The CO 2 respired by leaves is , where root and shoot substrate is defined as imported C, and plant substrate is total photosynthate. Estimates were obtained from C isotope balances of shoots, roots and whole plants of sunflower and alfalfa using growth and respiration data collected at intervals of 1 to 2 weeks. e plant and e Shoot differed significantly from zero. e plant ranged between ----0.4 and ----0.9‰, whereas e Shoot was much greater ( ----0.6 to ----1.9‰). e Root was not significantly different from zero. The present results help to resolve the apparent conflict between leafand ecosystem-level 13 C discrimination in respiration.
A 13 C/ 12 C mass spectrometer was interfaced with a open gas exchange system including four growth chambers to investigate CO 2 exchange components of perennial ryegrass ( Lolium perenne L.) stands. Chambers were fed with air containing CO 2 with known .8 to ----2.5‰, and increased by ~ 10‰ following a shift from ----2.6 to ----46.7‰ due to isotopic disequilibria between photosynthetic and respiratory fluxes. Isotopic imbalances were used to assess (non-photorespiratory) respiration in light and the replacement of the respiratory substrate pool(s) by new photosynthate. Respiration was partially inhibited by light, but increased during the light period and decreased in darkness, in association with temperature changes. The labelling kinetics of respiratory CO 2 indicated the existence of two major respiratory substrate pools: a fast pool which was exchanged within hours, and a slow pool accounting for ~ 60% of total respiration and having a mean residence time of 3.6 d.
AbbreviationsA g and A n , gross and net assimilated C allocated to shoots; R , total respiration rate; R new , respiration rate of new C; R old , respiration rate of mobilized, old C; a n , r , r new and r old , specific rates of assimilation and respiration per unit shoot C; f R, new , fraction of new C in total respiratory CO 2 ; ∆ w i , instantaneous relative growth rate; ∆ w , relative growth rate. Summary• Respiratory costs of Medicago sativa and Helianthus annuus individuals growing in hierarchically structured stands in a controlled environment were analysed with regard to the daily rate of carbon (C) assimilation.• Net assimilation of new C ( A n , g C d − 1 ) and respiration rates of new ( R new , g C d − 1 ) and old C ( R old , g C d − 1 ) were assessed by 13 CO 2 labelling and gas exchange measurements.• Specific respiration rate of old C ( r old , g C g) decreased exponentially with increasing shoot biomass, but was not affected by the instantaneous relative growth rate ( ∆ w i ). The growth coefficient g ( R new : A n ) was c . 0.32. In the most severely shaded subordinate plants, g was < 0.2, but low g stimulated r old . The contribution of R new to total respiraton ( f R, new ) and the carbon use efficiency CUE (1 -R /( A n + R new )) were c . 0.68 and 0.62 for ∆ w i > 0.1, respectively. For ∆ w i < 0.1, f R, new and CUE decreased with decreasing ∆ w i in both dominant and subordinate plants.• The results suggest that R old was closely related to maintenance, whereas R new was primarily involved in growth.
Vertical gradients of leaf nitrogen (N) per unit leaf area (NLA) are viewed as plastic responses that optimize N utilization with respect to carbon assimilation. However, it has been shown that plant species, sowing density and N availability affect the steepness of the NLA gradient relative to the photon flux density (PFD) gradient. This paper tests the hypothesis that such variation is related to the N status of the plant. The N status was analysed using the concept of the critical N concentration (Ncrit) in which shoot N per unit dry mass (NSM) decreases with shoot mass, and a negative deviation of actual NSM from Ncrit indicates N shortage in the plant. The hypothesis was tested with contrasting grassland species Medicago sativa, Dactylis glomerata and Taraxacum officinale by varying PFD and N availability, plant density and hierarchical positions of individuals within stands. Combinations of all treatments showed a general negative correlation between the N allocation coefficient (i.e. the slope of the NLA-PFD relationship) and NSM for all three species. Thus, NLA, relative to PFD, gradients became steeper with increasing shoot mass and increasing N shortage in the plant. These data are consistent with the view that internal N availability is an important factor in modifying the NLA gradient.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.Summary 1 A large-leafed and a small-leafed genotype of Trifolium repens were grown with homogeneous low or high phosphate (P) supply, or with heterogeneous P supply so that the plant grew from a low P patch into a high P patch. Intraplant distribution of recently acquired 32P, morphological and physiological characteristics and biomass allocation were measured so that genotypic variation in physiological integration for P and its implications for growth could be assessed. 2 Low vs. high homogeneous P supply induced differing proportional reductions in the values of plant characteristics with magnitude for percentage of branching of nonrooted ramets > leaf size > petiole length > internode length > stolon diameter and rate of ramet production. 3 In homogeneously supplied plants, only 5% of 32P exported from a single root was transported to proximal ramets. Genotypes differed in physiological integration: under heterogeneous P supply 50% of 32P exported from the first root of the high P patch was transported basipetally in the small-leafed compared with only 3% in the large-leafed genotype. 4 Despite the genotypic difference in 32P distribution under heterogeneous P supply, the dry mass and morphology of proximal ramets supplied with low P were unaffected by P supply to distal ramets in both genotypes. 5 The size of distal ramets in heterogeneously supplied plants was smaller than in plants with homogeneous high P supply. Consequently, in both genotypes placement of ramets and ramet size were influenced by both the local environment and by the environment of proximal ramets (i.e. by the nutritional status of the whole plant). 6 Compared to the large-leafed genotype, the small-leafed genotype had less rapid production of biomass, smaller responses of relative growth rates to different rates of P supply, more ramets with leaves when grown in low P supply, and, when exposed to heterogenous P supply, an elevated tissue concentration of phosphorus in leaves. It was concluded that the genotypes differed in growth strategy in a manner consistent with predictions based on fertility level within their habitat of origin and that thorough assessment of physiological integration of P nutrition within genotypes of T. repens required measurement of all the processes involved in acquisition, allocation and utilization of P.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.