Soil microbe ‘home team’ helps Ponderosa Pines cope with warmer drier conditions.

Early findings suggest that familiar soil microbes help Ponderosa Pines to grow at warmer, drier sites.

Figure Caption: Aboveground biomass of ponderosa pine growing with different soil organisms communities at three sites along a temperature and moisture gradient. The bars indicate standard error of the mean – so only difference which are larger than the size of those ‘error bars’ are likely to be significant. Notice that plants are typically much smaller when grown in sterile potting soil, with a big benefit from having a home-team at the warm-dry sites.

In the semi-arid southwest, acquiring enough water and essential nutrients to survive can be tricky for trees like Ponderosa pines. So they get help from a variety of soil organisms, namely a special group of microbes known as ‘mycorrhizae’ – fungi that live inside plant roots. These fungi give soil nutrients and water to the trees in exchange for some of the carbon the tree makes from photosynthesis – a mutually beneficial trade arrangement. But with climate change bringing warmer conditions and higher evaporation rates to the region – that may mean less available water for plants.
   
Research by SEGA graduate student Mike Remke, advised by Matt Bowker from the NAU School of Forest is investigating how these important interactions between Ponderosas (as well as some other native plant species) and their fungal trading partners are likely to be affected by these environmental shifts. They’re particularly interested to know whether (and to what extent) a plant’s ability to migrate to new places (in order to maintain a favorable climate) is dependent on its microbial partners moving as well.
 
To do this, in June this year over 100 Ponderosa pine seedlings were planted at two SEGA sites on the Kaibab Plateau, just north of the Grand Canyon – with the help of volunteers from the Grand Canyon Trust- SEGA program.

The trees, started from seeds collected near Flagstaff, were planted in large tree pots, forcing them to grow either with a ‘home team’ of microbes they have always lived with OR with an ‘away team’ of unfamiliar soil microbes in sterilized soil. The trees have been planted at 3 different types of sites. One batch have been planted where the seed came from, a second batch at a site that is warmer and drier (to simulate climate warming) and a third batch at a cooler, wetter site. The main hypothesis being tested is that plants invest more carbon into a ‘home team’ of familiar soil microbes, regardless of which site they are at – and in turn receive greater benefits from their mycorrhizal team mates.

Although it’s early days, the preliminary data suggest that things are more complicated than the researchers were expecting. As you’ll see in the graph - plants in warm dry environments grow best paired with their home team soil organisms. They show nearly the same amount of growth as plants growing at their home site which have not been moved. This suggests that the soil microbes effectively help to protect or ‘buffer’ the pines against the more stressful growing conditions.  But strangely almost the opposite pattern is observed at the cool, wet site – with plants growing in pots with their home team soil microbes so far being slightly smaller than those without familiar microbes. Perhaps that’s because with abundant water, the trees just don’t need to bother with a trading partner.

To find out how this story develops keep following Mike Remke’s blog at:

http://www.mremke.com/#!Environment-Matters-An-update-to-my-SEGA-Experiment-with-Ponderosa-Pine/q34h6/57c4c3f77f91096d51a55180

and on the Bowker Lab blog posts here:

http://bowkerlab.blogspot.com/2016/06/plant-soil-feedbacks-ponderosa-pine-and.html