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1.
Atmospheric CO2 enrichment can affect plants directly via impacts on their performance, and indirectly, by environment‐specific traits passed down from the mother plant to the offspring. Such maternal effects can significantly alter plant species composition, especially in annual ecosystems where the entire community is recruited from seeds each year. This study assessed impacts of future, high CO2 (440 and 600 ppm) and pre‐industrial, low CO2 (280 ppm) on seed traits and offspring performance in three plant functional groups (grasses, legumes, forbs) comprising 17 annual species of a semi‐arid Mediterranean community. In grasses, seed size and seed‐reserve utilization as expressed by root elongation tended to be higher at high than at low maternal CO2, but total seed protein concentration and protein pool decreased with increasing maternal CO2. The response of seed size to high CO2 increased with increasing leaf‐mass fraction in grasses, and decreased with decreasing concentration of leaf non‐structural carbohydrates in legumes. Offspring development was studied at ambient CO2, and showed reduced emergence success of high‐CO2 progeny compared with low‐CO2 progeny in forbs. Total biomass was lower in high‐CO2 than in low‐CO2 offspring across all functional groups. The biomass response to high maternal CO2 in legume offspring correlated inversely with seed size, resulting in up to 25% lower biomass in large‐seeded species. Under the scenario of maternal effects combined with projected changes in biomass and seed production under direct exposure to high CO2, legumes might gain and forbs and grasses might lose from future CO2 enrichment. Most changes in seed traits and offspring performance were greater between pre‐industrial and near‐future CO2 than between near‐ and remote‐future CO2 concentrations. Hence, maternal effects of increasing CO2 may contribute to current changes in plant productivity and species composition, and they need to be considered when predicting impacts of global change on plant communities. 相似文献
2.
How might wild relatives of modern cereals have responded to past, and how might they respond to future, atmospheric CO2 enrichment under competitive situations in a dry, low‐nutrient environment? In order to test this, Aegilops and Hordeum species, common in semiarid annual grasslands of the Middle East, were grown in nine model ecosystems (400 kg each) with a natural matrix of highly diverse Negev vegetation established on native soil shipped to Basel, Switzerland. In a simulated, seasonally variable climate of the northern Negev, communities experienced a full life‐cycle in 280 (preindustrial), 440 (immediate future) and 600 ppm of CO2 (end of the next century). Neither Aegilops (A. kotschyi and A. peregrina), nor Hordeum spontaneum showed a significant biomass response to CO2 concentrations exceeding 280 ppm The reproductive output remained unaffected or even declined (A. peregrina) under elevated CO2. Non‐structural carbohydrates in leaf tissues increased and N concentration decreased with increasing CO2 concentration. N concentration, germination success and seedling development of newly formed grains were either unchanged or reduced in response to high CO2 treatment of parent plants. In a separate fertilizer × CO2 trial with A. kotschyi nested in smaller model communities, we found no effect of P addition, but a 2–3‐fold biomass increase by NPK addition compared to the unfertilized control. A significant stimulation of biomass by CO2 enrichment (+ 44% between 280 and 600 ppm) was obtained only in the NPK treatment. These data suggest that increased CO2 concentration had little direct effect on growth and reproduction in these ‘wild cereals’ in the recent past, and the same seems to hold for their future, except if N‐rich fertilizer is added. 相似文献
3.
If long‐term responses of photosynthesis and leaf diffusive conductance to rising atmospheric carbon dioxide (CO2) levels are similar or predictably different among species, functional types, and ecosystem types, general global models of elevated CO2 effects can effectively be developed. To address this issue we measured gas exchange rates of 13 perennial grassland species from four functional groups across 11 years of long‐term free‐air CO2 enrichment (eCO2, +180 ppm above ambient CO2) in the BioCON experiment in Minnesota, USA. Eleven years of eCO2 produced consistent but modest increases in leaf net photosynthetic rates of 10% on average compared with plants grown at ambient CO2 concentrations across the 13 species. This eCO2‐induced enhancement did not depend on soil N treatment, is much less than the average across other longer‐term studies, and represents strong acclimation (i.e. downregulation) as it is also much less than the instantaneous response to eCO2. The legume and C3 nonlegume forb species were the most responsive among the functional groups (+13% in each), the C4 grasses the least responsive (+4%), and C3 grasses intermediate in their photosynthetic response to eCO2 across years (+9%). Leaf stomatal conductance and nitrogen content declined comparably across species in eCO2 compared with ambient CO2 and to degrees corresponding to results from other studies. The significant acclimation of photosynthesis is explained in part by those eCO2‐induced decreases in leaf N content and stomatal conductance that reduce leaf photosynthetic capacity in plants grown under elevated compared with ambient CO2 concentrations. Results of this study, probably the longest‐term with the most species, suggest that carbon cycle models that assume and thereby simulate long‐lived strong eCO2 stimulation of photosynthesis (e.g.> 25%) for all of Earth's terrestrial ecosystems should be viewed with a great deal of caution. 相似文献
4.
Climbing plants have profound influences on tropical forest dynamics and may take particular advantage from atmospheric CO2 enrichment, thus potentially enhancing tree turnover. Here we test the effect of a four‐step CO2‐enrichment on growth of three typical Yucatan (Mexico) climbers, across two low photon flux densities, representing typical understory situations. In pairs of two, species of Gonolobus (Asclepiadaceae), Ceratophytum (Bignoniaceae) and Thinouia (Sapindaceae) were grown on Yucatan forest soil in growth cabinets, which simulated the diurnal climate variation. Biomass increased non‐linearly in response to CO2 enrichment from 280 (preindustrial) to 420 ppm and 560 ppm, but then (700 ppm) leveled off. The relative effect of CO2‐enrichment between the two lower (280–420 ppm) CO2 concentrations was 63% at low light (LL == 42 µmol m2?2 s2?1), compared to 37% at high light (HL = 87 µmol m2?2 s2?1). This overall response of species pairs was the combined effect of linear and non‐linear responses of the individual species across CO2 treatments. Plant biomass was 61% larger in HL compared to LL. The species‐specific response depended on the neighbor, a species grew with h, irrespective of plant size. Stem length increased, but not consistently across species and light conditions. Specific stem length (SSL, length per dry mass) declined non‐linearly in all three species as CO2 concentration increased (more pronounced at LL than at HL). SLA (leaf area per unit leaf dry mass) became lower as CO2 concentration increased (more pronounced in HL). Enhanced vigor of climbers under elevated CO2 as documented here may accelerate tropical forest dynamics and lead to greater abundance of early succesional tree species. This could reduce forest carbon stocking in the long run. 相似文献
5.
This study explored consumption of a generalist herbivore feeding on leaf tissue of various plant species of a calcareous
grassland, and tested whether consumption levels and preferences changed when plants were exposed to 5 years of in situ CO2 enrichment. The first part of this experiment tested whether the consumption patterns of slugs (Deroceras reticulatum) observed in single-species feeding tests were altered when slugs were given a choice of food sources. Overall consumption
increased 270% when slugs were given a choice, and they preferred having a choice of food sources more than they preferred
having any one food source. Surprisingly, slugs consumed fewer legumes and grasses and more non-leguminous forbs when given
a choice. In the second part of this experiment, feeding behaviors of slugs in response to elevated CO2 were investigated by feeding them leaves of two legumes, one grass, and a non-leguminous forb (Trifolium medium, Lotus corniculatus, Bromus erectus, and Sanguisorba minor, respectively) in two or four species combinations. In the leguminous species mix, the non-leguminous species mix, and the
combined mix (legumes and non-legumes), neither overall consumption by herbivores nor species preference was significantly
altered by long-term CO2 enrichment. In the combined species mix, slugs preferred legumes to non-legumes (P=0.012) and exhibited a weak functional group preference shift from non-legumes to legumes (P=0.089) in response to CO2 enrichment. This is the first time such a shift has been observed, and provides evidence that there may be multiple herbivore
responses to rising atmospheric CO2 concentrations. Numerous single-species feeding tests using insects have shown that consumption by herbivores may increase
when herbivores are fed plants grown in enriched CO2 atmospheres. This study clearly demonstrates the limited applicability of non-choice feeding trials to generalist herbivores
in species-rich communities.
Received: 19 August 1999 / Accepted: 20 April 2000 相似文献
6.
Plants may be more sensitive to carbon dioxide (CO2) enrichment at subambient concentrations than at superambient concentrations, but field tests are lacking. We measured soil‐water content and determined xylem pressure potentials and δ13C values of leaves of abundant species in a C3/C4 grassland exposed during 1997–1999 to a continuous gradient in atmospheric CO2 spanning subambient through superambient concentrations (200–560 µmol mol2?1). We predicted that CO2 enrichment would lessen soil‐water depletion and increase xylem potentials more over subambient concentrations than over superambient concentrations. Because water‐use efficiency of C3 species (net assimilation/leaf conductance; A/g) typically increases as soils dry, we hypothesized that improvements in plant‐water relations at higher CO2 would lessen positive effects of CO2 enrichment on A/g. Depletion of soil water to 1.35 m depth was greater at low CO2 concentrations than at higher CO2 concentrations during a mid‐season drought in 1998 and during late‐season droughts in 1997 and 1999. During droughts each year, mid‐day xylem potentials of the dominant C4 perennial grass (Bothriochloa ischaemum (L.) Keng) and the dominant C3 perennial forb (Solanum dimidiatum Raf.) became less negative as CO2 increased from subambient to superambient concentrations. Leaf A/g—derived from leaf δ13C values—was insensitive to feedbacks from CO2 effects on soil water and plant water. Among most C3 species sampled—including annual grasses, perennial grasses and perennial forbs—A/g increased linearly with CO2 across subambient concentrations. Leaf and air δ13C values were too unstable at superambient CO2 concentrations to reliably determine A/g. Significant changes in soil‐ and plant‐water relations over subambient to superambient concentrations and in leaf A/g over subambient concentrations generally were not greater over low CO2 than over higher CO2. The continuous response of these variables to CO2 suggests that atmospheric change has already improved water relations of grassland species and that periodically water‐limited grasslands will remain sensitive to CO2 enrichment. 相似文献
7.
Vincent Allard † Paul C. D. Newton Mark Lieffering Jean-Francois Soussana† Phillipe Grieu‡ Cory Matthew§ 《Global Change Biology》2004,10(9):1553-1564
The effects of elevated atmospheric CO2 (475 μL L?1) on in situ decomposition of plant litter and animal faecal material were studied over 2 years in a free air CO2 enrichment (FACE) facility. The pasture was grazed by sheep and contained a mixture of C3 and C4 grasses, legumes and forbs. There was no effect of elevated CO2 on decomposition within plant species but marked differences between species with faster decomposition in dicots; a group that increased in abundance at elevated CO2. Decomposition of mixed herbage root material occurred at a similar rate to that of leaf litter suggesting that any CO2‐induced increase in carbon allocation to roots would not reduce rates of decomposition. Sheep faeces resulting from a ‘high‐CO2 diet’ decomposed significantly slower during summer but not during winter. The overall outcome of these experiments were explored using scenarios that took account of changes in botanical composition, allocation to roots and the presence of herbivores. In the absence of herbivores, elevated CO2 led to a 15% increase in the rate of mass loss and an 18% increase in the rate of nitrogen (N) release. In the presence of herbivores, these effects were partially removed (11% increase in rate of mass loss and 9% decrease in N release rate) because of the recycling occurring through the animals in the form of faeces. 相似文献
8.
Legumes are an important component of plant diversity that modulate nitrogen (N) cycling in many terrestrial ecosystems. Limited knowledge of legume effects on soil N cycling and its response to global change factors and plant diversity hinders a general understanding of whether and how legumes broadly regulate the response of soil N availability to those factors. In a 17‐year study of perennial grassland species grown under ambient and elevated (+180 ppm) CO2 and ambient and enriched (+4 g N m?2 year?1) N environments, we compared pure legume plots with plots dominated by or including other herbaceous functional groups (and containing one or four species) to assess the effect of legumes on N cycling (net N mineralization rate and inorganic N pools). We also examined the effects of numbers of legume species (from zero to four) in four‐species mixed plots on soil N cycling. We hypothesized that legumes would increase N mineralization rates most in those treatments with the greatest diversity and the greatest relative limitation by and competition for N. Results partially supported these hypotheses. Plots with greater dominance by legumes had greater soil nitrate concentrations and mineralization rates. Higher species richness significantly increased the impact of legumes on soil N metrics, with 349% and 505% higher mineralization rates and nitrate concentrations in four‐species plots containing legumes compared to legume‐free four‐species plots, in contrast to 185% and 129% greater values, respectively, in pure legume than nonlegume monoculture plots. N‐fertilized plots had greater legume effects on soil nitrate, but lower legume effects on net N mineralization. In contrast, neither elevated CO2 nor its interaction with legumes affected net N mineralization. These results indicate that legumes markedly influence the response of soil N cycling to some, but not all, global change drivers. 相似文献
9.
The role of legumes as a component of biodiversity in a cross-European study of grassland biomass nitrogen 总被引:14,自引:0,他引:14
E. M. Spehn M. Scherer‐Lorenzen B. Schmid A. Hector M. C. Caldeira P. G. Dimitrakopoulos J. A. Finn A. Jumpponen G. O'Donnovan J. S. Pereira E.‐D. Schulze A. Y. Troumbis C. Krner 《Oikos》2002,98(2):205-218
To investigate how plant diversity loss affects nitrogen accumulation in above‐ground plant biomass and how consistent patterns are across sites of different climatic and soil conditions, we varied the number of plant species and functional groups (grasses, herbs and legumes) in experimental grassland communities across seven European experimental sites (Switzerland, Germany, Ireland, United Kingdom (Silwood Park), Portugal, Sweden and Greece). Nitrogen pools were significantly affected by both plant diversity and community composition. Two years after sowing, nitrogen pools in Germany and Switzerland strongly increased in the presence of legumes. Legume effects on nitrogen pools were less pronounced at the Swedish, Irish and Portuguese site. In Greece and UK there were no legume effects. Nitrogen concentration in total above‐ground biomass was quite invariable at 1.66±0.03% across all sites and diversity treatments. Thus, the presence of legumes had a positive effect on nitrogen pools by significantly increasing above‐ground biomass, i.e. by increases in vegetation quantity rather than quality. At the German site with the strongest legume effect on nitrogen pools and biomass, nitrogen that was fixed symbiotically by legumes was transferred to the other plant functional groups (grasses and herbs) but varied depending on the particular legume species fixing N and the non‐legume species taking it up. Nitrogen‐fixation by legumes therefore appeared to be one of the major functional traits of species that influenced nitrogen accumulation and biomass production, although effects varied among sites and legume species. This study demonstrates that the consequences of species loss on the nitrogen budget of plant communities may be more severe if legume species are lost. However, our data indicate that legume species differ in their N2 fixation. Therefore, loss of an efficient N2‐fixer (Trifolium in our study) may have a greater influence on the ecosystem function than loss of a less efficient species (Lotus in our study). Furthermore, there is indication that P availability in the soil facilitates the legume effect on biomass production and biomass nitrogen accumulation. 相似文献
10.
We conducted an experiment on responses of weedy species from an orchard ecosystem to elevated CO2 (700–800 μmol mol−1) under low phosphorus (P) soil in an environment-controlled growth chamber. Twelve local weedy species, Poa annua L., Lolium perenne L., Avena fatua L., Vicia cracca L., Medicago lupulina L., Kummerowia striata (Thunb.) Schindl., Veronica didyma Ten., Plantago virginica L., Gnaphalium affine D.Don., Echinochloa crusgalli var. mitis (L.) Beauv., Eleusine indica (L.) Gaertn. and Setaria glauca (L.) P. Beauv., grouped into four functional groups (C3 grass, C3 forb, legume and C4 grass), were used in the experiment. The total plant biomass, P uptake, and mycorrhizal colonization were measured. The results showed that the total biomass of the 12 weedy species tended to increase under elevated CO2. But changes in the total biomass under elevated CO2 significantly differed among functional groups: legumes showed the greatest increase in the total biomass of all functional groups, following the order C3 forbs > C4 grasses > C3 grasses. Elevated CO2 significantly increased mycorrhizal colonization and P uptake of legumes, C3 forbs and C4 grasses but did not change C3 grasses. Positive correlations between mycorrhizal colonization and shoot P concentration, and between total P uptake and total biomass were found under elevated CO2. The results suggested that the interspecific difference in CO2 response at low P availability was caused by the difference in CO2 response in mycorrhizae and P uptake. These differences among species imply that plant interaction in orchard ecosystems may change under future CO2 enrichment. 相似文献
11.
Effects of elevated CO2 and cutting frequency on plant community structure in a temperate grassland 总被引:1,自引:0,他引:1
Florence Teyssonneyre Catherine Picon-cochard Robert Falcimagne Jean-François Soussana 《Global Change Biology》2002,8(10):1034-1046
Monoliths of a fertile, N limited, C3 grassland community were subjected (or not) to an atmospheric CO2 enrichment (600 µmol mol‐‐1) using a Mini‐FACE system, from August 1998 to June 2001 and were subjected to two contrasting cutting frequencies (3 and 6 cuts per year). We report here the effects of the CO2 and cutting frequency factors on the plant community structure and its diversity. Species‐specific responses to elevated CO2 and cutting frequency were observed, which resulted in significant changes in the botanical composition of the grassland monoliths. Elevated CO2 significantly increased the proportion of dicotyledones (forbs + legumes) and reduced that of the monocotyledones (grasses). Management differentiated this response as elevated CO2 increased the proportion of forbs when infrequently and of legumes when frequently defoliated. However, among the two dominant forbs species only one was significantly enhanced by elevated CO2. Moreover, not all grass species responded negatively to high CO2. At a low cutting frequency, the observed decline under ambient CO2 in species diversity (Shannon‐Weaver index) and in forb species number was partly alleviated by elevated CO2. This experiment shows that the botanical composition of temperate grasslands is likely to be affected by the current rise (+ 0.5% per year) in the atmospheric CO2 concentration, and that grassland management guidelines may need to be adapted to a future high CO2 world. 相似文献
12.
Christiane Roscher Susanne Thein Alexandra Weigelt Vicky M. Temperton Nina Buchmann Ernst-Detlef Schulze 《Plant and Soil》2011,341(1-2):333-348
Highly variable effects of legumes have been observed in biodiversity experiments, but little is known about plant diversity effects on N2 fixation of legume species. We used the 15N natural abundance method in a non-fertilized regularly mown 6-year biodiversity experiment (Jena Experiment) to quantify N2 fixation of 12 legume species. The proportion of legume N derived from the atmosphere (%Ndfa) differed significantly among legume species. %Ndfa values were lower in 2004 after setting-up the experiment (73?±?20) than in the later years (2006: 80?±?16; 2008: 78?±?12). Increasing species richness had positive effects on %Ndfa in 2004 and 2006, but not in 2008. High biomass production of legumes in 2004 and 2006 declined to lower levels in 2008. In 2006, legume positioning within the canopy best explained variation in %Ndfa values indicating a lower reliance of tall legumes on N2 fixation. In 2008, larger %Ndfa values of legumes were related to lower leaf P concentrations suggesting that the availability of phosphorus limited growth of legumes. In summary, diversity effects on N2 fixation depend on legume species identity, their ability to compete for soil nutrients and light and may vary temporally in response to changing resource availability. 相似文献
13.
KRISTINE Y. CROUS PETER B. REICH MARK D. HUNTER DAVID S. ELLSWORTH 《Global Change Biology》2010,16(7):2076-2088
Determining underlying physiological patterns governing plant productivity and diversity in grasslands are critical to evaluate species responses to future environmental conditions of elevated CO2 and nitrogen (N) deposition. In a 9‐year experiment, N was added to monocultures of seven C3 grassland species exposed to elevated atmospheric CO2 (560 μmol CO2 mol?1) to evaluate how N addition affects CO2 responsiveness in species of contrasting functional groups. Functional groups differed in their responses to elevated CO2 and N treatments. Forb species exhibited strong down‐regulation of leaf Nmass concentrations (?26%) and photosynthetic capacity (?28%) in response to elevated CO2, especially at high N supply, whereas C3 grasses did not. Hence, achieved photosynthetic performance was markedly enhanced for C3 grasses (+68%) in elevated CO2, but not significantly for forbs. Differences in access to soil resources between forbs and grasses may distinguish their responses to elevated CO2 and N addition. Forbs had lesser root biomass, a lower distribution of biomass to roots, and lower specific root length than grasses. Maintenance of leaf N, possibly through increased root foraging in this nutrient‐poor grassland, was necessary to sustain stimulation of photosynthesis under long‐term elevated CO2. Dilution of leaf N and associated photosynthetic down‐regulation in forbs under elevated [CO2], relative to the C3 grasses, illustrates the potential for shifts in species composition and diversity in grassland ecosystems that have significant forb and grass components. 相似文献
14.
Interactions between the moth Spodoptera littoralis and two of its host plants, alfalfa (Medicago sativa) and cotton (Gossypium hirsutum) were examined, using plants grown under ambient (350 ppm) and elevated (700 ppm) CO2 conditions. To determine strength and effects of herbivore‐induced responses assays were performed with both undamaged (control) and herbivore damaged plants. CO2 and damage effects on larval host plant preferences were determined through dual‐choice bioassays. In addition, larvae were reared from hatching to pupation on experimental foliage to examine effects on larval growth and development. When undamaged plants were used S. littoralis larvae in consumed more cotton than alfalfa, and CO2 enrichment caused a reduction in the preference for cotton. With damaged plants larvae consumed equal amounts of the two plant species (ambient CO2 conditions), but CO2 enrichment strongly shifted preferences towards cotton, which was then consumed three times more than alfalfa. Complementary assays showed that elevated CO2 levels had no effect on the herbivore‐induced responses of cotton, whereas those of alfalfa were significantly increased. Larval growth was highest for larvae fed undamaged cotton irrespectively of CO2 level, and lowest for larvae on damaged alfalfa from the high CO2 treatment. Development time increased on damaged cotton irrespectively of CO2 treatment, and on damaged alfalfa in the elevated CO2 treatment. These results demonstrate that elevated CO2 levels can cause insect herbivores to alter host plant preferences, and that effects on herbivore‐induced responses may be a key mechanism behind these processes. Furthermore, since the insects were shown to avoid foliage that reduced their physiological performance, our data suggest that behavioural host plant shifts result in partial escape from negative consequences of feeding on high CO2 foliage. Thus, CO2 enrichment can alter both physiology and behaviour of important insect herbivores, which in turn may to impact plant biodiversity. 相似文献
15.
J. Wagner A. Lüscher C. Hillebrand B. Kobald N. Spitaler W. Larcher 《Plant, cell & environment》2001,24(9):957-966
Field experiments in managed grassland have shown that the response of vegetative growth to elevated CO2 is nitrogen‐dependent in grasses, but independent in N2‐fixing legumes. In the present study, we tested whether this is also true for reproduction. We evaluated reproductive growth, flowering phenology, seed development, reproductive success and seed germination in the grass Lolium perenne L. and the legume Trifolium repens L., growing in monocultures in a free air carbon dioxide enrichment (FACE) system at ambient (35 Pa) and elevated (60 Pa) partial pressure of CO2 and two levels of nitrogen fertilization (14 and 56 g N m?2 a?1). In both species, elevated CO2 had no significant effect on sexual reproduction. In L. perenne, reproduction was mainly nitrogen‐dependent. The weak interactions between CO2 and mineral N supply (13% more flowers and 8% more grains per spike at high N, 7% less flowers and 8% less grains at low N) were not significant. Under elevated CO2, grain maturation was slightly enhanced and grain weight tended to decrease. No influence could be ascertained in the date of anthesis, the temporal pattern of grain growth, the rate of grain abortion and germination. Trifolium repens, grown under CO2 enrichment at both levels of N fertilization, flowered 10 d earlier, tended to form more inflorescences per ground area and more flowers (8–12%) and seeds (>18%) per inflorescence than at ambient CO2. The temporal pattern of seed growth was about the same in all treatments; embryo development, however, was accelerated in fumigated plants. The number of aborted seeds per pod, seed size, thousand‐seed weight and germinability did not show any influence of CO2. Fumigated plants at high N were attacked slightly more frequently by seed‐eating weevils, which lowered the seed output per pod. In summary, the reproductive response of L. perenne and T. repens to CO2 enrichment on the flower and inflorescence level was far weaker than expected from the results on vegetative growth. 相似文献
16.
This study investigated the effect of elevated CO2 on the post‐fire resprouting response of a grassland system of perennial grass species of Cumberland Plain Woodland. Plants were grown in mixtures in natural soil in mesocosms, each containing three exotic grasses (Nassella neesiana, Chloris gayana, Eragrostis curvula) and three native grasses (Themeda australis, Microlaena stipoides, Chloris ventricosa) under elevated (700 ppm) and ambient (385 ppm) CO2 conditions. Resprouting response after fire at the community‐ and species‐level was assessed. There was no difference in community‐level biomass between CO2 treatments; however, exotic species made up a larger proportion of the community biomass under all treatments. There were species‐level responses to elevated CO2 but no significant interactions found between CO2 and burning or plant status. Two exotic grasses (N. neesiana and E. curvula, a C3 and a C4 species respectively), and one native grass (M. stipoides, a C3 species) significantly increased in biomass, and a native C4 grass (C. ventricosa) significantly decreased in biomass under elevated CO2. These results suggest that although overall productivity of this community may not change with increases in CO2 and fire frequency, the community composition may alter due to differential species responses. 相似文献
17.
Atmospheric CO2 enrichment usually changes the relative contributions of plant species to biomass production of grasslands, but the types of species favored and mechanisms by which change is mediated differ among ecosystems. We measured changes in the contributions of C3 perennial forbs and C4 grasses to aboveground biomass production of tallgrass prairie assemblages grown along a field CO2 gradient (250–500 μmol mol?1) in central Texas USA. Vegetation was grown on three soil types and irrigated each season with water equivalent to the growing season mean of precipitation for the area. We predicted that CO2 enrichment would increase the forb contribution to community production, and favor tall‐grasses over mid‐grasses by increasing soil water content and reducing the frequency with which soil water fell below a limitation threshold. CO2 enrichment favored forbs over grasses on only one of three soil types, a Mollisol. The grass fraction of production increased dramatically across the CO2 gradient on all soils. Contribution of the tall‐grass Sorghastrum nutans to production increased at elevated CO2 on the two most coarse‐textured of the soils studied, a clay Mollisol and sandy Alfisol. The CO2‐caused increase in Sorghastrum was accompanied by an offsetting decline in production of the mid‐grass Bouteloua curtipendula. Increased CO2 favored the tall‐grass over mid‐grass by increasing soil water content and apparently intensifying competition for light or other resources (Mollisol) or reducing the frequency with which soil water dipped below threshold levels (Alfisol). An increase in CO2 of 250 μmol mol?1 above the pre‐industrial level thus led to a shift in the relative production of established species that is similar in magnitude to differences observed between mid‐grass and tallgrass prairies along a precipitation gradient in the central USA. By reducing water limitation to plants, atmospheric CO2 enrichment may alter the composition and even structure of grassland vegetation. 相似文献
18.
Melissa A. Pastore Tali D. Lee Sarah E. Hobbie Peter B. Reich 《Global Change Biology》2019,25(9):3031-3044
Uncertainty about long‐term leaf‐level responses to atmospheric CO2 rise is a major knowledge gap that exists because of limited empirical data. Thus, it remains unclear how responses of leaf gas exchange to elevated CO2 (eCO2) vary among plant species and functional groups, or across different levels of nutrient supply, and whether they persist over time for long‐lived perennials. Here, we report the effects of eCO2 on rates of net photosynthesis and stomatal conductance in 14 perennial grassland species from four functional groups over two decades in a Minnesota Free‐Air CO2 Enrichment experiment, BioCON. Monocultures of species belonging to C3 grasses, C4 grasses, forbs, and legumes were exposed to two levels of CO2 and nitrogen supply in factorial combinations over 21 years. eCO2 increased photosynthesis by 12.9% on average in C3 species, substantially less than model predictions of instantaneous responses based on physiological theory and results of other studies, even those spanning multiple years. Acclimation of photosynthesis to eCO2 was observed beginning in the first year and did not strengthen through time. Yet, contrary to expectations, the response of photosynthesis to eCO2 was not enhanced by increased nitrogen supply. Differences in responses among herbaceous plant functional groups were modest, with legumes responding the most and C4 grasses the least as expected, but did not further diverge over time. Leaf‐level water‐use efficiency increased by 50% under eCO2 primarily because of reduced stomatal conductance. Our results imply that enhanced nitrogen supply will not necessarily diminish photosynthetic acclimation to eCO2 in nitrogen‐limited systems, and that significant and consistent declines in stomatal conductance and increases in water‐use efficiency under eCO2 may allow plants to better withstand drought. 相似文献
19.
Rising atmospheric CO2 concentrations may alter C cycling and community composition, however, long-term studies in (semi-)natural ecosystems are still rare. In May 1998, the Giessen FACE (Free Air Carbon dioxide Enrichment) experiment started in a grassland ecosystem near Giessen, Germany, consisting of three enrichment (E plots) and three ambient control rings (A plots). Carbon dioxide concentrations were raised to +20% above ambient all-year-round during daylight hours. The wet grassland (Arrhenatheretum elatioris Br.-Bl.; not ploughed for >100 years) has been fertilized with 40 kg ha−1 yr−1 N, and mown two times each year for decades. Since 1993, the biomass has been monitored and since 1997 it was divided into grasses, legumes and non-leguminous forbs.During the 5 years prior to CO2 enrichment, the annual biomass yield from the A plots was non-significantly higher (3%) than the later E plots yield. Under CO2 enrichment, the biomass increased significantly from the third enrichment year on by 9.8%, 7.7% and 11.2% in the years 2000–2002, respectively. The increase was surprisingly high considering the moderate CO2 enrichment regime of only +20% and sub-optimal N supply, possibly suggesting a non-linear response of temperate grassland ecosystems to rising atmospheric CO2 levels.The leaf area index did not change significantly under elevated CO2, nor did the soil moisture in the top 15 cm increase. No correlation existed between the magnitude of the yield stimulation under elevated CO2 and the precipitation sums preceding the respective harvests. The grass biomass increased significantly under FACE, while the forb biomass declined strongly in the fourth and fifth year. The legume fraction was mostly below 1% of the total yield, and did not respond to CO2 enrichment. These findings are in contrast to other grassland results and possible reasons are discussed. 相似文献
20.
Are mature forest trees carbon limited at current CO2 concentrations? Will ‘mid‐life’, 35 m tall deciduous trees grow faster in a CO2‐enriched atmosphere? To answer these questions we exposed ca. 100‐year‐old temperate forest trees at the Swiss Canopy Crane site near Basel, Switzerland to a ca. 540 ppm CO2 atmosphere using web‐FACE technology. Here, we report growth responses to elevated CO2 for 11 tall trees (compared with 32 controls) of five species during the initial four treatment years. Tested across all trees, there was no CO2 effect on stem basal area (BA) increment (neither when tested per year nor cumulatively for 4 years). In fact, the 4th year means were almost identical for the two groups. Stem growth data were standardized by pretreatment growth (5 years) in order to account for a priori individual differences in vigor. Although this experiment was not designed to test species specific effects, one species, the common European beech, Fagus sylvatica, showed a significant growth enhancement in the first year, which reoccurred during a centennial drought in the third year. None of the other dominant species (Quercus petraea, Carpinus betulus) showed a growth response to CO2 in any of the 4 years or for all years together. The inclusion or exclusion of single individuals of Prunus avium and Tilia platyphyllos did not change the picture. In elevated CO2, lateral branching in terminal shoots was higher in Fagus in 2002, when shoots developed from buds that were formed during the first season of CO2 enrichment (2001), but there was no effect in later years and no change in lateral branching in any of the other species. In Quercus, there was a steady stimulation of leading shoot length in high‐CO2 trees. Phenological variables (bud break, leaf fall, leaf duration) were highly species specific and were not affected by elevated CO2 in any consistent way. Our 4‐year data set reflects a very dynamic and species‐specific response of tree growth to a step change in CO2 supply. Stem growth after 4 years of exposure does not support the notion that mature forest trees will accrete wood biomass at faster rates in a future CO2‐enriched atmosphere. 相似文献