B6nassy, C., 1955. R6marques sur deux Aphelinid6s: Aphelinus mytilaspidis Le Baron et Aphytis proclia Walker. Annls l~piphyt. 6: 11-17. Lord, F. T. & MacPhee, A. W., 1953. The influence of spray programs on the fauna of apple orchards in Nova Scotia II. Oyster shell scale. Can. Ent. 79: 196-209. Pickett, A. D., 1946. A progress report on long term spray programs. Rep. Nova Scotia Fruit Grow. Ass. 83 : 27-31. Pickett, A. D., 1967. The influence of spray programs on the fauna of apple orchards in Nova Scotia XIV. Can. Ent. 97: 816-821. Tothill, J. D., 1918. The predacious mite Hemisarcoptes malus Shimer and its relation to the natural control of the oyster shell scale Lepidosaphes ulmi L. Agric. Gaz. Can. 5 : 234-239.

http://link.springer.com/content/pdf/10.1007/BF01976688.pdf

Soil enzymes: Kuprevich, V. F. & Shcherbakova, T. A.: Translated from the Russian edition (1966), published by the Indian National Scientific Documentation Centre, New Delhi 1971. 392 pp., offset printing from type script, paper cover. Obtainable from U.S. Department of Commerce, National Technical Information Service, Springfield, Va. 22151

Polluted soil and water impact the quality of food and nutrients of human and animal biota. Soil and water are mainly polluted by effluent discharges from industries, which are broadly classified into metallic and nonmetallic pollutant-bearing effluents. In order to tackle this problem, a plant-based technology called phytoremediation is used to clean contaminated lands. Phytoremediation is based upon several processes such as phytodegradation, phytovolatilization, phytoaccumulation and phytoextraction. These methods are efficient, eco-friendly and economic. This paper reviews the methods and mechanisms involved in phytoremediation of heavy metals, and enhancement processes.

Phytoremediation of heavy metals: mechanisms, methods and enhancements

Acute and diffuse contamination of soil by organic and inorganic pollutants causes wide concerns and intentional or accidental introduction of these substances poses serious impact in public health and environment. Heavy metals are elements not degradable and can be teratogenic, mutagenic, endocrine disruptors. PAHs are elements of difficult management and they can cause carcinogenesis and toxicity in human. Different techniques have been used for the remediation of contaminated soils, but the phytoremediation is proposed as possible alternative, convenient and environmentally friendly than traditional physicochemical techniques. Phytoremediation employs different plant species able to accumulate or degrade different contaminants and, the biomass produced can be used for other purposes such as cogeneration of energy and/or biofuels production, obtaining benefits to health, environment and cost management. A better knowledge of phytoremediation potential is essential in order to increase the use of this technique in the near future for remediation of contaminated lands in the economic and sustainable way. This review provides additional information about the application of phytoremediation processes in soils contaminated by heavy metals and polycyclic aromatic hydrocarbons using herbaceous and woody plants.

Phytoremediation of contaminated soils by heavy metals and PAHs. A brief review

Increasing industrialization and urbanization result in emission of pollutants in the environment including toxic heavy metals, as cadmium and lead. Among the different heavy metals contaminating the environment, cadmium raises great concern, as it is ecotoxic and as such can heavily impact ecosystems. The cell wall is the first structure of plant cells to come in contact with heavy metals. Its composition, characterized by proteins, polysaccharides and in some instances lignin and other phenolic compounds, confers the ability to bind non-covalently and/or covalently heavy metals via functional groups. A strong body of evidence in the literature has shown the role of the cell wall in heavy metal response: it sequesters heavy metals, but at the same time its synthesis and composition can be severely affected. The present review analyzes the dual property of plant cell walls, i.e., barrier and target of heavy metals, by taking Cd toxicity as example. Following a summary of the known physiological and biochemical responses of plants to Cd, the review compares the wall-related mechanisms in early- and later-diverging land plants, by considering the diversity in cell wall composition. By doing so, common as well as unique response mechanisms to metal/cadmium toxicity are identified among plant phyla and discussed. After discussing the role of hyperaccumulators’ cell walls as a particular case, the review concludes by considering important aspects for plant engineering.

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Target or barrier? The cell wall of early- and later-diverging plants vs cadmium toxicity: differences in the response mechanisms

Abstract In many low input agricultural systems, phosphorus (P) is one of the most limiting mineral nutrients for plant production. Although applying P fertilizer, if available, is the most performing practice, this should be accompanied by other measures. The use of genetically enhanced plants with improved P acquisition efficiency may represent a sustainable solution to increase crop yields in these systems. This review is intended to provide a summary on adaptation mechanisms of crop plants facing P deficiency as the starting point to develop a research approach for improving P acquisition efficiency. P acquisition efficiency in this review refers to external P efficiency. The suggested research approach includes three strategies: molecular assisted plant breeding, deployment of transgenic plants and the use of agricultural practices. The natural source for improving P nutrition of plants is the existing large genetic variation for plant traits that are associated with P acquisition efficiency and will therefore be emphasized in this review.

Strategies for improving phosphorus acquisition efficiency of crop plants [Approved article]

Soil aggregate-associated bacterial metabolic activity and community structure in different aged tea plantations

The objectives of the present study were to compare nine dominant plant species growing in mine tailings and nonmining areas in terms of biomass and Cd concentrations and to search for Cd accumulation and tolerance. Also, more detailed experiments were conducted on Athyrium wardii using a pot experiment to assure its Cd-accumulation ability and tolerance as a potential phytostabilizer of Cd-polluted soils. Nine dominant plant species growing on Pb/Zn mine tailings and their corresponding nonmining ecotypes were investigated for their potential to phytostabilize Cd. The performance of A. wardii exposed to high levels of Cd was investigated under controlled conditions. A field study revealed that the Cd concentrations in the roots of these plants ranged from 0.21 to 251.07 mg kg−1, and the highest concentrations were found in A. wardii, which reached a concentration of 69.78, 251.07, and 126.35 mg kg−1 during the early growth stage (May), vigorous growth stage (August), and late growth stage (October), respectively. The Cd concentrations of roots among the nine mining ecotypes were positively correlated with available content of Cd in the rhizosphere soils, whereas a negative correlation was observed in the nonmining ecotypes. A pot experiment showed that the mining ecotype of A. wardii had a higher biomass production and Cd retention capacity in roots than that of the nonmining ecotype. Due to the relatively high tolerance to Cd and the capacity of roots to retain this metal, A. wardii may be useful for the phytostabilization of soils contaminated by Cd.

Cd accumulation and phytostabilization potential of dominant plants surrounding mining tailings

Establishment of tea plantations (Camellia sinensis L.) could markedly change the pools of soil organic carbon (SOC) and labile organic carbon (LOC). However, the effects of different chronosequence phases on the quantity and quality of SOC in such plantations were poorly understood. In this study, we investigated SOC dynamics following farmland conversion to tea plantations of 16-, 23-, 31-, and > 50 years old in Zhongfeng Township of Mingshan County, Sichuan, which is in southwest China. We specifically examined the effects of the age of various tea plantations on the concentrations of SOC and LOC, including readily oxidizable carbon (ROC), water soluble organic carbon (WSOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and mineralizable organic carbon (MOC) within soil water-stable aggregates. We found that the contents of very coarse fraction (> 5 mm) and very fine fraction (  5 mm and mean weight diameter (MWD) in 23 year old tea plantation were seen to be higher when compared with > 50 years, indicating that maximum soil stability was within soil macro-aggregates. SOC, ROC, POC, MBC, and MOC contents were reduced with the decreasing of particle size except for WSOC. On the whole, the SOC concentrations in > 50 yr. of tea plantations at two soil depths were significantly lower than those of 23 yr. In addition to WSOC, other LOC contents changed in trends parallel to SOC, demonstrating that tea plantation reaching up to about 23 years contributed more to the soil quality than > 50 yr.

Effect of tea plantation age on the distribution of soil organic carbon fractions within water-stable aggregates in the hilly region of Western Sichuan, China

Effect of tea plantation age on the distribution of soil organic carbon and nutrient within micro-aggregates in the hilly region of western Sichuan, China

Variations in microbial biomass and activity within aggregate fractions can provide valuable information regarding mechanisms for enhancing carbon (C) sequestration and nutrient status in agricultural soils. The effects of different chronosequence phases on these variations in tea (Camellia sinensis L.) plantations have not yet been well documented. In this study, we assessed the relationship between tea plantation age and microbial biomass and activity at the aggregate scale. Microbial biomass C and respiration rate were determined in different size fractions from soil depths of 0–20 and 20–40 cm under four tea plantations of varying ages (16, 23, 31, and 53 years) in the hilly region of Western Sichuan, China. Aggregates were separated by an improved dry-sieving procedure into four fractions: > 2 mm (large macro-aggregates), 2–1 mm (medium macro-aggregates), 1–0.25 mm (small macro-aggregates), and < 0.25 mm (micro-aggregates). All the tea plantations we observed were dominated by large macro-aggregates with values of 41.25%–61.12% at both soil depths. Their proportion and mean weight diameter (MWD) were higher in 23-year tea plantation than those in other plantations, indicating that the soil structure in the 23-year tea plantation was more stable than the others. Notably, we found that aggregate stability is closely correlated with microbial biomass and their relationship is dependent on aggregate size. Aggregates with different particle sizes exhibited different levels of microbial biomass C and respiration rate regardless of tea plantation age. The soil properties we examined were at their highest levels in large macro-aggregates, implying that microorganisms associated with these fractions are more biologically active there than elsewhere in the present ecosystem. Decreases in soil microbial biomass and activity after 23 years of tea planting occurred mainly due to reduction in large macro-aggregates in the whole soil over time. To this effect, it is crucial to establish appropriate management protocol tailored to the prevention of soil structure degradation after 23 years of tea planting in such plantations.

Zicheng Zheng

Papers

Soil aggregate-associated bacterial metabolic activity and community structure in different aged tea plantations

Cd accumulation and phytostabilization potential of dominant plants surrounding mining tailings

Effect of tea plantation age on the distribution of soil organic carbon fractions within water-stable aggregates in the hilly region of Western Sichuan, China

Effect of tea plantation age on the distribution of soil organic carbon and nutrient within micro-aggregates in the hilly region of western Sichuan, China

Distribution of microbial biomass and activity within soil aggregates as affected by tea plantation age