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Climate change is leading to increased heavy rainfall, making plant submergence in flood-prone pastures more common. Forage legumes play a vital role in boosting herbage production and quality, especially when grown with grasses in low nitrogen input areas. However, their tolerance to complete submergence and subsequent recovery remains poorly understood. This study evaluated eight forage legumes after 5 or 10 days of complete submergence: (1) Lotus tenuis ; (2) Lotus corniculatus ; (3) Lotus japonicus ; (4) Trifolium repens ; (5) Trifolium fragiferum ; (6) Trifolium pratense ; (7) Trifolium michelianum ; and (8) Melilotus albus. We assessed physiological and growth traits related to tolerance and recovery. All species survived except M. albus and T. michelianum. For the six surviving species, growth parameters linked to recovery were more prominent in Lotus species than in Trifolium species. Lotus species maintained higher biomass, improved stomatal conductance, and increased chlorophyll concentration in young leaves, along with a quicker recovery of PSII efficiency. In contrast, T. pratense showed the least tolerance and recovery, indicating its unsuitability for waterlogged areas. L. tenuis emerged as the most promising species for submergence tolerance, with L. corniculatus also showing potential, particularly in areas prone to short-term flooding. Variable adaptability to complete submergence was observed among Lotus and Trifolium species, while Melilotus albus and Trifolium michelianum did not survive. Lotus species demonstrated superior recovery growth from submergence compared to Trifolium species, particularly Lotus tenuis , making it suitable for flood-prone areas. The better performance of Lotus species after submergence was due to their ability to maintain higher stomatal conductance, increased chlorophyll concentration in young leaves, and quicker recovery of PSII efficiency. [ABSTRACT FROM AUTHOR]

Underwater germination could risk seedling survival, suggesting the need for control through seed perception of environmental cues. These cues include diurnally alternating temperatures tied to drained soils or shallow water tables. We examined high-amplitude alternating temperatures impact on underwater germination. Besides, the conditions experimented by seeds in the soil (e.g. hydration/dehydration phases) change their germinability so we tested if osmopriming could affect underwater germination. We worked with Echinochloa colona seedlots from extensive crop fields, exposing seeds to sequential submergence and drained treatments in combination with cues that promote germination. While a 10℃ difference between maximumand minimumdaily temperatures maximised germination in drained conditions, higher amplitudes (>15℃) alternating temperatures promoted E. colona underwater germination under hypoxic water (pO2 < 4.1 kPa). KNO3 osmopriming in drained conditions promoted later underwater germination even under hypoxic water; however, PEG 6000 osmopriming induced seeds to enter secondary dormancy inhibiting underwater germination. KNO3 improved E. colona underwater germination under air-equilibrated floodwater (pO2: 16.5-17.4 kPa) yet not under hypoxic conditions. This suggests that germination can proceed in flooded nitrate-fertile soils as long as it remains aerobic. Hypoxic submergence did not inhibit the induction of hypersensitivity to light in E. colona seeds. This research expands our understanding of wetland seed germination ecophysiology, shedding light on the inducible nature of underwater germination in hydrophyte weeds. [ABSTRACT FROM AUTHOR]

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 11 days 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. [ABSTRACT FROM AUTHOR]

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