Tallgrass Prairie & Oak Savanna Fire Science

“Grass species with smoke-released seed dormancy: A response to climate and fire regime but not photosynthetic pathway”

This open access article was published Oct. 17, 2022 in Plant Biology. Access the article via the permanent web address (DOI) (https://doi.org/10.1111/plb.13479)

Abstract

Both C3 and C4 photosynthetic pathways and smoke-released seed dormancy occur among grasses. C4 species evolved from C3 species as seasonality and fire frequency increased and might therefore imply that their smoke sensitivity increased.

I searched the worldwide literature for reports on germination responses among grasses, whose photosynthetic pathway was known, to treatment by smoke. Data were obtained for 217 species and 126 genera. While subfamilies tended to be C3 (Pooideae), C4 (Chloridoideae) or a mixture (Panicoideae), a beneficial smoke response was independent of their photosynthetic pathway. The only exceptions were Danthonioideae (C3, non-smoke responsive) and Triodia (C4, smoke responsive). One third of both C3 and C4 genera were smoke responsive.Even within genera, 90% of species showed contrasting smoke responses, confirming that smoke sensitivity is rarely taxonomically constrained.

Data on photosynthetic pathway, climate, fire regime and vegetation were compiled for 15 regions that formed four distinct groups: 1) In warm climates with aseasonal rainfall, C4 grasses are moderately better represented, with crown fires and limited smoke responses. 2) In cool regions, most species are C3, with surface-crown fires and lack smoke responses. 3) In warm regions with summer rain (savannas), most species are C4, with surface fires and lack smoke responses. 4) In Mediterranean-climate regions with summer drought, most species are C3, with crown fires and smoke-released dormancy. Thus, even though C3 and C4 grasses are equally capable of expressing smoke sensitivity, their response depends on the region’s climate and fire regime that also dictate which photosynthetic pathway dominates.

Highlights

On a world scale, smoke-released seed dormancy exists equally among 40% of C3 and C4 grass species and one-third of genera and is not taxonomically constrained.
Some floras have only C3 grasses (summer dry) and some only C4 (summer wet) and most are dominated by one or the other.
Smoke sensitivity and photosynthetic pathway are readily divided into four regional types based on climate and fire regime.
Smoke sensitivity is poorly represented in frequently-burnt C4 grassland/savannas but is almost universal in intensely-burnt C3 mediterranean shrubland/forests.
Moderate levels of smoke sensitivity among C3/C4 grasses under intermediate climates confirm that the presence/absence of smoke sensitivity elsewhere is unrelated to photosynthetic pathway.

Keywords: C3; C4; grasses; photosynthetic pathways; savanna; seed germination; smoke

Citation

Lamont, Byron B. "Grass species with smoke‐released seed dormancy: A response to climate and fire regime but not photosynthetic pathway." Plant Biology (2022).