National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki, Japan.
School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi Hachioji, Tokyo, Japan.
Ann Bot. 2022 Jan 8;129(1):15-28. doi: 10.1093/aob/mcab117.
Mangrove plants are mostly found in tropical and sub-tropical tidal flats, and their limited distribution may be related to their responses to growth temperatures. However, the mechanisms underlying these responses have not been clarified. Here, we measured the dependencies of the growth parameters and respiration rates of leaves and roots on growth temperatures in typical mangrove species.
We grew two typical species of Indo-Pacific mangroves, Bruguiera gymnorrhiza and Rhizophora stylosa, at four different temperatures (15, 20, 25 and 30 °C) by irrigating with fresh water containing nutrients, and we measured growth parameters, chemical composition, and leaf and root O2 respiration rates. We then estimated the construction costs of leaves and roots and the respiration rates required for maintenance and growth.
The relative growth rates of both species increased with growth temperature due to changes in physiological parameters such as net assimilation rate and respiration rate rather than to changes in structural parameters such as leaf area ratio. Both species required a threshold temperature for growth (12.2 °C in B. gymnorrhiza and 18.1 °C in R. stylosa). At the low growth temperature, root nitrogen uptake rate was lower in R. stylosa than in B. gymnorrhiza, leading to a slower growth rate in R. stylosa. This indicates that R. stylosa is more sensitive than B. gymnorrhiza to low temperature.
Our results suggest that the mangrove species require a certain warm temperature to ensure respiration rates sufficient for maintenance and growth, particularly in roots. The underground temperature probably limits their growth under the low-temperature condition. The lower sensitivity of B. gymnorrhiza to low temperature shows its potential to adapt to a wider habitat temperature range than R. stylosa. These growth and respiratory features may explain the distribution patterns of the two mangrove species.
红树林植物主要分布在热带和亚热带潮间带滩涂，其分布范围的局限性可能与其对生长温度的响应有关。然而，这些响应的机制尚不清楚。在这里，我们测量了典型红树林物种叶片和根系的生长参数和呼吸速率对生长温度的依赖性。
我们用含有养分的淡水灌溉两种典型的印度-太平洋红树林物种，Bruguiera gymnorrhiza 和 Rhizophora stylosa，在四个不同的温度（15、20、25 和 30°C）下生长，并测量了生长参数、化学成分、叶片和根系 O2 呼吸速率。然后，我们估算了叶片和根系的构建成本以及维持和生长所需的呼吸速率。
由于净同化率和呼吸速率等生理参数的变化，而不是叶面积比等结构参数的变化，两种物种的相对生长率都随生长温度的升高而增加。两种物种都需要一个生长的阈值温度（B. gymnorrhiza 为 12.2°C，R. stylosa 为 18.1°C）。在较低的生长温度下，R. stylosa 的根氮吸收速率低于 B. gymnorrhiza，导致 R. stylosa 的生长速度较慢。这表明，R. stylosa 对低温比 B. gymnorrhiza 更为敏感。
我们的研究结果表明，红树林物种需要一定的温暖温度来确保维持和生长所需的呼吸速率，特别是在根部。地下温度可能限制了它们在低温条件下的生长。B. gymnorrhiza 对低温的敏感性较低，表明它比 R. stylosa 更有可能适应更广泛的栖息地温度范围。这些生长和呼吸特征可能解释了这两种红树林物种的分布模式。
