Growth Respiration Coefficient Research Articles

Improving crop modeling to better simulate maize yield variability under different irrigation managements

Crop models have been used for investigating crop responses to environmental stresses for decades. The study objectives were to (i) calibrate and validate a simple crop model (Hybrid-Maize) using in-situ measured data from sixteen uniquely managed treatments as part of the University of Nebraska-Lincoln Testing Ag Performance Solutions (TAPS) program in North Platte, NE, and (ii) carry out sensitivity analysis and parameter estimation using a multi-parameter optimization approach. Sixteen Arable Mark 1 sensors and thirty two Mark 2 sensors (Arable Labs Inc., San Francisco, CA) collecting hourly and daily weather and crop information in 2019 and 2020 respectively, were installed in the TAPS subsurface drip irrigation experimental plots which were planted with maize and subjected to different irrigation and nitrogen practices. Hybrid-Maize was used for simulating maize yield on the sixteen treatments in 2019 and 2020. Sensitivity analysis showed that initial light use efficiency (LUE), potential kernel filling rate (G5), potential number of kernels per ear (G2), growth respiration coefficient of grain (GRG), empirical parameter determining the relative contribution of a soil layer to water uptake (SLW), and maximum photosynthetic rate (MPR) were the most sensitive parameters to yield. A novel multi-parameter optimization (MPO) approach based on kriging was used for calibrating these six parameters, and the best parameter sets which were later used for model validation. Calibration results showed that there seemed to be strong linear relationships between total water received (WR) and some of the parameters. By using each year’s MPO averages of the six parameters instead of default values, ME, MAE, RMSE, uRMSE, and nRMSE were all reduced by about 69%, 66%, 60%, 27%, and 61% respectively for validation treatments. The advantage of using in-situ sensors, coupled with the suitability of the calibrated model for simulating maize yield under different irrigation management, will make the model more useful in future field-scale research with focus on developing decision support tools for in-season crop management and yield forecasts.

Respiratory costs of producing and maintaining stem biomass in eight co-occurring tree species.

Given the importance of carbon allocation for plant performance and fitness, it is expected that competition and abiotic stress influence respiratory costs associated with stem wood biomass production and maintenance. In this study, stem respiration (R) was measured together with stem diameter increment in adult trees of eight co-occurring species in a sub-Mediterranean forest stand for 2years. We estimated growth R (Rg), maintenance R (Rm) and the growth respiration coefficient (GRC) using two gas exchange methods: (i) estimating Rg as the product of growth and GRC (then Rm as R minus Rg) and (ii) estimating Rm from temperature-dependent kinetics of basal Rm at the dormant season (then Rg as R minus Rm). In both cases, stem basal-area growth rates governed intra-annual variation in R, Rg and Rm. Maximum annual Rm occurred slightly before or after maximum Rg. The mean contribution of Rm to R during the growing season ranged from 56% to 88% across species using method 1 and from 23% to 66% using method 2. An analysis accounting for the phylogenetic distance among species indicated that more shade-tolerant, faster growing species exhibited higher Rm and Rg than less shade-tolerant, slower growing ones, suggesting a balance between carbon supply and demand mediated by growth. However, GRC was not related to species growth rate, wood density, or drought and shade tolerance across the surveyed species nor across 27 tree species for which GRC was compiled. The GRC estimates based on wood chemical analysis were lower (0.19) than those based on gas exchange methods (0.35). These results give partial support to the hypothesis that wood production and maintenance costs are related to species ecology and highlight the divergence of respiratory parameters widely used in plant models according to the methodological approach applied to derive them.

Calibration and Validation of the Hybrid-Maize Crop Model for Regional Analysis and Application over the U.S. Corn Belt

Abstract Detailed parameter sensitivity, model validation, and regional calibration of the Hybrid-Maize crop model were undertaken for the purpose of regional agroclimatic assessments. The model was run at both field scale and county scale. The county-scale study was based on 30-yr daily weather data and corn yield data from the National Agricultural Statistics Service survey for 24 locations across the Corn Belt of the United States. The field-scale study was based on AmeriFlux sites at Bondville, Illinois, and Mead, Nebraska. By using the one-at-a-time and interaction-explicit factorial design approaches for sensitivity analysis, the study found that the five most sensitive parameters of the model were potential number of kernels per ear, potential kernel filling rate, initial light use efficiency, upper temperature cutoff for growing degree-days’ accumulation, and the grain growth respiration coefficient. Model validation results show that the Hybrid-Maize model performed satisfactorily for field-scale simulations with a mean absolute error (MAE) of 10 bu acre−1 despite the difficulties of obtaining hybrid-specific information. At the county scale, the simulated results, assuming optimal crop management, overpredicted the yields but captured the variability well. A simple regional adjustment factor of 0.6 rescaled the potential yield to actual yield well. These results highlight the uncertainties that exist in applying crop models at regional scales because of the limitations in accessing crop-specific information. This study also provides confidence that uncertainties can potentially be eliminated via simple adjustment factor and that a simple crop model can be adequately useful for regional-scale agroclimatic studies.

Respiratory Q10 of marigold (Tagetes patula) in response to long‐term temperature differences and its relationship to growth and maintenance respiration

Acclimation of respiration to temperature is not well understood. To determine whether whole plant respiration responses to long‐term temperature treatments can be described using the Q10 concept, the CO2 exchange rate of marigolds (Tagetes patula L. ‘Queen Sophia’), grown at 20°C or 30°C, was measured for 62 days. When plants of the same age were compared, plants grown at 20°C consistently had a higher specific respiration (Rspc) than plants grown at 30°C (long‐term Q10= 0.71–0.97). This was due to a combination of greater dry mass at 30°C and a decrease in Rspc with increasing mass. When plants of the same dry mass were compared, the long‐term Q10 was 1.35–1.55; i.e. Rspc was higher at 30°C than at 20°C. Whole plant respiration could be accurately described by dividing respiration into growth and maintenance components. The maintenance respiration coefficient was higher at 30°C than at 20°C, while the growth respiration coefficient was lower at 30°C, partly because of temperature‐dependent changes in plant composition. These results suggest difficulties with interpreting temperature effects on whole plant respiration, because conclusions depend greatly on whether plants of the same age or mass are compared. These difficulties can be minimized by describing whole plant respiration on the basis of growth and maintenance components.

The growth respiration component in eddy CO2 flux from a Quercus ilex mediterranean forest

AbstractEcosystem respiration, arising from soil decomposition as well as from plant maintenance and growth, has been shown to be the most important component of carbon exchange in most terrestrial ecosystems. The goal of this study was to estimate the growth component of whole‐ecosystem respiration in a Mediterranean evergreen oak (Quercus ilex) forest over the course of 3 years. Ecosystem respiration (Reco) was determined from night‐time carbon dioxide flux (Fc) using eddy correlation when friction velocity (u*) was greater than 0.35 m s−1We postulated that growth respiration could be evaluated as a residual after removing modeled base Reco from whole‐ecosystem Reco during periods when growth was most likely occurring. We observed that the model deviated from the night‐time Fc‐based Reco during the period from early February to early July with the largest discrepancies occurring at the end of May, coinciding with budburst when active aboveground growth and radial growth increment are greatest. The highest growth respiration rates were observed in 2001 with daily fluxes reaching up to 4 g C m−2. The cumulative growth respiration for the entire growth period gave total carbon losses of 170, 208, and 142 g C m−2 for 1999, 2001, and 2002, respectively. Biochemical analysis of soluble carbohydrates, starch, cellulose, hemicellulose, proteins, lignin, and lipids for leaves and stems allowed calculation of the total construction costs of the different growth components, which yielded values of 154, 200, and 150 g C for 3 years, respectively, corresponding well to estimated growth respiration. Estimates of both leaf and stem growth showed very large interannual variation, although average growth respiration coefficients and average yield of growth processes were fairly constant over the 3 years and close to literature values. The time course of the growth respiration may be explained by the growth pattern of leaves and stems and by cambial activity. This approach has potential applications for interpreting the effects of climate variation, disturbances, and management practices on growth and ecosystem respiration.

Respiratory Q10 of Lettuce Increases with Increasing Plant Size

Literature reports on the Q10 for respiration vary widely, both within and among species. Plant size and metabolic activity may be responsible for some of this variation. To test this, respiration of whole lettuce plants was measured at temperatures ranging from 6 to 31 °C during a 24-h period. Subsequently, plant growth rate (in moles of carbon per day) was determined by measuring the CO2 exchange rate of the same plants during a 24-h period. Environmental conditions during this 24-h period resembled those that the plants were exposed to in the greenhouse. The measured growth rate was then used to estimate the relative growth rate (RGR) of the plants. The respiratory Q10 ranged from 1.4 for small plants to 1.75 for large plants. The increase in Q10 with increasing plant size was highly significant, as was the decrease in Q10 with increasing RGR. However, growth rate had little or no effect on the respiratory Q10. One possible explanation for these findings is that the Q10 depends on the ratio of growth to maintenance respiration (which is directly related to RGR). The growth respiration coefficient generally is considered to be temperature-insensitive, while the maintenance respiration coefficient normally increases with increasing temperature. Based on this concept, the Q10 for the maintenance respiration coefficient can be estimated as the estimated Q10 at a RGR of zero (i.e. no growth and thus no growth respiration), which was 1.65 in this experiment. Although the concept of dividing respiration into growth and maintenance fractions remains controversial, it is useful for explaining changes in respiratory Q10 during plant development.

TEMPERATURE EFFECTS ON PHOTOSYNTHESIS, GROWTH RESPIRATION, AND MAINTENANCE RESPIRATION OF MARIGOLD

TEMPERATURE EFFECTS ON PHOTOSYNTHESIS, GROWTH RESPIRATION, AND MAINTENANCE RESPIRATION OF MARIGOLD

Long‐term carbon budget of the above‐ground parts of a young hinoki cypress (Chamaecyparis obtusa) stand

The carbon budget of the above‐ground parts of a young hinoki (Chamaecyparis obtusa) stand was analyzed over a 4‐year period to evaluate trends in changes in carbon use efficiency and growth conversion (biosynthetic) efficiency with stand development. Litter production of the stand was estimated from the stem cross‐sectional area at the crown base. A biomass increment was estimated using the stem volume of individual trees in the stand, measured at monthly intervals. Net production, estimated from litter production and the biomass increment, was 7.40, 8.44, 8.45 and 8.29 Mg C ha−1 year−1 for Years I–IV, respectively. The respiration rate of the entire above‐ground parts of selected sample trees were measured at monthly intervals using the enclosed whole‐tree method. The Q10 value of respiration decreased with increasing air temperature. Respiration rate was partitioned into growth and maintenance components using a two‐component functional model. The maintenance respiration coefficient increased in the following order: winter, spring, autumn and summer. The maintenance respiration coefficient also decreased with either stand development or age for all seasons. The growth respiration coefficient, which did not vary with stand development, was 0.69 ± 0.08 (mean ± SE), 0.61 ± 0.03, 0.54 ± 0.03 and 0.67 ± 0.07 g C g−1 C for winter, spring, summer and autumn, respectively. The growth conversion efficiency of the stand was 0.76, 0.72, 0.72 and 0.75 for Years I–IV, respectively. Carbon use efficiency was estimated to be 0.58, 0.57, 0.54 and 0.53 for Years I–IV, respectively. The hypothesis that respiration reduces productivity in old stands could not be validated for this hinoki stand.

Spatial and seasonal variations in stem respiration of beech trees (Fagus sylvatica)

Stem respiration of adult beech (Fagus sylvatica L.) trees was measured in the field in eastern France at several levels in the crown and along the stem. Strong variations in respiration rates throughout the season and within the trees were mainly caused by gradients in stem tem- perature, growth rates and distribution of living cells. The higher respiration rates, were measured in the upper crown. During the non-growing season, maintenance respiration ranged between 7.2 and 528 µmol m -3 s -1 at breast height and in the upper crown, respectively. Q10 increased along the stem from 1.3 at breast height to 2.0 in the upper crown. There was a linear relationship between (N) and the percentage of living cells in the wood, but respiration increased strongly with (N). Growth respiration accounted for 45-76% of annual stem respiration, and the growth respiration coefficient was close to 0.2 g C respired g -1 C fixed.

Effects of elevated carbon dioxide concentration and temperature on needle growth, respiration and carbohydrate status in field-grown Scots pines during the needle expansion period

We determined effects of long-term elevation of carbon dioxide concentration ([CO2]) and temperature on growth, respiration and carbohydrate concentration in needles of field-grown Scots pine (Pinus sylvestris L.) trees during the needle expansion period. Sixteen 20-year-old Scots pine trees were individually enclosed in closed-top, environmentally controlled chambers for 4 years in one of four environments: ambient conditions (CON); elevated [CO2] (EC); elevated temperature (ET); and a combination of both (EC + ET). Needle growth, carbohydrate concentration and dark respiration were measured at 3-day intervals throughout the needle expansion period. Dark respiration was partitioned into growth and maintenance components by regressing specific respiration rate against specific growth rate. In all treatments, growth, carbohydrate concentration and daily dark respiration rates of needles followed a similar seasonal pattern throughout the needle expansion period. Treatments EC, ET and EC + ET increased individual needle area and dry weight compared with the CON treatment. Carbohydrate concentrations in needles were increased by EC, but reduced by ET and EC + ET. Daily respiration rates increased slightly in the early stage of needle expansion and decreased gradually in the late stage when needles were exposed to EC, but increased consistently throughout the growing period when needles were exposed to ET or EC + ET. Partitioning of respiration into its two functional components showed that the growth respiration coefficient was unaffected by the treatments, whereas maintenance respiration was reduced by EC but increased by ET and EC + ET. Maintenance respiration was more sensitive to elevated temperature than growth respiration. We conclude that the difference in respiration rates between expanding and expanded needles should be taken into account when estimating the respiratory responses of needles to elevated [CO2] and temperature.

Stem growth and respiration in loblolly pine plantations differing in soil resource availability.

Stem respiration and growth in 10-year-old loblolly pine (Pinus taeda L.) plantations were measured monthly during the third year of fertilization and irrigation treatments to determine whether soil resource availability differentially altered growth and respiration in stem tissue. Fertilized trees had significantly greater stem biomass, stem nitrogen concentration ([N]) and growth rate than unfertilized trees. Stem respiration (Rt) was significantly greater in fertilized trees when expressed on a per unit surface area (Rt,a, micromol CO2 m-2 s-1), sapwood volume (Rt,v, micromol CO2 m-3 s-1), or mass (Rt,w, nmol CO2 g-1 s-1) basis; however, there was no difference between treatments when expressed as a function of stem N content (Rt,n, micromol CO2 (mol N)-1 s-1). Irrigation had no significant effect on Rt or annual stem growth. Daily total respiration (Rd, mol CO2 m-2 day-1) and stem diameter growth both had a seasonal bimodal pattern with peaks in early spring and midsummer. Stem [N] declined significantly during the growing season. Stem growth rate and [N] explained 75% of the seasonal variation in temperature-normalized Rt,a. The mature tissue method was used to partition total stem respiration (Rt) into maintenance (Rm) and growth (Rg) components. There was a linear correlation between winter Rt,v, a measure of basal Rm, and sapwood N content; however, Rt,v per unit N was greater in January before diameter growth started than in the following December after growth ceased, indicating that Rt,v declined as stem diameter increased. Consequently, estimates of annual maintenance respiration (RM) based on January data were 44% higher than estimates based on December data. Growth respiration was correlated with stem growth rate (r2 = 0.55). The growth respiration coefficient (rg)-the slope of the relationship between Rg and stem growth rate-was 0.24. Respiration accounted for 37% of annual stem carbon budget. Stem carbon-use efficiency (CUE)-the ratio of stem growth to stem growth plus respiration-averaged 0.63 and was unaffected by fertilization.

Growth, respiration and nitrogen content in needles of Scots pine exposed to elevated ozone and carbon dioxide in the field

Single Scots pine ( Pinus sylvestris L.) trees, aged 30 years, were grown in open-top chambers and exposed to two atmospheric concentrations of ozone (O 3; ambient and elevation) and carbon dioxide (CO 2) as single variables or in combination for 3 years (1994–1996). Needle growth, respiration and nitrogen content were measured simultaneously over the period of needle expansion. Compared to ambient treatment (33 nmol mol −1 O 3 and 350 μmol mol −1 CO 2) doubled ambient O 3 (69 nmol mol −1) significantly reduced the specific growth rates (SGRs) of the needles in the early stage of needle expansion and needle nitrogen concentration ( N 1) in the late stage, but increased apparent respiration rates (ARRs) in the late stage. Doubled ambient CO 2 (about 650 μmol mol −1) significantly increased maximum SGR but reduced ARR and N 1 in the late stage of needle expansion. The changes in ARR induced by the different treatments may be associated with treatment-induced changes in needle growth, metabolic activities and turnover of nitrogenous compounds. When ARR was partitioned into its two functional components, growth and maintenance respiration, the results showed that neither doubled ambient O 3 nor doubled ambient CO 2 influenced the growth respiration coefficients ( R g). However, doubled ambient O 3 significantly increased the maintenance respiration coefficients ( R m) regardless of the needle development stage, while doubled ambient CO 2 significantly reduced R m only in the late stage of needle expansion. The increase in R m under doubled ambient O 3 conditions appeared to be related to an increase in metabolic activities, whereas the decrease in R m under doubled ambient CO 2 conditions may be attributed to the reduced N 1 and turnover rate of nitrogenous compounds per unit. The combination of elevated O 3 and CO 2 had very similar effects on growth, respiration and N 1 to doubled ambient O 3 alone, but the interactive mechanism of the two gases is still not clear.

Temperature effect on maintenance and growth respiration coefficients of young, field‐grown hinoki cypress (Chamaecyparis obtusa)

AbstractRespiration measurements were made on the entire aboveground parts of young, field‐grown hinoki cypress (Chamaecyparis obtusa) trees at monthly intervals over a 5‐year period, to examine the effect of temperature on maintenance and growth respiration coefficients. The respiration rate of the trees was grouped on a monthly basis and then partitioned into maintenance and growth components. The maintenance respiration coefficient increased exponentially with air temperature. The maintenance respiration coefficient at a temperature of 0°C and its Q10 value were 0.205 mmol CO2 g−1 d.w. month−1 and 1.81, respectively. The growth respiration coefficient, which was virtually independent of temperature, had a mean value of 38.06±1.95 (SE) mmol CO2g−1 d.w. The growth rate increased exponentially with increasing temperature up to a peak at around 18°C, and thereafter declined, thereby resulting in the growth respiration rate being increasingly less sensitive to increasing air temperature. The reported decreases in the Q10 value of total respiration with increasing air temperature is due to the way in which the growth component of respiration responds to temperature.

Effects of elevated CO2 concentration on photosynthesis, respiration and carbohydrate status of coppice Populus hybrids

To determine how increased atmospheric CO2 will affect the physiology of coppiced plants, sprouts originating from two hybrid poplar clones (Populus trichocarpa × P. deltoides ‐ Beaupre and P. deltoides × P. nigra ‐ Robusta) were grown in open‐top chambers containing ambient or elevated (ambient + 360 μmol mol−1) CO2 concentration. The effects of elevated CO2 concentration on leaf photosynthesis, stomatal conductance, dark respiration, carbohydrate concentration and nitrogen concentration were measured. Furthermore, dark respiration of leaves was partitioned into growth and maintenance components by regressing specific respiration rate vs specific growth rate. Sprouts of both clones exposed to CO2 enrichment showed no indication of photosynthetic down‐regulation. During reciprocal gas exchange measurements, CO2 enrichment significantly increased photosynthesis of all sprouts by approximately 60% (P < 0.01) on both an early and late season sampling date, decreased stomatal conductance of all sprouts by 10% (P < 0.04) on the early sampling date and nonsignificantly decreased dark respiration by an average of 11%. Growth under elevated CO2 had no consistent effect on foliar sugar concentration but significantly increased foliar starch by 80%. Respiration rate was highly correlated with both specific growth rate and percent nitrogen. Long‐term CO2 enrichment did not significantly affect the maintenance respiration coefficient or the growth respiration coefficient. Carbon dioxide enrichment affected the physiology of the sprouts the same way it affected these plants before they were coppiced.

Growth and maintenance respiration rates of aspen, black spruce and jack pine stems at northern and southern BOREAS sites.

We measured stem respiration rates during and after the 1994 growing season of three common boreal tree species at sites near the northern and southern boundaries of the closed-canopy boreal forest in central Canada. The growth respiration coefficient (r(g); carbon efflux per micro mole of carbon incorporated in structural matter) varied between 0.25 and 0.76, and was greatest for black spruce (Picea mariana (Mill.) B.S.P.), least for jack pine (Pinus banksiana Lamb.) and intermediate for trembling aspen (Populus tremuloides Michx.). There was a consistent trend for higher r(g) at northern sites than at southern sites. Maintenance respiration rates at 15 degrees C (r(m)) varied from 0.5 to 2.7 nmol C mol(-1) C(sapwood) s(-1). Values of r(m) were high at sapling-stage jack pine sites and mature black spruce sites, and low at mature trembling aspen and mature jack pine sites. We found significant relationships between annual maintenance respiration and sapwood relative growth rate and sapwood volume per unit of stem surface area that explained much of the within-stand and between-stand variability. Because of the large differences in parameter values among sites, we conclude that the use of stand-specific respiratory parameters may improve model predictions of ecosystem process models over the use of generic parameter values.

The effect of elevated CO2 on the chemical composition and construction costs of leaves of 27 C3 species

ABSTRACTWe determined the proximate chemical composition as well as the construction costs of leaves of 27 species, grown at ambient and at a twice‐ambient partial pressure of atmospheric CO2. These species comprised wild and agricultural herbaceous plants as well as tree seedlings. Both average responses across species and the range in response were considered. Expressed on a total dry weight basis, the main change in chemical composition due to CO2 was the accumulation of total non‐structural carbohydrates (TNC). To a lesser extent, decreases were found for organic N compounds and minerals. Hardly any change was observed for total structural carbohydrates (cellulose plus hemicellulose), lignin and lipids. When expressed on a TNC‐free basis, decreases in organic N compounds and minerals were still present. On this basis, there was also an increase in the concentration of soluble phenolics.In terms of glucose required for biosynthesis, the increase in costs for one chemical compound – TNC – was balanced by a decrease in the costs for organic N compounds. Therefore, the construction costs, the total amount of glucose required to produce 1 g of leaf, were rather similar for the two CO2 treatments; on average a small decrease of 3% was found. This decrease was attributable to a decrease of up to 30% in the growth respiration coefficient, the total CO2 respired [mainly for N AD(P)H and ATP] in the process of constructing 1 g of biomass. The main reasons for this reduction were the decrease in organic N compounds and the increase in TNC.

Growth and maintenance respiration of leaflet, stipule, tendril, rachis, and petiole tissues that make up the compound leaf of pea (Pisum sativum)

Respiratory changes during development, as well as growth and maintenance coefficients, were measured in organs of a typical compound leaf at the seventh node position of a pea (Pisum sativum) plant. The leaf consists of both laminar (leaflets and stipules) and cylindrical organs (tendrils, rachis, and petiole). Young tissue of each organ had relatively high respiration rates that declined as the tissue expanded. The respiration rates of leaflet, stipule, and tendril tissue throughout maturation were significantly greater than those of the other organs. The growth respiration coefficients were not significantly different among laminar and cylindrical organs. Maintenance respiration, expressed on a total dry mass basis and on a carbohydrate-corrected dry mass basis, as well as in vitro photosynthetic rates, were significantly lower in petioles and rachises than in tendrils or the leaflets and stipules. No difference in maintenance respiration of organs was observed when rates were expressed on a protein basis. A linear relationship between mass-based respiration and organ protein concentration was observed, suggesting that the energy costs involved in protein turnover may account, in part, for the differences in maintenance respiration among the organs. Taken together, our data show that although the tendril is structurally similar to the rachis, petioles, and stem, which have a role in supporting the canopy of this climbing plant, the respiratory properties of tendrils are more like those of leaflets and stipules, thus parallelling the photosynthetic characteristics of these organs in the compound leaf. Keywords: development, leaflets, Pisum sativum, respiration, stipules, tendrils.

Whole plant respiration and photosynthesis of wheat under increased CO2 concentration and temperature: long‐term vs. short‐term distinctions for modelling

AbstractShort‐ and long‐term effects of elevated CO2 concentration and temperature on whole plant respiratory relationships are examined for wheat grown at four constant temperatures and at two CO2 concentrations. Whole plant CO2 exchange was measured on a 24 h basis and measurement conditions varied both to observe short‐term effects and to determine the growth respiration coefficient (rg), dry weight maintenance coefficient (rm), basal (i.e. dark acclimated) respiration coefficient (rg), and 24 h respiration:photosynthesis ratio (R:P). There was no response of rg to short‐term variation in CO2 concentration. For plants with adequate N supply, rg was unaffected by the growth‐CO2 despite a 10% reduction in the plant's N concentration (%N). However, rm was decreased 13%, and rb was decreased 20% by growth in elevated CO2 concentration relative to ambient. Nevertheless, R:P was not affected by growth in elevated CO2. Whole plant respiration responded to short‐term variation of ± 5 °C around the growth temperature with low sensitivity (Q10= 1.8 at 15 °C, 1.3 at 30 °C). The shape of the response of whole plant respiration to growth temperature was different from that of the short term response, being a slanted S‐shape declining between 25 and 30 °C. While rm, increased, rg decreased when growth temperature increased between 15 and 20 °C. Above 20 °C rm became temperature insensitive while rg increased with growth temperature. Despite these complex component responses, R:P increased only from 0.40 to 0.43 between 15° and 30 °C growth temperatures. Giving the plants a step increase in temperature caused a transient increase in R:P which recovered to the pre‐transient value in 3 days. It is concluded that use of a constant R:P with respect to average temperature and CO2 concentration may be a more simple and accurate way to model the responses of wheat crop respiration to ‘climate change’ than the more complex and mechanistically dubious functional analysis into growth and maintenance components.

Growth and maintenance components of leaf respiration of cotton grown in elevated carbon dioxide partial pressure

ABSTRACTElevated atmospheric carbon dioxide partial pressures have been shown to have variable direct and indirect effects on plant respiration rates. In this study, growth, leaf respiration, and leaf nitrogen and carbohydrate partitioning were measured in Gossypium hirsutum L. grown in 35 and 65 Pa CO2 for 30d. Growth and maintenance coefficients of leaf respiration were estimated using gas exchange techniques both at night and during the day. Elevated CO2 stimulated biomass production (107%) and net photo‐synthetic rates (35–50%). Total day‐time respiration (Rd) was not significantly affected by growth CO2 partial pressure. However, night respiration (Rn) of leaves grown in 65 Pa CO2 was significantly greater than that of plants grown in 35 Pa CO2. Correlation of Rd and Rn with leaf expansion rates indicated that plants in both CO2 treatments had equivalent growth respiration coefficients but maintenance respiration was significantly greater in elevated CO2. Increased maintenance coefficients in elevated CO2 appeared to be related to increased starch accumulation rather than to changes in leaf nitrogen.

Growth and maintenance respiration in leaves of Liriodendron tulipifera L. exposed to long‐term carbon dioxide enrichment in the field

summarySpecific respiration rate (SRR) was mathematically partitioned into its growth and maintenance components for leaves of yellow‐poplar (Liriodendron tulipifera L.) after 3 yr of CO2 enrichment in open‐top field chambers. Despite the absence of a CO2 effect on individual leaf expansion or specific growth rate (SGR), increasing the CO2 concentration to ambient +150 or +300 cm3 m−3 decreased SRR by 28 to 45% compared with ambient‐grown controls. These lower leaf respiration rates were correlated with reduced leaf nitrogen concentrations. As described by the two‐component model of growth and maintenance respiration, SRR was a linear function of SGR. Ambient‐grown leaves had a growth respiration coefficient of 704 mg CO2 g−1 dry mass compared with 572 and 570 mg CO2 g−1 for leaves grown at the two higher CO2 concentrations. Leaves from the elevated CO2 treatments had an average maintenance respiration coefficient of 88 mg CO2 g−1 dry mass d−1 compared with 135 mg CO2 g−1 d −1 for leaves from the ambient treatment. Incorporating these growth and maintenance coefficients into a leaf growth simulation model indicated that total respiration would be reduced by 21 to 26 % for a leaf exposed to + 150 or + 300 cm3 m−3 CO2 throughout its 50‐d lifespan compared with one grown at ambient CO2 conditions. Reductions in total respiration were dominated by a lower rate of maintenance respiration, while the contribution of a lower specific rate of growth respiration was largely offset by a greater dry mass for leaves grown at elevated CO2 concentrations. Although reductions in the respiratory loss of carbon could be beneficial, respiration is unlikely to decrease without a concomitant decrease in other metabolic processes. Whether these reductions are beneficial or detrimental to the long‐term growth of plants exposed to elevated CO2 remains unresolved.