Climate models project more frequent and severe soil dry–wet (DW) events in semi-arid regions, but whether historical moisture stress leaves lasting effects on soil carbon (C) and nitrogen (N) transformations upon new organic inputs remains unclear. We investigated the legacy effects of four successive DW cycles on microbial C and N dynamics in a semi-arid cropland soil. After the pre-treatment, both continuously moistened (CM) and DW-exposed soils were rewet to the same moisture level with addition of concentrated oat straw leachate as a complex organic substrate. Soil respiration rates, microbial and soil C and N pools, metabolic quotient (qCO2), enzyme activities, and phospholipid fatty acid profiles were determined on days 0, 3, and 14. A history of DW cycles increased cumulative CO2-C release by 29

Long-term continuous cropping of foxtail millet (Setaria italica) typically exacerbates Fusarium wilt and autotoxicity; however, rare healthy plants (HP) thrive in monoculture fields with > 8 years of cultivation. We hypothesized that HP rhizospheres develop disease-suppressive capacities mediated by a keystone bacterium. In the long-term continuous cropping plots, the HP had much higher aboveground and belowground biomass, panicle weight per plant, and grain weight per panicle than the diseased plants (DP). The growth performance of HP in the long-term continuous cropping plots was even similar to that of control plants in the non-continuous cropping plots (foxtail millet-maize (Zea mays L.) rotation). Compared to DP, HP rhizospheres showed lower F. oxysporum abundance and reduced cinnamic acid level, while soil slurry inoculation assays confirmed this suppressiveness. 16 S rRNA gene sequencing revealed that HP rhizospheres enriched Bacillus amyloliquefaciens (ASV1275; 4.8 × higher than DP rhizospheres). From the HP rhizosphere soils, we isolated B. amyloliquefaciens YD35 (99.8

Plants release a variety of small molecules into soils through litters and root exudates, playing an important role in dynamic fraction of soil organic matter. However, these molecules’ specific roles in regulating microbial processes and carbon cycling remain poorly understood. This study aimed to investigate the degradation dynamics of the plant-derived pentacyclic triterpenoid friedelin and its effects on soil microbial activity and community composition. A 480-day laboratory incubation experiment was conducted with an abandoned cropland soil amended with friedelin at 0, 5 and 25 μg g−1. The degradation kinetics was examined during the entire incubation period. Soil respiration rates, microbial biomass, metabolic quotient (qCO2), and phospholipid fatty acid (PLFA) profiles were determined at the early stage. Friedelin followed exponential degradation kinetics, with half-lives of 68.7 and 189.1 days for the low and high doses, respectively. Friedelin addition significantly stimulated soil respiration and increased the microbial qCO2. The PLFA profiles revealed that friedelin enriched fast-growing bacterial groups and actinomycetes while increasing the ratio of cyclopropyl fatty acids to their monoenoic precursors, an indicator of physiological stress. Unexpectedly, the abundance of arbuscular mycorrhizal fungi biomarker increased, whereas that of saprophytic fungi was unaffected. The observed respiratory pulse was strongly correlated with the shifts in bacterial community and stress status, rather than increased general carbon availability. The results indicated that friedelin, at environmentally relevant concentrations, may directly alter microbial community composition, induce physiological stress, and accelerate respiratory carbon loss. This highlights the importance of specific plant metabolites in mediating soil ecological processes and plant-soil feedbacks.

Foxtail millet is a dietary staple cultivated in arid and semiarid regions worldwide but its sustainable cultivation is strongly restricted by continuous cropping obstacles. Here, we compared the performance of foxtail millet, rhizosphere soil fungi communities under non-continuous cropping, and two and eight years of continuous monocultures (C0, C2, and C8, respectively) to explore the underlying mechanisms. The emergence rates and yield of foxtail millet decreased under continuous monoculture, and the magnitude increased with years of the monoculture. The C8 soil slurry alone and in combination with bactericide (Bronopol) significantly suppressed the emergence rates and root length of foxtail millet, whereas the presence of fungicide (Captan) almost entirely attenuated the suppressive effects, indicating that fungi, but not autotoxicity, are responsible for the negative effects of the continuous cropping on the performance of foxtail millet. Eight-year of monoculture decreased the relative abundance of the fungal genera Acaulium, Gymnoascus, Mortierella, Solicoccozyma, and Pseudombrophila, stimulated the relative abundance of the fungal genera Fusarium, Acremonium, and Cephalotrichum. An F. oxysporum strain, YDSi-3, was isolated from the C8 rhizosphere soil, which induced root-rot disease in foxtail millet. The concentrations of phenolic acids, especially cinnamic acid, significantly increased in the C8 rhizosphere soil. The application of cinnamic acid largely increased the abundance of F. oxysporum in C0 soils. Overall, our findings suggest that the negative effects of continuous cropping on foxtail millet may be attributed to pathogenic fungal accumulation because of the phenolic-acid enrichment in the rhizosphere.

Forest ecosystems contain a substantial terrestrial reservoir of soil organic carbon (SOC). Here, a “Detritus Input and Removal Treatments” experiment was conducted to explore the effects of litter and roots on soil labile, persistent, and total organic C (TOC) pools in the coniferous, broad-leaved, and coniferous-broad-leaved mixed forests (CF, BF, and CBF, respectively) in the subtropical and warm temperate transition zone in Henan province, eastern China. After 2–3 years of detritus manipulations, neither litter addition nor root exclusion affected soil temperature or moisture. In contrast, litter removal increased soil temperature but decreased soil moisture, regardless of forest types. Litter addition marginally decreased labile OC and TOC contents in the BF but not in the CF and CBF. Litter removal reduced labile OC and TOC contents in the CF and BF and persistent OC contents in the CF only. Root exclusion decreased labile OC contents in the CBF only, but reduced persistent OC and TOC contents in the CF and CBF. Structural equation models suggested that litter but not root manipulation altered SOC pools via changing soil temperature and moisture in the BF, whereas the effects of litter and root manipulation on SOC pools were not related to the changes in soil temperature and moisture in the CF and CBF. Our results suggest that the impact of litter and roots on SOC pools depends on forest types, which may indicate differential responses of SOC storage among forests under global change scenarios.

Redistribution of precipitation across seasons is a widespread phenomenon affecting dryland ecosystems globally. However, the impacts of shifting seasonal precipitation patterns on carbon (C) cycling and sequestration in dryland ecosystems remain poorly understood. In this study, we conducted a 10-yr (2013-2022) field manipulative experiment that altered the timing of growing-season precipitation peaks in a semi-arid grassland. We found that the delayed precipitation peak suppressed plant growth and thus reduced gross ecosystem productivity, ecosystem respiration, and net ecosystem productivity due to middle growing-season water stress. Surprisingly, shifting more precipitation to the early growing season can advance plant development, increase the dominance of drought-tolerant forbs, and thus compensate for the negative impacts of middle growing-season water stress on ecosystem C cycling, leading to a neutral change in grassland C sink. Our findings indicate that greater precipitation and plant development in spring could act as a crucial mechanism, maintaining plant growth and stabilizing ecosystem C sink. This underscores the urgent need to incorporate precipitation seasonality into Earth system models, which is crucial for improving projections of terrestrial C cycling and sequestration under future climate change scenarios.

Soil carbon (C) and nitrogen (N) transformations are typically interlinked because of the conserved elemental stoichiometry of microbes, which can be remarkably altered by intensified temperature variations and dry-wet (DW) cycles. However, the interactive effects of temperature and DW cycles on soil C and N transformations and how microbial communities mediate these processes remain largely unknown. In this study, we subjected a semiarid grassland soil from northern China to four successive DW cycles at 15, 25, and 35 C-degrees. The soil respiratory rates during incubation, labile C and N fractions, activities of C and N acquisition enzymes, community -level physiological profiles, and microbial community composition at the end of the incubation were determined. Soil respiration rates decreased with drying but sharply increased with wetting, particularly at higher temperatures. Soil DW cycles did not significantly affect cumulative C mineralization and net N mineralization at 15 C. However, they decreased cumulative C mineralization by 24.5% and 23.4% and increased net N mineralization by 48.6% and 41.7% at 25 and 35 C-degrees, respectively, indicating a decoupling of C and N mineralization at higher temperatures. As the temperature increased, soil DW cycles decreased cellobiohydrolase and peroxidase activities and the microbial use of amino acids and lipids but increased N-acetyl-beta-glucosaminidase activities and the microbial use of saccharide polymers and recalcitrant amines. Moreover, soil DW cycles increased the abundances of gram -positive bacteria and actinomycetes and gram -positive -to -gram -negative bacteria ratios with increasing temperature, particularly at 35 C-degrees. Overall, our findings suggest that DW cycles at higher temperatures decelerated the mineralization of organic soil C by decreasing cellobiohydrolase and peroxidase activities. However, DW cycles at higher temperatures improved N mineralization by shaping the microbial communities to excrete more recalcitrant -organic -N acquisition enzymes, thereby meeting their high N requirements.

Concurrent changing precipitation regimes and atmospheric nitrogen (N) deposition can have profound influences on soil carbon (C) cycling. However, how N enrichment regulates the responses of soil C fluxes to increasing variability of precipitation remains elusive. As part of a field precipitation gradient experiment with nine levels of precipitation amounts (-60 %, -45 %, -30 %, -15 %, ambient precipitation, +15 %, +30 %, +45 %, and +60 %) and two levels of N addition (0 and 10 g N m- 2 yr- 1) in a semi -arid temperate steppe on the Mongolian Plateau, this work was conducted to investigate the responses of soil respiration to decreased and increased precipitation (DP and IP), N addition, and their possible interactions. Averaged over the three years from 2019 to 2021, DP suppressed soil respiration by 16.1 %, whereas IP stimulated it by 27.4 %. Nitrogen addition decreased soil respiration by 7.1 % primarily via reducing microbial biomass C. Soil respiration showed symmetric responses to DP and IP within all the four precipitation variabilities (i.e., 15 %, 30 %, 45 %, and 60 %) under ambient N. Nevertheless, N addition did not alter the symmetric responses of soil respiration to changing precipitation due to the comparable sensitivities of microbial biomass and root growth to DP and IP under the N addition treatment. These findings indicate that intensified precipitation variability does not change but N addition could alleviate soil C releases. The unchanged symmetric responses of soil respiration to precipitation variability under N addition imply that N deposition may not change the response pattern of soil C releases to predicted increases in precipitation variability in grasslands, facilitating the robust projections of ecosystem C cycling under future global change scenarios.

为探究定位培肥矿区复垦土壤过程中不同有机肥对土壤磷素累积状况及环境流失风险的差异.以山西省孝义市采煤塌陷复垦土壤为研究对象,研究不同有机肥(鸡粪、猪粪、牛粪)和化肥在4个施磷水平下(0,25,50,100 kg/hm2)培肥4年后对矿区复垦土壤全磷、Olsen—P、Mehlich3—P、CaCl2—P以及磷饱和度(DPS)的影响及其之间的变化关系.结果表明:(1)施用有机肥增加土壤中磷素含量,且施磷量越大,对磷素含量的影响越明显,特别是土壤全磷、Olsen—P和Mehlic3—P,并使CaCl2—P呈增加的趋势;与不施磷处理和化肥相比,施用有机肥提高了土壤磷饱和度(DPS);总体来看,不同施肥处理对土壤磷素含量的影响均表现为鸡粪≥猪粪＞牛粪＞化肥.(2)各施肥处理土壤Olsen—P与Mehlich3—P、Olsen—P与CaCl2—P、Mehlich3—P与CaCl2—P之间存在显著的线性相关性.(3)与猪粪、牛粪和化肥处理相比,鸡粪处理对矿区复垦土壤磷素流失风险影响最大,当磷饱和度(DPS)≥39.31％、Olsen—P≥26.24 mg/kg、Meh-lich3—P≥49.06 mg/kg时,土壤CaCl2—P含量迅速增加.因此,可将上述指标作为矿区复垦土壤磷素流失的临界值,超过此值,土壤磷素流失风险加大,需要警惕对地表、地下水体的污染.

为探究咪唑乙烟酸对抗性及常规谷子品种生理特性及产量构成的影响及其抗性机理,以抗咪唑乙烟酸谷子品种冀谷35和常规谷子品种冀谷38、冀谷41、晋谷21、晋谷59、长农44、龙谷39和中谷9为研究对象,采用盆栽及田间试验比较其苗期生理特性和产量构成对咪唑乙烟酸的响应.盆栽试验结果显示:咪唑乙烟酸按有效成分93.5 g/hm2施用,显著降低了常规谷子品种幼苗期地上部分鲜重(降幅达21.60％～72.83％)及叶绿素a(45.20％～92.12％)、叶绿素b(18.10％～93.36％)、类胡萝卜素(42.58％～84.21％)和总叶绿素的含量(45.73％～92.38％);叶绿素荧光参数表观光合电子传递速率和最大光化学产量分别下降20.4％～37.0％ 和6.9％～24.8％,非光化学淬灭系数和调节性能量耗散的量子产量分别显著上升了101.0％～322.1％和113.7％～319.7％.而对抗性品种冀谷35的地上部分鲜重、叶绿素含量及叶绿素荧光参数均无显著影响.咪唑乙烟酸显著降低了常规谷子品种的过氧化氢酶(CAT)活性,降幅达19.70％～56.58％,增加叶片丙二醛(MDA)含量达16.70％～68.80％,提高抗性谷子品种冀谷35的CAT活性达52.48％,但对其MDA含量无显著影响.抗性品种冀谷35经咪唑乙烟酸处理后乙酰乳酸合成酶(ALS)活性变化较小,而常规品种冀谷38的ALS从药后13 d起,活性较对照开始显著下降.田间试验结果显示:苗期喷施咪唑乙烟酸显著降低了常规谷子品种谷穗的穗长、穗粗、穗重、穗粒重及理论产量;显著增加了抗性谷子品种冀谷35的穗重、穗粒重及理论产量,增幅为7.8％～8.6％.研究表明,冀谷35通过维持体内靶标酶ALS活性稳定,增强对过氧化氢的清除能力,减轻膜脂过氧化,使其对咪唑乙烟酸具有高抗药性.

化感物质衍生物吡喃酮防除杂草效果好,且对作物有较高的安全性,为了明确化感物质衍生物吡喃酮对黑土微生物群落结构的影响,试验设置低(0.25 mg/kg,正常施用)和高(2.5 mg/kg,模拟高质量分数污染)2个吡喃酮添加水平,同时设不添加为对照(CK),利用高通量测序技术对吡喃酮处理7、60 d后土壤细菌16S rRNA的V3+V4区域和真菌ITS1区域进行测序分析.结果表明,吡喃酮处理7、60 d后,黑土细菌和真菌的Shannon和Chao1指数与CK相比均无显著变化.培养7 d后,低质量分数吡喃酮处理显著提高了细菌鞘氨醇单胞菌属、真菌葡萄穗霉属的相对丰度,显著降低了真菌子囊菌门的相对丰度;高质量分数吡喃酮处理显著提高了细菌绿弯菌门相对丰度,显著降低了真菌子囊菌门的相对丰度,培养60 d后恢复至对照水平.培养60 d后,低质量分数处理显著提高了真菌葡萄穗霉属、镰刀菌属的相对丰度,显著降低了篮状菌属的相对丰度;高质量分数处理显著提高了真菌镰刀菌属和真菌葡萄穗霉属的相对丰度,显著降低了细菌鞘氨醇单胞菌属、细菌Haliangium和真菌篮状菌属的相对丰度.吡喃酮对黑土其他优势菌门、菌属均无显著影响.正常施用吡喃酮对黑土微生物群落结构影响较小,具有较高的安全性.

Mutualistic interactions with arbuscular mycorrhizal fungi (AMF) greatly affect the outcome of plant-plant competition, especially for invasive plants competing against native plants. We examined the effects of AMF on the competition between invasive Asteraceae plants and the phylogenetically related native plants. We compared the performance of seven invasive Asteraceae plants from different genera with that of their phylogenetically related native counterparts in response to AMF in monocultures and mixed cultures. We investigated how interactions with AMF impact the competition between Asteraceae relatives. Total biomass increased with AMF colonization in both invasive and native plants. Arbuscular mycorrhizal fungi improved the competitiveness of invasive plants, but decreased that of native plants. Competition increased the shoot nitrogen, phosphorus and root myristic acid concentrations and relative expression of fatty acid transporter genes (RiFAT1 and RiFAT2) in AMF-colonized invasive plants, but decreased those in AMF-colonized native plants. Structural equation models indicated that the presence of AMF increased the uptake of phosphorus, but not nitrogen, by invasive plants, which probably provided more myristic acids to symbiotic AMF in return. These results suggest that invasive Asteraceae plants have greater mutualistic interactions with AMF than their phylogenetically related native counterparts, potentially contributing to invasion success.

The development of new herbicides based on allelochemicals is a potential strategy of weed control in arable field. Pyrone, a novel derivative of tricin, has significant inhibitory effects on weeds. Its safety for crops, especially for millet that are sensitive to commercial herbicides, is still poorly understood. In this study, germination test and pot experiments were conducted to evaluate the safety of pyrone on 20 millet varieties, compared with 2,4-D. The results showed that, except that Jinfen109 was sensitive to high concentration 2,4-D, both pyrone and 2,4-D had no effect on the germination rates of other varieties. Results of the pot experiment showed that pyrone treatment significantly increased the chlorophyll content of millet by 9.0%-67.9%, which was the greatest for Jigu 42. Pyrone treatment did not affect maximal photochemical efficiency, potential photochemical activity, actual photochemical efficiency, and non-photochemical quenching coefficient. On the contrary, 2,4-D significantly inhibited the fluorescence parameters of millet varieties. Pyrone treatment increased the activities of superoxide dismutase, peroxidase and catalase in leaves of Dunza16, Jigu 39, Jigu 41 and Jingu 28, with the magnitude of enhancement being higher than 2,4-D. The results indicated that the allelochemical derivative pyrone is highly safe to the growth of millet seedlings and has the potential to be a new herbicide to millet field.

The incidence of herbicide-resistant blackgrass is escalating in wheat fields; the development of alternatives to traditional herbicides is crucial. Allelopathic wheat can suppress blackgrass. Herein, we investigated the influence of allelopathic wheat on herbicide-resistant blackgrass. Mesosulfuron-methyl-resistant and -susceptible blackgrass were used. We examined i) root interactions between allelopathic wheat and both blackgrass biotypes, ii) allelochemical 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) production by allelopathic wheat in a root segregation experiment, and iii) responses of allelopathic wheat to root exudates. Signal chemicals in the root exudates of both blackgrass biotypes were characterised. Allelopathic wheat inhibited the growth of roots more than shoots for resistant and susceptible blackgrass. Allelopathic wheat inhibited roots of resistant blackgrass more than those of susceptible blackgrass. Allelopathic wheat significantly shaped blackgrass root behaviour. Resistant blackgrass caused a lower relative increase in DIMBOA production by allelopathic wheat. Root segregation with 30 μm nylon led to greater growth inhibition of blackgrass and a relative increase in allelochemical DIMBOA. Root exudates from blackgrass induced DIMBOA production, but more so for susceptible blackgrass. The concentration of (−)-loliolide, a potential signal chemical, was much lower in the root exudates from resistant than susceptible blackgrass. Allelopathic wheat can interfere with the growth of mesosulfuron-methyl-resistant blackgrass through allelochemical-mediated root interactions. Such allelopathic interference can provide insight into weed management.

淡水湖泊湿地生态系统中,微生物在生物地球化学循环和能量流动方面具有重要作用,是湿地行使其生态功能的重要参与者.以我国五大淡水湖泊湿地为研究对象,基于16S rRNA基因测序数据的分析,利用距离衰减关系模型、冗余分析、Mantel检验、方差分解分析和共发生网络分析探究了土壤细菌和古菌群落构建在不同湖泊湿地之间的差异及其共现性特征.结果 发现:在地理气候因子(样点经纬度、海拔和年均降水)与土壤理化因子(pH,TOC,NH4+-N和NO3--N)的共同驱动下,五大淡水湖泊湿地细菌和古菌群落存在显著的生物地理分布特征;各湿地共有的优势类群和具有共发生网络模块化结构的微生物类群,是参与湿地生态系统中产甲烷、甲烷氧化、硫酸盐还原、硝化等一系列核心生物地球化学过程并相互依存或竞争的类群.虽然五大淡水湖泊在微生物群落组成上存在一定的生物地理学差异,但微生物群落在湿地生态系统中所发挥的功能方面联系紧密,更具整体性.

Soils play a vital role in the global carbon (C) cycle, yet little is known about the calcium (Ca)-mediated stabilization of soil organic carbon (SOC) in calcareous soils. With wet sieving, density fractionation and an incubation experiment from field soils, we investigated the effects of long-term fertilization on the Ca-mediated stabilization of aggregate-associated organic C and on the SOC stock at a soil depth of 0–20 cm in a reclaimed Cambisol on the Loess Plateau of China. Compared to the initial soil, after ten years the SOC stock increased by 50%, 76%, 94% and 110% in soils amended with no fertilizer (control), 100% chemical fertilizer, 50% chemical fertilizer plus 50% chicken manure compost and 100% chicken manure compost, respectively. The specific C mineralization rate (SCMR, rate per unit SOC) decreased as silt and clay > macroaggregate > microaggregate, indicating that SOC in microaggregates was more stable than in macroaggregates and the silt and clay fraction. The exchangeable Ca in the bulk soil (P < 0.001) and soil aggregates (P < 0.001) were positively correlated with the SOC, whereas the Ca carbonate (CaCO3) was negatively correlated with the SCMR (P < 0.001). The application of compost not only increased the exogenous C inputs but also promoted the transformation of CaCO3 to exchangeable Ca compared with the sole chemical fertilization. Furthermore, organic fertilization significantly increased the organic C in the heavy fraction (> 2.0 g cm−3) compared with the sole chemical fertilization, which was positively correlated with the mass proportion of macroaggregates (P < 0.001). These results indicate that organic fertilization can enhance the availability of Ca for C binding possibly by forming organo-Ca complexes, which in turn improve soil aggregation, and thus contribute to a long-term SOC sequestration in reclaimed soils of the Loess Plateau of China.

Freeze-thaw cycles strongly affect the transformation of soil phosphorus (P) and shape the composition of P pools. This study aimed to investigate the effects of successive freeze-thaw cycles on the transformation of soil labile P and enzymatically hydrolysable organic P (Po) fractions. Accordingly, five physico-chemically distinct soils were subjected to two, five, and ten freeze-thaw cycles, with each cycle including incubation at -10 degrees C (freeze) for 12 h and 5 degrees C (thaw) for 12 h. Control soils were maintained at 5 degrees C, and the bicarbonate-extractable P and hydrolysable P-o fractions were analysed at the end of the incubation period (10 d). Freeze-thaw cycles increased the levels of bicarbonate-extractable inorganic P, bicarbonate-extractable P-o, labile monoester P, and phytate-like P, but had no effect on the diester P and unknown P-o contents. The interaction between soil type and freeze-thaw cycles significantly affected the NaHCO3-extractable P-i, and phytate-like P fractions, but did not affect the bicarbonate-extractable P-o, and labile monoester P fractions. The extent of increase in NaHCO3-extractable P-i largely depended on the amount of organic matter in the soil. In most cases, bicarbonate-extractable P and hydrolysable P-o fractions reached their maximum levels after two freeze-thaw cycles and declined or remained constant thereafter. Our results suggest that freeze-thaw cycles exacerbated the transformation of soil labile P fractions, including enzymatically hydrolysable P-o species, especially in the earlier stages.

Soil drying-rewetting(DRW) events affect nutrient transformation and microbial community composition; however, little is known about the influence of drying intensity during the DRW events. Therefore, we analyzed soil nutrient composition and microbial communities with exposure to various drying intensities during an experimental drying-rewetting event, using a silt loam from a grassland of northern China, where the semi-arid climate exposes soils to a wide range of moisture conditions, and grasslands account for over 40% of the nation’s land area. We also conducted a sterilization experiment to examine the contribution of soil microbes to nutrient pulses. Soil drying-rewetting decreased carbon(C) mineralization by 9%–27%. Both monosaccharide and mineral nitrogen(N) contents increased with higher drying intensities(drying to ≤ 10% gravimetric water content), with the increases being 204% and 110% with the highest drying intensity(drying to 2% gravimetric water content), respectively, whereas labile phosphorus(P)only increased(by 105%) with the highest drying intensity. Moreover, levels of microbial biomass C and N and dissolved organic N decreased with increasing drying intensity and were correlated with increases in dissolved organic C and mineral N, respectively,whereas the increases in labile P were not consistent with reductions in microbial biomass P. The sterilization experiment results indicated that microbes were primarily responsible for the C and N pulses, whereas non-microbial factors were the main contributors to the labile P pulses. Phospholipid fatty acid analysis indicated that soil microbes were highly resistant to drying-rewetting events and that drought-resistant groups were probably responsible for nutrient transformation. Therefore, the present study demonstrated that moderate soil drying during drying-rewetting events could improve the mineralization of N, but not P, and that different mechanisms were responsible for the C, N, and P pulses observed during drying-rewetting events.

Polyamines are important bioactive molecules involved in regulating H2O2 homeostasis, which is recognized as a major stimulus of oxidative stress under aluminum (Al) exposure. In this study, we investigated the involvement of spermidine oxidation in Al-induced oxidative stress, and its modulation by exogenous putrescine (Put) in two wheat genotypes differing in Al tolerance. Aluminum caused more severe oxidative damage at the root apexes in the Al-sensitive genotype Yangmai-5 than in the tolerant Xi Aimai-1, but these effects were significantly reversed by exogenous Put and polyamine oxidase (PAO) inhibitors. Aluminum caused a more significant increase in cell wall-bound PAO (CW-PAO) activity in Yangmai-5 than in Xi Aimai-1. Inhibiting of CW-PAO reduced H2O2 accumulation, restored Spd decline in both genotypes, indicating its potential role in Al-induced H2O2 production through catalyzing Spd oxidation. Additionally, Al significantly increased the activity of plasma membrane-NADPH oxidase, another H2O2 generator, in wheat roots. Put application significantly inhibited the activity of CW-PAO and plasma membrane-NADPH oxidase, and reduced H2O2 accumulation in Al-stressed wheat roots. Antioxidant enzymes were significantly stimulated by Al, but not Put. Overall, Put may protect wheat roots against Al-induced oxidative stress through regulating H2O2 production by inhibiting CW-PAO and plasma membrane-NADPH oxidase.

To identify more carbon (C)-friendly agricultural technology, we studied the coupling impact of film mulching during summer fallow and sowing method on carbon footprint (CF) of dryland winter wheat (Triticum aestivum L.) on the Loess Plateau. From 2011 to 2014, a two-factor split block design was conducted with the following treatments: water-permeable film mulching in the summer fallow season (FM) or no mulching in the summer fallow season (FMO) with either conventional drill sowing (DS) or drill sowing beside a common film (DSF). The greenhouse gases (GHG) emissions associated with agricultural inputs were 7013.3, 5908.3, 5298.5, and 4193.5 kg CO2-eq.ha(-1).yr(-1) for FM x DSF, FMO x DSF, FM x DS, and FMO x DS treatments, respectively, which contributed > 80% of total GHG emissions during the winter wheat production. Fertilizer, especially P205 fertilizer, was the largest contributor to GHG emissions from agricultural inputs. The CF of dryland winter wheat was 1.14 to 3.60 kg CO2-eq kg(-1), which was the lowest under the FM x DS treatment while the largest under the FM x DSF treatment. Film mulching during summer fallow with drill sowing (FM x DS) could be a C-friendly technology for winter wheat production on the Loess Plateau.