Abstract
The presence of grassland biomes and species cannot be predicted by examining bottom up causes such as precipitation and temperature. Top down causes including herbivory and fire seem to be major controlling aspects with other factors secondary. We examined soil depth and competitive ability of two North American C4 grasses in a greenhouse experiment. Changes in dry mass were determined and competitive intensity was calculated for both species. Species were grown separately or together in pots 30, 90, or 180 cm deep. When grown in monoculture, Schizachyrium scoparium total and belowground dry mass increased from the 30 to 90 cm depth, with no further significant increase from 90 to 180 cm. Aboveground dry mass did not increase significantly with depth. Total dry mass of Buchloe dactyloides increased significantly with depth when grown in monoculture. Aboveground dry mass increased from 30 to 90 cm depth but not from 90 to 180 cm. Belowground dry mass of B. dactyloides did not increase significantly with depth. In 180 cm pots, 53% of S. scoparium root dry mass was in the top 30 cm; 74% of B. dactyloides root dry mass was in the top 30 cm. Roots of B. dactyloides were not found deeper than 90 cm. Aboveground dry mass of S. scoparium was not different in mixture or monoculture at any depth. Buchloe dactyloides aboveground dry mass in mixture was significantly lower than monoculture at the 30 cm depth, but not at 90 or 180 cm. The greatest competitive intensity was in the shallow soil pots. Soil depth could partially explain mosaics found in C4 grasslands where both species were found together with S. scoparium on deeper soils and B. dactyloides on shallower soils.
Highlights
Native prairies in North America once covered almost four million km2, but today only about one percent remains, with most converted to domestic use [1]
No significant differences were found in aboveground dry mass plant−1 of Schizachyrium scoparium with increasing soil depth; aboveground dry mass doubled in the 90 cm pots and remained the same at 35.5 ± 7.1 g·plant−1 dry mass in the 180 cm pots (Figure 1(a))
Total dry mass for S. scoparium increased from 20 g·plant−1 to 42 g·plant−1 and to 48 g·plant−1 as soil depth increased (Figure 1(c)), with dry mass being significantly different in the 90 and 180 cm pots compared to the 30 cm pots, but deeper pots were not significantly different from each other
Summary
Native prairies in North America once covered almost four million km, but today only about one percent remains, with most converted to domestic use [1]. Grassland communities’ seem relatively uniform, but on a small scale, they resemble a mosaic of miniature successions or patches and species composition may be controlled by different factors including resources [3,4]. These successions start with large or small scale distur-. Bances creating patches or openings caused by fire, burrowing animals, large or small grazers, and drought [3] These gaps or patches may serve as a reset mechanism [5] to reopen mature grasslands to early successional species [3] and proceed in time toward a mature community. These patches may contain few or many species in various combinations and should be viewed both temporally and spatially [6]
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