I was staying at a beachside hotel in southwestern Florida when I noticed a high sprawling grassy area that crept up from the beach and threatened to move into the parking lot.
Curious about what type of grass could grow in such a salty environment, I came closer, expecting it to be something like Paspalum vaginatum, which I saw quite a bit of when I was traveling in Caribbean islands.
However, the leaves looked wrong for that species, and after awhile I found some inflorescence that confirmed it as that inveterate world traveler, the common bermuda grass (Cynodon dactylon)!
This species, which graces the lawns of many warmer climes, is a pretty remarkable grass that I’ve met all over my travels both here in America and in Asia. The fact that it is also very salt tolerant, and can withstand living in the usually inhospitable sands of beaches was thus not really that surprising.
High salt environments can kill plants due to various mechanisms. The high salt concentrations outside the plant roots will draw water away from the plant through osmosis. The two components of salt (sodium chloride – NaCl) can also separately disrupt plant metabolism. Sodium ions can interfere with the ability of the plant to pull essential minerals like potassium and calcium from the soil, while chloride ions can accumulate in the leaves and causing the leaves to looked burned and discolored.
According to recent research studies, C. dactylon, that rather common lawn grass that most people would not give a second glance towards, manages to somehow survive such assaults through anatomical and physiological defenses in its more salt tolerant populations.
In terms of anatomical defenses, this usually involved strengthening of the various barriers against the external environment:
In roots, there was an increase in the exodermis and sclerenchyma, endodermis, cortex and pith parenchyma. These were all critical for checking water loss and enhancing water storage capability.
In stems, there was an increases in stem area (succulence), epidermis and sclerenchyma thicknesses (preventing water loss), cortex thickness(increasing water storage), and an increase in the number and area of vascular tissue (increased water conduction).
In terms of physiological adaptations, C. dactylon has even more interesting changes.
One thing that it does is restrict the uptake of Na+, while at the same time increasing its uptake of other ions (such as K+ and Ca2+) in its roots and shoots, using an elevated photosynthetic capacity. It also tries to fend off the effects of higher salt outside by accumulating large amounts of organic osmotica such as free amino acids and proline, which helps prevent the movement of water away from the plant cells.
So the next time you go to a beach and see this grass creeping along the sand, pause for a bit and think how cool it is that such a seemingly mundane and common organism can survive in so many different environments.
Literature Cited:
Hameed, M., & Ashraf, M. (2008). Physiological and biochemical adaptations of Cynodon dactylon (L.) Pers. from the Salt Range (Pakistan) to salinity stress. Flora-Morphology, Distribution, Functional Ecology of Plants, 203(8), 683-694.
Hameed, M. A. N. S. O. O. R., Ashraf, M. U. H. A. M. M. A. D., Naz, N., & Al-Qurainy, F. (2010). Anatomical adaptations of Cynodon dactylon (L.) Pers. from the Salt Range Pakistan to salinity stress. I. Root and stem anatomy. Pak. J. Bot, 42(1), 279-289.
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