An oxygen isotope chronometer for cellulose deposition: the successive leaves formed by tillers of a C perennial grass.

Multiannual time series of (palaeo)hydrological information can be reconstructed from the oxygen isotope composition of cellulose (δ O ) in biological archives, for example, tree rings, but our ability to temporally resolve information at subannual scale is limited. We capitalized on the short and predictable leaf appearance interval (2.4 d) of a perennial C grass (Cleistogenes squarrosa), to assess its potential for providing highly time-resolved δ O records of vapour pressure deficit (VPD). Plants grown at low (0.63 kPa) or high (1.58 kPa) VPD were swapped between VPD environments and exposed to the new environment for 7 d with simultaneous CO labelling. Then, leaves were sampled by age/position along individual tillers. Five leaves at different developmental stages were growing simultaneously. The period of most-active leaf elongation, from 10 to 90% of final length, lasted 6.6 d, and ~80% of all carbon and oxygen incorporation in whole-leaf cellulose occurred within 7 d. Cellulose deposition stopped at (or shortly after) full leaf expansion. The direction of change, low-to-high or high-to-low VPD, had no differential effect on new oxygen and carbon incorporation in cellulose. Successive leaves produced by tillers of C. squarrosa provide a δ O record useful for reconstructions of short-term hydrological dynamics.