Importance of Natural Resources

Weixin Cheng (UGA Ecology in the 80s)


So, I was asked earlier if I’m very excited
or getting so nervous at the same time. I will make all the mistakes that haven’t
been made. To start with, by the way, this is my younger
daughter [points to screen]. The clothes Judy Meyer gave us for her. That’s the future, right? [applause] At the time I tried to put slides together,
I struggled – there’s so many things we could talk about. At the end I decided to follow Bruce Haines’s
mind, in a sense – he’s not with us anymore – science leading to the stories. I started here mostly because of Dr. Odum’s
philosophy of ecosystems. I gave up Cornell and Berkeley and came here. One of the things that I really benefited
from was the idea of this very late paper in his life, about pulse paradigm. We were able to find this paradigm for soil
organic matter decomposition. They’re not simple monotonistic lines all
the time. Sometimes they do have pulses, which is really
what they together stress for later. In terms of the idea of studying soil organic
matter, I couldn’t put all the photos on the slides, I just highlight four of my committee
members when I was here. And that’s pretty much my research topic
for the following three decades. That’s because at the time, all the directional
information was telling me soil organic carbon is super important, for ecosystems, for the
globe, for the earth system, and for the carbon of global cycle. Because soil organic carbon is twice as much
carbon as the atmosphere has. It’s a very critical mass of carbon that
regulates earth system, regulates land ecosystem services. So that’s why I focused, but the idea, the
recognition came from here, the Insitute of Ecology, UGA. You recognize the photos there, right? Of course Dave Coleman’s my major professor. I did this for him but because he has a cold,
he couldn’t be here. What a bummer, huh? And Dac Crossley, he was here yesterday. Dac, are you here? No. Alright. Well, Paul Hendrix. Hendrix leading us, all the activity at HorseShoe
Bend. I learned so much from him. He’s such a nice guy. I will say, a nice person can have such radiant
energy that can make the whole world better, that all of the consequences the person may
not recognize, but it happens. So I really benefited a great deal. And this is Peter Hartel, used to be at the
Crop and Soil Sciences. I guess he’s not here today. So, the first topic, I’m saying that I lead
the story with a little bit of science. It’s about rhizosphere priming. How do we define this here? Basically, the idea is about how plant roots
regulate soil carbon dynamics. Because typically when I got here, we’d do
soil incubation without roots, without plants, and we used that … model to understand. My question came up with all my mentors and
professors here, well that’s not very realistic. If you walk into the system, the real ecosystem,
with everything in it. There are roots, there’s soil fauna, there
are microbes, there might be different kind of plants, not just one. So how could you think that way (or weight?)
is realistic, can be used? That was the question. So what is the rhizosphere priming effect? It’s when you compare soil without plants versus
soil with all the rest, all the plants and roots. This is a photo right after my defense. You see me there – I don’t look like that
now. This is my committee members, five of them. And two of them are not with us anymore, Bruce
Haines in the back and Frank is there. I was so lucky. I will say this. Thinking back to this place, the Institute
of Ecology, Odum School of Ecology, UGA, is the place that gave me the most valuable,
which is the social capital, which is the interpersonal learning that I got. It really benefited me a lot for my whole
life. So, why did it matter, the rhizosphere priming
effect? I actually gave you a few lines there. Basically saying that it’s an important factor in determining the soil carbon cycle. Without it they’re really overs and unders. It’s way off basically. In fact maybe we can model this. In fact, nitrogen release – Monica, we should
talk about that. And then phosphorus mobilization is seven times difference, the highest magnitude. So over all when we add all this together
you can say that people normally recognize temperature and moisture as two key regulators. Actually plant roots can rival somewhat that
two. Some evidence from the elevated CO2 study
from F.A.C.E. they call it “Free air CO2 enrichment.” This paper, which I’m not an author of,
summarizes some of the results, basically concluded, I stress, the red, the priming
that really captures the real data in the model, basically they say you have to include
this rhizosphere priming effect global vs the model, otherwise you’re off. But my study, mostly of laboratory studies,
this figure shows total 57 observations of the priming effect from about 18 papers in
a summary, in a review paper. You see the range of the effect is about,
this [pointing] is in reference to the soil without roots, so it’s about 50 % to 100
%, most of the observed averages. That means if you have roots, if you have
the plant inputs, the soil carbon decomposes roughly two times as fast than just the soil
incubation. And the mechanism, why there is a priming
effect, actually traces back here. It’s mostly because this idea of microbial
loop. Faster microbial turning over. That is, growing much faster if you have roots,
if you have plant inputs. So I’d really like to attribute this to
our great professor Larry Pomeroy, and the whole team. And Judy you’re also in this. And again, I couldn’t put a lot [on the
slide]. When I was here, Mary Ann Moran and Bob Hossett
and Bill Wiebe helped me a great deal on this aspect of the microbial cycle. How we measure it, how we quantify it, how
we could understand those little ones that we couldn’t normally see. I will say soil organic matter in many respects
is like dark matter: we still don’t know much. So in part two, I borrow a French word there. Since I moved to California I started to drink
wine. [Laughter] And then I started to learn some
of the vocabulary that my two daughters also wanted me to do. So the word “terroir” has a lot to do
with the place, the culture, the makeup of the environment and substantially what’s
below ground. So this part is my recent activity in China,
for collaborations. This key data came from two long-term experiments
that Dave Coleman summarized in Big Ecology, some of the long term ecological research. Monica [Turner] studied many decades – such a valuable long term experiment that we can get something out of them, no other
way we could. This is out of 23 years of a long term experiment in two locations in North Eastern China. The people before me did a treatment. One is they started with all agricultural land. One piece of land they laid aside and let
it go through old field succession, and the other nearby they go bare fallow, they kept
the plants away manually, for 23 years. At that time we sampled this, when we measured the carbon
cycle that took place. Because of time I’m not going to get into
the details of it, we conclude with this study that soil with organic carbon decomposition
has set of two characteristics. One is quite intrinsic to the location, to
the system. It’s indicative of that ecosystem. Whereas the other site is extrinsic, It’s basically influenced by the outside
environment, disturbance, recent changes. The two are quite different. Because of time, I don’t have a lot of time
here I guess. This is the key result of that study. This is our two-year-long lab incubation,
this is our two-year-long field measurements. [Pointing] That one has a temperature treatment. The lower bars are ten degrees, the higher
bars are twenty degrees. This is ten degrees, this is twenty degrees. This is one location, this is another location. These are the two treatments. So what was striking to us at the time we
got the data out, the 23 years of bare fallow, no plant input, did not change decomposition
rate if you express it per unit of soil organic matter. So that’s very striking, because many other
things have changed. This table [pointing] is too much. I’ll just summarize it. Just don’t look at the numbers. Organic matter declined somewhere from 30
to 50% with the treatment. Carbon age changed from about 300-500 mean
age to 1400-1600 years old when you have bare fallow. All the new carbon’s gone, all the old carbon’s
there. But per unit of soil carbon, the decomposition
rate is literally the same. That’s what I call its “intrinsic rate.” It’s the place that matters. Two different places, whole different decomposition
rates. And so we also think the soil structure as
aggregates, they generalize. So we basically conclude, for the intrinsic
part of decomposition to have much longer time scales. I learned this from Bruce Haines, that we
need to analyze things based on different scales. I also learned from Monica [Turner] when she was here
and Jamie Cox , scale for understanding such instrumental things, you have to think
about it. And actually the idea of proportionality came
from Dick Wiegert’s modeling class. He used the soil carbon, soil organic matter
as one example of how you can simplify ecosystem modeling by proportionality. He’d say, for example, many of the soil
activities are in fact quite proportional to the soil organic matter content. So now many years later, 30 years later, I
was able to find, with many other’s help, the actual proof or evidence of it. And Frank Golley started me here as my first
major professor, I transferred to Dave later, he has such visions, and thinking in broad
schemes, so he led me to the whole field with big proportions. But you can see my portion was way smaller
than Monica [Turner] or many other people here, probably, very small scale stuff. So let me finish up. Back to my committee. And I will say this place had a lot to do with
social capital. I learned a great deal because I’m here. Otherwise I wouldn’t be. Thank you so much.


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