How does the soil moisture influence yield and water use of black locust ? Kontakt Name: Dario Mantovani Email: mantdar2@gmail.com Internationale Graduiertenschule der BTU Cottbus Fachklasse Ökosystemforschung Dario Mantovani 1,2 , Maik Veste 3 , Dirk Freese 2 1 Brandenburg University of Technology, International Graduate School, Cottbus; 2 BTU, Chair of Soil Protection and Recultivation, Cottbus; 3 CEBra – Centre for Energy Technology Brandenburg e.V. Cottbus; Germany Fig. 2 Soil moisture (%) distribution along the profile, measured every 10 cm with the FDR profile probe, during the vegetative period, from the 1st of June to 11 November a) SWC14% b)SWC10% c)SWC7%. 1-Jun 6-Jul 17-Aug 28-Sep 11-Nov Data 0 10 20 0 10 20 Relative soil water content [%] 0 10 20 30 SWC 10 cm SWC 20 cm SWC 30 cm SWC 40 cm a b c Fig. 3 Cumulative water use a) SWC14% b)SWC10% c)SWC7% and experimental water balance d)SWC14% e)SWC10% f)SWC 7%, during the vegetative period, from the 1st of June to 11 November. . Fig. 5 Black locust water used (L) in relation to the above grounrd dry biomass (kg) produced during the vegetative period. Fig. 4 Mean weekly transpiration (L) in relation to the weekly mean vapour pressure deficit (kPa). Introduction The importance of black locust (Robinia pseudoacacia L.) for biomass production for bioenergy production with agroforestry and short rotation coppices (SRC) will increase in Brandenburg within the next decades. More detailed information about the link between the soil water availability, the evaporative atmospheric demand, the transpiration and yield is needed. For our study we developed a wick lysimeter system to investigate the transpiration-yield relation under different irrigation regimes. The lysimeter system The water consumption at whole plant level is determined by the experimental water balance with a novel wick lysimeter system [1], which allows us to study plant growth under semi-controlled environmental conditions (Fig. 1a). To avoid uncontrolled water input by rainfall we installed the lysimeters under a light- transmissive roof. The water amount for each treatment is controlled by an automatic irrigation system and supplied in relation to the volumetric soil water content (SWC) at 7%, 10% and 14% respectively. The tree transpiration is calculated by the following equation: Transpiration = Irrigation – Drainage +/- Storage. On leaf level, transpiration and net photosynthesis are determined with a portable mini cuvette system (Fig 1b). Results During the growing season, the SWC of the lysimeters was maintained within the preconceived values (Fig. 2). As expected from the hydraulic characteristics of the lysimeter, the drainage extension was efficient and no stagnancy occurred. Constant suction was performed by the hanging water column throughout the wick material. It has been particularly useful to evaluate the storage variation every 10 cm along the profile with high accuracy for the weekly water budget. The influence of the soil water availability on the cumulative tree transpiration and the water balance of the lysimeter experiment is shown in Fig. 3. Well-watered plants show a high transpiration rate, which increased with an increasing vapour pressure deficit (VPD) during warm days (Fig. 4). On leaf level, black locust showed high transpiration rates up to 10 mmol m -2 s -1 . With decreasing soil water content, water uptake is limited and transpiration is reduced (5 mmol m -2 s -1 ) and regulated by the stomata. From the linear relation between the cumulative transpiration and the above ground dry biomass, we calculated a transpiration coefficient of 415.3 L kg -1 of dry biomass (Fig 5). Conclusions Under well-watered conditions black locust is not a water saving tree and has a high transpiration rate, even on leaf level. Its water use efficiency (WUE) is lower (2.41 kg m -3 ), compared to other fast-growing trees like willows (5.5 kg m -3 ) [3] or poplars (4.1 kg m -3 ) [4]. However, black locust was able to produce biomass even under limited soil water conditions, therefore it is a suitable tree species for the rather dry conditions of the region. References [1] Mantovani, D., Freese, D., Veste, M., Hüttl, R.F. (2011): Modified wick lysimeters for critical water use efficiency evaluation and yield crop modelling. LFZ Raumberg-Gumpenstein (ed.) Conference proceedings 14th Lysimeter Conference “Lysimeters in Climate Change Research and Water Resources Management“, 245-248 [2] Mantovani, D., Veste, M., Freese, D. (2012): Evaluation of fast growing tree transpiration under different soil moisture regimes using wick lysimeters, i-Forest Journal of Biogeoscience and Forestry, submitted. [3] Lindroth A, Verwijst T, Halldin S (1994). Water-use efficiency of willow: variation with season, humidity and biomass allocation. Journal of Hydrology 156:1-19. [4] Yin C, Wang X, Duana B, Luob J, Li C (2005) Early growth, dry matter allocation and water use efficiency of two sympatric Populus species as affected by water stress. Environmental and Experimental Botany 53: 315-322 Fig. 1 a) Black locust estabilished in wick lysimeter , in spring 2011, b) portable minicuvette system. a b