Growth In Elevated CO2 Research Articles

Elevated CO2 and plant growth: cellular mechanisms and responses of whole plants

Abstract Much research has focused on the photosynthetic responses of plants to elevated CO2 , with less attention given to the post-photosynthetic events which may lead to changes in the growth of tissues, organs and whole plants. The aim of this review is to identify how plant growth is altered in elevated CO2 and to determine which growth processes or cellular mechanisms are sensitive to carbon supply. For leaves, both the expansion of individual leaves and the initiation of leaf primordia are stimulated in elevated CO2. When lamina growth is promoted, this is usually associated with increased leaf cell expansion rather than increased leaf cell production. Using several clones of hybrid poplar (Populus euramericana, P. interamericana) two native herbs (Plantago media, Sanguisorba minor) and bean (Phaseolus vulgaris) we have identified the mechanism through which leaf cell expansion is promoted in elevated CO2. Changes in the water relations, turgor pressure (P) and yield turgor (Y) of growing leaves cannot explain increased cell expansion; this appears to occur because cell wall loosening is promoted, as suggested by three pieces of evidence. (i) The rate of decline of water potential (ψ) with time is accelerated when growing leaves are placed in psychrometers and allowed to relax, (ii) Instron-measured cell wall extensibility (WEX), is greater for leaves exposed to elevated CO2 and (iii) the activity of the putative wall loosening enzyme, XET is increased for leaves of P. vulgaris exposed to elevated CO2. Species differences do, however, exist; in the herb Lotus corniculatus small stimulations of leaf growth in elevated CO2 are due to increased leaf cell production and decreased cell size in elevated CO2. These results are discussed in relation to the concept of functional types. There is evidence to suggest that both cell production and cell expansion are promoted in roots of plants exposed to elevated CO2. For native herbs (Anthyllis vulneraria, Lotus corniculatus, P. media and S. minor), increased root growth in elevated CO2 is due to increased cell elongation. In contrast to leaves, this appears to occur because both root cell turgor pressure (P) and root cell wall extensibility (WEX) are promoted by exposure of shoots to elevated CO2. In longer-term studies on root growth, the effects of additional carbon on the production of root primordia and root branching are of overriding importance, suggesting that carbon supply may influence some aspect of the cell cycle, when effects on the extension of individual roots may not be apparent.

Elevated CO2 , water relations and biophysics of leaf extension in four chalk grassland herbs.

Diurnal measurements of leaf or leaflet, extension, water relations and cell wall extensibility (ø) were made on young growing leaves of four chalk downland herbs (Sanguisorba minor Scop., Lotus corniculatus L., Anthyllis vulneraria L. and Plantago media L.) growing in controlled environment cabinets and exposed to either ambient or elevated CO2 . This study revealed differences in that effect of CO2 and the- control of leaf growth between the four species. Leaf extension rate (LER) increased significantly at night (average over 8 h) in elevated C02 for S. minor A. vulneraria and P. Media with a significant increase over the first 4h of darkness for S. minor, L, corniculatus and P. media, whilst for S. minor and P. media average day-time LER (over 16 h) also increased significantly in elevated CO2 , as compared with ambient CO2 . Water potential (ψpS), solute potential (ψpS), turgor pressure (P), yield turgor (Y) and the effective turgor for growth (Pe) were measured using psychrometers. Bollrte potentials of s, minor, A. vulneraria and P. media decreased significantly following exposure to elevated co2 with a Significant reduction in ψpS, during the day in A. Vulneraria. Turgor pressure increased significantly in elevated CO2 as compared with ambient CO2 in A. vulneraria but there was no effect of elevated CO2 on P in the uther species. effects of CO2 on ψpS; or ψpS; were observed, Leaf cell wall extensibility (ø) increased significantly in leaves of V. minor, L. corniculatus and P. exposed to elevated Co2 . whereas in A. vulneraria, there was no effect of CO2 on extensibility. These results suggest that the mechanism by which elevated CO2 promotes leaf growth differs between species arisce in S. minor, L. corniculatus, and p media. CO2 through an influence on cell wall properties, whist in A vulneraria higher values of P explain that increased leaf growth in elevated CO2 for this species.

Red spruce seedling gas exchange in response to elevated CO2, water stress, and soil fertility treatments

The interactive influences of ambient (374 μL•L−1) or elevated (713 μL•L−1) CO2, low or high soil fertility, well-watered or water-stressed treatment, and rooting volume on gas exchange and growth were examined in red spruce (Picearubens Sarg.) grown from seed through two growing seasons. Leaf gas exchange throughout two growing seasons and growth after two growing seasons in response to elevated CO2 were independent of soil fertility and water-stress treatments, and rooting volume. During the first growing season, no reduction in leaf photosynthesis of seedlings grown in elevated CO2 compared with seedlings grown in ambient CO2 was observed when measured at the same CO2 concentration. During the second growing season, net photosynthesis was up to 21% lower for elevated CO2-grown seedlings than for ambient CO2-grown seedlings when measured at 358 μL•L−1. Thus, photosynthetic acclimation to growth in elevated CO2 occurred gradually and was not a function of root-sink strength or soil-fertility treatment. However, net photosynthesis of seedlings grown and measured at an elevated CO2 concentration was still over 2 times greater than the photosynthesis of seedlings grown and measured at an ambient CO2 concentration. Growth enhancement by CO2 was maintained, since seedlings grown in elevated CO2 were 40% larger in both size and weight after two growing seasons.

Direct and Indirect Effects of Atmospheric Carbon Dioxide Enrichment on Leaf Respiration of Glycine max (L.) Merr.

Long-term and short-term effects of CO2 enrichment on dark respiration were investigated using soybean (Glycine max [L.] Merr.) plants grown at either 35.5 or 71.0 Pa CO2. Indirect effects, or effects of growth in elevated CO2, were examined using a functional model that partitioned respiration into growth and maintenance components. Direct effects, or immediate effects of a short-term change in CO2, were examined by measuring dark respiration, first, at the CO2 partial pressure at which plants were grown, and second, after equilibration in the reciprocal CO2 partial pressure. The functional component model indicated that the maintenance coefficient of respiration increased 34% with elevated CO2, whereas the growth coefficient was not significantly affected. Changes in maintenance respiration were correlated with a 33% increase in leaf total nonstructural carbohydrate concentration, but leaf nitrogen content of soybean leaves was not affected by CO2 enrichment. Thus, increased maintenance respiration may be a consequence of increased nonstructural carbohydrate accumulation. When whole soybean plants were switched from low CO2 to high CO2 for a brief period, leaf respiration was always reduced. However, this direct effect of CO2 partial pressure was approximately 50% less in plants grown in elevated CO2. We conclude from this study that there are potentially important effects of CO2 enrichment on plant respiration but that the effects are different for plants given a short-term increase in CO2 partial pressure versus plants grown in elevated CO2.

The effects of oxides of nitrogen and carbon dioxide enrichment on growth and content of ribulose-1, 5-bisphosphate carboxylase-oxygenase and nitrite reductase in glasshouse lettuce

SummaryDifferent systems of CO2 enrichment and heating were used to produce glasshouse atmospheres with varying concentrations of NOx and CO2 (ambient NOx and CO2, ambient NOx and 1000 vpm CO2, and three concentrations of NOx varying between 0.5 and 2.5 vpm with concurrent CO2 concentrations between 1000−2500 vpm). The growth response of winter lettuce in these environments was assessed for three contrasting culti- vars (Ambassador, Berlo and Pascal). Contents of ribulose-1, 5-bisphosphate carboxylase-oxygenase (RuBPco) and nitrite reductase (NiR) in the leaf tissue were also determined using immunoblotting and enzyme-linked immunosorbent assay (ELISA). ‘Ambassador’ produced the heaviest “head” weights, but on marketable criteria ‘Berlo’ performed better. COz enrichment enhanced yields, but the High NOx treatments reduced growth relative to that in the Low NOx and unpolluted environments. Growth assessments suggested a greater tolerance of NOx in cvs Berlo and Pascal than in cv. Ambassador. Immunoblots showed that the antibodies used here were specific. Using these antibodies in ELISA, ‘Pascal’ was found to contain more RuBPco and NiR on a leaf area basis than ‘Ambassador’. There were reductions in RuBPco and NiR contents in response to growth in elevated CO2. Elevated CO2 caused a reduction in RuBPco and NiR in ‘Ambassador’, but in ‘Pascal’ only RuBPco levels were reduced. This may account for the greater relative tolerance of ‘Pascal’ and the sensitivity of ‘Ambassador’ to NOx pollution.

Increased root growth in elevated CO2: a biophysical analysis of root cell elongation

A biophysical analysis of root expansion was conducted in four chalk downland herbs (Sanguisorba minor Scop., Lotus corniculatus L., Anthyllis vul-neraria L. and Plantago media L.) exposed to either ambient or elevated CO2in controlled environment cabinets. Measurements of fine (F) and extra-fine (EF) root extension rate (RER), water relations, and cell wall tensiometric extensibility revealed differences in the diurnal pattern of root growth between species. After 35 d of exposure to elevated CO2, RER of both F and EF roots increased significantly in darkness and on illumination for S. minor, whilst for A. vulneraria (EF roots only) and L. corniculatus a significant increase occurred at night whereas for P. media a significant increase occurred during the day. Cells measured in the zone of elongation were longer in all species exposed to elevated CO2. Water potential ({Psi}), solute potential ({Psi}), turgor pressure (P), yield turgor (Y) and effective turgor (Pe) were measured by stress-relaxation of excised root tips placed in psychro-meters. Solute potentials decreased significantly for all species following exposure to elevated CO2. In S. minor and L. corniculatus, P and Pe, respectively, were higher in elevated CO2. No significant effects of CO2 on Y were observed (not shown). Root cell wall tensiometric extensibility, measured as % plasticity, increased in all species exposed to elevated CO2. These results suggest that root growth is enhanced following increased cell expansion and that increased P and cell wall tensiometric extensibility are both important for root growth in elevated CO2.

A branch bag and CO2 control system for long‐term CO2 enrichment of mature Sitka spruce [Picea sitchensis (Bong.) Carr.

ABSTRACTThis paper describes the construction and performance of branch bags and a CO2 control system used to fumigate branches of mature Sitka spruce trees with air enriched in CO2 (700 μmolmol‐1). It contains some examples of results obtained using the system over the course of the first two growing seasons. The branch bags have run continuously for 2 years with very few problems. CO2 concentrations were within 20 μmol mol‐1 of the target concentration for more than 90% of the time. Temperatures within the bags were slightly higher than ambient (1–2 °C) and this had some effect on phenology. Attenuation of quantum flux density (photosynthetically active radiation) was 10–15%. The branch bag system has enabled investigation into the effects of elevated CO2 on mature tissue without the problems and expense of fumigating whole trees. Growth in elevated CO2 resulted in an increase in starch and a decrease in soluble protein content of needles. Stomatal conductance was higher in elevated CO2 grown needles, and there was some evidence of an increase in photosynthetic capacity.

Increased photosynthetic capacity of Scirpus olneyi after 4 years of exposure to elevated CO2

Abstract. While a short‐term exposure to elevated atmospheric CO2 induces a large increase in photosynthesis in many plants, long‐term growth in elevated CO2 often results in a smaller increase due to reduced photosynthetic capacity. In this study, it was shown that, for a wild C3 species growing in its natural environment and exposed to elevated CO2 for four growing seasons, the photosynthetic capacity has actually increased by 31%. An increase in photosynthetic capacity has been observed in other species growing in the field, which suggests that photosynthesis of certain field grown plants will continue to respond to elevated levels of atmospheric CO2

Canopy photosynthesis of crops and native plant communities exposed to long‐term elevated CO2

Abstract. There have been seven studies of canopy photosynthesis of plants grown in elevated atmospheric CO2: three of seed crops, two of forage crops and two of native plant ecosystems. Growth in elevated CO2 increased canopy photosynthesis in all cases. The relative effect of CO2 was correlated with increasing temperature: the least stimulation occurred in tundra vegetation grown at an average temperature near 10°C and the greatest in rice grown at 43°C. In soybean, effects of CO2 were greater during leaf expansion and pod fill than at other stages of crop maturation. In the longest running experiment with elevated CO2 treatment to date, monospecific stands of a C3 sedge, Scirpus olneyi (Grey), and a C4 grass, Spartina patens (Ait.) Muhl., have been exposed to twice normal ambient CO2 concentrations for four growing seasons, in open top chambers on a Chesapeake Bay salt marsh. Net ecosystem CO2 exchange per unit green biomass (NCEb) increased by an average of 48% throughout the growing season of 1988, the second year of treatment. Elevated CO2 increased net ecosystem carbon assimilation by 88% in the Scirpus olneyi community and 40% in the Spartina patens community.