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

Abstract

Phleum alpinum and Poa pratensis are major forage species that often grow in various environments in Tierra del Fuego, Argentina. To investigate how these species acclimate to the different irradiance of the microenvironments where they grow we performed a greenhouse experiment. 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 relationships chlorophyll a/b and carotenoids/chlorophyll also increased. Maximum photosynthetic rate and light compensation point increased as light availability also increased. Values for these variables varied with time. However, the relationship of these values between the irradiance treatments was not modified in P. alpinum. Contrarily, temporal changes of those variables determined 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 study environments.