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Root-Zone Warming Differently Benefits Mature And Newly Unfolded Leaves Of Cucumis Sativus L. Seedlings Under Sub-Optimal Temperature Stress

PLOS ONE(2016)

Cited 19|Views6
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Abstract
Sub-optimal temperature extensively suppresses crop growth during cool-season greenhouse production. Root-zone (RZ) warming is considered an economical option to alleviate crop growth reduction. In this study we cultivated cucumber seedlings in nutrient solution under different air-RZ temperature treatments to investigate the effects of RZ warming on seedling growth-and photosynthesis-related parameters in leaves. The air-RZ temperature treatments included sub-optimal RZ temperature 13 degrees C and sub-optimal air temperature 20/12 degrees C (day/night) (S13), RZ warming at 19 degrees C and sub-optimal air temperature (S19), and RZ warming at 19 degrees C and optimal air temperature 26/18 degrees C (day/night) (O19). In addition, for each air-RZ temperature treatment, half of the seedlings were also treated with 2% (m/m) polyethylene glycol (PEG) dissolved in nutrient solution to distinguish the effect of root-sourced water supply from RZ temperature. At the whole-plant level, S19 significantly increased the relative growth rate (RGR) by approximately 18% compared with S13, although the increase was less than in O19 (50%) due to delayed leaf emergence. S19 alleviated both diffusive and metabolic limitation of photosynthesis in mature leaves compared with S13, resulting in a photosynthetic rate similar to that in O19 leaves. In newly unfolded leaves, S19 significantly promoted leaf area expansion and alleviated stomatal limitation of photosynthesis compared with S13. PEG addition had a limited influence on RGR and leaf photosynthesis, but significantly suppressed new leaf expansion. Thus, our results indicate that under sub-optimal temperature conditions, RZ warming promotes cucumber seedling growth by differently benefiting mature and newly unfolded leaves. In addition, RZ warming enhanced root-sourced water supply, mainly promoting new leaf expansion, rather than photosynthesis.
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Key words
leaves,root-zone,sub-optimal
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