Soil water effect on crop growth, leaf gas exchange, water and radiation use efficiency of Saccharum spontaneum L. ssp. aegyptiacum (Willd.) Hackel in semi-arid Mediterranean environment

Great effort has been placed to identify the most suited bioenergy crop under different environments and management practices, however, there is still need to find new genetic resources for constrained areas. For instance, South Mediterranean area is strongly affected by prolonged drought, high vapour pressure deficit (VPD) and extremely high temperatures during summertime. In the present work we investigated the soil water effect on crop growth and leaf gas exchange of Saccharum spontaneum L. ssp. aegyptiacum (Willd.) Hackel, a perennial, rhizomatous, herbaceous grass. Furthermore, the net increase of biomass production per unit light intercepted [radiation use efficiency (RUE)] and per unit water transpired [water use efficiency (WUE)] was also studied. To this end a field trial was carried out imposing three levels of soil water availability (I₁₀₀, I₅₀ and I₀, corresponding to 100%, 50% and 0% of ETm restutition) under a semi-arid Mediterranean environment. Leaf area index (LAI), stem height, biomass dry matter yield, CO₂ assimilation rate, and transpiration rate resulted significantly affected by measurement time and irrigation treatment, with the highest values in I₁₀₀ and the lowest in I₀. RUE was the highest in I₁₀₀ followed by I₅₀ and I₀; on the other hand, WUE was higher in I₀ than I₅₀ and I₁₀₀. At LAI values greater than 2.0, 85% photosynthetically active radiation was intercepted by the Saccharum stand, irrespective of the irrigation treatment. Saccharum spontaneum spp. aegyptiacum is a potential species for biomass production in environment characterized by drought stress, high temperatures and high VPD, as those of Southern Europe and similar semi-arid areas.