180
Variation in plant phenolics is driven by several interacting factors. In general,
polyphenolic concentrations in foliage are highest during the summer months
(Feeny 1970). Summer coincides with both the onset of herbivory and the highest
levels of photosynthetic activity. Herbivory-induced polyphenolic production is a
well-documented aspect of plant-insect interactions (Herms and Mattson 1992;
Baldwin 1994). The composition and quantity of phenolics vary among taxa at
small and large phylogenetic scales. At large phylogenetic scales, condensed tannins are common in woody plants but almost absent in herbaceous species (Haslam
1989). At narrow phylogenetic scales, the concentration of polyphenolics is also
under genetic control, and often there is considerable variation within the same species that can have important influences on belowground processes including litter
decomposition and nutrient cycling (Lindroth et al. 2002; Schweitzer et al. 2005;
Madritch et al. 2006, 2007).
8.3.3 Plant Diversity
Plant diversity, which can be accurately remotely sensed at some spatial scales
(Wang et al. 2019; Gholizadeh et al. 2019), can influence belowground processes
through its effects on productivity as well as on chemical diversity (Meier and
Bowman 2008). Belowground diversity may be intrinsically linked to aboveground
diversity because high plant diversity may provide a high diversity of litter quality
and quantity to belowground systems that subsequently result in a high diversity of
decomposers (Hooper et al. 2000). The specific relationship between aboveground
plant communities and belowground microbial communities is context, system, and
scale dependent (De Deyn and van der Putten 2005; Wu et al. 2011; Cline et al.
2018). For instance, Chen et al. (2018) found that plant diversity is coupled with soil
beta diversity but not soil alpha diversity in grassland systems. Nonetheless, if
aboveground diversity is indeed linked to belowground diversity, then aboveground
estimates of plant diversity and plant traits could provide robust estimates of belowground processes.
Early work that focused on the influence of aboveground species diversity on
litter decomposition yielded idiosyncratic results (Gartner and Cardon 2004;
Hättenschwiler et al. 2005), with some studies reporting no effect of plant species
diversity (e.g., Naeem et al. 1999; Wardle et al. 1999; Wardle et al. 2000; Knops
et al. 2001), some reporting unpredictable results (Wardle and Nicholson 1996), and
some reporting positive effects of plant species diversity on litter decomposition
(Hector et al. 2000). Similar to aboveground processes, BEF studies that link
aboveground diversity with belowground processes initially focused on aboveground species diversity (Scherer-Lorenzen et al. 2007; Ball et al. 2008; Gessner
et al. 2010). The idiosyncratic relationship between species diversity and belowground processes led others to identify aboveground functional diversity and composition as more important to belowground processes than species diversity (Dawud
et al. 2017).
M. Madritch et al.
Variation in plant phenolics is driven by several interacting factors. In general,
polyphenolic concentrations in foliage are highest during the summer months
(Feeny 1970). Summer coincides with both the onset of herbivory and the highest
levels of photosynthetic activity. Herbivory-induced polyphenolic production is a
well-documented aspect of plant-insect interactions (Herms and Mattson 1992;
Baldwin 1994). The composition and quantity of phenolics vary among taxa at
small and large phylogenetic scales. At large phylogenetic scales, condensed tannins are common in woody plants but almost absent in herbaceous species (Haslam
1989). At narrow phylogenetic scales, the concentration of polyphenolics is also
under genetic control, and often there is considerable variation within the same species that can have important influences on belowground processes including litter
decomposition and nutrient cycling (Lindroth et al. 2002; Schweitzer et al. 2005;
Madritch et al. 2006, 2007).
8.3.3 Plant Diversity
Plant diversity, which can be accurately remotely sensed at some spatial scales
(Wang et al. 2019; Gholizadeh et al. 2019), can influence belowground processes
through its effects on productivity as well as on chemical diversity (Meier and
Bowman 2008). Belowground diversity may be intrinsically linked to aboveground
diversity because high plant diversity may provide a high diversity of litter quality
and quantity to belowground systems that subsequently result in a high diversity of
decomposers (Hooper et al. 2000). The specific relationship between aboveground
plant communities and belowground microbial communities is context, system, and
scale dependent (De Deyn and van der Putten 2005; Wu et al. 2011; Cline et al.
2018). For instance, Chen et al. (2018) found that plant diversity is coupled with soil
beta diversity but not soil alpha diversity in grassland systems. Nonetheless, if
aboveground diversity is indeed linked to belowground diversity, then aboveground
estimates of plant diversity and plant traits could provide robust estimates of belowground processes.
Early work that focused on the influence of aboveground species diversity on
litter decomposition yielded idiosyncratic results (Gartner and Cardon 2004;
Hättenschwiler et al. 2005), with some studies reporting no effect of plant species
diversity (e.g., Naeem et al. 1999; Wardle et al. 1999; Wardle et al. 2000; Knops
et al. 2001), some reporting unpredictable results (Wardle and Nicholson 1996), and
some reporting positive effects of plant species diversity on litter decomposition
(Hector et al. 2000). Similar to aboveground processes, BEF studies that link
aboveground diversity with belowground processes initially focused on aboveground species diversity (Scherer-Lorenzen et al. 2007; Ball et al. 2008; Gessner
et al. 2010). The idiosyncratic relationship between species diversity and belowground processes led others to identify aboveground functional diversity and composition as more important to belowground processes than species diversity (Dawud
et al. 2017).
M. Madritch et al.