Variations in nitrogen isotopic values among various particle-sized fractions in modern soil in northwestern China

Ratios of stable nitrogen isotopes in organic matter derived from plants and preserved in soil are potential tracers for nitrogen cycles in natural ecosystems and valuable for evaluation of climate change. However, the rela-tionship between nitrogen isotopic compositions in surface soil and in plant litter during the decomposition process from plant litter to soil organic matter is not well understood. By using nitrogen isotopic analysis of soil parti-cle-sized fractions, nitrogen isotope discrimination between plant litter and surface soil organic matter in various modern ecosystems in northwestern China was conducted. The results of our study indicate that: (1) in general, the nitrogen isotopic compositions of particle-sized fractions from surface soil are different, and δ15N values increase from plant litter to fine soil organic matter; (2) the δ15N values in the soil particle-sized fractions become larger with increasing relative humidity and temperature, and the largest variation in the δ15N values is from -5.9‰ to -0.3‰; and (3) under a controlled climate, significant nitrogen isotope differences in δ15N values (Δδ15Nplant-soil) between plant litter and bulk soil organic matter were observed, with the values of 1.52 to 4.75 at various sites. Our results suggested that comparisons of Δδ15N values between bulk soil and the particle-sized fractions of soil could reveal the effect of humidity on transferring process of nitrogen from plant to soil in arid and semi-arid ecosystems.

Subsoil tillage enhances wheat productivity,soil organic carbon and available nutrient status in dryland fields

Tillage practices during the fallow period benefit water storage and yield in dryland wheat crops.However,there is currently no clarity on the responses of soil organic carbon(SOC),total nitrogen(TN),and available nutrients to tillage practices within the growing season.This study evaluated the effects of three tillage practices(NT,no tillage;SS,subsoil tillage;DT,deep tillage)over five years on soil physicochemical properties.Soil samples at harvest stage from the fifth year were analyzed to determine the soil aggregate and aggregate-associated C and N fractions.The results indicated that SS and DT improved grain yield,straw biomass and straw carbon return of wheat compared with NT.In contrast to DT and NT,SS favored SOC and TN concentrations and stocks by increasing the soil organic carbon sequestration rate(SOCSR)and soil nitrogen sequestration rate(TNSR)in the 0-40 cm layer.Higher SOC levels under SS and NT were associated with greater aggregate-associated C fractions,while TN was positively associated with soluble organic nitrogen(SON).Compared with DT,the NT and SS treatments improved soil available nutrients in the 0-20 cm layer.These findings suggest that SS is an excellent practice for increasing soil carbon,nitrogen and nutrient availability in dryland wheat fields in North China.

Effect of six years of nitrogen additions on soil chemistry in a subtropical Pleioblastus amarus forest, Southwest China

Soil chemistry influences plant health and carbon storage in forest ecosystems. Increasing nitrogen(N) deposition has potential effect on soil chemistry. We studied N deposition effects on soil chemistry in subtropical Pleioblastus amarus bamboo forest ecosystems. An experiment with four N treatment levels(0, 50, 150,and300 kg N ha-1a-1,applied monthly, expressed as CK,LN,MN, HN,respectively) in three replicates. After6 years of N additions, soil base cations, acid-forming cations, exchangeable acidity(EA), organic carbon fractions and nitrogen components were measured in all four seasons. The mean soil pH values in CK,LN,MN and HN were 4.71, 4.62, 4.71, and 4.40, respectively, with a significant difference between CK and HN. Nitrogen additions significantly increased soil exchangeable Al3+,EA, and Al/Ca,and exchangeable Al3+ in HN increased by 70%compared to CK. Soil base cations(Ca2+, Mg2+, K+, and Na+) did not respond to N additions. Nitrogen treatments significantly increased soil NO3--N but had little effect on soil total nitrogen, particulate organic nitrogen, or NH4~+-N. Nitrogen additions did not affect soil total organic carbon, extractable dissolved organic carbon,incorporated organic carbon, or particulate organic carbon.This study suggests that increasing N deposition could increase soil NO3--N, reduce soil pH, and increase mobilization of Al3+. These changes induced by N deposition can impede root grow and function, further may influence soil carbon storage and nutrient cycles in the future.

Effects of continuous nitrogen addition on microbial properties and soil organic matter in a Larix gmelinii plantation in China

Continuous increases in anthropogenic nitrogen（N） deposition are likely to change soil microbial properties, and ultimately to affect soil carbon（C） storage.Temperate plantation forests play key roles in C sequestration, yet mechanisms underlying the influences of N deposition on soil organic matter accumulation are poorly understood. This study assessed the effect of N addition on soil microbial properties and soil organic matter distribution in a larch（Larix gmelinii） plantation. In a 9-year experiment in the plantation, N was applied at100 kg N ha-1 a-1 to study the effects on soil C and N mineralization, microbial biomass, enzyme activity, and C and N in soil organic matter density fractions, and organic matter chemistry. The results showed that N addition had no influence on C and N contents in whole soil. However,soil C in different fractions responded to N addition differently. Soil C in light fractions did not change with N addition, while soil C in heavy fractions increased significantly. These results suggested that more soil C in heavy fractions was stabilized in the N-treated soils. However,microbial biomass C and N and phenol oxidase activity decreased in the N-treated soils and thus soil C increased in heavy fractions. Although N addition reduced microbial biomass and phenol oxidase activity, it had little effect on soil C mineralization, hydrolytic enzyme activities, d13 C value in soil and C–H stretch, carboxylates and amides, and C–O stretch in soil organic matter chemistry measured by Fourier transform infrared spectra. We conclude that N addition（1） altered microbial biomass and activity without affecting soil C in light fractions and（2） resulted in an increase in soil C in heavy fractions and that this increase was controlled by phenol oxidase activity and soil N availability.

Assessment of Soil C and N Stocks and Fractions across 11 European Soils under Varying Land Uses

In this study, we measured the stocks and pool sizes of soil organic carbon (SOC) and total soil nitrogen (TN), and their natural 13C and 15N abundance across a wide range of temperate European ecosystems. The objectives were to examine any distinct isotope patterns with land use or climate, and how C and N in these different ecosystems are distributed among soil organic matter (SOM) fractions to better predict soil C and N dynamics and longer term persistence. Soils were sampled to 30 cm depth at 11 sites of the Nitro Europe (NEU) network and included four forests, three grasslands and four croplands. Surface soil samples were fractionated using a combined size-density fractionation protocol separating light (LF) from heavy particulate organic matter (hPOM) by density and silt-from-clay-associated SOM by size. Down-profile natural abundance 15N patterns pointed towards a closed N cycle in the forest sites, while 13C patterns suggested differences in plant water use efficiency across the C3 grassland sites. The forests and grassland sites stored the majority of surface SOC and TN in the LF and hPOM pools. Sustained sequestration of C and N in these rather labile pools will rely on management practices that minimize soil disturbance and increase C input. We also found that the mineral fraction (silt and clay) in the cropland soils stored less C and N per unit of fraction mass compared to the forests and grasslands, which points towards a lower mineral-OM stabilization efficiency of cropland soils. Finally, our study revealed total POM (LF plus hPOM) as a strong predictor of SOC and TN differences, particularly among the non-cropped sites. This study shows that these sites, independent of soil type and climate, store a large fraction of C and N in POM pools that are particularly vulnerable to soil disturbance such as caused by land use change.

Soil Organic Fractions in Cultivated and Uncultivated Soils of Costal Area in Bangladesh

Assessment of soil organic matter fractions can be instrumental in understanding the causes of limited nitrogen supply, and thus soil fertility restoration. A study was conducted in cultivated and uncultivated saline soil, in order to assay soil organic carbon (SOC), its particle-size fractions and their influence on cultivation and soil fertility at Sundarbans costal area in Bangladesh. Soil samples were taken from the 0 - 15 and 15 - 30 cm depths from four cultivated fields and from four nearby sites in a native mangrove forest as references. Soil samples were physically fractionated into sand (2000-50 μm), silt (50-2 μm) and clay (<2 μm). Total SOC and N were analyzed in bulk samples and each size fraction, and the Carbon Management Index (CMI), a widely used indicator of soil quality, was calculated for each field. The CMI in cultivated soils was far below the 100% in reference soils, reaching 38.16%, 25.70%, 32.21% and 34.43% in Field 1, Field 2, Field 3 and Field 4 respectively. SOC and N concentrations decreased in particle size separates in the order clay > silt > sand. The SOC pool and N in the clay-sized fraction were correlated to soil fertility indicators. More N was stored in the silt + clay size fractions, a generally more stable pool, than in the more labile sand-sized pool. The SOC pool in sand size fractions was far below in cultivated soils than in a reference uncultivated soil. Thus, the sand-sized pool emerged as the most likely cause of limited N supply in cultivated soils.

Does Soil Disturbance Affect Soil Phosphorus Fractions?

Increased turnover of organic matter as a result of soil disturbance (e.g. by soil tillage) is described in principle, but the direct influence of soil disturbance on soil P turnover especially for organic farming systems has not been sufficiently proven. The objective of the study was to evaluate the short term effect of soil disturbance on different soil P fractions in a soil shaking experiment. Four soils were incubated for 10 days in the dark with three different disturbance treatments: 1) no disturbance, 2) overhead shaking for 2 h at the beginning of the experiment and 3) continuous overhead shaking at 5 r. p. m. The four investigated soils were: 1) a silty loam soil with long term bio-compost application and 2) the corresponding soil without bio-compost application, 3) a long-term organically managed clay loam soil and 4) a clay loam soil with long time application of pig manure, all not and from Baden-Württemberg, Germany. We determined NaHCO3-, NaOH- and H2SO4-extractable inorganic and organic P fractions (Pi and Po, resp.) in a sequential extraction. Furthermore, the potentially plant available P as Calcium-acetate-lactate-extractable P (CAL-P) and P extractable by electro-ultra-filtration (EUF-P), and aqua regia extractable total P (PT) were determined. Furthermore, we determined microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), and acid phosphatase activity in soil. The organically managed soil had the highest PT contents (1300 mg·kg-1). The soil with pig manure application had the smallest potentially labile P fractions (NaHCO3-Pi and -Po and NaOH-Pi). The ecologically managed soil had the biggest organic P fractions (114 mg·kg-1 NaHCO3-Po and 463 mg·kg-1 NaOH-Po), but, this soil was the lowest in CAL-P (5 mg·kg-1). Short term soil disturbance had effects on labile organic P fractions of two of the four analyzed soils, but inorganic P was rather unaffected. In the compost amended COMP(+) soil, there was an incorporation of P from the less available NaOH-P fractions into the more available NaHCO3-Po fraction. However, if taking all investigated soils and treatments into account, the effects of soil disturbance were limited and not consistent.

几种改良剂对酸性紫色土氮组分及酶活性的影响

活性氮组分对农业生态系统的生产力、稳定性及其环境效益至关重要.土壤中的胞外酶(纤维素酶、乙酰氨基肽酶和过氧化物酶)对外源氮的输入反应强烈且迅速,通过测定土壤胞外酶活性,可以了解土壤氮素变化.为探究几种改良剂施用对酸化花椒园土壤活性氮组分特征及相关胞外酶活性的影响,厘清改良剂与土壤活性氮组分及酶活性之间的关系,为紫色土酸化治理及养分管理提供科学依据.采用田间试验,设置不施肥(CK)、单施化肥(F)、石灰+化肥(SF)、有机肥+化肥(OM)、生物炭+化肥(BF)及酒糟灰渣+化肥(JZ)6个处理,研究不同处理土壤pH值和全氮、活性氮组分及土壤纤维素酶(S-CL)、过氧化物酶(S-POD)和乙酰氨基肽酶(S-NAG)活性,阐明其相互关系.结果表明:(1) JZ和SF两个处理均显著提高土壤pH值(p<0.05),分别比对照提高了3.39和2.25;与对照处理相比,OM处理土壤全氮质量分数提高了61.45%,显著增加了土壤氮库存量(p<0.05);(2) JZ和OM处理土壤PON质量分数较对照处理分别提高了102.20%和101.45%;F和OM处理土壤MBN较对照处理分别提高了44.28%和19.08%,土壤DON分别提高了72.35%和57.61%;截至2022年6月,JZ处理土壤矿质氮质量分数提高最为显著(p<0.05),硝态氮和铵态氮质量分数较对照处理分别提高了1.63倍和5.43倍;(3)施用了改良剂的4个处理均显著提高了土壤胞外酶活性(p<0.05),其中JZ处理S-CL和S-POD活性最高,较对照处理分别提高了134.72%和96.27%,F和OM处理S-NAG活性提高较显著,较对照处理分别提高了190.63%和75.59%.综上所述,酸性紫色土壤施用石灰、酒糟灰渣及有机肥中和土壤酸度效果最显著,同时提高土壤胞外酶活性,有利于土壤氮库积累和活性氮组分转化.

长期不同施肥模式对大麦–双季稻田根际土壤有机氮组分的影响

根际土壤有机氮组分在土壤养分和作物氮素营养中具有重要作用。本研究依托长期(37年)定位施肥试验田,设置4个施肥处理:不施肥对照(CK)、单独施用化肥(CF)、秸秆还田+化肥(RF)和30%有机肥+70%化肥(OM),于晚稻成熟期测定大麦–双季稻田根际土壤基础理化性质、微生物生物量氮和有机氮组分(氨基酸态氮、氨基糖态氮、酸解氨态氮、酸解未知态氮、非酸解性氮)含量。研究表明:相对CK处理,RF和OM处理显著增加了稻田根际土壤有机碳、全氮、铵态氮和硝态氮的含量。RF和OM处理土壤微生物生物量氮含量分别比CK处理增加了19.8%和30.7%。酸解性氮作为根际土壤全氮的主体部分,占全氮的59.61%~72.06%;各处理根际土壤酸解性氮含量大小顺序表现为OM>RF>CF>CK。各施肥处理中,酸解有机氮中的氨基糖态氮、氨基酸态氮和酸解未知态氮含量均以OM处理最大,分别比CK处理增加139.3%、47.9%和110.0%;酸解氨态氮以RF处理最大,比CK处理增加69.9%。土壤有机碳、全氮、铵态氮、硝态氮与土壤氨基酸态氮、氨基糖态氮、酸解未知态氮以及微生物生物量氮均呈极显著(P<0.01)正相关。因此,秸秆、有机肥配施化肥均能有效提高大麦–双季稻田根际土壤的供氮能力,是改善稻田土壤肥力的有效手段。

不同种植模式对坡耕地红壤有机碳氮组分的影响

探究不同种植模式下红壤有机碳、氮组分的变化规律,为改善红壤质量具有重要意义。通过小区试验,以玉米//萝卜间作(MS)、玉米//大豆间作(MR)、单种玉米(MM)、单种大豆(RR)和单种萝卜(SS)为研究对象进行探讨。结果显示,间作能够促进土壤有机碳(SOC)、全氮(TN)和微生物量碳(MBC)、氮(MBN)及可溶性有机碳(DOC)、氮(DON)含量的增加,其中MBC和MBN含量的提升效果较显著。MR处理的SOC、MBC和DOC含量较MM和RR处理分别提高18.40%~31.60%和5.40%~52.10%,TN、MBN和DON含量分别提高13.40%~84.30%和19.20%~64.40%;MS处理SOC、MBC和DOC含量较MM和SS处理分别提高5.10%~9.60%和12.00%~53.80%,TN、MBN和DON含量分别提高2.70%~31.00%和0.80%~23.42%。其中,MBC和DON含量占SOC和TN的比重较大,分别为1.00%~1.71%和5.10%~14.18%。相关性分析表明,各碳、氮组分含量与土壤有机碳、氮呈显著正相关,其中DOC与SOC、MBN与TN之间的相关系数均高于0.70,说明DOC与MBN可较好地反映土壤SOC和TN的动态变化。综上所述,间作种植是有利于研究区内坡耕地水土保持和土壤肥力的关键技术措施之一。

尕海湿地区沼泽草甸生长季土壤碳氮组分对增温施氮的响应

[目的]为探究高寒湿地土壤碳氮组分对气候变暖和氮沉降的响应特征。[方法]以尕海湿地沼泽草甸为研究对象,采用开顶箱增温(OTC)和外源氮素(NH_(4)NO_(3))添加模拟未来气候变暖及氮沉降试验,分别设置对照(CK)、增温(W)、施氮(N)和增温施氮(WN)4种处理。在试验进行1.5年后对土壤碳氮组分含量进行测定。[结果](1)开顶箱增温装置提高0-20 cm土层平均温度1.126℃,显著降低0-10 cm土层土壤含水量(SMC)、pH、全氮(TN)、微生物量氮(MBN)、铵态氮(NH_(4)^(+)-N)、有机碳(SOC)和可溶性有机碳(DOC)含量,提高硝态氮(NO_(3)^(-)-N)含量。(2)施氮显著降低NH_(4)^(+)-N、SOC和10-20 cm土层微生物生物量碳(MBC)及DOC含量,增加土壤TN、MBN和NO_(3)^(-)-N含量。(3)增温施氮显著增加土壤SMC、TN、NO_(3)^(-)-N和MBC含量,降低MBN、NH_(4)^(+)-N和DOC含量。(4)相关分析显示,土壤水分与各理化因子均存在正相关性,土壤碳氮组分间均呈正相关性。[结论]模拟增温施氮缓解尕海湿地植物生长的温度和氮的限制,促进TN的积累,对土壤微生物量碳氮影响较大,导致土壤微生物量碳氮及分布特征发生转换。

长期种植紫花苜蓿对复垦土壤碳氮磷养分转化的影响

为研究长期种植紫花苜蓿对复垦土壤质量改善和生物改土的效果,以种植作物地和撂荒地为对照,分析建筑复垦地多年种植紫花苜蓿土壤有机碳(SOC)、全氮(TN)和全磷(TP)含量的化学计量特征变化。结果表明,长期种植紫花苜蓿显著降低土壤电导率(EC),对表层土壤保水效果较好,显著提升土壤有效养分含量(P<0.05);与作物地和撂荒地相比,苜蓿地土壤SOC和TN含量显著提高(P<0.05),但0~20 cm土壤TP含量显著低于作物地。3种土地利用类型0~20 cm土壤化学计量差异显著,苜蓿地土壤C/N显著低于作物地和撂荒地(P<0.05),而土壤C/P和N/P则表现为苜蓿地显著高于作物地和撂荒地(P<0.05)。种植紫花苜蓿有助于提升土壤有机碳氮活性组分,0~20 cm土层苜蓿地颗粒有机碳(POC)、易氧化有机碳(ROC)和微生物生物量碳(MBC)含量较作物地分别提高88.38%、17.24%和39.16%(P<0.05),苜蓿地颗粒有机氮(PON)、微生物生物量氮(MBN)和酸解有机氮组分含量最高,PON和MBN比作物地显著提高135.29%和17.39%,较撂荒地显著提高207.69%和28.41%。因此,长期种植紫花苜蓿对土壤质量和有机碳氮活性组分均有改善作用,研究结果可为退化土壤修复和复垦土壤生物改土效果提供参考。

猪粪配施菌剂对侵蚀红壤碳氮组分及竹柏生长的影响

【目的】探究猪粪配施微生物菌剂对侵蚀红壤碳氮组分及竹柏生长的影响,为侵蚀劣地改良及获得适合竹柏生长的施肥方案提供依据。【方法】以盆栽竹柏为供试材料,测定土壤碳氮组分含量以及竹柏的生长、生理指标,探讨对照以及化肥、猪粪、猪粪+低量菌剂、猪粪+中量菌剂、猪粪+高量菌剂处理对侵蚀红壤碳氮组分含量及竹柏生长的影响。【结果】(1)猪粪配施菌剂可显著提高土壤总有机碳(soil organic carbon,SOC)和易氧化有机碳(easily oxidized organic carbon,EOC)含量,对可溶性有机碳(dissolved organic carbon,DOC)和颗粒有机碳(particulate organic carbon,POC)含量没有显著的提升作用;高剂量菌剂对土壤碳组分含量的提升效果最佳。(2)配施菌剂与单施猪粪处理相比,硝态氮(NO^(-)_(3)-N)含量提高了43.75%~68.75%,可溶性有机氮(dissolved organic nitrogen,DON)含量提高了13.59%~24.46%,氨基酸态氮(amino acid nitrogen,AAN)含量提高了11.08%,微生物量氮(microbial biomass nitrogen,MBN)含量提高了6.99%~36.65%,对铵态氮(NH^(+)_(4)-N)含量无明显的提升作用。(3)施用菌剂可促进竹柏的生长发育,高量菌剂对竹柏株高、地径增长量的提升效果最佳;中量菌剂对竹柏可溶性糖和可溶性蛋白含量的提升效果最佳。【结论】猪粪配施适量微生物菌剂可有效改良侵蚀红壤,提高侵蚀红壤的碳氮组分含量,促进竹柏的生长发育。

不同有机肥替代20%化肥氮的稻田土壤有机氮组分积累特征

为了探明不同有机肥等比例替代化肥下土壤有机氮各组分积累特征,依托长期施肥定位试验,以不施氮肥(CK)和施用化肥氮(NPK)为对照,检测分析了猪粪(PM)、商品有机肥(OM)和早稻紫云英+晚稻水稻秸秆(RMS)替代20%化肥氮处理下土壤有机氮组分含量及其占全氮的比例。结果表明:全氮和有机氮组分含量在NPK和CK处理之间差异不明显;与NPK处理相比,有机肥替代化肥各处理的土壤全氮含量提高了5.2%~8.5%,尤其是PM处理;且3种有机肥替代化肥的酸解氨基酸氮、酸解铵态氮和酸解氨基糖氮的含量分别显著提高了11.0%~18.8%、10.8%~18.5%和16.7%~31.1%,其占全氮比例分别提高了4.4%~11.1%、2.1%~12.6%和7.5%~24.5%,增加了土壤速效氮含量,尤其是RMS处理;其原因可能是有机肥替代化肥不同程度地增加了微生物生物量碳氮,增强了氮转化相关酶活性,促进了难分解有机氮组分向易分解有机氮组分的转化。综上,有机肥等比例替代化肥均能有效提高土壤氮素积累和供应,其中猪粪更有利于氮素积累,秸秆更有利于增强氮素供应潜力。

有机氮部分替代化学氮肥对土壤有机氮组分的影响

为综合评价有机肥替代化肥应用效果,指导南方稻田科学施肥,研究了不同比例有机氮部分替代化学氮肥对土壤有机氮组分的影响。试验地位于湖南省长沙县高桥镇湖南省农业科学院科研试验基地,共设置5个处理:单施化肥(NPK);15%有机肥替代(15M);30%有机肥替代(30M);45%有机肥替代(45M);60%有机肥替代(60M)。2021年晚稻收获后,测定0~20 cm土层土壤全氮、可溶性有机氮、微生物生物量氮、有机氮组分含量。结果表明:相比单施化肥,有机氮部分替代化学氮肥显著提高了稻田耕层土壤的全氮含量,在等量氮磷养分投入条件下,15M、30M、45M和60M处理相比单施化肥处理土壤全氮分别提高了2.73%、10.93%、11.47%和20.77%;有机氮部分替代化学氮肥提高了土壤可溶性有机氮和微生物生物量氮含量,其中可溶性有机氮提高了24.53%~72.89%,微生物生物量氮提高了0.92%~44.42%;有机氮部分替代化学氮肥增加了土壤酸解氨基酸氮、酸解铵态氮和酸解氨基糖氮含量,降低了土壤非酸解氮含量;土壤全氮与可溶性有机氮、微生物生物量氮呈极显著正相关,可溶性有机氮、微生物生物量氮均与土壤酸解铵态氮、酸解氨基酸氮、酸解氨基糖氮存在极显著正相关关系。相比单施化肥,有机氮部分替代化学氮肥提高了土壤全氮、活性氮(可溶性有机氮和微生物生物量氮)以及酸解氮中酸解氨基酸氮、酸解铵态氮和酸解氨基糖氮的含量,有利于提高土壤供氮能力。土壤酸解铵态氮、酸解氨基酸氮和酸解氨基糖氮是影响土壤活性氮的关键因子,本研究中以60M处理替代化学氮肥培肥效果最优。

亚热带米槠天然林土壤有机氮组分对模拟氮沉降的响应

随着人类活动向大气排放越来越多的氮化合物,生态系统中的氮含量逐渐呈现饱和状态,亚热带地区已成为全球氮沉降最严重的区域之一。土壤有机氮组分能直观反映土壤氮素有效性对氮沉降的响应。以福建三明格氏栲自然保护区内的米槠天然林为研究对象,探讨不同施氮水平[0,40,80 kg N/(hm^(2)·a)]对土壤有机氮组分的影响。结果表明:(1)高氮处理下土壤有机氮(SON)含量(1.23 g/kg)显著高于对照处理(0.89 g/kg),高氮处理的土壤活性氮组分(LPⅠ-N+LPⅡ-N)含量(0.28 g/kg)显著高于低氮(0.24 g/kg)和对照处理(0.22 g/kg),而土壤惰性氮组分(RP-N)含量在高氮(0.94 g/kg)和低氮(0.82 g/kg)处理中都显著高于对照处理(0.68 g/kg)。(2)与对照和低氮处理相比,高氮处理显著提高土壤全氮(TN)、微生物生物量氮(MBN)、铵态氮(NH_(4)^(+)-N)含量和β-N-乙酰氨基葡萄糖苷酶(NAG)活性(p<0.05),硝态氮(NO 3--N)、可溶性有机氮(DON)含量和β-葡萄糖苷酶(βG)、纤维素水解酶(CBH)活性随着施氮量的增加均呈上升趋势。(3)冗余分析(RDA)表明,土壤TN、NAG酶与有机氮及其各组分呈显著正相关,而土壤MBN、NH_(4)^(+)-N与土壤有机氮及其各组分的相关性也较强。可见该区域氮沉降提高土壤氮养分有效性和微生物活性,这有助于进一步了解全球气候变化背景下亚热带森林土壤养分转化与循环机制。

耕作方式对旱地麦田土壤团聚体及其碳氮组分分布的影响

为明确蓄水保墒耕作方式下旱地麦田土壤团聚体稳定性、有机碳及碳组分和全氮及氮组分在不同粒径团聚体组分中的分布特征,深入了解不同耕作方式下土壤碳氮固持机制,以连续3 a(2017—2020年)实施不同耕作方式(免耕、深松、深翻)后冬小麦收获期0~20 cm土壤为研究对象,采用湿筛法测算土壤团聚体的构成与稳定性(R_(0.25),>0.25 mm团聚体含量;MWD,平均重量直径;GMD,几何平均直径),并测定各粒径团聚体有机碳(SOC)和碳组分(重组有机碳,HFOC;轻组有机碳,LFOC;易氧化有机碳,EOC;可溶性有机碳,DOC;颗粒有机碳,POC)含量、全氮(TN)和氮组分(硝态氮,NO^(-)_(3)-N;铵态氮,NH^(+)_(4)-N;可溶性有机氮,SON)含量,分析了碳氮组分的相关关系。结果显示:(1)免耕和深松处理>2 mm团聚体土壤比例较深翻处理分别提高8.8%和22.1%,免耕有利于增加<0.053 mm粉黏粒比例,较深松和深翻处理分别提高46.4%和27.7%。深松处理较深翻处理的R_(0.25)、MWD、GMD分别提高了2.8%、6.3%和9.0%;(2)免耕和深松处理较深翻提高土壤各粒径团聚体SOC、LFOC、EOC、DOC和POC含量。深松处理各粒径团聚体HFOC含量均高于深翻处理,免耕处理仅<0.053 mm团聚体HFOC含量比深翻高24.7%;(3)与深翻处理相比,免耕处理有利于提高>2 mm、0.25~2 mm、0.053~0.25 mm土壤团聚体TN、NO^(-)_(3)-N和NH^(+)_(4)-N含量;深松处理有利于增加土壤各粒径团聚体TN含量以及>2 mm和0.25~2 mm团聚体NO^(-)_(3)-N含量,各粒径团聚体NH^(+)_(4)-N含量低于深翻处理。免耕和深松处理各粒径团聚体SON含量均高于深翻处理。碳氮比(C/N)在不同粒径团聚体均表现为深松>免耕>深翻;(4)免耕和深松处理的0~20 cm土壤碳储量分别比深翻高85.4%和86.3%,土壤氮储量分别比深翻高48.1%和32.5%,而秸秆碳还田量分别比深翻低30.9%和16.4%;(5)通过结构方程模型分析发现,DOC和POC通过协同EOC变化,是影响SOC变化的主导因子。SON是协同TN提升的主导因子。因此,黄土高原旱地麦田实施深松技术可改善土壤团聚体结构,实现土壤固碳保氮的协同效应。

外源氮输入对闽江河口芦苇湿地土壤磷形态赋存特征的影响

河口湿地是响应全球气候变化和人类活动最为敏感的生态系统之一,是外源氮的一个重要“汇”,其对于生源元素循环过程可产生深刻的影响。在当前闽江河口区氮负荷增强背景下,探讨外源氮输入对湿地土壤磷形态赋存及其关键转化过程具有重要意义。为此,选择闽江河口鳝鱼滩的芦苇湿地为研究对象,基于野外原位氮输入模拟试验,研究了不同氮输入水平(N_(Nt),对照处理;N_(Lt),低氮处理;N_(Mt),中氮处理;N_(Ht),高氮处理)对湿地土壤磷形态赋存特征的影响。结果表明,外源氮输入不但增加了湿地土壤的TP含量,而且改变了其土层分布特征。除N_(Mt)与N_(Nt)处理下的TP含量相当外,N_(Lt)和N_(Ht)处理下的全磷(TP)含量相比N_(Nt)处理分别增加了3.5%和4.4%。氮输入整体上增加了湿地土壤的活性磷和闭蓄态磷含量,但降低了中等活性磷含量。相比N_(Nt)处理,N_(Mt)和N_(Ht)处理下的活性磷含量分别增加了6.5%和12.6%,而N_(Lt)、N_(Mt)和N_(Ht)处理下的闭蓄态磷含量分别增加了3.3%、3.9%和7.0%。中等活性磷在N_(Mt)处理下的降幅尤为明显,其值相比N_(Nt)处理降低了6.7%。不同氮处理下湿地土壤以闭蓄态磷占比最高(51.8%—54.1%),中等活性磷次之(38.1%—41.2%),活性磷最低(7.0%—7.9%)。不同氮处理下的各形态磷占比以HCl⁃Pi、Residual⁃P、NaOH⁃Po和NaOH⁃Pi较高,Sonic⁃Po和NaHCO3⁃Pi次之,而NaHCO3⁃Po、Resin⁃P和Sonic⁃Pi较低。研究发现,氮输入主要通过改变土壤养分及酸碱状况来进一步影响土壤中各形态磷的赋存。其中,N_(Mt)和N_(Ht)处理下活性磷含量的增加主要与Resin⁃P和NaHCO3⁃Po有关,N_(Lt)、N_(Mt)和N_(Ht)处理下闭蓄态磷含量的增加主要与Residual⁃P有关,而N_(Mt)处理下中等活性磷的显著降低主要与NaOH⁃Pi和Sonic⁃Po有关。

水氮耦合对滴灌棉田土壤有机碳组分及酶活性的影响

【目的】研究灌水量和施氮量对滴灌棉田土壤有机碳、氮含量及有机碳库稳定性的影响,为实现新疆棉花高效生产和可持续发展提供理论依据。【方法】采用两因素三水平完全随机区组设计进行棉花田间滴灌施肥试验,设置的3个灌水量(W)分别为360 mm (低量)、480 mm (适量)、600 mm (高量),3个施氮(N)水平分别为0 kg/hm^(2)、300 kg/hm^(2) (适量)和450 kg/hm^(2) (高量),共9个处理组合。棉花收获后,采集0—20 cm土层土壤,测定土壤有机碳(SOC)、水溶性有机碳(WSOC)、微生物生物量碳(MBC)、易氧化有机碳(EOC)和稳定态有机碳(NOC)含量,测定土壤脲酶(URE)、β-葡萄糖苷酶(BG)、N-乙酰基-β-D葡萄糖苷酶(NAG)活性。利用田间原位填埋尼龙网袋法测定各处理土壤有机物料(秸秆)分解率(OMDR),计算土壤碳库管理指数(CPMI)。【结果】与W600N450处理相比,2015和2016年W480N300处理土壤有机碳分别提高了8.9%和10.9%,C/N分别提高了16.2%和16.3%,EOC和NOC含量分别提高了11.8%~15.4%和14.3%~20.8%,WSOC含量分别降低了35.5%和21.8%。表明合理的水氮管理有利于提高土壤有机碳和稳定态有机碳含量,降低水溶性有机碳含量,提高土壤碳库的稳定性。与W480处理相比,W360处理MBC含量显著降低了13.1%,W600处理降低了WSOC和NOC含量;W360处理EOC含量两年分别降低了2.1%和5.3%,W600处理分别降低了4.1%和7.6%(P<0.05)。与N300处理相比,N0处理MBC含量降低了41.8%,N450处理降低了NOC含量,N0处理两年EOC含量分别降低了20.2%和16.7%,N450处理分别降低了3.8%和2.4%。表明施氮量对土壤有机碳组分含量的影响大于灌水量。同时,过量的灌水和施氮会降低稳定态有机碳含量,提高微生物生物量碳含量,不利于土壤有机碳的积累。高水(600 mm)和高氮(450 kg/hm^(2))显著提高了土壤酶活性,降低了土壤碳库管理指数。W480N300处理脲酶、β-葡萄糖苷酶和N-乙酰基-β-D-葡萄糖苷酶活性较W360N0分别提高了1.0%、22.4%和32.6%。W480N300处理下土壤CPMI最高。相关性分析结果表明,CPMI与活性有机碳(MBC、EOC)含量之间存在不同程度的正相关关系,与NOC含量存在负相关关系。【结论】在新疆滴灌施肥条件下,过高的灌水量和施氮量会降低土壤有机碳和稳定态有机碳含量,降低土壤碳库活度和碳库管理指数,提高微生物生物量碳含量以及酶活性,不利于维持土壤有机碳的稳定。本试验条件下,灌水480 mm配合施氮300 kg/hm^(2)的水氮管理有利于促进滴灌棉田土壤有机碳积累,提高有机碳活性。

长期氮沉降和地上凋落物处理对半干旱区沙质草地表层土壤碳氮组分的影响

为揭示半干旱区沙质草地生态系统中表层土壤C、N组分对长期氮添加和地上凋落物处理的响应特征,以科尔沁沙地西南部国家野外科学观测研究站建立的长期(9年)氮添加和凋落物处理样地为平台,测定并分析该样地表层土壤环境因子、铵态氮、硝态氮、总有机碳、不同碳氮组分。结果表明:(1)持续9年的氮添加和地上凋落物处理对表层土壤环境因子和不同碳氮组分无交互作用;(2)氮添加处理显著降低土壤pH(p<0.01),增加土壤中硝态氮的含量(p<0.05),其增长幅度为37.57%,并显著增加溶解性有机氮(DON)和易变活性氮(LON)的含量(p<0.01,p<0.05);(3)地上凋落物去除显著降低土壤总有机碳(TOC)、易变缓性碳(IOC)、微生物生物量碳(MBC)和微生物生物量氮(MBN)含量(p<0.05);(4)经过9年氮添加和地上凋落物处理,半干旱区沙质草地表层土壤中不同碳氮组分与土壤环境因子间相关性并不密切。即长期氮添加和地上凋落物处理会改变表层土壤不同碳、氮组分的含量,但并未显著改变各碳、氮组分的比值。研究结果为揭示长期氮添加和地上凋落物处理对半干旱区沙质草地土壤C、N贮存和预测未来土壤生物地球化学元素动态研究提供参考资料。