▪ Abstract The primary effect of the response of plants to rising atmospheric CO2 (Ca) is to increase resource use efficiency. Elevated Ca reduces stomatal conductance and transpiration and improves water use efficiency, and at the same time it stimulates higher rates of photosynthesis and increases light-use efficiency. Acclimation of photosynthesis during long-term exposure to elevated Ca reduces key enzymes of the photosynthetic carbon reduction cycle, and this increases nutrient use efficiency. Improved soil–water balance, increased carbon uptake in the shade, greater carbon to nitrogen ratio, and reduced nutrient quality for insect and animal grazers are all possibilities that have been observed in field studies of the effects of elevated Ca. These effects have major consequences for agriculture and native ecosystems in a world of rising atmospheric Ca and climate change.

More Efficient Plants : a consequence of rising atmospheric CO2

Plant responses to the projected future levels of CO2 were first characterized in short-term experiments lasting days to weeks. However, longer term acclimation responses to elevated CO2 were subsequently discovered to be very important in determining plant and ecosystem function. Free-Air CO2 Enrichment (FACE) experiments are the culmination of efforts to assess the impact of elevated CO2 on plants over multiple seasons and, in the case of crops, over their entire lifetime. FACE has been used to expose vegetation to elevated concentrations of atmospheric CO2 under completely open-air conditions for nearly two decades. This review describes some of the lessons learned from the long-term investment in these experiments. First, elevated CO2 stimulates photosynthetic carbon gain and net primary production over the long term despite down-regulation of Rubisco activity. Second, elevated CO2 improves nitrogen use efficiency and, third, decreases water use at both the leaf and canopy scale. Fourth, elevated CO2 stimulates dark respiration via a transcriptional reprogramming of metabolism. Fifth, elevated CO2 does not directly stimulate C4 photosynthesis, but can indirectly stimulate carbon gain in times and places of drought. Finally, the stimulation of yield by elevated CO2 in crop species is much smaller than expected. While many of these lessons have been most clearly demonstrated in crop systems, all of the lessons have important implications for natural systems.

Elevated CO2 effects on plant carbon, nitrogen, and water relations: six important lessons from FACE

Although trees have responded to global warming in the past - to temperatures higher than they are now - the rate of change predicted in the 21st century is likely to be unprecedented. Greenhouse gas emissions could cause a 3-6°C increase in mean land surface temperature at high and temperate latitudes. Despite this, few experiments have isolated the effects of temperature for this scenario on trees and forests. This review focuses on tree and forest responses at boreal and temperate latitudes, ranging from the cellular to the ecosystem level. Adaptation to varying temperatures revolves around the trade-off between utilizing the full growing season and minimizing frost damage through proper timing of hardening in autumn and dehardening in spring. But the evolutionary change in these traits must be sufficiently rapid to compensate for the temperature changes. Many species have a positive response to increased temperature - but how close are we to the optima? Management is critical for a positive response of forest growth to a warmer climate, and selection of the best species for the new conditions will be of vital importance. Contents Summary 369 I. Introduction 370 II. Photosynthesis and respiration 370 III. Soil organic matter decomposition and mineralization 373 IV. Phenology and frost hardiness 376 V. Whole tree experimental responses to warming 380 VI. Changes in species distribution at warmer temperatures 381 VII. Adaptation and evolution 383 VIII. Ecosystem level responses to warming 387 Acknowledgements 390 References 390 Appendix I. Temperature response functions 399.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.2001.00057.x

Tree and forest functioning in response to global warming

The McCree-de Wit-Penning de Vries-Thornley Respiration Paradigms: 30 Years Later

We measured respiration of 20-year-old Pinus radiata D. Don trees growing in control (C), irrigated (I), and irrigated + fertilized (IL) stands in the Biology of Forest Growth experimental plantation near Canberra, Australia. Respiration was measured on fully expanded foliage, live branches, boles, and fine and coarse roots to determine the relationship between CO(2) efflux, tissue temperature, and biomass or nitrogen (N) content of individual tissues. Efflux of CO(2) from foliage (dark respiration at night) and fine roots was linearly related to biomass and N content, but N was a better predictor of CO(2) efflux than biomass. Respiration (assumed to be maintenance) per unit N at 15 degrees C and a CO(2) concentration of 400 micro mol mol(-1) was 1.71 micro mol s(-1) mol(-1) N for foliage and 11.2 micro mol s(-1) mol(-1) N for fine roots. Efflux of CO(2) from stems, coarse roots and branches was linearly related to sapwood volume (stems) or total volume (branches + coarse roots) and growth, with rates for maintenance respiration at 15 degrees C ranging from 18 to 104 micro mol m(-3) s(-1). Among woody components, branches in the upper canopy and small diameter coarse roots had the highest respiration rates. Stem maintenance respiration per unit sapwood volume did not differ among treatments. Annual C flux was estimated by summing (1) dry matter production and respiration of aboveground components, (2) annual soil CO(2) efflux minus aboveground litterfall, and (3) the annual increment in coarse root biomass. Annual C flux was 24.4, 25.3 and 34.4 Mg ha(-1) year(-1) for the C, I and IL treatments, respectively. Total belowground C allocation, estimated as the sum of (2) and (3) above, was equal to the sum of root respiration and estimated root production in the IL treatment, whereas in the nutrient-limited C and I treatments, total belowground C allocation was greater than the sum of root respiration and estimated root production, suggesting higher fine root turnover or increased allocation to mycorrhizae and root exudation. Carbon use efficiency, the ratio of net primary production to assimilation, was similar among treatments for aboveground tissues (0.43-0.50). Therefore, the proportion of assimilation used for construction and maintenance respiration on an annual basis was also similar among treatments.

/pdf/foliage-fine-root-woody-tissue-and-stand-respiration-in-5dboxf6f32.pdf

Foliage, fine-root, woody-tissue and stand respiration in Pinus radiata in relation to nitrogen status.

Protein turnover is generally regarded as a major maintenance process, but experi­ mental evidence to support this contention is scarce. Here we quantify the component of dark respiration rate associated with overall protein turnover of tissues in vivo. The effect of an inhibitor of cytosolic protein synthesis (cycloheximide, CHM) on dark respiration was tested on a cell suspension from potato (Solanum tuberosum L.) and quantified on leaf discs of expanding and full-grown primary leaves of bean (Phaseo­ lus vulgaris L.). The in vivo effect of CHM on protein biosynthesis was assessed by monitoring the inhibition of the induction of the ethylene-forming enzyme (EFE) activity. The present method yields the energy costs of turnover of the total pool of proteins irrespective of their individual turnover rates. Average turnover rates were derived from the respiratory costs and the specific costs for turnover. Inhibition of respiration by CHM was readily detectable in growing-cell suspensions and discs of expanding leaves. The derived respiratory costs of protein turnover in expanding leaves were maximally 17-37o/c of total respiration. Turnover costs in full-grown primary leaves of bean amounted to 17-21% of total dark respiration. The maximum degradation constants (i.e. "Ki-values) derived for growing and full-grown leaves were up to 2.42 x 106 and 1.12 x 10-6 s1 , respectively.

/pdf/respiratory-energy-requirements-and-rate-of-protein-turnover-29tztipxjs.pdf

Respiratory energy requirements and rate of protein turnover in vivo determined by the use of an inhibitor of protein synthesis and a probe to assess its effect

The present study explores the potential contribution of the energy requirements associated with nocturnal carbohydrate export to (1) the fraction of dark respira­ tion correlating with leaf nitrogen concentration and (2) the dark respiration of mature source leaves. To this end, we determined the nocturnal carbohydrate-export rates from leaves with an optimal nitrogen supply, and the correlation between the nitrogen concentration and the dark respiration of leaves. The specific energy costs of carbohydrate export from starch-storing source leaves were determined both experimentally and theor­ etically. The present estimate of the specific energy cost involved in carbohydrate export as obtained by linear regression (0. 70 mol C02 (mol sucrose) - 1 ), agrees well with both literature data obtained by different methods (0.4 7 to 1.26 mol C02 (mol sucrose) - 1 ) and the theoretically calculated range for starch-storing species (0.40 to 1.20 mol C02 (mol sucrose) - 1 ). The conversion of starch in the chloroplast to sucrose in the cytosol is a major energy-requiring process. Maximally 42 to '107'% of the slope of the relationship between respiration rate and organic nitrogen concentration of primary bean leaves, may be ascribed to the energy costs associated with nocturnal export of carbohyd­ rates. Total energy costs associated with export were derived from the product of the specific costs of carbo- hydrate export and the export rates, either measured on full-grown (primary) leaves of potato and bean or derived from the literature. These export costs account, on average, for 29% of the dark respiration rate in starch-storing species. We conclude that nocturnal carbohydrate export is a major energy-requiring pro­ cess in starch-storing species.

/pdf/the-respiratory-energy-requirements-involved-in-nocturnal-2vg7gvca80.pdf

The respiratory energy requirements involved in nocturnal carbohydrate export from starch-storing mature source leaves and their contribution to leaf dark respiration

The contribution of the alternative pathway in root respiration of Pisum sativum L. cv Rondo, Plantago lanceolata L., and Plantago major L. ssp major was determined by titration with salicylhydroxamate (SHAM) in the absence and presence of cyanide. SHAM completely inhibited the cyanide-resistant component of root respiration at 5 to 10 millimolar with an apparent K(i) of 600 micromolar. In contrast, SHAM enhanced pea root respiration by 30% at most, at concentrations below 15 millimolar. An unknown oxidase appeared to be responsible for this stimulation. Its maximum activity in the presence of low SHAM concentrations (1-5 millimolar) was 40% of control respiration rate in pea roots, since 25 millimolar SHAM resulted in 10% inhibition. In plantain roots, the maximum activity was found to be 15%. This hydroxamate-activated oxidase was distinct from the cytochrome path by its resistance to antimycin. The results of titrations with cyanide and antimycin indicated that high SHAM concentrations (up to 25 millimolar) block the hydroxamate-activated oxidase, but do not affect the cytochrome path and, therefore, are a reliable tool for estimating the activity of the alternative path in vivo. A considerable fraction of root respiration was mediated by the alternative path in plantain (45%) and pea (15%), in the latter because of the saturation of the cytochrome path.

Inhibition and stimulation of root respiration in Pisum and Plantago by hydroxamate. Its consequences for the assessment of alternative path activity

Maintenance of ion gradients across plant membranes is considered to be an impor­ tant process requiring respiratory energy in plant tissues. In order to test this hy­ pothesis, roots of intact plants of potato (Solanum tuberosum L. cv. Alcmaria and cv. Pimpernel) were incubated in a closed circulation system. Electrical conductivity of the solution surrounding these roots was continuously monitored to determine total ion efflux into demineralized water. Anion efflux rate from the symplast was 35 neq (g dry weight)1 s1 • In combination with literature data on the specific costs of ion transport, this efflux rate yields the respiration rate associated with re-uptake balanc­ ing efflux (i.e. maintenance of cellular ion concentrations). The results suggest that energy costs associated with re-uptake of ions may account for up to 25-50% of the total respiratory costs involved in ion influx.

/pdf/energy-requirements-for-maintenance-of-ion-concentrations-in-1jvsc1qy88.pdf

Energy requirements for maintenance of ion concentrations in roots

The rate of dry matter accumulation by seeds of Vicia faba L. cv. Minica increases with temperature in the range of 16 to 26°C. The duration of dry matter accumulation decreases with temperature, resulting in a decrease of final seed dry weight. In this study we test the hypothesis that a diffusion barrier for O2, located in the seed coat, inhibits seed respiration and growth. The rate of O2 uptake of intact seeds and of excised embryos and seed coats (separated seeds) was measured in air and buffer at 16, 20, and/or 26°C at various O2 concentrations and developmental stages. Oxygen uptake rates of intact seeds in buffer were only 9 to 15% of those in air. In buffer, the respiration rate of intact seeds decreased at a pO2 below air saturation (21 kilopascals), whereas separated seeds showed a decline of O2 uptake only below 80% of air saturation. In air, embryo excision had no effect on the sensitivity of seed respiration to pO2, at both 20 and 26°C. In air at 20°C, separated and intact seeds showed similar rates of O2 uptake. Oxygen uptake by intact seeds, both halfway and beyond the linear growth phase, showed a temperature coefficient Q10 of 2.3 and was insensitive to pO2 in the range of 80 to 100% of ambient. These results indicate that V. faba seed respiration in air is not limited by the diffusion of O2 into the seed.

R. De Visser

Papers

Respiratory energy requirements and rate of protein turnover in vivo determined by the use of an inhibitor of protein synthesis and a probe to assess its effect

The respiratory energy requirements involved in nocturnal carbohydrate export from starch-storing mature source leaves and their contribution to leaf dark respiration

Inhibition and stimulation of root respiration in Pisum and Plantago by hydroxamate. Its consequences for the assessment of alternative path activity

Energy requirements for maintenance of ion concentrations in roots

Control of Seed Respiration and Growth in Vicia faba by Oxygen and Temperature: No Evidence for an Oxygen Diffusion Barrier