72 research outputs found
Soil warming alters nitrogen cycling in a New England forest : implications for ecosystem function and structure
© The Author(s), 2011. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Oecologia 168 (2012): 819-828, doi:10.1007/s00442-011-2133-7.Global climate change is expected to affect
terrestrial ecosystems in a variety of ways. Some of the
more well-studied effects include the biogeochemical
feedbacks to the climate system that can either increase or
decrease the atmospheric load of greenhouse gases such
as carbon dioxide and nitrous oxide. Less well-studied are
the effects of climate change on the linkages between soil
and plant processes. Here, we report the effects of soil
warming on these linkages observed in a large field
manipulation of a deciduous forest in southern New
England, USA, where soil was continuously warmed 5°C
above ambient for 7 years. Over this period, we have observed significant changes to the nitrogen cycle that
have the potential to affect tree species composition in the
long term. Since the start of the experiment, we have
documented a 45% average annual increase in net nitrogen
mineralization and a three-fold increase in nitrification
such that in years 5 through 7, 25% of the nitrogen
mineralized is then nitrified. The warming-induced
increase of available nitrogen resulted in increases in the
foliar nitrogen content and the relative growth rate of
trees in the warmed area. Acer rubrum (red maple) trees
have responded the most after 7 years of warming, with
the greatest increases in both foliar nitrogen content and
relative growth rates. Our study suggests that considering
species-specific responses to increases in nitrogen availability
and changes in nitrogen form is important in
predicting future forest composition and feedbacks to the
climate system.This work was supported by the National Institute
for Climate Change Research (DOE-DE-FCO2-06-ER64157),
DOE BER (DE-SC0005421) and the Harvard Forest Long-Term
Ecological Research program (NSF-DEB-0620443)
Bacteria are important dimethylsulfoniopropionate producers in coastal sediments
Dimethylsulfoniopropionate (DMSP) and its catabolite dimethyl sulfide (DMS) are key marine nutrients, with roles in global sulfur cycling, atmospheric chemistry, signalling and, potentially, climate regulation. DMSP production was previously thought to be an oxic and photic process, mainly confined to the surface oceans. However, here we show that DMSP concentrations and DMSP/DMS synthesis rates were higher in surface marine sediment from e.g., saltmarsh ponds, estuaries and the deep ocean than in the overlying seawater. A quarter of bacterial strains isolated from saltmarsh sediment produced DMSP (up to 73 mM), and previously unknown DMSP-producers were identified. Most DMSP-producing isolates contained dsyB, but some alphaproteobacteria, gammaproteobacteria and actinobacteria utilised a methionine methylation pathway independent of DsyB, previously only associated with higher plants. These bacteria contained a methionine methyltransferase âmmtNâ gene - a marker for bacterial DMSP synthesis via this pathway. DMSP-producing bacteria and their dsyB and/or mmtN transcripts were present in all tested seawater samples and Tara Oceans bacterioplankton datasets, but were far more abundant in marine surface sediment. Approximately 108 bacteria per gram of surface marine sediment are predicted to produce DMSP, and their contribution to this process should be included in future models of global DMSP production. We propose that coastal and marine sediments, which cover a large part of the Earthâs surface, are environments with high DMSP and DMS productivity, and that bacteria are important producers within them
Methane fluxes in permafrost habitats of the Lena Delta: effects of microbial community structure and organic matter quality
For the understanding and assessment of recent and future carbon dynamics of arctic permafrost soils the processes of CH4 production and oxidation, the community structure and the quality of DOM were studied in two soils of a polygonal tundra. Activities of methanogens and methanotrophs differed significantly in their rates and distribution patterns among the two investigated profiles. Community structure analysis showed similarities between both soils for esterlinked PLFAs and differences in the fraction of unsaponifiable PLFAs and PLELs. Furthermore, a shift of the overall composition of the microbiota with depth at both sites was indicated by an increasing portion of iso- and anteiso-branched fatty acids related to the amount of straight chain fatty acids. Although permafrost soils represent a large carbon pool, it was shown, that the reduced quality of organic matter leads to a substrate limitation of the microbial metabolism. It can be concluded from our and previous findings firstly that microbial communities in the active layer of an Arctic polygon tundra are composed by members of all three domains of life, with a total biomass comparable to temperate soil ecosystems. And secondly that these microorganisms are well adapted to the extreme temperature gradient of their environment
Soil warming, carbonânitrogen interactions, and forest carbon budgets
Soil warming has the potential to alter both soil and plant processes that affect carbon storage in forest ecosystems. We have quantified these effects in a large, long-term (7-y) soil-warming study in a deciduous forest in New England. Soil warming has resulted in carbon losses from the soil and stimulated carbon gains in the woody tissue of trees. The warming-enhanced decay of soil organic matter also released enough additional inorganic nitrogen into the soil solution to support the observed increases in plant carbon storage. Although soil warming has resulted in a cumulative net loss of carbon from a New England forest relative to a control area over the 7-y study, the annual net losses generally decreased over time as plant carbon storage increased. In the seventh year, warming-induced soil carbon losses were almost totally compensated for by plant carbon gains in response to warming. We attribute the plant gains primarily to warming-induced increases in nitrogen availability. This study underscores the importance of incorporating carbonânitrogen interactions in atmosphereâoceanâland earth system models to accurately simulate land feedbacks to the climate system
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