Spatial distribution pattern and correlation of dominant populations in the shrub layer of Fengshui forest in Leizhou Peninsula, China.

To elucidate the spatial patterns of understory species in fragmented forests adjacent to human settlements, we examined the spatial distribution and intraspecific correlations of three dominant species Mallotus philippensis, Dasymashalon trichophorum, and Psychotria rubra by employing point pattern analysis, which were the top three in terms of importance value in the shrub layer of Fengshui forest in Leizhou Peninsula, Guangdong. The results showed that all the three species were mainly aggregated at the scale of 0-25 m, especially for young trees. The degree of aggregation gradually diminished with increasing age class. The spatial distribution patterns of three species were predominantly influenced by habitat heterogeneity, negative density dependence, and dispersal limitation. They showed positive association among different age classes, especially between young trees and middle age trees and between young trees and adult trees. Therefore, in the ecological restoration process of Leizhou Peninsula, M. philippensis, D. trichophorum, and P. rubra should be planted in clusters at a small scale within the range of 0-25 m, with the degree of clusters depending on plant morphology. For larger scales, a dispersed cultivation approach was advocated.

Co-planting alters plant iron deficiency in heavy metals contaminated soil amended with sludge.

Heavy metals (HMs)-induced iron (Fe) deficiency severely inhibits plant growth and thus hampers phytoremediation and revegetation in HMs-contaminated soil. We conducted a 12-month pot experiment to investigate the effects and mechanisms of co-planting on altering plant HM-induced Fe deficiency. The landscape tree Ilex rotunda was co-planted with Ficus microcarpa and Talipariti tiliaceum in sludge-amended soil. The responses of I. rotunda growth, elements uptake, and rhizosphere microbial community and metabolites were analyzed. The addition of sludge increased cadmium (Cd), zinc (Zn), and nickel (Ni) uptake and induced Fe deficiency-induced chlorosis in I. rotunda. This chlorosis was exacerbated when I. rotunda was co-planted with F. macrocarpa due to the increase in the abundance of sulfate reduction or Fe immobilization-associated bacteria and the relative level of isoprenyl alcohol and atropine in I. rotunda rhizosphere but the decrease in the contents of soil diethylenetriaminepentaacetic acid Fe (DTPA-Fe) (-16.19 %). Co-planting with T. tiliaceum or F. macrocarpa and T. tiliaceum decreased the contents of total or DTPA Zn/Cd/Ni in the soil while increased the contents of soil DTPA-Fe by 13.24 % or 11.34 % and the abundance of microbes which contributed to immobilizing HMs or activating Fe reduction, and then alleviated the chlorosis and the growth inhibition of I. rotunda. These results provide a new perspective on the phytoremediation and revegetation of HMs-contaminated soil.

Biochar alleviating heavy metals phytotoxicity in sludge-amended soil varies with plant adaptability.

Recycling sewage sludge (SS) to soil potentially causes soil heavy metal (HM) pollution and plant phytotoxicity. Biochar plays an important role in alleviating HM phytotoxicity, and responses vary with the feedstocks and usage of biochar. However, the effect of plant adaptability on biochar-mediated alleviation is poorly understood. Here, SS-derived biochar (SB) and rice straw-derived biochar (RB) applied at rates of 1.5% and 3% (W/W, SB1.5, SB3, RB1.5, and RB3) were used to improve the properties of soil amended with SS at 50% (W/W). Alleviation of phytotoxicity by biochar was further analyzed with SS-sensitive plant Monstera deliciosa and SS-resistant plant Ruellia simplex. Results revealed that both SB and RB significantly decreased the soil's bulk density and increased water retention. They also changed soil organic matter content and HMs fractionation. The addition of SB or RB alleviated the SS phytotoxicity, and they significantly promoted the growth and the root morphology and physiological index of M. deliciosa. But for R. simplex, these significant changes only synchronously occurred in SB3 treatment. The alleviation in M. deliciosa was more prominent and more closely connected with soil property changes than in R. simplex. Also, more soil property predictors were observed to play an important role in M. deliciosa growth than in R. simplex growth. These results indicated that biochar alleviating HMs phytotoxicity in SS-amended soil is associated with the changes of soil property. Moreover, the alleviation varies more prominently with plant adaptability than with biochar feedstocks and usage.

[Effects of surface and mixed application of sewage sludge on Neolamarckia cadamba root growth]. / è¡¨æ–½å’Œæ··æ–½æ±¡æ³¥å¯¹å›¢èŠ±æ ¹ç³»ç”Ÿé•¿çš„å½±å“.

The utilization of sewage sludge in forests is an important way of recycling. However, the effect of sewage sludge application on woody plant root growth has been rarely reported. The effects of surface application and mixed application of sewage sludge (mass ratio in 10%) on the dynamics in root morphology of a fast-growing tree species (Neolamarckia cadamba), soil pH, electric conductivity, and heavy metal content of roots in different soil layers were analyzed by a rhizobox experiment. The relationship between root length and soil pH value, electric conducti-vity, and root heavy metal content were further analyzed. Results showed that mixed application of sewage sludge inhibited root length, root surface area, and root volume. After 120 and 240 days of mixed application, total root length in the 0-20 cm soil layer was 76.9% and 67.4% of that of no sewage sludge application, respectively. Surface application of sewage sludge did not affect root length and root surface area but increased root volume. The mixed application of sewage sludge significantly increased soil pH, electric conductivity, and root heavy metal content. Root Cd contents in 0-20 cm and 20-40 cm soil layers with the mixed application of sewage sludge were 11.5 and 10.0 times as that of no sewage sludge application, respectively. Soil electric conductivity had a significant nega-tive correlation with root length in 0-20 cm soil layer among different treatments. Root Cd content had a significant negative correlation with root length in both the surface and the mixed applications of sewage sludge. These results indicated that mixed application of sewage sludge could inhibit N. cadamba root growth mainly by increasing soil electric conductivity and root Cd content, while the surface application of sewage sludge did not affect root growth.

Diversified effects of co-planting landscape plants on heavy metals pollution remediation in urban soil amended with sewage sludge.

Recycling sewage sludge (SS) as a soil amendment potentially causes soil heavy metals (HMs) contamination. This study investigated the potential roles of landscape plants co-planting in SS-amended soil remediation. Three landscape trees Mangifera persiciforma, Bischofia javanica, and Neolamarckia cadamba (NC), and three ground cover plants Dianella ensifolia, Syngonium podophyllum, and Schefflera odorata (SO) were selected for the tree-ground cover co-planting. Species in different co-planting treatments exhibited diversified effects on the growth, root morphology, HMs uptake, and HMs accumulation. Five plant characteristics including total root length, total surface of roots (diameter <2 mm), specific root length, shoot dry weight and root dry weight played crucial roles in plant HMs uptake. Structural equation modeling analysis revealed that different co-planting treatments drive species to develop an active, passive, or avoidance strategy to accumulate HMs, resulting in a diversity of HMs removal efficiency. Co-planting of NC with SO promoted NC and SO HMs accumulation and resulted in the greatest HMs contents decline (48.0% for Cd, 24.9% for Cu, 33.8% for Zn, and 27.2% for Ni) and the lowest potential ecological risk. Co-planting of landscape tree and ground cover plants with an active strategy can be a potential candidate for HMs phytoremediation of SS-amended soil.