Responses of the root morphology and photosynthetic pigments of ryegrass to fertilizer application under combined petroleum-heavy metal stress.

With developments in industry, petroleum and heavy metal pollution are increasingly affecting soil, significantly harming the environment, biosecurity, and human health. Therefore, the remediation of contaminated soil is becoming increasingly important. In this study, ryegrass (Lolium perenne L.) was planted in petroleum-heavy metal co-contaminated soil with the application of nitrogen and phosphorus fertilizers. Three treatments were set up: uncontaminated soil + ryegrass (SH); petroleum-heavy metal co-contaminated soil + ryegrass (SPGH); and petroleum-heavy metal co-contaminated soil + ryegrass + nitrogen and phosphorus fertilizer (SPGH + NP). The results showed that the petroleum-heavy metal co-contamination promoted increases in the root length, surface area, volume, and diameter of ryegrass roots, increasing the below-ground biomass and decreasing the photosynthetic pigment content in the early stages of the experiment. The ratios of chlorophyll a/b and chlorophyll/carotenoid also increased. However, the application of fertilizer reduced the length, surface area, volume, and diameter of ryegrass roots in the co-contaminated soil, and the below-ground biomass decreased while the above-ground biomass increased. Furthermore, the photosynthetic pigment content was significantly higher than that in the unfertilized treatment and the chlorophyll a/b ratio decreased while the chlorophyll/carotenoid ratio increased. Therefore, fertilizers could alleviate the toxic effects of petroleum-heavy metal combined pollution on ryegrass roots and promote the synthesis of chlorophyll and other pigments, thus reducing the inhibitory effect of petroleum-heavy metal combined pollution on ryegrass growth and facilitating the remediation of the polluted soil.

Variation of microbial activities and communities in petroleum-contaminated soils induced by the addition of organic materials and bacterivorous nematodes.

Bacterivorous nematodes are abundant in petroleum-contaminated soils. However, the ecological functions of bacterivorous nematodes and their impacts together with the addition of organic materials on the activity and diversity of microorganisms in petroleum-contaminated soils remain unknown. To assess such effects, six treatments were established in this study, including uncontaminated nematodes-free soil (Control), petroleum-contaminated soil (PC), petroleum-contaminated soil + 5 nematodes per gram dry soil (PCN), and petroleum-contaminated soil + 5 nematodes per gram dry soil + 1% wheat straw (PCNW), or + 1% rapeseed cake (PCNR), or + 1% biochar (PCNB). Results showed that the enzyme activities in the six treatments generally increased firstly and then decreased during the incubation period. Compared with Control, the invertase activity in PCNW, PCNR, and PCNB increased by 80.6%, 313.5%, and 12.4%, respectively, whereas the urease activity in PC, PCN, PCNW, PCNR, and PCNW increased by 1.2%, 25.5%, 124.3%, 105.3%, and 25.5%, respectively. Petroleum pollution, inoculation of bacterivorous nematodes, and the addition of organic materials all significantly boosted the concentrations of phospholipid fatty acids (PLFAs) of soil bacteria, actinobacteria, and total microorganisms, and increased the concentrations of both G+ and G- bacteria PLFAs and the ratio of G-/G+. The concentration of fungi PLFAs and the ratio of fungi to bacteria were significantly higher in PCNW and PCNR than those in other treatments. Overall, adding bacterivorous nematodes and organic materials to the petroleum-contaminated soil significantly improved soil microbial activity and community structure, suggesting that bacterivorous nematodes could be used for the bioremediation in petroleum contaminated soils.

[Characteristics of phosphorus adsorption and desorption of soils from wetlands recovered from farmlands in Caizi Lake].

In this study, topsoil samples were collected from wetlands recovered from farmlands respectively for 3, 5, 9 and 11 years around Caizi Lake, Anhui, China. Their characteristics of adsorption and desorption of phosphorus were examined with comparison to soils sampled from an adjacent vegetable farmland and a non-cultivated wetland. Phosphorus adsorption curves of all studied soils could be modeled by Langmuir and Freundlich equations (P < 0.01). The maximum P adsorption (Xm), adsorption constant K and maximum buffer capacity (MBC) of all the 6 soil samples were in the ranges of 478-1074 mg x kg(-1), 0.14-0.61 and 68.6-661.5 mg x kg(-1), respectively. These three parameters all tented to increase with the recovered years but did not reach the values of the non-cultivated wetland. However, the P desorption rate ranging from 6.2% to 14.6%, increased first and then decreased with the recovered years and was significantly higher than that of the non-cultivated wetland. It was concluded that the P immobilization would increase with the recovery years of cultivated wetlands, which could be affected by the soil organic carbon and clay contents of the wetland soil.

Changes in microbial community structure and function within particle size fractions of a paddy soil under different long-term fertilization treatments from the Tai Lake region, China.

Greenhouse gas (GHG) production and emission from paddy soils impacts global climate change. Soil particle size fractions (PSFs) of different sizes act as soil microhabitats for different kinds of microbial biota with varying conditions of redox reactions and soil organic matter (SOC) substrates. It is crucial to understand the distribution of soil microbial community structure within PSFs and linkage to the GHG production from paddy soils of China. The change of bacterial and methangenic archaeal community and activity relating to CH(4) and CO(2) production with PSFs under different fertilizer applications was studied in this paper. The fertilization trial was initiated in a paddy soil from the Tai Lake region, Jiangsu, China with four treatments of non-fertilized (NF), fertilized with inorganic fertilizers only (CF), inorganic with pig manure (CFM) and inorganic with straw return (CFS), respectively since 1987, and the PSFs (<2 microm, 2-20 microm, 20-200 microm, and 200-2000 microm) were separated by a low energy sonication dispersion procedure from undisturbed samples. Analysis of bacterial community within different size particles was conducted by PCR-DGGE. The results indicated significant variation of bacterial community structure within different PSFs. The methane was predominantly produced in the coarser fractions, while more species and higher diversity of bacteria survived in the size of <2 microm fractions, in which the bacterial community structure was more significantly affected by fertilizer application practices than in the other coarser fractions. Higher bacterial species richness and more diversities in the smallest size fractions was due to the vicinity between microbes, access to carbon resource outside the microaggregates, and smaller pore size as protective agent suitable habitats for microbes rather than high SOC. Whereas, higher CO(2), CH(4) production and methanogenic archaeal community in coarser fractions may be contributed to storage of labile organic carbon in these fractions. It indicated that availability of SOC in PSFs is mainly factor affected survival of methanogenic archaeal community structure, whereas, bacterium community habitation more affected by physical protection of their location in PSFs. Their activity greatly depended on liability of SOC access to PSFs. Fertilizer application caused more change of bacteria community in clay fraction and greatly increased bacterium and methanogen activity in coarser fractions but only a slight effect on methanogenic archaeal community in the particle size fractions.

[Change of organic carbon pools and the responses to soil warming during laboratory incubations under different temperatures of 3 kinds of paddy soils in Tai Lake Region, China].

Change of soil organic carbon (SOC) storage under global warming scenarios was paid much attention of the soil and global change studies. To address the features of SOC loss of paddy soils in response to global warming, the authors used 3 representative paddy soils from the Tai Lake region, China to incubate at laboratory respectively under 20 degrees C and 25 degrees C and the change dynamics of total organic carbon(TOC), soluble organic carbon (DOC) and microbial biomass carbon (MBC) were monitored in time intervals. The TOC dynamics could be described with primary reaction equations with the constants varied with soil types and incubation temperature. While soil warming strengthened TOC loss of a Fe-leached Stagnic Anthrosol and a Gleyic Stagnic Anthrosol, no significant difference of TOC was detected in a Fe-accumulic Stagnic Anthosol under different temperature incubations. Q10 quotient, a measurement of soil SOC sensitivity to warming, of the studied soils decreased in the order: 11.1-14.1 for the Gleyic Stagnic Anthrosol < 4.4-4.6 for Fe-leached Stagnic Anthrosol < 0.63-0.73 for the Fe-accumulic Stagnic Anthosol. This indicated that paddy soils could be a group of human managed soils with sensitive response to global warming, whereas the inter-soil group difference in this sensitivity may be greater than that existing between the soils from different eco-zones. The different patterns of DOC and MBC change during the incubation of the 3 studied soils were indicative of different features of soil microbial community of the studied 3 types of paddy soils, which influenced the carbon bio-availability under different temperatures. Thus, change of SOC pools due to soil warming can be accounted for not only by nature of SOC of the soils but changes of microbial activity and even the community associated with soil properties. This study evidences that SOC loss due to soil warming is not a temperature-controlled kinetically decomposition process at least. Further studies should be dedicated on the SOC loss in relation to the interactions between SOC-soil minerals-soil micro-biota.

[Estimating of decadal accumulation rates of heavy metals in surface rice soils in the Tai Lake region of China].

Estimation of decadal accumulation of some heavy metals in surface rice soils from the Tai Lake region, southern Jiangsu Province, China was made by means of calculating the monitoring data and/or analysis data of the archived soil samples. For the last decade, the estimated annual accumulation rate for Cu or Zn, Pb and Cd was 0.3-1 mg.(kg.a)-1, 0.2-1 mg.(kg.a)-1 and 0.3-3 micrograms.(kg.a)-1 respectively, the apparent pollution loading was, therefore, respectively 0.5-1 kg.(hm2.a)-1, 0.5-1.0 kg.(hm2.a)-1, 0.5-3.0 kg.(hm2.a)-1 [symbol: see text] 0.8-10 x 10(-3) kg.(hm2.a)-1. The accumulation rate for the content of available form was shown to be greater than that of total content. The non-point source pollution marked bigger contribution to the total annual loading for the Pb and Cd than the other source pollutions, while the Cd loading was prominently higher than those reported in Europe. These results may indicate that the food safety in this region may be constrained by the soil pollution of these heavy metals at high accumulation rates.