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Carbon quality (polyphenols) In some ecosystems non-lignin carbon compounds
(e.g., phenolics) explain more variation in decomposition than does either N or lignin (Hättenschwiler et al. 2011). Phenolics are the most widely distributed class of
secondary plant metabolites and interact strongly with several aspects of nutrient
cycling (Hättenschwiler and Vitousek 2000). Simple phenolics can prime (Fontaine
et al. 2007), while large complex polyphenolics can retard (Coq et al. 2010) decomposition. Carbon quality—including the chemical composition of polyphenolics—
can be more important to litter decomposition than is litter nutrient concentration
(Hättenschwiler and Jørgensen 2010). Plant polyphenolics can be accurately measured via near-infrared spectroscopy (NIRS; Rupert-Nason et al. 2013), and by airborne imaging spectroscopy (Kokaly et al. 2009; Asner et al. 2014; Madritch et al.
2014; Serbin and Townsend, Chap. 3).
Though typically considered primarily for their aboveground defensive properties, phenolics in plant residues (leaf litter and roots) can have large influences on
decomposition. Simple phenolics can increase soil respiration by providing a simple carbon source for microorganisms (Horner et al. 1988; Schimel et al. 1996;
Madritch et al. 2007). Tannins are defined, in part, by their ability to bind to proteins
(Bate-Smith 1975). The attributes of nonstructural polyphenolics that make them
effective plant pathogen defenses also affect nonpathogenic fungi and microbes
once litter enters the detrital food web; tannins do not discriminate between enzymes
of plant pathogenic fungi or decomposing fungi. If tannins bind covalently with
proteins to form polyphenolic-protein complexes, they become highly recalcitrant,
and only basidiomycetes with polyphenol oxidase and earthworms can take advantage of these complex N sources (Hättenschwiler and Vitousek 2000). The inhibitory role of tannins on soil enzymes varies with specific tannin structure, which
varies widely among species (Triebwasser et al. 2012). Tannins also have a limited
ability to bind with carbohydrates and cellulose to form recalcitrant complexes
(Horner et al. 1988; Kraus et al. 2003). The ability of polyphenolics to complex with
proteins and other biochemicals is the primary method by which they influence soil
respiration, litter decomposition, and soil N fluxes.
In addition to their influence on decomposition, nonstructural polyphenolics
(which do not include lignin) influence N cycling by binding to and promoting
retention of N-rich compounds including ammonium, amino acids, and proteins
(Hättenschwiler and Vitousek 2000). Ayres (1997) suggested that condensed tannins may be more important to N cycling than to herbivore defense, since condensed tannins frequently have no anti-herbivory activity. Hättenschwiler et al.
(2011) also proposed that polyphenolics, and tannins in particular, may be an important N conservation and recovery strategy for some species. This appears to be the
case in Populus tremuloides systems, where high-tannin genotypes recovered more
N than did low-tannin genotypes, especially when under severe herbivory (Madritch
and Lindroth 2015). The high reactivity and branching structure of reactive hydroxyl
sites also allow polyphenolics to complex with clay particles in soil and thereby
influence several micronutrients in addition to N (Schnitzer et al. 1984).
8 Linking Foliar Traits to Belowground Processes
Carbon quality (polyphenols) In some ecosystems non-lignin carbon compounds
(e.g., phenolics) explain more variation in decomposition than does either N or lignin (Hättenschwiler et al. 2011). Phenolics are the most widely distributed class of
secondary plant metabolites and interact strongly with several aspects of nutrient
cycling (Hättenschwiler and Vitousek 2000). Simple phenolics can prime (Fontaine
et al. 2007), while large complex polyphenolics can retard (Coq et al. 2010) decomposition. Carbon quality—including the chemical composition of polyphenolics—
can be more important to litter decomposition than is litter nutrient concentration
(Hättenschwiler and Jørgensen 2010). Plant polyphenolics can be accurately measured via near-infrared spectroscopy (NIRS; Rupert-Nason et al. 2013), and by airborne imaging spectroscopy (Kokaly et al. 2009; Asner et al. 2014; Madritch et al.
2014; Serbin and Townsend, Chap. 3).
Though typically considered primarily for their aboveground defensive properties, phenolics in plant residues (leaf litter and roots) can have large influences on
decomposition. Simple phenolics can increase soil respiration by providing a simple carbon source for microorganisms (Horner et al. 1988; Schimel et al. 1996;
Madritch et al. 2007). Tannins are defined, in part, by their ability to bind to proteins
(Bate-Smith 1975). The attributes of nonstructural polyphenolics that make them
effective plant pathogen defenses also affect nonpathogenic fungi and microbes
once litter enters the detrital food web; tannins do not discriminate between enzymes
of plant pathogenic fungi or decomposing fungi. If tannins bind covalently with
proteins to form polyphenolic-protein complexes, they become highly recalcitrant,
and only basidiomycetes with polyphenol oxidase and earthworms can take advantage of these complex N sources (Hättenschwiler and Vitousek 2000). The inhibitory role of tannins on soil enzymes varies with specific tannin structure, which
varies widely among species (Triebwasser et al. 2012). Tannins also have a limited
ability to bind with carbohydrates and cellulose to form recalcitrant complexes
(Horner et al. 1988; Kraus et al. 2003). The ability of polyphenolics to complex with
proteins and other biochemicals is the primary method by which they influence soil
respiration, litter decomposition, and soil N fluxes.
In addition to their influence on decomposition, nonstructural polyphenolics
(which do not include lignin) influence N cycling by binding to and promoting
retention of N-rich compounds including ammonium, amino acids, and proteins
(Hättenschwiler and Vitousek 2000). Ayres (1997) suggested that condensed tannins may be more important to N cycling than to herbivore defense, since condensed tannins frequently have no anti-herbivory activity. Hättenschwiler et al.
(2011) also proposed that polyphenolics, and tannins in particular, may be an important N conservation and recovery strategy for some species. This appears to be the
case in Populus tremuloides systems, where high-tannin genotypes recovered more
N than did low-tannin genotypes, especially when under severe herbivory (Madritch
and Lindroth 2015). The high reactivity and branching structure of reactive hydroxyl
sites also allow polyphenolics to complex with clay particles in soil and thereby
influence several micronutrients in addition to N (Schnitzer et al. 1984).
8 Linking Foliar Traits to Belowground Processes