Soil microorganisms of a native shrub and exotic grasses along a nitrogen deposition gradient in southern California

Sigüenza, Concepción; Crowley, David E.; Allen, Edith B.

doi:10.1016/j.apsoil.2005.02.015

Cited by 50 publications

(31 citation statements)

References 64 publications

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“…This result supports the hypothesis that invasive grasses have invaded CSS and other mediterranean-climate systems partially due to a greater ability to increase growth in response to N addition (Talluto and Suding 2008, Fenn et al 2010, Sharma et al 2010. One possible mechanism is that N addition appears to decrease the amount of arbuscular mycorrhizal (AM) fungi that colonizes roots of natives while not impacting the endophytes that colonize invasive grasses, thus giving an advantage to the invasives (Egerton-Warburton and Allen 2000, Siguenza et al 2006). It is also possible that an increase in abundance of nonnative grasses in added-N plots could result in a positive feedback that further increases soil N level, due to higher N in grass litter than in native shrub litter (Wolkovich et al 2010).…”

Section: Discussionsupporting

confidence: 77%

Altered water and nitrogen input shifts succession in a southern California coastal sage community

Kimball

Goulden

Suding

et al. 2014

Ecological Applications

144

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Vegetation‐type conversions between grasslands and shrublands have occurred worldwide in semiarid regions over the last 150 years. Areas once covered by drought‐deciduous shrubs in Southern California (coastal sage scrub) are converting to grasslands dominated by nonnative species. Increasing fire frequency, drought, and nitrogen deposition have all been hypothesized as causes of this conversion, though there is little direct evidence. We constructed rain‐out shelters in a coastal sage scrub community following a wildfire, manipulated water and nitrogen input in a split‐plot design, and collected annual data on community composition for four years. While shrub cover increased through time in all plots during the postfire succession, both drought and nitrogen significantly slowed recovery. Four years after the fire, average native shrub cover ranged from over 80% in water addition, ambient‐nitrogen plots to 20% in water reduction, nitrogen addition plots. Nonnative grass cover was high following the fire and remained high in the water reduction plots through the third spring after the fire, before decreasing in the fourth year of the study. Adding nitrogen decreased the cover of native plants and increased the cover of nonnative grasses, but also increased the growth of one crown‐sprouting shrub species. Our results suggest that extreme drought during postfire succession may slow or alter succession, possibly facilitating vegetation‐type conversion of coastal sage scrub to grassland. Nitrogen addition slowed succession and, when combined with drought, significantly decreased native cover and increased grass cover. Fire, drought, and atmospheric N deposition are widespread aspects of environmental change that occur simultaneously in this system. Our results imply these drivers of change may reinforce each other, leading to a continued decline of native shrubs and conversion to annual grassland.

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Section: Discussionsupporting

confidence: 77%

Altered water and nitrogen input shifts succession in a southern California coastal sage community

Kimball

Goulden

Suding

et al. 2014

Ecological Applications

144

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“…The exotic invasive grasses escape any potential long-term nutrient stress by having a short lifespan with high seed production. The diversity and density of arbuscular mycorrhizal spores in soil at CSS sites along a N-deposition gradient was significantly reduced at high N deposition sites (.10 kg NÁha À1 Áyr À1 ; Egerton-Warburton and Allen 2000, Sigu¨enza et al 2006b) along an urban-to-rural N-deposition gradient (Padgett et al 1999). Further studies suggested a negative feedback of N deposition, mediated via selection for growth-depressing mycorrhizal strains that are not effective mutualists (Sigu¨enza et al 2006a).…”

Section: Mediterranean Vegetationmentioning

confidence: 95%

Global assessment of nitrogen deposition effects on terrestrial plant diversity: a synthesis

Bobbink

Hicks

Galloway

et al. 2010

Ecological Applications

2,292

1,710

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Abstract. Atmospheric nitrogen (N) deposition is a recognized threat to plant diversity in temperate and northern parts of Europe and North America. This paper assesses evidence from field experiments for N deposition effects and thresholds for terrestrial plant diversity protection across a latitudinal range of main categories of ecosystems, from arctic and boreal systems to tropical forests. Current thinking on the mechanisms of N deposition effects on plant diversity, the global distribution of G200 ecoregions, and current and future (2030) estimates of atmospheric N-deposition rates are then used to identify the risks to plant diversity in all major ecosystem types now and in the future.This synthesis paper clearly shows that N accumulation is the main driver of changes to species composition across the whole range of different ecosystem types by driving the competitive interactions that lead to composition change and/or making conditions unfavorable for some species. Other effects such as direct toxicity of nitrogen gases and aerosols, long-term negative effects of increased ammonium and ammonia availability, soil-mediated effects of acidification, and secondary stress and disturbance are more ecosystem-and site-specific and often play a supporting role. N deposition effects in mediterranean ecosystems have now been identified, leading to a first estimate of an effect threshold. Importantly, ecosystems thought of as not N limited, such as tropical and subtropical systems, may be more vulnerable in the regeneration phase, in situations where heterogeneity in N availability is reduced by atmospheric N deposition, on sandy soils, or in montane areas.Critical loads are effect thresholds for N deposition, and the critical load concept has helped European governments make progress toward reducing N loads on sensitive ecosystems. More needs to be done in Europe and North America, especially for the more sensitive ecosystem types, including several ecosystems of high conservation importance.The results of this assessment show that the vulnerable regions outside Europe and North America which have not received enough attention are ecoregions in eastern and southern Asia (China, India), an important part of the mediterranean ecoregion (California, southern Europe), and in the coming decades several subtropical and tropical parts of Latin America and Africa. Reductions in plant diversity by increased atmospheric N deposition may be more widespread than first thought, and more targeted studies are required in low background areas, especially in the G200 ecoregions.

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“…Across a gradient of N deposition in the eastern United States, changes in microbial N cycling activity are seen in some forest types but not others (McNulty et al 1991;Lovett and Rueth 1999). Shifts in abundance and species composition of mycorrhizal fungi, which form the crucial interface between roots and soil for most plants, have been observed in response to N deposition in Europe, Alaska, and southern California (Arnolds 1991;Lilleskov et al 2001;Siguenza et al 2006). Herbivorous insects tend to prefer plants with higher N concentration, and there is some evidence that increased N may be predisposing trees to attack by insect pests such as the hemlock woolly adelgid (Adelges tsugae) (e.g., McClure 1991) and the beech scale (Cryptococcus fagisuga) (Latty et al 2003).…”

Section: Forestsmentioning

confidence: 99%

Effects of Air Pollution on Ecosystems and Biological Diversity in the Eastern United States

Lovett

Tear

Evers

et al. 2009

Annals of the New York Academy of Sciences

193

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Conservation organizations have most often focused on land-use change, climate change, and invasive species as prime threats to biodiversity conservation. Although air pollution is an acknowledged widespread problem, it is rarely considered in conservation planning or management. In this synthesis, the state of scientific knowledge on the effects of air pollution on plants and animals in the Northeastern and Mid-Atlantic regions of the United States is summarized. Four air pollutants (sulfur, nitrogen, ozone, and mercury) and eight ecosystem types ranging from estuaries to alpine tundra are considered. Effects of air pollution were identified, with varying levels of certainty, in all the ecosystem types examined. None of these ecosystem types is free of the impacts of air pollution, and most are affected by multiple pollutants. In aquatic ecosystems, effects of acidity, nitrogen, and mercury on organisms and biogeochemical processes are well documented. Air pollution causes or contributes to acidification of lakes, eutrophication of estuaries and coastal waters, and mercury bioaccumulation in aquatic food webs. In terrestrial ecosystems, the effects of air pollution on biogeochemical cycling are also very well documented, but the effects on most organisms and the interaction of air pollution with other stressors are less well understood. Nevertheless, there is strong evidence for effects of nitrogen deposition on plants in grasslands, alpine areas, and bogs, and for nitrogen effects on forest mycorrhizae. Soil acidification is widespread in forest ecosystems across the eastern United States and is likely to affect the composition and function of forests in acid-sensitive areas over the long term. Ozone is known to cause reductions in photosynthesis in many terrestrial plant species. For the most part, the effects of these pollutants are chronic, not acute, at the exposure levels common in the eastern United States. Mortality is often observed only at experimentally elevated exposure levels or in combination with other stresses such as drought, freezing, or pathogens. The notable exceptions are the acid/aluminum effects on aquatic organisms, which can be lethal at levels of acidity observed in many surface waters in the region. Although the effects are often subtle, they are important to biological conservation. Changes in species composition caused by terrestrial or aquatic acidification or eutrophication can propagate throughout the food webs to affect many organisms beyond those that are directly sensitive to the pollution. Likewise, sublethal 100Annals of the New York Academy of Sciences doses of toxic pollutants may reduce the reproductive success of the affected organisms or make them more susceptible to potentially lethal pathogens. Many serious gaps in knowledge that warrant further research were identified. Among those gaps are the effects of acidification, ozone, and mercury on alpine systems, effects of nitrogen on species composition of forests, effects of mercury in terrestrial food webs, interactiv...

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Soil microorganisms of a native shrub and exotic grasses along a nitrogen deposition gradient in southern California

Cited by 50 publications

References 64 publications

Altered water and nitrogen input shifts succession in a southern California coastal sage community

Altered water and nitrogen input shifts succession in a southern California coastal sage community

Global assessment of nitrogen deposition effects on terrestrial plant diversity: a synthesis

Effects of Air Pollution on Ecosystems and Biological Diversity in the Eastern United States

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