a three-year (2019–2021) maize field study was conducted to evaluate three treatments: no mulching (CK), plastic film mulching (PM), and straw mulching (SM). This study assessed the effects of these practices on the alpha diversity and composition of the bacterial community and Rs, and explore the roles of soil abiotic and biotic factors in driving Rs. The results indicated that PM significantly increased bacterial alpha diversity (as indicated by ASVs, Chao1, and Shannon indices) in the early growth stage of maize and decreased the bacterial abundance and Shannon index in the late growth stage, whereas SM increased that. Furthermore, PM and SM significantly altered the bacterial community, with PM enriched Chloroflexi and Firmicutes, while SM promoted Gamaproteobacteria and Bacteroidota. Cumulative Rs under PM varied interannually, increasing in 2019 and 2020 but decreasing by 9.1

The continuous supply of phosphorus(P)is indispensable in crop production.However,P resources are non-renewable,and environmental concerns like eutrophication associated with its loss from agroecosystems make the sustainable management of P resources essential for ensuring global food security.This study was designed to reduce mineral P inputs through management practices.A field experiment comprising a wheat-maize rotation system was conducted in the Guanzhong Plain of Shaanxi Province,China from 2018-2023.The eight treatments included CK(without P),FP(conventional P application);RP(recommended P);RP80(20％reduction in RP);SRP80(20％reduction in RP with straw wrapping);ARP80(20％reduction in RP with ammonium sulfate instead of urea);SARP80(20％reduction in RP with straw wrapping and ammonium sulfate instead of urea);and SARP60(40％reduction in RP with straw wrapping and ammonium sulfate instead of urea).Crop yield,P uptake,and P fertilizer use efficiency were measured during harvest and throughout the entire period of the study.At the end of the experiment,P fractions were estimated using the Tiessen-Moir P classification method.The results revealed that the grain yields of all the treatments except for RP80 were significantly increased compared to CK,with increases of 14.9-28.8％.Furthermore,agronomic efficiency,apparent P use efficiency,P recovery rate,and partial factor productivity were significantly improved for the treatments that received 20％less P with straw wrapping.Moreover,the enhancement measures significantly increased labile and moderately labile P in the soil.Therefore,straw wrapping with ammonium sulfate instead of urea is one of the most effective ways to reduce mineral P inputs while increasing the efficiency of P in wheat-maize rotation systems.

Microplastic pollution and drought stress potentially threaten soil functions (e.g., straw decomposition) in semi-arid agroecosystems of the Loess Plateau. large decomposers (e.g., earthworms) can promote straw decomposition by modulating soil physico-chemical properties and microbial communities. However, whether, how, and to what extent earthworms can mitigate these negative effects. Here, we conducted a microcosm experiment to test the effects of microplastic pollution (no microplastic addition vs. biodegradable microplastic vs. non-degradable microplastic), and drought stress (ambient vs. drought) on microbial decomposition of straw in the presence vs. absence of earthworms. We found that both biodegradable and non-degradable microplastics enhanced microbial decomposition of straw by 11 % and 29 %, respectively, by boosting microbial diversity and total biomass. Drought, conversely, reduced microbial decomposition by 30 %. Notably, earthworms mitigated drought effects by promoting microbial decomposition by 22 % through increasing soil carbon and nutrient availability, as well as microbial biodiversity and biomass. Overall, these findings suggest that large soil decomposers can substantially alleviate the detrimental effects of global changes on ecosystem functions by enhancing the community complexity of small detritivores.

Rapid population growth and intensive agricultural expansion have heightened the urgency to reclaim saline-alkali soils for crop production. Among potential soil amendments, preliminary studies show that nano biochar improves stressed soils, but its effects on organic carbon in saline-alkali soils remain unclear. This study investigated the impacts of nano biochar derived from maize-straw biochar (300 °C pyrolysis, ball-milled) on organic carbon dynamics and salt leaching in saline-alkali soils through a 120-day greenhouse column experiment. Treatments included control (CK), maize straw (S), biochar (B), nano biochar (NB), straw + biochar (SB), and straw + nano biochar (SNB), applied at equal carbon inputs. Periodic leaching with groundwater simulated field conditions, followed by analyses of soil and leachate organic matter via pyrolysis gas chromatography and fluorescence spectroscopy. Additionally, maize seedling growth was assessed over 15 days post-experiment. Results indicated NB and SNB significantly improved soil water retention, decreased soil pH, Na+ accumulation, and exchangeable sodium, and increased exchangeable calcium content. These treatments also elevated microbial biomass carbon and promoted formation of complex, monocyclic aromatic-rich organic carbon structures. Early-stage leaching reduced larger, hydrophobic dissolved organic matter fractions, enriching smaller phenolic and quinonic molecules. Combined straw and nano biochar application amplified microbial activity and organic carbon transformation, enhancing soil redox conditions, reducing carbon losses and salt buildup, and improving maize seedling growth. These findings highlight nano biochar's potential for remediating saline-alkali soils and optimizing organic carbon dynamics. Although production cost remains a constraint, the SNB strategy with reduced nano biochar input and renewable straw application shows strong potential for scalable saline-alkali soil remediation.

There are considerable studies focusing on impacts of straw returning on PAHs degradation and bioavailability in PAHs-contaminated upland soils, while similar research in paddy soils is limited. Incubation experiments and pot trials were conducted to study effects of straw returning on PAHs degradation in paddy soils and PAHs accumulation in rice, respectively. There are threshold effects of straw returning on PAHs degradation in PAHs-contaminated paddy soils. The inflection point of PAHs degrading was recorded under 0.8 % wheat straw treatment (conventional (CS) and pretreated wheat straw (PS)), which increased PAHs degradation by 18.13-32.36 %. The lowest PAHs concentrations in rice were recorded under 1 % straw (CS and PS) treatment, which was attributed to the highest PAHs degradation in rhizosphere soils. Compared to CS treatment, PS treatment significantly (p < 0.05) increased PAHs degradation by 7.93-10.28 % and PAHs concentrations in rice by 12.38-45.87 % due to that increasing dissolved organic carbon (DOC) enhanced PAHs concentrations in porewater of rhizosphere soils. Higher diversity enhanced the metabolic pathways and function genes to degrade PAHs by improving bacterial phenotypes and biochemical processes under 1 % wheat straw and PS treatment. The present study firstly demonstrated that the effects of straw returning on PAHs degradation in PAHs-contaminated paddy soils and PAHs concentrations in rice depended on amount and methods of straw returning.

The alteration of stand age instigates modifications in soil properties and microbial communities. Understanding the impacts of stand age on soil enzyme stoichiometry and microbial nutrient limitations in

Straw return in situ is a common agronomic measure in China that has been widely used not only to increase crop yields and improve soil nutrients but also to remove PAHs from agricultural soil. Nevertheless, the safety risk of food crops grown in PAHs-contaminated agricultural soils and human health risk of wheat grains amended with crop straw remain uncertain. A pot experiment, PAHs-contaminated agricultural soils cultivated with winter wheat amended with different ratios of corn straw (0%, 1%, 2.5%, and 5%, w/w) was conducted. The results showed that PAHs concentrations in rhizosphere soil, roots, straws, and grains were significantly (P < 0.05) decreased by 48.32%–50.01%, 11.85%–42.67%, 9.78%–28.03%, and 14.16%–31.67%, respectively, compared with no corn straw addition (CK). But the transfer factors of PAHs from roots to straws (TFstraw/root) were significantly (P < 0.05) increased. A correlation heatmap showed that PAHs concentrations in roots, straws, and grains were positively (P < 0.01) correlated with those in the rhizosphere soil. These findings indicated that corn straw declined PAHs accumulation in winter wheat due to the increase of PAHs dissipation in the rhizosphere soil, although it enhanced PAHs transfer in winter wheat. The incremental lifetime cancer risk (ILCR) model indicated that corn straw significantly (P < 0.05) declined human health risk by 29.73%–45.05%. Overall, corn straw apparently reduced PAHs accumulation in winter wheat, ecological risk, and human health risk via enhancing PAHs dissipation in the rhizosphere soil. These present findings provide an important scientific basis and theoretical guidance for agricultural safety production.

Understanding the long-term responses of crop yield and soil organic carbon to fertilization is necessary to sustain food supply in a context of global change. The time-course of winter wheat yield and soil organic carbon were established in a 31-year long experiment with four fertilization regimes: unfertilized control; fertilized with mineral nitrogen and phosphorus, NP; fertilized with mineral N, P and K, NPK; and fertilized with manure and mineral NPK, MNPK. Over the time series, mean temperature increased at 0.054 degree celsius year- 1 (i.e. 1.67 degrees over the course of the experiment) and annual precipitation increased at 8.9 mm year- 1. Yield did not show trends in unfertilized controls, increased at 210 kg ha-1 year- 1 in the first 20 years and decreased slightly afterwards in the NP and NPK treatments, and increased at 310 kg ha-1 in the MNPK treatment until 2006, and leveled off afterwards. Soil organic carbon increased linearly with rates from 0.05 g kg-1 year- 1 in unfertilized controls to 0.24 g kg-1 year- 1 in MNPK. In fertilized crops, yield correlated nonlinearly with annual precipitation, and linearly with average temperature during the growing season. Across fertilizer treatments, yield correlated nonlinearly with soil organic carbon and the thresholds of soil organic carbon for peak yield increased with water supply. It is concluded that the combination of organic and inorganic fertilizers contributed to yield and soil organic carbon against the background of a warmer and wetter climate.

Manure replacing synthetic fertilizer is a viable practice to ensure crop yield and increase soil organic carbon (SOC), but its impact on greenhouse gas (GHG) emissions is inconsistent, thus remains its effect on CF unclear. In this study, a 7-year field experiment was conducted to assess the impact of replacing synthetic fertilizer with manure on crop productivity, SOC sequestration, GHG emissions and crop CF under winter wheat-summer maize cropping system. Five treatments were involved: synthetic nitrogen, phosphorus, and potassium fertilizer (NPK) and 25%, 50%, 75%, and 100% of manure replacing synthetic N (25%M, 50%M, 75%M, and 100%M). Compared with NPK treatment, 25%M and 50%M treatments maintained annual yield (winter wheat plus summer maize) and sustainable yield index (SYI), but 75%M and 100%M treatments significantly decreased annual yield, and 100%M treatment also significantly reduced annual SYI. The SOC content exhibited a significant increasing trend over years in all treatments. After 7 years, SOC storage in manure treatments increased by 3.06-11.82 Mg ha- 1 relative to NPK treatment. Manure treatments reduced annual GHG emissions by 14%-60% over NPK treatment. The CF of the cropping system ranged from 0.16 to 0.39 kg CO2 eq kg- 1 of grain without considering SOC sequestration, in which the CF of manure treatments lowered by 18%-58% relative to NPK treatment. When SOC sequestration was involved in, the CF varied from -0.39 to 0.37 kg CO2 eq kg- 1 of grain, manure treatments significantly reduced the CF by 22%-208% over NPK treatment. It was concluded that replacing 50% of synthetic fertilizer with manure was a sound option for achieving high crop yield and SYI but low CF under the tested cropping system.

Different types of carbon substrates were widely used in soil remediation. However, differences of their impacts and related mechanisms on degradation of polycyclic aromatic hydrocarbons (PAHs) and microbial community structures in contaminated soil still remain unclear. Here, we investigated the effects of corn straw (S), glucose (G), straw combined with glucose (SG), and sodium azide (N, as an abiotic control) on PAHs fractions and bacterial communities in soil. After 70 days’ microcosm experiments, total PAHs concentrations were significantly reduced by 30.9%, 19.5% and 44.6% under S, G and SG treatments. Water soluble, acid soluble and residual PAHs under all treatments were significantly decreased after 70 days of incubation, while organically bound PAHs were increased by 11.4%, 22.7% and 36.1% under G, S and SG treatments. Additionally, straw and glucose application increased relative abundance related PAHs-degrading bacteria and the copy numbers of gram-negative (PAHs-RHDα GN) and gram-positive genes (PAHs-RHDα GP) in the contaminated soil. Redundancy analysis (RDA) and Random Forest (RF) indicated that PAHs fractions are crucial factors for biodegradation of PAHs in PAHs-contaminated soils amended with carbon substrates. These suggested that carbon substrates contributed to PAHs conversion from residual PAHs (nonlabile fractions) to organically bound PAHs and thus increased the potential for PAHs conversion to water-soluble and organic acid-soluble PAHs, which were more easy to be utilized by soil microorganisms. This study revealed the new insights of different carbon substrates on degradation and dynamic changes of PAHs fractions and the better potential of combined application of straw and glucose in enhancing degradation of PAHs in PAHs-contaminated soils.

Contrasting fertilization modifies soil phosphorus (P) transformation and bioavailability, which impact crop P uptake and P migration in the soil profile. A long-term (25-year) fertilizer experiment was employed to investigate crop yield, P uptake and changes in sequentially extracted P fractions in the soil profile, and their relationships on a calcareous soil derived from loess material under a winter wheat and summer maize double-cropping system. The experiment involved seven nutrient management treatments: control (CK, no nutrient input), N, NK, NP, and NPK, representing various combinations of synthetic nitrogen (N), phosphate (P), and potassium (K) applications, as well as combinations of NPK fertilizers with either crop residues (SNPK, where S refers to maize stalk or wheat straw) or manure (MNPK, where M refers to dairy manure). Wheat and maize yields were significantly higher with P input fertilizer relative to the P-omitted treatments. Long-term application of P-containing fertilizers markedly raised the contents of inorganic (Pi) and organic (Po) P fractions at 0–20 cm depth compared with the P-omitted treatments. Moreover, both Pi and Po fractions were markedly higher under MNPK than under NPK and SNPK treatments. For achieving high yield for wheat and maize, the critical contents of labile P were 54 and 63 mg kg−1, and those of moderately labile P were 48 and 49 mg kg−1, respectively, defined by the linear plateau model. In addition, the change points of labile P and moderately labile P were 99 and 70 mg kg−1, above which CaCl2-P content significantly increased. Moreover, long-term P input significantly accumulated different P fractions in the deeper soil layers up to 100 cm, with large portions of organic P being a composite of labile and moderately labile P, especially in MNPK treatment. Our results suggest that excessive P supply with organic manure resulted in massive P accumulation in the topsoil and promoted soil P fraction transformation and availability in the deep soil layers, especially in an organic P form that has often been neglected.

[Objective]Soil moisture has an important impact on N2O emissions.This study attempted to simulate the cumulative process of soil N2O emission under different soil moisture conditions by using a mixed dynamic equation,and to analyze the influence of soil water on N2O production pathway and its variation rule in order to provide theoretical and practical guidance for reducing N2O gas emissions through improving soil management.[Methods]Soil N2O emission characteristics,the dynamics of ammonium and nitrate nitrogen content,and oxygen consumption were studied under different soil moisture conditions[40％water-holding capacity(WHC),60％WHC,80％WHC,100％WHC,and flooded].[Results]① TheN2O emission rates reached maximum values at 24 h.Emissions from the flooded treatment[3.46 μg/(kg·h)]were 54.5-178.9 times greater than from the other treatments.② The cumulative emission of soil N2O increased with increasing incubation time,and the rapid rise stage occurred in the first 48 h for the flooded treatment.The rapid rise stage occurred in the first 96 h for other treatments.The cumulative N2O emissions for soil under the flooded treatment(44.6 μg/kg)were 67.1,29.2,20.8,and 10.4 times greater than under 40％ WHC,60％ WHC,80％ WHC and 100％ WHC,respectively,at the end of incubation.③ Except for the coefficient of determination(R2)of 0.878 for the pseudo-second-order dynamic equation under the flooded treatment,all coefficients of determination were greater than 0.920 for all dynamic equations under all soil moisture treatments.The denitrification process accounted for 9.3％～13.2％ of the N2O emissions,and the nitrification process accounted for 86.8％～90.7％ of the N2O emissions at the initial 24 h of incubation.At the end of incubation(480 h),the denitrification process accounted for 37.8％～47.5％ of the N2O emissions,and the nitrification process accounted for 52.5％～62.2％ of the N2O emissions.[Conclusion]The higher the soil moisture content,the greater the emission of N2O,and an emission rate pulse appeared at 24 h.N2O was mainly generated by denitrification under flooded conditions.N2O was mainly generated by nitrification under the 40％～100％ WHC conditions.The mixed dynamic equation was able to well simulate the cumulative emission process of soil N2O during the incubation experiment,and can be used to distinguish the amount and proportion of N2O emissions occurring by denitrification and nitrification processes.These results provide a new idea and method for studying the pathways of soil N2O production and emission.The results need to be further verified by field experiments and isotope tracing methods etc.

【Objectives】We studied the possibility of decreasing phosphorus（P） fertilizer application rate and improving its efficiency.【Methods】The treatments included no P application（CK）,recommended P application rate（RP）,15% off RP（85%RP）,straw-wrapped P fertilizer application at 85%RP（St85%RP）,and85%RP plus substituting urea with ammonium sulfate（Am85%RP）.P fertilizer was broadcast in the RP treatment,and band application was adopted for the other treatments.The crop yield,P fertilizer efficiency,soil P pool,and crop mycorrhizal infection rate were investigated.【Results】Compared with CK,all the other treatments except85%RP significantly increased maize（17.1%-32.6%） and wheat（8.9%-12.8%） grain yields（P＜0.05）,and the total yield of maize and wheat（13.1%-22.5%）.Compared with RP,P reduction treatments occasionally decreased crop yields,e.g.the maize yield in 2018 and the wheat yield in 2020 under 85%RP.85%RP,St85%RP,and Am85%RP had（P＜0.05） higher P recovery rate,apparent use efficiency,and partial factor productivity than RP.Further,St85%RP recorded significantly higher P efficiencies than 85%RP.Compared with CK,P application（P＜0.05） increased the soil available phosphorus（AP） and the microbial biomass phosphorus（MBP） contents.The soil AP and MBP under 85%RP were（P＜0.05） lower than RP.St85%RP and Am85%RP did not decrease the soil AP.St85%RP（P＜0.05） increased the MBP and the water-soluble phosphorus（WSP） contents.The apparent soil P balance under RP was slightly surplus and was closer to being balanced,while P reduction treatments recorded deficits.Compared with RP,St85%RP and Am85%RP improved the mycorrhizal infection rate of wheat roots.【Conclusions】In the winter wheat-summer maize cropping system in Guanzhong,a reduction of 15%phosphate input under the recommended P application rate causes a deficit in the apparent soil phosphorus balance,increasing the risk of yield reduction.Reducing 15% of P fertilizer with straw-wrapped P fertilizer or replacing urea with ammonium sulfate could improve available soil P,microbial biomass P,and the mycorrhizal infection rates of wheat roots,thus improving P absorption and utilization in wheat.In addition to improving P fertilizer utilization efficiency,yield reduction risk caused by P reduction was minimized,which improved crop yield.This indicates that the two treatments are highly efficient regulation techniques for improving P fertilizer efficiency.

为研究施加钝化剂、叶面肥对大田小麦-玉米轮作Cd吸收转运的影响,实现安全利用类耕地农作物的安全生产,通过大田轮作试验的方式,选用小麦秸秆生物炭、钙镁磷肥为土壤钝化剂,叶面硒肥为叶面阻隔剂,在田间共设置6个处理:小麦和玉米常规种植(CK)、基施生物炭(B)、基施钙镁磷肥(P)、叶面喷施硒肥(F)、叶面喷施硒肥的同时基施生物炭(BF)、叶面喷施硒肥的同时基施钙镁磷肥(PF).小麦和玉米成熟后对其籽粒、秸秆、根系3部分的Cd含量进行检测,并对耕地土壤的pH值、有效态Cd、全量Cd进行测定.结果表明:与CK处理相比,小麦和玉米各处理土壤pH值有不同程度的升高,其中B处理和BF处理会显著提升土壤pH值;小麦和玉米各处理土壤中全量Cd无明显变化;P处理和PF处理可显著降低土壤有效态Cd含量.与CK处理相比,各处理农作物籽粒中Cd含量均有不同程度的降低,且叶面阻隔联合土壤钝化技术(BF、PF)的效果更好.较CK处理,PF处理小麦和玉米籽粒Cd含量下降最明显,降幅分别为39.91％、43.51％,BF处理小麦和玉米籽粒Cd含量分别下降了22.58％、33.53％,F、B处理和P处理变化较小,降低效果表现为B处理

Purpose Polycyclic aromatic hydrocarbons (PAHs) are universal in agricultural soils, and threaten food security and sustainable agricultural development. Straw return is widely used as soil amendment for promoting sustainable farmland use and remedying pollution of PAHs. However, the effects and related mechanisms of different residual parts of crops on the remediation of PAHs-contaminated soils are still unclear. Materials and methods In this study, CO 2 emissions, concentrations of dissolved organic carbon (DOC) and soil microbial biomass carbon (MBC), concentrations and fractions of PAHs were measured to investigate whether the response of PAHs degradation to maize straw and root stubble addition at four levels (0%, 1%, 2.5%, and 5%, w/w) was different in PAHs-contaminated soils. Partial least squares path modeling (PLS-PM) was utilized to investigate the transformation of four fractions of PAHs (water-soluble, organic acid-soluble, organically bound, and residual PAHs). Results The present research demonstrated that 5% straw addition (49.05%) significantly ( p < 0.05) enhanced PAHs degradation rate compared to 5% root addition (45.60%). The reason for this is that the former significantly ( p < 0.05) increased concentrations of DOC (from 6.62 to 11.34%) and MBC (from 7.66 to 23.63%) in soils more than the latter. Based on random forest analysis (a model strength of 99.19%, p < 0.001), DOC, MBC and PAHs fractions were the major contributors to the degradation of PAHs, with their contributions ranging from 14.43 to 30.28%. Furthermore, PLS-PM analysis (a goodness-of-fit of 0.872) revealed that the transformation from lower bioavailable fractions (organically bound and residual PAHs) to more bioavailable fractions (water-soluble and organic acid-soluble PAHs) was the primary factor influencing PAHs degradation. Conclusions Our findings demonstrated that the efficiency of PAHs degradation under higher ratio of straw addition was significantly higher than that of root stubble in PAHs-contaminated soils, which was due to the transformation of PAHs fractions caused by increasing of DOC and MBC.

For years, biochar has been successfully used for the remediation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils, not only for improving their removal from soil but also for reducing their uptake by crops. However, the underlying mechanism of biochar application reducing PAH uptake and accumulation in winter wheat remains unclear. Pot trials were conducted on a PAH-contaminated soil amended with bamboo biochar, coconut shell biochar, and maize straw biochar (MSB) for an entire growth period of winter wheat. Compared with no biochar control (CK), application of the three types of biochar significantly (P < 0.01) reduced grain PAH concentration, total equivalent concentration (TEC), and incremental lifetime cancer risk (ILCR), indicating that biochar application, especially MSB, reduced the risk of exposure to PAHs in wheat grain. Furthermore, all three types of biochar significantly (P < 0.05) reduced PAH uptake and accumulation in wheat roots and stems, probably because biochar application enhanced the degradation of PAHs in the rhizosphere soil. Compared with CK, application of the three types of biochar significantly (P < 0.05) reduced the concentration of PAHs in the rhizosphere soil by 15.9%–33.7%. It was found that the degradation rate of high-molecular-weight (HMW) PAHs (5- and 6-ring PAHs) was significantly (P < 0.05) higher than that of low-molecular-weight (LMW) PAHs (2–4-ring PAHs) regardless of the type of biochar used. Additionally, all three types of biochar significantly increased the relative abundance of the dominant bacterial phyla and genera in soil. Redundancy and correlation analyses also showed that there was a strong correlation between the removal rate of PAHs and dominant bacteria in the rhizosphere soil. This study indicated that biochar effectively reduced the health risk from dietary exposure to PAHs in wheat grains by increasing the abundance of bacteria related to PAH degradation, promoting the biodegradation of PAHs in the rhizosphere soil, and consequently reducing PAH uptake by wheat.

陕北黄土高原丘陵沟壑区是山地苹果重要产区,为提升山地果园土壤养分和果实品质及产量,以"肥水蚓坑"措施为基础,通过田间试验探讨不施肥、单施化肥、有机无机肥配施(牛粪+化肥、菇渣+化肥、牛粪+菇渣+化肥)等不同施肥对山地果园土壤养分、叶片营养、苹果产量与品质的影响.结果表明:(1)不施肥处理的土壤有机质含量和速效养分含量均低于施肥处理,其中,单施化肥处理低于有机无机肥配施处理,牛粪+菇渣+化肥处理的效果优于其他施肥处理.(2)施肥处理的苹果叶片不同生育期的全氮、磷、钾含量均显著高于不施肥对照,有机无机肥配施处理优于单施化肥处理.(3)不施肥处理与施肥处理的苹果果实硬度和果形指数无显著差异,施肥处理均可显著提高苹果产量和果实可溶性固形物、可溶性糖及维生素C含量,牛粪+菇渣+化肥优于其他处理,单施化肥的果实可滴定酸含量显著高于不施肥和有机无机肥配施.单施化肥的果实糖酸比与不施肥无显著差异,却显著低于有机无机肥配施.综上,"肥水蚓坑"结合有机无机肥配施可以减少化肥的施用,提高土壤养分含量,确保苹果提质增产,牛粪+菇渣+化肥(牛粪:菇渣=1:1)是山地苹果提质增产的优质管理模式,值得在陕北黄土丘陵沟壑区山地果园推广应用.