Physiological and Morphometric Response of Forage Grass Species and Their Biomass Distribution Depending on the Term and Frequency of Water Deficiency.

Periodic and repeated water scarcity has become an increasing concern on grasslands, causing not only to a reduction in productivity but also negative alterations in the carbon balance. The objective of this work was to comprehensively investigate some physiological performance traits of forage grasses, their roots morphometric features and distribution of biomass under simulated water deficit applied in different terms over a period of study. Plants were exposed to water shortage for 21 days, and then grown in optimal substrate moisture conditions. The gas exchange parameters and the main traits of root system architecture of three grass forage species and their cultivars were analyzed: Festulolium braunii (Richt.) A. Camus, cvs. Felopa and Sulino, Lolium perenne L., cvs. Bajka and Gagat and Festuca arundinacea Schreb. cvs. Odys and Rahela. Rapid decrease in the values of parameters related to the gas exchange process in grasses in the following days of water shortage was noticed. Water use efficiency (WUE) value was low in drought conditions due to increased transpiration of plants and was associated with a low C:N ratio in shoots. No obvious, positive effect of previously experienced drought stress on survival of tested grass species after another stress was observed. Cutting of plants after drought period most probably underlied the lack of memory and also additional factor weakened plant regrowth. When the drought was applied for the second time in spring during intensive plant growth, higher biomass allocation to the roots was observed. It was associated with the reduction of plant dry biomass, a decrease of carbon accumulation and the C:N ratio in the shoots. Due to the drought applied for the second time in summer, some biometric features of the roots were strongly and positively correlated with WUE, which is an important feature from the point of view of yield optimization and moisture use by plants. [ABSTRACT FROM AUTHOR]