Tropentag, September 19 - 21, 2012 in Göttingen "Resilience of agricultural systems against crises"

Transpiration Response of C3 and C4 Plants of Northern Chinese Steppe Ecosystem to Water Vapor Pressure Deficits (VPD)

¹Northeast Normal University, Institute of Grassland Science, Key Laboratory for Vegetation Ecology, China
²University of Hohenheim, Inst. of Plant Production and Agroecology in the Tropics and Subtropics, Germany

Abstract

Since water is often limiting plant growth in semi-arid ecosystems, the regulation of transpiration is an essential component of adaptation strategies. Transpiration of plants is usually increasing with water vapor pressure deficits (VPD) of the atmosphere; however, different species vary in the regulation of water losses which might help to explain plant community dynamics in semi-arid environments. Chamber experiments were performed with five dominant plant species originating from steppe ecosystems of Northern China. These comprised three C3 plants and two C4 annual grasses. Canopy transpiration of these five plants cultivated in pots under full water supply was measured in a chamber allowing to adjust VPDs ranging from 0.5 (low pressure deficit) to 2.5 kPa (high deficit). The results showed that C3 plant Leymus chinensis reached a maximum transpiration rate at VPD 1.3 kPa with little or no further increase in transpiration rate above this value as VPD was increased. In contrast, the other four species showed continued linear increase in transpiration rate with increasing VPD. The annual dicotyledonous species showed highest transpiration rates, while C4 annual grasses showed less water loss per unit leaf area. These results indicated different water household strategies of dominant plant species in the Songnen grassland. L. chinensis with high transpiration under low VPD and down regulation under higher VPD indicate effective stomata regulation during mid-day VPD peaks resulting in water conservation. Low transpiration rates of C4 annuals might be explained with comparably small rooting systems limiting the water uptake under high pressure gradients. The C3 annual dicotyledonous plant, however follows an opportunistic strategy with high water consumption. Plants photosynthetic performance combined with morphological and functional traits are promising indications for studying the adaptation mechanisms of plant species under semi-arid conditions.

Keywords: C3, C4, stomata, transpiration, vapour pressure deficit, grassland

Contact Address: Marcus Giese, University of Hohenheim, Inst. of Plant Production and Agroecology in the Tropics and Subtropics, Stuttgart, Germany, e-mail: m.gieseuni-hohenheim.de