Xy. Yin et al., A generic equation for nitrogen-limited leaf area index and its application in crop growth models for predicting leaf senescence, ANN BOTANY, 85(5), 2000, pp. 579-585
Appropriate quantification of leaf area index (LAI) is important for accura
te prediction of photosynthetic productivity by crop growth models. Estimat
ion of LAI requires accurate modelling of leaf senescence. Many models use
empirical turnover coefficients, the relative leaf-death rate determined fr
om frequent held samplings, to describe senescence during growth. In this p
aper, we first derive a generic equation for nitrogen-determined pholosynth
etically active LAI (LAI(N)), and then describe a method of using this equa
tion in crop growth models to predict leaf senescence. Based on the theory
that leaf-nitrogen at different horizons of a canopy declines exponentially
, LAI(N), which is counted from the top of the canopy to the depth at which
leaf-nitrogen equals the minimum value for leaf photosynthesis, is calcula
ted analytically as a function of canopy leaf-nitrogen content. Ar each tim
e-step of crop growth modelling, LAI(N) is compared to an independent calcu
lation of the non-nitrogen-limited LAI assuming no leaf death during that t
ime-step (LAI(NLD)). In early stages, LAI(N) is higher than LAI(NLD); but W
ith the advancement of crop growth, LAI(N) will become smaller than LAI(NLD
). The difference between LAI(NLD) and LAI(N), whenever LAI(N) is smaller t
han LAI(NLD), gives the estimate of leaf area senesced at the time-step; th
e senesced leaf area divided by specific leaf area (SLA) gives the estimate
of senesced leaf mass. The method was incorporated into two crop models an
d the models adequately accounted for the LAI observed in held experiments
for rice and barley. The novel features of the approach are that: (1) it su
ggests a coherent, biologically reasonable picture of leaf senescence based
on the link with photosynthesis and leaf nitrogen content; (2) it avoids t
he use of empirical leaf-turnover coefficients; (3) it avoids over-sensitiv
ity of LAI prediction to SLA; and (4) it is presumably of sufficient genera
lity as to he applicable to plant types other than crops. The method can be
applied to models where leaf-nitrogen is used as an input variable or is s
imulated explicitly. (C) 2000 Annals of Botany Company.