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1.
Niklaus Pascal A. Wohlfender Monika Siegwolf Rolf Körner Christian 《Plant and Soil》2001,233(2):189-202
Stimulated plant production and often even larger stimulation of photosynthesis at elevated CO2 raise the possibility of increased C storage in plants and soils. We analysed ecosystem C partitioning and soil C fluxes in calcareous grassland exposed to elevated CO2 for 6 years. At elevated CO2, C pools increased in plants (+23%) and surface litter (+24%), but were not altered in microbes and soil organic matter. Soils were fractionated into particle size and density separates. The amount of low-density macroorganic C, an indicator of particulate soil C inputs from root litter, was not affected by elevated CO2. Incorporation of C fixed during the experiment (Cnew) was tracked by C isotopic analysis of soil fractions which were labelled due to 13C depletion of the commercial CO2 used for atmospheric enrichment. This data constrains estimates of C sequestration (absolute upper bound) and indicates where in soils potentially sequestered C is stored. Cnew entered soils at an initial rate of 210±42 g C m–2 year–1, but only 554±39 g Cnew m–2 were recovered after 6 years due to the low mean residence time of 1.8 years. Previous process-oriented measurements did not indicate increased plant–soil C fluxes at elevated CO2 in the same system (13C kinetics in soil microbes and fine roots after pulse labelling, and minirhizotron observations). Overall experimental evidence suggests that C storage under elevated CO2 occurred only in rapidly turned-over fractions such as plants and detritus, and that potential extra soil C inputs were rapidly re-mineralised. We argue that this inference does not conflict with the observed increases in photosynthetic fixation at elevated CO2, because these are not good predictors of plant growth and soil C fluxes for allometric reasons. C sequestration in this natural system may also be lower than suggested by plant biomass responses to elevated CO2 because C storage may be limited by stabilisation of Cnew in slowly turned-over soil fractions (a prerequisite for long-term storage) rather than by the magnitude of C inputs per se. 相似文献
2.
We investigated microbial responses in a late successional sedge-dominated alpine grassland to four seasons of CO2 enrichment. Part of the plots received fertilizer equivalent to 4.5g N m−2 a−1. Soil basal respiration (R
mic
), the metabolic quotient for CO2 (qCO2=R
mic
/C
mic
), microbial C and N (C
mic
and N
mic
) as well as total soil organic C and N showed no response to CO2 enrichment alone. However, when the CO2 treatment was combined with fertilizer addition R
mic
and qCO2 were statistically significantly higher under elevated CO2 than under ambient conditions (+57% and +71%, respectively). Fertilizer addition increased microbial N pools by 17%, but
this was not influenced by elevated CO2. Microbial C was neither affected by elevated CO2 nor fertilizer. The lack of a CO2-effect in unfertilized plots was suprising in the light of our evidence (based on C balance) that enhanced soil C inputs
must have occurred under elevated CO2 regardless of fertilizer treatment. Based on these data and other published work we suggest that microbial responses to elevated
CO2 in such stable, late-successional ecosystems are limited by the availability of mineral nutrients and that results obtained
with fertile or heavily disturbed substrates are unsuitable to predict future microbial responses to elevated CO2 in natural systems. However, when nutrient limitation is removed (e.g. by wet nitrogen deposition) microbes make use of the
additional carbon introduced into the soil system. We believe that the response of natural ecosystems to elevated CO2 must be studied in situ in natural, undisturbed systems. 相似文献
3.
The effects of elevated CO2 on plant biomass and community structure have been studied for four seasons in a calcareous grassland in northwest Switzerland.
This highly diverse, semi-natural plant community is dominated by the perennial grass Bromus erectus and is mown twice a year to maintain species composition. Plots of 1.3 m2 were exposed to ambient or elevated CO2 concentrations (n = 8) using a novel CO2 exposure technique, screen-aided CO2 control (SACC) starting in March 1994. In the 1st year of treatment, the annual harvested biomass (sum of aboveground biomass
from mowings in June and October) was not significantly affected by elevated CO2. However, biomass increased significantly at elevated CO2 in the 2nd (+20%, P = 0.05), 3rd (+21%, P = 0.02) and 4th years (+29%, P = 0.02). There were no detectable differences in root biomass in the top 8 cm of soil between CO2 treatments on eight out of nine sampling dates. There were significant differences in CO2 responsiveness between functional groups (legumes, non-leguminous forbs, graminoids) in the 2nd (P = 0.07) and 3rd (P < 0.001) years of the study. The order of CO2 responsiveness among functional groups changed substantially from the 2nd to the 3rd year; for example, non-leguminous forbs
had the smallest relative response in the 2nd year and the largest in the 3rd year. By the 3rd year of CO2 exposure, large species-specific differences in CO2 response had developed. For five important species or genera the order of responsiveness was Lotus corniculatus (+271%), Carex flacca (+249%), Bromus erectus (+33%), Sanguisorba minor (no significant CO2 effect), and six Trifolium species (a negative response that was not significant). The positive CO2 responses in Bromus and Carex were most closely related to increases in tiller number. Species richness was not affected by CO2 treatment, but species evenness increased under elevated CO2 (modified Hill ratio; P = 0.03) in June of the 3rd year, resulting in a marginally significant increase in species diversity (Simpson's index; P = 0.09). This and other experiments with calcareous grassland plants show that elevated atmospheric CO2 concentrations can substantially alter the structure of calcareous grassland communities and may increase plant community
biomass.
Received: 12 July 1997 / Accepted: 14 September 1998 相似文献
4.
We investigated the effects of elevated CO2 (600 μl l−1 vs 350 μl l−1) and phosphorus supply (1 g P m−2 year−1 vs unfertilized) on intact monoliths from species-rich calcareous grassland in a greenhouse. Aboveground community dry mass
remained almost unaffected by elevated CO2 in the first year (+6%, n.s.), but was significantly stimulated by CO2 enrichment in year two (+26%, P<0.01). Among functional groups, only graminoids contributed significantly to this increase. The effect of phosphorus alone
on community biomass was small in both years and marginally significant only when analyzed with MANOVA (+6% in year one, +9%
in year two, 0.1 ≥P > 0.05). Belowground biomass and stubble after two seasons were not different in elevated CO2 and when P was added. The small initial increase in aboveground community biomass under elevated CO2 is explained by the fact that some species, in particular Carex flacca, responded very positively right from the beginning, while others, especially the dominant Bromus erectus, responded negatively to CO2 enrichment. Shifts in community composition towards more responsive species explain the much larger CO2 response in the second year. These shifts, i.e., a decline in xerophytic elements (B. erectus) and an increase in mesophytic grasses and legumes occurred independently of treatments in all monoliths but were accelerated
significantly by elevated CO2. The difference in average biomass production at elevated compared to ambient CO2 was higher when P was supplied (at the community level the CO2 response was enhanced from 20% to 33% when P was added, in graminoids from 17% to 27%, in legumes from 4% to 60%, and in
C. flacca from 120% to 298% by year two). Based on observations in this and similar studies, we suggest that interactions between CO2 concentration, species presence, and nutrient availability will govern community responses to elevated CO2.
Received: 12 July 1997 / Accepted: 28 March 1998 相似文献
5.
Plant nutrient responses to 4 years of CO2 enrichment were investigated in situ in calcareous grassland. Beginning in year 2, plant aboveground C:N ratios were increased
by 9% to 22% at elevated CO2 (P < 0.01), depending on year. Total amounts of N removed in biomass harvests during the first 4 years were not affected by
elevated CO2 (19.9 ± 1.3 and 21.1 ± 1.3 g N m−2 at ambient and elevated CO2), indicating that the observed plant biomass increases were solely attained by dilution of nutrients. Total aboveground P
and tissue N:P ratios also were not altered by CO2 enrichment (12.5 ± 2 g N g−1 P in both treatments). In contrast to non-legumes (>98% of community aboveground biomass), legume C/N was not reduced at
elevated CO2 and legume N:P was slightly increased. We attribute the less reduced N concentration in legumes at elevated CO2 to the fact that virtually all legume N originated from symbiotic N2 fixation (%Ndfa ≈ 90%), and thus legume growth was not limited by soil N. While total plant N was not affected by elevated CO2, microbial N pools increased by +18% under CO2 enrichment (P = 0.04) and plant available soil N decreased. Hence, there was a net increase in the overall biotic N pool, largely due increases
in the microbial N pool. In order to assess the effects of legumes for ecosystem CO2 responses and to estimate the degree to which plant growth was P-limited, two greenhouse experiments were conducted, using
firstly undisturbed grassland monoliths from the field site, and secondly designed `microcosm' communities on natural soil.
Half the microcosms were planted with legumes and half were planted without. Both monoliths and microcosms were exposed to
elevated CO2 and P fertilization in a factored design. After two seasons, plant N pools in both unfertilized monoliths and microcosm communities
were unaffected by CO2 enrichment, similar to what was found in the field. However, when P was added total plant N pools increased at elevated CO2. This community-level effect originated almost solely from legume stimulation. The results suggest a complex interaction
between atmospheric CO2 concentrations, N and P supply. Overall ecosystem productivity is N-limited, whereas CO2 effects on legume growth and their N2 fixation are limited by P.
Received: 12 July 1997 / Accepted: 15 April 1998 相似文献
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Water relations of nutrient-poor calcareous grassland under long-term CO2 enrichment were investigated. Understanding CO2 effects on soil moisture is critical because productivity in these grasslands is water limited. In general, leaf conductance
was reduced at elevated CO2, but responses strongly depended on date and species. Evapotranspiration (measured as H2O gas exchange) revealed only small, non-significant reductions at elevated CO2, indicating that leaf conductance effects were strongly buffered by leaf boundary layer and canopy conductance (leaf area
index was not or only marginally increased under elevated CO2). However, these minute and non-significant responses of water vapour loss accumulated over time and resulted in significantly
higher soil moisture in CO2-enriched plots (gravimetric spot measurements and continuous readings using a network of time-domain reflectometry probes).
Differences strongly depended on date, with the smallest effects when soil moisture was very high (after heavy precipitation)
and effects were largest at intermediate soil moisture. Elevated CO2 also affected diurnal soil moisture courses and rewetting of soils after precipitation. We conclude that ecosystem-level
controls of the water balance (including soil feedbacks) overshadow by far the physiological effects observed at the leaf
level. Indirect effects of CO2 enrichment mediated by trends in soil moisture will have far-ranging consequences on plant species composition, soil bacterial
and faunal activity as well as on soil physical structure and may indirectly also affect hydrology and trace gas emissions
and atmospheric chemistry.
Received: 21 December 1997 / Accepted: 3 August 1998 相似文献
9.
Yunhai Zhang Jing Wang Carly J Stevens Xiaotao Lü Nianpeng He Changhui Wang Xingguo Han 《Journal of Plant Ecology》2018,11(5):685
Aims
Nitrogen (N) enrichment caused by human activities threatens biodiversity and alters plant community composition and structure. It has been found that heavy and infrequent N inputs may over-estimate species extinction, but it remains unclear whether plant community structure will equally respond to frequent reactive N enriched conditions. 相似文献
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Earthworms make up the dominant fraction of the biomass of soil animals in most temperate grasslands and have important effects
on the structure and function of these ecosystems. We hypothesized that the effects of elevated atmospheric CO2 on soil moisture and plant biomass production would increase earthworm activity, expressed as surface cast production. Using
a screen-aided CO2 control facility (open top and open bottom rings), eight 1.2-m2 grassland plots in Switzerland have been maintained since March 1994 at ambient CO2 concentrations (350 μl CO2 l−1) and eight at elevated CO2 (610 μl CO2 l−1). Cumulative earthworm surface cast production measured 40 times over 1 year (April 1995–April 1996) in plots treated with
elevated CO2 (2206 g dry mass m−2 year−1) was 35% greater (P<0.05) than that measured in plant communities maintained at ambient CO2 (1633 g dry mass m−2 year−1). At these rates of surface cast production, worms would require about 100 years to egest the equivalent of the amount of
soil now found in the Ah horizon (top 15 cm) under current ambient CO2 concentrations, and 75 years under elevated CO2. Elevated atmospheric CO2 had no influence on the seasonality of earthworm activity. Cumulative surface cast production measured over the 7-week period
immediately following the 6-week summer dry period in 1995 (no surface casting) was positively correlated (P<0.05) with the mean soil water content calculated over this dry and subsequent wetter period, when viewed across all treatments.
However, no correlations were observed with soil temperature or with annual aboveground plant biomass productivity. No CO2-related differences were observed in total nitrogen (Ntot) and organic carbon (Corg) concentration of surface casts, although concentrations of both elements varied seasonally. The CO2-induced increase in earthworm surface casting activity corresponded to a 30% increase of the amount of Ntot (8.9 mg N m−2 vs. 6.9 mg N m−2) and Corg (126 mg C m−2 vs. 94 mg C m−2) egested by the worms in one year. Thus, our results demonstrate an important indirect stimulatory effect of elevated atmospheric
CO2 on earthworm activity which may have profound effects on ecosystem function and plant community structure in the long term.
Received: 3 November 1996 / Accepted: 11 January 1997 相似文献
13.
放牧和刈割是内蒙古草原的两种主要利用方式,然而,长期放牧和刈割对大针茅草原土壤微生物群落的影响知之甚少,因此,以内蒙古大针茅草原为研究对象,设置放牧和刈割两种利用方式,以围封不利用为对照,基于高通量测序技术,研究大针茅草原在不同利用方式下土壤微生物组成及多样性的变化,并结合土壤理化因子进一步探究土壤微生物群落组成的主要影响因素。研究结果表明:不同利用方式下土壤细菌α多样性指数无显著差异,而刈割显著提高了土壤真菌Observed_species、Chao1和ACE指数;土壤细菌群落的优势菌门是变形菌门(Proteobacteria)和放线菌门(Actinobacteria),土壤真菌群落的优势菌门是子囊菌门(Ascomycota)和被孢霉门(Mortierellomycota),不同利用方式下部分微生物类群的相对丰度差异显著,放牧显著提高了细菌群落的变形菌门、疣微菌门(Verrucomicrobia)和芽单胞菌门(Gemmatimonadetes)的相对丰度,刈割显著提高了真菌群落的担子菌门(Basidiomycota)相对丰度,此外,放牧和刈割均显著降低了厚壁菌门(Firmicutes... 相似文献
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15.
MARCEL G. A.
Van Der HEIJDEN SEBASTIAAN VERKADE SUSANNE J.
De BRUIN 《Global Change Biology》2008,14(11):2626-2635
Nitrogen (N) inputs to ecosystems have increased worldwide, often leading to large changes in plant community structure and reducing plant diversity. Yet, the interaction of increased N availability with other factors that determine plant community composition, are still poorly understood. Here, we test whether the impact of N addition on plant communities depends on the presence of arbuscular mycorrhizal fungi (AMF). AMF are widespread plant symbionts that facilitate growth of many plant species. We hypothesize that AM fungi reduce the negative impact of N addition on plant communities by supporting growth of species that are sensitive to N enrichment.We established experimental grassland microcosms consisting of 18 plant species. These microcosms were subjected to high and low N supply and were inoculated with AMF or remained nonmycorrhizal. Both N addition and AMF had a big impact on plant community composition, but with opposite effects. N addition induced a 2.8‐fold increase in grass biomass and reduced legume biomass. Grasses dominated the microcosms at high N supply, especially when AMF were absent. In contrast, AMF enhanced biomass of all legumes species (on average 6.8‐fold) and reduced the relative abundance of grasses. The proportion of legume biomass out of total shoot biomass at high N supply was 19% with AMF and only 3% without AMF. Our results show that responses of plant communities to N enrichment depend on AMF and that AMF can reduce the negative impact of increased N availability on plant community structure by reducing grass dominance. 相似文献
16.
Warming and free-air CO2 enrichment alter demographics in four co-occurring grassland species 总被引:2,自引:2,他引:0
Williams AL Wills KE Janes JK Vander Schoor JK Newton PC Hovenden MJ 《The New phytologist》2007,176(2):365-374
Species differ in their responses to global changes such as rising CO(2) and temperature, meaning that global changes are likely to change the structure of plant communities. Such alterations in community composition must be underlain by changes in the population dynamics of component species. Here, the impact of elevated CO(2) (550 micromol mol(-1)) and warming (+2 degrees C) on the population growth of four plant species important in Australian temperate grasslands is reported. Data collected from the Tasmanian free-air CO(2) enrichment (TasFACE) experiment between 2003 and 2006 were analysed using population matrix models. Population growth of Themeda triandra, a perennial C(4) grass, was largely unaffected by either factor but population growth of Austrodanthonia caespitosa, a perennial C(3) grass, was reduced substantially in elevated CO(2) plots. Warming and elevated CO(2) had antagonistic effects on population growth of two invasive weeds, Hypochaeris radicata and Leontodon taraxacoides, with warming causing population decline. Analysis of life cycle stages showed that seed production, seedling emergence and establishment were important factors in the responses of the species to global changes. These results show that the demographic approach is very useful in understanding the variable responses of plants to global changes and in elucidating the life cycle stages that are most responsive. 相似文献
17.
Helen L. Hayden Pauline M. Mele Damian S. Bougoure Claire Y. Allan Sorn Norng Yvette M. Piceno Eoin L. Brodie Todd Z. DeSantis Gary L. Andersen Amity L. Williams Mark J. Hovenden 《Environmental microbiology》2012,14(12):3081-3096
The microbial community structure of bacteria, archaea and fungi is described in an Australian native grassland soil after more than 5 years exposure to different atmospheric CO2 concentrations ([CO2]) (ambient, + 550 ppm) and temperatures (ambient, + 2°C) under different plant functional types (C 3 and C 4 grasses) and at two soil depths (0–5 cm and 5–10 cm). Archaeal community diversity was influenced by elevated [CO2], while under warming archaeal 16S rRNA gene copy numbers increased for C 4 plant Themeda triandra and decreased for the C 3 plant community (P < 0.05). Fungal community diversity resulted in three groups based upon elevated [CO2], elevated [CO2] plus warming and ambient [CO2]. Overall bacterial community diversity was influenced primarily by depth. Specific bacterial taxa changed in richness and relative abundance in response to climate change factors when assessed by a high‐resolution 16S rRNA microarray (PhyloChip). Operational taxonomic unit signal intensities increased under elevated [CO2] for both Firmicutes and Bacteroidetes, and increased under warming for Actinobacteria and Alphaproteobacteria. For the interaction of elevated [CO2] and warming there were 103 significant operational taxonomic units (P < 0.01) representing 15 phyla and 30 classes. The majority of these operational taxonomic units increased in abundance for elevated [CO2] plus warming plots, while abundance declined in warmed or elevated [CO2] plots. Bacterial abundance (16S rRNA gene copy number) was significantly different for the interaction of elevated [CO2] and depth (P < 0.05) with decreased abundance under elevated [CO2] at 5–10 cm, and for Firmicutes under elevated [CO2] (P < 0.05). Bacteria, archaea and fungi in soil responded differently to elevated [CO2], warming and their interaction. Taxa identified as significantly climate‐responsive could show differing trends in the direction of response (‘+’ or ‘?’) under elevated CO2 or warming, which could then not be used to predict their interactive effects supporting the need to investigate interactive effects for climate change. The approach of focusing on specific taxonomic groups provides greater potential for understanding complex microbial community changes in ecosystems under climate change. 相似文献
18.
Yang Yu Lang Zheng Yijun Zhou Weiguo Sang Jianing Zhao Lu Liu Chao Li Chunwang Xiao 《Journal of Plant Ecology》2021,14(3):384
温带草原退化后土壤微生物群落结构和功能的变化
草原退化是草原生产力维持面临的一个重大挑战,这一过程显著影响着草原生态系统的能量流动和土壤养分变化过程,进而直接或间接地影响着土壤微生物。我们的研究目的首先是调查不同草原退化程度(即未退化、中度退化和严重退化)如何影响着内蒙古温带草原的土壤微生物组成、多样性和功能,其次是阐明哪些生物和非生物因素导致了这些变化。我们的研究主要通过高通量测序技术分析土壤微生物的群落组成,并且采用FAPROTAX工具和FUNGuild工具分别预测细菌群落和真菌群落的功能。研究发现:草原退化显著降低了土壤细菌的多样性,但对真菌多样性影响不大。地下生物量、土壤有机碳和总氮与细菌的多样性变化呈显著正相关关系。草原退化显著增加了绿弯菌门的相对丰度(由2.48%提高到8.40%),降低了厚壁菌门的相对丰度(由3.62%降低到1.08%)。其次,草原退化也显著增加了球囊菌门的相对丰度(从0.17%提高到1.53%),降低了担子菌门的相对丰度(从19.30%降低到4.83%)。致病菌的相对丰度在草原退化过程中显著下降。此外,草原退化对土壤细菌群落的功能有显著的影响,尤其是与土壤碳氮循环相关的土壤细菌群落。我们的结果表明,土壤细菌群落对草原退化的响应比真菌群落更敏感。 相似文献
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Plant community dynamics in a calcareous grassland under climate change manipulations 总被引:1,自引:0,他引:1
Sternberg Marcelo Brown Valerie K. Masters Gregory J. Clarke Ian P. 《Plant Ecology》1999,143(1):29-37
This study investigates the effects of field manipulations of local climate to determine the potential impact of climate change on plant community dynamics in a calcareous grassland. The experimental site is located in a grassland at the Wytham estate, Oxfordshire, UK. The one hectare study area is within a 10 ha abandoned arable field on Jurassic corallian limestone. Two climate change scenarios were used: warmer winters with increased summer rainfall and warmer winters with summer drought. Plant cover and species richness were significantly increased in plots receiving supplemented summer rainfall, while the amount of litter was significantly reduced. Litter formation was significantly increased by winter warming and drought. The responses of the plant community to the climate manipulations were related to the life-history attributes of the dominant species. Seedling recruitment was limited by microsite availability, which also varied in the different climate manipulations. The results are discussed in terms of successional dynamics. They suggest that warmer winters may delay succession, as gap formation in the sward will provide sites for colonisation of annuals, thereby enabling their persistence in the sward. Under wetter conditions during summer, perennial grasses tend to close the sward, thereby inhibiting the establishment of later successional species. 相似文献