The Primary Productivity of Puccinellia Maritima and Spartina Anglica: A Simple Predictive Model of Response to Climatic Change

Abstract

A simple analytic model in which primary production is predicted from solar radiation interception and conversion efficiencies was developed for two salt-marsh grasses which utilise different photosynthetic pathways: Spartina anglica a C₄ species and Puccinellia maritima a C₃ species. Interception efficiency was predicted as a function of the leaf area index and the canopy extinction coefficient. Leaf area index in turn was predicted as a function of thermal time, development stage and leaf longevity. Conversion efficiency was considered a function of photosynthetic pathway, atmospheric CO₂ concentration and temperature pre-history. The model was validated by predicting production from climatic data for eastern England in 1978. These predictions agreed closely with the measured primary production of both species in that year. Assuming a doubling of atmospheric CO₂ concentrations and a 3°C increase in air temperatures throughout the year the model was then used to predict, and analyse the causes of change in, production for the year 2050. The model suggests that although the productivity of the C₃ species will increase, due primarily to increased conversion efficiency through reduced photorespiratory losses, productivity of the C₄ species may increase similarly through the effect of increased air temperature decreasing the incidence of photoinhibitory damage and accelerating leaf canopy development. The potential advantages of analytic models in predicting effects of climate change on primary production are discussed.