A comparison of the application of different waste products to a lettuce crop: Effects on plant and soil properties

A romaine-type lettuce (Lactuca sativa L.) was cultivated during three successive crop seasons in an agricultural land near the Wastewater Treatment Plant (WWTP) of Alcázar de San Juan. Four fertilization treatments were compared, including: two different organic fertilizer treatments consisting of (i) air-dried sewage sludge (SS), and (ii) municipal solid waste compost (MSWC), (iii) an inorganic treatment of commercial fertilizer (FER), and (iv) a control treatment in which no fertilizer was applied (CONT). The highest yield was observed in the SS treatment in all crop seasons. In the organic treatment plots there was an increase in macronutrients and organic matter in the soil. An accumulation of heavy metals in the soil was not observed but there was an increase in microbial population in the organic treatment plot, especially in the SS treatment plot. In plant tissue, the continued addition of fertilizers did not produce an accumulative effect of macro- and micronutrients. Low heavy metal content (Cr, Cd, Pb and Hg) was observed in all treatments and crop seasons. Microbiological content was more numerous in the first crop season in SS-treated plants, mainly in lettuce leaves but also in the soil.     

Quercus ilex L. as bioaccumulator for heavy metals in urban areas: Effectiveness of leaf washing with distilled water and considerations on the trees distance from traffic

In recent years the use of plants as bioaccumulators or bioindicators has increased because enable the prediction of pollution for monitoring purposes, even in urban environments where traffic is a major source of heavy metals pollution. In this study we hypothesized holm oak (Quercus ilex L.) a valid trapping species for heavy metals. We also hypothesized that metals capture capacity by deposition on the crown is connected to the surrounding environmental characteristics and the distance of trees from the source of pollution. The study was conducted in the city of Florence. Holm oaks were selected in different sites near to heavy traffic roads. Concentrations of Zn, Pb, Cd, Cu, Fe, Mn, Cr, and Ba were analyzed through two methods: leaf washing with distilled water and leaf unwashing.One-year-old leaves (new leaves) were also compared with previous-year leaves (old leaves). Our results demonstrated the good capacity of this species to capture heavy metals (Pb, Fe, Mn, Cr, and Ba), particularly due to the presence of old leaves, which enhance the crown deposition surface. Washing was effective and it allowed testing the behaviour with regard to microelements: new leaves showed high Cu concentration, while old leaves had high Pb concentration. The dispersion of metals through the atmosphere was assessed through regression analysis, in two comparable gardens: leaves at farther distance from the traffic were richer in Zn, Pb, Mn, and Ba. The physical context of the surrounding environment was probably altering the distribution of heavy metals as barriers to dispersion, which can reach tens of metres from the source of pollution. Therefore, this work suggests that wind modelling and trees distribution and characteristics should be taken into consideration to evaluate the pollutants dispersion, especially for planning of recreational urban green areas.     

冀北坝上及坝下地区华北落叶松林土壤碳储量的比较

为了解冀北坝上坝下地区华北落叶松林土壤碳汇功能的差异,对河北省北部坝上坝下地区的华北落叶松林的土壤有机碳含量及碳密度进行了对比研究。结果表明,坝下地区华北落叶松人工林各土层土壤有机碳含量高于坝上地区,但其差异随土层深度的变化而有所不同;坝上及坝下地区18年生华北落叶松林土壤有机碳密度未表现出明显差异,分别为15.6 kg/m²和13.2 kg/m²;40年生华北落叶松林土壤有机碳密度则有显著差异,分别为21.9 kg/m²和27.9 kg/m²;坝上及坝下地区华北落叶松人工林土壤有机碳含量的垂直分布表现出不同的变化趋势,坝上地区土壤有机碳含量随土壤深度增加而下降的趋势较缓,而坝下地区下降趋势更为明显。     

Seasonal dynamics of soil nitrogen availability and phosphorus fractions under urban forest remnants of different vegetation communities in Southern China

Urban forest remnants are a useful tool to study forest response to global change with urbanization. Soil nutrient status in urban forests has not been well understood, especially under the pressure of rapid urbanization in developing countries. In this study, ion-exchange resin bags and a modified Hedley P fractionation procedure were used to measure seasonal dynamics of soil N forms (ammonium and nitrate) and P fractions (available, labile, slow, occlude and weathered mineral P) under urban forest remnants across a successional sequence and non-forest land in the city of Nanchang, Southern China. Results showed that soil N availability varied with season and vegetation community (P < 0.05). Soil P fractions showed minimal seasonal variation except available P, while their averages generally increased with forest development from non-forest land to coniferous forest to conifer-broadleaf mixed forest to evergreen broad-leaved forest. The ratios of fresh soil N forms to P fractions generally decreased with forest development, while N forms absorbed by resins to P fractions generally increased from non-forest land to coniferous forest, then decreased from conifer-broadleaf mixed forest to evergreen broad-leaved forest. It is suggested that urban older forest remnants could easily move to N saturation status and soil P enrichment, causing urban water pollution due to the accumulative effect of elevated atmospheric N deposition and exogenous P input with urbanization.