Wernerehl Robert W, Givnish Thomas J
State Botanist, Massachusetts Natural Heritage and Endangered Species Program, Westborough, 01581, MA, USA.
Department of Botany, University of Wisconsin-Madison, Madison, 53706, WI, USA.
Am J Bot. 2025 Jan;112(1):e16457. doi: 10.1002/ajb2.16457. Epub 2025 Jan 8.
Five C grasses (Bouteloua curtipendula, Schizachyrium scoparium, Andropogon gerardii, Sorghastrum nutans, Spartina pectinata) dominate different portions of a moisture gradient from dry to wet tallgrass prairies in the Upper Midwest of the United States. We hypothesized that their distributions may partly reflect differences in flooding tolerance and context-specific growth relative to each other.
We tested these ideas with greenhouse flooding and drought experiments, outdoor mesocosm experiments, and a natural experiment involving a month-long flood in two wet-mesic prairies.
Bouteloua promptly succumbed to inundation, so flooding intolerance likely excludes it from wet and wet-mesic prairies. Competition is likely to exclude short-statured Bouteloua from productive mesic sites. Schizachyrium is excluded from wet prairies by low flooding tolerance, demonstrated by all experiments. Sorghastrum had low flooding tolerance in both greenhouse and natural experiments, suggesting that physiological intolerance excludes it from wet prairies. Spartina had by far the greatest growth under the wettest mesocosm conditions; this and comparisons of species growth in monocultures vs. mixtures suggests that competition helps it dominate wet prairies. Indeed, quadrat presence of Spartina increased by 57% two years after flooding of two prairies, while that of upland grasses declined by 44%. The high flooding tolerance, lack of significant differences from other species in drought tolerance, and tall stature of Andropogon suggest that broad physiological tolerance combined with competitive ability allows it to thrive across the prairie moisture gradient.
Flooding helps shape the distributions of dominant prairie grasses, and its effects may become more important as extreme rain events continue to increase.
在美国中西部上游，五种C4禾本科植物（垂穗草、糙毛裂稃草、大须芒草、星毛冠芒草、栉叶碱茅）在从干旱到湿润的高草草原的不同湿度梯度区域占主导地位。我们假设它们的分布可能部分反映了彼此在耐淹性和特定环境下生长方面的差异。
我们通过温室淹水和干旱实验、室外中型生态系统实验以及一项涉及两个湿润中生草原为期一个月洪水的自然实验来验证这些想法。
垂穗草很快就被水淹致死，因此不耐水淹可能使其无法生长在湿润和湿润中生草原。竞争可能会使矮小的垂穗草无法生长在生产力较高的中生地带。所有实验均表明，糙毛裂稃草因耐淹性低而无法生长在湿润草原。在温室和自然实验中，星毛冠芒草的耐淹性都很低，这表明生理上的不耐受使其无法生长在湿润草原。在最湿润的中型生态系统条件下，栉叶碱茅的生长量是最大的；这一点以及单一栽培与混栽条件下物种生长的比较表明，竞争有助于其在湿润草原占主导地位。事实上，在两个草原被水淹两年后，栉叶碱茅的样方出现率增加了57%，而高地禾本科植物的样方出现率下降了44%。大须芒草耐淹性高、耐旱性与其他物种无显著差异且植株高大，这表明广泛的生理耐受性与竞争能力使其能够在整个草原湿度梯度上生长繁茂。
水淹有助于塑造优势草原禾本科植物的分布，随着极端降雨事件持续增加，其影响可能会变得更加重要。
