The Sources of Carbon and Nitrogen Supplying Leaf Growth. Assessment of the Role of Stores with Compartmental Models

Abstract

Patterns of synthesis and breakdown of carbon (C) and nitrogen (N) stores are relatively well known. But the role of mobilized stores as substrates for growth remains less clear. In this article, a novel approach to estimate C and N import into leaf growth zones was coupled with steady-state labeling of photosynthesis ( 13 CO 2 / 12 CO 2 ) and N uptake ( 15 NO 3 2 / 14 NO 3 2 ) and compartmental modeling of tracer fluxes. The contributions of current C assimilation/N uptake and mobilization from stores to the substrate pool supplying leaf growth were then quantified in plants of a C 3 (Lolium perenne) and C 4 grass (Paspalum dilatatum Poir.) manipulated thus to have contrasting C assimilation and N uptake rates. In all cases, leaf growth relied largely on photoassimilates delivered either directly after fixation or short-term storage (turnover rate 5 1.6-3.3 d 21 ). Long-term C stores (turnover rate , 0.09 d 21 ) were generally of limited relevance. Hence, no link was found between the role of stores and C acquisition rate. Short-term (turnover rate 5 0.29-0.90 d 21 ) and long-term (turnover rate , 0.04 d 21 ) stores supplied most N used in leaf growth. Compared to dominant (well-lit) plants, subordinate (shaded) plants relied more on mobilization from long-term N stores to support leaf growth. These differences correlated well with the C-to-N ratio of growth substrates and were associated with responses in N uptake. Based on this, we argue that internal regulation of N uptake acts as a main determinant of the importance of mobilized long-term stores as a source of N for leaf growth.

Carbon allocation and carbon isotope fluxes in the plant-soil-atmosphere continuum: a review

“…Carbon fluxes are determined by measuring the redistribution of label after the system has reached an isotopic steady state (Allen et al, 2009). Steadystate 13 CO 2 labeling in combination with the application of compartmental models have been used to characterize different metabolic pools with distinct turnover times, feeding growth (Lattanzi et al, 2005) or respiration (Lehmeier et al, 2008) of leaves or heterotrophic plant parts. A more detailed analysis of δ 13 C in particular metabolites -going beyond the separation into different C pools (e.g.…”

Root and Shoot Respiration of Perennial Ryegrass Are Supplied by the Same Substrate Pools: Assessment by Dynamic 13C Labeling and Compartmental Analysis of Tracer Kinetics

“…As is the general case for compartmental analyses (Farrar, 1990;Lattanzi et al, 2005), ours was based on the assumptions that (1) the system is in a steady state, (2) fluxes obey first-order kinetics, and (3) pools are homogeneous and well mixed (Farrar, 1990;Lattanzi et al, 2005). Assumption 1 was well satisfied in the experiment: specific growth and respiration rates of shoots and roots were constant (see "Results" and "Discussion").…”

“…This model was translated into a set of differential equations (similar to Lattanzi et al, 2005), which described the system in terms of fluxes between pools and the environment, and implemented in a custommade program using the free software R (R Development Core Team, 2007). This program systematically tested millions of preset values for pool sizes, fluxes between pools, and delays to find the lowest root mean squared error (RMSE).…”

“…This is best done using the mathematical methodology of compartmental analysis (Atkins, 1969;Jacquez, 1996), which has been applied to various problems of the assimilation, transport, and metabolism of carbon in plants (Moorby and Jarman, 1975;Prosser and Farrar, 1981;Rocher and Prioul, 1987;Bü rkle et al, 1998;Lattanzi et al, 2005). A pool is defined here as a set of compounds that exhibit the same proportion of labeled carbon atoms; that is, a pool represents a "space" in which the isotopic composition is uniform (Rescigno, 2001).…”

Seasonal variations of belowground carbon transfer assessed by in situ <sup>13</sup>CO<sub>2</sub> pulse labelling of trees

“…The kinetics of the label recovered in soil CO 2 efflux were described using a four-pool model similar to those describing the supply of carbon for leaf growth (Lattanzi et al, 2005) or for root respiration (Lehmeier et al, 2008). The model was fitted on the observed CLR FS values (Fig.…”