A VALIDATED MODEL TO PREDICT THE EFFECTS OF ENVIRONMENT ON THE GROWTHOF LETTUCE (LACTUCA-SATIVA L) - IMPLICATIONS FOR CLIMATE-CHANGE

A mechanistic model is described that predicts the effects of changes to the environment on the growth, yield and maturity of lettuce. The m odel assumes that lettuce has structural and storage carbon pools. The storage pool is supplied by photosynthesis and depleted by respirator y losses and the conversion of assimilate to the structural pool. The model incorporated both instantaneous effects of temperature and CO2, and long term effects of thermal time on photosynthetic rate. The rate of structural dry-matter production was related to a simple temperatu re dependent partitioning coefficient. The model was calibrated on eig ht separate crops of lettuce and validated With independent data from seven sources. The validated model was then used to simulate changes i n head weight and time to maturity with systematic changes in temperat ure (-2 to +5 degrees C in 1K steps) and carbon dioxide (350 to 700 pp m in 50 ppm steps) superimposed on baseline meteorological data from R othamsted (1984-1995). These predicted that changes to temperature of up to +3 degrees C would reduce the production time from about 96 to 7 9 d for April plantings, and from 63 to 52 d for August plantings. Hea d weight would increase by approximately 32% with an increase in CO2 o f from 350 to 700 ppm, whilst the magnitude of this response varied li ttle with planting date. For any sowing date, increasing temperature w as predicted to have little effect on final head weight, however, head weight was predicted to decrease with later transplanting. The potent ial effects of changes to climate on lettuce production are discussed.