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This study conducted a large root box experiment with Schefflera arboricola monoculture, Neolamarckia cadamba monoculture, and co-planting of Schefflera arboricola and Neolamarckia cadamba. The dynamic changes in Cu, Zn, Cd, and Hg contents in fresh and litter leaves of Schefflera arboricola and Neolamarckia cadamba and their litter leaves yield were analyzed for three months (September, October, and November 2020) after the surface application of 2% (W/W) sewage sludge (SS). The relationship between the heavy metal contents of fresh and litter leaves and the changes in the heavy metal return amount in litter leaves were further analyzed. The results were as follows: (1) N. cadamba had significantly higher Cu contents in fresh and litter leaves than those of S. arboricola, while had significantly lower Zn and Cd contents than those of S. arboricola. (2) The fresh leaves of S. arboricola had the lowest Zn content and the highest Hg content in November. (3) The fresh leaves of monoculture and co-planting Neolamarckia cadamba had the highest Zn, Cd, and Hg contents in November. (4) The Hg content in the litter leaves of co-planting of N. cadamba increased significantly with the time of SS application, while those of Cu, Zn, and Cd contents showed no significance. (5) The Cd content in fresh leaves was significantly and positively correlated with the Hg and Cd contents of litter leaves in Schefflera arboricola in both September and November. (6) The highest yield of litter leaves and the highest return amount of Cu, Zn, Cd, and Hg in S. arboricola occurred one month after SS application (September), while those in Neolamarckia cadamba occurred two months after SS application (October). In summary, the application time of SS showed a greater effect on the heavy metal contents in fresh leaves of N. cadamba and Schefflera arboricola than those in litter leaves; there was a positive correlation between the Cd content in the fresh leaves and the Cd and Hg contents in the litter leaves of S. arboricola; the heavy metal pollution risk of the litter leaves of S. arboricola and Neolamarckia cadamba was easy to occur in one month (September) and two months (October) after SS application, respectively. This study provides a reference for safe SS utilization and reasonable litter disposal in the landscape.

Co-application of sewage sludge (SS) with biochar in landscape/forestry soil is a common strategy for enhancing soil fertility and reducing the bioavailability of potential toxic elements (PTEs) derived from SS, such as Cd, Pb, Cu, Zn, and Ni. However, due to variability of biochar quality and uncertainties in responses of different plant species, whether the co-application benefits the landscape/forestry plant system remains elusive. Here, we tested the effectiveness of three types of biochar (SS-derived biochar (SB), rice straw-derived biochar (RB), and litter-derived biochar (LB)), which were added to soil amended with SS at 50% (w/w) at rates of 1.5%, 3%, and 4.5% as growth media for the landscape plant Aglaonema modestum (A. modestum). We analyzed the substrate's physicochemical properties and assessed the alleviation of phytotoxicity by biochar application. A significant increase in the fertility index of substrate was observed in all the treatments with biochar addition. The addition of biochar reduced the potential mobility of PTEs while increasing their residual fraction in media. Nonetheless, it has been found that the addition of biochar has ineffective or even negative effects on A. modestum growth (height, biomass, root length) and nutrient absorption. Importantly, the reduction in root biomass and the increased activity of root antioxidant enzymes (SOD, POD, CAT, and MDA) indicate contamination stress of biochar on the roots of A. modestum. Toxic elements of concern—namely Cu, Cd, and Pb—were not significantly higher in tissues of A. modestum saplings planted in biochar-SS-amended soil. However, elevated levels of other elements that may pose toxicity concerns, such as Ni and Zn, increased in tissues at high biochar dosages. Based on the Entropy–Weight TOPSIS method, it was further confirmed that compared to the treatment without biochar, all treatments except for 3.0% LB application resulted in poorer A. modestum comprehensive growth. Our results emphasize the need for detailed research on the response of specific plants to biochar in specific environments, including plant adaptability and the unexplored toxicity of biochar, to understand the large variations and mechanisms behind these ineffective or negative effects before the large-scale co-utilization of SS and biochar in landscape/forestry soils. [ABSTRACT FROM AUTHOR]

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 aPinus caribaeastand 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 m2plots (each pair a control and treatment) were established in the center of aP. caribaeastand 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 theP. caribaeadecreased 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. [ABSTRACT FROM PUBLISHER]

The land application of sewage sludge has the potential risk of transferring heavy metals to soil or groundwater. The agricultural reuse of sludge leachate could be a cost-effective way to decrease metal contamination. Sludge leachate collected during the phytoremediation of sludge by co-cropping withSedum alfrediiandZea mayswas used for irrigating vegetables in a field experiment. Results indicate that the concentrations of Cu, Zn, Pb, and Cd in sludge leachates complied with the National Standards for agricultural irrigation water in China. For the vegetable cropIpomoea aquatica, nutrients obtained only from the sludge leachate were not sufficient to support growth. For the second crop,Brassica parachinensis, no differences in biomass were observed between the treatment with leachate plus a half dose of inorganic fertilizer and the treatment with a full dose of inorganic fertilizers. The concentrations of heavy metals inI. aquaticaandB. parachinensiswere not significantly affected by the application of sludge leachates. Compared with initial values, there were no significant differences in Zn, Cd, Cu, and Pb concentrations in soil following treatment with sludge leachate. This study indicates that on range lands, sludge phytoremediation can be conducted at the upper level, and the generated sludge leachate can be safely and easily used in crop production at the lower level. [ABSTRACT FROM PUBLISHER]

The relationships between above-ground stem, branch, leaf masses and stand density index (SDI) were analysed in Populus × euramericana (Dode) Guinier stands in Jiangsu Province, China. The allometric equations developed in this study accurately estimated masses of above-ground and specific above-ground tree components in stands with different SDIs. The relationship between the mean above-ground mass w and the ratio of stem to the above-ground (wS/w) was examined. With increasing w, the stem mass ratio wS/w increased. Mean masses of above-ground and tree components decreased significantly with increasing SDI at age 9 years, indicating the presence of competition-induced limitations to growth. The mean above-ground mass–SDI and mean component mass–SDI were strongly correlated with above-ground mass-SDI and tree component mass–SDI, respectively. An equation describing the relationship between the mean leaf area u and SDI was developed, which fitted well for the u-SDI data. Stem mass increment exponentially increased with increasing leaf area index. [ABSTRACT FROM PUBLISHER]

The productions, seasonal dynamics, macronutrient contents and decomposition rates of the litterfalls of four typical stands, e.g., Pinus massoniana plantation, secondary evergreen broadleaved forest, Acacia mangium plantation and Schima superba-Acacia mangium plantation at the scenic Baiyunshan of Guangzhou were studied. The litterfall productions of four stands in 1998 were 8.34, 6.77, 6.31 and 11.54 t.hm-2, respectively. The seasonal dynamics of litterfall amounts demonstrated the single-peak model with the peak period in June and July. The total amounts of macronutrients returned to the forest land by means of litters in the four stands in 1998 were 26.30, 69.81, 54.9 and 152.24 kg.hm-2, respectively. The annual decomposition rates of the litterfalls were 24.4%, 53.4%, 52.4% and 57.4%.