Phenological modifications in plants by various edaphic factors.

Abstract

Various mechanical, chemical and physical soil analyses were carried out, in addition to weather observations, for 3 years at several sites along an oceanic-continental gradient in a fjord district in western Norway. All the environmental factors observed were correlated with the spring and a few late-season phenophases of many native and cultivated woody plants and some herbs by simple, linear correlations and by stepwise multiple and partial analyses. Different techniques were used to try and eliminate many intercorrelations between various environmental factors. As expected, air temperature measurements in nearly all analyses from these temperate region districts gave the most significant correlations with the phenology of the plants, the temperature during the night generally being the most important in mainly vegetative periods, e.g. to leaf bud break in spring, and the temperature during the day affecting the more generative phases, such as the period between leaf bud break and flowering. The other environmental factors, however, showed strong variation in correlation significance among the various species studied and also with different phenophases of the same species. Various hypotheses are put forward to explain such variation. Air humidity (including precipitation) and/or soil moisture (including intercorrelated parameters, e.g. soil grain size and bulk density) were relatively often found to be of importance. In the stepwise multiple analyses for leaf bud break of the birch (Betula pubescens), for instance, the amount of precipitation was the second factor to enter the analyses by a positive correlation with the developmental rate, after the most important factor, the night temperature. Positive correlations with a high clay content and bulk density in the soil indicated that high soil moisture is also favourable for early bud break in the birch. Other phenophases that seemed to be favoured by a good water supply were leaf bud break of the bird cherry (Prunus padus) and rowan (Sorbus aucuparia), and flowering of the hazel (Corylus avellana), common lilac (Syringa vulgaris), plum ('Victoria') and currant ('Red Dutch') and also, to some degree, the goat willow (Salix caprea). The amount of ions (P, K, Mg and Ca) often showed negative correlations with the developmental rate, particularly of earlier phenophases of both native and cultivated plants (except for the apple 'Gravenstein' and pear 'Moltke'), possibly, indicating that a high nutrient level delayed plant development. A similar explanation might be given for the observation that high pH in the soil often seemed to delay plant development (leaf bud break of Betula, Sorbus, Syringa and plum, and flowering of Corylus, bluebell (Campanula rotundifolia) and red currant). According to the analyses there seemed to be a tendency for plants that are particularly dependent on warm weather for leaf bud break, e.g. the ash (Fraxinus excelsior), and flowering, e.g. Prunus, pear, apple and, to some degree, the raspberry ('Preussen'), to be less dependent on other environmental factors for their development. For instance, if there were any effects of water for these plants, they were negative for moisture and soil factors intercorrelated with water.