Nutrients acquisition

These plant responses are largely controlled by the internal status of plant (40). On the other hand, it has been shown that the occurrence of nutrient-rich patches in the soil can trigger changes in root architecture and also in the capacity for nutrient acquisition (46,47). Recent results indicate that this behavior is dependent not only on internal (metabolic) signals but also on the capacity to sense... 

Most phytoactive compounds do not persist in soil in a free and active form for very long, yet they have been plausibly implicated, for example, in a mechanism of infection or nutrient acquisition therefore some suitable explanation must be found. The right set of circumstances was invoked by Uren and Reisenauer (17) to explain how labile reducing agents may be protected physically from Oi and be directed toward insoluble oxides of Mn. The right set of circumstances may have relevance in other situations, and some po.ssibilities are discussed later in this chapter. 

Root products are all the substances produced by roots and released into the rhizo.sphere (Table 2) (17). Although most root products are C compounds, they include ions, sometimes O, and even water. Root products may also be classified on the basis of whether they have either a perceived functional role (excretions and secretions) or a nonfunctional role (diffusates and root debris). Excretions are deemed to facilitate internal metabolism, such as respiration, while secretions are deemed to facilitate external proces.ses, such as nutrient acquisition. Both excretion and secretion require energy, and some exudates may act as either. For example, protons derived from CO2 production in respiration are deemed excretions, while those derived from an organic acid involved in nutrient acquisition are deemed secretions. 

Nonaroinatic organic acids such as citric have been implicated in nutrient acquisition since last century (73) and, in spite of the certainty with which some... 

N. C. Uren and H. M. Reisenauer, The role of root exudates in nutrient acquisition. Adv. Plant Nutr. 3 19 (1988). 

D. L. Jones, A. C. Edwards, K. Donachie, and P. R. Darrah, Role of proteinaceous amino acids relea.sed in root exudates in nutrient acquisition from the rhizosphere. Plant Soil /5S 183 (1994). 

P. H. Vaast and R. J. Zasoski, Effect of VA-mycorrhizac and nitrogen sources on rhizosphere soil characteristics, growth and nutrient acquisition of coffee seedlings (Coffea arahica L.), Plant and Soil I473. ... 

A schematic repre.sentation of the possible interaction between humic substances and mechanisms of nutrient acquisition located at the plasma membrane is shown in Fig. 2. 

R. J. Ryel and M. M. Caldwell, Nutrient acquisition from soils with patchy nutrient di.stributions as a.ssessed with simulation models. Ecology 79 2725 (1998). 

H. A. Azaizeh, H. Marschner, V. Rdmheld, and L. Wittenmayer, Effects of a vesic-ular-arbuscular mycorrhizal fungus and other soil microorganisms on growth, mineral nutrient acquisition and root exudation of soil-grown maize plants, Mycorrhiui 5 321 (1995). 

The choice of rootstocks was until recently thought to primarily affect the growth and vigour of the tree and to only have a minor effect on intrinsic fruit quality. However, recent research has shown that, under low input organic production practice, the choice of rootstock can have a significant influence on tree fitness and tree nutrient acquisition, and thereby also on fruit quality (Weibel et al., 2006a). 

Pahlow, M., Riebesell, U. and Wolf-Gladrow, D. A. (1997). Impact of cell shape and chain formation on nutrient acquisition by marine diatoms, Limnol. Oceanogr., 42, 1660-1672. 

Kirk (2003) has developed a simple model to compare root requirements for aeration with those for efficient nutrient acquisition in rice. The main features of the rice root system are summarized in Figure 6.4. The model considers roots in the anoxic soil beneath the fioodwater—soil interface, receiving their oxygen solely from the aerial parts of the plant. 

Kirk GJD. 2003. Rice root properties for internal aeration and efficient nutrient acquisition in submerged soil. New Phytologist 159 185-194. 

The phyllosphere (or aerial) parts of plants represent a challenge for the survival of microbes. The exposure to high doses of UV, fluctuations in temperature, and relative humidity all compromise viability (Heaton and Jones, 2008 Whipps et ah, 2008). Bacteria (epiphytes) that exist within the phyllosphere have evolved specialized mechanisms to improve stress tolerance and nutrient acquisition. Pseudomonas spp. form the predominant bacterial population recovered on the leaves of plants (Brandi and Amundson, 2008 Lindow and Brandi, 2003). Epiphytic pseudomonad s produce fluorescent or pigmented compounds that afford protection to UV. 

Although the products of humification may be described as conditionally recalcitrant (apparent recalcitrance varying with community composition, oxygen availability, solar radiation, and residence time), SDP is the refractory residue of microbial metabolism. It represents the difference between what bacteria consume and what the environment proffers. This asymmetry is a consequence of cellular organization and the economics of nutrient acquisition. 

Also, Schmidt et al. (2005) found a significant increase in root hair density by working with Arabidopsis thaliana, which were treated with water extractable humic substances (WEHS), suggesting that these substances induce a nutrient acquisition response that favors the uptake of nutrients via an increase in the absorptive surface area. Furthermore, a phenotypical analysis of an array of mutants harbouring defects in root epidermal patterning revealed that root hair density of the ttg and gl2 mutants, defective in cell specification, was significantly modified, indicating an effect at/or downstream of the determination of the cells. 

Schmidt, W., Cesco, S., Santi, S., Pinton, R., and Varanini, Z. (2005). Water-extractable humic substances as nutrient acquisition signals for root hairs development in Arabidopsis. In Rizosphere 2004—Perspectives and Challenges,Hartmann, A., Schmid, M., Wenzel, W., and Hinnsinger, P., eds., GSF-Berich, Neuherberg, p. 71. 

Pinton, R., Cesco, S., Schmidt W., and Varanini, Z. (2006). Role of humic substances as rhizospheric signals affecting root growth and mechanisms of nutrient acquisition. In Proceedings, 13th Meeting of the International Humic Substances Society, Karlsruhe, vol. 45-1, pp. 45 18. 

Varanini, Z., and Pinton, R. (2007). Root membrane activities relevant to nutrient acquisition at the plant-soil interface. In The Rhizosphere Biochemistry and Organic Substances at the Soil-Plant Interface, 2nd edition, Pinton, R., Varanini, Z., and Nannipieri, P., eds., CRC Press, Boca Raton, FL, pp. 151-172. 

This chapter reviews the distribution, mechanism and impact of mineral tunnelling by soil ectomycorrhizal fungi (EMF). Most trees in boreal forests live in close relation with EMF (Smith Read, 1997). These EMF mediate nutrient uptake they form an extension of the tree roots. In turn they obtain carbohydrates from the tree. Over the years ectomycorrhizal (EM) research has a strong focus on nutrient acquisition by EMF from organic sources (Read, 1991). In boreal forest systems, however, minerals could also be an important nutrient source, especially for calcium, potassium and phosphorus (Likens et al, 1994, 1998 Blum et al, 2002). Recent developments in EM research suppose a role for EMF in mobilizing nutrients from minerals (see Wallander, Chapter 14, this volume). 

The availability of scarce plant nutrients in deep soil is only relevant to our understanding of secondary forest nutrient acquisition if plants are able to absorb these nutrients with deeply penetrating root systems. Enticing evidence for such an extensive approach to nutrient acquisition is supported by the distribution of fine-root biomass (diameter = 0-1 mm) in the secondary forest, as compared to that in the neighboring mature forest and active cattle pasture (Fig. 9.2). Fine root biomass to 6 m depth is virtually identical in mature and secondary forests, and is > 10 times greater at depth than in the active cattle pasture. Hence, after 16 years of recovery, some of the trees, lianas and palms of the secondary forest had re-established root systems to at least 6 m depth. 

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