Shade alters grass growth and architecture by reducing root biomass

Variable tree cover characterizes tropical grassy biomes. Light
availability in the ground layer becomes increasingly limited as tree
cover increases while open canopy environments are associated with a
flammable grassy ground layer. Grass species dominating the ground layer
of these ecosystems have adopted strategies to persist and proliferate
with frequent fire. However, there is limited understanding of how grass
growth and flammability traits respond to changes in light availability.
We experimentally grew 14 grass species characteristic of the Malagasy
Central Highlands for one year with four treatments of light exclusion
ranging from 0 – 60%. Six plant functional traits and four leaf
flammability traits were measured: plant height, bulk density, aboveground
biomass, belowground biomass, ratio of root to shoot biomass, specific
leaf area, leaf heat release capacity, temperature of maximum
decomposition, total heat release and peak heat release rate. Belowground
biomass, the ratio of root to shoot biomass and bulk density were
substantially negatively affected by decreasing light availability while
aboveground biomass showed no significant change although, there was a
trend towards smaller plants at high shade. Specific leaf area increased
with declining light availability. In terms of leaf flammability,
unexpectedly, only leaf total heat release was significantly positively
affected and the other traits were not. These suggest that any field
alterations in grass flammability would be primarily underpinned by
changes in plant architecture and potentially microclimate. The reductions
observed in belowground biomass suggests that grasses would be rapidly
lost from shaded environments with a diminished competitive capacity to
resprout.