Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Assimilation and allocation of carbon in soybeans
Abstract
Information on carbon assimilation and allocation patterns in a range of environmental conditions are needed to better optimize the choice of plant type and cultural practices appropriate for a given environment. Carbon Dioxide assimilation and allocation was measured in determinate and indeterminate soybeans during the 1987 and 1988 growing seasons near Mead, Nebraska. Distinctively different environmental conditions prevailed during the two seasons. Sums of precipitation and irrigation were 541 and 289 mm and yields averaged 322 and 236 g m$\sp{-2}$ in 1987 and 1988, respectively. Yields were consistently higher in the determinate crops. The development of a transportable open chamber canopy gas exchange system is described. Measured carbon dioxide exchange rates were repeatable and comparable in magnitude to previously reported values. Under well-watered conditions, peak rates of net canopy photosynthesis (P$\sb{\rm n}$) ranged from 20 to 25 $\mu$mol m$\sp{-2}$ (ground area) s$\sp{-1}$. During the R5 and R6 pod filling development stages, available soil water ($\theta\sb{\rm w}$) was depleted rapidly and midday P$\sb{\rm n}$ ranged between 4 and 15 $\mu$mol m$\sp{-2}$ s$\sp{-1}$. Midday values of soil CO$\sb2$ flux (R$\sb{\rm g}$) ranged from 1 to 5 $\mu$mol m$\sp{-2}$ s$\sp{-1}$ and generally followed the pattern of $\theta\sb{\rm w}$. A model of leaf photosynthesis was employed in conjunction with submodels of light interception and crop dark respiration to simulate P$\sb{\rm n}$. Simulated values of P$\sb{\rm n}$ were used in conjunction with measured values to evaluate the influence of $\theta\sb{\rm w}$. Above a threshold values of $\theta\sb{\rm w}$ $\approx$ 60-70%, $\theta\sb{\rm w}$ had little influence on P$\sb{\rm n}$. Below this $\theta\sb{\rm w}$ value, every 10% decrease in $\theta\sb{\rm w}$ resulted in 19% decrease in P$\sb{\rm n}$. Photosynthetic activity at different levels in the canopy and carbon allocation patterns were examined using $\sp{14}$CO$\sb2$ labeling techniques. The photosynthetic activity in the middle and lower layers of the determinate and indeterminate canopies were similar over the entire season. During reproductive growth photosynthesis in the upper third of the indeterminate canopy was 27% greater than photosynthesis in the upper third of the determinate canopy. During vegetative and early reproductive growth about 50% of assimilated carbon was partitioned to leaf material, about 21 to 48% to stems and 5 to 14% to roots. The fraction of current assimilate partitioned to leaves and roots steadily decreased as the crops began pod filling. Early in reproductive growth the determinate crop partitioned almost two times more carbon to the pods (36%) than the indeterminate crop (17%). Later in the season the indeterminate and determinate crops partitioned similar amounts of carbon to the pods.
Subject Area
Botany
Recommended Citation
Garcia, Richard Louis, "Assimilation and allocation of carbon in soybeans" (1991). ETD collection for University of Nebraska-Lincoln. AAI9133291.
https://digitalcommons.unl.edu/dissertations/AAI9133291