Effects of Different Fertilization Treatments on Soil Microbial Biomass,Soil Enzyme Activities and Related Nutrients in Continuous-cropping Sugarcane Field

[Objective] This study was conducted to expound the fertility improvement effect in continuous-cropping sugarcane field and provide reference for establishment of rational sugarcane fertilization system and improvement of soil quality in continuous-cropping sugarcane field. [Method] The soil in the experimental region is latosolic red soil which was planted with sugarcane for 11 years continuously, and 8 treatments including sole application of chemical fertilizers, sole application of organ- ic fertilizer, and combined application of organic fertilizer and chemical fertilizers were designed according to different fertilization measures. The effects of different fertilization treatments on soil microbial biomass, soil enzyme activities and related fertility factors were determined. [Result} Different fertilization treatments all showed soil microbial biomass N, C and P and activities of soil acid phosphatase, catalase, sucrase and urease higher than the CK. Soil microbial biomass N increased by 5.56%-67.13%, soil microbial biomass C increased by 4.01%-20.40%, and soil mi- crobial biomass P increased by 6.39%-67.02%. The activity of acid phosphatase was improved by 12.96%-35.19%, the activity of catalase was improved by 18.24% -78.93%, the activity of sucrase was improved by 3.00%-42.00%, and the activity of urease was improved by 1.21%-23.43%. However, the soil nutrients of different fertilization treatments increased non-significantly （P〉0.05）. Soil microbial biomass N, C and P and activities of acid phosphatase, catalase and urease were in significant （P〈0.05） or very significant correlation （P〈0.01） with contents of soil rapidly available P, rapidly available K and total N. [Conclusion] The evaluation of improvement of soil fertility in continuous-cropping sugarcane field using soil microbial biomass and enzyme activities as indexes is more comprehensive and sensitive.

C:N:P stoichiometry and nutrient limitation of the soil microbial biomass in a grazed grassland site under experimental P limitation or exces

Introduction:The availability of essential nutrients,such as nitrogen(N)and phosphorus(P),can feedback on soil carbon(C)and the soil microbial biomass.Natural cycles can be supplemented by agricultural fertiliser addition,and we determined whether the stoichiometry and nutrient limitation of the microbial biomass could be affected by an unbalanced nutrient supply.Methods:Samples were taken from a long-term trial(in effect since 1968)with annual applications of 0,15 and 30 kg P ha^(−1) with constant N and potassium.Soil and microbial biomass CNP contents were measured and nutrient limitation assessed by substrate-induced respiration.Linear regression and discriminant analyses were used to identify the variables explaining nutrient limitation.Results:Soil and biomass CNP increased with increasing P fertiliser,and there was a significant,positive,correlation between microbial biomass P and biomass C,apart from at the highest level of P fertilisation when the microbial biomass was over-saturated with P.The molar ratios of C:N:P in the microbial biomass remained constant(homeostatic)despite large changes in the soil nutrient ratios.Microbial growth was generally limited by C and N,except in soil with no added P when C and P were the main limiting nutrients.C,N and P,however,did not explain all the growth limitation on the soils with no added P.Conclusions:Increased soil C and N were probably due to increased net primary production.Our results confirm that C:N:P ratios within the microbial biomass were constrained(i.e.homeostatic)under near optimum soil conditions.Soils with no added P were characterised by strong microbial P limitation and soils under high P by over-saturation of microorganisms with P.Relative changes in biomass C:P can be indicative of nutrient limitation within a site.

Seasonal changes in soil properties,microbial biomass and enzyme activities across the soil profile in two alpine ecosystems

Microbial biomass and extracellular enzyme activities control the rate of soil organic carbon decomposition,thereby affecting soil carbon pool.However,seasonal dynamics of soil microbial properties at different depths of the soil profile remain unclear.In this study,we sampled soils in the early,middle and late growing season at different soil depths(0–100 cm)in two alpine ecosystems(meadow and shrubland)on the Tibetan Plateau.We measured plant belowground biomass,soil properties,microbial biomass and extracellular enzyme activities.We found that soil properties changed significantly with sampling time and soil depth.Specifically,most of soil properties consistently decreased with increasing soil depth,but inconsistently varied with sampling time.Moreover,root biomass and microbial biomass decreased with increasing soil depth and increased with sampling time during the growing season.However,microbial extracellular enzyme activities and their vector properties all changed with depth,but did not vary significantly with time.Taken together,these results show that soil properties,microbial biomass and extracellular enzyme activities mostly decline with increasing depth of the soil profile,and soil properties and microbial biomass are generally more variable during the growing season than extracellular enzyme activities across the soil profile in these alpine ecosystems.Further studies are needed to investigate the changes in soil microbial community composition and function at different soil depths over the growing season,which can enhance our mechanistic understanding of whole-profile soil carbon dynamics of alpine ecosystems under climate change.

The impact of landslides on chemical and microbial properties of soil in a temperate secondary forest ecosystem

In forest ecosystems,landslides are one of the most common natural disturbances,altering the physical,chemical and microbial characteristics of soil and thus further altering ecosystem properties and processes.Although secondary forests comprise more than 50%of global forests,the influence of landslides on the soil properties in these forests is underappreciated.Therefore,this study investigates the influence of landslides on the chemical and microbial nature of the soil.Study of these modifications is critical,as it provides baseline evidence for subsequent forest revegetation.We selected four independent landslides and adjacent secondary forest stands as references in a temperate secondary forest in northeastern China.Soils were obtained from each stand at 0–10 cm and 10–20 cm depths to determine chemical and microbial properties.Soil total carbon(TC),total nitrogen(TN),nitrate(NO_(3)^(-)-N),available phosphorus(P),microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),microbial biomass phosphorus(MBP)and phenol oxidase,exoglucanase,β-glucosidase,N-acetyl-β-glucosaminidase,L-asparaginase and acid phosphatase activities were 29.3–70.1%lower at the 0–10 cm soil depth in the landslide sites than at the secondary forest sites,whereas total phosphorus(TP)and ammonium(NH_(4)^(+)-N)were unaffected by the landslides.N-related enzymes,N-acetyl-β-glucosaminidase and L-asparaginase were reduced by more than 65%in the landslide sites,consistent with the decrease in nitrate concentration at the same 0–10 cm depth.At a depth of 10–20 cm,the variations in the soil properties were consistent with those at the 0–10 cm depth.The results demonstrated that soil chemical and microbial properties were significantly disrupted after the landslides,even though the landslides had occurred 6 years earlier.A long time is thus needed to restore the original C and nutrient levels.In temperate secondary forests,soil TC and TN contents were found to be more suitable for estimating the state of soil restoration than soil TP content.

A Study of Soil-dynamics Based on a Simulated Drought in an Alpine Meadow on the Tibetan Plateau

Extreme weather events have played an important role in driving the ecosystem dynamics in high altitude areas, but the underlying mechanism remains unclear. To understand if and how the soil processes of an ecosystem react to extreme drought, we manipulated a once-in-a-century meteorological extreme drought in an alpine meadow on the Tibetan Plateau, which is also known as the ＂forerunner of global weather changes＂. The extremity was determined by statistical extreme weather events with respect to a historical reference period from April to September during 1962 - 2004, where the local historical precipitation data was calculated and intensified to loo-year recurrent drought event with Gumbel I distribution. The indicators we measured included soil microbial biomass C/N/P and soil enzymatic activities of phosphatase （AP） disbounding organic phosphate, cellobiohydrolase （CBH）, β- glucocidase （BG）, N-releasing enzyme N-acetyl- glucosaminidase （NAG） as well as soil respirations, during and after the treatments. It was found that the manipulated event induced a rapid shift in microbial biomass and activities, indicating a lower resistance of the underground process. However, the microbial and biochemical parameters saw rapid recovery after the event, which meant the soil processes enjoyed high resilience. The high responsiveness and lag-time effects of the soil indicators rendered new horizons for us to evaluate the interaction between the extremes and the ecosystem stability. Our study indicated that the once-in-a-century extreme drought induced very short term response in the soil biotic process, and the soil processes worked to buffer against such events under the observation period.

Characteristics of soil nutrients and their relationship with soil microbial properties in Artemisia sacrorum communities in the loess hilly region

Artemisia sacrorum communities with different growth years were selected to analyse soil nutrient characteristics,the variation in soil microbial properties,and their relationships in the loess hilly region.The results showed that with an increase in the number of growth years,soil microbial biomass carbon and nitrogen contents as well as soil phosphatase and urease activities initially decreased and then increased in the A.sacrorum communities.The soil organic carbon,organic nitrogen,and total nitrogen contents as well as soil respiration rate showed an increasing trend and reached a maximum at age(a)37.The soil available phosphorus content first decreased and then increased,with the lowest level observed at 18 a.By contrast,soil available potassium initially increased and then decreased.Soil microbial biomass carbon had a significant positive correlation with soil organic carbon,total nitrogen and organic nitrogen,while soil respiration had a significant positive correlation with organic nitrogen,soil phosphatase and organic carbon.Soil respiration had a highly significant positive correlation with organic carbon and total nitrogen,while soil phosphatase had a highly significant positive correlation with total nitrogen and organic nitrogen.In the A.sacrorum communities,the soil organic carbon and total nitrogen contents were mainly affected by soil respiration,soil available potassium content was mainly affected by soil urease activity,and soil organic nitrogen content was mainly affected by soil phosphatase activity.These findings indicate that soil basal respiration,urease activity and phosphatase activity were the major microbial factors affecting the characteristics of the soil nutrients in the A.sacrorum communities.In conclusion,the natural restoration process of A.sacrorum communities can enhance soil microbial activity and improve soil quality.

长期化肥与不同有机物料配施对土壤微生物生态化学计量特征和群落结构的影响

【目的】研究长期化肥与不同有机物料配施对黄泥田土壤养分含量、土壤微生物生物量化学计量特征以及土壤微生物群落结构的影响,探讨微生物群落结构对养分变化的响应特征及其与微生物生物量化学计量变化的关系。【方法】田间试验开始于2011年,种植制度为单季稻。选取不施肥(CK)、单施化肥(NPK)、化肥配施紫云英(NPKGM)、化肥配施牛粪(NPKCM)和化肥配施水稻秸秆(NPKRS)5个处理。2022年水稻收获后采样,测定土壤有机质(SOM)、可溶性有机碳(DOC)、可溶性有机氮(DON)及全氮(TN)、全磷(TP)和有效磷(AP)、无机氮(IN)含量以及微生物生物量碳、氮、磷含量,并计算化学计量比;利用磷脂脂肪酸(PLFA)方法,分析微生物群落结构并计算相应指标。【结果】与NPK处理相比,化肥与紫云英、牛粪、水稻秸秆配施均能提高土壤有机质和养分含量,其中与牛粪配施的提升效果最好,SOM、TN、AP含量分别提高了40.7%、41.6%、108.6%。与CK相比,化肥与不同有机物料配施均显著提高了土壤MBC/MBN,降低了MBC/MBP和MBN/MBP,以配施牛粪处理的MBC/MBP最低。与NPK处理相比,化肥与不同有机物料配施均增加了土壤细菌、真菌、放线菌和总微生物生物量,降低了真菌/细菌(F/B)和革兰氏阳性菌/革兰氏阴性菌(G^(+)/G^(−))。冗余分析表明,土壤TN(P<0.05)是影响土壤微生物群落的最为关键环境因子,其次是土壤TP(P<0.05)。线性回归分析表明,MBC/MBN与DOC/(DON+IN)呈显著负相关,MBC/MBP与DOC/AP、MBN/MBP与(DON+IN)/AP均呈显著正相关。相关性分析表明,微生物生物量化学计量比的变化可能与F/B、G^(+)/G^(−)的值的变化密切相关,说明真菌与细菌、革兰氏阳性菌与革兰氏阴性菌等优势种群发生变化,可以在一定程度上引起微生物生物量化学计量比的变化。【结论】化肥与紫云英、牛粪、秸秆等有机物料配施,不仅可有效提高黄泥田土壤有机质和养分含量,还可改变土壤微生物生物量化学计量特征和微生物群落,其中与低化学计量比的牛粪配施效果最好。F/B、G^(+)/G^(−)的值与土壤微生物生物量化学计量比有相关关系,这种群落结构的重塑可能是黄泥田中土壤微生物响应底物化学计量比变化的有效策略。

青藏高原典型冰川小流域土壤微生物生物量及胞外酶活性分布特征

土壤微生物释放的胞外酶是决定碳(C)、氮(N)、磷(P)生物地球化学循环的关键因素,为了阐明青藏高原典型小流域土壤微生物生物量和胞外酶活性沿海拔和土层的分布特征并揭示影响该分布格局的主要养分限制状况,于2021年8月采集了青藏高原廓琼岗日冰川小流域5个海拔梯度(4900 m;5000 m;5100 m;5200 m;5300 m)中4个土壤发生层(A层:腐殖质层、E层:淋溶层、B层:淀积层和C层:母质层)的土壤样品,定量分析了土壤基本理化性质、微生物生物量、胞外酶活性等指标。结果表明:1)微生物生物量碳氮磷的海拔差异变化规律不同,随着土层加深微生物生物量碳氮磷随海拔变化越小。同时,各海拔之间微生物生物量均有随土层加深而显著降低的趋势(P<0.05);2)四种酶活性的海拔间变化规律各异,但整体呈现随海拔升高而升高的趋势且在表层(A和E层)增长趋势更明显,而且随土层加深显著降低(P<0.05);3)该区域土壤微生物受到碳和磷共同限制,土层越深限制越高,而且海拔越高C限制越强,但P限制降低;4)青藏高原典型冰川小流域土壤微生物生物量和胞外酶活性在海拔和土层之间存在较明显的差异,可能是由于土壤养分含量的差别造成的。整体而言,青藏高原典型冰川小流域土壤养分含量影响土壤微生物生物量和胞外酶活性在海拔和土层之间的分布特征。为深入理解青藏高原冰川小流域土壤养分循环提供了数据基础和科学依据。

不同有机物料还田对白浆土土壤化学计量特征及胞外酶活性的影响

为探究不同有机物料还田对白浆土土壤化学计量特征及胞外酶活性的影响,在东北白浆土地区开展2 a定位试验,设置常规耕作对照(CK,无秸秆无有机肥添加)、秸秆还田(S)、有机肥还田(M)和秸秆搭配有机肥还田(SM)共4个处理。结果表明,与CK相比,施用有机物料均可增加土壤有机碳、全氮和全磷含量,分别增加1.81%~6.91%、1.54%~7.48%和2.04%~7.26%,但对土壤C∶N、C∶P、N∶P无显著影响。施用有机物料均可显著增加土壤碳、氮、磷获取酶的活性,其中土壤氮获取酶活性的增加最为显著,增幅为60.03%~131.15%,且有机肥还田和秸秆搭配有机肥还田对3种土壤获取酶的提升效果优于秸秆还田处理。胞外酶化学计量散点图结果表明,土壤微生物群落受碳和磷的共同限制,而有机物料的投入可缓解这种限制;基于随机森林分析发现,土壤有效磷、碱解氮、微生物生物量碳、微生物量氮和微生物量磷是影响土壤微生物碳和磷限制指标的重要因素。

宁南拱棚辣椒连作对土壤养分、酶活性及微生物量的影响

以“牛角椒巨丰一号”辣椒为试材,针对初始连作年限为1年(一号)、2年(二号)、9年(三号)、11年(四号)的4座拱棚,采用控制变量法,进行持续3年的土壤养分、酶活性以及微生物量测定,研究连作对土壤性状的影响,以期对宁南拱棚辣椒连作障碍的形成机理、消减措施等提供参考依据。结果表明:连作年限对微生量碳氮磷、主要养分指标(有机质、全氮、全磷、速效钾、速效磷、速效氮)及过氧化氢酶、脲酶和蔗糖酶影响显著(P<0.05)。土壤微生物量磷随着连作年限的增加整体呈下降趋势,而微生物量碳氮无明显趋势性变化。随着连作年限的增加,各大棚土壤养分整体均呈上升趋势,其中速效磷的增长最为显著,三号棚增加最多,比采样第1年分别增加了218.41%、523.20%;四号棚中全氮含量随连作年限增加而减少,有机质、全磷、速效钾无显著变化;速效氮随连作年限增加也无明显变化规律。土壤过氧化氢酶随连作年限无明显的变化规律,土壤脲酶在各个大棚均呈现明显的下降趋势,短期连作可以显著提高土壤蔗糖酶活性,但随着连作年限的增加又逐年下降,而土壤碱性磷酸酶短期连作与长期连作下均无明显变化。

土壤碳氮磷和酶化学计量特征对原始林转换的响应

为了解区域典型农林用地土壤碳、氮、磷、胞外酶生态化学计量特征,采用时空代换法研究湘西北本底一致、土地利用史清晰的常绿阔叶原始林及其转换而来的人工林地、果园、坡耕地和水田0~40 cm土层中有机碳含量、全氮含量、全磷含量、胞外酶活性、计量比值及其与活性碳、氮、磷组分的关系。结果表明,与原始林相比,果园和坡耕地土壤有机碳、全氮、全磷含量的降幅(40%~79%)较高,且深层土壤(20~40 cm)和表土(0~20 cm)的降幅类似,表明原始林转换为果园、坡耕地不利于深层土壤有机碳和养分的保存。果园、坡耕地、水田和原始林土壤碳、氮、磷含量的比值无显著差异。杉木人工林土壤碳、氮、磷含量比值较原始林高60%~124%,说明人工林土壤存在较强的氮、磷素共同限制作用。与原始林相比,土地利用方式转换后,土壤胞外酶活性降低18%~64%;果园和坡耕地表土碳磷获取酶计量比(E_(C/P))也显著降低,而深层土壤E_(C/P)显著升高。土壤中碳含量、氮含量、磷含量、酶活性及其计量比值与活性碳、氮、磷组分含量显著相关。原始林转换导致表土和深层土壤中的碳含量、氮含量、磷含量、胞外酶活性大幅下降,微生物底物有效性降低,表明土壤质量/健康退化。土壤碳、氮、磷含量计量比和酶计量比值对原始林转换的响应较弱,对土壤健康的指示作用有待进一步探索。

不同柑橘种植年限土壤胞外酶生态化学计量特征及其驱动因子解析

土壤胞外酶生态化学计量特征可用于评估微生物对资源和养分的获取情况,是评价土壤肥力和微生物活性的重要指标。然而,高强度集约化柑橘种植对土壤胞外酶计量特征的影响机制尚不清楚。为探讨集约化农业种植对土壤酶化学计量特征及其对种植年限的响应,本研究以三峡库区河岸带不同种植年限柑橘为研究对象,采集根际土壤,测定与碳氮磷循环相关的胞外酶活性和功能微生物基因丰度,通过胞外酶生态化学计量特征去评估土壤微生物对氮磷养分及资源的需求状况。结果表明,柑橘种植年限的增加会提高土壤有效氮和有效磷的含量,其中磷素累积更为明显。种植30 a的柑橘土壤有效磷含量约为5 a柑橘土壤的3.5倍,远高于柑橘生长需求阈值。柑橘种植年限增加会显著降低土壤碳磷循环相关酶活性,增加氮获取酶活性。从功能基因角度来看,编码碱性磷酸酶的phoD基因丰度显著下降,从4.84×10^(7)copies·g^(-1)下降至9.24×10^(6)copies·g^(-1)。土壤功能微生物基因丰度的下降是导致碱性磷酸酶活性降低的直接因素。土壤酶化学计量特征也随着柑橘种植年限的增加而改变。土壤酶矢量角度由58.21°降低至18.70°,表明土壤微生物对养分的需求由磷限制转换为氮限制,低柑橘种植年限土壤微生物以磷限制为主,高柑橘年限土壤微生物以氮限制为主。高强度柑橘种植过程中,需减少磷肥施用,增加有机肥等碳源投入,提高微生物活性。研究结果可为高强度集约化柑橘种植土壤质量提升和果园的可持续管理提供理论依据。

不同有机物料改善富磷菜田土壤微生物结构功能和蔬菜磷素吸收利用研究

【目的】碳是微生物代谢活动的优质养分和能量来源,对根际微生物的群落结构和生态功能具有重大影响。解析碳驱动微生物周转对作物吸收利用磷的影响,探索富磷土壤中磷素高效利用的绿色途径。【方法】蔬菜田间试验分别在山东东营(潮土)和淄博(褐土)进行,供试作物依次为番茄、西葫芦。设置不施肥对照(CK)、优化施肥(OPT)、优化施肥+腐植酸(OPT+HA)、优化施肥+蚯蚓粪(OPT+EC)、优化施肥+菌渣(OPT+MR) 5个处理。在拉秧期采集土样分析土壤碳、磷养分含量,碳、磷相关胞外酶活性以及土壤细菌群落特征。【结果】1)有机物料投入提高了番茄和西葫芦产量及磷吸收积累量。2)在OPT基础上,增施HA、EC和MR可显著提高土壤肥力和酶活性,以MR的提升效果最为显著。在东营,增施MR处理土壤微生物生物量碳(MBC)和可溶性有机碳(DOC)含量较OPT处理分别提高了17.46%和17.03%,土壤β-葡萄糖苷酶(β-GC)和酸性磷酸酶(ACP)活性分别显著提高了19.75%和13.12%,土壤有效磷含量显著降低了28.50%;在临淄,增施MR土壤各类碳组分含量较OPT处理均有显著提高,增幅在16.19%~54.30%,土壤β-GC活性显著提高了24.55%。3)增施EC和MR显著提高了土壤细菌群落Chao1指数和Shannon指数;增施MR显著提高了土壤中突柄杆菌(Prosthecobacter)、堆囊菌属(Sorangium)相对丰度,增施HA显著提升了土壤中Vermiphilaceae、MWH_CFBk5、Pedobacter相对丰度;增施EC的土壤中富集了Fodinicola和Phaselicystis,改变了土壤微生物群落结构。【结论】在优化施肥基础上,增施有机物料,尤其是菌渣,可有效提高土壤可溶性有机碳比例,增加土壤β-葡萄糖苷酶活性,显著改善土壤微生物群落结构,提高有益菌群丰度,增强土壤磷的活化,进而提高了蔬菜对磷的吸收和利用,降低了土壤中有效磷含量。因此,在富磷土壤上,优化施肥配合增施菌渣是提高土壤微生物活性及蔬菜磷素吸收积累的可行措施。

污泥生物质炭对杨树人工林土壤环境质量的影响

通过田间试验,研究了污泥生物质炭(SSBC)施用对杨树人工林土壤理化性质、重金属含量、土壤微生物生物量碳氮以及土壤酶活性的影响。试验设置4个处理:不施生物质炭对照(0t/hm^(2))、低量生物质炭(15t/hm^(2))、中量生物质炭(30t/hm^(2))及高量生物质炭(60 t/hm^(2))。结果表明:SSBC的施用可降低土壤pH,增加土壤电导率;随着SSBC用量的增加,土壤营养成分和重金属含量均呈现增加趋势,其中土壤有机碳增加18.4%~47.9%,全氮增加20.4%~46.5%,全磷增加27.9%~74.9%,有效氮增加4.2%~23.1%,有效磷增加16.3%~28.3%,且重金属污染可控。SSBC提高微生物生物量碳氮含量,并使土壤β-葡糖苷酶、N-乙酰-葡糖苷酶和蛋白酶活性分别显著增加17.1%~35.3%、18.1%~36.8%和29.3%~70.3%,其中中量生物质炭处理的增幅最大。总之,SSBC的应用不仅显著增加土壤营养成分,而且改善部分微生物环境,致使土壤环境质量一定程度上有所改善。

施肥对宁夏主要类型土壤-微生物-胞外酶化学计量特征的影响

【目的】研究施肥对宁夏主要类型土壤碳氮磷、微生物生物量碳氮磷、胞外酶活性及其化学计量特征的影响,为农田养分调控和土壤可持续利用提供科学依据。【方法】以宁夏主要类型土壤(灌淤土、黄绵土、灰钙土)为研究对象,分析施肥(不施肥(对照)、单施化肥、化肥配施有机肥)对土壤有机碳(C)、全氮(N)、全磷(P),微生物生物量C、N、P(MBC、MBN、MBP)含量和胞外酶(β-葡糖苷酶(BG)、α-纤维素酶(CBH)、β-乙酰葡糖胺糖苷酶(NAG)、亮氨酸氨基肽酶(LAP)、碱性磷酸酶(AKP))活性的影响,并且分析了土壤碳氮磷含量与微生物生物量碳氮磷、胞外酶活性及其化学计量特征的相关性。【结果】(1)施肥和土壤类型均对土壤C、N、P含量影响极显著,而二者的交互作用仅对土壤C影响显著。土壤类型对C/P、N/P影响极显著,施肥对C/N、C/P影响显著。与对照相比,化肥配施有机肥处理显著增加了黄绵土C含量以及各类型土壤N、P含量和N/P。(2)施肥对土壤MBC、MBN、MBP含量及其化学计量比影响显著或极显著,而土壤类型仅对MBP含量及MBC/MBP影响极显著,二者交互作用对MBP含量和MBC/MBP、MBN/MBP影响极显著。3个土壤类型中,化肥配施有机肥处理对黄绵土MBC、MBN、MBP含量的增加作用最为明显,而对黄绵土MBC/MBN、MBC/MBP、MBN/MBP的降低作用最为明显。(3)施肥和土壤类型对土壤胞外酶化学计量特征有极显著影响,二者的交互作用对CBH、NAG、LAP、AKP活性有极显著影响。与对照相比,化肥配施有机肥显著降低了灰钙土LAP、NAG、AKP活性。(4)相关性分析表明,土壤有机碳与(NAG+LAP)/AKP呈显著正相关,而与(BG+CBH)/(NAG+LAP)、(BG+CBH)/AKP呈显著负相关。土壤全P与(BG+CBH)/(NAG+LAP)、(BG+CBH)/AKP呈极显著正相关,而与(NAG+LAP)/AKP呈极显著负相关。土壤C/N与MBC/MBP、MBN/MBP呈显著或极显著正相关,而与MBP呈显著负相关。【结论】化肥配施有机肥有利于增加宁夏主要类型土壤全量养分和微生物生物量,维持土壤养分平衡,但在实际应用中应考虑土壤类型的差异。

Soil microbial attributes along a chronosequence of Scots pine(Pinus sylvestris var. mongolica) plantations in northern China

Soil microorganisms play a key role in soil organic matter dynamics, nutrient cycling, and soil fertility maintenance in forest ecosystems, and they are influenced by stand age and soil depth. However, few studies have simultaneously considered these two factors. In this study, we measured soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), soil basal respiration (SBR) rate, and potential extracellular enzyme activity (EEA) in soil to a depth of 60 cm under 10-, 30-, and 40-year-old Scots pine (Pinus sylvestris var. mongolica) stands (Y10, Y30, and Y40, respectively) in plantations in northern China in 2011. Soil water content (SWC), soil pH, soil organic carbon (SOC), and soil total nitrogen (STN) were also measured to explore their effects on soil microbial indices across different stand ages and soil depths. Our results showed that SMBC, SMBN, and the SBR rate were generally higher for the Y30 stand than for the Y10 and Y40 stands. Potential EEA, except forα-glucosidase, decreased significantly with increasing stand age. Soil organic carbon,STN, SWC, and soil pH explained 67%of the variation in soil microbial attributes among the three stand ages. For the same stand age, soil microbial biomass and the SBR rate decreased with soil depth. Lower microbial biomass, lower SBR rate, and lower EEA for the mature Y40 stand indicate lower substrate availability for soil microorganisms, lower soil quality, and lower microbial adaptability to the environment. Our results suggest that changes in soil quality with stand age should be considered when determining the optimum rotation length of plantations and the best management practices for afforestation programs.

放牧强度对高寒草地土壤微生物胞外酶化学计量的影响

土壤微生物是土壤养分释放或固持的重要调节者。本实验以青藏高原高寒草原为研究对象,以藏羊放牧强度控制实验为平台(对照(CK,0),轻度放牧(LG,2 sheep·hm^(-2)),中度放牧(MG,4 sheep·hm^(-2)),重度放牧(HG,6 sheep·hm^(-2))),开展不同放牧强度下高寒草地土壤和微生物养分变化特征及其对土壤微生物养分代谢的影响研究。结果显示:总体上,土壤碳氮磷含量在放牧干扰下呈减少趋势,而微生物碳氮磷含量及其化学计量的变化幅度较小;重牧的碳获取酶(β-葡萄糖苷酶)活性及化学计量显著高于其余处理。此外,中牧和重牧的C∶P不平衡和N∶P不平衡高于CK,而C∶N不平衡低于CK,这表示在中度或重度放牧下高寒草地主要受到碳、磷的限制。当面对自身与资源之间的养分不匹配时,高寒草地土壤微生物主要通过增加碳获取酶的分泌,来缓解在重牧下的养分限制。

贺兰山东坡不同海拔梯度土壤酶化学计量特征

土壤胞外酶是生物地球化学循环的主要参与者,与微生物的代谢需求和养分供应密切相关。然而,对干旱区山地生态系统沿海拔梯度土壤微生物养分限制状况及其驱动因素尚不清楚。基于此,以贺兰山海拔1300—2700m范围内7个海拔梯度的土壤为研究对象,揭示贺兰山土壤理化性质、胞外酶活性及微生物养分限制的海拔分布格局,分析影响微生物养分限制的驱动因素。结果表明:随着海拔梯度的升高,土壤含水率(SWC)和有机碳(SOC)含量逐渐增加,容重(BD)和pH整体呈现逐渐降低的趋势。海拔显著影响土壤胞外酶活性,五种参与土壤碳(C)、氮(N)、磷(P)循环的酶活性随着海拔的升高整体呈现逐渐上升的变化趋势,总体表现出中低海拔酶活性较低,高海拔酶活性较高。胞外酶矢量分析显示,矢量长度在中低海拔处较高,而矢量角度则在高海拔处较高,表明贺兰山土壤微生物在中低海拔和高海拔分别具有相对较强的C和P限制。土壤含水率、容重、C、N、P含量与土壤胞外酶活性及其化学计量比显著相关,是调控土壤胞外酶活性随海拔变化的主要因子,说明胞外酶在旱区山地生态系统土壤物质循环过程中具有重要的作用。该研究结果对揭示土壤微生物和胞外酶之间养分元素循环的耦合机理,为深入探讨贺兰山森林生态系统物质循环和不同海拔梯度植被有效管理提供科学依据。

连作年限对植烟土壤养分和微生物量及胞外酶化学计量特征的影响

【目的】研究烤烟不同连作年限对云南典型砂质红壤微生物量和胞外酶活性化学计量特征的影响,结合土壤理化性状探究其相关机制,为缓解烟草连作障碍提供理论参考。【方法】以连作1、2、4、6和9 a的植烟砂质红壤为研究对象,测定其土壤理化性状、微生物量碳、微生物量氮和微生物量磷以及土壤碳、氮、磷营养元素循环相关的土壤胞外酶活性。运用生态化学计量学和冗余分析(redundancy analysis,RDA)对土壤肥力属性与土壤胞外酶活性的关系进行分析。【结果】(1)随着连作年限的增加,土壤有机碳、全氮、全磷、铵态氮和硝态氮含量均呈先降低后升高的变化趋势,且以连作4 a时最低。(2)连作土壤pH值为5.68~6.43;在连作1~6 a范围内,随着连作年限的增加土壤pH值呈下降趋势,连作9 a时土壤pH值升高。(3)RDA分析表明:土壤有机碳含量、全磷含量和pH值与土壤胞外酶活性显著相关。土壤胞外酶化学计量分析表明:连作1、2和6 a时,土壤中微生物受到较强的碳源限制;而所有连作年限的土壤中微生物都受到氮源限制。【结论】烤烟连作4 a后,土壤pH值以及碳、氮、磷元素发生显著变化,且与土壤氮循环相关的土壤胞外酶活性增强,将土壤中的有机氮转化为无机氮以保持土壤氮的平衡。

秸秆覆盖和配施有机肥对侵蚀坡耕地土壤胞外酶化学计量特征的影响

【目的】土壤胞外酶化学计量特征能够反映养分的有效性和限制性,探究侵蚀生境有机物料添加对耕地土壤酶活性特征的影响,从微生物作用机制认识坡耕地的退化诱因。【方法】研究在我国西南紫色土丘陵区坡耕地观测径流小区进行,试验已进行了8年。设置4个保护性措施处理:无秸秆覆盖无有机肥添加对照(CK)、有机肥替代20%化肥氮(OM)、秸秆覆盖替代20%化肥氮(SW)、秸秆覆盖+有机肥替代20%化肥氮(OMSW)。采集侵蚀区和沉积区0—20 cm耕层土样,测定土壤胞外酶活性和颗粒组成及土壤不同形态C、N、P含量,分析土壤胞外酶化学计量特征、土壤养分化学计量比和土壤可蚀性因子的关联性。【结果】坡耕地各处理沉积区土壤β-葡萄糖苷酶(BG)、乙酰氨基葡萄糖苷酶(NAG)、亮氨酸氨基肽酶(LAP)、碱性磷酸酶(AKP)活性分别显著高于侵蚀区52.31%、50.60%、16.97%、13.11%。土壤胞外酶活性计量比约为1∶0.79∶1.13,偏离1∶1∶1,4种处理的土壤酶活性表现为SW>OMSW>CK>OM。4种处理矢量角度均表现为侵蚀区>沉积区(P<0.05),矢量长度表现为侵蚀区<沉积区(P<0.05)。4种处理的矢量角度均大于45°,同时4个处理的矢量长度均在1∶1线上方,坡耕地总体受磷限制(养分限制)和碳限制(能量限制)。【结论】坡耕地侵蚀加速了土壤碳、氮、磷的周转速率,各处理沉积区土壤BG、NAG、LAP、AKP活性显著高于侵蚀区。坡耕地总体受养分限制(磷限制)和能量限制(碳限制),土壤胞外酶活性计量比偏离1∶1∶1,侵蚀区受养分限制较重,而沉积区受能量限制较重,侵蚀−沉积作用促使坡耕地土壤由磷限制转变为碳限制。秸秆覆盖并添施有机肥可以缓解土壤胞外酶活性化学计量失衡,其中秸秆覆盖可以显著增加土壤酶活性,缓解土壤磷限制,促进土壤养分循环。