WOW returns! (Why oh why?)

It’s spring, and everyone is itching to buy stuff at the nursery.  I’m there too, with my camera as well as my wallet.  I thought you might enjoy some of my “Things to avoid when you are plant shopping” collection:

These are called “Serpentine.”  I call them unnatural.  Like foot-binding.

Rootstock revolt.  The surest way to kill off your grafted scion.

A botanical bow?  Or a horticultural harp?

And check out the pot!  If there’s enough root mass in there to crack the pot, you can bet it’s long past its potting up date.

Love broccoli?  Then why not have a broccoli tree???

Looking for a maintenance nightmare?  Then this beheaded beauty is for you!

Don’t ever unwrap this plant.  It will immediately fall over and/or break.  Just keep it as is – call it your turtleneck tree.

Here we go again…

Despite Linda’s assertion to the contrary, I was not cow-tipping nor was I sampling micro-brews last week when I missed my regular post.  As usual, the beginning of spring is a busy time on the research side of my appointment.  This past week we began setting up for a major new project.  The goal of our newest study is to look at physiological traits of street trees that may enable them to better withstand future climate change. 

If you think about it, trees that are planted today may experience future climates in their lifetimes that will be different than the climates under which they were selected.  So how do we ensure that trees that are planted today can withstand a potentially different environment in 50 or 75 years?  It’s a very complex question.  An easy response would be to plant species or seed sources that have evolved in warmer, southern locations.  The problem is climate change is predicted to occur gradually so southern trees moved northward today will be subject to increased frost and freeze damage in the interim.

Grad student Dana Ellison (L) and undergrad research aide Aniko Gaal (R) pot up shade tree liners for a new project.

Another approach, and the one we are investigating, is that trees that are best suited for the future may be those that have a high degree of phenotypic plasticity.  What is phenotypic plasticity?  Simply stated is the relative ability of a species or genotype to acclimate to changes in their environment.  In our case we are going to look at the photosynthetic response of a range of street tree cultivars in order to identify their optimum temperature for photosynthesis or Topt.  But we know from other studies that Topt can vary depending on the environment to which trees are acclimated.  So we will acclimate our trees to a range of temperatures in a greenhouse study and determine which species or cultivars are best able adjust their physiology to changing environmental conditions.  In addition to the greenhouse study we will out-plant trees from the same cultivars in a parallel field study with the Greening of Detroit.  Working with the Greening we will identify sites around Detroit with contrasting temperature regimes and plant trees at these locations.  We will follow up with a similar suite of measurements as our greenhouse trial.

Will one study tell us everything we need to know about selecting street trees for a changing climate?  Of course not.  But it provides some important base line information and insights on approaching the problem.  Trees in urban and community forests are already operating at the margins and subject to myriad of stresses.  The argument can be made that urban ecosystems are among those most at risk under climate change.  Trees are an important component of many climate change mitigation strategies but they must be able to survive and grow in order to contribute this function.

The study “Urban tree selection in a changing climate” is funded by Michigan State University Project GREEEN, with material and in-kind support from J. Frank Schmidt and Sons Nursery, Nursery Supplies, Inc., Renewed Earth, Inc., and the Greening of Detroit.

Our visiting professor takes on veggie nutrition

First, let me give a blanket apology for all of us GPs – this is the first time ever all four of us have NOT posted in the same week.  I’m on the road this week with my high schooler checking out colleges, and I think the other three are out drinking beer and tipping cows somewhere.  So our visiting GP veggie specialist extraordinaire has graciously stepped in to answer a reader’s question about the apparent decline in vegetable nutrition.  Here’s Charlie:

Your United States Department of Agriculture tracks information about all kinds of things, like dry bean production and farm wage data.  They also measure nutrient content of foods (not pesticide residues–that’s for the FDA).  Some curious researchers have wondered if the nutritional content of vegetables has changed since the mid-20th century.  The data exist, so why not look through them?

Authors of a well-cited publication from 2004 have done just that.  Specifically, Davis, Epp, and Riordan did (J. Amer. College Nutr., 23:669-682).  What they found, for example, is if you ate cauliflower in 1950, you probably ate more protein, phosphorous, iron, and thiamin than if you ate the same amount cauliflower in 1999.  They measured the ratio of the nutritional concentration in 1999 compared to the concentration in 1950 [smartly, they adjusted 1950 moisture content to match that of 1999]. If ratio was 1, there was no difference in the concentration.  If the ratio was 0.5, then 1999 cauliflower had half the nutrition of 1950 cauliflower.  They had to use some statistical trickery (they didn’t know error or the number of samples from 1950), but some people might just call that ‘educated assumptions’.  When these ‘educated assumptions’ must be made, I’m a big fan of being conservative with them–in this case, that means that if there is a tiny difference, the researchers wouldn’t catch it.  Being conservative with statistics makes the differences that show up more robust.  Even with the most conservative assessment, the authors show that 26% of the time when nutrients are studied in vegetables, the concentration was lower in 1999 than in 1950.  However, 11% of the time, the concentration was higher in 1999.

The primary author of that paper published a summary of evidence in 1999 (HortScience 44:15-19).  The average numbers for a bunch of studies show similar declines, but statistically, there seems to be a significant decline in specific nutrients in about ¼ to ⅓ of vegetables studied over time. 

‘Jade Cross’ brussel sprouts

Why would this be happening?  Well one reason might be dilution.  The review article gave an example of raspberries: growing raspberries with more phosphorous fertilizer gave more yield (on a dry weight basis), and higher phosphorous concentration in the fruit.  But the plants still took up the same amount of calcium (or only slightly more), irrespective of how many pounds of raspberries were produced.  More pounds of raspberries with the same pounds of calcium removed from the soil means less calcium per pound of raspberries.  That makes sense. The plants can make much of their own dry matter (photosynthesis!), but they can’t make calcium.  I have some questions about using the dilution argument for the 2004 paper: if dry matter didn’t change, but concentration of macronutrients went down, the concentration of something else had to go up–but what?  Is the decline in specific things large relative to the concentration of that thing but small relative to the total dry matter? 

‘Graffitti’ cauliflower

The dilution effect may be the cause sometimes, but what causes the dilution effect?  Atmospheric CO2, or changes in production practices like irrigation, pest control, and fertility might be important, but I like the ‘breeding’ explanation.  Breeders don’t care how much calcium the plant has.  They care if it yields well (dry matter), is resistant to pests and diseases, is pretty or unusual, tastes good, etc.  If a trait is not selected for in a breeding program, it might go away over time.  So maybe the answer is to breed veggies that accumulate (or make, if it’s a vitamin) more nutrients, or to grow more of the existing varieties that might, by chance, already have relatively high nutrient concentrations (they do exist).  There may be a market for selling broccoli that has certifiably more calcium in it, and for change to happen in the marketplace, it has to be profitable.  For right now, you have no idea if the broccoli you buy is a low-calcium or a high-calcium variety because consumers don’t demand to know.

The un-interesting headline reads “some vegetables may be declining in average nutrient concentrations over time”.  The interesting (and false)
headline would be “vegetables aren’t good for you anymore”.  From the cauliflower example above:  in 1999, a serving of cauliflower would have about 2.5% of your recommended daily iron, 6.3% of your phosphorous, 3.5% of your protein, and 4.8% of your thiamine.  In 1950, it would have been 6.1% of your iron, 10.3% of your phosphorous, 4.3% of your protein, and 9.2% of your thiamine.  Your vegetables aren’t devoid of nutrition, they’re good for you.  Easter candy probably has none of those things.  If you’re worried, have a multivitamin, or better yet, eat MORE vegetables.  But vegetables grown in 1950 are rather old by now, I’d avoid them if I were you.  Meanwhile, know that a) science is aware of the issue, b) it’s not universal.