Ezio Riggi

Physiological responses of Arundo donax ecotypes to drought: a common garden study

Genetic analyses have suggested that the clonal reproduction of Arundo donax has resulted in low genetic diversity. However, an earlier common garden phenotyping experiment identified specimens of A. donax with contrasting biomass yields (ecotypes 6 and 20). We utilized the same well‐established stands to investigate the photosynthetic and stress physiology of the A. donax ecotypes under irrigated and drought conditions. Ecotype 6 produced the largest yields in both treatments. The A. donax ecotypes exhibited identical high leaf‐level rates of photosynthesis (PN) and stomatal conductance (Gs) in the well‐watered treatment. Soil drying induced reductions in PN and Gs, decreased use of light energy for photochemistry, impaired function of photosystem II and increased heat dissipation similarly in the two ecotypes. Levels of biologically active free‐abscisic acid (ABA) and fixed glycosylated‐ABA increased earlier in response to the onset of water deficit in ecotype 6; however, as drought progressed, the ecotypes showed similar increases in both forms of ABA. This may suggest that because of the low genetic variability in A. donax the genes responding to drought might have been activated similarly in the two ecotypes, resulting in identical physiological responses to water deficit. Despite the lack of physiological ecotypic differences that could be associated with yield, A. donax retained a high degree of PN and biomass gain under water deficit stress conditions. This may enable utilization of A. donax as a fast growing biomass crop in rain‐fed marginal lands in hot drought prone climates.

Moderate Drought Stress Induces Increased Foliar Dimethylsulphoniopropionate (DMSP) Concentration and Isoprene Emission in Two Contrasting Ecotypes of Arundo donax

The function of dimethylsulphoniopropionate (DMSP) in plants is unclear. It has been proposed as an antioxidant, osmolyte and overflow for excess energy under stress conditions. The formation of DMSP is part of the methionine (MET) pathway that is involved in plant stress responses. We used a new analytical approach to accurately quantify the changes in DMSP concentration that occurred in two ecotypes of the biomass crop Arundo donax subject to moderate drought stress under field conditions. The ecotypes of A. donax were from a hot semi-arid habitat in Morocco and a warm-humid environment in Central Italy. The Moroccan ecotype showed more pronounced reductions in photosynthesis, stomatal conductance and photochemical electron transport than the Italian ecotype. An increase in isoprene emission occurred in both ecotypes alongside enhanced foliar concentrations of DMSP, indicative of a protective function of these two metabolites in the amelioration of the deleterious effects of excess energy and oxidative stress. This is consistent with the modification of carbon within the methyl-erythritol and MET pathways responsible for increased synthesis of isoprene and DMSP under moderate drought. The results of this study indicate that DMSP is an important adaptive component of the stress response regulated via the MET pathway in A. donax. DMSP is likely a multifunctional molecule playing a number of roles in the response of A. donax to reduced water availability.