Effects of Drought on Water Relations, Mineral Uptake, Water-soluble Carbohydrate Accumulation and Survival of Two Contrasting Populations of Cocksfoot (Dactylis glomerata L.)

The role physiological responses in survival of prolonged soilmoisture deficit was investigated in vegetative plants of twoDactylis glomerata populations: KM2 (drought-resistant) andLutetia (susceptible). The plants were grown in 1 m-deep soilcolumns in a controlled environment. After 56 d of full irrigation,water was withheld for 80 d, by which time all soil moisturehad been consumed; the plants were then rewatered for a further19 d. As drought progressed, leaf extension decreased to zero,water status declined, and water-soluble carbohydrates (WSC)at first increased and then decreased. The most pronounced differencesbetween the two populations was that all KM2 tillers survivedthe drought, but 34% of Lutetia tillers died. In comparisonwith Lutetia, KM2 was characterized by (a) slower shoot growthrate, (b) greater root density at depth, (c) maintenance ofhigher lamina relative water content, (d) greater osmotic adjustmentin leaf bases, (e) higher concentration of WSC in tiller bases,(f) greater ability to export WSC out of dying leaves, (g) lowercontent of metal ions but improved maintenance of P status,and (h) lower proline:amino acid ratio. The contribution ofthese responses to tiller survival under severe drought in controlledenvironments is contrasted with performance and persistenceof swards in the field in the harsher Mediterranean environment.Copyright1995, 1999 Academic Press Dactylis glomerata L., cocksfoot, water-stress, osmotic asjustment, drought survival, root-growth, water-soluble carbohydrates, phosphate, proline, variety comparison     

A fungal endophyte reinforces population adaptive differentiation in its host grass species

Hereditary symbioses between fungal endophytes and grasses are relatively recent in the history of plant life. Given < 80 million yr of co-evolution, symbioses are likely to have impacted plant microevolutionary rather than macroevolutionary processes. Therefore, we investigated the microevolutionary role of the fungal endophyte Neotyphodium lolii in the adaptive differentiation of its host species Lolium perenne. Endophyte frequency in 22 natural L. perenne populations was established across a water availability gradient. Adaptive differentiation among five populations, and between symbiotic (S) and nonsymbiotic (NS) plants, was examined in a glasshouse experiment under nonlimiting and limiting water conditions. Genetic differentiation was subsequently assessed among populations, and between S and NS individuals, using 14 simple sequence repeats (SSR). Symbiosis frequencies were positively correlated to water availability. Adaptive population differentiation occurred following a trade-off between biomass production under nonlimiting water conditions and survivorship under water stress. Endophytic symbiosis increased plant survival in xeric populations, and reinforced competitiveness in mesic populations. No genetic difference was detected between S and NS plants within populations. Therefore, we conclude that the endophyte relationship is responsible for these effects. Local adaptation of the host plant, appears to be supported by the fungal endophyte.     

Persistence and production of perennial grasses under water deficits and extreme temperatures: importance of intraspecific vs. interspecific variability

Extreme climatic events are expected to increase in frequency and magnitude as a consequence of global warming. Grasslands cover a large proportion of the European continent and contribute to both agricultural production and ecosystem services through inter and intraspecific genetic variability. This study analysed the effects of summer droughts and heat waves on the persistence and production of perennial forage grasses. Mediterranean and temperate populations of Dactylis glomerata L. and Festuca arundinacea (Schreb.) were compared at both Mediterranean and temperate sites in France. By manipulating canopy temperatures and water availability, grass swards in the field were subjected to cumulative summer and spring water deficits (CSSWD) ranging from 329 to 707 mm to test different projected climatic conditions and extreme summer events. Under controlled summer heat waves (6–21 days at a mean daily canopy temperature higher than 30–35 °C), there was no increase in membrane damage to surviving aerial tissues. Plant stress was thus mainly generated through greater soil water deficit. Under the greatest CSSWD, annual biomass production was reduced on average by 60% and 30% with temperate and Mediterranean populations, respectively. Thresholds for a significant increase in summer tiller mortality were seen at CSSWD higher than 450 mm for temperate populations and 550 mm for Mediterranean populations. The latter displayed lower predawn leaf water potentials in summer and recovered through intense tillering in the subsequent seasons. Under the most extreme CSSWD, fewer than 20% of tillers of temperate populations survived and their nitrogen uptake ability was drastically altered. The higher potential productivity of Mediterranean populations in winter was associated with greater frost sensitivity. The identification of thresholds for vulnerability and the determination of the role of genetic diversity will improve the management of plant resilience and the design of new plant material to cope with climate change.