Influence of nutrient loading on reactions upon frost and drought stress of Rosa majalis

Abstract

Nutrient loading applies more fertilizer compared to non-loading. Conventional loading delivers nutrients to the plants in a more or less constant rate mainly using slow release fertilizer; for exponential loading liquid fertilizer is used increasing exponentially towards the end of the vegetation period. Nutrient loading aims to build nutrient reserves, especially N, in the plants to improve transplanting success. Until now the effect of this fertilization technique on abiotic stress reactions is not known. The reactions of Rosa majalis cultivated for one vegetation period (2010) without loading and with conventional or exponential loading were investigated in early frost (autumn 2010), late frost and drought (spring resp. summer 2011) under controlled conditions. In all treatments, the absolute level of damage, relative electrolyte leakage (REL), was low in early frost. However, relative electrolyte leakage significantly increased at-8°C for the exponentially loaded plants while this was the case only at-16°C for the conventionally loaded and non-loaded plants. Similarly for late frost, REL increased already at-5°C for the exponentially loaded plants and only at-9°C for the non-loaded and conventionally loaded ones. At-5°C the absolute level of damage was low for plants from all treatments and high for-9°C. In both frost experiments, possible cryoprotective compounds like sucrose and glucose in most cases did not differ between the previous fertilization treatments. However, concerning drought reactions, exponentially loaded plants had an advantage compared over conventionally loaded and nonloaded ones in postponing wilting. They closed their stomata earlier and synthesised highest concentrations of proline and sucrose compared to non-loaded and conventionally loaded plants. Possible reasons are discussed. The results indicate that the technique of exponential nutrient loading might be helpful to improve the plants' ability to perform well after being transplanted to drought prone sites. However, increased frost sensitivity has to be considered as well.