Cadmium and zinc in plants and soil solutions from contaminated soils

In an experiment using ten heavy metal-contaminated soils from six European countries, soil solution was sampled by water displacement before and after the growth of radish. Concentrations of Cd, Zn and other elements in solution (K, Ca, Mg, Mn) generally decreased during plant growth, probably because of uptake by plants and the subsequent redistribution of ions onto soil exchange sites at lower ionic strength. Speciation analysis by a resin exchange method showed that most Cd and Zn in non-rhizosphere solutions was present as Cd2+ and Zn2+, respectively. The proportion of free ions was slightly lower in rhizosphere solutions, mainly due to an increase in dissolved organic carbon during plant growth. Solution pH increased during plant growth, although the bulk soil pH generally remained constant. Cd concentrations in leaves and tubers were more closely correlated with their total or free ionic concentrations in rhizosphere solutions (adjusted R2 0.90) than with their concentrations in soils (adj. R2 0.79). Cd concentrations in non-rhizosphere solutions were only poorly correlated with Cd concentrations in leaves and tubers. In contrast to Cd, there were no soil parameters that individually predicted Zn concentrations in leaves and tubers closely. However, multiple correlation analysis (including Zn concentrations in rhizosphere solutions and in bulk soils) closely predicted Zn concentrations in leaves and tubers (adj. R2 = 0.85 and 0.70, respectively). This suggests that the great variability among soils in the solubility of Zn affected the rate of release of Zn into solution, and thus Zn uptake. There was no such effect for Cd, for which solubility varied much less. Furthermore, the plants may have partly controlled Zn uptake, as they took up relatively less at high solution concentrations of Zn.Free ionic concentrations in soil solution did not predict concentrations of Cd or Zn in plants better than their total concentrations in solution. This suggests that with these soils, analysis of Cd and Zn speciation is of little practical importance when their bioavailability is assessed.     

Introduction. Speciation in plants and animals: pattern and process

Although approximately 150 years have passed since the publication of On the origin of species by means of natural selection, the definition of what species are and the ways in which species originate remain contentious issues in evolutionary biology. The biological species concept, which defines species as groups of interbreeding natural populations that are reproductively isolated from other such groups, continues to draw support. However, there is a growing realization that many animal and plant species can hybridize with their close relatives and exchange genes without losing their identity. On occasion, such hybridization can lead to the origin of new species. A key to understanding what species are and the ways in which they originate rests to a large extent on a detailed knowledge of the nature and genetics of factors that limit gene flow between species and the conditions under which such isolation originates. The collection of papers in this issue addresses these topics and deals as well with some specific issues of hybrid speciation and the causes of species radiations. The papers included arise from a 1-day symposium on speciation held during the Sixth Biennial Meeting of the Systematics Association at Edinburgh in August 2007. In this introduction, we provide some background to these papers and highlight some key points made. The papers make clear that highly significant advances to our understanding of animal and plant speciation are currently being made across the range of this topic.     

Nickel and rubidium uptake by whole oat plants in solution culture

Nickel and rubidium uptake by oat plants ( Avena sativa L. cv. Victory) were examined in relation to solution temperature, solution concentrations, metabolic inhibitors, anaerobic root conditions, transpiration and time. Over a 4-h period, uptake rates for both Ni²⁺ and Rb⁺ remained constant at 23°C. Decreasing temperatures to 2°C, 20 μ M concentrations of 2,4-dinitrophenol (DNP), or anaerobic root conditions decreased Ni²⁺ and Rb⁺ uptake rates by 97 to 86% in whole plants. Treatment of excised roots with 20 μ M DNP decreased Ni²⁺ uptake by 93%. Nickel and Rb⁺ uptake rates measured as a function of the external solution concentration followed a typical parabolic curve. K_m (0.012 m M ) and V_max [2.72 μmol (g dry weight)^-1 h^-1] values for Ni²⁺ were nearly 7 times lower than those for Rb⁺ [0.09 m M and 19.2 μmol (g dry weight)^-1 h^-1]. In all experiments, Ni²⁺ and Rb⁺ showed qualitatively similar uptake patterns, but Rb⁺ uptake was quantitatively more sensitive than Ni²⁺ to experimental manipulations.     

Radiotracer analysis of cadmium speciation in soil solutions using electrophoresis,dialysis, centrifugation,and ultrafiltration

Speciation of carrier-free¹⁰⁹Cd, added in cationic form to prefiltered extracts obtained by leaching forest soil samples with distilled water, was analyzed using electrophoresis, dialysis, centrifugation, and ultrafiltration. Rapid establishment of isotopic equilibrium between the added¹⁰⁹Cd and stable cadmium present in the extracts was observed. All the data obtained indicated that¹⁰⁹Cd and also stable cadmium were present in the analyzed extracts in the form of neutral or negatively charged organic complexes or small colloids. The results of electrophoresis enabled the characterization, at least semiquantitative, of the abundance and electrophoretic mobility of the forms present. The incomplete dialysis of¹⁰⁹Cd from the soil extracts through cellophane membrane against water proved the presence of organic associates with molecular weights higher than 10⁴. Dialysis against the same, but unlabeled extract was always complete, indicating the reversible (labile) nature of the organic forms of cadmium. Assessment of the stability constants of the organic forms using a simple discrete two-site model suggested that humate and/or fulvate complexes of cadmium were formed.     

Mobilization of Cu and Zn by root exudates of dicotyledonous plants in resin-buffered solutions and in soil

It has been frequently suggested that root exudates play a role in trace metal mobilization and uptake by plants, but there is little in vivo evidence. We studied root exudation of dicotyledonous plants in relation to mobilization and uptake of Cu and Zn in nutrient solutions and in a calcareous soil at varying Cu and Zn supply. Spinach (Spinacia oleracea L.) and tomato (Lycopersicon esculentum L.) were grown on resin-buffered nutrient solutions at varying free ion activities of Cu (pCu 13.0–10.4) and Zn (pZn 10.1–6.6). The Cu and Zn concentrations in the nutrient solution increased with time, except in plant-free controls, indicating that the plant roots released organic ligands that mobilized Cu and Zn from the resin. At same pCu, soluble Cu increased more at low Zn supply, as long as Zn deficiency effects on growth were small. Zinc deficiency was observed in most treatment solutions with pZn ≥ 9.3, but not in nutrient solutions of a smaller volume/plant ratio in which higher Zn concentrations were observed at same pZn. Root exudates of Zn-deficient plants showed higher specific UV absorbance (SUVA, an indicator of aromaticity and metal affinity) than those of non-deficient plants. Measurement of the metal diffusion flux with the DGT technique showed that the Cu and Zn complexes in the nutrient solutions were highly labile. Diffusive transport (through the unstirred layer surrounding the roots) of the free ion only could not explain the observed plant uptake of Cu and of Zn at low Zn²⁺ activity. The Cu and Zn uptake by the plants was well explained if it was assumed that the complexes with root exudates contributed 0.4% (Cu) or 20% (Zn) relative to the free ion. In the soil experiment, metal concentrations and organic C concentrations were larger in the solution of planted soils than in unplanted controls. The SUVA of the soil solution after plant growth was higher for unamended soils, on which the plants were Zn-deficient, than for Zn-amended soils. In conclusion, root exudates of dicotyledonous plants are able to mobilize Cu and Zn, and plants appear to respond to Zn deficiency by exuding root exudates with higher metal affinity.     

镍污染对土壤微生物的生态效应

镍是高等植物和某些微生物必需的微量营养元素之一,在它们的生命活动中起着重要作用;但浓度较高时,也是一种极毒元素。大量的研究表明,镍污染土壤中微生物的生长、代谢、群落结构和种群多样性会受到不同程度的影响;微生物在长期受重金属威迫的环境中形成其适应性。利用微生物形成的这种适应机制,采用微生物技术治理重金属污染的土壤是可能的。本文还对镍污染土壤的微生物评价指标体系、土壤环境容量、微生物技术开发和综合治理技术开发等的进一步研究作了展望。     

Studies on soil rhizosphere: speciation and availability of Cd

ABSTRACT

The rhizosphere soils of two durum wheat (Triticum turgidum var. durum L.) cultivars Kyle and Areola grown in two selected soils of southern Saskatchewan were collected both at 2-week and 7-week plant growth stages. The cadmium availability index (CAI), determined as M NH₄CI-extractable Cd, pH and the distribution of the particulate- bound Cd species of the soils were carried out and the data were discussed in comparison with those of the corresponding bulk soil. At the 2-week growth stage, the pH of the rhizosphere soil was less than that of the corresponding bulk soil and the CAI values were higher in the rhizosphere soil, indicating that more Cd was complexed with the low-molecular-weight organic acids (LMWOAs) at the soil-root interface and was extractable by M NH₄CI. Compared with the bulk soils, the CAI values were 2–9 times higher in the soil rhizosphere of the plots fertilized with Idaho monoammonium phosphate fertilizer at 2-week growth stage, which is attributed to the combined effects of the Cd introduced into the soil rhizosphere from the fertilizer (Cd content of the fertilizer was 144 mg kg^?1) and complexation reactions of phosphate and LMWOAs with soil Cd. At 7-week plant growth stage, such differences were not observed. The increased amounts of carbonate-bound and metal-organic complex-bound Cd species of the rhizosphere soils are due to the increased amounts of carbonate, a product of plant respiration, and the LMWOAs at the soil-root interface, respectively. Simple correlation analysis of the data showed that the CAI of the rhizosphere soils of the control plots correlated at least two orders of magnitude better with the metal-organic complex-bound Cd whereas the CAI of the rhizosphere soils treated with Idaho phosphate correlated better with carbonate-bound Cd species in comparison to other species.     

Fate of aluminium and nickel in soil. Evaluation through lysimeters under laboratory conditions

ABSTRACT

Nanomaterials (Nms) applications and environmental deposition are continuously increasing. Aluminum (Al) and nickel (Ni) fate in soil, both from gamma alumina-based Nms and as chloride salts were evaluted through lysimeters. After 85 days of treatment, which included irrigation and collection of eluates, the soil of each lysimeter was divided into four sections. The metal concentration was analyzed in eluates, soil samples, and extracts. Al and iron (Fe) present in soil eluted from Control lysimeter. Al from Nms suspension treatment was quantified in the eluates since 30 days on. Ni eluted upon solid salt deposition on top of one device. These results indicate that Al and Ni applied under certain conditions on soil, could leach and reach groundwater. The total concentration and bioavailability (extractable metals) of Al and Fe in soils showed similar patterns. Ni was retained only in the soil of devices treated with chloride salts. Bioavailability % results were of concern for Ni under certain conditions of treatment: 15.57% and 11.08% in two chloride salt-treated lysimeters versus 0.55% and 0.47% of those in control and treated with Nms lysimeters. Conducting studies with different kinds of soil and longer treatment periods should be useful to understand Nms-metals fate in the environment. The results presented here constitute important evidences both for significant metal release from Nms and elution and for considerable Ni bioavailability, after deposition on soil in the form of Nms or as a chloride salt, respectively. Then, possible toxic effects could occur through exposure of aquatic and terrestrial organisms.     

Transformations in soil and availability to plants of15N applied as inorganic fertilizer and legume residues

Summary A pot experiment was conducted to study the transformations of organic and inorganic N in soil and its availability to maize plants. Inorganic N was in the form of¹⁵N labelled ammonium sulphate (As) and¹⁵N labelledSesbania aculeata (Sa), a legume, was used as organic N source. Plants utilized 20% of the N applied as As; presence of Sa reduced the uptake to 14%. Only 5% of the Sa-N was taken up by the plants and As had no effect on the availability of N from Sa. Losses of N from As were found to be 40% which were reduced to 20% in presence of Sa. Losses of N were also observed from Sa which increased in the presence of As. Application of As had no effect on the availability of soil or Sa-N. However, more As-N was transported into microbial biomass and humus components in the presence of Sa.Plants derived almost equal amounts of N from different sourcesi.e., soil, Sa and As. However, more As-N was transported into the shoots whereas the major portion of nitrogen in the roots was derived from Sa.     

Cadmium availability at different soil pH to transgenic tobacco overexpressing ferritin

Knowledge on physiological mechanisms and plant metabolism can be used to enhance metal uptake. The capacity to uptake metals of transgenic tobaccos overexpressing ferritin in plastids (P6) or in cytoplasm (C5) and a control tobacco (A) is assessed in three polluted soils from the same soil series, with a similar Cd content, but displaying pH from 5.8 to 7 (8b2, 8b3, S11). Differences in dry leave weight were not significant between the three tobaccos growing on each soil. Iron concentration in ferritin overexpression either in P6 or in C5 tobaccos increased only on the S11 soil, which had a soil pH 7, in comparison to A tobacco. In both 8b2 and 8b3 soils at pH lower than 7, the leaf Fe content was not different between the three tobaccos. Only the P6 tobacco growing in the S11 soil accumulated more Cd, Zn and Mn compared with the A and C5 tobaccos. This increase represents, compared to A tobacco, 88% for Fe, 120% for Mn, 30% for Cd, 80% for Zn. In soils with a pH higher than 7, the ferritin synthesis is over-expressed in the P6 tobacco cells inducing a iron deficiency. These metal accumulations were increased, owing to a rhizosphere modification. The A and P6 tobaccos uptake Cd in the same soil pool. The Cd totality in the 8b2 soil is labile and in the S11 soil, the labile Cd represents 86–88% of the total Cd.     

Isolation and partial characterization of nickel complexes in higher plants

The essential trace element, nickel, is readily taken up by plants. The biochemical properties of the nickel complex in intrinsically labeled potato and alfalfa were compared and contrasted to ionic nickel. Potato and alfalfa exhibit a similar in vivo nickel complex. The approximate mol wt is 2200–2400 daltons. The complex has a lower polarity than thoes ionic nickel. The majority of the complex is a cationic species with a minor anionic species. This is confirmed with electrophoresis, ion exchange chromatography and the two nickel conplexes' affinity for cationic and anionic resins. Protein does not appear to be associated with either complex.     

裸燕麦EMS突变体库筛选与分析

燕麦是重要的粮饲兼用作物,构建燕麦EMS突变体库对燕麦功能基因组学研究和遗传改良有重要意义。本试验利用化学诱变剂甲基磺酸乙酯(EMS,ethyl methane sulfonate)处理燕麦品种花早2号,获得了4083株M1材料;对其中2000个单株种植了M2株行,进行全生育期调查,鉴定其表型变化;对2份黄化苗突变材料种植了M3家系,进行相关突变性状的稳定性验证。结果表明,燕麦经EMS处理后代变异巨大,在M2发现表型突变材料196份,变异率为9.8%,变异类型非常丰富,包括幼苗习性、叶片性状、分蘖、株高、穗部形态及成熟期等突变株系。M3证实突变的黄化苗特性可以稳定遗传。本研究建立了燕麦EMS诱变体系,获得的燕麦变异类型丰富,为燕麦功能基因组学研究和燕麦遗传改良奠定了材料基础。     

天然高寒草地转变为燕麦人工草地对土壤线虫群落的影响

为查明高寒草地上种植燕麦(Avena sativa)对土壤线虫群落的影响,于2014年7、9月用土钻法和湿漏斗法(Baermann法)对西南民族大学青藏高原畜牧业高科技研发示范基地内燕麦地(Oat grassland,OG)和天然草地(Natural grassland,NG)的土壤线虫群落进行调查。共分离土壤线虫10179条,隶属于2纲8目50科143属,平均密度477条/100g干土。燕麦地与天然草地土壤线虫群落结构具有明显差异,影响群落结构的主要类群为拟丽突属(Acrobeloides)、原杆属(Protorhabditis)、丝尾垫刃属(Filenchus)和盘旋属(Rotylenchus),但不同月份间存在差异。燕麦地的土壤线虫群落密度、食细菌线虫密度、食真菌线虫密度和自由生活线虫成熟度指数(MI)均显著高于天然草地(P<0.01;P<0.05;P<0.001;P<0.01),植物寄生线虫成熟度指数(PPI)则显著低于天然草地(P<0.05)。两种草地7月份的土壤线虫群落类群数和香农多样性指数(H′)均显著低于9月(P<0.05),仅燕麦地...     

Nature of nickel complexes in Psychotria douarrei and other nickel-accumulating plants

The nature of nickel complexes in various Ni accumulating plant species, mainly from New Caledonia, was investigated by techniques including gel chromatography, ion-exchange chromatography, high performance liquid chromatography, and a combination of gas-liquid chromatography and mass spectrometry. Psychotria douarrei contained Ni complexed mainly (63%) as a negatively-charged malate complex balanced by a cationic aquo complex. Phyllanthus serpentinus had anionic Ni bound as 42% citrate and 4O% malate. All other species studied, contained Ni as an anionic citrate complex.     

Relative contributions of soil chemistry, plant physiology and rhizosphere induced changes in speciation on Ni accumulation in plant shoots

The aim of this study is to rank the relative importance of soil properties, root uptake and root-to-shoot redistribution on the transfer of the trace element nickel from soil to the shoots of non hyperaccumulatings plants. Two contrasting soils and seven plant species have been studied using the radioactive isotope, ⁶³Ni. Shoots and roots were analysed separately and the specific activity of each plant has been measured. The isotopic exchange properties of rhizosphere soil where compared with control non rhizosphere soil. Possible changes in Ni speciation in the rhizosphere have been assessed by comparing the isotopic exchange properties of the rhizosphere and control soil and by comparing the specific activities of Ni in each plant. The capacity of soil to immobilise added radiotracer largely determines root uptake, leading to between a 4- and 40-fold difference between soils for a given species. The redistribution of nickel from roots to shoots was fairly constant for plants grown on the rendzina, but varied strongly between species for the acid soil. This variation enhanced the contrast between species of the soil-to-shoot transfer factor. Root action significantly enhanced immobilisation of added nickel in an acid soil due to the modification of speciation of initially non exchangeable soil nickel, but had little effect on a neutral rendzina. Changes in rhizosphere pH were similar on the two soils. In the acid soil, these pH changes were accompanied by changes in Ni speciation but a causative link has not been established. In the neutral soil pH changes may have modified root uptake properties.     

Speciation in the White-breasted Nuthatch (Sitta carolinensis): a multilocus perspective

Inferring the evolutionary and ecological processes that have shaped contemporary species distributions using the geographic distribution of gene lineages is the principal goal of phylogeographic research. Researchers in the field have recognized that inferences made from a single gene, often mitochondrial, can be informative regarding the pattern of diversification but lack conclusive information regarding the evolutionary mechanisms that led to the observed patterns. Here, we use a multilocus (20 loci) data set to explore the evolutionary history of the White‐breasted Nuthatch (Sitta carolinensis). A previous single‐locus study found S. carolinensis is comprised of four reciprocally monophyletic clades geographically restricted to the pine and oak forests of: (i) eastern North America, (ii) southern Rocky Mountain and Mexican Mountain ranges, (iii) Eastern Sierra Nevada and Northern Rocky Mountains and (iv) Pacific slope of North America. The diversification of the clades was attributed to the fragmentation of North American pine and oak woodlands in the Pliocene with subsequent divergences owing to the Pleistocene glacial cycles. Principal component, clustering and species tree analyses of the multilocus data resolved the same four groups or lineages found in the single‐locus study. Coalescent analyses and hypothesis testing of nested isolation and migration models indicate that isolation and not gene flow has been the major evolutionary mechanism responsible for shaping genetic variation, and all the divergence events within S. carolinensis have occurred in response to the Pleistocene glacial cycles.     

Nutrient composition of Douglas-fir rhizosphere and bulk soil solutions

Rhizosphere soil solution is the direct source of nutrients for plant uptake. The nutrient composition of rhizosphere soil solution can be very different from that of bulk soil solution due to root exudation, nutrient uptake and rhizosphere microorganism activity. This study examined the nutrient composition of Douglas-fir rhizosphere soil solution in two soils belonging to the Nisqually and Pitcher soil series and compared rhizosphere solution with that of bulk soil solution. Fertilized and unfertilized Nisqually soils were also compared. Soil solutions were collected using centrifugation. Results indicated that nutrient concentrations in the rhizosphere solutions were typically higher than that of bulk soil solutions when no fertilizer was applied. Differences in the concentrations of nutrients between the rhizosphere and bulk soil solutions were masked by the addition of fertilizers. Rhizosphere solution pH also appeared to be affected by the concentration of NH₄ and NO₃ in the solution. With a higher concentration of NH₄ relative to NO₃ in the rhizosphere soil solution, the solution pH of the rhizosphere was lower than that of the bulk soil, but with a lower concentration of NH₄ relative to NO₃, the solution pH of the rhizosphere was higher than that of the bulk soil solution.     

Rate of Chromosome changes and Speciation in Reptiles

The chromosome changing rate (i.e. the number of chromosome rearrangements per million years) was studied in 1329 reptile species in order to evaluate the karyological evolutionary trend and the existence of possible correlations between chromosome mutations and some aspects of the evolution of this class. The results obtained highlight the existence of a general direct correlation between chromosome changing rate and number of living species, although different trends can be observed in the different orders and suborders. In turtles, the separation of pleurodires from cryptodires was accompanied by a considerable karyological diversification. Among pleurodires, the evolution of the Chelidae and Pelomedusidae was also characterised by chromosome variation, while in cryptodires a marked karyological homogeneity is observed between and within infraorders. Similarly there is no correlation between changing rate and species number in crocodiles, where the evolution of the families and genera has entailed few chromosome mutations. Chromosome variability was greater in lizards and snakes. In the formers variations in chromosome changing rate accompanied the separation of the infraorders and the evolution of most of the families and of some genera. The origin of snakes has also been accompanied by a marked karyological diversification, while the subsequent evolution of the infraorders and families has entailed a high level of chromosome variability only in colubroids. The karyological evolution in reptiles generally entailed a progressive reduction in chromosome changing rate, albeit with differences in the diverse orders and suborders. This trend seems to be consistent with the “canalization model” as originally proposed by Bickham and Baker in [Bickham, J.W. & R J. Baker, 1979. Bull. Carnegie Mus. Nat. Hist. 13: 70–84.]  However, several inconsistencies have been found excluding that in this class the ultimate goal of chromosome variations was the achievement of a so-called ``optimum karyotype' as suggested by the above-mentioned theory. Other mechanisms could underpin chromosome variability in Reptiles. Among them a genomic composition more or less favourable to promoting chromosome rearrangements and factors favouring the fixation of a mutant karyotype in condition of homozygosis. Turtles and crocodiles would have a genome characterised by large chromosomes and a low level of chromosome compartmentalisation limiting the recombination and the frequency of rearrangements. A low rate of chromosome variability modifying little if at all the gene linkage groups would have favoured a conservative evolutionary strategy. In the course of evolution, lizards and snakes could have achieved a genome characterised by smaller chromosomes and a higher level of compartmentalisation. This would have raised the frequency of recombination and consequently an evolutionary strategy promoting a higher degree of variability and a greater level of speciation.     

Effect of soil microorganisms and labile C availability on soil respiration in response to litter inputs in forest ecosystems: A meta‐analysis

Litter inputs can influence soil respiration directly through labile C availability and, indirectly, through the activity of soil microorganisms and modifications in soil microclimate; however, their relative contributions and the magnitude of any effect remain poorly understood. We synthesized 66 recently published papers on forest ecosystems using a meta‐analysis approach to investigate the effect of litter inputs on soil respiration and the underlying mechanisms involved. Our results showed that litter inputs had a strong positive impact on soil respiration, labile C availability, and the abundance of soil microorganisms, with less of an impact related to soil moisture and temperature. Overall, soil respiration was increased by 36% and 55%, respectively, in response to natural and doubled litter inputs. The increase in soil respiration induced by litter inputs showed a tendency for coniferous forests (50.7%)> broad‐leaved forests (41.3%)> mixed forests (31.9%). This stimulation effect also depended on stand age with 30‐ to 100‐year‐old forests (53.3%) and ≥100‐year‐old forests (50.2%) both 1.5 times larger than ≤30‐year‐old forests (34.5%). Soil microbial biomass carbon and soil dissolved organic carbon increased by 21.0%‐33.6% and 60.3%‐87.7%, respectively, in response to natural and doubled litter inputs, while soil respiration increased linearly with corresponding increases in soil microbial biomass carbon and soil dissolved organic carbon. Natural and doubled litter inputs increased the total phospholipid fatty acid (PLFA) content by 6.6% and 19.7%, respectively, but decreased the fungal/bacterial PLFA ratio by 26.9% and 18.7%, respectively. Soil respiration also increased linearly with increases in total PLFA and decreased linearly with decreases in the fungal/bacterial PLFA ratio. The contribution of litter inputs to an increase in soil respiration showed a trend of total PLFA > fungal/bacterial PLFA ratio > soil dissolved organic carbon > soil microbial biomass carbon. Therefore, in addition to forest type and stand age, labile C availability and soil microorganisms are also important factors that influence soil respiration in response to litter inputs, with soil microorganisms being more important than labile C availability.     

连续施用保水材料对旱作条件下土壤特性及燕麦生长的影响

以坝莜一号为材料,研究连续4a施用保水材料聚丙烯酰胺(PAM)与聚丙烯酸钾(PAM-K),对旱作农田不同土层土壤微生物量变化与相应土层土壤含水量、容重、电导率、养分及燕麦生长的影响。结果表明,旱区农田施用PAM-K和PAM的微生态效应存在时空差异,以连续施用4a效果最佳,其大小顺序表现为连续施用4a施用3a2a1a对照。连续施用4a PAM-K和PAM,0—60 cm土层土壤含水量平均增加了27.18%和34.40%;土壤容重、土壤电导率分别平均降低了2.33%和6.64%、29.50%和22.70%;相对显著增加了耕层土壤养分(有机质、碱解氮、有效磷、速效钾)含量;土壤微生物生物量碳、氮、磷增幅平均达24.11%、31.89%、46.52%和69.96%、35.21%、52.70%,尤其是连续施用4a PAM,10—20cm土层土壤微生物量氮增幅达98.95%及0—10cm、20—40cm土层土壤微生物生物量碳和土壤微生物量磷的增加最明显,增幅分别达31.13%和74.49%、62.27%和49.91%。连续施用4a PAM-K和PAM,植株鲜重、干重、株高、籽粒产量,分别增加了90.53%和146.91%、101.56%和128.13%、33.67%和76.39%、19.27%和22.40%。可见,连续多年施用PAM-K和PAM对施入层(0—20 cm)和近施入层(20—40 cm)改善效果显著;PAM对旱区土壤的适宜性优于PAM-K,可改善土壤质量,提高作物产量。