Effects of returning peach branch waste to fields on soil carbon cycle mediated by soil microbial communities.

In recent years, the rise in greenhouse gas emissions from agriculture has worsened climate change. Efficiently utilizing agricultural waste can significantly mitigate these effects. This study investigated the ecological benefits of returning peach branch waste to fields (RPBF) through three innovative strategies: (1) application of peach branch organic fertilizer (OF), (2) mushroom cultivation using peach branches as a substrate (MC), and (3) surface mulching with peach branches (SM). Conducted within a peach orchard ecosystem, our research aimed to assess these resource utilization strategies' effects on soil properties, microbial community, and carbon cycle, thereby contributing to sustainable agricultural practices. Our findings indicated that all RPBF treatments enhance soil nutrient content, enriching beneficial microorganisms, such as Humicola, Rhizobiales, and Bacillus. Moreover, soil AP and AK were observed to regulate the soil carbon cycle by altering the compositions and functions of microbial communities. Notably, OF and MC treatments were found to boost autotrophic microorganism abundance, thereby augmenting the potential for soil carbon sequestration and emission reduction. Interestingly, in peach orchard soil, fungal communities were found to contribute more greatly to SOC content than bacterial communities. However, SM treatment resulted in an increase in the presence of bacterial communities, thereby enhancing carbon emissions. Overall, this study illustrated the fundamental pathways by which RPBF treatment affects the soil carbon cycle, providing novel insights into the rational resource utilization of peach branch waste and the advancement of ecological agriculture.

Heavy grazing reduces soil bacterial diversity by increasing soil pH in a semi-arid steppe.

Background: In a context of long-term highly intensive grazing in grassland ecosystems, a better understanding of how quickly belowground biodiversity responds to grazing is required, especially for soil microbial diversity. Methods: In this study, we conducted a grazing experiment which included the CK (no grazing with a fenced enclosure undisturbed by livestock), light and heavy grazing treatments in a desert steppe in Inner Mongolia, China. Microbial diversity and soil chemical properties (i.e., pH value, organic carbon, inorganic nitrogen (IN, NH4+-N and NO3--N), total carbon, nitrogen, phosphorus, and available phosphorus content) both in rhizosphere and non-rhizosphere soils were analyzed to explore the responses of microbial diversity to grazing intensity and the underlying mechanisms. Results: The results showed that heavy grazing only deceased bacterial diversity in the non-rhizosphere soil, but had no any significant effects on fungal diversity regardless of rhizosphere or non-rhizosphere soils. Bacterial diversity in the rhizosphere soil was higher than that of non-rhizosphere soil only in the heavy grazing treatment. Also, heavy grazing significantly increased soil pH value but deceased NH4+-N and available phosphorus in the non-rhizosphere soil. Spearman correlation analysis showed that soil pH value was significantly negatively correlated with the bacterial diversity in the non-rhizosphere soil. Combined, our results suggest that heavy grazing decreased soil bacterial diversity in the non-rhizosphere soil by increasing soil pH value, which may be due to the accumulation of dung and urine from livestock. Our results highlight that soil pH value may be the main factor driving soil microbial diversity in grazing ecosystems, and these results can provide scientific basis for grassland management and ecological restoration in arid and semi-arid area.

Effects of allyl isothiocyanate fumigation on medicinal plant root knot disease control, plant survival, and the soil bacterial community.

BACKGROUND: Allyl isothiocyanate (AITC) is a natural product with high volatility that is used as a biofumigant to alleviate soil-borne plant diseases, and problems such as root knot nematodes (RKNs) that necessitate continuous cropping. However, little research has assessed the effects of AITC fumigation on medicinal plants. RESULTS: AITC significantly reduced the population of RKNs in soil (p < 0.0001) and showed an excellent RKN disease control effect within 6 months after sowing Panax notoginseng (p < 0.0001). The seedling survival rate of 2-year-old P. notoginseng was approximately 1.7-fold higher after soil treatment with AITC (p = 0.1008). 16S rRNA sequencing indicated that the AITC treatment affected bacterial richness rather than diversity in consecutively cultivated (CC) soil. Furthermore, biomarkers with statistical differences between AITC-treated and untreated CC soil showed that Pirellulales (order), Pirellulaceae (family), Pseudomonadaceae (family), and Pseudomonas (genus) played important roles in the AITC-treated group. In addition, the microbiome functional phenotypes predicted using the BugBase tool suggested that AITC treatment is more conducive to improving CC soil through changes in the bacterial community structure. Crucially, our research also suggested that AITC soil treatment significantly increases soil organic matter (p = 0.0055), total nitrogen (p = 0.0054), and available potassium (p = 0.0373), which promotes the survival of a succeeding medicinal plant (Polygonatum kingianum). CONCLUSION: AITC is an ecologically friendly soil treatment that affects the top 10 bacterial richness but not diversity. It could also provide a basis for a useful agricultural soil management measure to alleviate soil sickness.

Effects of peach branch organic fertilizer on the soil microbial community in peach orachards.

Peach branches is a by-product of peach industry. Making peach branch waste into peach branch organic fertilizer (PBOF) is a promising strategy of ecological utilization. In this study, the effects of PBOF on the yield and quality of peach fruit, chemical properties of bulk soil, and soil bacterial communities were investigated in a peach orchard. The results showed that the yield and sugar/acid ratio of two high-level PBOF treatments (SDH.4 and SKR.4) was higher than no fertilization treatment (CK), but there was no significant difference compared to the commercial organic fertilizer treatment (SYT.4). Moreover, the three fertilizer treatments increased soil nutrients such as soil organic matter (SOM) and available potassium (AK), compared to CK. Furthermore, PBOF increased the relative abundance of beneficial bacteria, and enhanced the soil bacterial co-occurrence pattern and the potential function of bacterial communities to degrade exogenous compounds. In addition, thanks to the local policy of encouraging the use of PBOF, the use cost of PBOF is lower than commercial organic fertilizer, which is conducive to the development of ecological agriculture.

Identifying the effects of cropping with different pear cultivars on microbial community composition and networks in orchard soils.

The role of plant genotype in determining the assembly of soil microorganisms is widely accepted; however, the effects of cropping with different cultivars of perennial crop plants on the composition of soil microbial communities are not fully understood. In the current study, high-throughput amplicon sequencing and real-time PCR were used to investigate the major features of bacterial community composition, ecological networks, and soil physicochemical properties in three replicate pear orchards, each planted with monocultures of pear cultivars Hosui (HS) or Sucui (SC) of similar ages. A distinct difference in the composition of microbial communities was observed between soils of HS and SC orchards. A significantly greater relative abundance of Verrucomicrobia and Alphaproteobacteria whereas a significantly lower relative abundance of Betaproteobacteria were found in soils of HS cropped orchards than that in SC orchards. Sphingomonas sp., belonging to the Alphaproteobacteria, was recognized as a key species in the co-occurrence network of the microbial interactions. Moreover, redundancy analysis, the Mantel correlation test, and random forest analysis showed that soil pH was the dominant driver in determining microbial community composition in HS soils, whereas soil organic matter was the primary factor determining microbial community composition in SC soils. Altogether, we provide evidence that soils in HS orchards harbor unique microbial communities enriched with respect to microbial groups associated with nutrient cycling, whereas soils in SC orchards are dominated by a group of beneficial microbes exhibiting plant growth promotion. These findings have implications for science-based guidance for manipulation of the soil microbiome to achieve sustainable food production.

Effects of rice-prawn (Macrobrachium nipponense) co-culture on the microbial community of soil.

In the Lixiahe region of China, co-culture has been rapidly promoted in flooded paddy fields owing to its ecological and economic benefits. Rice-prawn co-culture can reduce the damage of crab and shrimp to rice growth and paddy field and substantially change the soil microbial community and soil fertility. In this study, we compared changes in the soil microbial community and soil fertility in waterlogged paddies under conventional rice culture (CR), rice-prawn (Macrobrachium nipponense) co-culture (RP), and pond culture (PC). The microbial abundance in RP was significantly higher than that in CR. RP soil microbial diversity was significantly higher than PC soil microbial diversity. The dominant bacteria in RP soil were Proteobacteria, Chloroflexi, and Bacteroidetes. Compared with those in CR, total organic matter (TOM) and total nitrogen in RP were relatively stable, available potassium and available phosphorus (AP) decreased, and other indicators increased significantly. Soil fertility significantly benefited from co-culture, with total organic carbon (TOC) increasing. Interactive relationship analysis showed that TOM, TOC, AP, and NH4+-N were the main factors affecting the microbial community. Co-occurrence network analyses showed that network modularity increased with co-culture, indicating that a unique soil microbial community formed under co-culture, improving the adaptability and tolerance to co-culture. Thus, RP is a suitable culture method for this commercially important species. The results of this study can inform the practical operation of fertilizer use and sustainable development of rice-prawn aquaculture systems. KEY POINTS: • Microbial abundance and diversity increased under rice-prawn co-culture. • Co-culture significantly improved soil fertility, with an increase in TOC. • Rice-prawn co-culture is an ecologically suitable culture method for prawns.

[Changes of persistent soil seed bank along a precipitation gradient in forest-steppe ecotone]. / æ£®æž—è‰åŽŸè¿‡æ¸¡å¸¦æŒä¹ åœŸå£¤ç§å­åº“æ²¿é™æ°´æ¢¯åº¦çš„æ ¼å±€.

This study aimed to examine the responses of persistent soil seed bank to future precipitation reduction of global climate change in the forest-steppe ecotone of Hulunbuir. Samples of soil seed bank were collected from 0-10 cm soil layer along a precipitation gradient. We examined the density, species composition, diversity of seed bank and their relationship with vegetation. Structural equation model was used to explore the direct impact of annual precipitation on soil seed bank and the indirect impact through vegetation, soil nitrogen, soil phosphorus, and soil pH. The results showed that seed bank density and species richness were negatively correlated with annual precipitation. The species diversity of soil seed banks in grasslands was higher than that in forests. The similarity between soil seed bank and vegetation was generally low. The results of structural equation model showed that the effects of annual precipitation on seed bank density and species richness were negative, with the standard path coefficients of -0.051 and -0.122, respectively. The direct effect of annual precipitation on seed bank density and species richness were positive. Precipitation had indirect and positive effect on seed bank density and species richness through soil nitrogen, a significantly indirect negative effect on seed bank species richness through soil pH and soil available phosphorus, and a significantly indirect negative effect on seed bank density through soil pH. The reduction of precipitation under furture climate change might alter the hedging strategies of plants. The persistent soil seed bank in the forest-steppeecotone had a potential buffering effect against future precipitation reduction.

Combined intensive management of fertilization, tillage, and organic material mulching regulate soil bacterial communities and functional capacities by altering soil potassium and pH in a Moso bamboo forest.

Intensive management is a common practice in agricultural and forestry ecosystems to improve soil quality and crop yield by influencing nutrient supply and soil microbiota; however, the linkage between soil nutrients and bacterial community and functional capacities in intensively managed economic forests has not been well studied. In this study, we investigated the soil properties such as available potassium (AK), available nitrogen (AN), available phosphorus (AP), ammonium (NH 4 + ), nitrate (NO 3 - ), organic matter (OM), total nitrogen (TN), total phosphorus (TP), bacterial diversity and community composition, potential functions of rhizome roots, and soil microbiota across a chronosequence of intensively managed Moso bamboo (Phyllostachys edulis) forests. Our results demonstrated that the combined intensive management (deep tillage, fertilization, and organic material mulching) in this study caused a significant increase in the concentrations of AK, AN, AP, NH 4 + , NO 3 - , OM, TN, and TP (P < 0.05). However, they led to a remarkable decrease in pH (P < 0.05). Such changes lowered the Shannon diversity of the soil and rhizome root microbiota but did not significantly affect the community composition and functional capacity. Soil bacterial community variation was predominantly mediated by soil total potassium (TK) (15.02%), followed by pH (11.29%) and AK (11.13%). We further observed that Nitrospirae accounted for approximately 50% of the variation in soil pH, NO 3 - , NH 4 + , and AK, indicating its importance in soil nutrient cycling, especially nitrogen cycling. Accordingly, we propose that the management-induced changes in soil parameters reshaped the bacterial community structure and keystone bacterial assemblage, leading to the differentiation of microbial functions.

Evaluation of change in the peat soil properties affected by different fire severities.

The tropical peatland ecosystems of Indonesia provide direct economic benefits to local communities and act to maintain local weather patterns. The impact of burning tropical peat swamp forests of land clearing for palm oil plantations can have significant consequences on the change in the characteristics of peat soil. The aim of this study was to determine the physical, chemical, and biological properties of peat soils by field and laboratory testing and analysis to understand changes in the nature and characteristics of peatlands at four locations in the Pelalawan Regency of Riau Province. The results showed that the effect of burning peat swamp forests can lead to a change in the physical, chemical, and biological properties of the peat soils. Soil permeability and the soil microbial population can significantly decrease with increasing fire severity. The effect of different fire severities on the characteristics of peat soil is verified to contribute to advanced management of the tropical peatland in the future.

Effects of Fe-Mn impregnated biochar on enzymatic activity and bacterial community in phthalate-polluted brown soil planted with wheat.

A pot experiment was carried out on brown soil polluted by dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) to investigate the effects of biochar (BC) derived from corn straw and Fe-Mn oxide modified biochar composites (FMBC) on the bioavailability of DBP and DEHP, as well as ecosystem responses in rhizosphere soil after wheat ripening. The results indicate that the application of BC and FMBC significantly increases soil organic matter, pH, available nitrogen (AN), Olsen phosphorus, and available potassium (AK); reduces the bioavailability of DBP and DEHP; enhances the activities of dehydrogenase, urease, protease, ß-glucosidase, and polyphenol oxidase; and decreases acid phosphatase activity. No changes in richness and diversity, which were measured by Illumina MiSeq sequencing, were observed following BC and FMBC application. The bacterial community structure and composition varied with DBP/DEHP concentrations and BC/FMBC additions in a nonsystematic way and no significant trends were observed. In addition, FMBC exhibited better performance in increasing soil properties and decreasing the bioavailability of DBP and DEHP compared with BC. Hence, the FMBC amendment may be a promising way of developing sustainable agricultural environmental management.

Contrasting effects of nitrogen addition on rhizosphere soil CO2, N2O, and CH4 emissions of fine roots with different diameters from Pinus tabulaeformis forest using laboratory incubation.

Nitrogen (N) addition has variable effects on chemical composition, function, and turnover of roots with different diameters. However, it is unclear whether N addition has variable effects on greenhouse gas (GHG) emission in rhizosphere soil. We performed N addition (0-9 g N m-2 y-1) experiment in a Pinus tabulaeformis forest and a lab-incubation experiment to determine the effects of N addition on carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions in rhizosphere soils of roots with different diameters (very fine roots: <0.5 mm, intermediate fine roots: 0.5-1.0 mm, largest fine roots: 1.0-2.0 mm). Nitrogen addition significantly promoted CO2 emission and CH4 uptake, with maximum values (CO2, 623.15 mg C kg soil-1; CH4, 1794.49 µg C kg soil-1) in the 6 or 9 g N m-2 y-1 treatments (P < 0.05). Nitrous oxide emissions were inhibited, with the greatest inhibitory effect in the 9 g N m-2 y-1 treatment (48.63 µg N kg soil-1). Total phosphorus (TP) content significantly decreased and increased in rhizosphere soil and non-rhizosphere soil after N addition, respectively, while organic carbon (OC), total N (TN), ammonium (NH4+), and nitrate (NO3-) contents in rhizosphere soil increased. A greater change in chemical properties occurred in rhizosphere soil of largest fine roots than very fine roots. Carbon dioxide and nitrous oxide emissions in rhizosphere soil among root sizes exhibited similar responses to N addition. While CH4 uptake was more responsive to N addition in rhizosphere soil with very fine roots than with largest fine roots. Basically, OC, TN, NO3-, and NH4+ were key soil components driving GHG emissions; NO3- promoted CH4 uptake and N2O emissions, NH4+ inhibited CO2 emissions. GHG response to N addition varied greatly, particularly in rhizosphere soil with different root sizes mainly related to its chemical properties.

Both Soil Bacteria and Soil Chemical Property Affected the Micropredator Myxobacterial Community: Evidence from Natural Forest Soil and Greenhouse Rhizosphere Soil.

Myxobacteria are abundant micropredators in soil, and are social bacteria with multicellular behavior and producers of versatile secondary metabolites. The interaction between predator and prey populations is an important component in the soil microbial food web, and this is expected to shape the composition and dynamics of microbial communities. Here we hypothesize the regulation of bacterial abundance and community composition on soil myxobacterial community. Field investigation indicated that the relative abundance of Myxococcales in subtropical and tropical forest soil from South China was 1.49-4.74% of all the 16S rRNA gene sequences, and myxobacterial community composition differed between subtropical and tropical forest. The canonical correspondence analysis and variation partitioning analysis indicated that biotic factor (bacterial community composition) showed slightly stronger explanation for variation of myxobacteria than soil properties (soil pH and soil organic matter). Based on the rhizosphere bacterial network, the greenhouse mesocosm experiment showed that most of the myxobacterial links were with Gram-negative bacteria, except that some nodes from Haliangiacea and Polyangiaceae interacted with actinomycetes and actinomycetes-like Gram-positive bacteria. We inferred that myxobacteria preferential predation on specific bacterial taxa may explain the influence of bacteria on myxobacterial community. Further study confirming the biological process of myxobacterial predation in situ is necessary to advance the understanding of the ecological role of predation behavior in the microbial world.

[Response of Soil Enzyme Activity and Chemical Properties to Nitrogen Addition in a Korean Pine Plantation].

Soil enzymes participate in numerous complex biochemical processes that take place in the soil and play an important role in the material circulation of terrestrial ecosystems. To explore the response of soil enzyme activities and chemical properties to nitrogen deposition in temperate forests, this study analyzed four soil enzyme activities based on the nitrogen addition experiment plot of Korean pine (Pinus koraiensis) plantation, which was located in the Liangshui National Natural Reserve, Heilongjiang Province. The results showed that the activities of N-acetyl-glucosidase (NAG) and alkaline phosphatase (AKP) increased significantly with increasing nitrogen application concentration. The activity of beta-glucosidase (BG) and acid phosphatase (ACP) was not significantly different among different nitrogen application treatments. The contents of total carbon, total nitrogen, total phosphorus, and available nitrogen and four enzyme activity in the upper soil (0-10 cm) under the same nitrogen application level were significantly higher than those in the lower soil (10-20 cm), but the pH values were not significantly different. Total carbon has an extremely significant positive correlation with NAG, BG, AKP, and ACP. Total nitrogen has an obvious or extremely significant positive correlation with BG, NAG, and AKP as well as ACP. The available nitrogen has an obvious and highly significant positive correlation with NAG and AKP. The total phosphorus has an obvious and extremely significant positive correlation with ACP and AKP, respectively. The nitrogen application level and the soil layer had different effects on soil enzyme activity and soil chemical properties. Long-term large input of nitrogen can directly or indirectly change soil chemical properties and affect soil enzyme activity.

Evaluating the effects of transgenic Bt rice cultivation on soil stability.

Insecticidal crystal (Cry) proteins produced by genetically modified rice that enter the soil via pollen dispersal, plant residues, and root exudation may disturb soil health. In the present study, we assessed the influences of transgenic Bt rice (i.e., HH1 with Cry1Ab/Cry1Ac) cultivation on the dynamics of soil carbon and nutrients under field conditions during 2013-2016. Transgenic treatments (transgenic Bt rice vs. its parental line (i.e., MH63) of non-Bt rice) have no consistently significant effects on soil property, including available nitrogen, available phosphorus, available potassium, total nitrogen, and total phosphorus, while apparent seasonal changes were observed. Besides, the variations of soil nutrients in the paddy field of transgenic Bt rice did not exceed their resistance capacities, except total organic carbon (TOC; RS (resistance) = 1.51) and total potassium (TK; RS = 2.62) in 2013 and TK (RS = 1.94) in 2014. However, the TOC and soil nutrient of TK in the paddy field of transgenic Bt rice have recovered to the pre-perturbation status after harvest (RL (resilience) = 1.01, F = 0.01, P = 0.91; RL = 0.98, F = 0.34, P = 0.58; RL = 0.99, F = 1.26, P = 0.29). Moreover, the paddy yield of transgenic Bt rice was consistently higher than that of its parental line of non-Bt rice. These results suggested that the cultivation of transgenic Bt rice has no adverse impact on soil stability in terms of soil carbon and nutrients and paddy yield.

Revegetation of a barren rare earth mine using native plant species in reciprocal plantation: effect of phytoremediation on soil microbiological communities.

Over-exploration of rare earth elements causes soil desertification and environmental degradation. However, the restoration of rare earth mine tailings requires the recovery of both vegetation and soil microbiota. Accordingly, the present study aimed to compare the efficacy of restoring mine tailings using organic compost and native plants (Miscanthus sinensis, Pinus massoniana, Bambusa textilis, or a mixture of all three). After three years, the mixed plantation harbored tenfold greater plant richness than that in the barren land. Among these, M. sinensis played a dominant role across all restored areas. The microbial communities of the soils were assessed using high-throughput 16S rDNA gene sequencing. A total of 34,870 16S rDNA gene sequences were obtained and classified into 15 bacterial phyla and 36 genera. The dominant genus across all the restored soils was Burkholderia, and the bacterial diversity of restored soils was greater than that of soils from either unrestored or natural (unexploited) areas, with the M. sinensis plantation yielding the greatest diversity. The effects of phytoremediation were mainly driven by changes in nutrient and metal contents. These results indicate that M. sinensis significantly improves phytoremediation and that mixed planting is ideal for restoring the soils of abandoned rare earth mines.

Soil Bacterial Function Associated With Stylo (Legume) and Bahiagrass (Grass) Is Affected More Strongly by Soil Chemical Property Than by Bacterial Community Composition.

Soil microbes are driver of nutrient cycling, with microbial function affected by community composition and soil chemical property. Legume and grass are ubiquitous in many ecosystems, however, their differential effects on microbial function are less understood. Here we constructed compartmented rhizobox planted with stylo (Stylosanthes guianensis, legume) or bahiagrass (Paspalum natatum, grass) to compare their influences on bacterial function and to investigate the determinant of bacterial function. Soils in root compartment and in near (0-5 mm from root compartment) or far (10-15 mm from root compartment) rhizosphere were sampled. Soil chemical properties, bacterial community composition and function were characterized. Results indicate that plant species and distance significantly affected bacterial function. The activities of beta-xylosidase, nitrate reductase and phosphomonoesterase were higher in stylo soil than in bahiagrass soil, while leucine-aminopeptidase activity and nosZ abundance were vice versa. Rhizosphere effect was obvious for the activities of beta-glucosidase, beta-xylosidase, chitinase, and the abundances of AOB-amoA, nirS, nosZ. Statistical analysis revealed that soil chemical property was significantly associated with bacterial function, with a higher coefficient than bacterial community composition. These data suggest that stylo and bahiagrass differentially affect bacterial function, which is affected more strongly by soil chemical property than by community composition.

Sugar Composition in Asparagus Spears and Its Relationship to Soil Chemical Properties.

Glycoside hydrolases require carboxyl groups as catalysts for their activity. A retaining xylanase from Streptomyces olivaceoviridis E-86 belonging to glycoside hydrolase family 10 possesses Glu128 and Glu236 that respectively function as acid/base and nucleophile. We previously developed a unique mutant of the retaining xylanase, N127S/E128H, whose deglycosylation is triggered by azide. A crystallographic study reported that the transient formation of a Ser-His catalytic dyad in the reaction cycle possibly reduced the azidolysis reaction. In the present study, we engineered a catalytic dyad with enhanced stability by site-directed mutagenesis and crystallographic study of N127S/E128H. Comparison of the Michaelis complexes of N127S/E128H with pNP-X2 and with xylopentaose showed that Ser127 could form an alternative hydrogen bond with Thr82, which disrupts the formation of the Ser-His catalytic dyad. The introduction of T82A mutation in N127S/E128H produces an enhanced first-order rate constant (6 times that of N127S/E128H). We confirmed the presence of a stable Ser-His hydrogen bond in the Michaelis complex of the triple mutant, which forms the productive tautomer of His128 that acts as an acid catalyst. Because the glycosyl azide is applicable in the bioconjugation of glycans by using click chemistry, the enzyme-assisted production of the glycosyl azide may contribute to the field of glycobiology.

Effects of yam/leguminous crops intercropping on soil chemical and biological properties of yam field.

We investigated the effects of yam/leguminous crops intercropping on soil chemical and biological properties as well as soil comprehensive fertility in a field experiment. Results showed that compared with the monoculture, both yam/alfalfa and yam/clover intercropping increased the concentrations of nitrate nitrogen (N), available phosphorus (P) and available potassium (K) in the 0-20 cm and 20-40 cm soil layers, while reduced soil pH and electrical conductivity (EC) in early growth period and rhizome rapid expansion period of yam. Intercropping with leguminous crops enhanced the activities of urease, alkaline phosphatase and catalase, and also enhanced soil basal respiration in the 0-20 cm and 20-40 cm soil layers during the whole growth period of yam. There was no influence of intercropping on soil sucrase activity and dehydrogenase activity. The effects of intercropping with leguminous crops on soil fertility at yam harvest were further analyzed by combining the membership function model and principal component analysis. Results showed that intercropping with leguminous crops could significantly increase the soil comprehensive fertility in the 0-20 cm and 20-40 cm soil layers. Therefore, it might be an effective measure to improve soil fertility and environmental quality, as well as alleviate continuous cropping obstacles of yam by yam/leguminous crops intercropping through enhancing soil biological diversity.

Feasibility of four wastes to remove heavy metals from contaminated soils.

Soil washing is one of the permanent techniques to remove heavy metals, and washing agent is a key influence factor for this technique, but there is still lack of high-efficiency, eco-friendly, and inexpensive agents. In this study, four wastes including pineapple peel (PP), soybean straw (SS), broad bean straw (BBS) and tea residue (TR) were employed to remove cadmium (Cd), lead (Pb) and zinc (Zn) in contaminated soils. The Fourier transform infrared spectroscopy (FTIR) analysis indicated that hydroxyl, carboxyl, amine, carbonyl and amide groups were involved in the interaction with metal ions by complexation or ion exchange. We then investigated the influences of various conditions including washing solution concentration, pH, and washing time. The metal removal efficiencies with these agents increased as the concentration augmented from 5 to 80 g L-1, decreased or presented an asymmetric V-shaped curve with increasing pH from 2.5 to 7.5, and fit intraparticle diffusion or Elovich model with washing time increasing. PP has the highest removals for Cd (90.1%), Pb (18.6%), and Zn (15.2%) in soil A, and 85.8, 24.8, and 69.4% in soil B, respectively. The relatively high metal removal was mainly attributed to effective removal of the exchangeable and acid soluble fractions. Moreover, single washing not only lowered the potential ecological risk of the heavy metals, but moderated the effects on soil chemical properties. Therefore, PP was a feasible washing agent to remediate soils contaminated by heavy metals.