Relative Importance Of Biological Processes Research Articles

The Relative Importance of Phytoplankton Light Absorption and Ecosystem Complexity in an Earth System Model

AbstractWe investigate the relative importance of ecosystem complexity and phytoplankton light absorption for climate studies. While the complexity of Earth System models (ESMs) with respect to marine biota has increased over the past years, the relative importance of biological processes in driving climate‐relevant mechanisms such as the biological carbon pump and phytoplankton light absorption is still unknown. The climate effects of these mechanisms have been studied separately, but not together. To shed light on the role of biologically mediated feedbacks, we performed different model experiments with the EcoGENIE ESM. The model experiments have been conducted with and without phytoplankton light absorption and with two or 12 plankton functional types. For a robust comparison, all simulations are tuned to have the same primary production. Our model experiments show that phytoplankton light absorption changes ocean physics and biogeochemistry. Higher sea surface temperature decreases the solubility of CO2 which in turn increases the atmospheric CO2 concentration, and finally the atmospheric temperature rises by 0.45°C. An increase in ecosystem complexity increases the export production of particulate organic carbon but decreases the amount of dissolved organic matter. These changes in the marine carbon cycling, however, hardly reduces the atmospheric CO2 concentrations and slightly decreases the atmospheric temperature by 0.034°C. Overall we show that phytoplankton light absorption has a higher impact on the carbon cycle and on the climate system than a more detailed representation of the marine biota.

How Plants Influence Resilience of Salt Marsh and Mangrove Wetlands to Sea-Level Rise

This review evaluates the importance of plants and associated biological processes in determining the vulnerability of coastal wetlands to sea-level rise. Coastal wetlands occur across a broad sedimentary continuum from minerogenic to biogenic, providing an opportunity to examine the relative importance of biological processes in wetland resilience to sea-level rise. We explore how plants influence sediment accretion, elevation capital (vertical position in the tidal frame), and compaction or erosion of deposited material. We focus on salt marsh and mangrove wetlands, which occupy a similar physiographic niche and display similar physical and biological controls on resilience to sea-level rise. In both habitats, plants stabilize emergent mudflats and help sustain the wetland position in the tidal frame relative to ocean height through both surface and subsurface process controls on soil elevation. Plants influence soil elevations by modifying (1) mineral sediment deposition and retention, (2) organic matter contributions to soil volume, and (3) resistance to compaction and erosion. Recognition of the importance of plants in coastal wetland resilience to sea-level rise is key to accurate predictions about the future fate of salt marshes and mangrove forests and for development of effective management and restoration plans.

The origin of NO3− and N2 in deep subsurface fracture water of South Africa

Deep (>0.8km depth) fracture water with residence time estimates on the order of several Ma from the Witwatersrand Basin, South Africa contains up to 40μM of NO3−, up to 50mM N2 (90 times air saturation at surface) and 1 to ~400μM NH3/NH4+. To determine whether the oxidized N species were introduced by mining activity, by recharge of paleometeoric water, or by subsurface geochemical processes, we undertook N and O isotopic analyses of N species from fracture water, mining water, pore water, fluid inclusion leachate and whole rock cores.The NO2−, NO3− and NH3/NH4+ concentrations of the pore water and fluid inclusion leachate recovered from the low porosity quartzite, shale and metavolcanic units were ~104 times that of the fracture water. The δ15N–NO3− and δ18O–NO3− of the pore water and fluid inclusion leachate, however, overlapped that of the fracture water with the δ15N–NO3− ranging from 2 to 7‰ and the δ18O–NO3− ranging from 20 to 50‰. The δ15N–NO3− of the mining water ranged from 0 to 16‰ and its δ18O–NO3− from 0 to 14‰ making the mining water NO3− isotopically distinct from that of the fracture, pore and fluid inclusion water. The δ15N–N2 of the fracture water and the δ15N–N from the cores ranged from −5 to 10‰ and overlapped the δ15N–NO3−. The δ15N–NH4+ of the fracture water and pore water NH3/NH4+ ranged from −15 to 4‰. Although the NO3− concentrations in the pore water and fluid inclusions were high, mass balance calculations indicate that NO3− accounts for ≤10% of the total rock N, whereas NH3/NH4+ trapped in fluid inclusions or NH4+ present in phyllosilicates account for ≥90% of the total N.Based on these findings, the fluid inclusion NO3− appears to be the source of the pore water and fracture water NO3− rather than paleometeoric recharge or mining contamination. Irradiation experiments indicate that radiolytic oxidation of NH3 to NO3− can explain the fluid inclusion NO3− concentrations and, perhaps, its isotopic composition, but only if the NO3− did not attain isotopic equilibrium with the hydrothermal fluid 2billion years ago. The δ15N–N, δ15N–N2 and δ15N–NH4+ suggest that the reduction of N2 to NH4+ also must have occurred in the Witwatersrand Basin in order to explain the abundance of NH4+ throughout the strata. Although the depleted NO3− concentrations in the fracture water relative to the pore water are consistent with microbial NO3− reduction, further analyses will be required to determine the relative importance of biological processes in the subsurface N cycle and whether a complete subsurface N cycle exists.

Community-level analysis of spatiotemporal plant dynamics

We present an approach for the analysis of spatiotemporal patterns and scale-dependence in the dynamics of plant communities that combines well-known methods to reduce complexity arising from the high-dimensionality of ecological data. Our approach takes into account both correlations and autocorrelations in the structure and dynamics of the community. In application to a sand dune annual plant community, we find answers to questions regarding the nature of community response in space and time, and identify significant spatiotemporal interactions and spatiotemporal scales. Community-level spatial correlograms reveal a fixed pattern in time that is not apparent from species-level dynamics. In this sense, the community is shown to be more stable than the sum of its parts. This form of stability is not a simple artifact of averaging species-specific responses, and points to some consistency in species interactions. Temporal correlograms are highly spatially-specific. In this sense, the inclusion of the spatial information is shown to change our view of temporal dynamics. The relative importance of biological processes versus an environmental gradient is examined in the temporal community response. We find that community response to rainfall is also spatially-specific and that the temporal autocorrelation dynamics shows similar patterns even when the effect of rainfall is removed. Our findings are relevant to both empirical and theoretical work aimed at understanding the interaction between space and time in ecological communities.

A literature review and evaluation of the. Hedley fractionation: Applications to the biogeochemical cycle of soil phosphorus in natural ecosystems

The Hedley fractionation recognizes plant-available forms (Resin Pi, Bicarb Pi, and Bicarb Po) and refractory forms (NaOH Pi, NaOH Po, sonic Pi, sonic Po, HCl Pi, Residual P) of soil phosphorus. This updated survey of the recent literature shows that the sequential fractionation proposed by Hedley et al. can also be used to separate forms of organically bound soil phosphorus from the geochemically bound fractions. We consider that biological P includes all the extracted organic fractions (Bicarb Po, NaOH o, sonic Po) and geochemical P includes the remaining fractions (Resin Pi, Bicarb Pi, NaOH Pi, sonic Pi, HCl Pi) and the Po and Pi in the Residual fraction. Data from the Hedley fractionation suggest that the contribution of geochemical versus biological processes to soil phosphorus availability varies with pedogenesis. The pool of primary phosphate declines and the NaOH and sonicated-NaOH phosphorus fractions increase as phosphorus becomes geochemically fixed to the iron and aluminum oxides in more highly weathered soils. The sum of organic-P fractions — biological P — is an increasing proportion of total available P as a function of soil development. Therefore, the Hedley fractionation provides a valuable index of the relative importance of biological processes to soil phosphorus content across a soil weathering gradient.