Empirical records provide incontestable evidence for the global rise in carbon dioxide (CO2) concentration in the earth's atmosphere. Plant growth can be stimulated by elevation of CO2; ...photosynthesis increases and economic yield is often enhanced. The application of more CO2 can increase plant water use efficiency and result in less water use. After reviewing the available CO2 literature, we offer a series of priority targets for future research, including: 1) a need to breed or screen varieties and species of horticultural plants for increased drought tolerance; 2) determining the amount of carbon sequestered in soil from horticulture production practices for improved soil water-holding capacity and to aid in mitigating projected global climate change; 3) determining the contribution of the horticulture industry to these projected changes through flux of CO2 and other trace gases (i.e., nitrous oxide from fertilizer application and methane under anaerobic conditions) to the atmosphere; and 4) determining how CO2-induced changes in plant growth and water relations will impact the complex interactions with pests (weeds, insects, and diseases). Such data are required to develop best management strategies for the horticulture industry to adapt to future environmental conditions.
Efforts to characterize carbon (C) cycling among atmosphere, forest canopy, and soil C pools are hindered by poorly quantified fine root dynamics. We characterized the influence of ...free-air-CO₂-enrichment (ambient +200 ppm) on fine roots for a period of 6 years (Autumn 1998 through Autumn 2004) in an 18-year-old loblolly pine (Pinus taeda) plantation near Durham, NC, USA using minirhizotrons. Root production and mortality were synchronous processes that peaked most years during spring and early summer. Seasonality of fine root production and mortality was not influenced by atmospheric CO₂ availability. Averaged over all 6 years of the study, CO₂ enrichment increased average fine root standing crop (+23%), annual root length production (+25%), and annual root length mortality (+36%). Larger increase in mortality compared with production with CO₂ enrichment is explained by shorter average fine root lifespans in elevated plots (500 days) compared with controls (574 days). The effects of CO₂-enrichment on fine root proliferation tended to shift from shallow (0-15 cm) to deeper soil depths (15-30) with increasing duration of the study. Diameters of fine roots were initially increased by CO₂-enrichment but this effect diminished over time. Averaged over 6 years, annual fine root NPP was estimated to be 163 g dw m⁻² yr⁻¹ in CO₂-enriched plots and 130 g dw m⁻² yr⁻¹ in control plots (P= 0.13) corresponding to an average annual additional input of fine root biomass to soil of 33 g m⁻² yr⁻¹ in CO₂-enriched plots. A lack of consistent CO₂x year effects suggest that the positive effects of CO₂ enrichment on fine root growth persisted 6 years following minirhizotron tube installation (8 years following initiation of the CO₂ fumigation). Although CO₂-enrichment contributed to extra flow of C into soil in this experiment, the magnitude of the effect was small suggesting only modest potential for fine root processes to directly contribute to soil C storage in south-eastern pine forests.
Elevated CO2 and plant structure: a review Pritchard, SetH. G.; Rogers, HugO. H.; Prior, Stephen A. ...
Global change biology,
10/1999, Letnik:
5, Številka:
7
Journal Article
Recenzirano
Summary
Consequences of increasing atmospheric CO2 concentration on plant structure, an important determinant of physiological and competitive success, have not received sufficient attention in the ...literature. Understanding how increasing carbon input will influence plant developmental processes, and resultant form, will help bridge the gap between physiological response and ecosystem level phenomena. Growth in elevated CO2 alters plant structure through its effects on both primary and secondary meristems of shoots and roots. Although not well established, a review of the literature suggests that cell division, cell expansion, and cell patterning may be affected, driven mainly by increased substrate (sucrose) availability and perhaps also by differential expression of genes involved in cell cycling (e.g. cyclins) or cell expansion (e.g. xyloglucan endotransglycosylase). Few studies, however, have attempted to elucidate the mechanistic basis for increased growth at the cellular level.
Regardless of specific mechanisms involved, plant leaf size and anatomy are often altered by growth in elevated CO2, but the magnitude of these changes, which often decreases as leaves mature, hinges upon plant genetic plasticity, nutrient availability, temperature, and phenology. Increased leaf growth results more often from increased cell expansion rather than increased division. Leaves of crop species exhibit greater increases in leaf thickness than do leaves of wild species. Increased mesophyll and vascular tissue cross‐sectional areas, important determinates of photosynthetic rates and assimilate transport capacity, are often reported. Few studies, however, have quantified characteristics more reflective of leaf function such as spatial relationships among chlorenchyma cells (size, orientation, and surface area), intercellular spaces, and conductive tissue. Greater leaf size and/or more leaves per plant are often noted; plants grown in elevated CO2 exhibited increased leaf area per plant in 66% of studies, compared to 28% of observations reporting no change, and 6% reported a decrease in whole plant leaf area. This resulted in an average net increase in leaf area per plant of 24%. Crop species showed the greatest average increase in whole plant leaf area (+ 37%) compared to tree species (+ 14%) and wild, nonwoody species (+ 15%). Conversely, tree species and wild, nontrees showed the greatest reduction in specific leaf area (– 14% and – 20%) compared to crop plants (– 6%).
Alterations in developmental processes at the shoot apex and within the vascular cambium contributed to increased plant height, altered branching characteristics, and increased stem diameters. The ratio of internode length to node number often increased, but the length and sometimes the number of branches per node was greater, suggesting reduced apical dominance. Data concerning effects of elevated CO2 on stem/branch anatomy, vital for understanding potential shifts in functional relationships of leaves with stems, roots with stems, and leaves with roots, are too few to
make generalizations. Growth in elevated CO2 typically leads to increased root length, diameter, and altered branching patterns. Altered branching characteristics in both shoots and roots may impact competitive relationships above and below the ground.
Understanding how increased carbon assimilation affects growth processes (cell division, cell expansion, and cell patterning) will facilitate a better understanding of how plant form will change as atmospheric CO2 increases. Knowing how basic growth processes respond to increased carbon inputs may also provide a mechanistic basis for the differential phenotypic plasticity exhibited by different plant species/functional types to elevated CO2.
Rising atmospheric CO₂ concentration will affect belowground processes and forest function. However, the direction and magnitude of change for many soil processes are unknown. We used minirhizotrons ...to observe fine root and fungal dynamics in response to elevated CO₂ in a model regenerating longleaf pine community in open-top chambers. The model community consisted of five plant species common to xeric sandhills longleaf pine stands: Pinus palustris, Quercus margaretta, Aristida stricta, Crotalaria rotundifolia, and Asclepias tuberosa. Elevated CO₂ significantly increased both fine root and mycorrhizal tip standing crop by more than 50% in the deeper soil horizon (17-34 cm). Rhizomorph standing crop was nearly doubled in both deep and shallow soil (P = 0.04). Survivorship results for fine roots and rhizomorphs varied between soil depths. Fine root survivorship was likely influenced more by changes in community composition and species interactions driven by elevated CO₂ rather than by direct effects of elevated CO₂ on the fine roots of individual species. In this system, it appears that elevated CO₂ led to a greater reliance on fungal symbionts to meet additional nutrient requirements rather than substantially increased root growth.
Growth of crops in CO2-enriched atmospheres typically results in significant changes in root growth and
development. Increased root carbohydrates stimulate root growth either directly (functioning as ...substrates) or
indirectly (functioning as signal molecules) by enhancing cell division or cell expansion, or both. Although highly
variable, the literature suggests that, generally, initiation and stimulation of lateral roots is favored over the
elongation of primary roots, leading to more highly branched, shallower root systems. Such architectural shifts can
render root systems less efficient, perhaps contributing to the lower specific root activities often reported.
Allocation of carbon (C) to roots fluctuates through the life of the plant; root functional and growth responses
should therefore not be viewed as static. In annual crops, C allocation to belowground processes changes as
vegetative growth switches to reproduction and maturation. Reductions in C allocation to roots over time might
cause temporal shifts in root deployment, perhaps affecting root demography. However, significant changes in root
turnover (defined here as root flux or mortality relative to total root pool size) as a result of decreased root
longevities in crop plants are unlikely. Consideration of changing C allocation to roots, a more thorough
understanding of the mechanistic controls on root longevity, and a better characterization of the rooting habits (life
histories) of different crop species will further our understanding of how increasing atmospheric CO2 will affect
root demography. This knowledge will lead the way toward a more thorough understanding of the linkage of
atmosphere with belowground plant function and also that of plant function with soil biology and structure.
Ultimately, successful modeling of global C and nitrogen (N) cycles will require empirical data concerning spatial
and temporal deployment of roots for a range of crop species grown under different agricultural management
systems.
Carbon is an essential component of life and, in its organic form, plays a pivotal role in the soil's fertility, productivity, and water retention. It is an integral part of the ...atmospheric-terrestrial C exchange cycle mediated via photosynthesis; furthermore, it emerged recently as a new trading commodity, i.e., "carbon credits." When carefully manipulated, C sequestration by the soil could balance and mitigate anthropogenic CO2 emissions into the atmosphere that are believed to contribute to global warming. The pressing need for assessing the soil's C stocks at local, regional, and global scales, now in the forefront of much research, is considerably hindered by the problems besetting dry-combustion chemical analyses, even with state-of-the-art procedures. To overcome these issues, we developed a new method based on gamma-ray spectroscopy induced by inelastic neutron scattering (INS). The INS method is an in situ, nondestructive, multielemental technique that can be used in stationary or continuous-scanning modes of operation. The results from data acquired from an investigated soil mass of a few hundred kilograms to an approximate depth of 30 cm are reported immediately. Our initial experiments have demonstrated the feasibility of our proposed approach; we obtained a linear response with C concentration and a detection limit between 0.5 and 1% C by weight.
To evaluate the contribution of agriculture to climate change, the flux of greenhouse gases from different cropping systems must be assessed. Soil greenhouse gas flux (CO2, N2O, and CH4) was assessed ...during the final growing season in a long-term (10-year) study evaluating the effects of crop management (conservation and conventional) and atmospheric CO2 (ambient and twice ambient) on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). Seasonal soil CO2 flux was significantly greater under elevated (4.39 Mg CO2-C ha-1) versus ambient CO2 (3.34 Mg CO2-C ha-1) and was generally greater in the conventional (4.19 Mg CO2-C ha-1) compared with the conservation (3.53 Mg CO2-C ha-1) system. Soil flux of both N2O (range, -1.5 to 53.4 g N2O-N ha-1 day-1) and CH4 (range, -7.9 to 24.4 g CH4-C ha-1 day-1) were low throughout the study and rarely exhibited differences caused by treatments. Global warming potential (calculated based on flux of individual gases) was increased by elevated CO2 (33.4%) and by conventional management (17.1%); these increases were driven primarily by soil CO2 flux. As atmospheric CO2 continues to rise, our results suggest adoption of conservation management systems represents a viable means of reducing agriculture's potential contribution to global climate change.
Increasing atmospheric CO2 concentration has led to concerns about potential effects on production agriculture as well as agriculture's role in sequestering C. In the fall of 1997, a study was ...initiated to compare the response of two crop management systems (conventional and conservation) to elevated CO2. The study used a split-plot design replicated three times with two management systems as main plots and two CO2 levels (ambient=375 μL L-1 and elevated CO2=683 μL L-1) as split-plots using open-top chambers on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system was a grain sorghum (Sorghum bicolor (L.) Moench.) and soybean (Glycine max (L.) Merr.) rotation with winter fallow and spring tillage practices. In the conservation system, sorghum and soybean were rotated and three cover crops were used (crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)) under no-tillage practices. The effect of management on soil C and biomass responses over two cropping cycles (4 years) were evaluated. In the conservation system, cover crop residue (clover, sunn hemp, and wheat) was increased by elevated CO2, but CO2 effects on weed residue were variable in the conventional system. Elevated CO2 had a greater effect on increasing soybean residue as compared with sorghum, and grain yield increases were greater for soybean followed by wheat and sorghum. Differences in sorghum and soybean residue production within the different management systems were small and variable. Cumulative residue inputs were increased by elevated CO2 and conservation management. Greater inputs resulted in a substantial increase in soil C concentration at the 0-5 cm depth increment in the conservation system under CO2-enriched conditions. Smaller shifts in soil C were noted at greater depths (5-10 and 15-30 cm) because of management or CO2 level. Results suggest that with conservation management in an elevated CO2 environment, greater residue amounts could increase soil C storage as well as increase ground cover.
Although considerable effort is being spent studying exotic plant pests, little consideration has been given as to how invasive plants might react to the increasing concentration of CO2 in the ...atmosphere. Tropical spiderwort (Commelina benghalensis L.) is considered one the world's worst weeds and is becoming more of a problem in agricultural settings of the southeastern USA. Growth responses of tropical spiderwort were evaluated using plants grown in containers with a soilless potting medium under ambient and elevated (ambient + 200 μmol mol−1) levels of CO2 in open‐top field chambers. Although plant height was unaffected by CO2, leaf and flower number tended to increase (approximately 23%) when exposed to elevated CO2 Aboveground plant parts exhibited significant increases in dry weight when exposed to high CO2; leaf, flower, stem, and total shoot dry weights were increased by 36, 30, 48, and 44%, respectively. Total plant dry weight was increased by 41% for plants grown under high CO2 Root dry weight and root length were unaffected by CO2 concentration. Tropical spiderwort allocated more biomass to stems and tended to allocate less to roots when plants were exposed to high CO2 Plant carbon concentration and content tended to be higher in CO2–enriched plants, whereas plant nitrogen concentration tended to be lower; thus, elevated CO2–grown plants had higher C/N ratios. Also, the amount of biomass produced per unit nitrogen was higher for plants exposed to elevated CO2 The growth response of this plant is in the upper range typical for C3 plants.
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