By Jan Lankhorst
In early September, just days after the successful LEMONTREE annual meeting and subsequent summer school, I landed in Lubbock, Texas. The experimental group has been meeting online since the beginning of the project but other than one short EGU conference, and one (seemingly even shorter) annual meeting, we’ve not met face to face, let alone worked together. Being in Lubbock, Texas, was such a different experience from being in the Netherlands. It didn’t take long to get acclimated though, as every single person from the Smith Ecophysiology lab (PhUnFETTy lab) was welcoming in both a personal and professional setting.
In a first attempt to understand the interacting role of soil nitrogen and phosphorus on P-model relevant parameters, I set up an experiment together with Alissar Cheaib under the shared supervision of Hugo de Boer (UU) and Nick Smith (TTU). With later help of Evan Perkowski and Monika Kelley, we managed to collect a lot of data in a very short time. The objective of the experiment was to test leaf level and plant level changes in plants either inoculated or uninoculated with nitrogen-fixing bacteria to different nitrogen : phosphorus ratios. Although there were many setbacks, with the generous assistance of the Texas Tech team we managed to pull through and collect interesting results.
Our experiment was aimed at assessing the photosynthetic coordination theory and the effect of soil N : P ratios thereon. From field, and field experimental data we can learn a lot about a plant’s response to soil nitrogen or phosphorus addition and infer causality. Diving deeper into the mechanistic background requires exact, quantifiable, experimental approaches. Here we did a first stab at looking into the effect of soil N : P ratios on leaf biochemistry. As the current EEO theory mainly encompasses leaf N tradeoffs, adding leaf P to the theoretical framework is quite the challenge. Hence, we opted for a first stab at looking at N:P ratios and had 2 * 3 treatments. Either a low or high application and either a N:P ratio of 5 (“N-limited”) or a N:P ratio of 15 (“Co-limited”) or a N:P ratio of 45 (“P-limited”). We had soybeans (Glycine max) either inoculated or uninoculated, expecting a stronger phosphorus limitation in inoculated plants. Also we expected that the coordination of Jmax ~ Vcmax could be resource dependent, as Vcmax, through RuBisCo investment, has a strong demand for nitrogen, and Jmax, through RuBP regeneration, might be more phosphorus demanding.
From our preliminary analyses we however see a lower Jmax ~ Vcmax ratio when N is more limiting than P (NP: 5). This effect is non-significantly different for inoculated or uninoculated plants. But these are only preliminary results and we will likely revisit some statistics in the coming months.
Being the ECR lead of the CNP (Carbon, Nitrogen, Phosphorus cycles synthesis) working group also added another dimension to the stay. It was very useful to work besides more experienced members from the N-cycle review paper such as Evan Perkowski. We finalized the P-cycle formulations in current land
surface models after thoroughly reading the model descriptions and many subsequent discussions. Also discussing with Nick Smith has been very useful for more direction in the CNP working group, as it works wonders to be able to talk more often, less time-constrained and in a more relaxed setting than only once per month via Teams or Zoom.
The stay was enriching in a professional as well as a social way. I’ve met many interesting lab-members, with whom the two weekly lab-meetings were organized. In these sessions there were presentations, theory discussions, lab business and even a book-discussion on plant trait ecology with almost philosophical discussions. The differences in size and setup, and even the whole organization of the universities between the Netherlands and the United States was a great learning experience. I’ve also joined fieldwork from a related lab on the highest mountain of Texas, where monitoring species occurrence and specimen collection was the main goal. We’ve spent a weekend camping at the foot of the mountains, and spent the days sampling, labelling, and pressing plant specimens. Although it wasn’t really a learning experience, as my knowledge of the endemic flora of Texas was very limited (and quite frankly, still is), it was one of the best overall experiences in my time in Texas.
I’ve been invited to several social activities and I’ve made many friends with whom I’m still in contact. They showed me the second largest canyon of the United States where we made a day-trip hike through it. The most memorable social activity has to be celebrating Thanksgiving with the whole lab at the Smith’s family house. During this potluck dinner we‘ve played games and shared good food and good stories, and made great memories!
