Effects of fertiliser and intercropping on cadmium uptake by maize

This study investigated the effect of fertilisation and intercropping on the uptake of cadmium (Cd) by maize plants (Zea mays L. var. Guangtian-2). Maize was intercropped with soybean, peanut, chickpea, alfalfa, adzuki bean, garden pea, amaranth, Chinese mustard, and flowering Chinese cabbage. The results showed that most legumes substantially enhanced Cd uptake by maize under different fertiliser treatments. Cd accumulation in the leaf tissues of maize was increased by garden pea to 1.5 times the amount in the control (maize alone) with PK fertiliser. Maize intercropped with garden pea absorbed 1225 μg plant^?1 Cd and transferred 925.9 μg plant^?1 Cd to above ground tissues. Adzuki bean proved as the most valuable intercrop for enhancing Cd extraction from soil by maize owing to its relatively large maize bioconcentration factor of 5.9 and large transfer factor of 0.47 in the no fertiliser treatment. The results suggest that legumes caused a greater effect than non-legumes on Cd concentration in maize under different fertilisers; application of NPK fertiliser had positive effects on Cd level in intercropped maize.     

Distribution of contaminant trace metals inadvertently provided by phosphorus fertilisers: movement,chemical fractions and mass balances in contrasting acidic soils

The frequent use of phosphorus (P) fertilisers accompanied by nitrogen and potassium sources may lead to a serious long-term environmental issue because of the presence of potentially hazardous trace metals (TM) in P fertilisers and unknown effects on the TM chemical fractions in agricultural soils. A 16-month-long column experiment was conducted to investigate the mobility and chemical forms of Cd, Cu, Cr, Ni, and Zn introduced into a Mollisol and an Andisol through surface incorporation (0–2 cm) of triple superphosphate (TSP) fertiliser. The effects of urea and potassium chloride (KCl) applications were investigated as well. After 15 cycles of 300-mm irrigation, TSP addition increased the 4 M HNO₃ extractable TM concentration in the upper (0–5 cm) section of soils. Beyond this depth, metals showed no significant mobility, with minimal leaching losses (<?1.9%, 25-cm depth). The TM chemical forms in the 0–5 cm section were significantly (p?<?0.01) affected by the soil type and fertilisers addition. Cadmium, Ni, and Zn were the elements which appeared in a larger proportion (up to 30%) in the most labile fraction (KNO₃ extractable) in fertilised soils. The impact of urea depended on the nitrification-related changes in soil pH, while fertilisation with KCl tended to increase the KNO₃ fraction of most metals probably due to K⁺ exchange reactions. Chromium remained minimally affected by the urea and KCl applications since this contaminant is strongly bound to the less labile solid phases. The low mobility of TM was governed mainly by their interaction with the solid phases rather than by their speciation at soil pH. The mass balance showed that the geochemical processes underwent in time by the P fertiliser increased the amount of TM extracted by the chemical fractionation scheme, therefore the reaction period of TSP with soil particles should be taken into account for evaluating TM availability. Long-term soil fertilisation could inadvertently contribute to an increased concentration and availability of these P fertilisers-born contaminants in the cultivated layer of acidic soils.     

Determination of the levels of selected metals in seeds,flowers and fruits of medicinal plants used for tapeworm treatment in Ethiopia

The level of accumulation of selected essential and non-essential metals, namely; Ca, Cu, Fe, Zn, Mn, Cd, Pb, and Cr have been investigated in the seeds, fruits, and flowers of some medicinal plants utilized for tapeworm treatment in Ethiopia and their respective soil samples. These include seed of Cucurbita maxima (Duba), fruit of Embelia abyssinica (Ankoko), flowers of Hagenia abyssinica (Kosso), and fruits of Rosa abyssinica (Kega) and their respective soil samples. A wet digestion procedure with a mixture of conc. HNO₃ and HClO₄ for the plant samples and a mixture of conc. HNO₃, HCl, and H₂O₂ for soil samples were used to solubilize the metals. Ca (1280–12,670?mg?kg^?1) was the predominant metal followed by Fe (104–420?mg?kg^?1), and Zn (18–185?mg?kg^?1) in all the plant materials except for Hagenia abyssinica flower from Hirna in which Mn (16–42?mg?kg^?1) followed by Fe. Among the non-essential toxic metals, Pb was not detected in Cucurbita maxima of Boji, Gedo and Hirna origins and in Rosa abyssinica of Hirna site. Similarly, Cr was not detected in Rosa abyssinica fruits of Boji and Gedo sites. The sampled soils were found to be between strongly acidic to weakly basic (pH: 4.7–7.1). In the soil samples, Ca (8528–18,900?mg?kg^?1) was the most abundant metal followed by Fe (417–912?mg?kg^?1), Zn (155–588?mg?kg^?1), Mn (54–220?mg?kg^?1), Cr (21–105. mg?kg^?1), Cu (11–58?mg?kg^?1), Pb (13–32?mg?kg^?1) and Cd (2.8–4.8?mg?kg^?1). The levels of most of the metals determined in the medicinal plants and the respective soil samples are in good agreement with those reported in the literature and the standards set for the soil by various legislative authorities.     

Evolution of egg size and fertilisation efficiency in sea stars: large eggs are not fertilised more readily than small eggs in the genus<Emphasis Type="Italic"> Patiriella</Emphasis> (Echinodermata: Asteroidea)

Fertilisation kinetics theory suggests that, when sperm are limiting, the larger eggs of broadcast-spawning marine organisms ought to be fertilised more frequently than smaller eggs, because they provide a bigger target for searching sperm. Whilst this effect has been demonstrated within species, it is not known if this pattern holds among species. We tested whether a large difference in egg size between congeneric seastars with contrasting planktotrophic and lecithotrophic modes of development results in differences in the likelihood of eggs being fertilised in sperm-limiting situations. Measurement of egg sizes and sperm swimming speeds led to the prediction that the sperm–egg collision rate constant for Patiriella calcar (420-µm-diameter egg) should be nine times greater than for P. regularis (140-µm-diameter egg). Although the eggs of P. calcar should be fertilised at greater rates in low sperm concentrations, they were not. When gametes were allowed to mix for 10 s, the hypothesis that P. calcar eggs required less sperm than P. regularis to ensure 50% of eggs were fertilised was rejected. When gametes were mixed for 5 min, P. regularis eggs were more frequently fertilised, but the difference was not statistically significant. We conclude there must be a difference between these species in the likelihood that when a sperm finds a conspecific egg it can successfully fertilise. This apparent uncoupling of egg size and likelihood of fertilisation suggests that fertilisation is not a major constraint on the evolution of egg size in these seastars.Communicated by G.F. Humphrey, Sydney     

Efficacy of rapeseed residue and eggshell waste on enzyme activity and soil quality in rice paddy

Addition of plant residue into soils improves soil physiochemical properties and its fertility. Rapeseed residue is an emerging N source to paddy soils via rice-rape double-cropping practice. The objective of this study was to evaluate the effects of rapeseed residue and eggshell waste on chemical changes and enzyme activity in the rice paddy soil. The powdered eggshells at 0, 1, 3, and 5% were applied once to 7.0 kg paddy repacked soils in each pot treated with the rapeseed residue or the conventional N, P, and K fertilisers. Eight rice seedlings (Oriza sativa L. cv. Ilmibyeo) (40 days after sowing) were transplanted to the treated each pot. The contents of total C (TC) and N (TN), and organic matter (OM) were significantly increased in soils treated with the rapeseed residue compared to the N, P, and K fertilisers. With the addition of eggshell containing ～92% CaCO₃, a considerable increase of soil pH was observed in soils treated with the rapeseed residue and the N, P, and K fertilisers, compared to the untreated soil. Activities of β-glucosidase, urease, and arylsulfatase enzymes were higher in soils treated with the rapeseed residue than soils treated with the N, P, and K fertilisers. The eggshell additions at 1, 3, and 5% into soils treated with the rapeseed residue increased enzyme activity mainly resulting from N mineralisation, whereas no change in enzyme activity was observed in the soils treated with the NPK fertiliser. The combined use of the rapeseed residue and the eggshells can be beneficial to improve soil environment.     

Fitting fertilisation kinetics models for free-spawning marine invertebrates

 To determine how fertilisation varied with sperm concentration for two species of scallop, Chlamys (Equichlamys) bifrons (Lamarck) and C. asperrima (Lamarck), we performed a simple series of sperm dilution experiments, and measured egg size and sperm swimming speeds. C. bifrons eggs were much larger (average diam=116.5 μm), and sperm swimming speeds faster (209.8 μm s⁻¹), than C. asperrima (71.2 μm, 166.0 μm s⁻¹). In both species, maximum fertilisation occurred at an ambient sperm concentration of around 100 sperm μl⁻¹; the maximum proportion of eggs fertilised was less than 0.70 in the C. bifrons experiments, but nearer 1.0 with C. asperrima. At high sperm concentrations (>100 sperm μl⁻¹), fertilisation decreased (presumably due to polyspermy) with increasing sperm concentration, but decreased more rapidly in C. bifrons than C. asperrima. A polyspermy-adjusted fertilisation kinetics model could be fitted to the experimental data, but unique parameter estimates could not be determined. Received: 7 October 1999 / Accepted: 8 July 2000     

Effects of Zn and ZnO nanoparticles and Zn2+ on soil enzyme activity and bioaccumulation of Zn in Cucumis sativus

The increased production and commercial use of nanoparticles (NPs), combined with a lack of regulation regarding their disposal, may result in the unwanted introduction of NPs to soils. In this study, the toxicity on soil enzyme activity and growth of Cucumis sativus treated with Zn or ZnO NPs was evaluated in pot soils. Specifically, C. sativus was cultivated in soils treated with Zn NPs, ZnO NPs or Zn²⁺ for eight weeks, after which the treatment effects on biomass and bioaccumulation were evaluated. In addition, the treatment effects on soil dehydrogenase, β -glucosidase and acid phosphatase were investigated. Soil enzyme activities were influenced by all treatments, with an especially large decrease in dehydrogenase activity in response to Zn²⁺ treatment. Biomass and root length also decreased in response to Zn²⁺ treatment. Finally, the Zn contents of C. sativus were much lower in the Zn NP and ZnO NP treatment groups than in the Zn²⁺ treatment group. Therefore, toxicity on soil microbial activity may have a greater influence than phytotoxicity due to immobilisation and aggregation of NPs in the soil.     

Effects of diterpenes derived from the soft coral Sinularia flexibilis on the eggs,sperm and embryos of the scleractinian corals Montipora digitata and Acropora tenuis

Sinularia flexibilis Quoy and Gaimard, 1833 is a dominant soft coral on many Indo-Pacific coral reefs, and has been found to release toxic compounds (diterpenes), which cause tissue necrosis and death in nearby scleractinian corals. This study investigates how S. flexibilis-derived diterpenes inhibit the development of Acropora tenuis Dana, 1846 and Montipora digitata Dana, 1846 eggs and larvae in vitro. Collection and experimental sites at Magnetic (146°49'E; 19°8'S) and Orpheus (146°28'E; 18°32'S) Islands, Queensland, Australia, were utilized during the spawning seasons of 1989–1992. Freshly spawned coral eggs were placed in solutions of three different terpenes, flexibilide, dihydroflexibilide and sinulariolide, at 5 and 10 ppm, before, during, and after fertilisation. The majority of eggs which were fertilised in the presence of the diterpenes lost their cellular integrity and burst just a few hours after treatment. Terpenes were not toxic to unfertilised eggs, nor to 24 h-old embryos, although sperm ceased swimming activity after 1 h of treatment. The terpenes were not fatal to the sperm because fertilisation still occurred in their presence. The ability of the soft coral-derived diterpenes to inhibit cell division suggests that they may have potential applications in cancer chemotherapy.     

Gametogenesis and larval development in Sabella spallanzanii (Polychaeta: Sabellidae) from the Mediterranean Sea

Sabella spallanzanii (Gmelin) is one of the best known and widely distributed Mediterranean polychaetes, but available data on its general biology has been inferred mostly from populations recently introduced to Australia. In the present paper, data on gametogenesis and larval development of a Mediterranean population from the Gulf of Taranto (Ionian Sea, Italy) are reported. Histological and electron microscopical analysis of gametogenesis showed that oogenesis, a long process beginning soon after spawning in February, is of extraovarian type. By contrast spermatogenesis is a very fast process lasting from September to December, when the coelomic cavity is completely packed with mature gametes and almost devoid of coelomocytes. During the period of spawning, some experiments of in vitro fertilisation were performed, always without success, while some of the collected females naturally spawned fertilised eggs (100%). Particularly interesting was the discovery of a small percentage of eggs which appeared fertilised but unspawned within the coelomic cavity of female. Investigation of the S. spallanzanii life cycle, from the naturally spawned fertilised eggs to embryonic and juvenile stages, was performed by daily microscopical observations and by SEM. Despite the presence of large eggs giving rise to a lecithotrophic larva, a long pelagic phase was observed, the longest found among Sabellidae. The larval development pattern is also described. Settlement began after about 2 weeks; metamorphosis occurred 10 d after settlement, when mucus was secreted abundantly and an external tube was formed. The long larval pelagic period and the development pattern, suggesting a high potential for dispersal, support both the introduction and invasive behaviour of the species in Australian waters. Received: 28 May 1999 / Accepted: 10 December 1999     

Functional variation of sperm morphology in sticklebacks

Some theoretical models of sperm competition make the assumption that in fish species with external fertilisation, sperm length relates positively to swimming speed at the expense of sperm longevity. Few studies have tested this assumption. We used the three-spined stickleback, Gasterosteus aculeatus L., to study functional sperm morphology. In this study, the relationship between males’ mean sperm length and fertilisation rate was investigated in vitro in a non-competitive situation. Fertilisation at different time points after sperm release was taken into account, and sperm morphology was quantified from scanning electron microscopy images. The time series of artificial fertilisations demonstrated that males which produced sperm with a longer tail fertilised faster, but their sperm had a shorter lifespan (or activity period). It was further suggested that males that produced sperm with a larger midpiece had greater fertilisation chances later on in the fertilisation process. Thus, in sticklebacks, there exists functional variation in sperm morphology, and sperm tail length is traded off against sperm longevity (or activity).     

配施的有机无机肥料氮在红壤性水稻土中的残留特征

（１５）Ｎ追踪结果显示，熟化上（Ａ）和低肥力土（Ｃ）有机、无机肥料配施的氮的残留特征均为随配施有机成分和土壤肥力水平的变化而变化．肥力制约残留水平，肥料氮总平衡影响残留率一利用率一损失率的关系；配施有机肥是造成氮残留差异的基本因素，相关分析表明，总残留主体为有机肥氮，残留率随有机肥Ｃ／Ｎ和木质素含量的增减而增减；影响无机肥氮残留的相关因素较复杂．有机氮残留量占总残留量的百分数与无视氮残留量占总残留量的百分数之比，在Ａ，Ｃ两种土壤中约为２．肥力对氮残留作用的实质是，肥料氮在低肥力土中具固持优势，而在熟化土中具矿化利用优势．肥力因素对无机氮残留的影响更显著．根据配施组合中有机成分Ｃ／Ｎ－木质素含量与氮残留／平衡特征的关系．将不同配施组合划分为三大类型。     

Copper distribution in chemical soil fractions and relationships with maize crop yield

Agricultural practices can lead to copper accumulation in soils and at high concentration it can become toxic for plants. One common toxic effect of copper on plants is a decrease of crop yield. Here, we studied 1) the crop yield of maize grown on plots of a soil intentionally enriched with copper sulphate and 2) the possible relationship between the copper concentration in chemical soil fractions and the maize crop yield. Anthropogenic copper is mainly bound to manganese oxides, to iron oxides and to the organic matter. Maize (Zea maize L.) was grown on outdoor experimental plots. The crop yield was evaluated for three development stages: the 6–10 leaf stage, the female flowering stage and the maturity stage, 2, 4 and 6 years after the soil copper enrichment. Strong crop yield reductions, proving a toxic effect of copper on maize growth were noted 2 years after the copper input at the maturity stage and 4 years after the copper input at the 6–10 leaf stage. Variations in maize crop yield are described with linear multiple regression equations including the variable copper content in soil, and other variables when needed such as soil pH, soil organic carbon level and the climatic variables, the precipitation rate and the ambient temperature. The crop yield study at the 6–10 leaf stage and at the female flowering stage does not provide significant regression equations, while the crop yield study at the maturity stage does. Request variables for the models are the total copper content or the copper bound to the organic matter and the meteorological data. Electronic Publication     

Male characteristics, sperm traits, and reproductive success in winter-spawning Celtic Sea Atlantic herring, Clupea harengus

The relationship between sperm characteristics and reproductive success was examined in male herring, Clupea harengus L. Males were categorised as being first-time or repeat spawners on the basis of their age; they were also grouped according to whether their sperm were immediately active and exhibited forward motion on contact with seawater (FM) or had little or only vibratory motion (VM). Unlike the Pacific herring C. pallasii Valencienes, Atlantic herring sperm is usually motile on contact with seawater. The age, weight and gonadosomatic index (testes mass as a percentage of somatic mass = GSI) were measured and used as characteristics for individual fish. Sperm traits measured were (1) adenosine triphosphate (ATP) concentration, (2) sperm count, (3) duration of sperm motility. Reproductive success for each male was estimated from the fertilisation rate and from the length of larvae at hatching. Fertilisation rates for all fish were generally >80%. The ATP concentration of non-activated spermatozoa was negatively correlated with fertilisation rate. Among repeat spawners, fish with higher GSIs produced larvae that were larger at hatching. Although VM sperm fertilised eggs at rates equivalent to fertilisation by FM sperm, the larvae produced by VM sperm were significantly smaller at hatching. Larval length tended to increase in parallel with the duration of sperm motility, but the relationship was not significant in these tests. The results did not indicate any age or size pattern to spawning readiness in male herring. Sperm that are not yet ready to be shed are not fully motile on contact with seawater, but are still capable of fertilising eggs that hatch successfully. There is likely to be a progression of males which come into spawning readiness within a spawning shoal; therefore it is possible that paternal influences would result in a progressive decrease in larval size over the spawning period in winter-spawning Celtic Sea herring. Received: 22 November 1997 / Accepted: 8 June 1998     

Analysis of the phenolic compounds in root exudates produced by a subalpine coniferous species as responses to experimental warming and nitrogen fertilisation

In terrestrial ecosystems, plant root exudates clearly play a crucial role in the belowground ecosystem. However, there have been few reports on root exudates from field-grown plants or mature trees in situ, especially when exposed to experimental warming. In this study, we adopted and modified a culture-based cuvette system developed especially for root exudation collection in the field to collect soluble root exudates of a subalpine coniferous species, Abies faxoniana, under experimental warming and nitrogen fertilisation treatments. We then analysed the chemical composition and relative abundance of root exudates using gas chromatography-mass spectrometry (GC-MS). The major chemical constituents of root exudates were phenols and their derivatives of all the different treatments, such as 2,6-di-tert-butyl-4-methylphenol. Experimental warming had significant effects on the relative contents of major compounds and an increase effect on the total phenolic acid compounds. By contrast, there were small significant effects of N fertilisation on root exudation and no significant effects of the warming×N fertilisation interaction. Meanwhile, warming also markedly increased soil polyphenol oxidase activity and it may be soil ecological adjustment response to changes of root exudation under global climate warming.     

Degradation characteristics of metribuzin in soils within the Nzoia River Drainage Basin,Kenya

Metribuzin, a triazinone herbicide, is heavily used within the expansive Nzoia River Drainage Basin in Kenya for the optimization of sugarcane yields. For field experiments, soils were spiked with metribuzin and amended with filter mud compost and Tithonia diversifolia leaves. Soils with history of metribuzin application (48 months) were also spiked with metribuzin but not amended with the organic materials. Degradation of metribuzin for the three variants was followed for a period of 102 days. Repeated exposure of metribuzin to soil and addition of filter mud compost to soil enhances the degradation of metribuzin with half dissipation times of 31 and 25 days. In soil amended with Tithonia diversfolia leaves, the half dissipation time was 32 days while in the control (unamended non history soil), it was 36 days. Laboratory studies showed that soil sterilization slowed the degradation of metribuzin, with a half dissipation time of 154 days. This confirmed that metribuzin was biochemically degraded in soil by an adapted community of microbes.     

Sperm economy and limitation in spiny lobsters

Sperm limitation, when female fertilisation success is constrained by the supply of sperm, is generally perceived to be an uncommon feature of reproduction in species which directly transfer gametes during copulation. Male size, previous copulations, and the balance of expected reproductive return and future mating opportunity may, however, limit the amount of sperm males transfer to females. We used laboratory experiments where mate size could be manipulated and its consequences on spermatophore size and clutch size determined, to show that in two genera of spiny lobsters (Crustacea: Palinuridae) male reproductive output limits the size of clutches brooded by females. In Panulirus argus from the Florida Keys, we show that while male size affects spermatophore area, males also vary the amount of ejaculate positively with female size. Furthermore, the area of the spermatophore has a greater influence than female size on subsequent clutch weight. In Jasus edwardsii from New Zealand, female size, male size and mate order all affect clutch weight. In both species, clutches fertilised by small males in the laboratory are significantly smaller than clutches fertilised by large males. These results suggest that to ensure they receive sufficient sperm, females should either mate several times prior to oviposition, mate as early as possible in the reproductive season, or choose large, preferably unmated males as partners and thus compete with other females for preferred males. Sperm-limited female fecundity has the potential to limit the egg production of fished populations where large males are typically rare. Received: 18 May 1998 / Received in revised form: 20 November 1998 / Accepted: 30 November 1998     

Use of Maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) for phytomanagement of Cd-contaminated soils: a critical review

Maize (Zea mays L.) has been widely adopted for phytomanagement of cadmium (Cd)-contaminated soils due to its high biomass production and Cd accumulation capacity. This paper reviewed the toxic effects of Cd and its management by maize plants. Maize could tolerate a certain level of Cd in soil while higher Cd stress can decrease seed germination, mineral nutrition, photosynthesis and growth/yields. Toxicity response of maize to Cd varies with cultivar/varieties, growth medium and stress duration/extent. Exogenous application of organic and inorganic amendments has been used for enhancing Cd tolerance of maize. The selection of Cd-tolerant maize cultivar, crop rotation, soil type, and exogenous application of microbes is a representative agronomic practice to enhance Cd tolerance in maize. Proper selection of cultivar and agronomic practices combined with amendments might be successful for the remediation of Cd-contaminated soils with maize. However, there might be the risk of food chain contamination by maize grains obtained from the Cd-contaminated soils. Thus, maize cultivation could be an option for the management of low- and medium-grade Cd-contaminated soils if grain yield is required. On the other hand, maize can be grown on Cd-polluted soils only if biomass is required for energy production purposes. Long-term field trials are required, including risks and benefit analysis for various management strategies aiming Cd phytomanagement with maize.     

Impact of litter removal on soil characteristics under a Pinus caribaea stand

ABSTRACT

Forest productivity is dependent on soil quality, which in turn is related to litter; yet there is limited understanding of the relationships between litter and soil quality. The effects of litter removal treatment on tree growth and soil properties were examined in a Pinus caribaea stand with the aim of providing an understanding of consequences of litter removal on soil patterns. This knowledge is important for planning appropriate long-term forest management. Three pairs of 30 × 30 m² plots (each pair a control and treatment) were established in the center of a P. caribaea stand in April 2002. The controls were left undisturbed with an intact litter layer, while litter was removed monthly from treated plots. The diameter and height of the P. caribaea decreased and soil quality was degraded over the experimental period in litter-removed (treated) plots. Litter removal also produced a significant increase in soil bulk density at 0–20 and 20–40 cm depths. The capillary porosity, capillary moisture capacity, and natural water content in controls at 0–20 and 20–40 cm depths were significantly greater than treated plots. The non-capillary porosity in controls at the 0–20 cm depth was also significantly higher than treated plots. The organic carbon, total nitrogen (N), total potassium (K) and alkalized N content in each layer, and available P and exchangeable K at 0–20 and 40–60 cm depths in control plots were significantly greater than litter-removed plots. The numbers of bacteria at 0–20 and 40–60 cm depths and of fungi at 20–40 and 40–60 cm depths were higher in control than treated plots. The number of actinomyces and urease, catalase, and acid phosphatase activities in controls at each depth were significantly greater than litter-removed plots.     

Characteristics of soil micro-and macro-arthropods and soil properties in Songnen Grassland of China during different periods of freeze–thaw season

ABSTRACT

Soil properties have an important influence on soil fauna in the grassland ecosystem. However, the relationship between the structural characteristics of soil fauna and properties in the grassland ecosystem in freeze–thaw season remains unclear. Hence, the feature of soil arthropods and properties in Songnen Grassland of China were investigated in fall–winter alternating (T1), completely frozen (T2) and winter–spring alternating periods (T3) during freeze–thaw season in three years. Results showed slight differences in the community composition of soil animals with Oribatida, Prostigmata and Mesostigmata as co-dominant groups in all sampling periods. The total number of individuals of soil arthropod at low temperature was low. The pH value, electrical conductivity (EC), and moisture content had the same order of T3?>?T2?>?T1. The activities of invertase and urease increased with increasing soil temperature, whereas protease activity had no relationship with soil temperature, soil moisture, EC and soil organic matter (SOM), activities of protease and urease were principal factors affecting individual abundance of soil animals. The sequence of their effect degrees was moisture content > EC > SOM > protease activity > urease activity. The changes in the quantitative characteristics of soil animals were related to soil properties. Therefore, soil properties can affect the structural characteristics of soil arthropod in the Songnen Grassland of China in the freeze–thaw season.     

The impacts of Robinia pseudoacacia litter cover and roots on soil erosion in the Loess Plateau,China

The impacts of vegetation on soil erosion are closely associated with the combined effects of above- and below-ground components. In this study, we explore the effects and contributions of Robinia pseudoacacia litter cover and roots on soil erosion. Experiment sites under natural conditions with vegetation cover, plant roots and bare ground plots were investigated for overland flow discharges of 0.5, 1.0 and 2.0?L?s^?1 and slope gradients of 8.7%, 17.6%, 26.8%, 36.4% and 46.6%. Results indicate that litter cover and roots have a significant impact on sediment reduction; soil loss was reduced by about 57% and plant roots had a greater impact on the reduction of soil erosion than litter cover. The combination of litter cover and plant roots had a significant effect on decreasing K_r, increasing τ_c and consequently strengthening soil resistance capacity to erosion. When plants and roots existed on the slopes, K_r decreased by 81% and 66%, and τ_c increased by 319% and 246%, respectively, in comparison with bare slopes. These results illustrate the importance of high-forest in controlling soil erosion by quantifying the specific contributions of litter cover and plant roots in erosion reduction in the Loess Plateau.