University of Minnesota
University of Minnesota
College of Biological Sciences

e244 - Natural Enemies, Plant Diversity and Plant Community Composition




Past work at CDR has shown that disease and insect herbivory are reduced in high-diversity plant communities (Mitchell et al. 2003, Haddad et al. 2011, Schnitzer et al. 2011), and that their lower abundances may contribute to the higher productivity observed at higher plant diversity. However, such short-term studies cannot address the possibility of long-term feedbacks between plant composition, plant diversity, microbial diversity, pathogens, and herbivores. To explore such feedbacks, we established two experiments (E244 and E245) in 2008 that use insecticides, fungicides, and fences to manipulate the presence of insects, soil fungi, foliar fungi, or vertebrate herbivores. The first experiment (E244) is nested within 32 BigBio plots (E120, section 3.1.1) such that the fungicide and insecticide treatments are crossed with plant community diversity. The second experiment (E245) is conducted in an old field and has an additional treatment (unfenced, or fenced to exclude vertebrate herbivores). In both experiments, we apply treatments and measure NDVI weekly to bi-weekly throughout the growing season in all plots. We annually harvest biomass of each plant species, determine plant species diversity, and sample root biomass in all 253 experimental plots.

These experiments test three hypotheses. (H1) Herbivore and microbe-induced reductions in productivity will be smaller in high-diversity than low-diversity plant communities (Mitchell et al. 2003, Schnitzer et al. 2011, Hillebrand et al. 2007). (H2) Exclusion of any consumer group reduces plant diversity, increases dominance of competitive species, and increases total aboveground herbaceous biomass (Hillebrand et al. 2007, Gruner et al. 2008, Schnitzer et al. 2011). (H3) Reduced fungal load leads to later leaf senescence and greater aboveground and seed biomass (Batrelsen et al. 2001, Bryson et al. 2000, Wise and Mueller 2011, Wu and von Tiedemann 2001).

Key Results


Counter to H2, plant diversity in the old field plots (E245) was higher in fungicide- and insecticide-treated plant communities after three years of treatment. Vertebrates had no effect on plant diversity, again counter to H2. While consumers did not alter plot-scale productivity in the old fields (Borer et al. In Prep), reduced fungal loads in the BigBio experiment (plots E244) led to increased plant productivity, with the greatest effects occurring in high-diversity plant communities (Kinkel et al. In Prep), in contrast to H1. Finally, foliar fungicides led to more rapid early-season increases in plant biomass and delayed senescence as predicted by H2 (Montgomery et al. In Prep).

Future Research


The first years of this experiment have shown that altered consumer compositions impact both plant diversity and productivity, but have not revealed if the plant changes are transient, nor if the changes in plant productivity and diversity may themselves impacts other aspects of the functioning of these systems. Therefore, we will continue to gather the data needed to test our original hypotheses.

We also will explore long-term feedbacks between consumers and plants and the effects of these feedbacks on community and ecosystem function. A growing body of evidence is showing important short- and long-term feedbacks between plant composition, productivity, and decomposition and vertebrates (Duffy 2002), invertebrates (Eisenhauer et al. 2011), and microbial heterotrophs (Diez et al. 2010, Kardol et al. 2007, Kulmatiski et al. 2008). We will use our experiment to examine two major areas in which feedbacks may be important in controlling ecosystem processes. First, our early result that productivity is independent of foodweb composition in natural plant communities (E245) but elevated with removal of fungi in the controlled BigBio communities (E244) suggests that feedbacks between foliar fungi and plant composition may be critical for understanding productivity in natural grasslands. In addition, while productivity was not altered in the early years of the experiment, long-term feedbacks between consumers and plant production could arise via positive feedbacks in which enemy removal leads to increased productivity, increasing soil nutrients and C. Alternatively negative feedbacks may arise because simplified foodwebs, particularly if lacking soil decomposers, lead to long-term accumulation of litter, reducing N mineralization and ground-level light, leading to a long-term reduction in diversity and productivity.

Methods for e244


Datasets for e244: Natural Enemies, Plant Diversity and Plant Community Composition

Dataset IDTitleRange of Years (# years with data)
adte244Leaf carbon, nitrogen and phosphorus2011-2011 (1 year)
aete244Multispectral Radiometry percent reflectance2008-2014 (7 years)
ple244Plant aboveground biomass data2007-2013 (7 years)
pce244Plant species percent cover data2008-2013 (6 years)
roote244Root biomass data2009-2014 (6 years)