不同土地利用类型对土壤氮素的影响

选取林地、园地和耕地3种土地利用类型,分析禹州市褐土土壤中氮素含量的研究结果表明:0～15 cm土层中,矿化氮含量为:林地>园地>耕地;土壤表层(0～5 cm)硝态氮含量林地最高,显著高于园地和耕地,而土壤表层铵态氮含量园地和林地显著高于耕地;不同土层中的,林地、园地和耕地的硝态氮和铵态氮含量差异显著(P<0.05)。在林地和园地0～5 cm土层中,硝态氮含量显著高于10～15 cm土层,而耕地中硝态氮含量无显著差异,其中林地的硝态氮含量随土壤深度的增加而降低。3种土地利用类型铵态氮含量主要集中分布在土壤0～10 cm土层中。     

土壤硝化和反硝化作用及影响因素研究进展

土壤硝化和反硝化作用是生态系统中氮循环的两个重要环节,是氮素损失的潜在途径,土壤硝化和反硝化作用可向大气中释放温室气体,由此带来环境危害。本文综述了国内外学者对土壤硝化和反硝化作用的研究现状,总结了土壤硝化和反硝化作用的研究方法及其影响因子。土壤硝化和反硝化作用是两个非常复杂的生态学过程,针对研究工作中存在的不足,提出建议:1)改进实验方法、加强对总硝化作用的研究;2)进一步探索森林生态系统中硝化和反硝化作用规律;3)注重对土壤中硝化和反硝化作用微生物学机理的研究。     

西南酸雨区重庆缙云山常绿阔叶林土壤氮矿化特征

【目的】探讨重庆缙云山2012—2014年土壤矿质氮(铵态氮和硝态氮)变化规律、输入来源与氮矿化特征,明确土壤氮矿化的驱动因素,以期为深入研究该地区土壤养分循环提供理论依据。【方法】在重庆缙云山选择能代表中亚热带森林生态系统的常绿阔叶林,设置1块20 m×20 m样地,内部布设5个4 m×4 m样方,于2012—2014年每年4—9月每月月末,采集上、中、下层(0~15,15~30和30~60 cm)土壤样品,同步观测样地内土壤呼吸速率,并收集穿透雨与干流;在实验室内测定土壤铵态氮(NH4^+-N)、硝态氮(NO3^--N)和全氮(TN)含量;并用原位培养法测定土壤氮素矿化速率。【结果】土壤铵态氮和硝态氮含量在年际、月际(除2012年铵态氮含量)及各土层间均差异显著(P<0.05),4—9月土壤铵态氮和硝态氮含量均呈递增趋势,上层土壤的铵态氮与硝态氮含量均表现为2013年>2012年>2014年,各土层间铵态氮含量表现为中层>下层>上层,硝态氮含量表现为随土层加深而递减趋势;土壤氨化速率和硝化速率的月际变化为单峰或先升后降再上升的趋势,年际变化均表现为2013年>2014年>2012年;土壤铵态氮含量与硝态氮含量在各土层间极显著(P<0.05)或显著(P<0.01)正相关,但与穿透雨和干流输入量相关性不显著;土壤氨化速率与硝化速率均与土壤呼吸速率极显著(P<0.01)正相关,而与土壤pH值极显著(P<0.01)负相关;土壤呼吸速率大于4μmol·m^-2 s^-1时,土壤氨化速率和硝化速率明显随pH上升而下降,土壤呼吸速率小于4μmol·m^-2 s^-1且土壤pH值为3.70~3.75时,氨化速率与硝化速率开始出现小幅上升,之后下降。【结论】重庆缙云山常绿阔叶林土壤矿质氮含量具有年际、月际及土层间差异;土壤矿质氮含量受穿透雨和干流氮(包括铵态氮和硝态氮)输入量的影响较小,而与相邻土层氮含量相关更紧密;土壤pH值升高对土壤的氨化和硝化速率有抑制作用,且其抑制作用大小随土壤呼吸速率大小不同而变。     

大兴安岭北部主要树种生长季根际土壤氮素含量特征

为了探讨大兴安岭地区主要树种(樟子松、兴安落叶松、白桦和山杨)根际土壤氮素的富集程度和差异性,选用抖落法采集根际和非根际土壤样品,对其全氮、铵态氮与硝态氮含量特征进行研究。结果表明:1)4个树种根际土壤全氮含量5—10月波动在1.22～5.43 g·kg-1之间,最大值均在5月;根际土壤铵态氮和硝态氮分别波动在22.41～53.75 mg·kg-1和0.79～2.06 mg·kg-1之间,含量均在7、8月较低,且兴安落叶松根际土壤月平均铵态氮和硝态氮含量均为最高。2)研究区无机氮素以铵态氮为主,占95%以上;根际土壤全氮、铵态氮和硝态氮含量均显著(P <0.05)高于非根际土壤,分别高出101.77%、29.26%和9.07%;兴安落叶松根际土壤全氮富集率达101.25%,铵态氮、硝态氮富集率均最高为39.37%和15.34%;樟子松根际土壤全氮、铵态氮、硝态氮富集率分别为95.98%、34.86%和7.84%;白桦全氮的富集率最高为125.73%,铵态氮、硝态氮富集率为30.30%和7.31%;山杨根际土壤氮素富集率最小。3)根际土壤铵态氮与全氮、硝态氮均呈极显著正相关,而全氮与硝态氮之间相关性不显著。4)4个树种根际土壤对氮素养分含量均具有明显的正根际效应,其中针叶树种对无机氮素的富集能力强于阔叶树种,且兴安落叶松对氮素的富集能力最强。因此,在森林经营和调整林分结构时可适当调整兴安落叶松树种比例,以提高森林生产力。     

东北人工红松针叶林和天然次生阔叶混交林林下土壤氮初级转化速率特征

[目的]为了解森林土壤氮素转化特征及土壤氮供应能力，为森林生态系统合理经营管理提供科学依据。[方法]以东北寒温带人工红松针叶林和天然次生阔叶混交林表层土壤为研究对象开展室内培养试验，采用¹⁵N同位素成对标记技术和FLUAZ数值优化模型，研究不同深度的土壤氮初级转化速率特征。[结果]林地土壤的氮初级转化速率受林型、土壤深度及二者间交互作用的影响。人工红松针叶林土壤氮初级矿化速率和无机氮固定速率显著低于天然次生阔叶混交林土壤，而初级硝化速率显著高于天然次生阔叶混交林土壤，2个林型土壤的氮初级转化速率都随着土壤深度的增加显著降低。土壤氮初级矿化速率和固定速率与土壤pH、有机碳、水溶性有机碳与水溶性有机氮含量呈显著正相关，土壤初级硝化速率与土壤pH呈显著负相关。人工红松针叶林土壤初级硝化速率与铵态氮固定速率比值显著高于天然次生阔叶混交林土壤，而对硝态氮的固定速率显著低于天然次生阔叶混交林土壤。[结论]2种林型土壤氮素转化特征差异明显，人工红松针叶林土壤的硝态氮产生能力较强而无机氮固持能力较弱，容易发生硝态氮的淋溶风险，天然次生阔叶混交林土壤氮矿化-固定过程耦合较好且硝化作...     

新宾县土壤氮素在林地、草地与耕地分布规律研究

选取林地、草地和耕地3种类型的土地,分析新宾满族自治县黑土土壤氮素含量在空间的分布情况,研究表明:0～5 cm、5～10 cm与10～15 cm的氮素含量均为林地草地耕地;林地、草地与耕地的铵态氮、硝态氮的含量均表现为随着土层深度增加而呈递减趋势;且林地表层硝态氮与全氮的含量最高,草地的铵态氮含量最高,但耕地3项指标均偏低,所以保护林业用地对环境具有极其重要的影响。     

河岸带落叶松林土壤氮素空间格局研究

通过对庞泉沟河岸带落叶松林的土壤氮素空间格局进行分析,了解河岸带全氮、铵态氮、硝态氮的储量以及氮素的空间格局,为河岸带对河流氮素的净化研究提供基础数据。结果表明：1）土壤表层氮素含量较高,土壤中全氮、铵态氮、硝态氮空间异质性明显,并且氮素在土壤层之间、高地连续体上存在不规则的垂直格局和水平格局。2）在高地连续体上,河岸带土壤全氮与硝态氮呈显著正相关（r=0.613）,全氮与铵态氮呈正相关（r=0.114）,全氮与与河岸带宽度呈负相关（r=-0.075）,铵态氮与硝态氮呈负相关（r=-0.004）。土壤氮素格局受多因素影响,氮素的形态与含量主要受地形、林分、降水以及土壤理化性质等因素的综合影响。     

添加葡萄糖对杉木人工林土壤氮素转化及净矿化和硝化的影响

以亚热带杉木人工林为研究对象,研究添加葡萄糖(C量水平分别是0,100,300,1 000,2 000,5 000 mg·kg-1)对土壤氮含量、氮素矿化和硝化的影响。结果表明,葡萄糖添加降低土壤无机氮含量和比例,硝态氮的降低幅度大于铵态氮;但是没有降低可溶性有机氮(SON)和pH值,甚至提高SON的比例。添加葡萄糖降低氮素净矿化和硝化速率,氮素矿化作用受到抑制。结果显示,随着葡萄糖添加,亲水性氮所占比例显著降低,这与氮的固持和转化有关,导致SON比例增加;分析表明,硝态氮和可溶性有机氮在提取液全氮中所占比例成显著的线性负相关关系(R2=0.902)。研究发现,1 000 mg·kg-1的葡萄糖C添加量可能是影响杉木人工林土壤氮素转化的分界点。     

氮存在形态对沉水植物氮去除效果的影响

在室内模拟条件下,探究了不同氮存在形态沉水植物苦草(Vallisneria natans L.)、黑藻(Hydrilla verticillata)对氮净化效果的影响。研究结果表明:硝化作用是铵态氮去除的主要途径,黑藻和苦草系统中硝化作用分别占外源铵态氮净化总量的63.26%和50.86%;沉水植物主要通过光合作用提高水体DO来促进铵态氮向硝态氮,并通过促进微生物的反硝化作用降低水体硝态氮浓度;铵态氮和硝态氮共存时,沉水植物优先吸收铵态氮;沉水植物对铵态氮的吸收能力较硝态氮强,苦草和黑藻对NH+4-N的吸收量分别为NO-3-N的3.70和2.31倍;苦草和黑藻对于TN的净化存在一个较优的铵态氮硝氮比,分别为3.5和2.0。黑藻对各形态氮具有更强的净化能力,且对水体有更好的增效作用。     

模拟氮沉降对杉木林土壤氮循环相关微生物的影响

【目的】土壤微生物数量是衡量土壤氮素循环生化功能变化的重要指标。通过野外模拟试验,探讨短期氮沉降中不同氮素形态的沉降量对土壤中可培养固氮菌、硝酸细菌、亚硝酸细菌和反硝化细菌数量的影响,以及初期的变化趋势对森林氮素调控和环境管理的重要意义,为深入研究氮沉降对杉木林森林生态系统的影响提供参考。【方法】2013年5月,在杉木幼龄林内建立30个1 m ×1 m的样方,进行5种氮沉降量[N0(对照)、N1(20 kg· hm －2a －1)、N2(40 kg·hm －2a －1)、N3(60 kg·hm －2a －1)、N4(80 kg·hm －2a －1)]和2种氮形态(I铵态氮、II硝态氮)的模拟沉降试验。分别于2013年6,8,10月从0～10 cm和10～20 cm 土层取样测定微生物数量。固氮菌数量测定采用稀释平板计数法,硝酸和亚硝酸细菌数量采用 MPN-Griess 比色法,反硝化细菌(厌氧)采用酚二磺比色法。【结果】各处理的0～10 cm土层中固氮菌数量均高于10～20 cm 土层;随着氮沉降量增加,可培养固氮菌数量先升高后降低。低于60 kg·hm －2 a －1铵态氮处理有利于固氮菌生长。0～10 cm 土层亚硝酸细菌数量,随铵态氮沉降量增加,先升高再降低最后趋于平缓,在 N1或 N2处理达到最大值;施硝态氮时,菌落数量先降低再升高最终趋于平稳。在6月,虽然铵态氮和硝态氮的氮沉降量相同,但0～10 cm 土层中的亚硝酸细菌数量差异极显著,10～20 cm土层差异显著。8月和10月的硝酸细菌数量变化趋势相同,均为随氮沉降量增加先上升再下降再上升,且在相同氮素沉降量的铵态氮和硝态氮处理间未出现显著差异。反硝化细菌的时间变化与其他菌落不同,施铵态氮时二土层的变化趋势相反,施加硝态氮时反硝化细菌的数量变化较平缓,NO3－-N的 N4处理有轻微抑制作用。【结论】0～10 cm土层的固氮菌数量大于10～20 cm土层,0～60 kg·hm －2 a －1铵态氮和0～80 kg·hm －2 a －1硝态氮均可促进固氮菌的生长。亚硝酸细菌在2种氮形态处理时的变化趋势相反,低铵态氮处理可促进亚硝酸细菌的生长,低硝态氮处理抑制其生长。氮形态对硝酸细菌数量影响不显著,低氮处理促进硝酸细菌数量的增长,而中氮处理开始出现抑制作用。氮沉降量对反硝化细菌影响不显著。     

Improving the evaluation of multiple-dowel-type connection strength

Our study focuses on predicting the ultimate short-term load carrying capacity of timber-to-timber connections with dowel-type fasteners. The wide range of possible configurations in practice makes the resolution of these values by tests unrealistic. Moreover, different current regulations do not consider some specific failure mechanisms. In many countries, the reduction of resistance involved by this phenomenon is taken into account by considering an effective number of dowels (n_ef) smaller than the actual number of dowels (n) in the connection. However, these different regulations disagree on the values of n_ef and on other points (spacing, partial coefficient of security, formulas). These discrepancies in design rules invite the fundamental research on this topic and, therefore, new methods are sought in order to estimate the load carrying capacities of the connections. In the light of these, our approach consists of predicting the load carrying capacity with the neural network numerical tool. The results obtained by this analysis tool are satisfactory, although the model remains complex. Subsequently, we focus on the simplification of this numerical model with classical regression techniques in order to implement it in a design code.     

<Emphasis Type="Italic">Ophiostoma</Emphasis> species associated with bark beetles infesting three <Emphasis Type="Italic">Abies</Emphasis> species in Nikko,Japan

Ophiostoma species were isolated from bark beetles and Abies mariesii, A. veitchii and A. homolepis attacked by the beetles in Nikko, Tochigi, central Honshu, Japan. One to two Ophiostoma species were frequently isolated from each species of bark beetle. Ophiostoma subalpinum was the most common associate of Cryphalus montanus. Ophiostoma sp. B as well as O. subalpinum was a common fungus associated with Polygraphus proximus. Ophiostoma europhioides was isolated from Dryocoetes hectographus and D. autographus as one of the common associates. Ophiostoma sp. J and Ophiostoma sp. S were frequently isolated from D. autographus and D. striatus, respectively. These fungi seem to have specific relationships with particular bark beetles. Ophiostoma sp. B, Ophiostoma sp. J and Ophiostoma sp. S have unique morphological characteristics and appear to be new species. Five trees of A. veitchii, approximately 43 years old, were inoculated with five Ophiostoma species to assess the relative virulence of the fungi. Ophiostoma subalpinum, Ophiostoma sp. B, and O. europhioides had relatively higher virulence than the other species studied.     

Parasitic Ichneumonoidea on the horse chestnut leaf miner, Cameraria ohridella (Lepidoptera: Gracillariidae) in Slovakia

Parasitic Hymenoptera from the suprafamily Ichneumonoidea attacking the horse chestnut leafminer Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae) were studied in southwest Slovakia during 2000 and 2001. The search for such species resulted in the determination of eight ichneumonid species, Gelis agilis (Fabricius), Itoplectis alternans (Gravenhorst), I. clavicornis (Thompson), I. maculator (Fabricius), Scambus annulatus (Kiss), S. brevicornis (Gravenhorst), Zatypota percontatoria (Müller), Adelognathus sp. and a braconid Colastes braconius Haliday. The most abundant species was S. annulatus. All these species recorded are polyphagous and often facultative hyperparasitoids, except C. braconius, which departs from this norm in not being hyperparasitic. The presence of more diversified native parasitoids and hyperparasitoids from the Ichneumonoidea predicate a slow successive adaptation of the parasitoid fauna to the invasive host, Cameraria ohridella.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Rehabilitation of diseased cacao fields in Peru through shade regulation and timing of biocontrol measures

The objective of this case study was to test the effectiveness of biocontrol for the rehabilitation of abandoned, diseased (moniliasis, witches' broom and black pod) cocoa and to develop testable hypotheses regarding the effect of shade and biocontrol timing. Three trial fields differed in their shade regimes. Biocontrol was administered starting either at flowering or pod filling. Disease incidence and yield were compared with cultural control alone. Biocontrol reduced moniliasis from 49% to 25%, independent of the shading regime and application time. Witches' broom was most severe without shade and unaffected by biocontrol. No significant effects on black pod were observed. Although biocontrol increased percentage healthy fruit independent of shading and timing, only the shaded plot with biocontrol from flowering onwards responded with increased yield. Our hypothesis is: 'In the rehabilitation of abandoned cacao, only fields under sustainable shade management and early onset of biocontrol can realise their production potential.' This revised version was published online in June 2006 with corrections to the Cover Date.     

Populations of adult fungus gnats and shore flies in British Columbia container nurseries as related to nursery environment,and incidence of fungi on the insects

Adult fungus gnat and shore fly populations were monitored in four container nurseries near Victoria, British Columbia. In general, populations of both insects were larger in summer than in winter. Also, both insects were more abundant in the nursery with a plastic-covered, soil floor, which favored moisture accumulation and build up of algae, liverworts and mosses, than in nurseries with other types of floors such as cement. Results of fungus isolations revealed that gnats and flies both harbor the seedling pathogens Botrytis cinerea and species of Fusarium and Phoma, plus several non-pathogenic fungi. The results are discussed in relation to nursery sanitation practices, their effects on gnat and fly populations, and some possible roles of these insects in seedling disease epidemiology.     

Insecticidal activity of certain medicinal plants

The methanol extracts of eight species of medicinal plants were tested for insecticidal activity in third instar larvae of Egyptian cottonworm (Spodoptera littoralis). All extracts showed a certain degree of larval toxicity. The extracts of Ocimum basilicum, Origanum majorana and Salvia officinalis appeared to be highly toxic. The extracts significantly affected the growth indexes [relative growth rate (RGR), efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD)].     

A new norlignan from Taxodium ascendens

A new norlignan, (2R,3R,4S,5S)-2,4-bis(4-hydroxyphenyl)-3,5-dihydroxy-tetrahydropyran (1), together with 9 known compounds were isolated from the branches and leaves of Taxodium ascendens. Their structures were mainly determined on the basis of MS, IR, 1D and 2D NMR spectral evidences. Methanol extract showed inhibitory activity on carbonic anhydrase II with an IC₅₀ value of 4.27 µg/ml, acetone extract and methanol extract inhibited activity of cathepsin B with IC₅₀ values of 2.12 and 3.71 µg/ml, respectively.     

Pinus contorta growth in northern Sweden as affected by soil scarification

The aim of this study was to quantify the effects of different soil scarification methods on tree growth. Soil scarification influenced stem volume and stem biomass yield of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) in a 17-year-old field trial in boreal Sweden. Soil scarification (disc trenching, mounding and ploughing) resulted in an average stem volume yield of 3.1 and 34.2 m³ ha^–1 on the poor and intermediate sites, respectively, while corresponding values for no soil scarification were 0.9 and 16.7 m³ ha^–1. In comparison to no scarification, ploughing increased volume yields by 500% on the poor site and by 200% on the intermediate sites. The ranking according to stem volume yield was ploughing > disc trenching = mounding no soil scarification. Averaged over the two sites, the mean annual increment of stem biomass was 219% and 145% higher (in d.w., 0.26 kg and 0.34 kg per sample tree) after ploughing compared with no soil scarification, for the average and dominant sample trees, respectively. Although not significant, the increased growth rate after soil scarification decreased the average stem basic wood density of the sample trees with 1.6% and 5.3%, at the poor and intermediate sites, respectively. In conclusion, soil scarification significantly increased the 17-year stem volume yield compared with no scarification. The results also indicate that the difference in stem biomass yield between ploughing and the other methods, especially no soil scarification, will increase even more in the near future.