Abstract Detail

Ecophysiology

Waring, Elizabeth [1], Perkowski, Evan [2], Smith, Nicholas [2].

Nitrogen acquisition strategy and photosynthetic demand drive allocation responses in cotton and soybean.

Nitrogen inputs to terrestrial ecosystems are increasing globally, which has increased plant nitrogen uptake. However, nitrogen allocation to different organs and processes is not well understood. Some Earth system models predict that the increased nitrogen uptake will be allocated to photosynthetic enzymes to increase photosynthetic capacity. However, photosynthetic optimization theory suggests that photosynthetic demand, not nitrogen availability, drives photosynthetic capacity. An extension of this theory predicts that increased nitrogen will be allocated to the construction of new leaves and stems as opposed to roots. Notably, neither hypothesis considers the role of nitrogen acquisition strategy nor the role of belowground carbon allocation on nitrogen acquisition. We tested these competing hypotheses in species with different nitrogen acquisition mechanisms, a nitrogen-fixing plant (soybean) and a non-nitrogen-fixing plant (cotton), under different levels of soil nitrogen availability and a gradient of photosynthetic demand implemented using shade cloths. We measured leaf, stem, and root biomass. We also analyzed total carbon and nitrogen content of each biomass tissue. Nitrogen allocation was calculated as the percent of nitrogen in total biomass found in each organ and carbon cost for nitrogen acquisition was calculated from the elemental analysis. The total biomass nitrogen increased with nitrogen availability in both species, with the greatest increases seen in the higher light availability treatments. All plants grown in 80% shade, regardless of nitrogen availability, had low amounts of nitrogen in their tissues as expected with the photosynthetic optimization theory. However, overall photosynthetic demand caused no change in nitrogen allocation to the leaves in either species. With increasing nitrogen availability, plants allocated more nitrogen to leaves at the expense of stems, an effect that coincided with an increase in leaf biomass allocation. Nitrogen availability caused larger increases in allocation of nitrogen to leaves in soybean compared to cotton. Allocation of nitrogen to the stems decreased with light as that nitrogen was re-allocated to the roots. The soybean roots were unaffected by nitrogen fertilization. The carbon cost for nitrogen acquisition was also unaffected by nitrogen fertilization in soybean but increased with light availability. Whole plant carbon cost for nitrogen acquisition in cotton, however, differed across nitrogen treatments within each light level treatment, where increased nitrogen fertilization decreased carbon costs within each light level. While nitrogen demand limits whole-plant photosynthesis, these results demonstrate that soil nutrient availability plays an important role in determining the magnitude by which nitrogen is allocated toward leaf production.

1 - Northeastern State University, Natural Sciences, 611 N. Grand Ave., Tahlequah, OK, 74464, United States
2 - Texas Tech University, Biological Sciences, Box 43131, Texas Tech Unviersity, Lubbock, TX, 79409, United States

Keywords:
Nitrogen fertilzation
Photosynthetic demand
Photosynthetic optimization theory
nitrogen-fixation
Resource acquistion.

Presentation Type: Oral Paper
Session: ECOPH2, Ecophysiology II
Location: Virtual/Virtual
Date: Thursday, July 30th, 2020
Time: 1:00 PM
Number: ECOPH2001
Abstract ID:760
Candidate for Awards:None