Nitrogen mineralization: challenges of a changing paradigm
TL;DR: A complete new conceptual model of the soil N cycle needs to incorporate recent research on plant–microbe competition and microsite processes to explain the dynamics of N across the wide range of N availability found in terrestrial ecosystems.
Abstract: Until recently, the common view of the terrestrial nitrogen cycle had been driven by two core assumptions—plants use only inorganic N and they compete poorly against soil microbes for N. Thus, plants were thought to use N that microbes “left over,” allowing the N cycle to be divided cleanly into two pieces—the microbial decomposition side and the plant uptake and use side. These were linked by the process of net mineralization. Over the last decade, research has changed these views. N cycling is now seen as being driven by the depolymerization of N-containing polymers by microbial (including mycorrhizal) extracellular enzymes. This releases organic N-containing monomers that may be used by either plants or microbes. However, a complete new conceptual model of the soil N cycle needs to incorporate recent research on plant–microbe competition and microsite processes to explain the dynamics of N across the wide range of N availability found in terrestrial ecosystems. We discuss the evolution of thinking abou...
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TL;DR: Overall, this review shows that soil microbes must be considered as important drivers of plant diversity and productivity in terrestrial ecosystems.
Abstract: Microbes are the unseen majority in soil and comprise a large portion of lifes genetic diversity. Despite their abundance, the impact of soil microbes on ecosystem processes is still poorly understood. Here we explore the various roles that soil microbes play in terrestrial ecosystems with special emphasis on their contribution to plant productivity and diversity. Soil microbes are important regulators of plant productivity, especially in nutrient poor ecosystems where plant symbionts are responsible for the acquisition of limiting nutrients. Mycorrhizal fungi and nitrogenfixing bacteria are responsible for c. 5‐20% (grassland and savannah) to 80% (temperate and boreal forests) of all nitrogen, and up to 75% of phosphorus, that is acquired by plants annually. Free-living microbes also strongly regulate plant productivity, through the mineralization of, and competition for, nutrients that sustain plant productivity. Soil microbes, including microbial pathogens, are also important regulators of plant community dynamics and plant diversity, determining plant abundance and, in some cases, facilitating invasion by exotic plants. Conservative estimates suggest that c. 20 000 plant species are completely dependent on microbial symbionts for growth and survival pointing to the importance of soil microbes as regulators of plant species richness on Earth. Overall, this review shows that soil microbes must be considered as important drivers of plant diversity and productivity in terrestrial ecosystems.
3,673 citations
Cites background from "Nitrogen mineralization: challenges..."
...%) is contained in dead organic matter as complex insoluble polymers such as proteins, nucleic acids and chitin, and these polymers are broken down into dissolved organic N (DON) by extracellular enzymes that are produced by soil microbes (Schimel & Bennett 2004)....
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...This growing awareness of the ability of plants to use organic N and compete with soil microbes for N has led to a radical rethink of terrestrial N cycling and especially the processes that control N availability to plants (Schimel & Bennett 2004)....
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TL;DR: It is suggested that more effectively integrating microbial ecology into ecosystem ecology will require a more complete integration of microbial physiological ecology, population biology, and process ecology.
Abstract: Microorganisms have a variety of evolutionary adaptations and physiological acclimation mechanisms that allow them to survive and remain active in the face of environmental stress. Physiological responses to stress have costs at the organismal level that can result in altered ecosystem-level C, energy, and nutrient flows. These large-scale impacts result from direct effects on active microbes' physiology and by controlling the composition of the active microbial community. We first consider some general aspects of how microbes experience environmental stresses and how they respond to them. We then discuss the impacts of two important ecosystem-level stressors, drought and freezing, on microbial physiology and community composition. Even when microbial community response to stress is limited, the physiological costs imposed on soil microbes are large enough that they may cause large shifts in the allocation and fate of C and N. For example, for microbes to synthesize the osmolytes they need to survive a single drought episode they may consume up to 5% of total annual net primary production in grassland ecosystems, while acclimating to freezing conditions switches Arctic tundra soils from immobilizing N during the growing season to mineralizing it during the winter. We suggest that more effectively integrating microbial ecology into ecosystem ecology will require a more complete integration of microbial physiological ecology, population biology, and process ecology.
1,828 citations
TL;DR: Features of the rhizosphere that are important for nutrient acquisition from soil are reviewed, with specific emphasis on the characteristics of roots that influence the availability and uptake of phosphorus and nitrogen.
Abstract: The rhizosphere is a complex environment where roots interact with physical, chemical and biological properties of soil. Structural and functional characteristics of roots contribute to rhizosphere processes and both have significant influence on the capacity of roots to acquire nutrients. Roots also interact extensively with soil microorganisms which further impact on plant nutrition either directly, by influencing nutrient availability and uptake, or indirectly through plant (root) growth promotion. In this paper, features of the rhizosphere that are important for nutrient acquisition from soil are reviewed, with specific emphasis on the characteristics of roots that influence the availability and uptake of phosphorus and nitrogen. The interaction of roots with soil microorganisms, in particular with mycorrhizal fungi and non-symbiotic plant growth promoting rhizobacteria, is also considered in relation to nutrient availability and through the mechanisms that are associated with plant growth promotion.
1,476 citations
Cites background from "Nitrogen mineralization: challenges..."
...The significance of soluble organic N for plant nutrition was first highlighted in solution culture studies and has since been demonstrated for soils in a range of different ecosystems (Jones and Darrah 1994a; Schimel and Bennett 2004)....
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...…and Cramer 2004), there is evidence that soluble organic forms of N (e.g. low molecular weight compounds such as amino acids) may also play a significant role (Chapin et al. 1993), but few studies have quantified the relative importance of each (Leadley et al. 1997; Schimel and Bennett 2004)....
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...1993), but few studies have quantified the relative importance of each (Leadley et al. 1997; Schimel and Bennett 2004)....
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TL;DR: In this paper, a new conceptual model that explicitly identifies the processes controlling soil organic matter availability for decomposition and allows a more explicit description of the factors regulating OM decomposition under different circumstances is presented.
Abstract: The response of soil organic matter (OM) decomposition to increasing temperature is a critical aspect of ecosystem responses to global change The impacts of climate warming on decomposition dynamics have not been resolved due to apparently contradictory results from field and lab experiments, most of which has focused on labile carbon with short turnover times But the majority of total soil carbon stocks are comprised of organic carbon with turnover times of decades to centuries Understanding the response of these carbon pools to climate change is essential for forecasting longer-term changes in soil carbon storage Herein, we briefly synthesize information from recent studies that have been conducted using a wide variety of approaches In our effort to understand research to-date, we derive a new conceptual model that explicitly identifies the processes controlling soil OM availability for decomposition and allows a more explicit description of the factors regulating OM decomposition under different circumstances It explicitly defines resistance of soil OM to decomposition as being due either to its chemical conformation (quality )o r its physico-chemical protection from decomposition The former is embodied in the depolymerization process, the latter by adsorption/desorption and aggregate turnover We hypothesize a strong role for variation in temperature sensitivity as a function of reaction rates for both We conclude that important advances in understanding the temperature response of the processes that control substrate availability, depolymerization, microbial efficiency, and enzyme production will be needed to predict the fate of soil carbon stocks in a warmer world
1,175 citations
TL;DR: It is proposed that a trait-based approach will help to develop strategies to preserve and promote carbon sequestration under global changes, and how the composition of key plant traits and soil biota related to carbon input, release and storage prevail in different biomes across the globe.
Abstract: Plant functional traits control a variety of terrestrial ecosystem processes, including soil carbon storage which is a key component of the global carbon cycle. Plant traits regulate net soil carbon storage by controlling carbon assimilation, its transfer and storage in belowground biomass, and its release from soil through respiration, fire and leaching. However, our mechanistic understanding of these processes is incomplete. Here, we present a mechanistic framework, based on the plant traits that drive soil carbon inputs and outputs, for understanding how alteration of vegetation composition will affect soil carbon sequestration under global changes. First, we show direct and indirect plant trait effects on soil carbon input and output through autotrophs and heterotrophs, and through modification of abiotic conditions, which need to be considered to determine the local carbon sequestration potential. Second, we explore how the composition of key plant traits and soil biota related to carbon input, release and storage prevail in different biomes across the globe, and address the biome-specific mechanisms by which plant trait composition may impact on soil carbon sequestration. We propose that a trait-based approach will help to develop strategies to preserve and promote carbon sequestration.
1,141 citations
Cites background from "Nitrogen mineralization: challenges..."
...The nutrient poor litter feeds back negatively to primary productivity, but traits that enable the uptake of organic nutrients without (Schimel & Bennett 2004) or with mycorrhizal fungi (Read & Perez-Moreno 2003), or of inorganic N through symbiosis with N-fixers, as in cryptogams (Cornelissen et…...
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...In unproductive soils, plants strongly compete with soil microbes for mineral nutrients (Bardgett et al. 2003), and this interaction might promote plant species with traits that provide higher nutrient competitivity, for example by utilizing organic nutrients (Schimel & Bennett 2004)....
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References
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TL;DR: The principles of ecological succession bear importantly on the relationships between man and nature and needs to be examined as a basis for resolving man’s present environmental crisis.
Abstract: The principles of ecological succession bear importantly on the relationships between man and nature. The framework of successional theory needs to be examined as a basis for resolving man’s present environmental crisis. Most ideas pertaining to the development of ecological systems are based on descriptive data obtained by observing changes in biotic communities over long periods, or on highly theoretical assumptions; very few of the generally accepted hypotheses have been tested experimentally. Some of the confusion, vagueness, and lack of experimental work in this area stems from the tendency of ecologists to regard “succession” as a single straightforward idea; in actual fact, it entails an interacting complex of processes, some of which counteract one another.
4,419 citations
TL;DR: The nature of crop responses to nutrient stress is reviewed and compares these responses to those of species that have evolved under more natural conditions, particularly in low-nutrient envi ronments.
Abstract: Our understanding of plant mineral nutrition comes largely from studies of herbaceous crops that evolved from ruderal species characteristic of nutri ent-rich disturbed sites (52). With the development of agriculture, these ancestral species were bred for greater productivity and reproductive output at high nutrient levels where there was little selective advantage in efficient nutrient use. This paper briefly reviews the nature of crop responses to nutrient stress and compares these responses to those of species that have evolved under more natural conditions, particularly in low-nutrient envi ronments. I draw primarily upon nutritional studies of nitrogen and phos phorus because these elements most commonly limit plant growth and because their role in controlling plant growth and metabolism is most clearly understood (51). Other more specific aspects of nutritional plant ecology not discussed here include ammonium/nitrate nutrition (79), cal cicole/calcifuge nutrition (51,88), heavy metal tolerance (4), and serpentine ecology (133).
4,176 citations
Book•
01 Sep 2011
TL;DR: In this paper, the Ecosystem Concept is used to describe the Earth's Climate System and Geology and Soils, and the ecosystem concept is used for managing and sustaining ecosystems.
Abstract: I. CONTEXT * The Ecosystem Concept * Earth's Climate System * Geology and Soils * II. MECHANISMS * Terrestrial Water and Energy Balance * Carbon Input to Terrestrial Ecosystems * Terrestrial Production Processes * Terrestrial Decomposition * Terrestrial Plant Nutrient Use * Terrestrial Nutrient Cycling * Aquatic Carbon and Nutrient Cycling * Trophic Dynamics * Community Effects on Ecosystem Processes * III. PATTERNS * Temporal Dynamics * Landscape Heterogeneity and Ecosystem Dynamics * IV. INTEGRATION * Global Biogeochemical Cycles * Managing and Sustaining Ecosystem * Abbreviations * Glossary * References
3,086 citations
Book•
01 Jan 1995
TL;DR: Quality Control and Quality Assurance in Applied Soil Microbiology and Biochemistry in applied soil microbiology and biochemistry and field methods.
Abstract: (Chapter Headings): Introduction. Quality Control and Quality Assurance in Applied Soil Microbiology and Biochemistry. Soil Sampling, Handling, Storage, And Analysis. Enrichment, Isolation and Counting of Soil Microorganisms. Estimation of Microbial Activities. Anaerobic Microbial Activities in Soil. Enzyme Activities. Micorbial Biomass. Community Structure. Field Methods. Bioremediation of Soil. Subject Index.
2,125 citations
Book•
01 Jan 1985
2,019 citations