Browsing by Subject "soil organic matter"
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Item Arctic worming: Human-facilitated earthworm invasion transforms soil organic matter budgets and pools in Fennoscandian forests(2018-12) Wackett, AdrianEarth’s high latitude ecosystems are already under dire threat from climate warming, permafrost thaw, and intensifying natural resource exploitation. In addition to these ongoing concerns, accelerating urbanization, agricultural expansion, and greater opportunities for recreation in high-latitude regions are likely to introduce a less conspicuous but potentially potent threat: non-native geoengineeing earthworms. Earthworms were eradicated from northern N. America (including Minnesota) during the last glaciation, and it is now established that humans are (re-) introducing exotic earthworm species into these forests with dramatic consequences on soil and ecosystem functioning. However, their invasiveness and capacity to modify high-latitude boreal and arctic forests like those in Fennoscandia remains largely unknown. Here I explore two inter-related hypotheses concerning earthworms and soils in Fennoscandian forests: H1) despite their different human history and proximity to the native range of Lumbricidae earthworms (Southern and Central Europe), I predicted that Pleistocene glaciations also extirpated earthworms from Fennoscandia, suggesting that European earthworms (if present) are also non-native and invasive in these landscapes; and H2) if introduced by humans, the invasive earthworms transform Fennoscandian forest soil morphologies and soil organic matter (SOM) dynamics by removing thick organic layers at the forest floor and forming A-horizon (mineral topsoil) in their wake. To address H1, I tested a series of sub-hypotheses stating that: 1) earthworms did not colonize the Fennoscandian landscape via dispersal by brackish seawater, nor were they introduced by early indigenous peoples (Sami) who followed the retreating glaciers into northern Fennoscandia; and 2) earthworms are spreading into Fennoscandian forests from ‘worm point sources’ created by modern human-mediated dispersal vectors such as farming, fishing, gardening, and logging (among others). Although I could not dispel the possibility that small epigeic-type earthworms may have entered the Fennoscandian landscape considerably earlier via water-mediated dispersal and/or by ‘hitch-hiking’ along with Sami settlers, I found that more impactful ‘geoengineering’ species are only present in arctic landscapes associated with more modern (i.e. last two centuries) human disturbance (supporting H1) and are radiating outward from these anthropogenic point sources into virgin arctic and boreal forests. Furthermore, in line with H2, expansion of these geoengineers into adjacent forests consistently induced changes to forest soil morphologies and nutrient cycling regimes, including rapid reduction of the SOM pool in organic horizons and re-allocation of this SOM into mineral horizons: wherein it is sorbed onto mineral surfaces and/or occluded within aggregates. This belowground transformation likely has significant aboveground consequences as well as implications for the long-term carbon balance of boreal and arctic ecosystems, which store more than half (~ 53%) of earth’s soil carbon. Furthermore, based on results from N. America, this ‘unseen’ invasion may also have cascading effects on fungal and microbial associations, plant communities, and overall ecosystem functioning. Considering that the arctic is already being disproportionately affected by climate change and that human activities in these regions are likely to accelerate as these regions warm, additional research assessing the ecological impacts of arctic worming is urgently needed.Item Chemical Characterization of the Degradation of Necromass from Four Ascomycete Fungi: Implications for Soil Organic Carbon Turnover and Storage(2020-12) Bruner, ValerieTerrestrial soils store approximately twice as much carbon as is currently in the atmospheric CO2 pool. Despite its importance in the global carbon cycle, much is still unknown about the source, turnover, and stability of the soil organic matter (SOM) pool. For example, fungi are known to play an important role in shaping the chemistry of SOM by degrading common biopolymers, and fungal biomass has been found to be a significant portion of living microbial SOM, dominating over bacteria in some soils by as much as 90%. And yet, despite growing evidence that microbial necromass, or dead microbial tissue, may be a larger contributor to SOM than previously thought, very little is known about the specific degradation patterns of fungal necromass, and subsequently its potential chemical contributions to long-lived SOM pools. This study addresses these knowledge gaps through a time-series analysis of the degradation patterns of fungal tissue from four different saprotrophic Ascomyota species in temperate restored prairie soils. Fungal tissue was buried in a temperate soil and harvested at intervals from 1 day to one month. After harvest, chemical analysis of the dried tissue by thermochemolysis pyrolysis-GCMS was used for relative quantitation of compounds derived from lipids, aromatics, carbohydrates, nitrogen-containing, and unspecified residues. The degradation of these specific molecules, bulk fungal tissue, and bulk C and N within the tissue, is modeled to (1) show that a small portion of fungal necromass persists in the environment even after the period of the experiment and could serve as a contributor to long-lived SOM, and (2) provide quantitative information on the contribution of fungal tissue to global SOM pools.Item Factors Controlling the Decomposition of Ectomycorrhizal Fungal Tissue and the Formation of Soil Organic Matter(2019-06) Ryan, Maeve ElizabethThe turnover of ectomycorrhizal (ECM) fungi accounts for up to half of the organic carbon found in forest soils and therefore represents an important pathway for the removal of carbon from the atmosphere to be stored belowground as long-lived soil organic matter (SOM). Understanding the flux of fungal necromass inputs to SOM, and their subsequent stabilization potential in forest soils, requires an understanding of the chemical changes that occur during the degradation of fungal tissue. Additionally, it is hypothesized that degradation of fungal necromass is slowed by high melanin content and accelerated by high nitrogen content. A field degradation study was carried out at the Cedar Creek Ecosystem Science Reserve in East Bethel, Minnesota. Necromass from four species of ECM fungi with varying degrees of melanization was buried in litter bags in a Pinus-dominated forest below the soil litter layer, allowed to degrade naturally, and harvested nine times over a period of 90 days. Harvest was more frequent during the first week to gain insight into the dynamic early decomposition period. Elemental analysis (EA), Fourier-transform infrared spectroscopy (FTIR), and thermochemolysis-gas chromatography-mass spectrometry (pyGCMS), including novel methods of quantifying the contribution from various types of biopolymers to the total remaining tissue, supplement mass loss data to provide an overview of the chemical changes that occur as fungal necromass decomposes. Each of the four species lost a significant amount of mass in the first seven days of incubation but, at the end of the three-month degradation sequence, a significant fraction of fungal necromass remained. This necromass was chemically distinct from undegraded necromass, containing more aromatic compounds, suggesting that the relative abundance of melanin, which is highly aromatic, increased as other cellular components degraded away. Although melanin content was hypothesized to slow degradation, a high-melanin species degraded at effectively the same rate as the two low-melanin species. Differences in degradation rates across species can be attributed to initial nitrogen content, while melanin content could explain differences in degradation rate within a species.Item Organic Matter Management(St. Paul, MN: University of Minnesota Extension Service, 2000) Lewandowski, AnnIn this publication: What is organic matter? What does organic matter do? How to build organic matter levels. Why are C:N ratios important? Pests and other problems.