Wednesday, September 18, 2013

Cold soil: a signal from below

Thinking about plant senescence as we turn the corner into fall. I realize it's not just sunlight that affects growth processes in plants. It's also soil temperature. 

Getting ready for the big move in in October, I've started emptying the pots with hot weather plants like coleus. The plants lost most of their color and a lot of their leaves over the past few weeks and the purple spikes of flowers have long gone to seed. As I turn the pots over I realize the soil is cold, even in the afternoon. 

Well it makes sense. Cold nights in the 40s and daytime highs that just reach 60 make for cold soil. A message to the plant roots that encourages slowing down. Some of the soil goes on top of the compost heap in back, now a mass of vegetable peelings, corn husks, and old corn cobs. That soil will introduce microorganisms to break down the remains, almost as if the black soil self regenerated. 

Some of the soil, the cleanest, will go into the soil container, to be re-mixed and used next spring for the new potted annuals. 

And some of the soil, the stuff I can't easily separate from tightly packed roots or stubborn stems, I'll throw back into the garden, whose surface seems to sink an inch or two every year. 

Cold soil in the pots reminds us that we're entering a time where everything, not just the house and not just the air, is readjusting for a new season. 

Monday, September 16, 2013

Questions about lichens: Form? Function? Biology?

Some years ago, I had the opportunity to take several series of electron micrographs of lichens. I was focusing on a project on the Cladonia lichens of Australasia and thanks to the National Science Foundation and the National Geographic Society I had the chance to explore far and wide, documenting my collections at the Australian National University in Canberra. 

It was an ambitious project. You might even call it audacious. Because work like this hadn't been undertaken with lichens before. The more time I spent with my colleague at ANU, Roger Heady, who was in charge of the electron microscope laboratory, the more we started to detect interesting patterns and processes in the lichen samples I brought to be photographed. Roger was an intrepid worker and he encouraged me to look close, to look closer, and to look a lot. We spent hours getting lost in growth patterns of lichens that were evident at a very small scale, about 100 microns (1/10 of a millimeter).

I published lots of data from that exploratory time, but by no means all of it. The academic lichen community, small and conservative, found it hard to swallow what was obvious to me: lichens attain their shape in a programmed, controlled, and predictable manner. 

Lots of other questions arose as well. I call them "biological questions" because they go beyond the questions of pure form and form-making in lichens. Pursuing lichens in the field I became ever more curious about their ecology. Lichens are part fungus and part photosynthetic organism (algae or photosynthetic bacteria). But very often I would find evidence of the lichen fungus (without its photosynthetic partner) in wood or on leaves. 

The first photo below shows a diffuse lichen body growing on a moss. Is the lichen growing in a purely epiphytic manner (using the moss as a kind of "platform") or have its fungal hyphae invaded the moss body?

The second picture shows part of a lichen colony growing on a rainforest leaf. Since many plants in the rainforest retain their leaves over a number of years, lichens, which are relatively slow growing, can establish there. Again, is this lichen growing epiphytically or have some of its hyphae (elongated cells) penetrated the leaf? The visual evidence for penetration is not particularly strong. But the situation is possible.

I asked these questions because I took several pictures of fungal hyphae, unmistakably belonging to the lichen, in rotting wood and in deposits of leaf litter, shown in the bottom photo. In this photo we see the hyphae ramifying throughout the cellulose-rich substrate. I haven't done experiments to show whether the fungal cells are also digesting the leaf litter, but their abundant presence is demonstrated in these pictures.

As a parting thought I encourage scientists and non-scientists as well to think beyond the boundaries of their discipline. Looking at the lichen "model" as a fungus and its photosynthetic partner, and not allowing any doubt to sneak in, is a too-narrow interpretation. Maybe we don't have the evidence yet, but maybe there are other nutritional modalities that lichens experience, maybe for specialized times during their life cycle. 

Sunday, September 8, 2013


I was sitting out in back yesterday when I started sneezing like anything. I don't get allergic easily and I don't have a cold, so I started looking for the culprit.

All around the house and garden this year we have been in a kind of grape heaven. The seedless champagne grapes I planted a few years ago have really come into their own. And Janet's concord vine took over the back and side of our house. Neighbors (not very perceptive ones) even pushed our vine down when it started to beautify their fence. 

Well the cause of all the sneezing was the grapes. Either that or the bugs, spiders, and birds hanging around in them. So I decided to cut. Five huge bowls later I was the dubious owner of a ton of redolent grapes. Nothing to do but clean them. 

That was a good choice of activity. Sometimes a little repetitive cleaning gives the brain a break. The fingers enjoyed handling the endless eyeballs and a sense of accomplishment set in. 

Once they were clean, I poured my grapes into a large pot and cooked them down, letting them cool overnight. This morning came the straining. Skins and seeds went into the compost and what was left? A big pot of foamy thick grape juice. The rest of the day I spent boiling it down. Until just a few minutes ago when the bottom of the pot was just the consistency of oatmeal when you take it off the flame. 

A little sour, very rich, with any luck Janet will enjoy the condensed fruit on top of her rice cakes for a few weeks. 

Friday, September 6, 2013

Potatoes and the praying mantis

Well the potato plants, which had grown massive and fulminant in June and July, look pretty sparse by now. Last night it dipped down into the cool 50s, so I figured I would start the tearing-down process, an arc of activity that ends in mid-late October, about six weeks from now.

The soil surprised me by how cool it was and even more surprising was my puny crop of potatoes. Lots of good soil, lots of great green growth, not a lotta potatoes. 

Well I'm always writing about how diverse my garden is so I guess I'll shrug off the understated potato performance and brag about our praying mantis. It was tiny when we first saw it in the garden a couple of months ago. Now all grown up and strange looking, the mantis is a success story. 

With so many plants and such diverse spaces, we host a real plethora of insects. The abundance and diversity of the insect community here on Cottage Street is underscored by the praying mantis. A consummate predator of insects, the voracious mantis proves again that there are plenty of good snacks that grow in this garden. It's just that not all of them are for us. So what if our potatoes didn't turn out so wonderfully? There are lots of Jerusalem artichokes, still not yet in bloom, growing under the soil.