American Journal of Botany最新文献

Premise: Phelipanche ramosa is an economically damaging parasitic plant that has been reported in North America since the late 1800s. While this species comprises a variety of genetically distinct host races in its native range, the genetic composition of adventive populations in the New World remains unexplored. On the basis of morphological and ecological variation, some have suggested that the closely related P. nana may also be present.

Methods: Genome skimming was used to assess the relationships of 30 populations of Phelipanche spanning the geographic and host ranges in North and South America, plus one P. nana reference population from Lebanon.

Results: Phylogenetic analysis indicated four distinct genetic groups, though plastome and nrDNA data supported conflicting signals of relationships among them. First, specimens from Chilean tomato fields were nearly indistinguishable genetically from the reference P. nana. Second, a pair of samples from Virginia showed similar nrDNA as the first group, but divergent plastomes. The remaining 24 samples sorted into two groups, one which parasitizes cultivated plants, especially tomato, and the other on roadside weeds in different parts of the United States.

Conclusions: The geographic and ecological cohesiveness of four distinct genetic groups supports a hypothesis of multiple introductions to the Americas, presumably from Eurasia, followed by little to no subsequent gene flow among them. However, such groups do not align with existing morphological or ecological species concepts for P. ramosa and P. nana. In practice, threat assessment of Phelipanche populations to agricultural settings should be evaluated regionally given the phylogeographic and ecological heterogeneity.

Premise: Five C₄ 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.

Methods: 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.

Results: 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.

Conclusions: Flooding helps shape the distributions of dominant prairie grasses, and its effects may become more important as extreme rain events continue to increase.

Microbes regulate many dimensions of plant performance with multiscale implications for plant fitness, competition, coexistence, and ecosystem functioning. Yet, this fascinating and diverse arena of study has been limited to a few thematic areas, ecosystems, and regions. In particular, despite growing evidence that microbes may be critical players in the dynamics of plant communities in tropical and subtropical ecosystems, these regions remain poorly represented in studies of plant–microbe interactions. Such geographical gaps limit our ability to draw general inferences to comprehend how microbial effects on plant community dynamics may vary with context and, by extension, respond to global environmental change. In this special section of the American Journal of Botany, we bring together a diverse set of research on plant–microbe interactions from tropical and subtropical ecosystems. These papers explore intraspecific variation of soil microbial communities, the context dependency of host-specific assembly of microbial communities on plants, and the new and exciting frontier of the microbiome of epiphytic plants. We hope that this compilation will fuel deeper forays into the many dimensions of plant–microbe interactions in megadiverse tropical and subtropical forests.