Hisashi Kon

A proposal for universal formulas for estimating leaf water status of herbaceous and woody plants based on spectral reflectance properties

The present study deals with the relationships between water status parameters of plant leaves and reflectances (Rλ) at characteristic wavelengths, between 522 and 2450 nm, as well as reflectance ratios, Rλ/R1430, Rλ/R1650, Rλ/R1850, Rλ/R1920, and Rλ/R1950, based on the air-drying experimental results of soybean (Glycine max Merr.), maize (Zea mays L.), tuliptree (Liriodendron tulipifera L.) and viburnum (Viburnum awabuki K. Koch.) plants. The water status parameters include leaf water content per unit leaf area (LWC), specific leaf water content (SWC), leaf moisture percentage of fresh weight (LMP), relative leaf water content (RWC) and relative leaf moisture percentage on fresh weight basis (RMP). Effective spectral reflectances and reflectance ratios for estimating the LWC, SWC, LMP, RWC and RMP were identified. With these spectral indices, approaches to estimating LWC, RWC and RMP were discussed. Eventually, an attempt on universal formulas was made for estimating the leaf moisture conditions of both herbaceous and woody plants as mentioned above. Moreover, applicability of these formulas was checked with the field experimental results of soybean and maize grown under water and nutrient stresses.

A combination model for estimating stomatal conductance of maize (Zea mays L.) leaves over a long term

Abstract In this study, an environmental variable model for estimating stomatal conductance of maize (Zea mays L.) leaves over a long term is developed, based on research results concerning responses of stomatal conductance to environmental variables. This model is actually a combination of optimized formulae for potential stomatal conductance during daytime, PSC, and for the relative degree of stomatal opening during daytime, RDO, with a basic form expressed as a multiplication of inter-day and intra-day factors. We call this environmental variable model as the combination model. Compared with other models presented in the past, this combination model is convenient in practical use because it can estimate not only maximum and average values but also instantaneous values of stomatal conductance during daytime. Also, the theoretical description of this model has been clarified by introducing into it the concept of environmental stress. As compared with Jarvis-type multiplication environmental variable models, we think this combination model is a refinement and development of the Jarvis-type models.