Current analytical techniques in soil biogeochemistry

Soil biogeochemistry is developed through studying the behavior of atoms in soils and landscapes and their compounds: molecules, organic-mineral complexes, and crystal structures, as well as biota. Biogeochemists and soil scientists developed new experimental methods as a result of these studies. The best results were shown by electron microscopy and spectral methods-nuclear gamma resonance, nuclear magnetic resonance (NMR), and synchrotron radiation based X-ray adsorption spectroscopy. They allowed for the acquisition of new evidence on the role of biota in the geochemistry of many chemical elements in the composition of both the mineral and organic parts of the soil. The latest key results of these investigations from around the world are given.     

Abstracts of nippon Dozyohiryogaku Zasshi

Aluminum toxicity and boron deficiency are the major factors that limit plant growth and development in acid soils and in B-deficient soils. Root growth inhibition is an early symptom of AI toxicity and B deficiency. Effects of AI and B supply and their interaction on the growth of wheat (Triticum aestivum L.) seedlings were investigated using hydroponics. Fifteen wheat cultivars commonly grown in Bangladesh were used and found to differ considerably in their tolerance to AI toxicity and B deficiency. The relative root length of all the wheat cultivars at 50 µM AI (pH 4.5) ranged from 27 to 71% relative to the control (0 µM AI). Among the cultivars, Inia66 and Kalyansona were found to be the most Al-tolerant and sensitive cultivars, respectively, based on the data of relative root length, malate exudation and AI content of roots. Malate was detected in all the cultivars in the presence of 100 µM AI (pH 4.3). Inia66 exuded a 6-fold larger amount of malate and the AI content of roots was 4 times lower than that in Kalyansona. The vigorous seedling growth was observed at 40 µM B among the series of B treatments. Considerable cultivar differences in response to 40 µM B were observed among the 15 cultivars. Kalyansona was considered to be the most sensitive and Kheri the most tolerant to B deficiency. The interaction effects of B ( 40 and 200 µM) and AI (50 µM) on seedling growth were also examined in Inia66 and Kalyansona. Root growth was inhibited in the presence of Al but B supply especially at 200 µM B in the Kalyansona cultivar caused a slight improvement.     

Kinetics of Zinc Uptake and Anatomy of Roots and Leaves of Coffee Trees as Affected by Zinc Nutrition

Abstract

The influence of silicon (Si) (2.5 mM), sodium chloride (NaCl) (100 mM), and Si (2.5 mM) + NaCl (97.5 mM) supply on chlorophyll content, chlorophyll fluorescence, the concentration of malondialdehyde (MDA), H₂O₂ level, and activities of superoxide dismutase (SOD; E.C.1.15.1.1.), ascorbate peroxidase (APx; E.C.1.11.1.11.), catalase (CAT; E.C.1.11.1.6.), guaiacol peroxidase (G-POD; E.C.1.11.1.7.) enzymes, and protein content were studied in tomato (Lycopersicon esculentum Mill c.v.) leaves over 10-day and 27-day periods. The results indicated that silicon partially offset the negative impacts of NaCl stress with increased the tolerance of tomato plants to NaCl salinity by raising SOD and CAT activities, chlorophyll content, and photochemical efficiency of PSII. Salt stress decreased SOD and CAT activities and soluble protein content in the leaves. However, addition of silicon to the nutrient solution enhanced SOD and CAT activities and protein content in tomato leaves under salt stress. In contrast, salt stress slightly promoted APx activity and considerably increased H₂O₂ level and MDA concentration and Si addition slightly decreased APx activity and significantly reduced H₂O₂ level and MDA concentration in the leaves of salt-treated plants. G-POD activity was slightly decreased by addition of salt and Si. Enhanced activities of SOD and CAT by Si addition may protect the plant tissues from oxidative damage induced by salt, thus mitigating salt toxicity and improving the growth of tomato plants. These results confirm that the scavenging system forms the primary defense line in protecting oxidative damage under stress in crop plants.     

Fate of Zinc Ammonia Acetate in Soils and Its Uptake by Corn

Zinc ammonium acetate (ZAA) is applied to soil with anhydrous ammonia as a carrier to improve corn (Zea mays L.) productivity. To study the fate of ZAA in the soils, a laboratory leaching experiment was conducted with ¹⁴C-ZAA and ⁶⁵Zn-ZAA using water or NH₄OH as carrier. Results showed that ZAA degraded in the soil and released CO₂. The released CO₂ was from the acetate component of ZAA and accounted for less than 0.06% of the total applied ¹⁴C. Using H₂O as carrier resulted in more CO₂ release than using NH₄OH, regardless of soil type. However, more ¹⁴C was detected in the leachate when using NH₄OH as a carrier than when using H₂O. A plant uptake experiment using ¹⁴C-ZAA and ⁶⁵Zn-ZAA indicated that four-leaf-stage corn seedlings absorbed higher amounts of ¹⁴C in the stem and root than in the leaves. The ⁶⁵Zn was detected in most tested plant parts. Our study showed that ZAA enhanced cytokinin levels in root and/or shoot tissues of corn seedlings, suggesting a secondary regulatory effect of ZAA in improving corn productivity.     

Interaction Between Salinity Stress and Verticillium Wilt Disease in Three Pistachio Rootstocks in a Calcareous Soil

ABSTRACT

The interaction between soil salinity and infection caused by Verticillium dahliae was studied in pistachio (Pistacia vera) in a greenhouse experiment. Treatments consisted of 0, 1400, 2800, and 4200 mg sodium chloride (NaCl) kg^{? 1} soil and three rootstocks (Sarakhs, Badami, and Qazvini cultivars). They were gradually exposed to salinity stress before and/or after root inoculation with a water suspension of 10⁷ conidia/mL of a pistachio isolate of V. dahliae. Salt stress significantly increased rootstock shoot and root colonization by V. dahliae. All rootstocks were susceptible to V. dahliae, but symptoms of the disease appeared earlier in Sarakhs, a salt sensitive cultivar. Moreover, salinity and V. dahliae interaction increased the concentrations of sodium (Na), potassium (K) and chloride (Cl), but decreased the K/Na ratio in all rootstocks. Shoot and root tissues of inoculated Sarakhs and Qazvini (a salt tolerant) contained the highest and the lowest concentrations of Na, K,and Cl, respectively. In salinity treatments, shoot and root dry weight of all rootstocks decreased as compared with controls. Sarakhs showed smaller shoot and root dry weight than Qazvini and Badami. Also, increasing the NaCl level increased accumulation of Na, K, and Cl in shoot and root of the rootstocks. Sarakhs showed higher concentrations of ions in the shoot and root. Based on shoot and root dry weights and ion accumulation, Sarakhs and Qazvini were susceptible and tolerant to salinity, respectively.     

Soil fertility properties on Agave angustifolia Haw. plantations

This study examined the variations in soil physical, chemical and biological properties from Agave angustifolia fields in three sites with different topographic conditions (valley, hill and mountain), in Oaxaca, Mexico, associated with the tillage systems, disk ploughing (DP), animal drawn ploughing (ADP) and minimum tillage (MT), respectively. Plant ages were 1.5–3.5 years (class 1), 3.6–5.5 years (class 2) and 5.6–7.5 years (class 3). Soil samples were taken at two soil depths (0–20 and 21–40 cm) from plots of 4000 m² within each site and plant age classes, during the spring of 2005. The main changes in soil properties were found in the mountain site. Soil bulk density (2.0 g cm⁻³), cone penetration resistance (CPR) (3.96 MPa), 0.7 and 1.0 mm water stable aggregates (WSA) (28.3 g kg⁻¹ and 102.2 g kg⁻¹, respectively) were higher in the mountain site than in the hill and valley fields. This result is consistent with the rocky substrate beneath the shallow soil. Soil organic carbon (SOC) (23.9 g kg⁻¹), available N (23.1 mg kg⁻¹) and soil microbial biomass carbon (SMBC) (969.6 μg g⁻¹) at the mountain site showed the highest values, suggesting that MT practiced in this topographic condition favours the organic matter accumulation and biological activity. Soil microbial biomass carbon and SOC seem to be the soil properties that were mainly affected by the sites and soil management associated with them. For the three sites, SOC, P_Olsen, available N, exchangeable Na⁺ and SMBC were higher at 0–20 cm depth than at 21–40 cm depth within each site. Exchangeable Ca²⁺ and K⁺, P_Olsen and CPR increased with plant age. In contrast, available N decreased. Soil chemical properties were more affected by the age of the plant than physical and biological properties. Results reported here represent a reference of the fertility properties of soils cultivated with A. angustifolia, which could be used in further studies focused on management and tillage systems.     

Cation exchange capacity of density fractions from paired conifer/grassland soils

The cation exchange capacity (CEC) of a soil depends on the type and amount of both mineral and organic surfaces. Previous studies that have sought to determine the relative contribution of organic matter to total soil CEC have not addressed differences in soil organic matter (SOM) composition that could lead to differences in CEC. The objectives of this study were (1) to compare the CEC of two distinct SOM pools, the “light fraction (LF)” composed of particulate plant, animal, and microbial debris, and the “heavy fraction (HF)” composed of mineral-bound organic matter; and (2) to examine the effects of differences in aboveground vegetation on CEC. Soil samples were collected from four paired grassland/conifer sites within a single forested area and density fractionated. LF CEC was higher in conifer soils than in grassland soils, but there was no evidence of an effect of vegetation on CEC for the HF or bulk soil. LF CEC (but not HF CEC) correlated well with the C concentration in the fraction. The mean CEC of both fractions (per kg fraction) exceeded that of the bulk soil; thus, when the LF and HF CEC were combined mathematically by weighting values for each fraction in proportion to dry mass, the resulting value was nearly twice the measured CEC of bulk soil. On a whole soil basis, the HF contributed on average 97% of the CEC of the whole soil, although this conclusion must be tempered given the inflation of CEC values by the density fractionation procedure.     

First record of <Emphasis Type="Italic">Grewia tenax</Emphasis> (Forssk.) Fiori in northern Oman,a valuable fruit producing shrub

Grewia tenax (Forssk.) Fiori is a wild fruit species with multiple uses in different parts of the Tropics and Subtropics. It is common on the Arabian Peninsula and has also been recorded in southern Oman. To date, no record of the species exists for the northern part of this country. To close this distributional gap, three sites in the al-Hajar mountains of northern Oman were surveyed in summer 2005 and spring 2006. During the botanical fieldwork, several flowering and fruiting plants were found in Wadi Bani Awf and Wadi Muaydin. In the latter area G. tenax fruits are eaten by local people. In addition to G. tenax, nine woody perennials with edible fruit were recorded. In northern Oman, fruits of Sideroxylon mascatense (A. DC.) Penn. and Ziziphus spina-christi (L.) Desf. are widely collected and sold on local markets. G. tenax shrubs were found to be heavily grazed indicating its high palatability to goats and sheep. The occurrence of G. tenax in the al-Hajar mountains is a new record to the flora of northern Oman and calls for further investigation of botanists and germplasm collectors.     

RAPD and ISSR fingerprinting in cultivated chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.) and its wild progenitor <Emphasis Type="Italic">Cicer reticulatum</Emphasis> Ladizinsky

Detection of genetic relationships between 19 chickpea cultivars and five accessions of its wild progenitor Cicer reticulatum Ladizinsky were investigated by using RAPD and ISSR markers. On an average, six bands per primer were observed in RAPD analysis and 11 bands per primer in ISSR analysis. In RAPD, the wild accessions shared 77.8% polymorphic bands with chickpea cultivars, whereas they shared 79.6% polymorphic bands in ISSR analysis. In RAPD analysis 51.7% and 50.5% polymorphic bands were observed among wild accessions and chickpea cultivars, respectively. Similarly, 65.63% and 56.25% polymorphic bands were found in ISSR analysis. The dendrogram developed by pooling the data of RAPD and ISSR analysis revealed that the wild accessions and the ICCV lines showed similar pattern with the dendrogram of RAPD analysis. The ISSR analysis clearly indicated that even with six polymorphic primers, reliable estimation of genetic diversity could be obtained, while nearly 30 primers are required for RAPD. Moreover, RAPD can cause genotyping errors due to competition in the amplification of all RAPD fragments. The markers generated by ISSR and RAPD assays can provide practical information for the management of genetic resources. For the selection of good parental material in breeding programs the genetic data produced through ISSR can be used to correlate with the relationship measures based on pedigree data and morphological traits to minimize the individual inaccuracies in chickpea.