Abstract
Genotypic variations of alfalfa (Medicago sativa L.) to both phosphorus (P) deficiency and water deficiency are evident on the Loess Plateau of China. Here, we compare the adaptive mechanisms between an introduced cultivar (Arkaxiya) and a landrace (Longzhong) subjected to P- and water-limited conditions. The two genotypes were grown in a soil medium with 0, 4.2, 8.4 and 16.8 μg applied P per gram dry soil. Three water treatments were imposed (maintained at 75–90%, 45–55% and 30–35% of pot capacity (PC)) 28 days after sowing (DAS). At high soil P and high soil water content (SWC), high rates of net photosynthesis (Pn) contributed to greater plant growth and P-use efficiency (PUE) in the introduced Arkaxiya compared to the landrace Longzhong. However, at low SWC, Longzhong had enhanced antioxidative defense (mainly SOD and CAT) compared to Arkaxiya. In addition, shorter shoot length and greater branching in Longzhong than Arkaxiya may also facilitate adaptation to low SWC. The contrasting adaptive mechanisms of the two genotypes provide a number of early-screening parameters associated with plant growth for the selection and introduction of alfalfa targeted at different rainfall and available P environments.
Highlights
Alfalfa is an important forage legume for the semiarid regions of the Loess Plateau of China [1,2].In the past 25 years, the areas growing alfalfa on the Loess Plateau have expanded dramatically to meet the huge demand for forage for animal industry
There was no difference in total dry mass between the two genotypes with nil-P applied in soil at all three soil water treatments
In the WW treatment, a similar amount of dry mass was allocated to roots as to leaves and stems (Table S1 and Figure S1), whereas a greater proportion of dry mass was allocated to roots with limited water supply (MS and severe water shortage (SS) treatments, Table S1)
Summary
Alfalfa is an important forage legume for the semiarid regions of the Loess Plateau of China [1,2]. In the past 25 years, the areas growing alfalfa on the Loess Plateau have expanded dramatically to meet the huge demand for forage for animal industry. The negative effects of water and P limitation will increase with the predicted increase in the incidence and severity of droughts with climate change on the Loess Plateau [6], as well as the future depletion of the non-renewable P resource [7]. Oxidative stress inevitably reduces CO2 assimilation and increases electron transfer from photosynthetic electron carriers toward O2 , and increases the reactive
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