Niche differences in phenology and rooting depth promote coexistence with a dominant C₄ bunchgrass

Abstract

Spatial and temporal niche differentiation are potential mechanisms of plant species’ coexistence in many communities, including many grasslands. In a 6-year field experiment, a dominant prairie bunchgrass, Schizachyrium scoparium, excluded species sharing similar phenology and rooting depth, but coexisted with species differing in phenology and rooting depth. We used a series of experimental plots that differed in S. scoparium abundance to measure the effect of S. scoparium on abundances of other species and on soil nitrate concentrations across time and depth. Because we found that S. scoparium most strongly reduced soil nitrate levels at mid-season and at shallow depths, we hypothesized that at higher S. scoparium abundance, species with mid-season phenology and shallow roots would be excluded and that deep-rooted and early season species would be more likely to persist. As predicted, the proportional number and cover of species exploiting different niches than S. scoparium (early season and deep-rooted species) increased across the S. scoparium abundance gradient. This work provides novel empirical evidence for the factors that contribute to species coexistence in the field. Our study suggests that spatial and temporal niche differentiation promote species coexistence in these grasslands.

Appendix

The appendix lists species found in the study and their phenology and rooting depth classification. B/P indicates species that exhibit both biennial and perennial life history at Cedar Creek Natural History Area. W. Annual indicates winter annual species, which germinate in the fall, overwinter as seedlings, and in the summer produce seed that germinates during the same growing season.

Species	Phenology	Rooting depth	Photo-synthetic pathway	Number of plots present	Life history
Agropyron repens	Early	Deep	C3	28	Perennial
Berteroa incana	Early	Deep	C3	12	B/P
Lychnis alba	Early	Deep	C3	16	B/P
Poa pratensis	Early	Deep	C3	14	Perennial
Polygonum convolvulus	Early	Deep	C3	16	Annual
Rudbeckia serotina	Early	Deep	C3	4	B/P
Vicia villosa	Early	Deep	C3	21	W. annual
Agrostis alba	Early	Shallow	C3	4	Perennial
Agrostis scabra	Early	Shallow	C3	2	Perennial
Crepis tectorum	Early	Shallow	C3	2	Biennial
Hedeoma hispida	Early	Shallow	C3	14	Annual
Lepidium densiflorum	Early	Shallow	C3	8	W. annual
Oxalis stricta	Early	Shallow	C3	2	Perennial
Rumex acetosella	Early	Shallow	C3	3	Perennial
Silene antirrhina	Early	Shallow	C3	4	Annual
Andropogon gerardi	Mid	Deep	C4	4	Perennial
Asclepias syriaca	Mid	Deep	C3	3	Perennial
Erigeron canadensis	Mid	Deep	C3	4	W. annual
Monarda fistulosa	Mid	Deep	C3	11	Perennial
Panicum oligosanthes	Mid	Deep	C4	2	Perennial
Petalostemum candidum	Mid	Deep	C3	1	Perennial
Sorghastrum nutans	Mid	Deep	C4	1	Perennial
Verbascum thapsus	Mid	Deep	C3	3	Biennial
Ambrosia artemisiifolia	Mid	Shallow	C3	14	Annual
Digitaria ischaemum	Mid	Shallow	C4	13	Annual
Setaria lutescens (glauca)	Mid	Shallow	C4	10	Annual