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|ŠUMARSKI LIST 11-12/2020 str. 46 <-- 46 --> PDF|
28.0%, respectively). Gypsy moth and water deficit differentially affected chlorophyll concentration in treated oak families (Chart 1). Values were lower in GM-treated family 2 plants versus the control. However, considerable changes in family 7 were evident only in plants under treatment D.
Recovery of physiological parameters after recovery period
Recovery period of all plants affected by stress factors (GM, D or D+GM) caused an increase in NRA of investigated families, both compared to the control and the measurements performed on stressed plants during the duration of the treatment (Chart 2). When compared with control, the increase was lowest for the GM treatment (49.3% for family 7 and 48.7% for family 2) and highest for the D+GM-treated plants (78.5% for family 7 and 73.3% for family 2) versus the control plants. Due to the increase of A in control plants in families 2 and 7 after recovery (from 6.59 to 9.24 µmolCO2 m-1 s-1 and from 6.44 to 7.35 µmolCO2 m-1 s-1, respectively), significant differences were recorded in treated plants after recovery period (Chart 2). After recovery Ci values were significantly higher in plants of family 7 under all stress treatments D, GM and D+GM (Chart 2), while Ci values in family 2 significantly decreased in drought recovered plants compared to control and treatments GM and D+GM. Stomatal conductance remained significantly decreased in D, GM and D+GM plants of family 2, while there were no significant differences between investigated plants of family 7. On the other hand, the transpiration rate remained decreased in all treatments after the recovery period. After recovery, plants from family 7 did not have significantly-decreased WUE, although values for GM, D and D+GM were lower than in control plants (3.13, 2.91, 3.63 and 4.21 µmolCO2 µmolH2O-1, respectively). Affected plants from family 2 had significantly smaller values of WUE in GM treatment (1.65 µmolCO2 µmolH2O-1) when compared to control plants from the same family (Chart 2). Watering of treated plants substantially affected chlorophyll content of the oak family 2 (Chart 2). Recovered plants under D and GM treatment had significantly lower chlorophyll content when compared to control (26.8, 25.0 and 34.5 µg cm-2, respectively). Chlorophyll content of recovered plants of family 7 did not differ significantly from the control plants.
Influence of the family, treatment, recovery and their interaction on the investigated physiological parameters
In most of the investigated parameters, origin of the seed (family) showed significant influence on the results. Nested ANOVA results (Table 1) showed significant impact of all calculated factors for NRA: origin (F=7.76***), treatment (F=26.31***) and recovery (F=665.0***). Analysis of variance showed that the effect of treatment was only significant for A (F=38.50*** at p<0.001), while the recovery period (date) and families showed no significant effect on net photosynthesis (F=3.51ns and F=1.17ns, respectively). On the other hand, sub stomatal concentration of CO2 (Ci) followed a similar pattern as A only for recovery time which had no effect on Ci (F=0.57ns), but origin of seedling significantly affected Ci (F=28.24*** at p<0.001). Transpiration rate (E) and stomatal conductance (gs) were both affected by the treatment and dependent upon the origin of plants (Table 1), while recovery period did not show an effect on gs (F=0.06ns). Analysis of variance of WUE of treated plants (Table 1) showed significant impact of all three factors: recovery time (F=16.21***), treatment (F=6.30***) and origin of plants (F=8.22***). Results of nested ANOVA (Table 1) showed significant effects, both of treatment (F=11.44***) and family (F=10.04***), while recovery period did not significantly affect chlorophyll content of the trees.
Vegetation responses to environmental conditions are mediated by a suite of functional traits affecting water relationships, resource acquisition and other aspects of plant function (Manzoni, 2014). Increase in photosynthetic rate commonly occurs following defoliation events, which is considered a photosynthetic up-regulation caused by the disturbance of a source:sink ratio and increased demand for carbohydrates to rebuild crowns (Pinkard et al., 2007). Various authors found opposite plant photosynthetic responses during defoliation. Peterson et al. (1996) found no alteration of photosynthesis in hardwoods under pest attack, while Turnbull et al. (2007) recorded increased photosynthesis in leaves of eucalyptus (Eucalyptus globulus Labill.) under partial defoliation. Decreased photosynthesis was recorded under defoliation treatments in this study.