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Summary Leek plants (Allium porrum L.) were grown on partly sterilized soil, in tall pots so that roots grew downwards unimpeded, with inoculum of the vesicular‐arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe placed either under the seedling or dispersed uniformly throughout the soil. The age of each individual root, and the distribution of infection in single roots were both determined in each of a series of sequential harvests. The development of the root systems was unaffected by placement of inoculum. Formation of adventitious roots continued up to 42 d, when branching commenced. The rate of initiation of roots was approximately exponential but more accurately fitted a logistic function. The increase with time in total length of root for the root system (Lt) was approximately exponential but the length of the single roots (Ltr) increased linearly. The total length of infection in whole root systems (Lir) also increased exponentially with time, but the rate of extension for the sum of the individual lengths of infected root (infection ‘segments’) in single roots (Ltr) was linear, with an apparent delay of approx. 5 d before infection could be observed. The rate of increase in Lir was very similar for placed (0.53 cm d1) and dispersed (0.58 cm d1) inocula, even though the number of infection segments per root differed widely. This suggests that the host controls the rate of growth of the fungus. On this basis, and assuming each root encountered a new propagule every 4 d, it was possible to predict the lengths and numbers of infection segments in single roots. The percentage infection in whole root systems and single roots, plotted against time, showed a delay, then a sharp rise to a final constant value. This pattern of development can be explained for single roots by simple arithmetical rules. Using these simple rules, and assuming that the rate of production of adventitious roots fitted either a logistic or exponential equation, it was possible to model the development of infection up to 42 d for a whole root system either algebraically or by numerical simulation.

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SUMMARYThe extent to which kiwifruit vines {Actinidia deliciosa var. deliciosa) recovered from transient waterlogging of the root system was determined under controlled conditions. Vines were waterlogged for periods varying from 1 to 7 days. The effects of decreasing concentrations of oxygen in the root zone on growth of the vine were rapid with substantial reductions occurring after being exposed to oxygen concentrations in the surrounding water of less than 0-125 mmol 1"^ for as little as 1 day. There was no evidence of recovery of growth once aeration was restored to the roots, except for the appearance of new roots at the base of the stems of vines that had been waterlogged for less than 5 days. The quantity of new roots grown was inversely related to the time of waterlogging. Although new roots were also found on the control vines, the quantities involved were very much less than for the vmes stressed for up to 4 days. No new roots were found for vines waterlogged for more than 4 days.The substantial loss of dry weight of roots of vines waterlogged for more than 3 days was due in part to a lack of growth and to a physical loss of root tissue. The loss of tissue resulted from the detachment of the cortex from the central stele through the dissolution of an entire layer of cortical cells which, in the control vines, were filled with starch. A microscopic examination of the cells of the root from waterlogged vines showed the cortical cells to be generally distorted with much of the intercellular material missing.The closure of the stomata within 2-3 h of the roots being waterlogged and the rapid desiccation of the leaves that followed the closure, was consistent with earlier findings with kiwifruit vines. Some recovery of stomatal activity occurred for vines that had been waterlogged for less than 4 days once the oxygen supply to the root was restored. For vines that had their roots submerged for only 1 day, stomatal activity was fully restored 3 days after the vines were removed from the water. In contrast, there was no recovery of stomatal activity for vines that had been waterlogged for more than 3 days.A feature of stomatal behaviour that was not related to the effects of oxygen stress was the cyclic pattern which developed. Each cycle repeated itself every 4-6 days and consisted of a period of high stomatal conductance followed by a sharp decline to a much lower level. A highly significant negative relationship was found between the level of photosynthetically active radiation and stomatal behaviour.It was concluded that the speed with which the roots die and the associated damage to the leaves under anoxic conditions greatly limits the ability of kiwifruit vines to resume growth once oxygen supply to the root has been restored.

Radiata pine (Pinus radiata D.Don) and red beech (Nothofagus fusca (Hook. f.) Oerst.) were grown for over 1 year at elevated (ELEV, 64 Pa) and ambient (AMB, 38 Pa) CO2 partial pressure in open-top chambers. Springtime measurements of overwintering leaves showed that light- and CO2-saturated photosynthetic rates (Amax) of pine leaves were similar for the two treatments (AMB: 6.7 � 1.08 μmol m-2 s-1, mean � 1 s.e.; ELEV: 6.6 � 0.47) but, for beech leaves, Amax was greater for AMB plants (8.8 � 0.90 μmol m-2 s-1) than for ELEV plants (6.10 � 0.71). Summertime measurements of leaves grown that spring showed that for pine, Amax was similar in the two CO2 treatments (AMB 14.9 μmol m-2 s-1 � 0.80; ELEV: 13.5 � 1.9) while, for beech, Amax was higher in AMB plants (21.0 � 1.1) than in ELEV plants (17.2 � 1.9), although the difference was not statistically significant. These results indicate downregulation of photosynthetic capacity of beech but not pine. Vcmax did not differ between treatments within species, suggesting that there was no acclimation of rubisco activity. Triose phosphate utilisation limitation may have contributed to the downregulation of Amax in beech. For pine, photosynthesis at treatment CO2 partial pressures was greater in ELEV plants in both spring and summer. For beech measured at treatment CO2 partial pressures, photosynthesis was greater in ELEV plants in summer, but was similar between treatments in the springtime.