Assessing Carbon Allocation of Maize Canopy with Leaf Mass per Area Profile.

Crop yield estimation depends on carbon allocation between plant organs. A large fraction of carbon is allocated to the leaves during the vegetative stage to support later reproductive stage. Yet, many crop models do not describe allocation at the individual leaf level, losing potential interaction with other physiological processes. The purpose of this study is to collect individual leaf area and biomass as a proxy for leaf-level carbon allocation and test common assumptions made in crop models. Firstly, specific leaf area (SLA) or its reciprocal leaf mass per area (LMA) is maintained constant regardless of leaf age and rank. Secondly, sink strength corresponds to leaf area development, so allocation finishes when the leaf is fully expanded. Last but not least, source-sink distance is negligible, so the effect of external sink change (i.e. ear development) is identical to all leaves. Pioneer hybrid 34N43 cultivar was grown at a field in Maryland in 2005. Non-limiting condition was assumed that nitrogen fertilization was applied twice and water was rain-fed with additional irrigation. 18 samples of LMA profile from 6 groups and 3 sampling dates were collected. The sampling dates approximately corresponded to V6, V12, and R1 stage, respectively. Unlike a traditional constant LMA value assumed in crop models (i.e. 250 cm2 g-1 = 0.004 g cm-2), LMA of individual leaf changed with respect to leaf age and rank. It was increasing when leaf ages and maximum at the youngest mature leaf. Ranks of fully expanded leaves were positively correlated with LMA, but the correlation of expanding leaves were unclear. High LMA was often found at high ranks, but also occasionally at low ranks under reproductive stage. Carbon allocation did not halt but still continue after full leaf expansion that mature leaves saw LMA increase even after ligule formation. Leaves of higher ranks received larger LMA increase, whereas occasional decrease could be associated with measurement error or leaf starch remobilization. External sink effect from ear development was not clear. The developing ear was assumed to be a strong external sink, expecting declination of LMA change rate proportional to source distance, forming a wedge shape in the profile around the rank of ear leaf. However, correlation was not statistically significant with the dataset. This study revealed interesting dynamics of LMA profile of maize canopy. We will continue building carbon allocation model that can capture individual leaf-level processes.