181
Foliar chemistry is relevant to biodiversity and ecosystem functioning studies
because plant chemistry varies widely among and within species and can influence
belowground microbial communities and biogeochemical cycles (Cadisch and
Giller 1997; Hättenschwiler and Vitousek 2000). It follows that variation in foliar
traits important to decomposition (e.g., tannin concentration) will affect belowground microbial communities and the basic biogeochemical cycles that sustain
forested ecosystems. Some studies have supported a chemical diversity approach
toward elucidating the belowground effects of aboveground diversity (Hoorens
et al. 2003; Smith and Bradford 2003). Epps et al. (2007) demonstrated that accounting for chemical variation was more informative regarding decomposition than was
species diversity. While the usefulness of trait-based dissimilarity approaches
remains somewhat equivocal (Frainer et al. 2015), there is increasing support for
such trait-based approaches in explaining variation in leaf litter decomposition
(Fortunel et al. 2009; Finerty et al. 2016; Jewell et al. 2017; Fujii et al. 2017). Handa
et al. (2014) found that variation in leaf litter decomposition across widely different
biomes was largely driven by commonly measured leaf traits such as N, lignin, and
tannin content. At large scales, species traits rather than species diversity per se
appears to at least partially drive variation in decomposition and belowground
nutrient cycling.
In experimental systems, plant communities with high biodiversity result in high
above- and belowground productivity (Tilman et al. 2001). The additional biomass
that an ecosystem produces in diverse assemblages over what is expected from
monocultures is called “overyielding” and has been documented in both grassland
and forest experiments (Grossman et al. 2018; Weisser et al. 2017). The additional
productivity results from several mechanisms acting simultaneously in more diverse
communities, such as reduced pathogen attack, reduced seed limitation, and
increased trait differences leading to “complementarity” in resource uptake (Weisser
et al. 2017). Complementarity in resource use, particularly light harvesting, results
in more efficient use of limiting resources and greater productivity (Williams et al.
2017). Similar patterns of greater productivity with higher diversity are observed in
forest plots globally (Liang et al. 2016) although such patterns are scale dependent,
and do not necessarily hold at large spatial extents (Chisholm et al. 2013). In naturally assembled grasslands, the relationship may not necessarily hold consistently
(Adler et al. 2011). An open question, then, is the extent to which diversity and
productivity are linked at large spatial scales in ecosystems globally. This is a question that can reasonably be addressed with remotely sensed measures of biodiversity
and ecosystem productivity if scaling issues are appropriately considered (Gamon
et al., Chap. 16). Plant diversity influences the quality of inputs and may allow for
niche partitioning among functionally different microbes and may also influence
productivity, the source of inputs of organic matter available to microbes, and
microbial diversity. Through these linkages, foliar diversity has the potential to
influence microbial diversity and function and hence belowground processes (Cline
et al. 2018). The extent to which diversity and productivity, measured aboveground,
can predict belowground microbial and soil processes is a question that is ready to
be tackled at a range of scales across continents.
8 Linking Foliar Traits to Belowground Processes
Foliar chemistry is relevant to biodiversity and ecosystem functioning studies
because plant chemistry varies widely among and within species and can influence
belowground microbial communities and biogeochemical cycles (Cadisch and
Giller 1997; Hättenschwiler and Vitousek 2000). It follows that variation in foliar
traits important to decomposition (e.g., tannin concentration) will affect belowground microbial communities and the basic biogeochemical cycles that sustain
forested ecosystems. Some studies have supported a chemical diversity approach
toward elucidating the belowground effects of aboveground diversity (Hoorens
et al. 2003; Smith and Bradford 2003). Epps et al. (2007) demonstrated that accounting for chemical variation was more informative regarding decomposition than was
species diversity. While the usefulness of trait-based dissimilarity approaches
remains somewhat equivocal (Frainer et al. 2015), there is increasing support for
such trait-based approaches in explaining variation in leaf litter decomposition
(Fortunel et al. 2009; Finerty et al. 2016; Jewell et al. 2017; Fujii et al. 2017). Handa
et al. (2014) found that variation in leaf litter decomposition across widely different
biomes was largely driven by commonly measured leaf traits such as N, lignin, and
tannin content. At large scales, species traits rather than species diversity per se
appears to at least partially drive variation in decomposition and belowground
nutrient cycling.
In experimental systems, plant communities with high biodiversity result in high
above- and belowground productivity (Tilman et al. 2001). The additional biomass
that an ecosystem produces in diverse assemblages over what is expected from
monocultures is called “overyielding” and has been documented in both grassland
and forest experiments (Grossman et al. 2018; Weisser et al. 2017). The additional
productivity results from several mechanisms acting simultaneously in more diverse
communities, such as reduced pathogen attack, reduced seed limitation, and
increased trait differences leading to “complementarity” in resource uptake (Weisser
et al. 2017). Complementarity in resource use, particularly light harvesting, results
in more efficient use of limiting resources and greater productivity (Williams et al.
2017). Similar patterns of greater productivity with higher diversity are observed in
forest plots globally (Liang et al. 2016) although such patterns are scale dependent,
and do not necessarily hold at large spatial extents (Chisholm et al. 2013). In naturally assembled grasslands, the relationship may not necessarily hold consistently
(Adler et al. 2011). An open question, then, is the extent to which diversity and
productivity are linked at large spatial scales in ecosystems globally. This is a question that can reasonably be addressed with remotely sensed measures of biodiversity
and ecosystem productivity if scaling issues are appropriately considered (Gamon
et al., Chap. 16). Plant diversity influences the quality of inputs and may allow for
niche partitioning among functionally different microbes and may also influence
productivity, the source of inputs of organic matter available to microbes, and
microbial diversity. Through these linkages, foliar diversity has the potential to
influence microbial diversity and function and hence belowground processes (Cline
et al. 2018). The extent to which diversity and productivity, measured aboveground,
can predict belowground microbial and soil processes is a question that is ready to
be tackled at a range of scales across continents.
8 Linking Foliar Traits to Belowground Processes