Water stress effects on growth, yield and quality traits of red beet

The response of red beet to drought stress was investigated in order to explore the adaptive changes in plant growth, dry mass production and partitioning, yield, and in accumulation of nutrient and bioactive molecules. Experiments were conducted in a glasshouse in 2012. Three water stress treatments were applied: (W100) 100% of water holding capacity (WHC), (W50) 50% of WHC, (W30) 30% of WHC. Water stress reduced storage root weight by 71% at W50 and 88% at W30 as well as leaf water content (LWC). With the progressive water stress, plant allocated less dry matter into roots leading to reductions of 43% and 67% in W50 and W30, respectively as compared to W100. Stomatal conductance was strongly reduced (from 496 to 211 mmol m-2 s-1 in W100 and W30, respectively); canopy temperature (CT) reflected the available water, with differences of 11 °C. Drought induced a significantly higher concentration of total phenolic content (TPC) (a 75% increase and betalains (52% and 70% increases in betacyanin and betaxanthin) and consequently a higher antioxidant activity was obtained. Minerals such as Mg, P and especially Zn (2.9 and 0.7 mg 100 g-1 DW in W50 and W100, respectively) and Fe (5.6 and 2.4 mg 100 g-1 DW in W30 and W100, respectively) were highly concentrated in water stressed roots as was NDF and ADF. In contrast, °Brix, pH and total not-structural sugars were reduced by water stress, although the sugar fractions of fructose and glucose concentrated more in W30 plant roots than W100 (18 and 33% higher, respectively). Red beet showed a strong plasticity in its adaptation to drought thanks to avoidance mechanisms, i.e. constrained leaf and storage root development, and tolerance mechanisms i.e. increased FLV and thermal dissipation. Interestingly, the high concentration in phytochemicals and nutrients may contribute to the maintenance of human health and may reduce the risk of chronic diseases. [...

Leaf traits as indicators of limiting growing conditions for lettuce (Lactuca sativa)

Lettuce growth under unstressed conditions was compared to growth under four limiting conditions, i.e. no phosphorus fertilization (0_P), no nitrogen fertilization (0_N), low light (LR) and water stress (WR) over two different growing periods. We investigated the adaptive changes in terms of the morphological and physiological leaf traits, identifying stress-specific and ‘stable’ indicators suitable for use in breeding programmes. The plants subjected to the WR treatments had lower leaf expansion and specific leaf area (SLA), as well as lower soil–plant analysis development (SPAD) values, stomatal conductance (POR), water index (WI) and leaf temperature (TIR) compared with plants in the unstressed CONTROL. Low light increased the leaf area (LA), SLA and leaf mass ratio (LMR). The 0_N treatment induced a general reduction in the normalised difference vegetation index (NDVI) values, as well as strong changes in LMR and SLA. In general, 0_P induced less pronounced effects than the other treatments. Principal component analysis indicated that the stable and suitable selection indicators of adaptive changes for low nitrogen and low light conditions were LA, SLA, leaf area per unit total plant mass (LAR), LMR, SPAD and POR, while SPAD, POR, TIR and WI were suitable indicators for drought