Carbon allocation

COt concentrations have been rising steadily over the last 40 years and are expected to continue to rise, though the magnitude of the increase is uncertain (222). This could be expected to have important consequences for photosynthesis and hence exudation. However, Whipps (13) reported that the loss of a,ssimilated carbon from Zea mays roots was unaffected by atmospheric CO concentrations up to 1000 )il r. In contrast, Norby et al., (223) found that carbon allocation to roots and root exudation increased in Liriodendron tuUpifera grown in the presence of elevated CO levels. In Pimts echinata seedlings, there was increased exudation under elevated CO after 34 weeks but not after 41 weeks (224). 

R. J. Norby, E. G. O Neill, W. G. Hood, and R. J. Luxmoore, Carbon allocation, root exudation and mycorrhizal colonisation of Pinus echinata seedlings grown under COj enrichment. Tree Physiology. L203 (1987). 

J. N. Holland, W. Cheng, and D. A. Crossley, Jr, Herbivore-induced changes in plant carbon allocation assessment of below-ground C fluxes using carbon-14, Oe-cologia I07-.S1 (1996). 

P. T. Rygiewicz and C. P. Andersen, Mycorrhizae alter quality and quantity of carbon allocated below ground. Nature 369 58 (1994). 

S. W.. Simard. D. M. Durall, and M. D. Jones, Carbon allocation and carbon transfer between Betula papyrtfera and Psuedotsuga nienziesii seedlings using a C pulselabelling method. Plant Soil /9/ 41 (1997). 

The phenolic acids of interest here [caffeic acid (3,4-dihydroxycinnamic acid), ferulic acid (4-hydroxy-3-methoxycinnamic acid), p-coumaric acid (p-hydroxycinnamic acid), protocatechuic acid (3,4-dihydroxybenzoic acid), sinapic acid (3,5-dimethoxy-4-hydroxyxinnamic acid), p-hydroxybenzoic acid, syringic acid (4-hydroxy-3,5-methoxybenzoic acid), and vanillic acid (4-hydroxy-3-methoxybenzoic acid)] (Fig. 3.1) all have been identified as potential allelopathic agents.8,32,34 The primary allelopathic effects of these phenolic acids on plant processes are phytotoxic (i.e., inhibitory) they reduce hydraulic conductivity and net nutrient uptake by roots.1 Reduced rates of photosynthesis and carbon allocation to roots, increased abscisic acid levels, and reduced rates of transpiration and leaf expansion appear to be secondary effects. Most of these effects, however, are readily reversible once phenolic acids have been depleted from the rhizosphere and rhizoplane.4,6 Finally, soil solution concentrations of... 

Reactions (1) - (4) pass on the catalyst in a warmed pipe in a recuperative mode. The main disadvantage of considered process is the necessity to use the surplus of H20 [1], The surplus is defined with molar ratio (mol H20)/C = N. Depending on operation conditions, tubular furnaces designs and the used catalyst 2 power consumption of hydrocarbons conversion process as a whole. Necessity of increase N is connected with allocation of carbon on the catalyst (the mechanism of carbon allocation is... 

Rosling, A., Lindahl, B. D. Finlay, R. D. (2004a). Carbon allocation to ectomycorrhizal roots and mycelium colonizing different mineral substrates. New Phytologist,... 

Table 5.1. Field-based estimates of carbon allocation to ectomycorrhizal fungi as a percentage of net primary production...

Axelsson, E. Axelsson, B. (1986). Changes in carbon allocation patterns in spruce and pine trees following irrigation and fertilization. Tree Physiology, 2, 189-204. 

Davidson, E. A., Savage, K., Bolstad, P. et al. (2002). Belowground carbon allocation in forests estimated from litterfall and IRGA-based soil respiration measurements. Agricultural and Forest Meteorology, 113, 39-51. 

HSgberg, P., Nordgren, A. Agren, G. I. (2002). Carbon allocation between tree root growth and root respiration in a boreal pine forest. Oecologia, 132, 579-81. 

Reid, C. P. P., Kidd, F. A. Ekwebelam, S. A. (1983). Nitrogen nutrition, photosynthesis and carbon allocation in ectomycorrhizal pine. Plant and Soil, 71, 415-32. 

The rapid allocation of trace quantities of to external AM fungal hyphae provides independent support for the observations by Johnson et al. (2002a, b) that carbon transfer to mycorrhizas occurs very quickly. Staddon et al. (2003b) concluded that the turnover rate of AMF hyphae was likely to be just 5-6 days. This corresponds well with the turnover rates by absorptive hyphal structures of 5-7 days observed in Artemisia triden-tata and Oryzopsis hymenoides communities (Friese Allen, 1991). However, it is not known from the Staddon et al. (2003b) study if the carbon allocated to the AMF was used for production of mycelial biomass or allocated into compounds that are rapidly respired, in accordance with the observations of Johnson et al. (2002a, b). 

Fig. 6.1. Schematic diagram showing the fate of carbon allocated to external AM fungal mycelium in relation to the soil physical environment and the morphology and chemical composition of the hyphae (modified from Zhu Miller, 2003).

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