CARBON GAINS BY DESICCATION-TOLERANT PLANTS AT ELEVATED CO2

1. There have been no reports of the long-term responses of the desicc ation-tolerant (DT) plants to elevated CO2. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccati on: a so-called poikilochlorophyllous desiccation-tolerant species (PD T), When the leaves of X. scabria are allowed to desiccate, the specie s shows many of the normal features of (P)DT plants. 2. However, the d uration of:photosynthesis in X. scabria is prolonged by 300% when the measurements are: made at 700 as opposed to 350 p.p.m. CO2. The implic ation is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity, This respons e could have far-reaching implications for the success of such species in a future climate. 3. Lichens and mosses, representing the homoioch lorophyllous DTs (HDT), retain their chlorophyll content and photosynt hetic apparatus during desiccation, We show the desiccation responses of two common HDT species (Cladonia convoluta and Tortula ruralis) to elevated CO2 for comparison, Both HDT species showed increased net CO2 uptake in the material grown at high CO2 by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation-tolerant plants will be among the main beneficiaries of a high CO2 future.