Modelling photosynthetic CO₂ fixation in radiata pine clones with contrasting crown characteristics at age five at Dalethorpe, Canterbury, New Zealand (2000)
AuthorsXu, Hongyuanshow all
A program was developed to simulate the individual tree photosynthesis of ten Pinus radiata D. Don clones at age 5, and a comparison was made between the clones at a given condition to estimate photosynthesis from leaf level to tree level. The model linked the sub-models of leaf level photosynthesis, crown shape, foliage area, foliage area density distribution, and light penetration probability within tree crowns together to estimate total net photosynthesis on individual tree level. This study was carried out at a radiata pine clonal experiment at the same site with the same treatment located at Dalethorpe, Canterbury, New Zealand. At leaf level, seasonal photosynthetic responses to light and temperature curves of 1-, 2- and 3-year-old needles were measured under controlled environmental conditions in the field. Needle net photosynthetic rates did not show statistically significant differences between clones. Net photosynthesis decreased with leaf age but increased with temperature (5°C - 20°C). Comparing the maximum photosynthetic rates under the same measurement conditions, there were no statistically significant differences among the ten clones or according to crown position (crown level and aspect i.e. north-, south-, east-, and west-facing). In describing crown shape, a simple crown shape was developed. The model can be used to calculate crown radii, the maximum crown radius, the crown base radius, crown volume and vertical volume distribution of different needle age classes. Above-ground biomass and needle surface area were estimated. The total above-ground biomass and its allocation showed significantly difference among growth difference clones. Tree height was poorly correlated with total biomass production, but DBH was strong correlated with needle, branch and total biomass. The vertical distributions of needle biomass, needle surface area, and needle surface area density were studied according to age class. In estimating light penetration within tree crowns, a simple light penetration program was developed. The program was based on data from crown architecture analysis, geometrical analysis of the light penetration distance within crowns and models of crown shapes. The program can be used to estimate the probability of direct light penetration at any given sun zenith angle and diffuse light penetration at any given direction with azimuth angle ∠θ and elevation angle ∠β. With the developed individual tree net photosynthesis process model, the influence of foliage mass, crown shape, light penetration probability, incoming sun zenith angle, crown light extinction coefficient k-value and needle photosynthetic capacity on total tree net photosynthesis was studied. Simulation results indicated that foliage mass was an important factor influencing total tree photosynthetic rate. However, other factors, such as crown shape and needle photosynthetic capacity, all influenced the variation of total tree photosynthetic rates in various environment conditions.