Estimating past leaf-to-air vapour pressure deficit from terrestrial plantdelta C-13

delta(13)C was determined in lignin extracted from present-day cladodes of Phyllocladus alpinus (a small coniferous tree) from seven well-lit sites ac ross New Zealand. The delta(13)C values ranged from -30.9 parts per thousan d to -23.6 parts per thousand and were compared with monthly means of tempe rature, precipitation, relative humidity and vapour pressure deficit from t he nearest recording stations. Of these parameters, the leaf-to-air vapour pressure deficit of the first month of cladode growth and expansion proved to be the most significantly correlated with lignin delta(13)C, over a rang e of 0.3 to 0.8 kPa, confirming the importance of atmospheric moisture cont ent on stomatal conductance. The carbon isotopic signature of lignin from f ossilised cladodes preserved under the Kawakawa Tephra (22.6 k C-14 yr BP) on the North Island is identical to that of the whole tissue, suggesting th at for this species at least, fossil material can be used to approximate th e lignin delta(13)C. The delta(13)C of species- and organ-specific fossil t errestrial plant material therefore provides an excellent method to quantif y past changes in leaf-to-air vapour pressure deficit. Copyright (C) 1999 J ohn Wiley & Sons, Ltd.