title: Stochastic and deterministic effects of a moisture gradient on soil microbial communities in the McMurdo Dry Valleys of Antarctica

authors: Lee, Kevin C.

subjects: Science & Technology

abstract: Antarctic soil supports surface microbial communities that are dependent on ephemeral moisture. Understanding the response to availability of this resource is essential to predicting how the system will respond to climate change. The McMurdo Dry Valleys are the largest ice-free soil region in Antarctica. They are a hyper-arid polar desert with extremely limited moisture availability. Microbial colonization dominates this ecosystem but surprisingly little is known about how communities respond to changing moisture regimes. We utilized the natural model system provided by transiently wetted soil at lake margins in the Dry Valleys to interrogate microbial responses along a well-defined contiguous moisture gradient and disentangle responses between and within phyla. We identified a striking non-linear response among bacteria where at low moisture levels small changes resulted in a large impact on diversity. At higher moister levels community responses were less pronounced, resulting in diversity asymptotes. We postulate that whilst the main drivers of observed community diversity were deterministic, a switch in the major influence occurred from abiotic factors at low moisture levels to biotic interactions at higher moisture. Response between and within phyla was markedly different, highlighting the importance of taxonomic resolution in community analysis. Furthermore, we resolved apparent stochasticity at high taxonomic ranks as the result of deterministic interactions taking place at finer taxonomic and spatial scales. Overall the findings provide new insight on the response to moisture and this will be useful in advancing understanding of potential ecosystem responses in the threatened McMurdo Dry Valleys system.

text: Stochastic and deterministic effects of a moisture gradient on soil microbial communities in the McMurdo Dry Valleys of Antarctica Antarctic soil supports surface microbial communities that are dependent on ephemeral moisture. Understanding the response to availability of this resource is essential to predicting how the system will respond to climate change. The McMurdo Dry Valleys are the largest ice-free soil region in Antarctica. They are a hyper-arid polar desert with extremely limited moisture availability. Microbial colonization dominates this ecosystem but surprisingly little is known about how communities respond to changing moisture regimes. We utilized the natural model system provided by transiently wetted soil at lake margins in the Dry Valleys to interrogate microbial responses along a well-defined contiguous moisture gradient and disentangle responses between and within phyla. We identified a striking non-linear response among bacteria where at low moisture levels small changes resulted in a large impact on diversity. At higher moister levels community responses were less pronounced, resulting in diversity asymptotes. We postulate that whilst the main drivers of observed community diversity were deterministic, a switch in the major influence occurred from abiotic factors at low moisture levels to biotic interactions at higher moisture. Response between and within phyla was markedly different, highlighting the importance of taxonomic resolution in community analysis. Furthermore, we resolved apparent stochasticity at high taxonomic ranks as the result of deterministic interactions taking place at finer taxonomic and spatial scales. Overall the findings provide new insight on the response to moisture and this will be useful in advancing understanding of potential ecosystem responses in the threatened McMurdo Dry Valleys system.

year: 2018

title: Investigation of intermittency in magnetohydrodynamics and solar wind turbulence: scale-dependent kurtosis

authors: Wan, Minping

subjects: magnetohydrodynamics (MHD)

abstract: The behavior of scale-dependent (or filtered) kurtosis is studied in the solar wind using magnetic field measurements from the ACE and Cluster spacecraft at 1 AU. It is also analyzed numerically with high-resolution magnetohydrodynamic spectral simulations. In each case the filtered kurtosis increases with wavenumber, implying the presence of coherent structures at the smallest scales. This phase coupling is related to intermittency in solar wind turbulence and the emergence of non-Gaussian statistics. However, it is inhibited by the presence of upstream waves and other phase-randomizing structures, which act to reduce the growth of kurtosis.

text: Investigation of intermittency in magnetohydrodynamics and solar wind turbulence: scale-dependent kurtosis The behavior of scale-dependent (or filtered) kurtosis is studied in the solar wind using magnetic field measurements from the ACE and Cluster spacecraft at 1 AU. It is also analyzed numerically with high-resolution magnetohydrodynamic spectral simulations. In each case the filtered kurtosis increases with wavenumber, implying the presence of coherent structures at the smallest scales. This phase coupling is related to intermittency in solar wind turbulence and the emergence of non-Gaussian statistics. However, it is inhibited by the presence of upstream waves and other phase-randomizing structures, which act to reduce the growth of kurtosis.

year: 2012

title: Keepa Te Wharau: a Ngati Rahiri rangatira

authors: Hart, Philip

abstract: Keepa Te Wharau’s whakapapa linked him, unusually, to both Ngati Maru and Ngati Haua. Through these connections he was associated with the Te Aroha district from an early age, visiting it on several occasions and even cultivating there, briefly. When the block was before the land court he gave evidence – though his evidence in a later succession case was clearly wrong, deliberately so. Having interests in several blocks of land, he falsely claimed not to have received money for the Aroha Block, using the excuse of drunkenness, for which he was before the court on several occasions. He would sell land, as would his children, to meet living expenses. He invested in two goldfields, Thames and Te Aroha, very modestly. A leading rangatira, he was notable for his loyalty to the Crown.

text: Keepa Te Wharau: a Ngati Rahiri rangatira Keepa Te Wharau’s whakapapa linked him, unusually, to both Ngati Maru and Ngati Haua. Through these connections he was associated with the Te Aroha district from an early age, visiting it on several occasions and even cultivating there, briefly. When the block was before the land court he gave evidence – though his evidence in a later succession case was clearly wrong, deliberately so. Having interests in several blocks of land, he falsely claimed not to have received money for the Aroha Block, using the excuse of drunkenness, for which he was before the court on several occasions. He would sell land, as would his children, to meet living expenses. He invested in two goldfields, Thames and Te Aroha, very modestly. A leading rangatira, he was notable for his loyalty to the Crown.

year: 2016