Bacterial Biodiversity-Ecosystem Functioning Relations Are Modified by Environmental Complexity

Peer reviewedPublisher PD

The geoaccumulation index and enrichment factor of mercury in mangrove sediment of Port Klang, Selangor, Malaysia.

Mangrove areas are important to the ecosystem. One of its crucial functions is as a sink of pollutants, especially metal ions. However, the accumulation of metals in mangrove sediment can generate negative impacts on plant growth, microbial activity, and soil fertility. Apart from that, the severity of the impact is highly influenced by the type of metal found in the sediment and the quality of sediment itself. One of the metals that have adverse effects on the environment is mercury. The objectives of this study are to determine the concentration and distribution of mercury and to assess the enrichment of mercury in Port Klang mangrove sediment by using geoaccumulation index and enrichment factor. Sediment samples were collected from 30 sampling points that cover Langat River and Klang River estuaries, Lumut Straits, Pulau Klang, and Pulau Indah. During sampling, water parameters such as pH, salinity, electrical conductivity, and total dissolved solids were measured in situ, whereas the total mercury in sediment samples was determined at the laboratory using inductively coupled plasma mass spectrometry. In this study, mercury was found to be concentrated along Lumut Strait especially in the mixing zone near the confluence of Langat River and at the jetty to Pulau Ketam. The geoaccumulation index and enrichment factor (calculated using logarithmized data of the reference element) found that three stations were enriched with mercury. In addition, geoaccumulation index was also observed to be more objective compared to enrichment factor whose results were influenced by the concentration of reference element used

Organic acid behaviour in a calcareous soil implications for rhizosphere nutrient cycling

Calcareous soils are frequently characterized by the low bioavailability of plant nutrients. Consequently, many vascular plant species are unable to successfully colonize calcareous sites and the floristic composition of calcareous and acid silicate soils has been shown to differ markedly. The root exudation of oxalate and citrate has been suggested to play a pivotal role in same nutrient acquisition mechanisms operating in calcareous soils. The aim of this study was therefore to investigate the nutrient extraction efficiency of three individual organic acids commonly identified in root exudates, i.e. citric, malic and oxalic acid. Our results clearly demonstrate the context dependent nature of nutrient release by organic acids. The degree of P extraction was highly dependent on which organic acid was added, their concentration and pH, and their contact time with the soil. P is generally more efficiently extracted by organic acids at a high pH and follows the series oxalate > citrate > malate. The opposite relationship between pH and extraction efficiency was apparent for most other cations examined (e.g. Zn, Fe), which are more efficiently extracted by organic acids at low pH. A serious constraint to the ecological importance of organic acid exudation in response to P deficiency is, however, their very low P mobilization efficiency. For every mol of soil P mobilized, 1000 mol of organic acid has to be added. It can, however, be speculated that in a calcareous soil with extremely low P concentrations it is still beneficial to the plants to exude organic acids in spite of the seemingly high costs in terms of carbon

Organic acid mediated P mobilization in the rhizosphere and uptake by maize roots

The exudation of organic acids into the rhizosphere by plant roots has been hypothesized to be one potential mechanism by which plants can enhance the mobilization of poorly soluble nutrients in the soil. The experiments undertaken in this study were aimed at determining whether the organic acids, citrate and oxalate, could enhance the uptake of P-33 from a calcareous soil with a high P fixation capacity (Typic rendoll). Soil-filled rhizosphere microcosms were constructed which allowed the growth of a single maize root axis through a (KH2PO4-)-P-33 labelled patch of soil. After passage of the root through the P-33-labelled soil, organic acids or distilled water (control) were added to the patch at concentrations of 1 and 10 mM over a subsequent 4-day period. While oxalate resulted in an approximately two-fold enhancement in shoot P-33 accumulation, citrate did not result in a significant enhancement of P-33 uptake above controls to which only distilled water were added. No synergistic effect on shoot P-33 accumulation was observed when both oxalate and citrate were added to the soil simultaneously. We hypothesize that the observed differences in shoot P-33 accumulation by the two organic acids were due primarily to the differences in their biodegradation rate and P mobilization reactions. This study demonstrates that in vivo, organic acids can cause a significant enhancement of plant P uptake, however, the magnitude of the P mobilization response is likely to be highly context dependent. (C) 2002 Published by Elsevier Science Ltd

Cadmium and copper change root-growth and morphology of Pinus-pinea and Pinus-pinster seedlings

Heavy metal loads in forest soils have been increasing over time due to atmospheric inputs. Accumulation in the upper soil layers could affect establishment of seedlings and forest regeneration. Mediterranean species show a high initial root development, allowing seedlings to reach the moisture of deeper soil layers. In the present work seedlings of stone pine (Pinus pinea L.) and maritime pine (Pinus pinaster Ait.), were grown in culture solution supplied with 0.0, 0.1, 1 or 5 mu M CdSO4 or with 1 mu M CdSO4 and 1 mu M CuSO4 combined. In both species tap-root elongation was drastically reduced in the 5 mu M Cd2+ and in the (Cd2+ + Cu2+) treatments. A supply of 0.1 or 1 mu M Cd2+, however, enhanced root elongation in Pious pinea without significantly influencing root elongation in Finns pinaster. In both species the root density (weight per unit length) and the width of the cortex increased in response to Cd2+ exposure. In Pinus pinaster the mitotic index decreased at the higher Cd2+ concentrations and when Cd2+ and Cu2+ were combined. The data suggest that cell elongation is more sensitive to Cd2+ than cell division. The number and length of the lateral roots were also affected by Cd2+ treatment to a higher degree in Pinus pinaster than in Pinus pinea, reflecting the different Cd-tolerance of the two species

Influence of copper on root-growth and morphology of Pinus-pinea L. and Pinus-pinaster Ait. seedlings

We assessed the effects of Cu on root growth and morphology of stone pine (Pinus pinea L.) and maritime pine (Pinus pinaster Ait.) seedlings grown in culture solutions supplied with 0.012 (control), 0.1, 1 or 5 mu M CuSO4. The presence of 5 mu M Cu in the nutrient solution completely inhibited root growth of both species within 3 days. In both species, taproot elongation was reduced in the presence of 1 mu M CU, although partial growth recovery occurred after 7 days of treatment. The presence of 0.1 mu M Cu in the culture solution slightly enhanced root elongation in P. pinnster, but did not significantly influence root elongation in P. pinea. In both species, root weight per unit length increased in response to Cu exposure, and in P. pinaster, root diameter was significantly increased. The Cu treatments also affected lateral root number and length. In the presence of 1 mu M Cu, both species formed only short lateral primordia. The 1 mu M Cu treatment increased the lateral root index (number of roots per cm of root length) of P. pinaster, but decreased that of P. pinea, compared with control values. Neither the 0.1 nor 1 mu M Cu treatment had a significant effect on the mitotic index of either species. We conclude that cell elongation is more sensitive to Cu than cell division. Cell membrane damage, as indicated by Trypan blue staining, occurred after 10 days of exposure to 1 mu M Cu

Metal pollution and forest decline

The chapter presents an overview on the antrophogenic sources of heavy metal pollution and the patterns of distribution of these contaminnats in natural environments. It presents authors' researches on the different sensitivity of forest species to heavy metals and on the role of mycorrhiza. Finally amelioration techniques are discussed

Cadmium and copper uptake and distribution in Mediterranean tree seedlings

Copper and cadmium uptake and distribution in 2-week-old seedlings of stone pine (Pinus pinea L.), maritime pine (Pinus pinaster Ait.) and ash (Fraxinus angustifolia Vahl.) were investigated. Seedlings were grown in culture solution at increasing concentrations of CuSO4 (0.012-5 mu M) and CdSO4 (0.0-5 mu M). All species accumulated copper in a larger amount than cadmium, Translocation to the shoot was strongly restricted for both metals, though higher cadmium mobility within the plant could be evidenced. A strong relationship between root content and growth inhibition was detected in the roots in response to copper but not to cadmium treatments, Among species P. pinea seemed to be more tolerant to cadmium, whereas F: angustifolia was highly sensitive to both cadmium and copper. X-ray microanalysis of root tip sections showed that copper and cadmium only accumulated in the root tips of F. angustifolia, copper mostly in the cell walls of the cortex layer, cadmium in the inner compartments of the cortex cells. It is suggested that in the two Pinus species the well developed root cap plays a protecting role against metal uptake at the root-tip zone