Young daughter cladodes affect CO2 uptake by mother cladodes of Opuntia ficus-indica

BACKGROUND AND AIMS: Drought damages cultivated C3, C4 and CAM plants in the semi-arid lands of central Mexico. Drought damage to Opuntia is common when mother cladodes, planted during the dry spring season, develop young daughter cladodes that behave like C3 plants, with daytime stomatal opening and water loss. In contrast, wild Opuntia are less affected because daughter cladodes do not develop on them under extreme drought conditions. The main objective of this work is to evaluate the effects of the number of daughter cladodes on gas exchange parameters of mother cladodes of Opuntia ficus-indica exposed to varying soil water contents. METHODS: Rates of net CO2 uptake, stomatal conductance, intercellular CO2 concentration, chlorophyll content and relative water content were measured in mature mother cladodes with a variable number of daughter cladodes growing in spring under dry and wet conditions. KEY RESULTS: Daily carbon gain by mother cladodes was reduced as the number of daughter cladodes increased to eight, especially during drought. This was accompanied by decreased mother cladode relative water content, suggesting movement of water from mother to daughter cladodes. CO2 assimilation was most affected in phase IV of CAM (late afternoon net CO2 uptake) by the combined effects of daughter cladodes and drought. Rainfall raised the soil water content, decreasing the effects of daughter cladodes on net CO2 uptake by mother cladodes. CONCLUSIONS: Daughter cladodes significantly hasten the effects of drought on mother cladodes by competition for the water supply and thus decrease daily carbon gain by mother cladodes, mainly by inhibiting phase IV of CAM.     

Gas exchange and growth responses to elevated CO2 and light levels in the CAM species Opuntia ficus-indica

Gas exchange and dry-weight production in Opuntia ficus-indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol⁻¹ CO₂ at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m⁻² d⁻¹). Elevated CO₂ and PPFD enhanced the growth of basal cladodes and roots during the 12-week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO₂ enhanced the growth of first-daughter cladodes but decreased the growth of the second-daughter cladodes produced on them. CO₂ enrichment enhanced daily net CO₂ uptake during the initial 8 weeks after planting for both basal and first-daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol⁻¹ CO₂. Cladode chlorophyll content was lower in elevated CO₂ and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO₂ and at higher PPFD. The total plant nitrogen content was lower in elevated CO₂. The effect of elevated CO₂ on net CO₂ uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO₂ uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol⁻¹ CO₂. Averaged for the two CO₂ treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD.     

Growth, CO2 uptake, and responses of the carboxylating enzymes to inorganic carbon in two highly productive CAM species at current and doubled CO2 concentrations

In Agave salmiana Otto ex Salm. var. salmiana grown for 4½ months in open-top chambers, 55% more leaves unfolded and 52% more fresh mass was produced at 730 than at 370μmol CO₂ mol^?1. A doubling of the CO₂ concentration also stimulated growth in another highly productive CAM species, Opuntia ficus-indica (L.) Miller, leading to earlier initial ion and 37% more daughter cladodes. Substantial net CO₂ uptake occurred earlier in the afternoon and lasted longer through the night for A. salmiana at 730 than at 370μmol CO₂ mol^?1, resulting in 59% more total daily net CO₂ uptake. The Michaelis constant (HCO₃^?) for PEPCasc was 15% lower for A. salmiana and 44% lower for O. ficus-indica when the CO₂ concentration was doubled; the percentage of Rubisco in the activated state in vivo was on average 64% higher at the doubled CO₂ concentration. Thus the substantial increases in net CO₂ uptake and biomass production that occurred in these two CAM species when the ambient CO₂ concentration was doubled resulted mainly from higher inorganic carbon levels for their carboxylating enzymes, a greater substrate affinity for PEPCase, and a greater percentage of Rubisco in the activated state.     

Daily and seasonal CO2 exchange in Scots pine grown under elevated O3 and CO2: experiment and simulation

Starting in early spring of 1994, naturally regenerated, 30-year-old Scots pine (Pinus sylvestris L.) trees were grown in open-top chambers and exposed in situ to doubled ambient O₃,doubled ambient CO₂ and a combination of O₃ and CO₂ from 15 April to 15 September. To investigate daily and seasonal responses of CO₂ exchange to elevated O₃ and CO₂, the CO₂ exchange of shoots was measured continuously by an automatic system for measuring gas exchange during the course of one year (from 1 Januray to 31 December 1996). A process-based model of shoot photosynthesis was constructed to quantify modifications in the intrinsic capacity of photosynthesis and stomatal conductance by simulating the daily CO₂ exchange data from the field. Results showed that on most days of the year the model simulated well the daily course of shoot photosynthesis. Elevated O₃ significantly decreased photosynthetic capacity and stomatal conductance during the whole photosynthetic period. Elevated O₃ also led to a delay in onset of photosynthetic recovery in early spring and an increase in the sensitivity of photosynthesis to environmental stress conditions. The combination of elevated O₃ and CO₂ had an effect on photosynthesis and stomatal conductance similar to that of elevated O₃ alone, but significantly reduced the O₃-induced depression of photosynthesis. Elevated CO₂ significantly increased the photosynthetic capacity of Scots pine during the main growing season but slightly decreased it in early spring and late autumn. The model calculation showed that, compared to the control treatment, elevated O₃ alone and the combination of elevated O₃ and CO₂ decreased the annual total of net photosynthesis per unit leaf area by 55% and 38%, respectively. Elevated CO₂ increased the annual total of net photosynthesis by 13%.     

Up-regulation of sucrose phosphate synthase in rice grown under elevated CO2 and temperature

Rice (Oryza sativa L. cv. IR-30) was grown season-long in outdoor, controlled-environment chambers at 33 Pa CO₂ with day/night/paddy-water temperatures of 28/21/25 °C, and at 66 Pa CO₂ with five different day/night/paddy-water temperature regimes (25/18/21, 28/21/25, 31/24/28, 34/27/31 and 37/30/34 °C). Sucrose phosphate synthase (SPS) activities in leaf extracts at 21, 48 and 81 days after planting (DAP) were assayed under saturating and selective (limiting) conditions. Diel SPS activity data indicated that rice SPS was light regulated; with up to 2.2-fold higher rates during the day. Throughout the growth season, leaf SPS activities were up-regulated in the CO₂-enriched plants, averaging 20 and 12% higher than in ambient-CO₂ grown plants in selective and saturating assays, respectively. Similarly, SPS activities increased 2.4% for each 1 °C rise in growth temperature from 25 to 34 °C, but de creased 11.5% at 37 °C. Leaf sucrose content was higher, and mirrored SPS activity better, than starch, although starch was more responsive to CO₂ treatment. Leaf sucrose and starch contents were significantly higher throughout the season in plants at elevated CO₂, but the N content averaged 6.5% lower. Increasing growth temperatures from 25 to 37 °C caused a linear decrease (62%) in leaf starch content, but not in sucrose. Consequently, the starch:sucrose ratio declined with growth temperature. The data are consistent with the hypothesis that the up-regulation of leaf SPS may be an acclimation response of rice to optimize the utilization and export of organic-C with the increased rates of inorganic-C fixation in elevated CO₂ or temperature growth regimes.     

An arabinogalactan from the skin of Opuntia ficus-indica prickly pear fruits

The cold-water extract from the skin of Opuntia ficus-indica fruits was fractionated by anion-exchange chromatography. The major fraction, which was purified by size exclusion chromatography, consisted of a polysaccharide composed of galactose and arabinose residues in the ratio 6.3:3.3, with traces of rhamnose, xylose and glucose, but no uronic acid. The results of methylation analysis, supported by (13)C NMR spectroscopy, indicated that this polysaccharide corresponded to an arabinogalactan having a backbone of (1-->4)-linked beta-D-galactopyranosyl residues with 39.5% of these units branched at O-3. The side-groups consisted either of single L-arabinofuranosyl units or L-arabinofuranosyl alpha-(1-->5)-linked disaccharides. This polysaccharide is thus an arabinogalactan that can be classified in the type I of the arabinogalactan family.     

Loblolly pine grown under elevated CO2 affects early instar pine sawfly performance

Seedlings of loblolly pine Pinus taeda (L.), were grown in open-topped field chambers under three CO₂ regimes: ambient, 150 l l^–1 CO₂ above ambient, and 300 l l^–1 CO₂ above ambient. A fourth, non-chambered ambient treatment was included to assess chamber effects. Needles were used in 96 h feeding trials to determine the performance of young, second instar larvae of loblolly pine's principal leaf herbivore, red-headed pine sawfly, Neodiprion lecontei (Fitch). The relative consumption rate of larvae significantly increased on plants grown under elevated CO₂, and needles grown in the highest CO₂ regime were consumed 21% more rapidly than needles grown in ambient CO₂. Both the significant decline in leaf nitrogen content and the substantial increase in leaf starch content contributed to a significant increase in the starch:nitrogen ratio in plants grown in elevated CO₂. Insect consumption rate was negatively related to leaf nitrogen content and positively related to the starch:nitrogen ratio. Of the four volatile leaf monoterpenes measured, only -pinene exhibited a significant CO₂ effect and declined in plants grown in elevated CO₂. Although consumption changed, the relative growth rates of larvae were not different among CO₂ treatments. Despite lower nitrogen consumption rates by larvae feeding on the plants grown in elevated CO₂, nitrogen accumulation rates were the same for all treatments due to a significant increase in nitrogen utilization efficiency. The ability of this insect to respond at an early, potentially susceptible larval stage to poorer food quality and declining levels of a leaf monoterpene suggest that changes in needle quality within pines in future elevated-CO₂ atmospheres may not especially affect young insects and that tree-feeding sawflies may respond in a manner similar to herb-feeding lepidopterans.     

Responses of carboxylating enzymes,sucrose metabolizing enzymes and plant hormones in a tropical epiphytic CAM orchid to CO2 enrichment

After exposure to a doubled CO₂ concentration of 750 µL L^?1 for 2 months, average relative growth rate (RGR) of Mokara Yellow increased 25%. The two carboxylating enzymes, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPCase), responded differently to CO₂ enrichment. There was a significant daytime down‐regulation in Rubisco activity in the leaves of CO₂‐enriched plants. However, PEPCase activity in CO₂‐enriched plants was much higher in the dark period, although it was slightly lower during the daytime than that at ambient CO₂. Leaf sucrose–phosphate synthase (SPS) and sucrose synthase (SS) activities in CO₂‐enriched plants increased markedly, along with a night‐time increase in total titratable acidity and malate accumulation. There was a remarkable increase in the levels of indole‐3‐acetic acid (IAA), gibberellins A₁ and A₃ (GA₁₊₃), isopentenyladenosine (iPA) and zeatin riboside (ZR) in the expanding leaves of plants grown at elevated CO₂. It is suggested that (1) the down‐regulation of Rubisco and up‐regulation of SPS and SS are two important acclimation processes that are beneficial because it enhanced both photosynthetic capacity at high CO₂ and reduced resource investment in excessive Rubisco capacity; (2) the increased levels of plant hormones in CO₂‐enriched M. Yellow might play an important role in controlling its growth and development.     

CO2 exchange of CAM exhibiting succulents in the southern Namib desert in relation to microclimate and water stress

The responses of CO₂ exchange and overnight malate accumulation of leaf and stem succulent CAM-plants to water stress and the particular climatic conditions of fog and föhn in the southern Namib desert have been investigated. In most of the investigated CAM plants a long term water stress gradually attenuated any uptake of external CO₂ and led to CO₂ release throughout day and night. No CAM-idling was observed. Rainfall or irrigation immediately restored daytime CO₂ uptake while the recovery of the nocturnal CO₂ uptake was delayed. Dawn peak of photosynthesis was only found in well watered plants but was markedly reduced by the short term water stress of a föhn-storm. Morning fog with its higher diffuse light intensity compared with clear days increased photosynthetic CO₂ uptake considerably. Even in well watered plants nocturnal CO₂ uptake and malate accumulation were strongly affected by föhn indicating that the water vapour pressure deficit during the night determines the degree of acidification.     

Effects of shade, drought and daughter cladodes on the CO2 uptake by cladodes of Opuntia ficus-indica

The effects of shade on the physiology of opuntias have received little attention, notwithstanding that shade regularly occurs in both wild stands and cultivated populations. This research evaluates the effects of shade on the physiology of cladodes of Opuntia ficus‐indica, with and without daughter cladodes, as they are exposed to progressive drought. The stress caused by shade, drought and daughter cladodes reduced photosynthesis by mother cladodes and was associated with decreases in relative water content, parenchyma thickness and chlorophyll content. Shade exacerbated the physiological drought of mother cladodes imposed by daughter cladodes and by reduced soil water content.     

Effects of elevated atmospheric CO2 concentrations on phloem sap composition of spring crops and aphid performance

Abstract

The concentration and composition of free amino acids and carbohydrates in the phloem sap of wheat and oilseed rape (OSR) and the effects on the performance of aphids (Rhopalosiphum padi and Myzus persicae) were determined under atmospheric carbon dioxide (CO₂) enrichment. The analysis of phloem sap showed that carbohydrates and amino acid levels of the host plants were significantly affected by elevated CO₂ level. Among carbohydrate concentrations in the phloem sap, significant increases were observed in fructose and glucose in spring wheat under CO₂ enrichment, whereas no changes were observed in OSR. These changes in plant chemistry affected the performance of herbivorous insects (i.e. aphids) in varying ways, positively affecting the relative growth rate (RGR) of R. padi in spring wheat and negatively affecting the RGR of M. persicae on OSR.     

Rhizodeposition under ambient and elevated CO2 levels

As global CO₂ levels rise, can soils store more carbon and so buffer atmospheric CO₂ levels? Answering this question requires a knowledge of the rates of C inputs to soil and of CO₂ outputs via decomposition. Below-ground inputs from roots are a major component of the C flow into soils but are still poorly understood. In this article, new techniques for measuring rhizodeposition are reviewed and discussed and the need for cross-comparisons between methods is identified. One component of rhizodeposition, root exudation, is examined in more detail and evidence is presented which suggests that current estimates of exudate flow into soils are incorrect. A mechanistic mathematical model is used to explore how exudate flows might change under elevated CO₂.     

Genetic transformation of prickly-pear cactus (Opuntia ficus-indica) by Agrobacterium tumefaciens

A system for genetic transformation of an elite prickly pear cactus (Opuntia ficus-indica L., cultivar Villa Nueva) by Agrobacterium tumefaciens was developed. Beginning with direct bacterial infection by using a hypodermic syringe to the meristematic tissue termed areoles, transgenic plants were obtained by selection with 100 mg l⁻¹ kanamycin. Transient and stable GUS activities were monitored on kanamycin-resistant shoots and regenerated plants, respectively. Genetic transformation of regenerated plants growing under selection was demonstrated by PCR and Southern blot analysis; transgene copy number in the genome of transgenic plants ranged from two to six, while the transformation frequency obtained by the system reported here was of 3.2%. This method may be useful for routine transformation and introduction of several important genes in prickly pear cactus.     

Characterization of carbon metabolism in Opuntia ficus-indica Mill. exhibiting the idling mode of Crassulacean acid metabolism

Upon transfer from well-watered conditions to total drought, long-day-grown cladodes of Opuntia ficus-indica Mill. shift from full Crassulacean acid metabolism (CAM) to CAM-idling. Experiments using ¹⁴C-tracers were conducted in order to characterize the carbon-flow pattern in cladodes under both physiological situations. Tracer was applied by ¹⁴CO₂ fumigations and NaH¹⁴CO₃ injections during the day-night cycle. The results showed that behind the closed stomata, mesophyll cells of CAM-idling plants retained their full capacity to metabolize CO₂ in light and in darkness. Upon the induction of CAM-idling the level of the capacity of phosphoenolpyruvate carboxylase (EC 4.1.1.31) was maintained. By contrast, malate pools decreased, displaying finally only a small or no day-night oscillation. The capacity of NADP-malic enzyme (EC 1.1.1.40) decreased in parallel with the reduction in malate pools. Differences in the labelling patterns, as influenced by the mode of tracer application, are discussed.Abbreviations CAM Crassulacean acid metabolism - PEP-Case phosphoenolpyruvate carboxylase     

Inter- and intra-generic differences in growth,reproduction, and fitness of nine herbaceous annual species grown in elevated CO2 environments

In assessing the capacity of plants to adapt to rapidly changing global climate, we must elucidate the impacts of elevated carbon dioxide on reproduction, fitness and evolution. We investigated how elevated CO₂ influenced reproduction and growth of plants exhibiting a range of floral morphologies, the implications of shifts in allocation for fitness in these species, and whether related taxa would show similar patterns of response. Three herbaceous, annual species each of the genera Polygonum, Ipomoea, and Cassia were grown under 350 or 700 ppm CO₂. Vegetative growth and reproductive output were measured non-destructively throughout the full life span, and vegetative biomass was quantified for a subsample of plants in a harvest at first flowering. Viability and germination studies of seed progeny were conducted to characterize fitness precisely. Early vegetative growth was often enhanced in high-CO₂ grown plants of Polygonum and Cassia (but not Ipomoea). However, early vegetative growth was not a strong predictor of subsequent reproduction. Phenology and production of floral buds, flowers, unripe and abscised fruits differed between CO₂ treatments, and genera differed in their reproductive and fitness responses to elevated CO₂. Polygonum and Cassia species showed accelerated, enhanced reproduction, while Ipomoea species generally declined in reproductive output in elevated CO₂. Seed quality and fitness (in terms of viability and percentage germination) were not always directly correlated with quantity produced, indicating that output alone may not reliably indicate fitness or evolutionary potential. Species within genera typically responded more consistently to CO₂ than unrelated species. Cluster analyses were performed separately on suites of vegetative and reproductive characters. Some species assorted within genera when these reproductive responses were considered, but vegetative responses did not reflect taxonomic affinity in these plants. Congeners may respond similarly in terms of reproductive output under global change, but fitness and prognoses of population persistence and evolutionary performance can be inferred only rarely from examination of vegetative characters alone.     

Response of 12 weedy species to elevated CO2 in low-phosphorus-availability soil

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.     

Influences of soil volume and an elevated CO2 level on growth and CO2 exchange for the Crassulacean acid metabolism plant Opuntia ficus-indica

Effects of the current (38 Pa) and an elevated (74 Pa) CO₂ partial pressure on root and shoot areas, biomass accumulation and daily net CO₂ exchange were determined for Opuntia ficus-indica (L.) Miller, a highly productive Crassulacean acid metabolism species cultivated worldwide. Plants were grown in environmentally controlled rooms for 18 weeks in pots of three soil volumes (2 600, 6 500 and 26 000 cm³), the smallest of which was intended to restrict root growth. For plants in the medium-sized soil volume, basal cladodes tended to be thicker and areas of main and lateral roots tended to be greater as the CO₂ level was doubled. Daughter cladodes tended to be initiated sooner at the current compared with the elevated CO₂ level but total areas were similar by 10 weeks. At 10 weeks, daily net CO₂ uptake for the three soil volumes averaged 24% higher for plants growing under elevated compared with current CO₂ levels, but at 18 weeks only 3% enhancement in uptake occurred. Dry weight gain was enhanced 24% by elevated CO₂ during the first 10 weeks but only 8% over 18 weeks. Increasing the soil volume 10-fold led to a greater stimulation of daily net CO₂ uptake and biomass production than did doubling the CO₂ level. At 18 weeks, root biomass doubled and shoot biomass nearly doubled as the soil volume was increased 10-fold; the effects of soil volume tended to be greater for elevated CO₂. The amount of cladode nitrogen per unit dry weight decreased as the CO₂ level was raised and increased as soil volume increased, the latter suggesting that the effects of soil volume could be due to nitrogen limitations.     

The effect of plant material grown under elevated CO2 on soil respiratory activity

The biodegradability of aerial material from a C4 plant, sorghum grown under ambient (345 µmol mol^–1) and elevated (700 µmol mol^–1) atmospheric CO₂ concentrations were compared by measuring soil respiratory activity. Initial daily respiratory activity (measured over 10 h per day) increased four fold from 110 to 440 cm³ CO₂ 100g dry weight soil^–1 in soils amended with sorghum grown under either elevated or ambient CO₂. Although soil respiratory activity decreased over the following 30 days, respiration remained significantly higher (t-test;p>0.05) in soils amended with sorghum grown under elevated CO₂ concentrations. Analysis of the plant material revealed no significant differences in C:N ratios between sorghum grown under elevated or ambient CO₂. The reason for the differences in soil respiratory activity have yet to be elucidated. However if this trend is repeated in natural ecosystems, this may have important implications for C and N cycling.     

Crassulacean acid metabolism (CAM) in leaves of Aloe arborescens mill

In the succulent leaves of Aloe arborescens Mill diurnal oscillations of the malic acid content, being indicative of Crassulacean Acid Metabolism (CAM), were exhibited only by the green mesophyll. In contrast, the malic acid level of the central chloroplast-free water-storing tissue remained constant throughout the day-night cycle. Apart from malate, the green tissue contained high amounts of isocitrat which was lacking in the water tissue. There was no significant transfer from the green mesophyll to the water tissue of ¹⁴C fixed originally via dark ¹⁴CO₂ fixation in the mesophyll. Both isolated mesophyll and water tissue were capable of dark CO₂ fixation yielding mainly malate as the first stable product. Both tissues have phosphoenolpyruvate carboxylase. However, the enzymes derived from the both sources could be distinguished by their molecular weights and by their kinetic properties, suggesting different phosphoenolpyruvate carboxylase proteins. The conclusion drawn from the experiments is that in a. arborescens the CAM cycle proceeds exclusively in the green mesophyll and that the water tissue, though capable of malate synthesis via -carboxylation of phosphoenolpyruvate, behaves as an independent metabolic system where CAM is lacking. This view is supported by the finding that the cell walls bordering the green mesophyll from the water tissue lack plasmodesmata, hence conveniant pathways of metabolite transport.Abbreviations CAM Crassulacean acid metabolism - PEP phosphoenolpyruvate - PEP-C phosphoenolpyruvate carboxylase