Forage Plant Ecophysiology under Different Stress Conditions.

Forage production often occurs in fragile environments with low fertility and various limitations [...].

Shaking off the blow: plant adjustments during submergence and post-stress growth in Lotus forage species.

Flooding significantly hampers global forage production. In flood-prone regions, Lotus tenuis and Lotus corniculatus are common forage legumes, yet little is known about their responses to partial or complete submergence. To address this, we evaluated 10 Lotus accessions subjected to 11days of either partial or complete submergence, analysing growth traits related to tolerance and recovery after de-submergence. Principal component analyses revealed that submergence associated growth parameters were linked to L. corniculatus accessions, whereas recovery was associated with L. tenuis accessions. Notably, in L. tenuis , recovery from complete submergence positively correlated with leaf mass fraction but negatively with root mass fraction, showing an opposite pattern than in L. corniculatus . Encouragingly, no trade-off was found between inherent growth capacity and submergence tolerance (both partial and complete) or recovery ability, suggesting genetic selection for increased tolerance would not compromise growth potential. L. tenuis exhibited accessions with both partial and complete submergence tolerance, making them versatile for flood-prone environments, whereas L. corniculatus accessions were better suited for partial submergence. These findings offer valuable insights to enhance forage production in flood-prone areas and guide the selection of appropriate Lotus accessions for specific flood conditions.

High Recovery from Either Waterlogging or Drought Overrides Any Beneficial Acclimation of Chloris gayana Facing a Subsequent Round of Stress.

Climate models predict that plants will face extreme fluctuations in water availability in future global change scenarios. Then, forage production will be more frequently subjected to the destabilizing pressure of sequentially occurring waterlogging and drought events. While the isolated effects of drought (D) and waterlogging (WL) are well characterized, little is known about the consequences when both stresses occur sequentially. We hypothesized that plants sequentially subjected to opposite water scenarios (D followed by WL or vice versa) are less stress tolerant than plants experiencing repetitions of the same type of water stress (i.e., D + D or WL + WL) due to contrasting acclimation and allocation to either shoots (WL) or roots (D). Chloris gayana (a tropical forage grass capable of tolerating either D and WL) plants were randomly assigned to nine treatments (a sequence of two stress rounds-WL or D-each followed by a recovery phase at field capacity). Relative growth rates and allometric responses were measured after each stress round and recovery period. In the first round of stress, both WL and D reduced plant RGR similarly, despite their allocation being opposite-prioritizing shoots or roots under WL and D, respectively. The high recovery displayed after either WL or D overrode any possible acclimation of the plants facing a second round of water stress. We conclude that the tolerance of C. gayana to sequential water stress (either for WL or D) is likely to depend more heavily on its recovery ability than on its previous adjustment to any stress scenario that may evoke memory responses. Knowledge like this could help improve forage grass breeding and the selection of cultivars for poorly drained soils subject to sequential stress events.

Submergence tolerance and recovery in Lotus: Variation among fifteen accessions in response to partial and complete submergence.

Several Lotus species are perennial forage legumes which tolerate waterlogging, but knowledge of responses to partial or complete shoot submergence is scant. We evaluated the responses of 15 Lotus accessions to partial and complete shoot submergence and variations in traits associated with tolerance and recovery after de-submergence. Accessions of Lotus tenuis, L. corniculatus, L. pedunculatus and L. japonicus were raised for 43 d and then subjected to aerated root zone (control), deoxygenated stagnant root zone with shoots in air (stagnant), stagnant root zone with partial (75 %) and complete submergence of shoots, for 7 d. The recovery ability from complete submergence was also assessed. We found inter- and intra-specific variations in the stem extension responses (i.e. promoted or restricted compared to controls) depending on water depth. Eight of 15 accessions promoted the stem extension when in partial submergence, while three of those eight (all L. tenuis accessions) had a restricted stem extension when under complete submergence. Two accessions (belonging to L. corniculatus and L. penduculatus species) also promoted the stem extension under complete submergence. The accessions that attained better recovery in terms of leaves produced after de-submergence, were those that had high leaf and root sugar concentration at de-submergence, and high thickness and persistence of gas films on leaves during submergence (all L. tenuis accessions). We conclude that all Lotus accessions were able to tolerate 7 d of partial and complete shoot submergence, despite adopting different stem extension responses.

Differential growth of Spartina densiflora populations under saline flooding is related to adventitious root formation and innate root ion regulation.

Global change anticipates scenarios of sea level rise that would provoke long lasting floods, especially in lowland areas of salt marshes. Our aim was to evaluate the morpho-physiological adjustment ability to deal with continuous saline flooding of Spartina densiflora Brogn. plants from lowlands and uplands along a subtle topographical gradient (0.2m differential altitude). Plants from both origins were subjected to continuous saline flooding (300mM NaCl) for 35 days. Responses associated to adventitious rooting, aerenchyma formation, concentration of Na+, K+ and Cl- in roots and shoots tissues, tillering and growth were assessed. Root responses differentiated populations given that lowland plants showed higher ability for adventitious root formation and innate superior root ion regulation than upland plants. High constitutive K+ concentration plus high Na+ exclusion in root tissues led to significant low values of Na+:K+ ratios in lowland plants. Better root functioning was, in turn, related with more consistent shoot performance as lowland plants maintained plant tiller number and shoot relative growth rate unaltered while upland plants decreased both parameters by 35 and 18%, respectively, when in saline flooding. The superior performance of lowland plants indicates that locally adapted populations can be promoted in salt marsh habitats with subtle differences at topographic level.