Plant carbon pools

Atrazine enters plants primarily by way of the roots and secondarily by way of the foliage, passively translocated in the xylem with the transpiration stream, and accumulates in the apical meristems and leaves (Hull 1967 Forney 1980 Reed 1982 Wolf and Jackson 1982). The main phytotoxic effect is the inhibition of photosynthesis by blocking the electron transport during Hill reaction of photosystem II. This blockage leads to inhibitory effects on the synthesis of carbohydrate, a reduction in the carbon pool, and a buildup of carbon dioxide within the leaf, which subsequently causes closure of the stomates, thus inhibiting transpiration (Stevenson et al. 1982 Jachetta et al. 1986 Shabana 1987). 

Rillig, M. C., Wright, S. F., Nichols, K. A., Schmidt, W. F., and Torn, M. S. (2001). Large contribution of arbuscular mycorrhizal fungi to soil carbon pools in tropical forest soils. Plant Soil 233,166-177. 

Plant productivity is determined by factors such as plant species composition, moisture, soil fertility, growing season length, and solar radiation—many of which are affected by human activities. All else equal, increases in primary productivity and production of plant tissues will lead to increases in soil C stock, while decreases will lead to decreases in soil C stock. The rate of change in soil C stock is determined by the difference between C inputs and outputs, as well as the turnover times of the soil C, which are often not known. Here we review briefly how some environmental factors are expected to alter productivity and explore how the effects on stock depend on the number of soil carbon pools and their turnover times. 

Paul, E. A., Morris, S. J., Conant, R. T., and Plante, A. F. (2006). Does the acid hydrolysis-incubation method measure meaningful soil organic carbon pools Soil Sci. Soc. Am. J. 70(3), 1023-1035. 

Stewart CE, Plante AF, Paustian K et al (2008) Soil carbon saturation linking concept and measurable carbon pools. Soil Sci Soc Am J 72 379-392... 

A synthetic coupled cycle of calcium and carbon through the oxalate-carbonate pathway is shown in Fig. 12.8. Atmospheric CO2 is fixed by the plants through photosynthesis to produce biomass. Inside the plant, oxalate crystals form. In addition, fungal mycelium may also accumulate oxalate. Mainly in the form of calcium oxalate (COM or COD), this carbon pool is used by oxalotrophic bacteria as a carbon, energy and electron source. The transformation of oxalate can occur in the soil... 

During the aquatic phase plants are detached from the sediments and drift with the current. They contribute to the carbon pool of the main channel of the Amazon River and also accelerate the colonization of newly created open areas formed by the deposition of sediments. Quick colonization creates a range of different stages of allogenic succession in the floodplains. The velocity of the successional process will depend upon the stability of the habitat. Isolated floodplain lakes, where deposition rates of sediments are small, show a slow but gradual colonization process while, processes on sand bars and mud flats in the river channel are more dynamic and often reversible (Junk and Piedade 1997). 

The interpretation of variations in is complicated. One complication results from isotopic disequilibria in carbon pools (Battle et al., 2000). Disequilibria occur because the taken up by plants, e.g., is representative of the currently in the atmosphere (allowing for discrimination), but the 6 C of CO2 released through decay represents not the 6 C of the current atmosphere but of an atmosphere several decades ago. As long as the 6 C of the atmosphere is changing, the 6 C in pools will reflect a mixture of earlier and current conditions. Uncertainties in the turnover of various carbon pools add uncertainty to interpretation of the signal. 

The nature of P mineralization in soils is a second factor mediating towards phosphorus availability not constraining tropical forest [CO2] responses. This is because, unlike nitrogen, phosphorus is mineralized independent of carbon in most soils. Thus, it has less potential to be locked up in the larger soil carbon pool that should occur as a result of increased plant productivity at higher [CO2]. 

Arnone, J. A., Ill and Korner (1995). Soil and biomass carbon pools in model communities of tropical plants under elevated COj. Oecoloyia 104,61-71. 

From this understanding of the behavior of the SOC pool, models such as Rothamsted (Jenkinson and Rayner, 1977) and Century (Parton et ai, 1993) have been developed that allow results from regional validation studies to be extrapolated to the global scale (Schimel et al, 1994). Such models divide the SOC pool up into three to five pools with turnover times ranging from years to thousands of years, and the sizes of the.se pools for a given. soil texture are determined by climate-driven interactions between plant carbon inputs, nutrients, microbial respiration, and leaching of DOC (Fig. 2). In some cases, the.se models have been tested... 

Extracellnlar enzymes play a pivotal role in catalyzing the rate-limiting steps during decomposition of plant detritns and soil organic matter, and release of bioavailable nntrients. The relationship between enzyme activity (snch as P-glucosidase activity) and microbial respiration and labile carbon pools, snch as MBC and DOC, suggests a role of these enzymes in carbon cycling. 

Pulchan [106] thus used DMBA as a derived marker of vascular plant material (trees and scrubs) in offshore sediments in Trinity Bay (Figs. 6-8). Such terrestrial organic matter may play a significant role in the productivity of marine ecosystems by adding to the marine carbon pool. 

C4 plants suppress photorespiration by concentrating CO2 at the site of ribulose-l,5-bisphosphate carboxylase (Rubisco). During photosynthesis in C4 leaves an inorganic carbon pool develops which is up to 10 x that expected by simple equilibration with external CO2 (1). The effective concentration of CO2 in bundle sheath cells requires that the mesophyll-bundle sheath cell interface be resistant to CO2 diffusion. The more "leaky" this interface is to CO2 the more energy must be expended by "overcycling" of the C4 cycle relative to net C02 assimilation to maintain a high bundle sheath CO2 concentration. The work presented here quantitatively examines the permeability of the bundle sheath-mesophyll interface to CO2 and its implications for C4 photosynthesis. 

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