Ecophysiology of Robinia and Populus in temperate agroforestry systems

  • Photosynthetic characteristics and simulation of annual leaf carbon gains of hybrid poplar (Populus nigra L. x P. maximowiczii Henry) and black locust (Robinia pseudoacacia L.) in a temperate agroforestry system
IMG 3431

A leaf net photosynthesis model is presented driven by light and modulated bytemperature and air humidity. From this the seasonal variation of CO2 uptake and release could be modelled to estimate the annual carbon fluxes of sun and shade leaves. In fully expanded leaves light is the major factor determining daily carbon balances, and highest observed daily carbon gains in sun leaves amounted to 748.9 mmol CO2 m-2 d-1 in poplar and to 536.3 mmol CO2 m-2 d-1 in black locust, while the annual carbon gains amounted to 46824 mol CO2 m-2 in black locust and 66803 mol CO2 m-2 in hybrid poplar. Results obtained via gas exchange measurements and from the leaf model clearly indicate a potentially better growth performance of the poplar compared to black locust on the investigated site. The presented photosynthesis model provides a good and realistic estimation for seasonal carbon balances on the leaf level for both species.

Küppers, M., Schmitt, D., Liner, S., Böhm, C., Kanzler, M., Veste, M. (2017): Photosynthetic characteristics and simulation of annual leaf carbon gains of hybrid poplar (Populus nigra L. x P. maximowiczii Henry) and black locust (Robinia pseudoacacia L.) in a temperate agroforestry system. Agroforestry Systems.

  • Spatial and temporal variation of drought impact on black locust (Robinia pseudoacacia L.) water status and growth

Stimulated by the rising demand for bioenergy, forestry practices for energy production are of increasing importance worldwide. Black locust (Robinia pseudoacacia L.) is a suitable tree species for biomass production in short-rotation plantations in East Germany, especially on marginal land where insufficient water and nutrients are a limiting factor for tree growth. Our study aims to clarify the spatial and temporal variability of the black locust growth through the analysis of the plant water status, and to evaluate the effect of adverse edaphic conditions on growth performances, amplified by periods of summer drought. The study was carried out at two sites presenting comparable climatic but different edaphic conditions: (i) fertile agricultural soil; and (ii) heterogeneous unstructured soil from a reclaimed post-mining area. During the vegetation period, the growth rate decreased in both sites following the plant water status in terms of pre-dawn leaf water potential. Particularly in the post-mining area, due to the adverse edaphic conditions, below the critical pre-dawn water potential value of -0.5 MPa, the stem growth was drastically reduced during a period of summer drought. However, the trees could cope with the extreme soil and weather conditions in the post-mining site without perishing.

Mantovani, D., Veste. M., Böhm, C., Vignudelli, M., Freese, D. (2015): Spatial and temporal variation of drought impact on black locust (Robinia pseudoacacia L.) water status and growth  iForest - Journal of Biogeosciences and Forestry 8: 743-747

  • Carbon allocation, nodulation, and biological nitrogen fixation of black locust (Robinia pseudoacacia L.) under soil water limitation

The pioneer tree black locust (Robinia pseudoacacia L.) is a drought-resistant tree and, in symbiosis with Rhizobium, able to fix dinitrogen from the atmosphere. It is, therefore, an interesting species for marginal lands where soil amelioration is sought in addition to economic gain. However, the interaction between soil water availability, carbon allocation and nitrogen fixation is important for a successful establishment of trees on marginal lands and has not yet been investigated for black locust. Twoyear-old trees were grown under various soil water conditions and drought cycles. The stable isotopic composition of C (δ 13C) and N (δ 15N) of the leaves was used to identify i) the effective drought condition of the treatments and ii) the portion N accrued from the atmosphere by the biological nitrogen fixation. Drought-stressed plants significantly reduced their total aboveground biomass production, which was linearly linked to tree transpiration. The shoot:root ratio values changed from 2.2 for the drought-stressed to 4.3 for the well-watered plants. Our investigation shows that drought stress increases the nodule biomass of black locust in order to maintain biological nitrogen fixation and to counteract the lower soil nitrogen availability. The biological nitrogen fixation of drought-stressed trees could be maintained at relatively higher values compared to the well-watered trees. The average leaf nitrogen content varied between 2.8% and 3.0% and was not influenced by the drought stress. Carbon fixation, carbon allocation, and biological nitrogen fixation are to some extent balanced at low irrigation and allow Robinia to cope with long-term water constraints. The combination of black locust’s ecophysiological and morphological plasticity make it interesting as a biomass source for bioenergy and timber production, even in nutrient-limited and drought-affected areas of Europe.

Mantovani, D., Veste. M., Boldt-Burisch, K., Fritsch, S., Koning, L., Freese, D. (2015): Carbon allocation, nodulation, and biological nitrogen fixation of black locust (Robinia pseudoacacia L.) under soil water limitation. Annals of Forestry Research 58 (2): 259-274.

  • Black locust (Robinia pseudoacacia L.) ecophysiological and morphological adaptations to drought and their consequence on biomass production and water-use efficiency
ROB1 (9)

Successful plantation efforts growing Robinia pseudoacacia L. (black locust) in the drier regions of Hungary and East Germany (Brandenburg), have demonstrated the potential of black locust as an alternative tree species for short-rotation biomass energy plantations. 

The response of black locust to water limitation was investigated in a lysimeter experiment. Plants were grown under three different soil moisture regimes, with values set at 35%, 70%, and 100% of the soil water availability, namely WA35, WA70, and WA100. Their morphological adaptation and productivity response to water constraint were assessed together with their water-use efficiency. Furthermore, the ecophysiological adaptation at the leaf level was assessed in terms of net photosynthesis and leaf transpiration.

During the growing season, plants in the WA35, WA70, and WA100 treatments transpired 239, 386, and 589 litres of water respectively. The plants subjected to the WA35 and WA70 treatments developed smaller leaves compared with the plants subjected to the WA100 treatment (66% and 36% respectively), which contributed to the total leaf area reduction from 8.03 m2 (WA100) to 3.25 m2 (WA35). The total above-ground biomass produced in the WA35 (646 g) and WA70 (675 g) treatments reached only 46% and 48% of the biomass yield obtained in the WA100 (1415 g). The water-use efficiency across all treatments was 2.31 g L−1. At vapour pressure deficit (VPD) values <1.4 kPa trees growing under the WA35 soil moisture regime showed a stomatal down-regulation of transpiration to 5.3 mmol m−2 s−1, whereas the trees growing under the WA100 regime did not regulate their stomatal conductance and transpiration was 11.7 mmol m−2 s−1, even at VPD values >2 kPa.

Black locust plants can adapt to prolonged drought conditions by reducing water loss through both reduced transpiration and leaf size. However, under well-watered conditions it does not regulate its transpiration, and therefore it cannot be considered a water-saving tree species.

Mantovani, D., Veste, M., Freese, D. (2014) Black locust (Robinia pseudoacacia L.) ecophysiological and morphological adaptations to drought and their consequence on biomass production and water use efficiency. New Zealand Journal of Forestry 44: 29.

  • Effects of drought frequency on growth performance and transpiration of young black locust (Robinia pseudoacacia L.)
Bild200 (1)

Black locust (Robinia pseudoacacia L.) is a drought-tolerant fast growing tree, which could be an alternative to the more common tree species used in short-rotation coppice on marginal land. The plasticity of black locust in the form of ecophysiological and morphological adaptations to drought is an important precondition for its successful growth in such areas. However, adaptation to drought stress is detrimental to primary production. Furthermore, the soil water availability condition of the initial stage of development may have an impact on the tree resilience. We aimed to investigate the effect of drought stress applied during the resprouting on the drought tolerance of the plant, by examining the black locust growth patterns. We exposed young trees in lysimeters to different cycles of drought. The drought memory affected the plant growth performance and its drought tolerance: the plants resprouting under drought conditions were more drought tolerant than the well-watered ones. Black locust tolerates drastic soil water availability variations without altering its water use efficiency (2.57 g L−1), evaluated under drought stress. Due to its constant water use efficiency and the high phenotypic plasticity, black locust could become an important species to be cultivated on marginal land.

Mantovani, D., Veste, M., Freese, D.  (2014): Effects of drought frequency on growth performance and transpiration of young  black locust (Robinia pseudoacacia L.). International Journal of Forestry Research, 2014, Article ID 821891: 11 pages. 

  • Evaluation of fast growing tree transpiration under different soil moisture regimes using wicked lysimeters.
ROB1 (6)

The cultivation of fast growing trees has high potential for bioenergy production on marginal lands. Information about the water use efficiency in combination with the ecophysiological response to drought stress is still incomplete. For the study of the transpiration-biomass relations satisfactory results can be obtained under controlled conditions by using lysimeters. Nonetheless, several technical problems related to the manufacturing can bias the outcome. Pan lysimeters are economical and relatively easy to assemble, however, saturation at the lower boundary can happen. On the other hand tension lysimeters, where the suction is applied by a vacuum pump, are effective but expensive and need constant maintenance. To avoid stagnancy and reduce production costs we assembled a tension controlled wick lysimeter, where the tension at the bottom layer is actively exerted by a hanging water column through the wick material (rockwool). We aim to assess the performance of the wick lysimeter coupled with an automatic irrigation system for the study of water use-yield relation black locust (Robinia pseudoacacia L.) under different irrigation regimes. The volumetric soil content for each treatment, namely low water (LW), medium water (MW) and high water amount (HW), was maintained at 0.07, 0.14 and 0.2 m3 m-3 respectively. During the vegetation period (161 days) the plants growing at LW reduced their water use by 60%, their leaf area by 40% and the total above ground biomass by 46%. As a result, we found a linear correlation (R2 = 0.98) between the relative biomass produced and the relative water use. The calculated relative water use efficiency (RWUE) for black locust total above ground dry biomass is 0.96. Furthermore, after the harvest we evaluated the effectiveness of the lysimeter and irrigation system: the soil moisture of the treatments was kept up at the predefined values and an unsaturated condition at the boundary layer was maintained throughout the vegetation period. Because of the improved design no roots grew into the drainage extension and no unexpected change of the lysimeters hydraulic property occurred. Considering the relatively low-cost material used and the low maintenance needed, compared to other tension controlled lysimeters, wick lysimeters are effective tools for forestry studies of young trees.

Mantovani, D., Veste, M., Badorreck, A., Freese, D. (2013): Evaluation of fast growing tree transpiration under different soil moisture regimes using wicked lysimeters. iForest - Journal of Biogeosciences and Forestry 6: 190-200.  

  • Influence of drought stress on photosynthesis, transpiration, and growth of juvenile black locust (Robinia pseudoacacia L.)

Nowadays, black locust (Robinia pseudoaccacia L.) is an important tree species in Central and Eastern Europe. The native range of black locust is classi ed by a humid to sub-humid climate with normal annual precipitation of 1,020 to 1,830 mm. However, in Central Europe, black locust is known to be relatively drought tolerant compared to other temperate deciduous tree species. As a pioneer species the tree grows under a wide range of conditions and is used for reclamation of former open-cast lignite mining areas in Brandenburg and cultivated in short-rotation plantations for the production of bioenergy wood. In order to evaluate the growth and ecophysiological performance of black locust to drought stress, a pot experiment was established at the Thünen-Institut, Hamburg. The photosynthetic performance was studied with a PAM 2100 chlorophyll  uorescence system and net CO2-exchange and transpiration were determined with a minicuvette system CMS 400. Under drought stress net photosynthesis and transpiration were reduced due to stomatal closure. The measured electron transport rate of the photosystem II showed an opposite trend to the net photosynthesis and increased also under drought stress and in- creasing temperature up 30 °C. This indicates a higher fraction of energy dissipation of electrons to photorespiration and the Mehler reaction to avoid photoinhibition under limited CO2-uptake under drought stress und high temperatures. To minimize transpiration on the plant level leaf area was drastically reduced during drought stress. The plants showed different adaptations and a high plasticity of the ecophysiological processes to cope with a long-term drought stress and high temperature, which allows growing also in drier regions.

Veste, M., Kriebitzsch, W.-U. (2013): Einfluss von Trockenstress auf  Photosynthese, Transpiration und Wachstum junger Robinien (Robinia pseudoacacia L.). Forstarchiv 84: 35-42.

  • Biological nitrogen-fixation by Robinia pseudoacacia
ROB1 (5)

Because of its N2-fixation ability black locust plays generally an important role for the improvement of soil fertility. This effect is of particular interest in the post-mining landscapes. 

In order to estimate the N2-fixation potential of black locust at marginal sites leaf samples were taken from black locust trees in short rotation plantations planted between 1995 and 2007 in post mining sites south of Cottbus (Brandenburg, NE Germany). The variation of the natural 15N abundance was measured to evaluate the biological nitrogen fixation. The nitrogen derived from the atmosphere can be calculated using a two-pool model from the quotient of the natural 15N abundances of the N2-fixing plant and the plant available soil N. Because representatively determining the plant available soil N is difficult, a non-N2-fixing reference plant growing at the same site with a similar root system and temporal N uptake pattern to the N2-fixing plant is often used. In our case we used red oak (Quercus rubra) as a reference. The average nitrogen content in the leaves of black locust ranged from 3.1% (C/N 14.8) in 15 years old trees to 3.4% (C/N 14.4) in 3 year-old trees, respectively. A higher content of nitrogen was found in leaves of re-sprouted trees with 4.3% (C/N 11.5). The estimated percentage of nitrogen derived from the atmosphere (% NdfA) in black locust was 63% – 83% compared to 56% in seabuckthorn (Hippophaë rhamnoides) and 79% in common broom (Genista scuparia). The annual leaf biomass production of black locust varied between 1325 (2 years old trees) and 2576 kg/ha a (4 years old trees). The estimated leaf nitrogen fixed by Robinia was approx. 30.5 - 59.2 kg/ha a. From the results, we can conclude that the biological nitrogen fixation by Robina is an important factor for the nitrogen balance of short-rotation plantations on nutrient poor-soils.

Veste, M., Böhm, C., Quinkenstein, A., Freese, D., (2013): Biologische Stickstoff-Fixierung der Robinie. AFZ-Der Wald 2/2013: 40-42.

© Maik Veste 2017 - Update 07Dec2017                                          Impressum