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The aim of this study is to rank the relative importance of soil properties, root uptake and root-to-shoot redistribution on the transfer of the trace element nickel from soil to the shoots of non hyperaccumulatings plants. Two contrasting soils and seven plant species have been studied using the radioactive isotope, 63Ni. Shoots and roots were analysed separately and the specific activity of each plant has been measured. The isotopic exchange properties of rhizosphere soil where compared with control non rhizosphere soil. Possible changes in Ni speciation in the rhizosphere have been assessed by comparing the isotopic exchange properties of the rhizosphere and control soil and by comparing the specific activities of Ni in each plant. The capacity of soil to immobilise added radiotracer largely determines root uptake, leading to between a 4- and 40-fold difference between soils for a given species. The redistribution of nickel from roots to shoots was fairly constant for plants grown on the rendzina, but varied strongly between species for the acid soil. This variation enhanced the contrast between species of the soil-to-shoot transfer factor. Root action significantly enhanced immobilisation of added nickel in an acid soil due to the modification of speciation of initially non exchangeable soil nickel, but had little effect on a neutral rendzina. Changes in rhizosphere pH were similar on the two soils. In the acid soil, these pH changes were accompanied by changes in Ni speciation but a causative link has not been established. In the neutral soil pH changes may have modified root uptake properties.

The effects of temperature and prior flooding of soil on P sorption were examined in 2 soils having a rice-based cropping system and showing an induced P deficiency problem in flooded rice-uplant crop rotations. The P sorption capacity of soil increased with increasing temperature as well as with prior flooding, the effects of the latter were, howerver, dominant. The bonding energy of sorption, calculated from the Langmuir isotherm, also increased with both temperature and prior flooding of soils, indicate that the effects of chemical changes associated with alternative anoxic and oxidized soil conditions are more significant in the P reversion process. The apparent heat of sorption reaction, calculated with the Freundlich isotherm and Van't Hoff's equation also increased due to prior flooding of soil.

Physical subsoil constraints limit crop production in many areas of southern Australia. There has been limited success in ameliorating these constraints. A field study commenced in 2005 at two adjacent field sites with and without a 4-year history of grazing lucerne, to determine whether the incorporation of organic (lucerne pellets and dynamic lifter at rates of 10–20 t ha−1) and inorganic (gypsum, coarse sand and MAP) amendments into a depth of 30–40 cm improves crop performance on a Sodosol with dense sodic subsoil. We reported previously that the organic amendments increased wheat yield in the first year by 70% above the untreated control. This paper reports the change in soil water dynamics and the performances of a wheat crop in 2006 and a canola crop in 2007. A drought occurred in 2006 with only 55% of the average annual rainfall. The growing season in 2007 was difficult for canola, due to an extended dry period in the spring. However, there was generally more water captured and stored in deeper soil layers during the summer fallow period in both years, in plots treated with organic amendments, compared to control plots, particularly at the non-lucerne site. The application of organic amendments also increased the crop shoot biomass prior to anthesis at both sites, and increased wheat yield by up to 54% at the non-lucerne site in 2006, and the canola yield at both sites in 2007. The residual effect from the incorporation in 2005 of organic amendments in the subsoil, a practice known as subsoil manuring, significantly increased wheat yield at the non-lucerne site in 2006, and canola yield at both sites in 2007. The increases in crop yield were mainly attributed to the use of extra soil water (stored during the summer fallow) at critical growth stages.

Copper (Cu) and cadmium (Cd) are toxic to plants at high levels. The current situation that many crops are growing on the farmlands with Cu or Cd contamination leads to a big threat to food safety. Based on the small RNA (sRNA) sequencing data, hundreds of the sRNAs responsive to excessive Cu or Cd treatment were extracted. Degradome sequencing data enabled us to identify the targets of the metal stress-responsive sRNAs. According to our results, many sRNAs are responsive to both treatments, indicating the interactions between the Cu and Cd signals. A total of 151 sRNAs are DCL (Dicer-like) 1-dependent, and 156 sRNAs are DCL2/3/4-dependent. Some sRNAs found their loci on rRNAs or tRNAs, and a total of 12 sRNAs were potentially originated from the TAS transcripts. Functional analysis of the regulatory network showed that some of the sRNA--target pairs played a potential role in plant reproduction, and some pairs were possibly implicated in hormone--stress signal interactions. Our study could inspire the development of an efficient approach, possibly through the manipulation of the sRNA-guided regulatory pathways, to improve the stress tolerance or reduce the toxic metal accumulation levels of plants.

Quá trình vận chuyển chủ động của sulfat trong các mô thực vật vừa bị cắt cho thấy có một giai đoạn cảm ứng từ 5 đến 15 giờ. Tính khả thi của cơ chế cảm ứng phụ thuộc vào việc chiết xuất một yếu tố ức chế hòa tan trong nước liên quan đến quá trình chuyển hóa tế bào. Actinomycin D và 5 fluorouracil ngăn chặn sự chuyển đổi sau cảm ứng sang quá trình vận chuyển chủ động cao hơn. Khi được thêm vào cuối giai đoạn cảm ứng, 5 fluorouracil không làm ảnh hưởng đến tốc độ vận chuyển chủ động.

The rice production is experiencing a shift from conventionally seedling-transplanted (TPR) to direct-seeded (DSR) cropping systems in Southeast Asia. Besides the difference in rice crop establishment, water regime is typically characterized as water-saving moist irrigation for DSR and flooding-midseason drainage-reflooding and moist irrigation for TPR fields, respectively. A field experiment was conducted to quantify methane (CH4) and nitrous oxide (N2O) emissions from the DSR and TPR rice paddies in southeast China. Seasonal measurements of CH4 and N2O fluxes from the DSR and TPR plots were simultaneously taken by static chamber-GC technique. Seasonal fluxes of CH4 averaged 1.58 mg m−2 h−1 and 1.02 mg m−2 h−1 across treatments in TPR and DSR rice paddies, respectively. Compared with TPR cropping systems, seasonal N2O emissions from DSR cropping systems were increased by 49 % and 46 % for the plots with or without N application, respectively. The emission factors of N2O were estimated to be 0.45 % and 0.69 % of N application, with a background emission of 0.65 and 0.95 kg N2O-N ha−1 under the TPR and DSR cropping regimes, respectively. Rice biomass and grain yield were significantly greater in the DSR than in the TPR cropping systems. The net global warming potential (GWP) of CH4 and N2O emissions were comparable between the two cropping systems, while the greenhouse gas intensity (GHGI) was significantly lower in the DSR than in the TPR cropping systems. Higher grain yield, comparable GWP, and lower GHGI suggest that the DSR instead of conventional TPR rice cropping regime would weaken the radiative forcing of rice production in terms of per unit of rice grain yield in China, and DSR rice cropping regime could be a promising rice development alternative in mainland China.

A method is described for the determination of concentration gradients in the vicinity of plant roots. Plants are grown in small containers in which the roots are separated from the soil by a screen of nylon cloth. Root hairs but not roots penetrate the screen into the soil. In order to investigate the rhizospheric soil, the soil is frozen by liquid nitrogen and sliced into layers about 0.06 mm thick by means of a refrigerated microtome.

A field investigation was conducted to understand the root distributions and elemental accumulations of Chinese brake (Pteris vittata L.), an As-hyperaccumulator, grown in soils with a gradient of As concentration near an arsenic sulphide mine. The root distribution was affected not only by the levels of soil As, but also by soil texture. Plants grew better in sandy loam soils than in clay soils. Increases in the ratio of frond biomass to underground biomass were correlated with decreasing soil As concentration. Root densities of the plant decreased from 0–10 cm, 10–20 cm to 20–30 cm in the soil profiles. Most of the roots were concentrated in the upper 0–10 cm layer. Under high As conditions, As concentrations in different tissues followed the trends: pinnae > rhizomes ≈ roots of 0–10 cm > roots of 10–20 cm > roots of 20–30 cm > petioles, however, As concentrations in pinnae were higher than those in rhizomes under low As conditions. The rhizomes and pinnae were the main As pools, storing 75–86% of the total As uptaken by the plants. The rhizome, a `buffer-storage' for plant As, maintained high concentrations of As under high soil As while the pinnae became the most important organ of storing the As under low soil As. Chinese brake might possess the ability of adjusting its As-storage under different soil As levels. The plant can not only hyperaccumulate As from the soils, but also enriched P and Ni from the soils and translocated them to the fronds. It is important to improve the root distribution for phytoremediation of As-contaminated soils using Chinese brake.

Little is known of the mechanisms employed by woody plants to acquire key resources such as water and nutrients in hyperarid environments. For phreatophytic plants, deep roots are necessary to access the water table, but given that most nutrients in many desert ecosystems are stored in the upper soil layers, viable shallow roots may be equally necessary for nutrient uptake. We sought to better understand the interaction between water and nutrient uptake from soil horizons differing in the relative abundance of these resources. To this end, we monitored plant water and nutrient status before and after applying flood irrigation to four phreatophytic perennial plant species in the remote hyperarid Taklamakan desert in western China. Sap flow in the roots of five plants of the perennial desert species Alhagi sparsifolia Shap., Karelina caspica (Pall.) Less., Calligonum caput medusea Schrenk, and Eleagnus angustifolia Hill. was monitored using the heat ratio method (HRM). Additionally we measured predawn and midday water potential, foliar nitrate reductase activity (NRA), xylem sap nutrient concentration and the concentration of total solutes in the leaves before, 12 and 96 h after flooding to investigate possible short-term physiological effects on water and nutrient status. Rates of sap flow measured during the day and at night in the absence of transpiration did not change after flooding. Moderately high rates of sap flow (HRM heat pulse velocity, 5–25 cm h−1) detected during the day in soils that had a near zero water content at the surface indicated that all species had contact to groundwater. There was no evidence from sap flow data that plants had utilised flood water to increase maximum rates of transpiration under similar climatic conditions, and there was no evidence of a process to improve the efficiency of water or nutrient uptake, such as hydraulic redistribution (i.e. the passive movement of water from moist soil to very dry soil via roots). Measurements of plant water status, xylem sap nutrient status, foliar NRA and the concentration of osmotically active substances were also unaffected by flood irrigation. Our results clearly show that groundwater acts as the major source of water and nutrients for these plants. The inability of plants to utilise abundant surface soil–water or newly available nutrients following irrigation was attributed to the absence of fine roots in the topsoil layer.