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Meadow fescue (Festuca pratensis), Italian ryegrass (Lolium multiflorum), their hybrid Festulolium braunii and perennial ryegrass (Lolium perenne) were grown hydroponically under vegetative (20 °C) and hardening (8 °C, 0 °C) regimes. The relative shoot/root growth ratio K, linear root growth rate and other parameters were estimated. When the temperature was lowered from 20 °C to 8 °C, the relative shoot/root growth ratio K of F. pratensis decreased to 0.6, i.e. much more than that of Lolium, suggesting that at 8 °C F. pratensis shoot growth blockage occurs. Further, by dropping the temperature from 8 °C down to 0 °C, the K ratio of F. pratensis increased significantly, while the linear root growth rate decreased much more markedly than in the other species – it suggests also a blockage of root growth. This growth slowdown of stress‐tolerant F. pratensis shoots and at a lower temperature also of its roots is inadequate to the direct impact of temperature and, thus, indicates a two‐step qualitative reorganization, i.e. transition into a qualitatively new state of stress. This phenomenon does not manifest itself in the less stress‐tolerant Lolium and Festulolium species but is expressed in stress‐tolerators, allowing them to achieve their strategic goal – to survive under extreme conditions.

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The study investigated the cultivars of non-obligatorily requiring vernalization plant Festulolium braunii and assessed the influence of non-hardy reproductive and hardy vegetative structures on overwintering effect. The study was conducted taking into account systemic relations between these types of structures. The results show the cultivars differ according to the percentage of headed and overwintered plants, when the cultivars with the most abundant heading -'Felopa' and 'Sulino' -are also better at overwintering. The positive correlation between heading and overwintering characteristics was also observed, what seemed to be a rather new finding. It can be explained by systemic effect: non-hardy later reproductive structures induce the post-generative regrowth of vegetative shoots, which during shorter days halt development and become potentially hardy. More detailed interpretation is also provided including discussion of causal mechanisms of the detected phenomenon. The authors suppose that these mechanisms constitute a survival strategy for such perennial plants. The observed late heading which represents reproductive structures could be applied in plant breeding as a marker of winter-hardiness among perennial grass plants which non-obligatorily demand vernalization.

Modern plant physiology deals with a plant at different hierarchical levels, from the ecosystem to molecular ones, so there is a demand to integrate the knowledge obtained at these levels. Examining plant growth and cold resistance, namely the intermediate levels (organism, organs, tissues, multicellular) often reveals the peculiarities of the functional–structural organization of the entire plant. The paper presents an integrated climatic hydroponic system, designed to implement a physical‐holistic experiment, accompanied by a particular methodology of systemic research. It covers the following main steps, which are the verification of the experimental system, production of high‐quality experimental material, including direct measurements and mathematical data analysis. The latter involves the decomposition of the phenomena under study, synthesis of data and the extraction of non‐linear components. The studies on the growth and stress of Poaceae plants (Lolium multiflorum, Festuca pratensis, Festulolium braunii) have already provided some significant results. A new boundary of the leaf meristem was proposed, adaptive growth bifurcations were discovered in the meristem, and a cells rounding phenomenon was detected. Using this top‐down approach, further research directions are delineated towards the lower hierarchical levels. Finally, the presented approach allows for the integration of data obtained at different plant investigation levels.