Xylem morphology determines the drought response of two Arundo donax ecotypes from contrasting habitats

Abstract

Arundo donax exhibits rapid growth and requires little nutrient input, making it an ideal perennial biomass crop species. However, this growth is accompanied by high rates of water use, potentially restricting the use of A. donax in rain-fed marginal lands. Here, we investigated the physiological and morphological responses to drought in two ecotypes of A. donax from contrasting habitats: one from an arid environment in Morocco, and the second from a warm humid sub-Mediterranean climate in central Italy. Prolonged drought resulted in identical reductions in leaf-level photosynthesis (P N ) and stomatal conductance (G s ) in the two ecotypes. However, water deficit induced an increase in xylem vessel diameter in the Moroccan plants, improving the movement of water along the stem, but also likely reducing the resistance to embolism. In contrast, the Italian ecotype reduced xylem vessel area, thus increasing resistance to water transport and xylem embolism. The increased xylem vessel size and associated vulnerability to embolism in the Moroccan plants may have contributed to an increase in the loss of leaf numbers, but also to higher relative water content (RWC) in the remaining leaves in comparison to the Italian ecotype, where a greater number of leaves persisted. Despite the Moroccan plants possessing stems with a lower basal area than their Italian counterparts, both ecotypes exhibited identical leaf to supporting stem area ratios under both control and water deficit conditions. This may account for the similarities observed in leaf area measures of P N and G s in this and previous studies of different A. donax ecotypes. Selection of A. donax ecotypes on the basis of xylem responses to drought may facilitate the development of varieties suited to arid environments prone to severe drought and wetter habitats where prolonged droughts occur less frequently.

Giant reed genotypes from temperate and arid environments show different response mechanisms to drought

“…As expected, the decrease in g s was accompanied by a decrease in P n (Fig. 1) in a typical hyperbolic relationship fashion confirming a strong diffusive limitation to P n under DR conditions (Nackley et al 2014, Haworth et al 2017a, 2017b. Consistently with biomass production, P n and g s decreased, respectively, by 30 and 59% with DR.…”

“…) in order to match the canopy water demands with the available soil water. Moreover, intra‐specific differences in hydraulic conductivity at the stems xylem vessels level have been previously reported for both genotypes; with the Moroccan genotype showing an increased xylem vessel diameter and therefore a larger hydraulic conductivity (Haworth et al ).…”

“…On the other hand, stem xylem vessels area and hydraulic conductance seem to be major constrains to maintain a higher water status in giant reed. Haworth et al () found that the Moroccan genotype increased its mean stem xylem vessels area and hydraulic conductance under DR at a higher extent than the Italian giant reed genotype. Such increments would facilitate water movement from roots to leaves, allowing the plants to maintain a higher water status under DR conditions.…”

“…Moreover, recent studies indicated restricted variability in overall water use and CO 2 gas exchange, and therefore biomass yield, in response to water stress of several giant reed genotypes (Mann et al 2013, Nackley et al 2014, Sanchez et al 2015, Pompeiano et al 2016, Romero-Munar et al 2017, Haworth et al 2017c. Even though such restricted variability could be related to the limited epigenetic variability among giant reed genotypes (Cosentino et al 2006, Ahmad et al 2008, Mariani et al 2010, Pilu et al 2014, Haworth et al 2017b, 2017c, Haworth et al (2017b) found different adaptive hydraulic stem conductivities in giant reed genotypes (the ones used in the present study) from two contrasting environments (Morocco and Northern Italy), due to the species plasticity to adapt to the prevailing climatic conditions and common abiotic stress in the respective regions of origin. Ahrar et al (2017) also showed large DR adaptation plasticity at the photosynthetic level of Bulgarian and Italian genotypes.…”

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

“…The same ecotypes were exposed to severe drought in another study and exhibited differences in xylem morphology associated with the response to soil drying (Haworth et al, 2017a). The rhizomes were cut into equal portions of 20 cm in length (at least one bud was visible on each portion) and planted in a common garden experiment at the experimental farm of the University of Catania, Sicily (37° 25′N 15° 03′E), in March 2015.…”