Eric Paterson

Effect of elevated atmospheric CO2 concentration on C-partitioning and rhizosphere C-flow for three plant species

Abstract The effects of elevated atmospheric CO 2 concentration on the partitioning of dry matter and recent assimilate was investigated for three plant species (rye grass, wheat and Bermuda grass). This was evaluated in plant-soil microcosm systems maintained at specific growth conditions, under two CO 2 regimes (450 and 720 μmol mol −1 ). The distribution of recent assimilate between plant, microbial and soil pools was determined by 14 CO 2 pulse chase, for each plant species at both CO 2 concentrations. Growth of rye grass and wheat (both C 3 ) was ca. doubled at the higher CO 2 concentration. Dry matter partitioning was also significantly affected, with an increased root-to-shoot ratio for wheat (0.72–1.03), and a decreased root-to-shoot ratio for rye grass (0.68-0.47) at elevated CO 2 . For Bermuda grass (C 4 ), growth and partitioning of dry matter and 14 C were not affected by CO 2 concentration. 14 C-allocation to the rhizospheres of rye-grass and wheat was found to be increased by 62 and 19%, respectively, at the higher CO 2 concentration. The partitioning of 14 C within the rhizospheres of the two C 3 species was also found to be affected by CO 2 concentration. At the higher CO 2 concentration, proportionately less 14 C was present in the microbial fraction, relative to that in the soil. This indicates altered microbial utilisation of root-released compounds at the higher CO 2 concentration, which may be a consequence of altered quantity or quality of rhizodeposits derived from recent assimilate.

Characterisation of the dynamics of C-partitioning within Lolium perenne and to the rhizosphere microbial biomass using 14C pulse chase

The dynamics of C partitioning with Lolium perenne and its associated rhizosphere was investigated in plant-soil microcosms using 14C pulse-chase labelling. The 14CO2 pulse was introduced into the shoot chamber and the plants allowed to assimilate the label for a fixed period. The microcosm design facilitated independent monitoring of shoot and root/soil respiration during the chase period. Partitioning between above- and below-ground pools was determined between 30 min and 168 h after the pulse, and the distribution was found to vary with the length of the chase period. Initially (30 min after the pulse), the 14C was predominantly (99%) in the shoot biomass and declined thereafter. The results indicate that translocation of recent photoassimilate is rapid, with 14C detected below ground within 30 min of pulse application. The translocation rate of 14C below ground was maximal (6.2% h-1) between 30 min and 3 h after the pulse, with greatest incorporation into the microbial biomass detected at 3 h. After 3 h, the microbial biomass 14C pool accounted for 74% of the total 14C rhizosphere pool. By 24 h, approximately 30% of 14C assimilate had been translocated below ground; thereafter 14C translocation was greatly reduced. Partitioning of recent assimilate changed with increasing CO2 concentration. The proportion of 14C translocated below ground almost doubled from 17.76% at the ambient atmospheric CO2 concentration (450 ppm) to 33.73% at 750 ppm CO2 concentration. More specifically, these changes occurred in the root biomass and the total rhizosphere pools, with two- and threefold 14C increases at an elevated CO2 concentration compared to ambient, respectively. The pulselabelling strategy developed in this study provided sufficient sensitivity to determine perturbations in C dynamics in L. perenne, in particular rhizosphere C pools, in response to an elevated atmospheric CO2 concentration.

Leaching of genetically modified Pseudomonas fluorescens through intact soil microcosms: Influence of soil type

SummaryThe leaching of a genetically modified Pseudomonas fluorescens through soil was investigated using intact (undisturbed) soil microcosms over a 2-month period. The microcosms comprised large cylindrical cores of three contrasting soil types (a loamy sand, a sandy loam, and a clay loam) supporting a grass/clover sward. Late log-phase cells of Pseudomonas fluorescens containing lux genes encoding for bioluminescence were applied to the surface of the soil cores. Eighteen hours after application of the inocula, the microcosms were subjected to simulated rain events (9 mm per event) at 3-day intervals and leachates were analysed for the concentration of genetically modified bacteria. The lux-modified pseudomonads were detected immediately in leachate from the clay looam with a steady decline in the concentration of cells with time. Leaching of pseudomonads from the sandy loam and loamy sand only occurred over a few rain events and total recoveries from the leachate were lower than from the clay loam. Leaching patterns are discussed in relation to differences in structure of topsoil and subsoil, which determine the pathways of water flow, and to the matric potential at inoculation, which determines the pore-size classes into which cells were first introduced.

Leaching of genetically modified Pseudomonas fluorescens through organic soils : influence of temperature, soil pH, and roots

SummaryThe effects of soil temperature and bulk soil pH on the vertical translocation of a genetically modified Pseudomonas fluorescens inoculum were studied in reconstituted soil microcosms, in the presence and absence of growing Lolium perenne roots. The inoculated microcosms received one rainfall event per day (5 mm h-1 for 6 h) for 5 days and the resulting leachate was quantitatively assayed for the presence of the modified pseudomonad. Soil temperature affected the total number of modified pseudomonads detected in the leachate over the 5 days, with significantly lower numbers detected at 25°C compared to 5°C. The bulk soil pH also affected leaching of the inoculum, with significantly greater numbers detected in the effluent at pH 7.5 than at pH 4.5. In the absence of L. perenne, greater numbers of the modified pseudomonads were detected in the pH 7.5 soil after 5 days of leaching compared to soil at pH 4.5. L. perenne roots decreased the number of cells of the inoculum that were leached and detected in the soil after 5 days of leaching. In the soil microcosms used for the pH study the distribution of the inoculum remaining with the soil was altered by L. perenne roots. At each pH value the proportion of cells detected within the soil below the surface 2 cm of the microcosms was greater in the presence of L. perenne roots. The results of this study indicate that soil temperature, bulk soil pH, and the presence of root systems are important factors in determining the extent of inoculum translocation, and should be considered in the design and interpretation of field experiments.

Further study of estertin trichlorides, Cl3SnCH2CH2CO2R. Lewis acidity towards acetonitrile. Crystal structure of Cl3SnCH2CH2CO2Pr-i

Abstract Crystals of Cl 3 SnCH 2 CH 2 CO 2 Pri-i are orthorhombic, space group P 2 1 2 1 2 1 with a 9.638(6), b 10.004(7) and c 12.848(8) A. The tin atom is five-coordinate with two chlorines and carbon equatorial and the remaining chlorine and the carbonyl oxygen axial, in a distorted trigonal-bipyramidal arrangement: (SnCl) ax 2.389(3), average (SnCl) eq 2.320(2), SnC 2.142(9), SnO 2.337(5) A. Apart from the equatorial chlorine and the terminal carbons in the isopropyl group, all non-hydrogen atoms are essentially coplanar. The molecule approaches C 2 v symmetry although not constrained to do so by the crystallographic space group. In MeCN solution, the compounds Cl 3 SnCH 2 CH 2 CO 2 R (I, R = Me, Pr-i, C 6 H 4 X (X = p -MeO, H, p -Cl, o -MeO or C 6 H 3 Cl 2 -2,4) form as equilibrium mixtures of 1/1 and 2/1 MeCN/I complexes; the chelate ring is broken in the 2/1 complexes. Equilibrium constants indicate that the strength of the intramolecular SnO coordination in I increases with the electron releasing ability of the R group.

Crystal structure and coordination chemistry of Cl3SnCH2CH2CH2CO2Et

Abstract The crystal and molecular structure of Cl3SnCH2CH2CH2CO2Et is reported. Crystals of Cl3SnCH2CH2CH2CO2Et are monoclinic, space group P21/c with a 8.0242(5), b 11.571(5), c 13.129(12) A and β 104.54(6)°. The tin atom is 5 coordinate with two chlorines and carbon equatorial and the remaining chlorine and the carbonyl oxygen axial, in a distorted trigonal bipyramidal arrangement: (SnCl)ax 2.382(4) A, average (SnCl)eq 2.310(3), SnC 2.125(12), SnO 2.405(8) A. The six-membered chelate ring is slightly boat-shaped. Coordination of the carbonyl group to tin persists in solution but is broken on complexation to Cl3SnCH2CH2CH2CO2Et by strong nitrogen donors (2,2′-bipyridyl, 1,10-phenanthroline and pyridine (2 moles)). Comparison of the formation constants for adducts of Cl3Sn(CH2)nCO2Et (A, n  2 or 3), both chelates with monodentate donors, D, suggests comparable acceptor strengths for A (n  2) and A (n  3) for 1/1 adduct formation but that A (n  2) is a weaker acceptor for 2D/A formation.

13C PLFAs: a key to open the soil microbial black box?

BackgroundPhospholipid fatty acid (PLFA) analysis is an effective non-culture-based technique for providing information on the living soil microbial community. The coupling of 13C tracers with PLFA analysis can indicate the response of microbial populations to environmental change and has been widely used to trace C flux in soil-plant systems.ScopeBased on studies applying 13C PLFA analysis, the current technological status, current applications and future opportunities are discussed and evaluated. First we describe some aspects of the labelling and analytical methodology. The approaches to study the incorporation of 13C substrate and rhizodeposition C into soil microbial communities are compared. We continue with the application of 13C-labelling to study soil microbial communities, including the utilization of soil mineralisation products, the C flux from plants into the soil microbial pool, the biodegradation of pollutants and on the application to a specific microbial group, i.e. methanotrophs. Additionally, some perspectives on the limitations of the 13C PLFA method and future research avenues are noted.ConclusionsAlthough including some limitations and complications, the 13C PLFA method provides an excellent tool for understanding the relationship between microbial populations and soil biogeochemical cycling, thus providing a key to open the soil microbial black box.

Temporal variability in domestic point source discharges and their associated impact on receiving waters.

Discharges from the widely distributed small point sources of pollutants such as septic tanks contribute to microbial and nutrient loading of streams and can pose risks to human health and stream ecology, especially during periods of ecological sensitivity. Here we present the first comprehensive data on the compositional variability of septic tank effluents (STE) as a potential source of water pollution during different seasons and the associated links to their influence on stream waters. To determine STE parameters and nutrient variations, the biological and physicochemical properties of effluents sampled quarterly from 12 septic tank systems were investigated with concurrent analyses of upstream and downstream receiving waters. The study revealed that during the warmer dryer months of spring and summer, effluents were similar in composition, as were the colder wetter months of autumn and winter. However, spring/summer effluents differed significantly (P<0.05) from autumn/winter for concentrations of biological oxygen demand (BOD), arsenic, barium (Ba), cobalt, chromium, manganese, strontium (Sr), titanium, tungsten (W) and zinc (Zn). With the exception of BOD, Ba and Sr which were greater in summer and spring, the concentrations of these parameters were greater in winter. Receiving stream waters also showed significant seasonal variation (P≤0.05) in alkalinity, BOD, dissolved organic carbon, sulphate, sulphur, lithium, W, Zn and Escherichiacoli abundance. There was a clear significant influence of STE on downstream waters relative to upstream from the source (P<0.05) for total suspended solids, total particulate P and N, ammonium-N, coliforms and E. coli. The findings of this study found seasonal variation in STE and place effluent discharges as a factor affecting adjacent stream quality and call for appropriate measures to reduce or redirect STE discharges away from water courses.

Acidity of Cl3SnCH2CH2CO2H

Abstract Interaction of Cl 3 SnCH 2 CH 2 CO 2 H with aniline bases in CH 2 Cl 2 solution has been studied by UV-visible spectroscopy. As measured by the extents of complexation with the bases, Cl 3 SnCH 2 CH 2 CO 2 H is a stronger acid than the corresponding esters, Cl 3 SnCH 2 CH 2 CO 2 R (Lewis acids) and also very much more stronger than the Bronsted acid, CH 3 CH 2 CO 2 H. The enhanced Bronsted acidity arises from the stabilisation of the anion, Cl 3 SnCH 2 CH 2 CO 2 − , by the intramolecular coordination of the tin centre by the carboxylate group.

Temporal Dynamism of Resource Capture: A Missing Factor in Ecology?

Temporal dynamism of plant resource capture, and its impacts on plant-plant interactions, can have important regulatory roles in multispecies communities. For example, by modifying resource acquisition timing, plants might reduce competition and promote their coexistence. However, despite the potential wide ecological relevance of this topic, short-term (within growing season) temporal dynamism has been overlooked. This is partially a consequence of historic reliance on measures made at single points in time. We propose that with current technological advances this is a golden opportunity to study within growing season temporal dynamism of resource capture by plants in highly informative ways. We set out here an agenda for future developments in this research field, and explore how new technologies can deliver this agenda.