Grain sorghum (Sorghum bicolor Pers.) responses to organic iron on calcareous soils

Effects of Fe-EDDHA (Sequestrene 138), Fe-polyflavonoid (Rayplex), and an experimental iron lignosulfonate on dry matter yields, Fe content, and plant chlorosis of grain sorghum were studied under controlled conditions, using a normal and an Fe-deficient soil (DTPA extract). Application rates of 20, 40, and 80 ppm Fe were employed. Dry matter yields increased due to Fe applications. The lignosulfonate (Fe-LS) produced maximum dry matter yields followed by Fe-EDDHA and the polyflavonoid (Fe-PF) material. At the 80 ppm rate Fe-EDDHA and Fe-PF produced moderate and slight toxic effects, respectively. No toxic effect was noted with the Fe-LS material. Fe-EDDHA was found to be the most effective for correcting iron chlorosis, while the other two sources were similar in this respect. Except for the Fe-LS applied to the normal soil, all other treatments increased Fe content of plant shoots. In the Fe-deficient soil, Fe application lowered the Ca, Mg, Zn, and Mn concentrations in the plants. In the case of the normal soil, concentrations of these elements increased at the 20 ppm rate and underwent no further changes with higher rates. Treatments did not influence K and P concentrations of plants.Additional index words: Micronutrients, Iron compounds.     

Effect of organic materials addition on transformation of added manganese dioxide to alkali calcareous soils

Summary A study was made of the effect of addition and incubation of two organic materials to two alkali calcareous soils on the transformation undergone by added MnO₂. It is found that decomposition of added organic materials has a solubilizing effect on soil Mn and the added MnO₂ as it resulted in a temporary marked increase in water-soluble plus exchangeable Mn. This increase was accompanied by a decrease in the easily reducible Mn suggesting that part of it is transformed to the divalent form. The intermediate decomposition products form complexes with Mn which are soluble at the pH range of alkaline soils. A great part of the added MnO₂ was recovered in the easily reducible form while it was not extracted by the Na₂-EDTA solution. However, the Na₂-EDTA extractable Mn increased appreciably upon MnO₂ and organic materials addition and incubation, suggesting that part of the added oxide is transformed to the insoluble chelated form. A new hypothesis on the Mn cycle in soils is presented. It is based on oxidation-reduction, and production and decomposition of natural chelating agents during incubation.     

Comparisons of three methods for organic and inorganic carbon in calcareous soils of northwestern china

With increasing interest in the carbon cycle on arid land, there is an urgent need to quantify both soil organic carbon (SOC) and inorganic carbon (SIC) thus to assess various methods. Here, we present a study employing three methods for determinations of SOC and SIC in the Yanqi Basin of northwest China. We use an elemental analyzer for both SOC and SIC, the Walkley-Black method for SOC, a modified pressure calcimeter method for SIC, and a simple loss-on-ignition (LOI) procedure for determinations of SOC and SIC. Our analyses show that all three approaches produce consistently low values for SOC (1-14 g kg(-1)) and high values for SIC (8-53 g kg(-1)). The Walkley-Black method provides an accurate estimate of SOC with 100% recovery for most soil samples. The pressure calcimeter method is as accurate as the elemental analysis for measuring SIC. In addition, SOC and SIC can be accurately estimated using a two-step LOI approach, i.e., (1) combustion at 375°C for 17 hours to estimate SOC, and (2) subsequent combustion at 800°C for 12 hours to estimate SIC. There are strong linear relationships for both SOC and SIC between the elemental analysis and LOI method, which demonstrates the capability of the two-step LOI technique for estimating SOC and SIC in this arid region.     

Atmospheric methane uptake by tropical montane forest soils and the contribution of organic layers

Microbial oxidation in aerobic soils is the primary biotic sink for atmospheric methane (CH₄), a powerful greenhouse gas. Although tropical forest soils are estimated to globally account for about 28% of annual soil CH₄ consumption (6.2 Tg CH₄ year^?1), limited data are available on CH₄ exchange from tropical montane forests. We present the results of an extensive study on CH₄ exchange from tropical montane forest soils along an elevation gradient (1,000, 2,000, 3,000 m) at different topographic positions (lower slope, mid-slope, ridge position) in southern Ecuador. All soils were net atmospheric CH₄ sinks, with decreasing annual uptake rates from 5.9 kg CH₄–C ha^?1 year^?1 at 1,000 m to 0.6 kg CH₄–C ha^?1 year^?1 at 3,000 m. Topography had no effect on soil atmospheric CH₄ uptake. We detected some unexpected factors controlling net methane fluxes: positive correlations between CH₄ uptake rates, mineral nitrogen content of the mineral soil and with CO₂ emissions indicated that the largest CH₄ uptake corresponded with favorable conditions for microbial activity. Furthermore, we found indications that CH₄ uptake was N limited instead of inhibited by NH₄ ⁺. Finally, we showed that in contrast to temperate regions, substantial high affinity methane oxidation occurred in the thick organic layers which can influence the CH₄ budget of these tropical montane forest soils. Inclusion of elevation as a co-variable will improve regional estimates of methane exchange in these tropical montane forests.     

Evolution of salt tolerance in Arabidopsis thaliana on siliceous soils does not confer tolerance to saline calcareous soils

Plant and Soil - Alkaline salinity constrains crop yield. Previously, we observed local adaptation of Arabidopsis thaliana to saline-siliceous soils (pH?≤?7) and to non-saline...     

土壤溶解性有机质及其表面反应性的研究进展

溶解性有机质(DOM)是土壤溶液中的一个重要的组成部分,在土壤化学和生物过程中起着十分重要的作用。虽然DOM在天然有机质中所占的比例并不高,但它将土壤中的矿物质、有机质联系在一起,并能调控环境污染物的迁移转化与归宿,因此国内外学者都很重视溶解性有机质对土壤环境中污染物环境行为影响的研究。综述了DOM的分类和分离技术,DOM的结构及其表征方法,DOM的表面反应性以及对有机污染物、重金属在土壤中吸附、迁移的影响等,并提出了有待于进一步研究的一些问题。     

Soil seed-bank composition reveals the land-use history of calcareous grasslands

We compared soil seed banks and vegetation of recent (established on abandoned arable fields) and ancient (continuously managed as pastures at least since 1830) calcareous grasslands if there is any impact of former arable field use. The study was carried out in two regions of Southern Germany with well-preserved dry grassland vegetation: the western Jurassic mountains (Kaltes Feld) and the climatically drier eastern part of Southern Germany (Kallmünz).Total number of species in the seed bank was similar in both regions, but species composition partly differed, reflecting phytogeographical differences between the regions. The total number of emerged seedlings showed a large disparity (5457 compared to 2523 seedlings/m² in Kaltes Feld and Kallmünz, respectively).Though there were differences in seed bank composition and size, we found a uniform pattern of plant traits (affiliation to phytosociological groups, Raunkiaer plant life-forms and seed longevity), which depended on the age of the grassland.The main conclusion is that seed banks in contemporary calcareous grasslands still reflect the history of former land use – in this case arable cultivation, even though it occurred a long time ago (up to 150 years). Indicators of former arable fields are germinable seeds of weeds which have persisted in the soil to the present. By contrast, weedy species are completely absent from the seed banks of ancient grasslands. Soil seed banks of recent grasslands may be of substantial conservation importance because they may store seeds of rare and endangered weed species such as Kickxia spuria, Silene noctiflora and Stachys annua, the majority of which have already gone extinct from the current vegetation of the study sites.     

Iron-phosphorus relationship in the nutrition of tomato seedlings grown on alluvial and calcareous soils

Summary In typical alluvial and calcareous soils of Egypt 5 levels of each of P and Fe were added to study their effect on the dry matter and on their uptake by tomato seedlings in greenhouse. Application of phosphorus significantly increased the dry matter yields and both P and Fe uptake by tomatoes grown on both soils. However, application of Fe had no significant effect on the dry matter and P-uptake by tomatoes grown on alluvial soil while they were significantly increased on the calcareous one.     

有机肥对石灰性土壤肥力属性的长期影响

用常规化学分析和差热分析方法研究了长期不同施肥模式下有机肥对土壤生态肥力的影响。结果表明,长期施用有机肥(厩肥、高秸处理)可显著提高土壤有机碳含量,其水散性G0复合体减少;水稳性G1、G2复合体增加,3种胶散复合体的有机碳含量提高,重组复合体中活性强的松结合态腐殖质较多。施入有机肥不仅可提高土壤有机无机复合体的总能量水平,而且也能提高复合体中松结态、稳结态、紧结态腐殖质的能态。高秸、厩肥处理的原土、重组、稳紧态复合体、紧结态复合体和3种胶散复合体焓变值较高,具有较高能态。施用有机肥的土壤全氮、全磷、重组磷及C/N比均呈提高趋势,pH值降低,其原土和重组复合体的阳离子交换量较高。     

Shifting stoichiometry: Long-term trends in stream-dissolved organic matter reveal altered C:N ratios due to history of atmospheric acid deposition

Dissolved organic carbon (DOC) and nitrogen (DON) are important energy and nutrient sources for aquatic ecosystems. In many northern temperate, freshwater systems DOC has increased in the past 50 years. Less is known about how changes in DOC may vary across latitudes, and whether changes in DON track those of DOC. Here, we present long-term DOC and DON data from 74 streams distributed across seven sites in biomes ranging from the tropics to northern boreal forests with varying histories of atmospheric acid deposition. For each stream, we examined the temporal trends of DOC and DON concentrations and DOC:DON molar ratios. While some sites displayed consistent positive or negative trends in stream DOC and DON concentrations, changes in direction or magnitude were inconsistent at regional or local scales. DON trends did not always track those of DOC, though DOC:DON ratios increased over time for ~30% of streams. Our results indicate that the dissolved organic matter (DOM) pool is experiencing fundamental changes due to the recovery from atmospheric acid deposition. Changes in DOC:DON stoichiometry point to a shifting energy-nutrient balance in many aquatic ecosystems. Sustained changes in the character of DOM can have major implications for stream metabolism, biogeochemical processes, food webs, and drinking water quality (including disinfection by-products). Understanding regional and global variation in DOC and DON concentrations is important for developing realistic models and watershed management protocols to effectively target mitigation efforts aimed at bringing DOM flux and nutrient enrichment under control.     

Laboratory measurements and simulations of ammonia volatilization from urea applied to calcareous Chinese loess soils

Ammonia volatilization is the major pathway for mineral nitrogen loss in the calcareous soils of the Chinese loess plateau, with maximum losses reaching 50% of the fertilizer-N applied. A volatilization-diffusion experiment was carried out in the laboratory using a forced-draft system and soil columns of 15.5 cm depth. Urea was surface applied at rates of 210 kg N ha^-1 to a soil with 10% CaCO₃ and a pH of 7.7. The amount of ammonia volatilized as well as the concentration profiles of ammoniacal-nitrogen and soil pH in the upper 50 mm of the soil columns after 4, 7 and 10 days were measured and subsequently modelled. The mechanistic model of Rachhpal-Singh and Nye, originally developed for neutral, non-calcareous soils, was modified to include the pH-buffering action of the soil carbonates. Model parameters were independently determined or taken from the literature. Measured and predicted cumulative NH₃ losses agreed very well in the first 10 days following fertilizer application. However, in contrast to the simulations, NH₃-volatilization was still proceeding in the experiment even after 13 days, with cumulative losses reaching 60% of the applied N. In addition to the high initial soil pH, the low bulk density and high volumetric air content of the soil columns used for the experiment proved decisive for the high rates of ammonia volatilization, provoking a strong increase in the amount of ammoniacal-N diffusing towards the soil surface as gaseous NH₃. The simulations showed that due to the high soil pH, the buffering action of the soil carbonates played a comparatively smaller role.     

Distribution of organic carbon and nitrogen in surface soils in the McMurdo Dry Valleys, Antarctica

The organic carbon and nitrogen contents of sediments in the upper 2 cm of the soils surrounding several lakes in the McMurdo Dry Valleys were measured in a relatively high-density sampling grid, in order to better understand the present-day distribution of organic matter in the ecosystem that is most readily transportable via aeolean processes. Carbon and nitrogen contents of the bulk sediments and size-differentiated sediments decreased in a series according to lake basins oriented along the Taylor Valley's main axis (Lake Fryxell > Hoare ≥ west lobe Bonney ≥ east lobe Bonney). Samples were also obtained around Lake Vida and showed this basin to contain less organic matter than those in the Taylor Valley. This regional spatial analysis supports the emerging view that each basin provides distinct environments for in situ microbial activity, lithogenic weathering, aeolian deposition and sorting that can be detected through synoptic sampling. Accepted: 2 August 1999     

Effects of forest management on soil N cycling in beech forests stocking on calcareous soils

The effects of forest management (thinning) on gross and net N conversion, the balance of inorganic N production and consumption, inorganic N concentrations and on soil microbial biomass in the Ah layer were studied in situ during eight intensive field measuring campaigns in the years 2002–2004 at three beech (Fagus sylvatica L.) forest sites. At all sites adjacent thinning plots (“T”) and untreated control plots (“C”) were established. Since the sites are characterized either by cool-moist microclimate (NE site and NW site) or by warm-dry microclimate (SW site) and thinning took place in the year 1999 at the NE and SW sites and in the year 2003 at the NW site the experimental design allowed to evaluate (1) short-term effects (years 1–2) of thinning at the NW site and (2) medium-term effects (years 4–6) of thinning under different microclimate at the SW and NE site. Microbial biomass N was consistently higher at the thinning plots of all sites during most of the field campaigns and was overall significantly higher at the SWT and NWT plots as compared to the corresponding untreated control plots. The size of the microbial biomass N pool was found to correlate positively with both gross ammonification and gross nitrification as well as with extractable soil NO₃⁻ concentrations. At the SW site neither gross ammonification, gross nitrification, gross ammonium (NH₄⁺) immobilization and gross nitrate (NO₃⁻) immobilization nor net ammonification, net nitrification and extractable NH₄⁺ and NO₃⁻ contents were significantly different between control and thinning plot. At the NET plot lower gross ammonification and gross NH₄⁺ immobilization in conjunction with constant nitrification rates coincided with higher net nitrification and significantly higher extractable NO₃⁻ concentrations. Thus, the medium-term effects of thinning varied with different microclimate. The most striking thinning effects were found at the newly thinned NW site, where gross ammonification and gross NH₄⁺ immobilization were dramatically higher immediately after thinning. However, they subsequently tended to decrease in favor of gross nitrification, which was significantly higher at the NWT plot as compared to␣the␣NWC plot during all field campaigns after␣thinning except for April 2004. This increase␣in␣gross nitrification at the NWT plot (1.73 mg N kg⁻¹ sdw day⁻¹ versus 0.48 mg N kg⁻¹ sdw day⁻¹ at the NWC plot) coincided with significantly higher extractable NO₃⁻ concentrations (4.59 mg N kg⁻¹ sdw at the NWT plot versus 0.96 mg N kg⁻¹ sdw at the NWC plot). Pronounced differences in relative N retention (the ratio of gross NH₄⁺ immobilization + gross NO₃⁻ immobilization to gross ammonification + gross nitrification) were found across the six research plots investigated and could be positively correlated to the soil C/N ratio (R = 0.94; p = 0.005). In sum, the results obtained in this study show that (1) thinning can lead to a shift in the balance of microbial inorganic N production and consumption causing a clear decrease in the N retention capacity in the monitored forest soils especially in the first two years after thinning, (2)␣the resistance of the investigated forest ecosystems to disturbances of N cycling by thinning may vary with different soil C contents and C/N ratios, e. g. caused by differences in microclimate, (3) thinning effects tend to decline with the growth of understorey vegetation in the years 4–6 after thinning.     

Involvement of surface polysaccharides in the organic acid resistance of Shiga Toxin-producing Escherichia coli O157:H7

In general, wild Escherichia coli strains can grow effectively under moderately acidic organic acid-rich conditions. We found that the Shiga Toxin-producing E. coli (STEC) O157:H7 NGY9 grows more quickly than a K-12 strain in Luria-Bertani (LB)-2-morpholinoethanesulphonic acid (MES) broth supplemented with acetic acid (pH 5.4). Hypothesizing that the resistance of STEC O157:H7 to acetic acid is as a result of a mechanism(s) other than those known, we screened for STEC mutants sensitive to acetic acid. NGY9 was subjected to mini-Tn5 mutagenesis and, from 50,000 colonies, five mutants that showed a clear acetic acid-sensitive phenotype were isolated. The insertion of mini-Tn5 in three mutants occurred at the fcl, wecA (rfe) and wecB (rffE) genes and caused loss of surface O-polysaccharide, loss of both O-polysaccharide and enterobacterial common antigen (ECA) and loss of ECA respectively. The other two mutants showed inactivation of the waaG (rfaG) gene but at different positions that caused a deep rough mutant with loss of the outer core oligosaccharide of lipopolysaccharide (LPS) as well as phenotypic loss of O-polysaccharide and ECA. With the introduction of plasmids carrying the fcl, wecA, wecB and waaG genes, respectively, all mutants were complemented in their production of O-polysaccharide and ECA, and normal growth was restored in organic acid-rich culture conditions. We also found that the growth of Salmonella LPS mutants Ra, Rb1, Rc, Rd1, Rd2 and Re was suppressed in the presence of acetic acid compared with that of the parents. These results suggest that the full expression of LPS (including O-polysaccharide) and ECA is indispensable to the resistance against acetic acid and other short chain fatty acids in STEC O157:H7 and Salmonella. To the best of our knowledge, this is a newly identified physiological role for O-polysaccharide and ECA as well as an acid resistance mechanism.     

Deep soil inventories reveal that impacts of cover crops and compost on soil carbon sequestration differ in surface and subsurface soils

Increasing soil organic carbon (SOC) via organic inputs is a key strategy for increasing long‐term soil C storage and improving the climate change mitigation and adaptation potential of agricultural systems. A long‐term trial in California's Mediterranean climate revealed impacts of management on SOC in maize‐tomato and wheat–fallow cropping systems. SOC was measured at the initiation of the experiment and at year 19, at five depth increments down to 2 m, taking into account changes in bulk density. Across the entire 2 m profile, SOC in the wheat–fallow systems did not change with the addition of N fertilizer, winter cover crops (WCC), or irrigation alone and decreased by 5.6% with no inputs. There was some evidence of soil C gains at depth with both N fertilizer and irrigation, though high variation precluded detection of significant changes. In maize?tomato rotations, SOC increased by 12.6% (21.8 Mg C/ha) with both WCC and composted poultry manure inputs, across the 2 m profile. The addition of WCC to a conventionally managed system increased SOC stocks by 3.5% (1.44 Mg C/ha) in the 0–30 cm layer, but decreased by 10.8% (14.86 Mg C/ha) in the 30–200 cm layer, resulting in overall losses of 13.4 Mg C/ha. If we only measured soil C in the top 30 cm, we would have assumed an increase in total soil C increased with WCC alone, whereas in reality significant losses in SOC occurred when considering the 2 m soil profile. Ignoring the subsoil carbon dynamics in deeper layers of soil fails to recognize potential opportunities for soil C sequestration, and may lead to false conclusions about the impact of management practices on C sequestration.     

Effect of high rates of sulphur on the CaCO3 and CaSO4 content of calcareous soils

Samples of two calcareous soils from central Iraq were amended with 2, 6 and 10 mg g⁻¹ soil of agriculturegrade sulphur and incubated for 4, 8 and 12 weeks at 30°C and 70% water-holding capacity. At the end of each incubation period, soils were analyzed for sulphate, CaCO₃ and CaSO₄. The sulphate content of the soils increased, whereas the CaCO₃ content decreased, with increasing S levels and incubation time. The gypsum formed was in proportion to the sulphur oxidised and the calcium released from CaCO₃.     

Return to Beringia: parasites reveal cryptic biogeographic history of North American pikas

Traditional concepts of the Bering Land Bridge as a zone of predominantly eastward expansion from Eurasia and a staging area for subsequent colonization of lower latitudes in North America led to early inferences regarding biogeographic histories of North American faunas, many of which remain untested. Here we apply a host-parasite comparative phylogeographical (HPCP) approach to evaluate one such history, by testing competing biogeographic hypotheses for five lineages of host-specific parasites shared by the collared pika (Ochotona collaris) and American pika (Ochotona princeps) of North America. We determine whether the southern host species (O. princeps) was descended from a northern ancestor or vice versa. Three parasite phylogenies revealed patterns consistent with the hypothesis of a southern origin, which is corroborated by four additional parasite lineages restricted to O. princeps. This finding reverses the traditional narrative for the origins of North American pikas and highlights the role of dispersal from temperate North America into Beringia in structuring northern diversity considerably prior to the Holocene. By evaluating multiple parasite lineages simultaneously, the study demonstrates the power of HPCP for resolving complex biogeographic histories that are not revealed by characteristics of the host alone.