Smith Lab News

Nov. 4, 2024: New paper on the impact of CO2 on ecosystem carbon-nitrogen cycling out in Global Change Biology

Nick led a new study published in Global Change Biology titled “Acclimation of photosynthesis to CO2 increases ecosystem carbon storage due to leaf nitrogen savings."

The paper shows that leaf nitrogen savings due to photosynthetic acclimation to elevated CO2 increases ecosystem carbon uptake storage through two mechanisms: (1) a direct alleviation of plant nitrogen limitation through reduced leaf nitrogen requirements and (2) an indirect reduction in plant nitrogen limitation through an enhancement of root growth that leads to increased plant nitrogen uptake.

The paper builds on previous work showing that plants optimally downregulate leaf nitrogen use via downregulation of photosynthetic proteins under elevated CO2 to enhance nitrogen use efficiency. This downregulation thus frees up nitrogen for use elsewhere, alleviating some nitrogen limitation. The model findings suggest that models that do not include photosynthetic acclimation to CO2 may overestimate future nitrogen limitation of terrestrial ecosystems and thus underestimate future terrestrial carbon uptake and storage.

This work was a collaborative effort with scientists from the Lawrence Berkeley National Lab and was funded by the National Science Foundation and Schmidt Sciences, LLC.

Smith, NG, Q Zhu, WJ Riley, and TF Keenan (2024). Acclimation of photosynthesis to CO2 increases ecosystem carbon storage due to leaf nitrogen savings. Global Change Biology 30(11): e17558.

Figure 5 from the paper. Caption: Change of total ecosystem carbon (2100 minus 2011) with (Panel (a); Simulation B) and without (Panel (b); Simulation A) considering leaf nitrogen savings due to photosynthetic acclimation to elevated CO2. (c) Absolute differences in ecosystem carbon between the two simulations (Simulation B – Simulation A; gC m-2).

Nov. 1, 2024: The lab celebrates Nick's birthday with a flannel party!

The lab has jokes!

Oct. 23, 2024: New Phytologist Tansley Review on ecosystem C-N interactions

Evan and Nick contributed to a new New Phytologist Tansley Review titled “Empirical evidence and theoretical understanding of ecosystem carbon and nitrogen cycle interactions.”

The paper was a collaborative effort from the LEMONTREE team and was led by Beni Stocker. The TTU work was funded by the National Science Foundation and Schmidt Sciences, LLC.

The paper reviews experimental and observational data to outline known and unknown interactions between carbon and nitrogen cycling from leaf to ecosystem scales under various environmental conditions, with a particular focus on soil nitrogen and atmospheric CO2. The paper then compares this to current theoretical understanding of these processes.

We find that nitrogen availability has a positive influence on tissue nitrogen and plant growth, but does not consistently impact photosynthetic traits. Soil nitrogen availability also reduces root:shoot ratios. Elevated CO2 also boosts productivity and photosynthesis, but reduces leaf nitrogen demand. However, elevated CO2 increases root allocation. All responses are consistent with theory and we show this using a model demonstration. Nonetheless, there is still some variability in experiments and observations that need further investigation.

Stocker, BD, N Dong, EA Perkowski, PD Schneider, H Xu, H de Boer, KT Rebel, NG Smith, K Van Sundert, H Wang, SE Jones, IC Prentice, and SP Harrison (In Press). Empirical evidence and theoretical understanding of ecosystem carbon and nitrogen cycle interactions. New Phytologist.

Figure 2 from the paper. Caption: Pathways of carbon–nitrogen (C–N) interactions in terrestrial ecosystems. The pathway indicated by the blue background colour represents the traditional approach implemented in many DGVMs, whereby the atmospheric environment (mainly temperature, radiation and vapour pressure deficit) exerts no direct effect on leaf C : N. The importance of representing pathways indicated by the red background colour is emphasised in this review. Direct effects of the atmospheric environment on acclimation have implications for the leaf C : N and, through that, on ecosystem N cycling.

Sept. 13, 2024: Evan's new paper on the effects of symbiotic nitrogen fixation on carbon costs to acquire nitrogen out now in AoB Plants!

The lab had a new paper published in AoB Plants yesterday, titled “Symbiotic nitrogen fixation reduces belowground biomass carbon costs of nitrogen acquisition under low, but not high, nitrogen availability”. The paper was led by current post-doc Evan Perkowski and was adapted from an undergraduate thesis conducted by Joseph Terrones. Nick and former lab undergraduate Hannah German also provided significant contributions to the paper.

The paper reports findings from a greenhouse experiment where soybean seedlings were grown under full-factorial combinations of two nitrogen fertilization treatments and two inoculation treatments. The experiment was designed to understand how symbiotic nitrogen fixation modifies plant responses to nitrogen availability. It was also a direct follow-up to some of Evan’s previous work suggesting that carbon costs to acquire nitrogen in plants that form associations with symbiotic nitrogen-fixing bacteria are less sensitive to changes in nitrogen availability than species that are not capable of forming these associations.

Overall, we found that inoculation with symbiotic nitrogen-fixing bacteria decreased soybean carbon costs to acquire nitrogen, but this pattern was only observed in the low nitrogen fertilization treatment where seedlings invested more strongly in nitrogen fixation pathways. These patterns were entirely driven by an increase in plant nitrogen uptake and were not associated with a change in belowground carbon allocation. These findings may help explain the prevalence of plants that form associations with symbiotic nitrogen-fixing bacteria under low soil nitrogen environments and give us insight into understanding how nitrogen acquisition strategy may mediate the effect of nitrogen availability on plant nutrient acquisition and allocation.

Perkowski EA, Terrones J, German HL, Smith NG. (2024) Symbiotic nitrogen fixation reduces belowground biomass carbon costs of nitrogen acquisition under low, but not high, nitrogen availability. AoB Plants plae051.

Figure 1 from the paper showing that carbon costs to acquire nitrogen decreased in inoculated plants grown under low nitrogen fertilization.

August 5, 2024: Lab presentations for ESA 2024

The lab will have a big showing at ESA in Long Beach, CA! In total, the lab will be giving 9(!) presentations highlighting a wide variety of different topics. If you will be in Long Beach, come say hi!

A full schedule of lab talks can be found on the flier below or in pdf form here.