The NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. 16 episodic ozone regimes in solardomes, with treatment means between 16 and 72 ppb. All trees 17 were kept fully watered for the first five weeks of exposure, after which half the trees continued 18 to be well-watered, whereas the other half were subjected to a moderate drought by applying 19 approximately 45% of the amount of water.
2021 Species-specific reductions in growth in response to both ozone and drought were found, which 22 could result in reduced potential carbon sequestration in future ozone climates. In well watered 23 conditions the ozone treatments resulted in total biomass reductions for oak (18%), alder (16%), 24 beech (15%), ash (14%), birch (14%) and hazel (7%) in the 72 ppb compared to the 32 ppb 25 treatment. For beech there was a reduction in growth in response to ozone in the well watered 2 26 treatment, but an increase in growth in response to ozone in the drought treatment, in contrast to 27 the decreased growth that would occur as a result of stomatal closure in response to either the 28 ozone or drought treatment, and therefore assumed to result from changes in hormonal signalling 29 which could result in stomatal opening in combined ozone and drought conditions.
3031 For alder, in addition to a decrease in root biomass there was reduced biomass of root nodules 32 with high compared to low ozone for both drought treated and well-watered trees. There was 33 also a large reduction in the biomass of nodules from drought trees compared to well-watered. It 34 is therefore possible that changes in the nitrogen dynamics of alder could occur due to reduced 35 nodulation in both drought and elevated ozone conditions. 1996, Pääkkönen et al. 1997 58 and reduced growth, e.g. on Quercus rubra (Samuelson et al. 1996). Some studies have 59 indicated that a change in biomass partitioning can occur in response to ozone, for example, a 60 decrease in the dry mass of roots and branches of Betula pendula attributed to ozone has been 61 shown at the end of the exposure (Riikonen et al. 2004). It is thought that decreased partitioning 62 to the roots may occur with increasing ozone exposure because the mature, lower leaves act as 63 the main source of assimilate for root growth, and these are frequently the most damaged by 64 ozone (Grantz et al. 2006, Cooley and Manning 1987, Okano et al. 1984 alder. All plant material was oven-dried at 65°C for a minimum of seven days before weighing.
166
Data analysis and statistics
167All data except that for root biomass were analysed using General Linear Model analysis (GLM) 168 in Minitab (Version 16) using the mean value per solardome as the input data. Root weight data 169 and for alder, root nodule biomass, were only available from the O332 and O372 treatments and 170 therefore comparisons of root weights and total tree biomass were made using two-way
181As a conse...