Effects of two water regimes on morphological traits, nutritive value and physiology of three Bituminaria bituminosa varieties from the Canary Islands

Morphological traits, nutritive values and physiological responses to two different water regimes of three Bituminaria bituminosa varieties: var. albomarginata, var. crassiuscula and var. bituminosa were evaluated in a greenhouse experiment. Two water regimes were imposed for 63 days; well-watered (WW) plants and deficit-watered (DW) plants, both starting from a high soil water content (dripping point). The three varieties showed similar aerial biomass reduction under reduced watering, 50% for var. albomarginata, 51% for var. bituminosa and 43% for var. crassiuscula. Var. Albomarginata showed lower shoot biomass under both water regimes than var. bituminosa (56.2% in WW plants and 55.2% in DW plants) and var. crassiuscula (52% in WW plants and 57.8% in DW plants). This lower shoot biomass could be attributed to the high initial soil water content imposed in this experiment, affecting early development. This hypothesis is supported by the lower root biomass production of var. albomarginata and its distribution. The DW treatment of this experiment was not sufficiently restrictive to cause morphological modifications, whilst of the forage quality variables analysed, only ash was affected. Var. crassiuscula and var. albomarginata had a lower specific leaf area (239 cm(2) g(-1) and 235 cm(2) g(-1), respectively) than var. bituminosa (352 cm(2) g(-1)), which might represent an important adaptation to high light intensity and temperature conditions. The values of stem mass fraction (SMF) and leaf mass fraction (LMF) for var. crassiuscula (SMF = 0.36 and LMF = 0.28) and var. albomarginata (SMF = 0.35 and LMF = 0.36) indicated better forage aptitude of these varieties than var. bituminosa (SMF = 0.50 and LMF = 0.19). All varieties showed good values of crude protein and digestibility, although important differences were found between leaf and stem. According to the studied morphological, nutritional and physiological traits, var. albomarginata showed the best aptitude for being introduced as permanent grasslands in some Mediterranean farming systems. However, the possible susceptibility of var. albomarginata to high water content in the soil could limit its introduction. These results help to inform the potential use of these three Canarian B. bituminosa varieties to improve Mediterranean rainfed grasslands of extensive farming systems.