High water-temperature tolerance in photosynthetic activity ofZostera marinaseedlings from Ise Bay, Mie Prefecture, central Japan

Abstract

Photosynthetic activities of seedlings of Zostera marina were successively measured using a gas volumeter for 6 days at seven light (0-400 mmol photons/m 2 per s) and 11 water temperature conditions (5-35°C). The seedlings were collected from mature plants (Ise Bay, central Japan), and stored and cultured in incubators accurately controlled at each test temperature. The maximum gross photosynthesis (Pmaxg) was recorded at an optimal water temperature of 29°C after 0 days. After 6 days, Pmaxg appeared at 25°C and most plants cultured at 29-30°C bleached and withered after the drastic increase of light compensation point (Ic). On the contrary, at 5-28°C, the photosynthetic activities either changed little (5-25°C) or recovered after a temporal reduction (26-28°C); seedlings survived and looked healthy after being cultured for 6 days. The recovery was thought to be an acclimation to tolerate higher water temperature. As a result, the critical upper water temperature for Z. marina seedlings was proposed as 28°C. The temperature was consistent with the previously reported maximum water temperature in habitats around the southern boundary of Z. marina in the northern hemisphere.

Response of a Habitat-Forming Marine Plant to a Simulated Warming Event Is Delayed, Genotype Specific, and Varies with Phenology

“…The experimental warming of 4.5°C to a maximum of 25°C never exceeded values previously established as stressful (28–30°C) for Z . marina [ 50 , 51 , 52 ], and in fact the warming treatment mean of 21°C was very close to the optimum temperature for eelgrass as a species [ 47 , 48 ]. While the threshold for eelgrass biomass decline can be lower if there are additional environmental stressors (i.e.…”

Future warmer seas: increased stress and susceptibility to grazing in seedlings of a marine habitat‐forming species

“…This increase in respiration as a result of metabolic demands likely led to the subsequent signs of stress observed in the seedlings (i.e., increased leaf necrosis and seedling mortality). Indeed, seedlings of the temperate Zostera marina and Z. japonica exhibit sublethal symptoms, such as increased leaf necrosis, bleaching (Abe, Kurashima, & Maegawa, ; Abe, Yokota, Kurashima, & Maegawa, ), or decreased growth (Niu et al., ) under warming. Furthermore, the lower leaf biomass observed at 29°C could also be attributed to a decrease in leaf formation rates or an increase in leaf mortality due to necrosis and consequent leaf shedding.…”