Annals of Botany

The answer is blowing in the wind

I remember well my first view of machair, the complex of dunes and grassland that occurs along the west coast of the Outer Hebridean islands of north-west Scotland. The white sand, the complex dunes and the plant communities of the grassland sward of the machair ‘plains’ combined to make a very strong impression. Equally impressive was the near hurricane-force wind that battered my tent, pitched in the machair during a field trip. The paper by Kent et al. from Plymouth and Bodmin, UK (pp. 869–877) describing the photosynthetic activity of sand-buried machair plant communities thus evoked vivid memories. These authors removed turves representing four different sub-communities within the machair ecosystem and then transferred them to a greenhouse. After acclimatization, turves were buried under 20 mm of sand for 2 or 6 weeks, mimicking the effects of transient burial by wind-blown sand in the natural situation. Gas exchange was measured in control and buried turves. As might be expected, burial completely prevented photosynthesis in these communities. Further, there was evidence that dark respiration rates were reduced, possibly indicating a maintenance type of metabolism during burial. The sand was then removed and photosynthetic rates were determined at 16–20 h and 40–44 h after sand removal. Although the data were somewhat variable, it was clear that photosynthetic capacity of the buried turves started to recover when the sand was removed. Indeed, it appeared that the turves subjected to longer burial resumed net carbon gain faster than those buried for a shorter time. However, there was some variation between the different ‘sub-communities’ in that the turves from dune slacks showed a much lower capacity for recovery than from the other three locations. Overall, however, the ability of these community samples to maintain their photosynthetic capacity during burial is regarded by the authors as an adaptation for survival in the machair ecosystem.