Temperature controls a dependence of barley plant growth on mineral nutrition level

The effect of temperature regime on growth and other morphological characteristics of barley plants (Hordeum distichum L., cv. Andrei) as dependent on the level of mineral nutrition was investigated in a controlled experiment. Plants were raised hydroponically at a high (0.22 g/(g day)) and low (0.05 g/(g day)) relative rates of the addition of mineral nutrients (RA). Mineral nutrients were daily added to the nutrient solutions in exponentially increased amounts to provide steady-state plant growth. At the optimum temperature regime (21/17 degrees C, day/night), the plant relative growth rate (RGR) was proportional to the preset RA during the entire exponential period. Low RA led to a decrease in the nitrogen content in plants, plant weight, and respiratory activity, as well as to the increase in the relative root weight. Biomass accumulation at lowered temperature regime (13/8 degrees C) and a high RA was 1.8-fold lower than at optimum temperature regime. Although under these conditions, the ratio of respiration to gross photosynthesis reduced threefold due to the decrease in the respiration rate, RGR of plants was equal to 0.11 +/- 0.02 g/(g day), which was twice lower than the preset RA. These pointed to the decrease in plant ability to maintain a certain ratio of photosynthesis to respiration within a day. At a deficiency of mineral nutrition and low temperature, RGR reached the preset RA. Plants adapted to lowered temperature by a shift of the temperature optimum of their metabolism (heat production) to lower values. As a whole, a low variability of such growth parameters as RGR, C/N, and root to shoot weight ratio at different RA and lowered temperatures testified to the lessening of growth limitation by the mineral nutrition.