Whole-Plant Transpiration in Response to Variable Water Pressure Deficit and Nitrogen Supply

Publication Type

Contribution to conference

Authors

Nimg, Q., Gao, Y., Giese, M., Asch, F., Wei, H.

Year of publication

2013

Published in

Agricultural development within the rural-urban continuum

Editor

Tielkes, E.

Pubisher

Cuvillier Verlag , Göttingen

Page (from - to)

422

Conference name

Tropentag 2013

Conference location

Hohenheim

Water and nitrogen (N) are essential resources for plants to maintain physiological activities.One crucial question is how transpiration is responding to variable N supply.In this study whole plant transpiration of two C3 perennial grasses (Leymus chinensis(Trin.)Tzvel. andLolium perenneL.) and two C4 annual grasses (Chloris virgataSwartz andSetairaviridis(L.) Beauv ) were measured in response to increasing atmospheric water vapour pressuredeficits (VPD) in a chamber based experiment. To study the effects of N availability on tran-spiration, plants were grown under different N levels (full water supply) ranging from deficient(0.01 mmol), normal (2 mmol), medium (8 mmol), high (16 mmol) N rates.All analysed species revealed increasing transpiration rates with VPD. C3 plants showed asharp increase of transpiration rates under the low VPD levels and a very low increase at higherlevels indicating stomata response. In contrast C4 species showed a linear increase of transpi-ration rates throughout all VPD levels. N addition reduced transpiration rates of all speciessuccessively with increasing N levels. Chamber measurements were confirmed byδ13C leafanalysis indicating less isotope discrimination under high N levels for the C3 species as a long-term proxy for less stomata gas exchange. Since biomass production of all species declinedwith increasing N limitation the water use efficiency consequentially decreased and nitrogenuse efficiency increased. This was in turn confirmed by increasing biomass N concentrationswith increasing N supply.Our results are challenging the current view that well N supported plants transpire more waterper unit leaf area compared to N deficient plants. One crucial point could be the whole planttranspiration dynamics, which not necessarily corresponds to the single leaf based gas exchangemeasurement practice. Furthermore standard leaf gas exchange analysis is usually not subjectedto variable VPD levels, which turned out to reveal differences among species and treatments.Further implications of our results might affect management practices in the way that well Nsupported plants show water saving traits if WUE is considered. Most interesting to analysenext is how transpiration responds to different N levels combined with water limitations.