Tropentag, September 17 - 19, 2013 in Stuttgart-Hohenheim "Agricultural development within the rural-urban continuum"

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

¹Chinese Academy of Sciences, State Key Laboratory of Vegetation and Environmental Change, China
²Northeast Normal University, Inst. of Grassland Science, China
³University of Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics, Germany

Abstract

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. and Lolium perenne L.) and two C4 annual grasses (Chloris virgata Swartz and Setaira viridis (L.) Beauv ) were measured in response to increasing atmospheric water vapour pressure deficits (VPD) in a chamber based experiment. To study the effects of N availability on transpiration, 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 a sharp increase of transpiration rates under the low VPD levels and a very low increase at higher levels indicating stomata response. In contrast C4 species showed a linear increase of transpiration rates throughout all VPD levels. N addition reduced transpiration rates of all species successively with increasing N levels. Chamber measurements were confirmed by δ¹³C leaf analysis 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 declined with increasing N limitation the water use efficiency consequentially decreased and nitrogen use efficiency increased. This was in turn confirmed by increasing biomass N concentrations with increasing N supply.
Our results are challenging the current view that well N supported plants transpire more water per unit leaf area compared to N deficient plants. One crucial point could be the whole plant transpiration dynamics, which not necessarily corresponds to the single leaf based gas exchange measurement practice. Furthermore standard leaf gas exchange analysis is usually not subjected to 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 N supported plants show water saving traits if WUE is considered. Most interesting to analyse next is how transpiration responds to different N levels combined with water limitations.

Keywords: C4, C3, δ¹³C, nitrogen, transpiration, VPD

Contact Address: Qiushi Ning, Chinese Academy of Sciences, State Key Laboratory of Vegetation and Environmental Change, Nanxincun 20 Xiangshan, 100093 Beijing, China, e-mail: ningqiushiibcas.ac.cn