Stimulation of grassland nitrogen cycling under carbon dioxide enrichment

Hungate, Bruce A.; Chapin, F. Stuart; Zhong, Hailin; Holland, Elisabeth A.; Field, Christopher B.

doi:10.1007/s004420050069

Cited by 161 publications

(111 citation statements)

References 32 publications

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“…Rising atmospheric CO # has the potential to influence this relationship, because it can increase above-and below-ground plant growth (Poorter, 1993 ;Curtis & Wang, 1998), alter the production and chemical constituents of plant litter (Cotrufo et al, 1994 ;Cotrufo & Ineson, 1995 ;King et al, 1997) and influence the types of organic substrate available for microbial metabolism in soil. Therefore, changes in litter production under elevated CO # could alter the microbial demand for N and the flow of N between soil microorganisms and plant roots, a subject that has received growing attention over the past several years (Berntson & Bazzaz, 1997, 1998Hungate et al, 1997aHungate et al, ,b, 1999Zak et al, 2000a).…”

Section: mentioning

confidence: 99%

“…However, the flow of substrates through microbial biomass is a key factor influencing soil N availability and C storage, so understanding the turnover of microbial biomass (biomass\assimilation rate) is central to predicting a change in soil C and N cycling under elevated CO # . At present, few studies have simultaneously measured a change in microbial biomass and the assimilation of C or N (Hungate et al, 1996(Hungate et al, , 1997aBerntson & Bazzaz, 1997, 1998Mikan et al, 2000 ;Zak et al, 2000a), making it difficult to predict how elevated CO # will influence the flow of C and N through microbial biomass. Nevertheless, a relatively large number of studies have measured microbial biomass (C or N) under a wide array of experiment settings in which plants are grown under ambient and elevated CO # (Table 3).…”

Section: Soil Microbial Biomassmentioning

confidence: 99%

“…There is considerable debate regarding the response of soil N dynamics to elevated CO # , because observations indicate that rates of soil N cycling can increase (Zak et al, 1993 ;Hungate et al, 1997a), decline (Berntson & Bazzaz, 1997, 1998 or not change (Zak et al, 2000b), even within the same ecosystem (Hungate et al, 1996). Understanding changes in rates of gross N mineralization and microbial immobilization lie at the heart of predicting whether elevated CO # will alter the amount of N available for plant uptake (i.e.…”

Section: Soil Nitrogen Dynamicsmentioning

confidence: 99%

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Elevated atmospheric CO₂, fine roots and the response of soil microorganisms: a review and hypothesis

et al. 2000

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There is considerable uncertainty about how rates of soil carbon (C) and nitrogen (N) cycling will change as CO # accumulates in the Earth's atmosphere. We summarized data from 47 published reports on soil C and N cycling under elevated CO # in an attempt to generalize whether rates will increase, decrease, or not change. Our synthesis centres on changes in soil respiration, microbial respiration, microbial biomass, gross N mineralization, microbial immobilization and net N mineralization, because these pools and processes represent important control points for the below-ground flow of C and N. To determine whether differences in C allocation between plant life forms influence soil C and N cycling in a predictable manner, we summarized responses beneath graminoid, herbaceous and woody plants grown under ambient and elevated atmospheric CO # . The below-ground pools and processes that we summarized are characterized by a high degree of variability (coefficient of variation 80-800%), making generalizations within and between plant life forms difficult. With few exceptions, rates of soil and microbial respiration were more rapid under elevated CO # , indicating that (1) greater plant growth under elevated CO # enhanced the amount of C entering the soil, and (2) additional substrate was being metabolized by soil microorganisms. However, microbial biomass, gross N mineralization, microbial immobilization and net N mineralization are characterized by large increases and declines under elevated CO # , contributing to a high degree of variability within and between plant life forms. From this analysis we conclude that there are insufficient data to predict how microbial activity and rates of soil C and N cycling will change as the atmospheric CO # concentration continues to rise. We argue that current gaps in our understanding of fine-root biology limit our ability to predict the response of soil microorganisms to rising atmospheric CO # , and that understanding differences in fine-root longevity and biochemistry between plant species are necessary for developing a predictive model of soil C and N cycling under elevated CO # .

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Section: mentioning

confidence: 99%

Section: Soil Microbial Biomassmentioning

confidence: 99%

Section: Soil Nitrogen Dynamicsmentioning

confidence: 99%

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Elevated atmospheric CO₂, fine roots and the response of soil microorganisms: a review and hypothesis

et al. 2000

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“…cell sloughing, exudation (O'Neill, 1994 ;Cardon, 1996 ;Darrah, 1996) and fine root mortality (Pregitzer et al, 1995 ;Canadell et al, 1996 ;Fitter et al, 1997). The positive effect of high CO # on overall soil water availability (Knapp et al, 1996 ;Owensby et al, 1997 ;Arnone & Bohlen, 1998 ;Niklaus et al, 1998b) might also stimulate above-ground (ANPP) and below-ground (BNPP) productivity by enhancing soil nutrient availability, particularly in seasonally dry grassland systems where high CO # might extend water availability into dry periods (Hungate et al, 1997a). In fact, increases in soil moisture under elevated CO # might contribute most to the stimulation of biomass production under elevated CO # in natural ecosystems (Hungate et al, 1997b ;Owensby et al, 1997 ;Leadley et al, 1999 (1996,1997) found a 29% increase in root mortality in intact monoliths of calcareous grassland and a 21% increase in native turf on peaty soil.…”

Section: mentioning

confidence: 99%

Dynamics of root systems in native grasslands: effects of elevated atmospheric CO₂

et al. 2000

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The objectives of this paper were to review the literature on the responses of root systems to elevated CO # in intact, native grassland ecosystems, and to present the results from a 2-yr study of root production and mortality in an intact calcareous grassland in Switzerland. Previous work in intact native grassland systems has revealed that significant stimulation of the size of root systems (biomass, length density or root number) is not a universal response to elevated CO # . Of the 12 studies reviewed, seven showed little or no change in root-system size under elevated CO # , while five showed marked increases (average increase 38%). Insufficient data are available on the effects of elevated CO # on root production, mortality and life span to allow generalization about effects. The diversity of experimental techniques employed in these native grassland studies also makes generalization difficult. In the present study, root production and mortality were monitored in situ in a species-rich calcareous grassland community using minirhizotrons in order to test the hypothesis that an increase in these two measures would help explain the increase in net ecosystem CO # uptake (net ecosystem exchange) previously observed under elevated CO # at this site (600 vs 350 µl CO # l −" ; eight 1.2-m# experimental plots per CO # level using the screen-aided CO # control method). However, results from the first 2 yr showed no difference in overall root production or mortality in the top 18 cm of soil, where 80-90% of the roots occur. Elevated CO # was associated with an upward shift in root length density : under elevated CO # a greater proportion of roots were found in the upper 0-6-cm soil layer, and a lower proportion of roots in the lower 12-18 cm, than under ambient CO # . Elevated CO # was also associated with an increase in root survival probability (RSP ; e.g. for roots still alive 280 d after they were produced under ambient CO # , RSP l 0.30 ; elevated CO # , RSP l 0.56) and an increase (48%) in median root life span in the deepest (12-18 cm) soil layer. The factors driving changes in root distribution and longevity with depth under elevated CO # were not clear, but might have been related to increases in soil moisture under elevated CO # interacting with vertical patterns in soil temperatures. Thus extra CO # taken up in this grassland ecosystem during the growing season under elevated CO # could not be explained by changes in root production and mortality. However, C and nutrient cycling might be shifted closer to the soil surface, which could potentially have a substantial effect on the activities of soil heterotrophic organisms as CO # levels rise.

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“…We lack comparable N20 data from other FACE sites, and results from short-term studies are mixed. Nitrous oxide fluxes measured in a California grassland FACE site in October [Hungate et al, 1997a] and in a Michigan forest open-top chamber experiment in July [Ambus and Robertson, 1999] were similar for both ambient and elevated CO2. However, emissions were higher in elevated plots following NH4NO3 application to a Swiss grassland in July [Ineson et al, 1998].…”

Section: Field N20 Fluxesmentioning

confidence: 99%

Influence of atmospheric CO₂ enrichment on nitrous oxide flux in a temperate forest ecosystem

Phillips

Whalen²,

Schlesinger

2001

Global Biogeochemical Cycles

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Abstract. Long-term exposure of native vegetation to elevated atmospheric carbon dioxide (CO2) is expected to increase the water content and the input of labile carbon (C) to soil, which could stimulate nitrification and denitrification and enhance nitrous oxide (N20) emissions. We measured N20 fluxes for 2 years in a Pinus taeda forest that was continuously enriched 200 txL L -• CO2 above the ambient atmospheric CO2 concentration (•560 t•L L -1) beginning 16 months prior to our study. Soil treated with elevated CO2 showed higher N20 emissions at low winter temperatures than the ambient CO2 control. Conversely, soil treated with elevated CO2 showed lower N20 emissions at high summer temperatures than the control soil. Annual N20 fluxes, however, were similar between treatments (•6600 t•g m-2). Factors that influence denitrification and N20 production were investigated in the laboratory using intact soil core incubations. Nitrate additions (0.17 mg KNO3-N g-l) to intact soil cores during laboratory incubations stimulated total N20 production as well as denitrification in both treatments, whereas glucose additions lowered N20 production in both treatments. These experiments demonstrated that N20 production is strongly limited by available nitrogen (N) and that the addition of labile C is likely to reduce the amount of N20 produced by nitrification. Our results collectively suggest that CO2 enrichment of this N-limited ecosystem may reduce N20 flux during the growing season, when soil C inputs and plant-microbial competition for NH4 + are high. Alternatively, elevated CO2 may enhance N20 flux in the winter, when conditions are moist and cold and plants are less active. The potential indirect effects of CO2 enrichment (greater soil moisture and labile C inputs) could reduce N20 flux from nitrification in summer and enhance N20 flux from denitrification in winter, resulting in no net change in total ecosystem N20 flux at the soil-atmosphere interface.

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Stimulation of grassland nitrogen cycling under carbon dioxide enrichment

Cited by 161 publications

References 32 publications

Elevated atmospheric CO₂, fine roots and the response of soil microorganisms: a review and hypothesis

Elevated atmospheric CO₂, fine roots and the response of soil microorganisms: a review and hypothesis

Dynamics of root systems in native grasslands: effects of elevated atmospheric CO₂

Influence of atmospheric CO₂ enrichment on nitrous oxide flux in a temperate forest ecosystem

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Stimulation of grassland nitrogen cycling under carbon dioxide enrichment

Cited by 161 publications

References 32 publications

Elevated atmospheric CO2, fine roots and the response of soil microorganisms: a review and hypothesis

Elevated atmospheric CO2, fine roots and the response of soil microorganisms: a review and hypothesis

Dynamics of root systems in native grasslands: effects of elevated atmospheric CO2

Influence of atmospheric CO2 enrichment on nitrous oxide flux in a temperate forest ecosystem

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Product

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Elevated atmospheric CO₂, fine roots and the response of soil microorganisms: a review and hypothesis

Elevated atmospheric CO₂, fine roots and the response of soil microorganisms: a review and hypothesis

Dynamics of root systems in native grasslands: effects of elevated atmospheric CO₂

Influence of atmospheric CO₂ enrichment on nitrous oxide flux in a temperate forest ecosystem