Monday, November 13, 2006

Growth Temperature and Carbon Dioxide Concentration Alters Forage Quality and Spectral Reflectance Patterns in Virginia Wildrye (Elymus virginicus L.).

Satya Sai Kumar Matcha1, Vijaya G. Kakani2, Giridara K. Surabhi1, and K. R. Reddy1. (1) MIssissippi State University, 117 Dorman Hall, Plant and Soil Sciences, Box 9555, Mississippi State, MS 39762, (2) University of Florida, Mississippi State, MS 39762

Remotely sensed leaf and canopy level information at various growth stages of native grass, Virginia wildrye (VWR) (Elymus virginicus L.) can be used to assess the impacts of changing climate on biomass yield and nutritive quality. An experiment was conducted in naturally-lit controlled environmental units in which VWR plants were grown in pots at five levels of temperature from18/10 to 38/30ºC and two CO2 concentrations ([CO2]) (360 and 720 mL L-1). Plants were supplied with half strength Hoagland’s nutrient solution for maintaining optimum water and nutrient levels. An ASD FieldSpec FR spectroradiometer was used to measure hyperspectral reflectance at both leaf and canopy levels. Simultaneously, growth, leaf pigments and leaf and stem forage quality parameters were measured and correlated with individual spectra and spectral ratios. Total plant dry weight, and dry weights of leaves, stems and roots decreased with increase in temperature. Elevated [CO2] did not alter either plant dry weights or plant response to temperature. Leaf protein content increased with increase in temperature in both [CO2] levels, and plants grown in ambient [CO2], in general, showed higher protein content. Correlation analysis showed that forage quality parameters such as crude protein (CF), neutral detergent fiber (NDF) and acid detergent fiber (ADF) can be estimated using specific waveband ratios better than single wavebands; R765/R975 for CF, R725/R1682 for NDF and R735/R1285 for ADF. Our results suggest that remote sensing techniques can be used to quantify forage quality both in the present and future warmer and elevated [CO2] conditions.