181 research outputs found
Sensitivities to nitrogen and water addition vary among microbial groups within soil aggregates in a semiarid grassland
No full textWe investigated whether enhanced nitrogen (N) and water inputs would redistribute the microbial community within different soil aggregate size classes in a field manipulation experiment initiated in 2005. Distribution of microbial groups was monitored in large macroaggregates (> 2000 mu m), small macroaggregates (250-2000 mu m), and microaggregates (< 250 mu m) in a semiarid grassland. Both arbuscular mycorrhizal (AM) fungi and saprophytic fungi were the most abundant in soil macroaggregates. The gram-negative bacteria were more abundant in soil microaggregates. Total phospholipid fatty acid (PLFA) concentration in general and actinomycetes in particular decreased with N addition under ambient precipitation but was unaffected by combined additions of N and water within the three soil aggregate fractions as compared to control plots. In contrast, the abundance of saprophytic fungi decreased with combined N and water addition, but it was not affected by N addition under ambient precipitation. The abundance of gram-positive bacteria increased with N addition under both ambient and elevated water conditions for all soil aggregate fractions. In summary, the higher short-term nutrient and water availabilities provoked a shift in soil microbial community composition and increased total PLFA abundance irrespectively of the level of soil aggregation. In the long term, this could destabilize soil carbon pools and influence the nutrient limitation of soil biota within different soil aggregate size classes under future global change scenarios
Increased soil organic matter after 28 years of nitrogen fertilization only with plastic film mulching is controlled by maize root biomass
No full textSoil carbon loss regulated by drought intensity and available substrate:a meta-analysis
No full textDrought is one of the most important climate change factors, but its effects on ecosystems are little understood. While known to influence soil carbon (C) cycling, it remains unresolved if altered rainfall patterns induced by climate change will stimulate positive feedbacks of CO2 into the atmosphere. Using a meta-analysis frame-work including 1495 observations from 60 studies encompassing a variety of ecosystems and soil types, we investigated drought effects on respiration rates, cumulative respiration during drying-rewetting cycles, metabolic quotient (qCO2), dissolved organic C (DOC), microbial biomass and fungi to bacteria (F:B) ratios from laboratory and field experiments. We show that C-rich soils (>2% organic carbon) increase CO2 release into the atmosphere after intense droughts, but that C-poor soils show a net decline in C losses. We explain this self-reinforcing mechanism of climate change in C-rich soils by: (i) high substrate availability that magnify bursts of CO2 release after drought events and (ii) a shift in microbial community with increased loss of C per unit of biomass. These findings shed light on important responses of soil CO2 emissions to drought, which could either offset or facilitate positive feedbacks to global warming. Our results should be considered in global climate models, as even small changes in soil CO2 emission have large repercussions for global warming
Stoichiometric N:P flexibility and mycorrhizal symbiosis favour plant resistance against drought
No full textDrought induces changes in the nitrogen (N) and phosphorus (P) cycle but most plant species have limited flexibility to take up nutrients under such variable or unbalanced N and P availability. Both the degree of flexibility in plant N:P ratio and of root symbiosis with arbuscular mycorrhizal fungi might control plant resistance to drought-induced changes in nutrient availability, but this has not been directly tested. Here, we examined the role of plant N:P stoichiometric status and mycorrhizal symbiosis in the drought-resistance of dominant and subordinate species in a semi-natural grassland. We reduced water availability using rainout shelters (control vs. drought) and measured how plant biomass responded for the dominant and subordinate species. We then selected a dominant (Paspalum dilatatum) and a subordinate species (Cynodon dactylon), for which we investigated the N:P stoichiometric status, mycorrhizal root colonization and water-use efficiency. The biomass of all dominant plant species, but not subordinate species, decreased under drought. Drought increased soil available nitrogen, and thus increased soil N:P ratio, due to decreasing plant N uptake. The dominant P. dilatatum showed a high degree of plant N:P homeostasis and a considerable reduction in biomass under drought. At the opposite, the more flexible subordinate species C. dactylon increased its N uptake and water-use efficiency, apparently due to stronger symbiosis with mycorrhizae, and maintained its biomass. Synthesis. We conclude that the maintenance of N:P homeostasis in dominant species, possibly because of a large root nutrient foraging capacity, becomes inefficient when water stress limits N mobility in the soil. By contrast, we demonstrate that higher stoichiometric N:P flexibility coupled with stronger mutualistic association with mycorrhizae allow subordinate species to better withstand drought perturbations. Using a stoichiometric approach in a field experiment, our study provides for the first time clear and novel understandings of the mechanisms involved in drought-resistance within the plant-mycorrhizae-soil system
Increased plant productivity and decreased microbial respiratory C loss by plant growth-promoting rhizobacteria under elevated CO2
No full textThis work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder in order to reproduce the material. Acknowledgements: We thank Drs. Yolima Carrillo and Feike Dijkstra for providing experimental facilities. We also thank Dr. Marcus Brock and Mark Schimelpfenig for laboratory assistance. This material is based upon work supported by the US Department of Agriculture, US Department of Energy's Office of Science (BER), through the Terrestrial Ecosystem Science program, and by the National Science Foundation (DEB# 1021559). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.Peer reviewe
Physicochemically protected organic carbon release is the rate-limiting step of rhizosphere priming in paddy soils
No full texthttp://dx.doi.org/10.13039/501100007928 Ningbo Science and Technology Bureauhttp://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of Chin
Veteran Still Writes
No full textPhotograph taken for a story in the Daily Oklahoman newspaper. Caption: "Sculptress Evelyn Raymond works on a statuary head of Feike Feikema, author of "This Cokecherry Tree," (Double.)
Exogenous P compounds differentially interacted with N availability to regulate enzymatic activities in a meadow steppe
No full textIncreased inputs of ecosystem nitrogen (N) and phosphorus (P) may affect the activity of soil enzymes that play essential roles in the metabolization of carbon (C), N and P for microbial growth. However, the associations between soil enzymatic activities and N and P availability remain poorly understood. We conducted a study in a meadow steppe to elucidate the effects of the addition of N, as ammonium nitrate (NH₄NO₃3), and two forms of P with contrasting solubility, comprising monopotassium phosphate (KH₂PO₄) and the less soluble triple superphosphate (Ca(H₂PO₄)₂, on activity of β-glucosidase (BG), N-acetyl-glucosaminidase (NAG) and acid and alkaline phosphomonoesterases (PMEs). In general, there was a positive effect of N on BG, NAG and alkaline PME activity as a result of enhanced soil N availability, plant-microbe nutrient competition and plant P uptake. Addition of KH₂2PO₄ increased activity of BG, NAG and alkaline PME, but had no impact on acid PME activity. Addition of Ca(H₂PO₄)2 increased NAG activity, but only increased activity of BG and alkaline PME with the addition of N. Concentration of soil available P and microbial biomass P increased with added P, particularly KH₂PO₄. These results provide the first evidence for the N- and P-mediated stimulation of microbial activity depending on the chemical form of added P in this ecosystem. Relationships between activity of BG and NAG, and between that of NAG and PME, were allometric, indicating disproportionate changes in activity of these soil enzymes. This further suggests shifts in microbial acquisition of C, N and P along with increases in availability of N and P that may potentially affect plant productivity. We conclude that scenarios of global environmental change, in which ecosystem availability of N and P is affected, may result in variable activity responses among soil enzymes, and the chemical form of P input should be considered as an important factor influencing meadow steppe grassland ecosystem function
Appendix A. Effects of the five scenarios on labeled-N fractions in belowground plant biomass.
No full textEffects of the five scenarios on labeled-N fractions in belowground plant biomass
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