Aspen genotypes create patches of ecosystem functioning that influence leaf litter decomposition

It is becoming increasingly apparent that the genetic variation within species is important to ecosystem level processes.  Recent research demonstrates that plant genotype influences litter decomposition, soil microbial communities, and belowground nutrient cycling.  However, the extent to which plant genotypes create spatial mosaics of genetically-mediated ecosystem processes is unclear.  Likewise, it is unknown whether plant genotypes create distinct microbial communities that are adapted to process genotype-specific leaf litter.  In central Wisconsin, USA, aspen (Populus tremuloides) clones have naturally colonized reclaimed agricultural land to create genetically distinct aspen stands. Using these natural aspen patches, we performed a litter transplant study in which leaf litter from different aspen genotypes was collected and allowed to decompose beneath multiple aspen genotypes. We use PLFA and extracellular soil enzyme activity profiles to demonstrate that different soil microbial communities developed beneath different clones. We then show that these differences in microbial communities influenced both leaf litter decomposition and belowground nutrient cycling such that native and foreign genotype litter was processed differently depending upon the genetic identity of the aspen stand in which it was placed. In addition, leaf litter decomposed fastest when placed beneath its own canopy. These results highlight a potential feedback mechanism through which plant genotype may influence plant fitness through nutrient availability.  They also demonstrate that the genotypes of forest tree species can create spatial mosaics of ecosystem functioning that control the rate of litter decomposition and nutrient release.