Settling velocity and pollination in the grass Diarrhena obovata

By Phillip C. Klahs

Inflorescence of Diarrhena obovata

Pollination is accomplished when pollen grains, containing male genetic information, are moved between plants and arrive at a flower with female flower parts. This is an important step in plant reproduction, and development of the seed will not occur until after fertilization. The pollen of wind pollinated plants must travel through the air to reach other plants, and to be successful in this journey pollen grains need to float in the air and travel with the wind. Settling velocity is a measurement of how fast objects fall, and tells us how long something will float in the air and the distances it can travel with certain wind speeds. Weight, density, and bumpy surface features affect the aerodynamics of the pollen grain, and these attributes can work together to slow the settling velocity.

Diarrhena obovata is a flowering plant in the grass family Poaceae that utilizes wind pollination, but lives in forest understories where wind is more turbulent and slower on average than open habitats. The blooming of D. obovata flowers and the aerodynamic properties of its pollen grains have evolved to ensure successful pollination in forest and edge habitats. This study tested when the flowers of D. obovata bloomed and how fast the pollen grains can fall through a column of still air, and determined they have a measured settling velocity of 3.77 meters per second. This is the first time the settling velocity of a forest grass has been measured even though the grass family is important ecologically and economically. 

Read the scientific publication in JPE.

Botanical gardens as arks for conserving pollinators and plant-pollinator interactions

 by Vilella-Arnizaut et al.

 

Botanical gardens have contributed to plant conservation in numerous ways for decades. However, little is known about the potential impact botanical gardens may have on pollinator conservation. This gap in knowledge is worth investigating since pollinator populations are experiencing global declines, partially due to habitat loss, among other factors. We are interested in understanding whether botanical gardens can function as a potential source for pollinator habitat, such as in native restoration gardens, in the hopes of aiding in the conservation of local pollinator populations.

Our study takes place in the Prairie Coteau region of South Dakota, where we sampled the plant and pollinator communities of 15 native temperate grassland remnants and 1 native grassland restoration site managed as part of a botanical garden. We compared the plant and pollinator communities to see whether the diversity of a native grassland restoration area inside a botanical garden is similar to the diversity found in remnant temperate grassland sites of the same region. We also analyzed these communities using an ecological network approach to examine how plant-pollinator communities in native temperate grasslands differ structurally from a native grassland restoration garden.

We found pollinator diversity within the botanical garden’s native grassland restoration site to be at the high end of the distribution of the remnant temperate grassland sites throughout the entire flowering season. The plant diversity and network community metrics remained similar between the two environments, except that remnant temperate grasslands had more links with pollinators than their garden counterpart. Nevertheless, these two environments did not experience much community overlap, suggesting the restoration grassland garden may demonstrate similar, or in some cases – greater diversity to native temperate grassland remnants in the same region. However, these two environments did not necessarily share the same kinds of plants and pollinators. 

Overall, our findings illustrate the promising role that native grassland restoration gardens within botanical gardens may play as refugia for local pollinator communities by supporting plant-pollinator interactions comparable to those found in native habitat remnants in the same region. Further research into this knowledge gap regarding the role of botanical gardens in pollinator conservation may help bolster current efforts to decelerate the global pollinator decline.

Read the scientific publication in JPE.