Presentation Information
[AOS26-P14]Evaluation of the lignin-derived material on seagrass growth
*Minako Ishizawa1, Yu Umezawa1, Keisuke Umebayashi1, Junsei Suzuki1, Kei Yamamoto1, Yasuyuki Matusita1 (1.Tokyo university of agriculture and technology)
Keywords:
Seagrass,Iron,Chelation
Seagrass beds, recognized as habitats that support high biodiversity and CO2 sequestration, are deteriorating due to multiple factors. Restoration efforts often fail because physical disturbance dislodges seedlings, and herbivory exceeds leaf growth rates. Therefore, we conceived that developing the rhizosphere could provide benefits such as enhanced tolerance to physical disturbance, increased growth due to faster nutrient uptake from roots, and increased carbon sequestration in anaerobic sediments. In terrestrial plants like rice, adding lignin-derived material-which chelates iron and enhances its uptake by the plants known to promote growth in both the rhizosphere and above-ground parts. Therefore, adding lignin-derived material is expected to be particularly effective at increasing seagrass growth in coral reef areas, where seagrass beds form in carbonate minerals with low iron content. Therefore, we conducted laboratory experiments using a representative seagrass species from subtropical regions, which are increasingly disappearing in Japan due to predation by green sea turtles. We verified whether the addition of lignin-based modifiers affects the internal composition of seagrasses and the growth rates of their leaves and roots.
Using Thalassia hemprichii collected from the Bise Reef in Okinawa Prefecture, Japan, we established the following treatments: 1) Control tank with weekly nutrient addition (i.e., Low NP), 2) Control tank with semiweekly nutrient addition (i.e., high NP), 3) 0.05% hydrothermal-treated kraft lignin (HKL) addition plus weekly nutrient addition, and 4) 0.05% HKL addition plus semiweekly nutrient addition. During incubation, leaf width and length were measured weekly, and SPAD values were measured as an indicator of leaf chlorophyll content. After the experiment, carbon and nitrogen content in leaves, carbon and nitrogen stable isotope ratios (δ13C and δ15N), chlorophyll concentration, and iron concentration in leaves, rhizomes, and roots were measured to evaluate the effects of HKL addition on the seagrass.
Iron accumulated in seagrass roots and rhizomes with HKL addition, while no increase in iron concentration was observed in the leaves. Furthermore, leaf chlorophyll concentration showed an increase only under high NP addition conditions, while this increase was not significant. Under low NP conditions, chlorophyll concentration decreased, probably due to nutrient limitation. The shift to relatively higher δ13C values in seagrass leaves in the HKL-added conditions indicated that carbon fixation was enhanced. However, an increase in leaf area was observed only in the high NP conditions, while leaf area decreased in the low NP conditions. Furthermore, no root growth was observed in the HKL-added conditions. While HKL addition to the rhizosphere promoted iron uptake by seagrass, the alleviation of iron limitation may have, in turn, induced nitrogen limitation. This likely limited the increase in leaf chlorophyll concentration and the associated growth rates. Therefore, it is necessary to conduct the next incubation studies under conditions with sufficient nutrient addition.
Using Thalassia hemprichii collected from the Bise Reef in Okinawa Prefecture, Japan, we established the following treatments: 1) Control tank with weekly nutrient addition (i.e., Low NP), 2) Control tank with semiweekly nutrient addition (i.e., high NP), 3) 0.05% hydrothermal-treated kraft lignin (HKL) addition plus weekly nutrient addition, and 4) 0.05% HKL addition plus semiweekly nutrient addition. During incubation, leaf width and length were measured weekly, and SPAD values were measured as an indicator of leaf chlorophyll content. After the experiment, carbon and nitrogen content in leaves, carbon and nitrogen stable isotope ratios (δ13C and δ15N), chlorophyll concentration, and iron concentration in leaves, rhizomes, and roots were measured to evaluate the effects of HKL addition on the seagrass.
Iron accumulated in seagrass roots and rhizomes with HKL addition, while no increase in iron concentration was observed in the leaves. Furthermore, leaf chlorophyll concentration showed an increase only under high NP addition conditions, while this increase was not significant. Under low NP conditions, chlorophyll concentration decreased, probably due to nutrient limitation. The shift to relatively higher δ13C values in seagrass leaves in the HKL-added conditions indicated that carbon fixation was enhanced. However, an increase in leaf area was observed only in the high NP conditions, while leaf area decreased in the low NP conditions. Furthermore, no root growth was observed in the HKL-added conditions. While HKL addition to the rhizosphere promoted iron uptake by seagrass, the alleviation of iron limitation may have, in turn, induced nitrogen limitation. This likely limited the increase in leaf chlorophyll concentration and the associated growth rates. Therefore, it is necessary to conduct the next incubation studies under conditions with sufficient nutrient addition.