Water stress impacts on respiratory rate, efficiency and substrates, in growing and mature foliage of Eucalyptus spp

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Abstract
In previous studies, water stress has induced variable and sometimes contradictory changes in respiration. We used isothermal calorimetry to measure the response of foliar respiration to water deficit in nine eucalypt genotypes. Specific growth rates (R SG) of shoots and leaves of variable age were measured independently, and the data were applied to both the growth-maintenance and enthalpy balance models. We calculated the oxidation state of respiratory substrate and the enthalpy change for the conversion of substrate carbon to biomass (ΔH B). Moderate water stress reduced the R SG of shoots by 38% (PPR SG was not affected by water deficit for shoots, but was significantly altered for leaves. Water deficit increased maintenance respiration by about 23% (P2 evolution and ATP production. Measured ΔH B in shoots and leaves were too small for reliable estimation of R SG by the enthalpy balance model. We also found significant effects of water stress on the oxidation state of substrate and ΔH B.