On Sat, 7 Sep 2013 19:22:06 -0700 (PDT), Higgs Boson wrote:
Thanks, Kay - very informative. Question: From the tree's POV, its raison d'etre -- along with all living things, including people -- is to reproduce the species. So why would it engage in such wild "mood-swings", rather than consistently reserving enough photosynthate (new term to me) to produce enough fruit which it "hopes" will create more trees?

Not mood swings, food swings. Put a pair of rats in a sealed warehouse with abundant food, and
you've got lots and lots of rats a year later. When the food gets short, only limited successful
reproduction go on, and the number of rat babies decline. When the food is all gone, the whole
population dies. Similar swings exist in plants, though plants are making stored "food" (photosynthate)
at the same time they're expending it for reproduction, so it's even more of a balancing act.

Planning ahead is not something most species can do. For a tree to "plan ahead" and "save for
the coming collapse", it would need some pretty sophisticated regulatory systems that I doubt exist.
Instead it seems to be "surplus energy" trigger -- store enough starch or sugar (photosynthate), and the
tree is triggered to make lots of flowers, which eventually, if everything goes right, turns into lots
of fruit.

This was also the problem with some of the Soviet plant breeding experiments, which hoped to produce
some supercrop that would allow you to harvest both above and belowground parts for food at the same time...
the problem was the plants didn't cooperate, and if you bred for a lot of fruit, the storage roots suffered
and vice-versa (look up Lysenko for a fascinating look at early 20th century genetic byways -- and think
about the eugenics movement of about the same period...)

Most fruit trees are now grafted onto a variety of root stocks. Some because the roots that cultivar
would grow are not sufficient to support the tree; some because you are trying to introduce other
characteristics, like trees that fruit before they're 40 ft tall, or roots that show reduced susceptibility
to particular diseases or insects or other pests. Sometimes it's done to bring a particular cultivar
to market more quickly.

There are some complex interactions between the grafted top and the roots that are still not
well understood, but not all cultivars will do well on a particular rootstock, just as not all
do well on their own roots. Some rootstock/cultivar pairings show particularly bad boom and bust
cycles of fruiting, some grafted plants show a smoother production curve. Same issues with
own-root plants -- some are boom and bust, some are fairly consistent. Generally, though, a grafted
tree will fruit sooner than an own-root.

If you're interested in rootstock compatibility issues, the apple breeders seem to have some of the easiest
literature to find and understand. And because apples can exist in a fairly wide range of climates and
climatic zones, there's also some bits to tease out about how choice of pairings can influence performance
in a particular climate. Or soil type. Or water regime. Similar literature may exist for oranges -- I've
just never worked with them much.

http://www.gardening.cornell.edu/fac...appleroot.html
http://www.uvm.edu/~mstarret/plantprop/chapter12.pps
http://springpropagationfair.com/rootstocks/
http://www.actahort.org/books/658/658_83.htm

Watching how plant sexuality adapts to particular conditions is one of those fascinations of biology.
For instance, tomato plants have perfect flowers -- male and female parts in the same flower. In good
times, tomato flowers outbreed -- the stamens grow away from the stigma, and pollen transfer tends
to take place from flower to flower and plant to plant. But when growing conditions are very bad,
tomatoes tend to inbreed -- the stamens tend to be right over the stigma, and the flower self-pollinates.
To be teleological, when you've got a good year, you can afford to waste seeds experimenting with possible
new combinations. But when you've got a bad year, sticking with tried and true combinations of genes
is a better bet.

Other plants are monoecious, like corn -- they have separate male and female flowers gathered into separate
inflorescences on the same plant. Combined with the fact that the staminate flowers tend to mature
before the pistillate flowers, this tends to enforce outbreeding -- gene exchange.

Still other species are dioecious -- separate male and female plants, definitely enforcing outbreeding.
Others are trioecious -- some plants are male, some are female, some have perfect (bisexual flowers). http://www.plosone.org/article/info%...l.pone.0035597 Some plants are switch hitters...
when conditions are crowded, they produce mostly male flowers; when populations are sparse, they switch
to perfect or mostly female flowers. Still others may switch from producing only male or only female flowers
to perfect flowers, often after many years of isolation, as in a seedling that has drifted onto a new
island and established.

And then there's the phenomenon of last-gasp flowering -- a tree, for instance, that's been in marginal
conditions for reproduction for years, and is now clearly in decline, will often put out a last crop
of flowers, even if it hasn't flowered for years. That's another poorly understood phenomenon.

And people think plants never do much interesting, especially over time...

Kay