Lack of genetic variation in tree ring δ13C suggests a uniform, stomatally-driven response to drought stress across Pinus radiata genotypes

We assessed the variation in delta C-13 signatures of Pinus radiata D. Don stemwood taken from three genetic trials in southern Australia. We sought to determine the potential of using delta C-13 signatures as selection criteria for drought tolerance. Increment cores were taken from P. radiata and were used to determine the basal area increment and the delta C-13 signature of extracted cellulose. Both growth increment and cellulose delta C-13 were affected by water availability. Growth increment and delta C-13 were negatively correlated suggesting that growth was water-limited. While there was significant genetic variation in growth, there was no significant genetic variation in cellulose delta C-13 of tree rings. This suggests that different genotypes of P. radiata display significant differences in growth and yet respond similarly to drought stress. The delta C-13 response to drought stress was more due to changes in stomatal conductance than to the variation in photosynthetic capacity, and this may explain the lack of genetic variation in delta C-13. The lack of genetic variation in cellulose delta C-13 of tree rings precludes its use as a selection criterion for drought tolerance among P. radiata genotypes.