Reproduction for one American grass is an open and shut case

New insights into the reproductive habits of a perennial grass, Danthonia compressa, may offer clues to understanding plant survival under changing environments. Gregory Cheplick’s research, published in AoB PLANTS, deciphers the dual reproductive strategy of this grass species, demonstrating how it adapts to fluctuating environmental conditions.

Danthonia compressa employs two types of reproduction: chasmogamous (CH) and cleistogamous (CL). Chasmogamous reproduction involves open flowers allowing cross-pollination, while cleistogamous involves self-fertilising closed flowers. Interestingly, these different flower types contribute to the plant’s survival in diverse conditions. The difference between the flowers starts with the panicles. A panicle is a flower cluster or inflorescence found in many plant species. It is characterised by a main stem (the rachis) with branches that further subdivide into smaller branches, each of which ends in a flower. Chasmogamous flowers grow on terminal panicles at the top of the plant. In contrast, cleistogamous flowers develop on axillary panicles, off the side of the plant, and also at the grass base as a “cleistogene.

Cheplick’s research showed that chasmogamous and cleistogamous reproductive habits displayed differing rates of seed set and fecundity across different habitats and over time. He discovered that chasmogamous reproduction was generally more variable, potentially impacted more by environmental changes, whereas cleistogamous reproduction was more stable. The axillary cleistogamous spikelets, including the basal cleistogene, provided additional fecundity, particularly in sunny environments and larger plants, highlighting the ecological significance of cleistogamy to plant fitness.

The study suggests that the heavy cleistogene could be critical for population persistence, acting analogously to the axillary bud bank of other perennial grasses. Essentially, a bud bank is a population of dormant buds that allows a plant to regrow after disturbances, such as grazing or fire.

The research also notes that larger tillers (the individual plants in a grass clump) produced heavier cleistogenes, suggesting that environmental conditions promoting plant growth can affect the reproductive strategy and success of Danthonia compressa. This indicates an intricate link between environment, plant size, and reproductive tactics. Cheplick concludes: 

Analysis of the patterns of CH and CL reproduction in the native perennial grass D. compressa showed spatial and temporal variation in the two reproductive modes over a 5-year period. Relative to CH reproduction, fecundity, seed mass and biomass allocation were less variable for CL reproduction from year to year. Axillary CL seeds and especially the large basal cleistogene were much heavier than CH seeds made on terminal panicles. Also, both axillary CL seed production and cleistogene mass increased with increasing tiller mass and matured later in the season than CH seeds. The undispersed CL seeds are likely to be important to seedling establishment within the maternal habitat and could function to maintain populations, especially along woodland edges where this species mostly occurs.

Cheplick 2023

READ THE ARTICLE
Cheplick, G.P. (2023) “Spatiotemporal variation of chasmogamy and cleistogamy in a native perennial grass: fecundity, reproductive allocation and allometry,” AoB PLANTS, 15(3), p. lad020. Available at: https://doi.org/10.1093/aobpla/plad020.