Potential Nitrification Rates of Semiarid Cropland Soils from the Central Ebro Valley,Spain

The nitrification capacity of agricultural soils has received little attention in semi arid Mediterranean environments in spite of the importance of the NO3 - in the ecosystem. In this study, a laboratory experiment was carried out to evaluate potential nitrification in six agricultural soils from semiarid Central Ebro Valley (northeastern Spain). Triplicate topsoil samples (0¨15 cm) were collected seasonally over a 2-year period. The nitrification capacity was evaluated by fresh soil incubation at 25°C and field capacity with a NH +- N source. Verhulst s equation was used to express the accumulation of NO3 - 4 - N with time. The potential nitrification rate (K max) was derived from the equation and used to quantitatively characterize the nitrification process. The K max , obtained by fitting a sigmoidal curve, allowed us to distinguish the nitrification capacity of each semiarid agricultural soil. The K max varied between seasons which indicate that time-variable soil properties (such as salinity and climate) influenced the nitriflcation rate even in an incubation experiment. On an annual average, K max for saline or highly gypsiferous soils ranged from 8.5 to 9.4 mg NO3 -N kg -1 d -1. For the rest of the soils. K max ranged from 36.3 to 43.7 mg NO3 -N kg -1 d -1. Potential nitrification rate was negatively correlated (P < 0.01) with soil salinity and positively correlated with total organic C, microbial activity, and microbial biomass. Highly gypsiferous soil showed a low K max (8.9 mg NO3 -N kg -1 soil d -1) with the lowest NO3 -N content in field samplings (7 kg NO3 3- N ha -1 as an annual average). This fact demonstrated certain inhibition of the nitrification that can be attributed to unbalanced properties in the highly gypsiferous soil.     

Influence of Dissolved Organic Carbon and Initial Moisture on Zinc Sorption by Two Arid Soils

Sorption of added zinc to irrigated soils in arid regions is an important process that may control the availability of zinc to growing plants . Two soil surface samples varying in clay , organic matter , and calcium carbonate content were selected from central and southwestern regions of Saudi Arabia and prepared in order to give different initial moisture contents ranging from air dried to 100 % of field capacity . The sorption experiment was conducted using Zn concentrations ranging from 5 to 25 mg L 1, prepared from ZnSO4 either in distilled water or in solutions containing 75 mg L 1 dissolved organic carbon (DOC). Results indicate that the amount of Zn sorbed in the presence of DOC was relatively high compared with the absence of DOC and Zn retention was strongly affected by the initial soil moisture content . Also , equilibrium Zn concentrations were quite low , while Zn retentions were high in all treatments . Data of Zn sorption were described by the Freundlich isotherm , and two linear portions were found in most cases . In the absence of DOC , retentions of added Zn were controlled by the available exchange sites and / or the precipitation of Zn as sparingly soluble forms. Zn ions in the presence of DOC were able to form soluble - Zn organic complexes that adsorb on the soil surfaces . The extent of such behavior was related to the variations in clay , organic matter , and calcium carbonate contents as well as the initial moisture of the soil . Results indicate that addition of DOC reduces the amount of extractable Zn from either soil Zn or the sorbed Zn by ammonium bicarbonate diethylenetriamine pentaacetic acid ( AB DTPA ). More than 80 % of the sorbed Zn was extracted by AB-DTPA , and the percentage of extracted / sorbed Zn decreased with the increase in sorbed Zn . The obtained results give evidence that initial moisture content and addition of DOC reduce the extractability of applied inorganic Zn by AB-DTPA extract in arid soils.     

Distribution of P Forms in Natural and Fertilized Forest Soils of the Central Western Spain: Plant Response to Superphosphate Fertilization

Soil responds dynamically to the addition of phosphates by establishing exchanges among the different reservoirs of P existing in the soil. The aim of this work was to find out the effects of surface applied fertilization with triple superphosphate at two concentrations (50 and 100 kg P ha -1 ) in soils of the Sierra de Gata mountains (Spanish Central System) on forms of soil P, the availability of P for plants, and the impact on above-ground production of the tree cover and grasses. Soil P was deter mined according to Hedley, and P availability was quantified using ion exchange membranes. The effects of P fertilization on P forms were observed mainly in the first 10 cm of the study soils; there were no significant differences at greater depths because of the high P sorption capacity of these soils. With a moderate fertilization of 50 kg P ha -1 only two of the four studied soils showed a significant increase in labile P contents and of P adsorbed by sesquioxides. An intense fertilization (100 kg P ha -1 ) had significant effects on the distribution of soil P, independently of the initial available P of soils. However, fertilization with triple superphosphate did not significantly affect the aerial production of the tree cover (except in the-rst year), whereas it did affect herbaceous production at two sites, possibly because they have a larger root mass near the soil surface.     

新疆伊犁地区野果林的群落特征及保护

新疆伊犁地区是我国野果林分布的主要地段.通过野外调查和资料收集,共获得67个野果林群落样方,分析了新疆伊犁地区野果林的群落结构及其分布特征.结果表明:野果林林下物种丰富,共记录维管束植物46科141属207种.群落分类将野果林划分为野核桃林、野苹果林、野杏林和野生樱桃李林4种类型.野杏林和野生樱桃李林的物种丰富度显著高...     

Analysis of genetic diversity in <Emphasis Type="Italic">Monilinia fructicola</Emphasis> from the Ebro Valley in Spain using ISSR and RAPD markers

The genetic diversity of Spanish and French field populations of Monilinia fructicola, a quarantine fungal pathogen in Europe, was compared with that of Californian, Uruguayan, and New Zealand M. fructicola populations using inter simple sequence repeat (ISSR) and random amplified polymorphic DNA (RAPD) markers. Unweighted pair-group method with arithmetic average (UPGMA) cluster analysis and principal component analysis (PCA) of the ISSR data set revealed that the Spanish and French M. fructicola isolates were more closely related between themselves than to the non-European isolates. The levels of genetic diversity in the Spanish and French isolates are lower than those of the non-European isolates, indicating that M. fructicola is a recently introduced pathogen. UPGMA cluster analysis and PCA of the combined ISSR + RAPD data set of the European M. fructicola populations revealed that the Spanish isolates were more closely related among themselves than with the French isolates. Analysis of molecular variance partitioned the genetic variance to among the two regions (Spain and France) (20%), among the regional populations (35%), and within the populations in each region (45%) suggesting restricted gene flow between the three European populations. The observed index of association (I_A) in each European M. fructicola populations indicates that the French and Spanish populations of M. fructicola are mainly asexually reproducing, with the Sudanell population potentially having a teleomorphic stage. The present finding of low genetic diversity in the Spanish and French M. fructicola populations is probably due to founder effects and genetic drift.     

哈密盆地土壤中锌的含量分布及锌肥效应研究

锌是维持动植物和人体正常生长发育必需的微量营养元素,它在地理环境中含量的多少与生命活力有密切联系,缺乏或过剩不仅会引起农作物的生理病害,导致产量和品质下降,同时还可以通过饲料和食物链对畜禽及人类产生不良影响,因而开展不同自然地理带和土壤类型中锌的化学地理研究具有现实和长远的意义。笔者1984至1986年对哈密盆地主要土类的微量元素锌的含量,有效态锌含量及分布进行了研究,并以春小麦、无核白葡萄为重点进行肥效试验,试图为挖掘已垦地的增产潜力,施用锌肥促进农业生产,作出锌的农业地理分区、了解环境-人-锌的关系和为改良低锌环境提供依据。     

阿尔泰山垂直地带性土壤中铁和锰的形态特征及发生学意义

阿尔泰山位于中国、蒙古和苏联的交界处,分布着较完整的垂直地带性土壤。有关阿尔泰山山地土壤的垂直分布规律,已有报道。本试验研究土壤中铁、锰的形态分布特征及垂直地带性,其结果有助于了解阿尔泰山山地土壤的发生发展过程,为合理开发利用阿尔泰山山地土壤资源的途径提供科学依据。     

宁夏中部干旱地带中药材资源利用及保护

介绍了宁夏中部干旱带的自然与社会发展状况,分析了在该地区发展药材生产及产业化开发的优势及可能对生态环境造成的影响,阐述了在该地区进行中药材种植的试验结果,对该区药材资源开发、生态环境保护、野生药材保护的措施及发展中药材生产的运作方式等提出了若干具有前瞻性的观点。     

Weed flora in the Rift Valley sugarcane plantations of Ethiopia as influenced by soil types and agronomic practises

A survey was carried out on 72 sugarcane fields in Wonji-Shoa and Methara sugarcane plantations in the Rift Valley, Ethiopia, to determine the composition and distribution of weeds and to assess the influence of soil types and crop management practises on weed species composition and distribution. A total of 180 weed taxa belonging to 40 families was recorded. Poaceae, Asteraceae, Euphorbiaceae, Fabaceae, and Malvaceae were the most abundant families based on the number of species recorded. Annuals were more common (137 taxa) than perennials (43 taxa). The most frequent and problematic weed species in the plantations, irrespective of the soil types and crop types, were Cyperus spp., Sorghum spp., Euphorbia hirta , Ipomoea cordofana , Rhynchosia malacophylla , Datura stramonium , Launaea cornuta , Portulaca oleracea , and Amaranthus spp., with a frequency of > 65%. Perennial, rhizomatous Cyperus spp. were more dominant in ratoon crops than in plant crops. A partial canonical correspondence analysis (pCCA) showed that soil types, fertilizer application, and crop cycles were the major factors influencing the species distribution in the plantations among all the variables considered in the study. The first pCCA axis structured weed species associated with light-textured soil in contrast to weeds on heavy soil. D. stramonium , Tagetes minuta , and Galinsoga parviflora were mostly associated with light-textured soil, while Xanthium strumarium , Hibiscus trionum , Vigna fischeri , and Ipomoea eriocarpa were mostly associated with heavy-textured soils. The second axis distinguished those species associated with fields receiving fertilizers versus those that were not fertilized. Rottboellia cochinchinensis and Phyllanthus tenellus were mainly associated with fertilized fields while E. hirta and L. cornuta were common on unfertilized fields.     

内蒙古阿荣旗沼泽地及其开垦与保护利用

内蒙古阿荣旗沼泽地面积为1020.8km2,但已开垦18.37%。从气候、地貌特征和生态角度介绍该旗沼泽地及其基本特征的基础上,剖析已开垦沼泽地的现状,并与1982年第二次土壤普查对比。结果表明,沼泽地的开垦对当地区域生态系统所产生的影响十分突出。针对已存在的问题,本文还提出了保护和合理利用该旗沼泽地的建议。     

Estimation of net primary productivity and its driving factors in the Ili River Valley,China

Net primary productivity(NPP), as an important variable and ecological indicator in grassland ecosystems, can reflect environmental change and the carbon budget level. The Ili River Valley is a wetland nestled in the hinterland of the Eurasian continent, which responds sensitively to the global climate change. Understanding carbon budget and their responses to climate change in the ecosystem of Ili River Valley has a significant effect on the adaptability of future climate change and sustainable development. In this study, we calculated the NPP and analyzed its spatio-temporal pattern of the Ili River Valley during the period 2000–2014 using the normalized difference vegetation index(NDVI) and an improved Carnegie-Ames-Stanford(CASA) model. Results indicate that validation showed a good performance of CASA over the study region, with an overall coefficient of determination(R2) of 0.65 and root mean square error(RMSE) of 20.86 g C/(m~2·a). Temporally, annual NPP of the Ili River Valley was 599.19 g C/(m~2·a) and showed a decreasing trend from 2000 to 2014, with an annual decrease rate of –3.51 g C/(m~2·a). However, the spatial variation was not consistent, in which 55.69% of the areas showed a decreasing tendency, 12.60% of the areas remained relatively stable and 31.71% appeared an increasing tendency. In addition, the decreasing trends in NPP were not continuous throughout the 15-year period, which was likely being caused by a shift in climate conditions. Precipitation was found to be the dominant climatic factor that controlled the inter-annual variability in NPP. Furthermore, the correlations between NPP and climate factors differed along the vertical zonal. In the medium-high altitudes of the Ili River Valley, the NPP was positively correlated to precipitation and negatively correlated to temperature and net radiation. In the low-altitude valley and high-altitude mountain areas, the NPP showed a negative correlation with precipitation and a weakly positive correlation with temperature and net radiation. The results suggested that the vegetation of the Ili River Valley degraded in recent years, and there was a more complex mechanism of local hydrothermal redistribution that controlled the growth of vegetation in this valley ecosystem.     

Occurrence and diversity of fungal pathogens associated with water hyacinth and their potential as biocontrol agents in the Rift Valley of Ethiopia

Water hyacinth poses serious socio-economic and environmental problems in Ethiopia. To integrate fungal pathogens into water hyacinth management, a survey was conducted in the Rift Valley of Ethiopia. Based on morphological characterization and DNA sequencing, 25 fungal species were identified that belong to nine genera. Alternaria tenuissima, A. alternata, Aspergillus niger, Phoma sp., Curvularia trifolii, Mucor fragilis, M. racemosus, A. fumigatus, Fusarium oxysporum, and F. equiseti were the most common fungi detected. However, their occurrence was influenced by water wave action, temperature, season, and altitude. Among the fungal pathogens, A. alternata, A. tenuissima, F. oxysporum, F. equiseti, and Neofisicoccum parvum were highly pathogenic to water hyacinth. Alternaria alternata and A. tenuissima did not cause disease symptoms on ecologically important plant species (e.g. Noug, Tef, and Coffee). Application of the fungal pathogens on water hyacinth plants also showed 11%–67%, 22%–72%, 15%–55%, and 12%–50% reduction in fresh weight, dry weight, plant height, and root length of water hyacinth, respectively. This study suggests that fungal species have the potential to control water hyacinth biologically and provides baseline data for biological control efforts in the future.     

Genetic structure and historical demography of Malus sieversii in the Yili Valley and the western mountains of the Junggar Basin,Xinjiang, China

 Malus sieversii, a wild progenitor of domesticated apple, is distributed in western Xinjiang of China, eastern part of Kazakhstan and Kyrgyzstan in Central Asia. To well understand the genetic structure and the historical demography of this important germplasm resource, we sampled 15 populations with 110 individuals of Malus sieversii from the Yili Valley and the western mountains of the Junggar Basin, Xinjiang, and sequenced two nrDNA fragments for these 110 individuals. Meanwhile, we modeled and compared species distributions under the current and the Last Glacial Maximum climatic conditions. The results showed that populations of M. sieversii from Xinjiang had low levels of genetic diversity and genetic differentiation. During the LGM period, populations of M. sieversii had lost their northern distributions in the western mountains of the Junggar Basin. M. sieversii has experienced a demographic expansion from the south of the Yili Valley to the north of the western mountains of the Junggar Basin during the warm interglacial epochs. Due to the high sensibility of M. sieversii to disturbance, we proposed more attention should be paid to the M. sieversii populations in the western mountains of the Junggar Basin.     

新疆奎屯河流域地下水资源开发引起的生态环境问题及对策

简要介绍了奎屯河流域水文地质条件及"三水"转化特征,分析了地下水资源开发利用现状,进而对不合理开发利用地下水,引发的一系列生态环境负效应,如:区域地下水位下降,植被退化,土地沙化,土地盐渍化等进行了剖析。针对存在的问题,提出了奎屯河流域地下水资源合理开发利用对策及维持地下水位的生态意义。     

额尔齐斯河土著鱼类资源衰退原因与保护措施

额尔齐斯河 (中国境内 )原有土著鱼类 2 3(亚 )种 ,随着人类活动的加剧 ,如水利设施的建设 ,过度捕捞 ,移植种类的生境侵占等 ,现已造成 3种土著鱼类消失 ,并且绝大多数土著鱼类资源衰退。本文就额尔齐斯河土著鱼类的开发与保护进行探讨。     

Hydrochemical characteristics and evolution of groundwater in the dried-up river oasis of the Tarim Basin,Central Asia

Intense human activities in arid areas have great impacts on groundwater hydrochemical cycling by causing groundwater salinization. The spatiotemporal distributions of groundwater hydrochemistry are crucial for studying groundwater salt migration, and also vital to understand hydrological and hydrogeochemical processes of groundwater in arid inland oasis areas. However, due to constraints posed by the paucity of observation data and intense human activities, these processes are not well known in the dried-up river oases of arid areas. Here, we examined spatiotemporal variations and evolution of groundwater hydrochemistry using data from 199 water samples collected in the Wei-Ku Oasis, a typical arid inland oasis in Tarim Basin of Central Asia. As findings, groundwater hydrochemistry showed a spatiotemporal dynamic, while its spatial distribution was complex. TDS and δ¹⁸O of river water in the upstream increased from west to east, whereas ion concentrations of shallow groundwater increased from northwest to southeast. Higher TDS was detected in spring for shallow groundwater and in summer for middle groundwater. Pronounced spatiotemporal heterogeneity demonstrated the impacts of geogenic, climatic, and anthropogenic conditions. For that, hydrochemical evolution of phreatic groundwater was primarily controlled by rock dominance and evaporation-crystallization process. Agricultural irrigation and drainage, land cover change, and groundwater extraction reshaped the spatiotemporal patterns of groundwater hydrochemistry. Groundwater overexploitation altered the leaking direction between the aquifers, causing the interaction between saltwater and freshwater and the deterioration of groundwater environment. These findings could provide an insight into groundwater salt migration under human activities, and hence be significant in groundwater quality management in arid inland oasis areas.     

Response of onion (Allium cepa L.) plants to fertilizers, weed competition duration, and planting times in the central Jordan Valley

The competitive ability of onion with weeds and the effects of weeds on onion crop growth and yield were investigated in three field experiments carried out in the central Jordan Valley during the 1997–1998 growing season. Fertilizer application to the onion plants in the presence of weeds significantly lowered the onion yield and reduced the bulb diameter, compared to the unfertilized, weed-infested onion crop. Weed competition and onion yield reduction increased with an increase in the fertilizer rate. All weed-free treatments with or without fertilizer gave a significantly higher onion yield than any of the fertilized, weedy plots. The highest yield of onion was obtained from the weed-free plots with a moderate application of fertilizer. Weed competition reduced the growth, bulb yield, and size of onion in the plots established from bulbs, seedlings, and seeds when compared to the relevant weed-free controls. The effect increased with competition duration and was more pronounced in direct-seeded onion than in the other two types of planting material. However, onion grown from bulbs or seedlings gave better growth, bulb weight, and number and was more competitive than the direct-seeded onion. The results showed that the minimum number of days of weed competition needed for a significant reduction in onion growth was 42 days when propagated from bulbs or seedlings and 21 days after direct-seeding. Onion grown from bulbs tolerated weed competition better and produced a higher bulb yield than that obtained from direct-seeded or transplanted onion, irrespective of the planting dates. December was found to be the best planting time for onion that was grown from bulbs and seedlings, while November was the best planting time for direct-seeded onion, provided the plots were weed-free throughout the growing season.     

Identifying water vapor sources of precipitation in forest and grassland in the north slope of the Tianshan Mountains,Central Asia

Identifying water vapor sources in the natural vegetation of the Tianshan Mountains is of significant importance for obtaining greater knowledge about the water cycle, forecasting water resource changes, and dealing with the adverse effects of climate change. In this study, we identified water vapor sources of precipitation and evaluated their effects on precipitation stable isotopes in the north slope of the Tianshan Mountains, China. By utilizing the temporal and spatial distributions of preci...     

Climate change,water resources and sustainable development in the arid and semi-arid lands of Central Asia in the past 30 years

The countries of Central Asia are collectively known as the five "-stans": Uzbekistan, Kyrgyzstan, Turkmenistan, Tajikistan and Kazakhstan. In recent times, the Central Asian region has been affected by the shrinkage of the Aral Sea, widespread desertification, soil salinization, biodiversity loss, frequent sand storms, and many other ecological disasters. This paper is a review article based upon the collection, identification and collation of previous studies of environmental changes and regional developments in Central Asia in the past 30 years. Most recent studies have reached a consensus that the temperature rise in Central Asia is occurring faster than the global average. This warming trend will not only result in a higher evaporation in the basin oases, but also to a significant retreat of glaciers in the mountainous areas. Water is the key to sustainable development in the arid and semi-arid regions in Central Asia. The uneven distribution, over consumption, and pollution of water resources in Central Asia have caused severe water supply problems, which have been affecting regional harmony and development for the past 30 years. The widespread and significant land use changes in the 1990 s could be used to improve our understanding of natural variability and human interaction in the region. There has been a positive trend of trans-border cooperation among the Central Asian countries in recent years. International attention has grown and research projects have been initiated to provide water and ecosystem protection in Central Asia. However, the agreements that have been reached might not be able to deliver practical action in time to prevent severe ecological disasters. Water management should be based on hydrographic borders and ministries should be able to make timely decisions without political intervention. Fully integrated management of water resources, land use and industrial development is essential in Central Asia. The ecological crisis should provide sufficient motivation to reach a consensus on unified water management throughout the region.