Pigments and photosynthesis of understory grasses: Light irradiance and soil moisture effects

Abstract

Phleum alpinum L. and Poa pratensis L. are major forage species that often grow in various environments in Tierra del Fuego, Argentina. We performed a greenhouse experiment to investigate how these species acclimate to the different irradiance of the microenvironments where they grow. Both grass species were exposed to three levels of incident irradiance (I4: 4%; I26: 26%, or I64: 64% of ambient sunlight) and two levels of soil moisture content (M30: 30-50% or M60: 60-80% of field capacity) under greenhouse conditions. As irradiance levels increased, the contents of chlorophyll per unit surface area and fresh weight basis increased, and the chlorophyll a/b and carotenoids/chlorophyll ratio also increased. Maximum photosynthetic rate and the light compensation point increased with increasing light availability. Values for these variables varied with time. However, the relationship of these values was not modified in P. alpinum between the irradiance treatments. Contrarily, temporal changes of those variables showed that the maximum photosynthetic rate was similar to that in March in all treatments in P. pratensis. Results indicated that P. alpinum and P. pratensis were able to acclimate to the various experimental environments.