Exploring the Connection Between Plants, Microbes, and Carbon Pools

This weeks topic in Ecosystem Ecology Overview

Dear Readers,

Welcome to the very “first” post relating to ecosystem ecology. I just recently arrived in Flagstaff to start my Ph.D. program and have been welcomed by the monsoon season. Let the thunder roll!

As some of you may know from my introduction post, I will be starting my Ph.D. program in two weeks, where I will be quantifying and predicting shifts in carbon pools in Northern Forests using accelerator mass spectrometry and other instruments. I am hoping to share and expand my knowledge alongside my community. Topics on this blog will broadly relate to ecosystem ecology, radiocarbon, biogeochemistry, and earth system science. I know, it sounds like a lot! However, the goal of this blog is to breakdown these subjects into components that will interests you, the reader! So let’s begin.

The first topic that I wanted to cover relates to plants and microbes and their role in carbon storage throughout ecosystems. Plants and microbes are essential for shaping many ecosystem processes –think biogeochemical cycles – nitrogen, phosphorous, sulfur, water, and carbon. In the same way that you can't make a cake without flour and eggs, plants and microorganisms are indispensable to the carbon storage process. Essentially, the rate at which carbon cycles through an ecosystem is largely influenced by primary productivity (plants) and decomposition (microbes).

As primary producers, plants are defined by their reliance on solar energy. Photosynthesis, surprisingly, is the sole process that can convert atmospheric CO2 into both organic molecules (carbon-based compounds) and living tissues.¹ During this process, plants use one unit of water (H2O) to produce one unit of oxygen (O2) for every unit of CO2 that they transform into simple sugars (i.e glucose). This particular form of photosynthesis is called C3, where other forms of photosynthesis include CAM and C4. We’ll dive into that on another day.

Photosynthate products from this 1:1 ratio reaction are used to promote the growth of plants. Plants have their own version of “stem cells,” called meristems. Most photosynthate products are allocated toward the growth of apical meristems (roots and shoots) to aid the plant in extending it’s rooting network and photosynthetic tissues. The roots and shoots of plants are both known to be contributing factors towards soil organic matter (SOM), followed by humification after plant death, which assimilates carbon into the soil.² Prior to plant death, carbon is also assimilated into the soil via root secretions of organic molecules into the rhizosphere. The use of carbon isotopes and carbon isotope tracers (13C and 14C) are some of the most well known tools used to study carbon translocation from plants to soil. So, let’s sum this up: Plants are primary producers, where the more productive they are the more they are able to both store carbon in plant structures and allocate carbon to soil. That’s where microbes come in!

The organic carbon that was previously stored in plants, and eventually assimilated to soil by either humification or secretion of organic molecules, is then decomposed by microbes. Where photosynthetic processes support the accumulation of soil carbon, microbes release heat and convert organic compounds into atmospheric CO2. Thus, carbon pools are a fine balance between plant inputs and microbe outputs. While microbes are more known for their role in breaking down organic matter and releasing it as atmospheric CO2, they also have the capacity to stabilize carbon pools³. So, why do scientists care about this? Well, the answer is related to climate change.

Both primary productivity and decomposition are influenced by temperature and precipitation. Moreover, all biogeochemical cycles, including carbon cycles, are coupled to water cycles. The IPCC (Intergovernmental Panel on Climate Change) has ran various models predicting both temperature and precipitation regimes under future climate parameters. Temperature projections relating to this model predict an overall increase in temperature regionally, however, precipitation projections have slight variations depending on the geographic region.⁴ With this being said, both plant and microbial influences on carbon pools will inevitably begin to shift. Current scientific interests across many fields relate to this subject. Will microbes increase atmospheric CO2? Will plants increase carbon storage via increased productivity rates? How do the microbe–plant interactions shift under current climate projections? Will carbon pools become a net sink or source of atmospheric CO2 in your surrounding ecosystems? These are all questions worth exploring!

Thanks for exploring this week’s topic in Ecosystem Ecology Overview. Stay tuned for next week’s post, where we will dive deeper into related subjects! As always, keeping smiling and stay safe!

1. Smith, R. L. and Smith, T. M. (1998). Key Processes of Exchange. In Elements of ecology (pp. 21–25). essay, Benjamin/Cummings.

2. Kuzyakov, Y. and Domanski, G. (2000). Carbon input by plants into the soil. Review. Z. Pflanzenernähr. Bodenk., 163: 421-431. https://doi.org/10.1002/1522-2624(200008)163:4<421::AID-JPLN421>3.0.CO;2-R

3. Liang, C. and Balser, T. 2012. Warming and nitrogen deposition lessen microbial residue contribution to soil carbon pool. Nat Commun 3, 1222. https://doi.org/10.1038/ncomms2224

4. Speizer, S., Raymond, C., Ivanovich, C., and Horton, R. M. 2022. Concentrated and Intensifying Humid Heat Extremes in the IPCC AR6 Regions. Geophysical Research Letters, 49(5), e2021GL097261.