Drought responses of an exotic tree (Eriobotrya japonica) in a tropical cloud forest suggest the potential to become an invasive species

New Forests - Eriobotrya japonica is a non-native tree expanding in secondary forests and threatening the tropical montane cloud forest of central Veracruz, Mexico. Our objective was to investigate...     

Water relations, gas exchange, and nutrient response to a long term constant water deficit

Wheat plants (Triticum aestivum) were grown for 43 days in a micro-porous tube nutrient delivery system. Roots were unable to penetrate the microporous tube, but grew on the surface and maintained capillary contact with the nutrient solution on the inside of the tube through the 5-micron pores of the porous tube. Water potential in the system was controlled at -0.4, -0.8, and -3.0 kPa by adjusting the applied pressure (hydrostatic head) to the nutrient solution flowing through the microporous tubes. A relatively small decrease in applied water potential from -0.4 to -3.0 kPa resulted in a 34% reduction of shoot growth but only a moderate reduction in the midday leaf water potential from -1.3 to -1.7 MPa. Carbon dioxide assimilation decreased and water use efficiency increased with the more negative applied water potentials, while intercellular CO2 concentration remained constant. This was associated with a decrease in stomatal conductance to water vapor from 1.90 to 0.98 mol m-2 s-1 and a decrease in total apparent hydraulic conductance from 47 to 12 micromoles s-1 MPa-1. Although the applied water potentials were in the -0.4 to -3.0 kPa range, the actual water potential perceived by the plant roots appeared to be in the range of -0.26 to -0.38 MPa as estimated by the leaf water potential of bagged plants. The amount of K, Ca, Mg, Zn, Cu, and B accumulated with each unit of transpired water increased as the applied water potential became less negative. The increase in accumulation ranged from 1.4-fold for K to 2.2-fold for B. The physiological responses observed in this study in response to small constant differences in applied water potentials were much greater than expected from either the applied water potential or the observed plant water potential. Even though the micro-porous tube may not represent natural conditions and could possibly introduce morphological and physiological artifacts, it enables a high degree of control of water potential that facilitates the investigation of many aspects of water relations not practical with other experimental systems.     

Developing regulatory programs for the control of acid precipitation

The U.S. Clean Air Act provides mechanisms by which the public welfare may be protected from ‘any known or anticipated adverse effects associated with the presence of (an) air pollutant in the ambient air’. The history of the U.S. Environment Protection Agency's (EPA) efforts to establish and defend a secondary ambient air quality standard for S oxides is reviewed. The role of acid rain in producing ‘welfare effects’ is described. Emphasis is given to the fact that a wide range of effects not simply limited to forest vegetation must be considered when designing pollution control programs. The possible effects of ignoring acid rain in developing control strategies to meet health related standards for S oxides, N oxides and particulates are mentioned. Researchers need to be aware of the kinds of information which are needed by regulatory agencies before a regulatory program can be designed for alleviating the threat. Concern and speculation are not adequate. Accurate dose-response information and cumulative damage estimates are needed to quantify the effects of acid rain. Of vital importance are: (1) discovery of pollutant concentrations, mechanisms, and atmospheric conditions which lead to harmful effects: and (2) identification of major sources of the pollutant. The effect such information could have on techniques for meeting groundlevel air-quality standards such as tall stacks and Intermittant Control Systems (ICS) is discussed. The desirability of an integrated research effort in this area to answer these needs is stressed. EPA efforts in this regard are mentioned.     

Long-term tillage effects on soil quality

Public interest in soil quality is increasing, but assessment is difficult because soil quality evaluations are often purpose- and site-specific. Our objective was to use a systems engineering methodology to evaluate soil quality with data collected following a long-term tillage study on continuous corn (Zea mays L.). Aggregate characteristics, penetration resistance, bulk density, volumetric water content, earthworm populations, respiration, microbial biomass, ergosterol concentrations, and several soil-test parameters (pH, P, K, Ca, Mg, Total-N, Total-C, NH₄-N, and NO₃-N) were measured on Orthic Luvisol soil samples collected from Rozetta and Palsgrove silt loam (fine-silty, mixed, mesic Typic Hapludalfs) soils. Plots managed using no-till practices for 12 years before samples were collected for this study had surface soil aggregates that were more stable in water and had higher total carbon, microbial activity, ergosterol concentrations, and earthworm populations than either the chisel or plow treatments. Selected parameters were combined in the proposed soil quality index and gave ratings of 0.48, 0.49, or 0.68 for plow, chisel, or no-till treatments, respectively. This indicated that long-term no-till management had improved soil quality. The prediction was supported by using a sprinkler infiltration study to measure the amount of soil loss from plots that had been managed using no-till or mold-board plow tillage. We conclude that no-till practices on these soils can improve soil quality and that the systems engineering methodology may be useful for developing a more comprehensive soil quality index that includes factors such as pesticide and leaching potentials.     

Iridium abundances across the ordovician-silurian stratotype

Chemostratigraphic analyses in the Ordovician-Silurian boundary stratotype section, bracketing a major extinction event in the graptolitic shale section at Dob's Linn, Scotland, show persistently high iridium concentrations of 0.050 to 0.250 parts per billion. There is no iridiumn concentration spike in the boundary interval or elsewhere in the 13 graptolite zones examined encompassing about 20 million years. Iridium correlated with chromium, both elements showing a gradual decrease with time into the middle part of the Lower Silurian. The chromium-iridium ratio averages about 10(6). Paleogeographic and geologic reconstructions coupled with the occurrence of ophiolites and other deep crustal rocks in the source area suggest that the high iridium and chromium concentrations observed in the shales result from terrestrial erosion of exposed upper mantle ultramafic rocks rather than from a cataclysmic extraterrestrial event.     

An unusual occurrence of probable Pleistocene corestone within a Cretaceous dioritic enclave,Peninsular Ranges,California

We here document an unusual occurrence of probable Pleistocene corestone within an ∼ 5 m by ∼ 5 m dioritic enclave contained within a Cretaceous tonalitic pluton, Santa Margarita Ecological Reserve, SW California. The enclave lies within ∼ 3.5 km of the seismically active ∼ 1.5–2 Ma Elsinore fault zone, and may have been subjected to ∼ 70–90 ground shaking events since ∼ 22,000–18,000 years ago. The studied corestone is elliptical with major axis measuring ∼ 55 cm and minor axis ∼ 26 cm in length. It is surrounded by a discontinuous ∼ 7 cm thick rind that breaks apart under slightly greater finger pressure than does the surrounding saprolite. In order to assess changes in the physical and chemical properties of the corestone, rind, and saprolite we collected along an ∼ 66.5 cm long traverse 4 samples from the corestone, 1 from the rind, and 5 from the saprolite for bulk and grain density, porosity, and major and trace element analyses. Textural and clay mineral data, along with the redistribution of elemental mass, indicate that the weathering of biotite, and to much lesser degrees apatite and the An-rich cores of plagioclase, played critical roles in the production of saprolite especially in a narrow ∼ 20 cm wide zone adjacent to the rind of the corestone. Within this zone bulk densities reach their minimum values, while porosities and positive volume strains reach their maximums. In addition, the maximum loss of K, Fe, Mn, and Ca mass occurred just inside this region, and is paralleled by the highest CIA values and highest additions of Si and Rb mass. In contrast, the masses of Na and Sr are progressively increased and decreased, respectively along the entire sampling traverse while the loss of Mg, Ti, and P mass is episodic with the greatest losses occurring within the narrow zone adjacent to the rind and at the end of the traverse. The above observations indicate that the conversion of biotite to expandable mixed-layered clay minerals, aided by the alteration of the An-rich cores of plagioclase, produced sufficient stress on grain boundaries that a weakening or loss of intercrystalline cohesion occurred. However, unlike the well documented isovolumetric development of saprolite in other areas, at the study site saprolitization was accompanied by a volume expansion. We speculate that repeated ground shaking in response to earthquakes generated in the nearby Elsinore fault zone may be responsible for this difference. Important byproducts of ground shaking would include additional weakening or loss of intercrystalline cohesion, and the production and enhancement of new and older fluid pathways respectively. The fact that the most intensely altered material at the study site lies adjacent to the boundary between the rind and saprolite, suggests that this interface acted to guide fluid flow around the corestone and rind and into the adjacent saprolite where elemental mass was redistributed down various paths leading to the underlying water table. Most of the leached elemental mass was removed from the area of the sampling traverse, but small increases in Si, Rb, and Na mass suggest redistribution of these elements from elevated areas outside the area sampled during this study. The result of the above complex set of processes is a variably porous and chemically altered saprolitic enclave that is still undergoing modification as it adjusts to the vicissitudes of the paralithic environment and continuing ground shaking during earthquakes generated along the Elsinore fault.