Fresh Water

Cover art from Wikipedia

I've been rewatching The Living Planet as of late, a classic nature documentary series from David Attenborough (his second actually) which aired in the early to mid 1980s. Though visually it can't quite stack up to some of his more recent work such as Planet Earth, it is interesting to see him taking a more active on-screen role in this series including acts such as narrating the segment on the oceans while in a diving suit, experiencing zero-gravity in a plane during the segment on the skies, and climbing to the top of a canopy tree in the jungle (during which he allegedly left his microphone on, treating his crew to a mix of panic, prayer, and profanity the entire way up).

One thing that really made The Living Planet unique however was that it really focused on the adaptations that various creatures of the earth had developed in order to more successfully survive in their environment. I thought it might be interesting to pick a plant species which would grow in each of these habitats, and cover some of the adaptations or characteristics it displays which allow it to really thrive there.

The first topic covered in the series (at least on the DVD I have, a Christmas Present from my friend Dave a year or two back) is Fresh Water. I actually do have a few photos of freshwater plants which I took upon moving here when I was doing some volunteering at Longwood.

Nymphaea, the Water Lily

Obviously since this plant grows in water instead of upon land, there are a few additional challenges it faces. First off, light does not travel through water as well as air, so it would be difficult for a truly underwater leaf to photosynthesize very effectively. The way the water lily has circumvented this is to ensure that its leaves grow on the surface of the water, able to photosynthesize without losing any of the brightness of the leaf. In fact, in many aquatic plants, the chlorophyll in the leaf tends to be exclusively on the top side, though I'm not sure if this is the case in Nymphaea.

Leaves float (so long as they are alive anyway) due to air pockets within their leaves, which exist due to gas exchange taking place during photosynthesis. It is worth noting how thin and flat this leaf is however, ensuring that water is unlikely to pool up on top of the leaf and cause it to sink.

A Lotus (Nelumbo), at Blithewold

It's not merely the leaves which hold this plant up though. As you can see in the above photo, this plant does have stems connected to these leaves, which in turn connect to roots and anchor it to the bottom of the water body. The shoots tend to be hollow, decreasing their density and encouraging their floating as well.

However, this erroneously sort of portrays the plant as fearing the water. There are obviously a good deal of benefits for the plant resulting from being submerged in water. For one, water retention becomes a non-issue. Land plants have stomates (stomata) in their leaves, essentially pores for gas exchange. They try to keep these closed as much as possible to reduce transpiration. Since aquatic plants don't have to worry about drying out, their stomata tend to be open most of the time.

So, suffice to say, plants can grow just fine in the water, as long as they can keep their leaves out of it.

I actually forget what this is, but note that even though the margins of the leaves are raised, there are still "gabs" through which the water could run off were the leaf to become submerged. I think this plant may have actually had a few other tissues which aided in its floating but can't quite remember... I'll have to check back in the summer.

I'm not sure how regularly I'm going to do these (I'd like to do some more Tree ID over the next few weeks), but the next one will probably be on the Jungle, focusing on how epiphytic orchids use their roots (and probably a bit more on orchids as well as I want to get down to the Longwood Orchid show and take some pictures).