The nature of the perennial response in Mediterranean grasses. I. Water relations and summer survival in Phalaris

Abstract

An important factor in the survival of Phalaris tuberosa, a typical Mediterranean perennial grass, is the ability of its deep root system to supply water during the summer to the dormant culms at the soil surface. This behaviour contrasts with that of the related annual P. minor, which is unable to exploit subsoil moisture, and dies as soon as the surface moisture is exhausted. The volume of water supplied by the perennial roots is sufficient to offset transpiration losses and maintain a favourable water balance in the dormant culms during the summer stress. The importance of this water source for survival is indicated by the death of plants whenever this supply is interrupted by severing deep roots. In field soils under drought conditions roots of the perennial have been followed to a depth of 7 ft in subsoil containing available moisture. The large metaxylem vessels and heavily suberized endodermis which are a feature of these roots suggest that they are well adapted to transport water up through the dry surface soil to the base of the dormant culms. The culms also show typical xerophytic characteristics which help to minimize water loss during the summer, and maintain favourable conditions for the survival of the dormant buds which develop at the basal nodes. These conclusions concerning the survival of the perennial have been drawn from plants growing under natural conditions, and also from more detailed studies under controlled environments. They appear to be of general significance for the perennial grasses adapted to the drier Mediterranean environments and form the basis of the perennial response found in this group.

Seasonal water relations of Lyginia barbata (Southern rush) in relation to root xylem development and summer dormancy of root apices

“…3a,b). Water supplied by perennial deep roots ( ‡ 1.5 m) is a core component of the survival strategy of some perennial grasses to survive summer drought (McWilliam & Kramer, 1968) and may also represent an important trait to sustain low rates of carbon assimilation in Lyginia (Fig. 3b).…”

Plant drought survival under climate change and strategies to improve perennial grasses. A review

“…In phalaris, the early onset and high level of senescence of herbage were observed to reduce transpiration (McWilliam 1968) while the development of an extensive root system and/or superior hydraulic conductance to maximise soil water uptake was noted as being important for ongoing production under drying conditions in tall fescue (Garwood and Sinclair 1979). Dehydration-avoiding plants are able to survive extended dry spells but can only do so if able to maintain high tissue water status.…”

“…Dehydration-avoiding plants are able to survive extended dry spells but can only do so if able to maintain high tissue water status. Indeed, McWilliam and Kramer (1968) demonstrated in phalaris that dehydration avoidance through the development of an extensive, deep root system (Cashmore 1934) and the ability to readily senesce foliage during summer is of great importance for the maintenance of the high plant water content that is typically observed in this grass. They showed that if this water harvesting ability is compromised by severing the root system, the plants rapidly die.…”

How can forage production in Nordic and Mediterranean Europe adapt to the challenges and opportunities arising from climate change?

“…The reduction in leaf tissue reduces total plant water loss (Gepstein, 2004;Munne Bosch and Alegre, 2004). A minimum water supply to the meristematic tissues is maintained (Karcher et al, 2008;McWilliam and Kramer, 1968;Volaire and Lelievre, 2001), and high concentrations of fructans and dehydrins contribute to osmoregulation and membrane stabilisation of these tissues (Hincha et al, 2000(Hincha et al, , 2002. High carbohydrate reserves are associated with superior plant resilience and recovery after severe drought (Boschma et al, 2003).…”