高山栎天然林土壤有机质及酶活性的通径分析

为探究高山栎天然林土壤生物学特性对土壤养分的影响,运用通径分析法,研究了云南省玉溪市磨盘山国家森林公园内的高山栎天然林土壤养分与土壤酶活性、微生物数量之间的关系。结果表明,土壤脲酶、过氧化氢酶、转化酶活性及细菌、放线菌、真菌、微生物总数量都是随着土层深度增加逐渐减小;影响土壤p H值的重要因素是脲酶、过氧化氢酶、转化酶活性与真菌数量;影响有机质、全氮、速效磷的重要因素是脲酶、过氧化氢酶、转化酶;影响土壤碱解氮的主要因子是脲酶、过氧化氢酶、真菌数量。总的来说,高山栎天然林土壤养分受土壤酶活性影响较大,受微生物数量影响较小。     

郑州市公园绿地表层土壤酶活性与土壤理化性质的关系

以郑州市6个公园绿地为研究对象,采集0～20 cm土层的108份土壤样品,测定其理化性质和土壤酶活性,并对其土壤酶活性及其与土壤理化性质进行相关性分析。结果表明,碧沙岗公园尿酶活性及磷酸酶活性最强,滨河公园过氧化氢酶活性最强,郑州绿博园多酚氧化酶活性最强;尿酶与速效钾呈正相关关系,与过氧化物酶呈负相关关系;过氧化氢酶与非毛管孔隙度、磷酸酶呈正相关关系,与速效磷、多酚氧化酶呈负相关关系;磷酸酶及蔗糖酶与土壤容重呈负相关关系,与非毛管孔隙度呈正相关关系;磷酸酶、蔗糖酶与水解性氮、阳离子交换量、有机质含量呈正相关关系;蔗糖酶与非毛管孔隙度呈正相关关系;多酚氧化酶与理化性质不相关。根据研究结果判断,土壤酶活性可以作为土壤肥力评价指标。     

乙酸乙酯萃取－高效液相色谱法测定水中阿特拉津

针对GB／T5750．9—2006监测方法所用萃取剂——二氯甲烷属于中等毒性污染物,通过对几种低毒有机溶剂的筛选,获得低毒性的乙酸乙酯作为替代萃取剂,并建立以乙酸乙酯萃取阿特拉津——高效液相色谱分析的新方法。比较用二氯甲烷、正辛烷、正己烷和乙酸乙酯4种有机溶剂进行萃取时对测定水中阿特拉津的影响。该方法对水中阿特拉津的检测限为0,0002mg／L,加标回收率范围84．5％～104．3％,标准偏差（SD）9．8μg／L,相对标准偏差（RSD％）5．2％。实验结果表明,该方法具有安全快速灵敏等特点,可用于水环境中阿特拉津的痕量检测。     

森林土壤化学性质与土壤酶活性典型相关分析

通过对岷江上游连香树、马尾松、桦树、云杉4类森林土壤土壤酶活性和土壤化学性质的研究,运用典范相关分析,证实过氧化氢酶与土壤有机碳的转化关系密切,土壤脲酶与土壤全N关系密切.     

森林土壤化学性质与土壤酶活性典型相关分析

通过对岷江上游四种(连香树、马尾松、桦树、云杉)森林土壤酶活性和土壤化学性质的研究,运用典范相关分析了土壤酶活性和土壤化学性质这两组典型变量之间的关系,结果表明:过氧化氢酶与土壤有机碳的转化关系密切,土壤脲酶与土壤全N关系密切,为维护地力提高森林生产力提供有关土壤生物化学活性方面的科学依据。     

森林土壤化学性质与土壤酶活性典型相关分析

通过对岷江上游4种(连香树、马尾松、桦树、云杉)森林土壤土壤酶活性和土壤化学性质的研究,运用典范相关分析了土壤酶活性和土壤化学性质这两组典型变量之间的关系。结果表明:过氧化氢酶与土壤有机碳的转化关系密切,土壤脲酶与土壤全N关系密切,为维护地力提高森林生产力提供了有关土壤生物化学活性方面的科学依据。     

代森锰锌对土壤酶活性的影响探讨

通过实验室模拟培养试验,研究了0、0.15、1.5、5mg＆#8226;kg-1的代森锰锌对济南（褐土）、菏泽（潮土）、烟台（棕壤）不同地区土壤脲酶、过氧化氢酶活性的影响。结果表明,不同浓度代森锰锌对土壤酶活性的影响有显著差异。0.15mg＆#8226;kg-1低浓度代森锰锌可以激活土壤中脲酶和过氧化氢酶的活性,而1.5、5mg＆#8226;kg-1高浓度代森锰锌对脲酶和过氧化氢酶有抑制作用,并且浓度越高,抑制作用越大;但在培养后期代森锰锌影响作用逐渐减弱,28d时基本恢复到对照水平。     

北京低山灌木林土壤氧化氢酶热力学特征的研究

本文对北京低山灌木林土壤过氧化氢酶热力学特征的研究结果表明：不同层次土壤过氧化氢酶在形成络合物时，要发生较大的应变和扭曲；土壤的活化熵为负值，表明活化络合物形成时，体系的有序性增加；各层土壤的活化自由能差异不大。     

桉树人工林地土壤酶活性与营养元素含量关系研究

运用典范相关分析 (canonicalcorrelationanalysis)对桉树人工林地土壤酶活性和土壤营养元素含量关系的研究表明 ,土壤过氧化氢酶、脲酶和蛋白酶活性与营养元素全P和全N含量关系最大 ,即正效应较大 ,它们对N、P的转化具有重要作用。转化酶活性在一定程度上对土壤养分K、P和Mg含量有一定的负相关作用。“综合土壤酶因子”可作为土壤肥力评价的一个指标     

滨海盐碱地枣园土壤酶活性与土壤养分、微生物的关系

对垦利县黄河口镇枣园的土壤酶活性进行研究。结果表明：随土层深度的增加，土壤酶活性下降。脲酶与过氧化物酶、过氧化氢酶极显著正相关，相关系数分别为0．996、0．943；脲酶与多酚氧化酶相关性不大，相关系数为0．377；过氧化氢酶与过氧化物酶呈显著正相关，相关系数为0．911；多酚氧化酶与其他3种酶的相关性不大。土壤酶与土壤养分、pH值、土壤微生物有较强的相关性，其中脲酶与土壤养分、pH值和固氮菌、真菌、细菌的相关性显著，相关系数在0．444以上；多酚氧化酶与土壤养分和微生物的相关系数较小；过氧化物酶和过氧化氢酶与土壤养分、pH值、纤维素分解菌和真菌的相关性显著，相关系数在0．451以上。     

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.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

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.     

Biogeochemical impacts of clearfelling and reforestation on blanket-peatland streams: II. major ions and dissolved organic carbon

Streams and drains in blanket-peatland forest in western Ireland were sampled weekly over 5 years, 1996–2000, using continuous, depth-proportional passive sampling. Analysis was for pH, alkalinity by Gran titration, anions by IC, metals by ICP, aluminium speciation by loaded-resin exchange, and dissolved organic carbon (DOC) by absorbance at 320 nm.

Effects of felling are identified graphically from two forest drains whose catchments (both about 1 ha) were clearfelled, and partial clearfelling of one larger catchment (somewhat over 1 km²), in summer 1999. Calcium concentrations and alkalinity were increased in the drain- and streamwater from the felled areas. The pH was increased in drains, while in the larger stream, pH range decreased while the mean increased. Phosphorus increased markedly with clearfell, in the absence of recent fertilising, and also increased with fertilising; these results are reported in an accompanying paper. Ammonium-nitrogen concentrations were increased in the two drains with felling, and temporarily decreased in the larger stream. Nitrate increased in some cases. Potassium and manganese concentrations also increased. Concentrations of DOC and organic monomeric aluminium increased gradually, subject to a continuing strong annual cycle. There were no clearfelling effects on concentrations of solphate, suspended solids or inorganic monomeric aluminium. In the two drains (fully clearfelled), concentrations of sodium, chloride and magnesium, and conductivity, were all reduced after felling. Fertilising effects other than for phosphorus were indistinct.

Effects of the combined clearfell–reforestation treatment were testable statistically, using randomised intervention analysis, between two larger streams (1 km²) as a treatment–control comparison. There were statistically significant positive responses in streamwater concentrations of nitrate, potassium, calcium, DOC and aluminium fractions. The implications for management practice depend on whether the loss of nutrients is sustainable for future crop productivity, and whether critical limits and loads of receiving ecosystems are exceeded.     

Effect of Drought on Growth and Mortality of Actively Growing Norway Spruce Container Seedlings Planted in Summer

Survival, root egress and height growth of 13-month-old actively growing Norway spruce ( Picea abies (L.) Karst.) container seedlings exposed to preplanting drying treatments (0, 4, and 8 days) and postplanting drought periods (1, 2, 3, and 4 weeks) were studied in the field between 5 July and 18 August 1999. The mortality of seedlings increased and the height growth and root egress decreased throughout the postplanting drought period. Postplanting performance was also affected by preplanting drying treatments. The results indicate that no risk of excessive mortality and growth restrictions occurs when actively growing seedlings are planted in summer, provided that seedlings are well watered before planting and the drought period does not exceed 3 weeks.     

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.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Defoliation by the Needle-shortening Pine Gall Midge,Thecodiplosis brachyntera,on Pines in Central Sweden

An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation.