典型干旱荒漠绿洲区耕层土壤养分空间变异

[目的]对干旱荒漠绿洲区耕层土壤养分空间特征进行研究,为绿洲土地资源的合理开发利用,以及土壤施肥方案的科学制定提供理论依据。[方法]基于GIS与地统计学方法对新疆维吾尔自治区精河县耕层土壤养分空间变异特征及影响因素进行分析。[结果](1)研究区内有效磷的空间变异性较强(变异系数Cv为67.45%),速效钾的空间变异性最弱(Cv为40.76%)。(2)有机质、碱解氮和有效磷存在较强的空间自相关性,其空间变异主要由地形、土壤质地和土壤类型等结构性因素所引起;速效钾为中等程度的空间自相关性,其空间变异不仅受结构性因素的影响,还与随机因素(即施肥和种植结构)有关。(3)各土壤养分元素在绿洲内部具有较高含量的片状和斑块状分布,而在绿洲外缘,其含量相对较低,且呈大面积的片状分布。[结论]精河县耕层土壤养分总体呈现出有机肥含量缺乏,磷钾肥相对丰富的特点。     

Rainfall and tillage effects on soil structure after alfalfa conversion to maize on a clay loam soil in New York

Soil degradation is accelerated when perennial crops are converted to annual row crops, primarily due to increased soil disturbance from tillage. Subsequent heavy rainfall may induce soil settling, reduce macroporosity and increase hardsetting upon drying. An experiment involving plow and no-tillage and two simulated rainfall treatments (‘wet’ and ‘dry’) was conducted on Kingsbury clay loam soil in northern New York in 1992 and 1993 to study their effects on soil structure under maize (Zea mays L.) after conversion from alfalfa (Medicago sativa L.), and to evaluate the use of spectral analysis of micropenetrometer observations for studying soil aggregation. Undisturbed soil cores were collected from the row and trafficked and non-trafficked interrow positions at the 0.05 and 0.15 m depths and used for laboratory measurement of soil strength and pore system properties. These well-structured soils show a high contribution (up to 0.15 m³ m⁻³) of macropores to the total porosity of the soil. Soil strength was generally slightly higher for no-till (NT) than plow till (PT), although only significant in 1992. Soil strength in the surface layer did not change significantly with drying. Spectral density patterns did not show strong treatment effects, although distinct peaks reflect 3.0–3.5 mm stable structural units within macroaggregates. Simulated rainfall treatments and tillage treatments generally did not strongly affect measured soil properties, presumably due to stable soil structure. Structurally stable clay loam soils show little effect of tillage or settling on soil physical properties in the first years after alfalfa to maize conversion, and have good potential for long-term annual crop production if properly managed.     

华北半干旱区土壤养分和植被特征的小尺度空间异质性研究

A field experiment was conducted at Kezuohouqi County, Inner Mongolia Autonomous Region of China, which was located on the southeastern edge of the Horqin Sandy Land, to study the spatial variability of soil nutrients for a small-scale, nutrient-poor, sandy site in a semi-arid region of northern China; to investigate whether or not there were ＂islands of fertility＂ at the experimental site; and to determine the key nutrient elements that sustained ecosystem stability. Results obtained from geostatistical analysis indicated that the spatial distribution pattern of soil total nitrogen （STN） was far different from those of soil organic matter （SOM）, total phosphorus （STP）, and total potassium （STK）. Compared to SOM, STP, and STK, STN had a lower structural heterogeneity ratio and a longer range, while other elements were all similar. In addition, STN had an isotropic spatial structure, whereas the others had an anisotropic spatial structure. The spatial structure patterns of herbage species, cover, and height also differed, indicating that spatial variability was subjected to different ecological factors. Differences in the spatial variability patterns among soil nutrients and vegetation properties showed that soil nutrients for a small-scale were not the primary limiting factors that influenced herbage spatial distribution patterns. Incorporating spatial distribution patterns of tree species, namely, Pinus sylvestris var. mongolica Litv. and shrub Lespedeza bicolor Turcz. in a research plot and using fractal dimension, SOM, STP, and STK were shown to contribute to the ＂islands of fertility＂ phenomenon, however STN was not, possibly meaning that nitrogen was a key limiting element. Therefore, during restoration of similar ecosystems more attention should be given to soil nitrogen.     

Ectomycorrhizal fungi identification in single and pooled root samples: terminal restriction fragment length polymorphism (TRFLP) and morphotyping compared

We describe here the results of a study conducted to evaluate a terminal restriction fragment length polymorphism (TRFLP) approach targeting rRNA genes for determination of ectomycorrhizal (ECM) communities colonizing the roots of loblolly pine (Pinus taeda L.). Root tips separated from soil cores were classified according to morphological characteristics and DNA was then extracted from each group of morphotyped tips. Labeled primers were used to generate terminal restriction fragments (TRF) for molecular fingerprinting of root colonizing fungi and to determine how well TRFLP could be used to discriminate between ectomycorrhizal types. Morphotypes generally correlated well with specific TRFs and sequence analysis confirmed that TRFs could be used to discriminate among fungal types. Sequence analysis indicated that important ECM fungi including Russulaceae, Thelephorales, and Tricholomataceae could be fingerprinted with TRFLP. In addition, a fixed proportion of the DNA extracted from each morphotype from the same core was used in a pooling experiment used to assess whether previously identified fungal species types could be distinguished from one another within reconstructed communities. Since some morphotypes share TRFs, dual analysis of ITS1 and ITS2 was necessary for accurate fingerprinting of fungal types. Approximately, 5.0±0.3 phylotypes were detected per core with TRFLP-corrected morphotyping as compared to 4.0±0.4 phylotypes using TRFLP on pooled community samples. TRFLP made on experimental sporocarp communities suggested that reduced ECM richness with TRFLP may be partly caused by differences in the amount of DNA available for PCR and primer bias. Nonetheless, TRFLP on pooled morphotypes accounted for more than 93% of colonized root tips. The method can be used to facilitate analysis of mycorrhizal communities using root tips collected from soil cores.     

Cadmium in upland forests after vitality fertilization with wood ash—a summary of soil microbiological studies into the potential risk of cadmium release

The use of wood ash in forestry has been questioned because of the potential risk associated with its cadmium (Cd) content (1–30 mg kg^–1). In agriculture, wood ash is only allowed for use as a fertilizer when its Cd content is below 3 mg kg^–1. This restriction has not been applied to forest soils and there is a lack of knowledge about the potentially harmful effects of the Cd in wood ash on forest ecosystems. This paper summarizes our recent studies on the microbial communities of boreal coniferous forest humus exposed to Cd-containing wood ash treatment. The main objectives of our studies were to test if the Cd in wood ash has the potential to affect the humus layer microflora of coniferous upland forests and if it has the potential to enter the human food chain. These objectives were tested both in laboratory and field experiments with ash and ash spiked with Cd (in laboratory 400 or 1,000 mg Cd kg^–1 as CdO or CdCl₂; in field 400 mg Cd kg^–1 as CdO). In one study the dissolution of ash was accelerated by irrigating it with simulated acid rain (SAR). Wood ash increased humus layer pH and microbial activities (respiration or thymidine incorporation rates) and changed its microfloral community structure (Biolog, PLFA, 16S or 18S rDNA PCR-DGGE) in both laboratory and field experiments. Spiking ash with Cd induced no further changes in the above-mentioned variables compared to ash alone. The Cd added with wood ash did not become bioavailable as detected with a bacterial biosensor Bacillus subtilis BR151(pTOO24). The form and level of Cd added in the ash had no further effect on the microbiological variables studied. Irrigation of ash with SAR did not increase the amount of bioavailable Cd, although the dissolution rate of the ash was increased. The concentration of Cd in soil water and in the berries of Vaccinium uliginosum and V. vitis-idaea, and the amount of humus bioavailable Cd did not increase with applied ash or ash spiked with Cd although the ash spiked with Cd increased the amount of humus total and extractable Cd in the 4-year field study. Only the ash spiked with Cd and not the unspiked normal wood ash resulted in significantly higher Cd concentrations in the mushroom Lactarius rufus and a slight increase in the berries of Empetrum nigrum (first year only). In conclusion, the Cd in wood ash did not become bioavailable and harmful to forest soil microbes, or leach into the humus layer even when treated with simulated acid rain. It is thus safe to use wood ash as a fertilizer in forests. However, since wood ash adds Cd to the environment, it is recommended that the same sites should not be fertilized with wood ash more than once. The effects of wood ash (3 t ha^–1) on forest soil humus layer microbes are long-term, lasting at least 20 years, and probably longer if higher application dose and/or hardened ash is used.     

不同土壤层次供应水分和养分对玉米幼苗生长和吸收养分的影响

本试验模拟滴灌方法 ,在不同土壤层次进行灌水和施用氮磷养分的盆栽玉米试验 ,旨在探讨在不同土壤层次供应水分和养分对夏玉米幼苗生长、根系空间构型及玉米对养分吸收的影响。试验表明 :在土壤深层进行滴灌可以有效降低土面蒸发 ,提高水分和养分的利用效率 ,从而显著提高玉米幼苗的生长量 ;在不同层次施肥灌水 ,对玉米根系在土壤中的空间构型影响很大 ,进行深层滴灌可以极大促进根系在较深土壤中的发育 ;在不同土层施肥灌水对玉米幼苗吸收N、P、K三种养分的能力也有影响 ,深层施肥灌水提高了玉米对 3种养分的吸收量     

Effects of ground fires on understorey bird assemblages in Amazonian forests

Avifaunal responses to understorey fire disturbance and subsequent changes in habitat structure were examined within 20 burnt and unburnt forest plots of 0.25 ha (10×250 m), 10-15 months after an unprecedented understorey fire swept through the Tapajós-Arapiuns Extractive Reserve of central Brazilian Amazonia following the severe 1997-1998 El-Niño dry season. Although these surface fires in the previously undisturbed primary forest were relatively mild, they resulted in dramatic changes in forest structure consistent with those found elsewhere in Amazonia. Bird species negatively affected by these changes tended to be the least common, the most disturbance-sensitive, and habitat specialists. Considering different guilds, ant followers, dead-leaf gleaners, terrestrial gleaners, and arboreal sallying insectivores were the most negatively affected, whereas nectivores and arboreal granivores became more abundant in the burnt forest. The results highlight the severe consequences of even relatively mild surface fires in neotropical forests, and the importance of controlling haphazard frontier expansion for the conservation of susceptible species that are endemic to fire-prone regions.     

渭干河灌区土壤水盐空间变异性研究

根据直线和网格布点法布置的150个取样点的测定资料,应用经典统计分析方法．探讨了垦荒地土壤电导率和重量含水率的空间变异性,并给出了不同置信水平及精度要求下两者的合理取样数目。应用自相关和半方差分析方法进一步讨论了土壤电导率及土壤重量含水率的空间变异结构和半方差函数模型。结果表明,垦荒地土壤电导率和重量含水率的空间变异都是有结构的,土壤电导率的最大相关域为9m,土壤重量含水率的最大相关域为6．4m。两者的半方差函数可用有基台的线型模型拟合。     

Neural network ensemble residual kriging application for spatial variability of soil properties

High quality, agricultural nutrient distribution maps are necessary for precision management, but depend on initial soil sample analyses and interpolation techniques. To examine the methodologies for and explore the capability of interpolating soil properties based on neural network ensemble residual kriging, a silage field at Hayes, Northern Ireland, UK, was selected for this study with all samples being split into independent training and validation data sets. The training data set, comprised of five soil properties: soil pH, soil available P, soil available K, soil available Mg and soil available S,was modeled for spatial variability using 1) neural network ensemble residual kriging, 2) neural network ensemble and 3) kriging with their accuracies being estimated by means of the validation data sets. Ordinary kriging of the residuals provided accurate local estimates, while final estimates were produced as a sum of the artificial neural network (ANN) ensemble estimates and the ordinary kriging estimates of the residuals. Compared to kriging and neural network ensemble,the neural network ensemble residual kriging achieved better or similar accuracy for predicting and estimating contour maps. Thus, the results demonstrated that ANN ensemble residual kriging was an efficient alternative to the conventional geo-statistical models that were usually used for interpolation of a data set in the soil science area.     

北方农牧交错带农林牧业生产结构类型空间分异特征研究

利用1996—2000年统计资料的11项指标,采用典型相关分析(CCA)方法,以中国北方农牧交错带为例,对其农林牧业生产结构类型的空间分异特征进行了分析。首先,确定了以种植业比重、林业比重、牧业比重为自变量组,其余指标为因变量组;其次,利用CANOCO4.5和CANODRAW4.1软件,将研究区划分为偏农、偏林、偏牧、农牧、牧农等5种农林牧业生产结构类型;最后,结合GIS技术,分析研究区农林牧业生产结构的空间分异特征。研究结果表明,由东南向西北,5种类型分布大体为偏农型、农牧型、牧农型、偏林型和偏牧型。