1
|
Viana IG, Saavedra-Hortúa DA, Mtolera M, Teichberg M. Different strategies of nitrogen acquisition in two tropical seagrasses under nitrogen enrichment. New Phytol 2019; 223:1217-1229. [PMID: 31059120 DOI: 10.1111/nph.15885] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 04/26/2019] [Indexed: 05/21/2023]
Abstract
Tropical marine seagrasses live in environments with low nutrient concentrations. However, as land development intensifies along tropical coastlines, the marine environment in which these organisms grow is becoming more nutrient-rich. Nitrogen (N) uptake, assimilation, translocation and storage under a diversity of N sources in enriched conditions were investigated in two tropical seagrass species, Cymodocea serrulata and Thalassia hemprichii, from an oligotrophic marine environment. Both seagrasses were able to take up different inorganic and organic N sources through their above- and belowground tissues when enriched with high N concentrations. The uptake rates of T. hemprichii were generally higher than C. serrulata in leaves and rhizome, whereas root uptake was systematically higher in C. serrulata. Acropetal and basipetal translocation was observed in both species. Reduction and assimilation of N, measured in terms of their nitrate reductase and glutamine synthetase activity, were correlated with nitrate and ammonium uptake rates, respectively. Cymodocea serrulata showed a tendency to immediately use the available N, whereas T. hemprichii allocated more N in assimilation and storage investment. The responses of these seagrasses to N-enrichment demonstrate their ability to adapt to over-enrichment by varying N sources in the first step of the eutrophication process.
Collapse
Affiliation(s)
- Inés G Viana
- Leibniz Centre for Tropical Marine Research GmbH, 28359, Bremen, Germany
- CIIMAR - Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Terminal de Cruzeiros do Porto de Leixões, 4450-208, Matosinhos, Portugal
- Department of Ecology and Animal Biology, University of Vigo, 36310, Vigo, Galicia, Spain
| | | | - Matern Mtolera
- Institute of Marine Sciences, Dar Es Salaam University, PO Box 668, Zanzibar, Tanzania
| | - Mirta Teichberg
- Leibniz Centre for Tropical Marine Research GmbH, 28359, Bremen, Germany
| |
Collapse
|
2
|
Collier CJ, Langlois L, Ow Y, Johansson C, Giammusso M, Adams MP, O'Brien KR, Uthicke S. Losing a winner: thermal stress and local pressures outweigh the positive effects of ocean acidification for tropical seagrasses. New Phytol 2018; 219:1005-1017. [PMID: 29855044 DOI: 10.1111/nph.15234] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 04/20/2018] [Indexed: 05/21/2023]
Abstract
Seagrasses are globally important coastal habitat-forming species, yet it is unknown how seagrasses respond to the combined pressures of ocean acidification and warming of sea surface temperature. We exposed three tropical species of seagrass (Cymodocea serrulata, Halodule uninervis, and Zostera muelleri) to increasing temperature (21, 25, 30, and 35°C) and pCO2 (401, 1014, and 1949 μatm) for 7 wk in mesocosms using a controlled factorial design. Shoot density and leaf extension rates were recorded, and plant productivity and respiration were measured at increasing light levels (photosynthesis-irradiance curves) using oxygen optodes. Shoot density, growth, photosynthetic rates, and plant-scale net productivity occurred at 25°C or 30°C under saturating light levels. High pCO2 enhanced maximum net productivity for Z. muelleri, but not in other species. Z. muelleri was the most thermally tolerant as it maintained positive net production to 35°C, yet for the other species there was a sharp decline in productivity, growth, and shoot density at 35°C, which was exacerbated by pCO2 . These results suggest that thermal stress will not be offset by ocean acidification during future extreme heat events and challenges the current hypothesis that tropical seagrass will be a 'winner' under future climate change conditions.
Collapse
Affiliation(s)
- Catherine J Collier
- Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns, Qld, 4870, Australia
| | - Lucas Langlois
- Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns, Qld, 4870, Australia
| | - Yan Ow
- School of Marine and Tropical Biology, James Cook University, Townsville, Qld, 4811, Australia
- Australian Institute of Marine Science, PMB No. 3, Townsville, 4810, Qld, Australia
- Experimental Marine Ecology Laboratory, Department of Biological Sciences, National University of Singapore, Singapore, 117557, Singapore
| | - Charlotte Johansson
- Australian Institute of Marine Science, PMB No. 3, Townsville, 4810, Qld, Australia
| | - Manuela Giammusso
- Australian Institute of Marine Science, PMB No. 3, Townsville, 4810, Qld, Australia
| | - Matthew P Adams
- School of Chemical Engineering, The University of Queensland, Brisbane, 4072, Qld, Australia
| | - Katherine R O'Brien
- School of Chemical Engineering, The University of Queensland, Brisbane, 4072, Qld, Australia
| | - Sven Uthicke
- Australian Institute of Marine Science, PMB No. 3, Townsville, 4810, Qld, Australia
| |
Collapse
|