Swedish University of Agricultural Sciences

About: Swedish University of Agricultural Sciences is a education organization based out in Uppsala, Sweden. It is known for research contribution in the topics: Population & Soil water. The organization has 13510 authors who have published 35241 publications receiving 1414458 citations. The organization is also known as: Sveriges Lantbruksuniversitet & SLU.

Ecological interpretations of nitrogen isotope ratios of terrestrial plants and soils

Abstract: Background Knowledge of biological and climatic controls in terrestrial nitrogen (N) cycling within and across ecosystems iscentral tounderstandingglobalpatternsof keyecosystemprocesses.Theratiosof 15 N: 14 Ninplants and soils have been used as indirect indices of N cycling parameters, yet our understanding of controls over N isotope ratios in plants and soils is still developing. Scope In this review, we provide background on the mainprocessesthataffectplantandsoilNisotoperatios. In a similar manner to partitioning the roles of state factors and interactive controls in determining ecosystem traits, we review N isotopes patterns in plants and soils across a number of proximal factors that influence ecosystem properties as well as mechanisms that affect these patterns. Lastly, some remaining questions that would improve our understanding of N isotopes in terrestrial ecosystems are highlighted. Conclusion Compared to a decade ago, the global patterns of plant and soil N isotope ratios are more resolved. Additionally, we better understand how plant and soil N isotope ratios are affected by such factors as mycorrhizal fungi, climate, and microbial processing. A comprehensive understanding of the N cycle that ascribes different degrees of isotopic fractionation for each step under different conditions is closer to being realized, but a number of process-level questions still remain.

A synthesis: The role of nutrients as constraints on carbon balances in boreal and arctic regions

Abstract: As in many ecosystems, carbon (C) cycling in arctic and boreal regions is tightly linked to the cycling of nutrients: nutrients (particularly nitrogen) are mineralized through the process of organic matter decomposition (C mineralization), and nutrient availability strongly constrains ecosystem C gain through primary production. This link between C and nutrient cycles has implications for how northern systems will respond to future climate warming and whether feedbacks to rising concentrations of atmospheric CO2 from these regions will be positive or negative. Warming is expected to cause a substantial release of C to the atmosphere because of increased decomposition of the large amounts of organic C present in high-latitude soils (a positive feedback to climate warming). However, increased nutrient mineralization associated with this decomposition is expected to stimulate primary production and ecosystem C gain, offsetting or even exceeding C lost through decomposition (a negative feedback to climate warming). Increased primary production with warming is consistent with results of numerous experiments showing increased plant growth with nutrient enrichment. Here we examine key assumptions behind this scenario: (1) temperature is a primary control of decomposition in northern regions, (2) increased decomposition and associated nutrient release are tightly coupled to plant nutrient uptake, and (3) short-term manipulations of temperature and nutrient availability accurately predict long-term responses to climate change.

The river as a chemostat: fresh perspectives on dissolved organic matter flowing down the river continuum

Abstract: A better understanding is needed of how hydrological and biogeochemical processes control dissolved organic car- bon (DOC) concentrations and dissolved organic matter (DOM) composition from headwaters downstream to large rivers. We exam- ined a large DOM dataset from the National Water Information System of the US Geological Survey, which represents approximately 100 000 measurements of DOC concentration and DOM composition at many sites along rivers across the United States. Application of quantile regression revealed a tendency towards downstream spatial and temporal homogenization of DOC concentrations and a shift from dominance of aromatic DOM in headwaters to more aliphatic DOM downstream. The DOC concentration-discharge (C-Q) relationships at each site revealed a downstream tendency towards a slope of zero. We propose that despite complexities in river networks that have driven many revisions to the River Continuum Concept, rivers show a tendency towards chemostasis (C-Q slope of zero) because of a downstream shift from a dominance of hydrologic drivers that connect terrestrial DOM sources to streams in the headwaters towards a dominance of instream and near-stream biogeochemical processes that result in preferential losses of aromatic DOM and preferential gains of aliphatic DOM. Resume : Une meilleure comprehension de l'influence des processus hydrologiques et biogeochimiques sur les concentrations de carbone organique dissous (COD) et sur la composition des matieres organiques dissoutes (MOD) des cours d'eau d'amont jusqu'aux grands fleuves est necessaire. Nous avons examine un imposant ensemble de donnees sur la MOD du Systeme national d'information sur l'eau de la commission geologique des Etats-Unis (US Geological Survey), qui represente environ 100 000 mesures de concentration de COD et de composition de MOD en de nombreux endroits le long de rivieres ala grandeur des Etats-Unis. L'application de la regression quantile a revele une tendance al'homogeneisation spatiale et temporelle vers l'aval des concentrations de COD et le passage d'une predominance de MOD aromatiques dans les cours d'eau d'amont aplus de MOD aliphatiques en aval. Les relations concentrations de COD-debit (C-D) achaque site ont revele une tendance vers une pente nulle vers l'aval. Nous proposons que, malgre les complexites des reseaux hydrographiques qui ont mene ade nombreuses revisions du concept du continuum fluvial, les rivieres tendent vers la chimiostase (pente nulle de la relation C-D) en raison du passage vers l'aval d'une predominance de facteurs hy- drologiques qui relient les sources de MOD terrestres aux cours d'eau d'amont, aune predominance de processus biogeochimiques dans le cours d'eau ou aproximite qui se traduisent par des pertes preferentielles de MOD aromatiques et des gains preferentiels de MOD aliphatiques. (Traduit par la Redaction)