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Nitrogen source and water regime effects on durum wheat photosynthesis and stable carbon and nitrogen isotope composition
Author(s) -
Lopes Marta S.,
Araus José L.
Publication year - 2006
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.2006.00595.x
Subject(s) - photosynthesis , transpiration , stomatal conductance , water use efficiency , nitrogen , chemistry , agronomy , ammonium , nitrate , chlorophyll , horticulture , biology , organic chemistry , biochemistry
Water stress and nitrogen (N) availability are the main constraints limiting yield in durum wheat ( Triticum turgidum L. var. durum ). This work investigates the combined effects of N source (ammonium–NH 4 + , nitrate–NO 3 – or a mixture of both–NH 4 + :NO 3 – ) and water availability (well‐watered vs. moderate water stress) on photosynthesis and water‐use efficiency in durum wheat (cv. Korifla) flag leaves grown under controlled conditions, using gas exchange, chlorophyll fluorescence and stable carbon isotope composition (δ 13 C). Under well‐watered conditions, NH 4 + ‐grown plants had lower net assimilation rates (A) than those grown with the other two N forms. This effect was mainly due to lower stomatal conductance (g s ). Under moderate water stress, differences among N forms were not significant, because water regime (WR) had a stronger effect on g s and A than did N source. Consistent with lower g s , δ 13 C and transpiration efficiency (TE) were the highest in NH 4 + leaves in both water treatments. These results indicate higher water‐use efficiency in plants fertilized with NH 4 + due to stomatal limitation on photosynthesis. Moreover, leaf δ 13 C is an adequate trait to assess differences in photosynthetic activity and water‐use efficiency caused by different N sources. Further, the effect of these growing conditions on the nitrogen isotope composition (δ 15 N) of flag leaves and roots was examined. Water stress increased leaf δ 15 N in all N forms. In addition, leaf δ 15 N increased as root N decreased and as leaf δ 13 C became less negative. Regardless of WR, the leaf δ 15 N of NO 3 – ‐grown plants was lowest. Based on stepwise and canonical discriminant analyses, we conclude that plant δ 15 N together with δ 13 C and other variables may reflect the conditions of N nutrition and water availability where the plants were grown. Thus well‐watered plants grown with NH 4 + :NO 3 – resembled those grown with NO3 – , whereas under water stress they were closer to plants grown with NH 4 + .