Spatial and Temporal Variation of Drought Impact on Black Locust (Robinia Pseudoacacia L.) Water Status and Growth

Research Article ii FF o o r r e e s s t t doi: 10.3832/ifor1299-008 Biogeosciences and Forestry vol. 8, pp. 743-747

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

Dario Mantovani (1-2), Maik Stimulated by the rising demand for bioenergy, forestry practices for energy Veste (1-3), Christian Böhm (1), production are of increasing importance worldwide. Black locust (Robinia Marco Vignudelli (4), Dirk Freese (1) pseudoacacia L.) is a suitable tree species for biomass production in short- rotation plantations in East Germany, especially on marginal land where insuf- ficient 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.

Keywords: Agroforestry, Drought Stress, Soil Water Availability, Soil Hetero- geneity, Reclamation

Introduction red, and therefore plant growth depends performance, taking into account the res- The interest in short-rotation coppice sys- mostly on the amount of rainfall. In those ponse of the plant to different edaphic tems rose over the last decades, aiming to areas characterized by unfavorable eda- conditions. There are several research improve the sustainability of the second phic conditions (Hüttl & Weber 2001), the works carried out at field scale, describing generation bioenergy crops. Besides their soil is mostly an unstructured clayed-sandy the black locust biomass production and its positive ecological functions, fast-growing material, extremely heterogeneous and relation to water constraint (Bongarten et trees like poplars and willows can be har- poor in organic materials and nutrients. As al. 1992). The link between the black locust vested and used for bioenergy production a result (Bungart et al. 2000), a decrease in growth and the soil water availability has (Weih 2004). Among the more common productivity is to be expected, due to the been recently clarified by Mantovani et al. tree species used in northern Europe for scarcity of nutrients. Furthermore, the soil (2014a, 2014b), however only in a control- bioenergy production, black locust (Robi- water availability during summer is more led lysimeter experiment. Therefore, in our nia pseudoacacia L.) is planted with remar- prone to water deficit than in agricultural work we aimed at evaluating the impact of kable success for reclamation in lignite soils under the same climatic conditions. summer drought periods and nutrient pau- opencast mining areas in Brandenburg (NE Since water and nutrient availability are the city on black locust growth performance in Germany – Grünewald et al. 2009, Böhm et main limiting factors for primary produc- the field, linking the plant water status to al. 2011). Here, due to the ongoing mining tion, there is a need to evaluate the the radial increment of the trunk during activities, the groundwater table is lowe- drought impact on the black locust growth the vegetation period. The spatial and temporal variability in leaf water potential and its implications for tree growth was taken (1) Brandenburg University of Technology Cottbus-Senftenberg, Institute of Soil Protection into account. More specifically we carried and Recultivation, Konrad-Wachsmann-Allee 6, D-03046 Cottbus (Germany); (2) CRA-OLI - out a critical comparison between black Centro di Ricerca per l’Olivicoltura, v. Nursina 2, I-06049 Spoleto (PG - Italy); (3) CEBra - locust growth performance under water Centre for Energy Technology Brandenburg e.V., Friedlieb-Runge-Strasse 3, D-03046 Cottbus limitation in two sites with different (Germany); (4) University of Bologna, Department of Agricultural Sciences, v. Fanin 44, I- edaphic but comparable climatic condi- 40127, Bologna (Italy) tions.

@ Dario Mantovani ([email protected]) Material and method

Received: Mar 26, 2014 - Accepted: May 15, 2015 Study sites The study area is located in southern Citation: Mantovani D, Veste M, Böhm C, Vignudelli M, Freese D (2015). Spatial and temporal Brandenburg, Germany, about 150 km variation of drought impact on black locust (Robinia pseudoacacia L.) water status and southeast of Berlin and is characterized by growth. iForest 8: 743-747. – doi: 10.3832/ifor1299-008 [online 2015-06-18] an average annual precipitation of 556 mm and a mean annual temperature of 9.3 °C Communicated by: Gianfranco Minotta (1951-2003, nearest climatic station Cott- bus, Deutscher Wetterdienst).

r selected trees was evaluated with dendro- t Fig. 1 - Schematic

s meters (DDL, Ecomatik, Dachau, Germany)

e diagram of the tree

r at breast height at both sites. The selected plantation in Forst o trees were located in the center of the tree F and Welzow-Süd. rows (in the subplots W4 and F4 – see Fig. d The figures are not n 1). The plant water status of 56 selected a in scale and the cir- trees was evaluated periodically, measu- s cles in the figure e ring the pre-dawn leaf water potential c are only represen-

n (Ψpd) of three leaves per tree, using the

e tative of the tree i Scholander pressure chamber (Plant Water c rows, not of the s Status Console 3000, Soilmoisture Inc., o single trees. Santa Barbara, CA, USA). The pre-dawn leaf e g water potential was measured starting two o i hours before sunrise. The trees were geo- B referenced by using a differential GPS sys- – tem (Trimble R8 GNSS /R6 /5800, Dayton, t s Ohio, USA). The spatial information, to- e r gether with the Ψpd values, was integrated o

F into a Geographic Information System i (ARCGIS Spatial Analyst software, ESRI, Redland, CA, USA) and used to create a dynamic map.

Statistical analysis A non-parametric analysis Mann-Whitney U-Test (α < 0.05) was performed to com- pare the two sites in terms of: (i) bulk density; (ii) saturated hydraulic conductivity; (iii) mean cumulative daily diameter increment, measured in the subplots F4 and W4; (iv) mean Ψpd recorded during the same day in different subplots within the same site. The non-parametric Spearmans’ ρ correlation (α < 0.01) was applied to link the mean weekly growth rates to the Ψpd. The analyses were carried out using the IBM SPSS® version 21 (SPSS Inc. Chicago, IL, For the experiment two different sites a width of 24 m. One plot of 11.4 × 105 m USA). For the geospatial analysis the were chosen: (i) Forst (51° 47′ 24″ N, 14° 37′ was selected at each site (Fig. 1), and split ARCGIS Spatial Analyst software (ESRI) was 57″ E), a fertile agricultural field characte- in 7 subplots of 11.4 × 15 m. used. Spatial and temporal variations of rized by sandy loam soil (Gleysol – FAO Air temperature, relative humidity and the Ψpd were evaluated by interpolating the 2006). While located close to the river precipitation values were measured using Ψpd values obtained in the different sub- Neiße, the annual variation of the ground- weather stations and stored on data log- plots during the vegetation period with the water table lies between 1.0 and 2.2 m gers (Delta-T devices Ltd., Cambridge, UK) inverse distance weighted interpolation below the soil surface. (ii) Welzow-Süd (51° in 10 min intervals. method (IDW). 37′ 23″ N, 14° 19′ 34″ E), a reclaimed post- mining site with a groundwater table lower Hydrological soil characteristics Results than 100 m below the soil surface due to The saturated hydraulic conductivity (Ks) the ongoing mining activity. The soil here is was determined in undisturbed soil cores Climatic conditions heterogeneous and consists mainly of (100 cm) sampled at both sites at 5, 20, and The mean daily air temperature and the sands and clayed-sands in an initial stage 40 cm depths in six replicates. We chose vapor pressure deficit (VPD) at both study (Regosol – FAO 2006), therefore it is still the permanent head method using a lab sites are shown in Fig. 2. In Welzow-Süd unstructured (Krümmelbein et al. 2012). permeameter (Eijkelkamp, Giesbeek, Ne- 30% and in Forst 25% of the measured days The total organic carbon (TOC) measured therlands). After measuring the Ks, the had a mean daily temperature lying bet- in Forst (10.1 g kg-1) was higher than in Wel- bulk density of the same cores was deter- ween 20 and 25 °C. The VPD instead sho- zow-Süd (2.9 g kg-1), while the total nitro- mined by oven-drying at 105 °C until con- wed more variation between the two sites, gen (TN) values amounted to 0.9 g kg-1 in stant weight of cores was reached. with 33% and 16% of the days above 5 hPa both sites. Pa-1 for Welzow-Süd and Forst, respectively Black locust bare-root seedlings were Plant growth and plant water status (Fig. 2b). The global radiation at both sites planted in Forst in the spring of 2010 and in For each subplot four fully developed was comparable, with values higher than Welzow-Süd in the spring of 2007. The trees were selected. The monthly tree 200 Wm-2 for approximately 60% of the plants were established in form of an agro- growth was recorded by measuring the days (Fig. 3a). During the vegetation period forestry system as a short-rotation coppice diameter at breast height (DBH) with a the total rainfall in Welzow-Süd amounted for bioenergy production. The design of polyethylene caliper. At the beginning of to 238 mm, while in Forst 301 mm were the agroforestry system at both sites was the experiment, in the spring of 2012 the recorded (Fig. 3b), the daily amount for comparable. The tree hedgerows consisted mean DBH was 18.4 ± 4 mm in Forst and each sites is shown in Fig. 4. of four double rows. Along the row the 35.4 ± 8 mm in Welzow-Süd, which suggest trees were planted every 0.85 m. The tree that, despite the adverse edaphic condi- Hydraulic conditions and soil moisture distance within and between the double tions, tree growth can be considered rela- The mean bulk density of the Gleysol in rows was 0.8 m and 1.8 m, respectively. tively normal also in the latter site. In addi- Forst was 1.6 g cm-3 and the Ks values mea- Crop alleys in between the hedgerows had tion, the daily growth rate of the four sured at 5, 20, and 40 cm depth were 59,

744 iForest 8: 743-747 Drought impact on black locust water status and growth y r t s e r o F

d n a

s e c n e i c s o e g o i B

–

t s e r o F i

Fig. 2 - Daily mean air temperature (a) and daily mean vapor Fig. 3 - Daily mean global radiation (a) and cumulative rainfall pressure deficit (b) measured at Forst and Welzow-Süd during (b) measured at Forst and Welzow-Süd during the vegetation the vegetation period (from June 1st to August 30th, 2012). period (from June 1st to August 30th, 2012).

17, and 27 cm day-1 respectively. Although Süd the plant diameter increased only 52% Spatial variation of pre-dawn water the structureless Regosol sampled in Wel- of the plants established in Forst. potential zow-Süd presented a comparable bulk den- Until July 25, 2015 for all the subplots -3 sity (1.7 g cm ), the Ks was significantly Weekly growth and plant water status measured at both sites the mean Ψpd va- higher, varying between values of 559 (p = The plant water status (Ψpd) in the sub- lues were > -0.5 MPa. At the Forst site, the 0.032), 223 (p = 0.036) and 73 (p = 0.42) cm plots F4 and W4 became more negative in mean Ψpd values decreased for all subplots day-1, measured at 5, 20, and 40 cm depth the final stages of the experiment (Fig. 6). until the mean minimum of -0.81 MPa was respectively. In August both sites faced a summer reached on August 24, and no significant drought period, which affected the tree differences between the subplots were Daily diameter increment growth. The correlation between the found. Conversely, starting from August 14 The dendrometers installed in the sub- weekly diameter increment rate and the the mean Ψpd decreased drastically at the plots F4 and W4 recorded the daily diame- Ψpd was significant (p = 0.689) only in Wel- Welzow-Süd site, reaching the minimum ter growth and we found no significant dif- zow-Süd, and their relation was better mean values of -1.56 MPa on August 24. ference (p = 0.067) between the sites until described by a logarithmic function (Y = Here, the differences between the sub- 2 July 25, 2012 (Fig. 5). The difference only -0.13·log(X) + 0.09, r = 0.60) with a drastic plots in terms of Ψpd became significant (p became significant (p = 0.038) towards the decrease of the diametric increment fol- = 0.028), ranging from -2.06 MPa in subplot end of the experiment when in Welzow- lowing the Ψpd reduction (Fig. 7b). W4 to -0.96 MPa in subplot W6. The soil

Fig. 4 - Daily rainfall amount at Forst (a) and Welzow-Süd (b) Fig. 5 - Mean and standard deviation of the trunk diameter recorded during the vegetation period (from June 1st to August increment measured in the F4 subplot (Forst) (a) and W4 sub- 30th 2012). plot (Welzow-Süd) (b) during the vegetation period (from June 1st to August 30th, 2012). iForest 8: 743-747 745 Mantovani D et al. - iForest 8: 743-747 y r t s e r o F d n a s e c n e i c s o e g o i B

– t s e r o F i

Fig. 6 - Pre-dawn leaf water potential and weekly diameter Fig. 7 - Weekly trunk diameter increase in relation to the pre- increase of trees in Forst (a) and Welzow-Süd (b) measured dawn leaf water potential of trees at the F4 subplot (Forst) (a) during the vegetation period (from June 1st to August 30th, and W4 subplot (Welzow-Süd) (b) measured during the vege- 2012). tation period (from June 1st to August 30th, 2012).

heterogeneity recorded at Welzow-Süd is rated hydraulic conductivity and the water trient availability. Consequently, stomatal well described by the spatial and temporal holding capacity of the soil at both sites, closure and the reduction of the leaf area variation of the Ψpd evaluated at this site enhancing its water storage capacity. The under drought conditions limited the tran- (Fig. 8). growth rate variation recorded at the two spiration (Bréda et al. 2006, Mantovani et sites became relevant from July onwards, al. 2014a, 2014b), and enabled the trees to Discussion when the Ψpd reduction occurred in Wel- tolerate long-term drought conditions due Besides the difference in precipitation, zow-Süd. Here the growth decrement was to its ecophysiological and morphological which led to an increased water input in probably caused by the combined effects adaptations (Xu et al. 2009, Veste & Krie- Forst, the different soil characteristics such of the reduced precipitation and soil water bitzsch 2013). However, the reduction of as soil texture and TOC influenced the satu- storage, higher VPD values and low nu- the CO2 uptake had drastic effects on the plant growth and consequently on the biomass production, as reported by Manto- Fig. 8 - Spatial vani et al. (2014a, 2014b), where the pri- interpolation of mary production was directly proportional the pre-dawn leaf to the water used, independently from the water potential drought stress frequency and duration. values measured Instead, water constraint caused changes at Welzow-Süd in the soil-root and leaf-atmosphere inter- using the Inverse faces. Consequently, CO2 uptake and tran- Distance Weighted spiration decrease limited the tree growth, (IDW) technique. and in extreme cases the tree survival was The values are at stake. The heterogeneity recorded in measured periodi- Welzow-Süd in terms of plant growth was cally on single related to the Ψpd and mirrored the hetero- trees during the geneous soil property which caused the vegetation period water availability variation in space and st (from June 1 to time, described by the dynamic maps in th August 30 ). Fig. 8. During the night the water potential of a non-transpiring plant equilibrated with the wettest water potential of the soil around the root system (Ritchie & Hinckley 1975). As recorded by Veste et al. (2008), the spatial heterogeneity of soil water availability is linked with the pre-dawn water potential of trees under water limitation. In addition to water constraint, the indirect effect of the nutrient uptake reduction did occur, caused by the poor edaphic conditions at Welzow-Süd. However, since the diametric increment was higher in Forst than in Welzow-Süd at similar water poten-

746 iForest 8: 743-747 Drought impact on black locust water status and growth y

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Environmental and genetic influences on short- and transpiration of young black locust (Ro- e nutrition may have contributed to increase r the primary production in Forst. Robinia rotation biomass production of black locust binia pseudoacacia L.). International Journal of o F pseudoacacia is less dependent on the up- (Robinia pseudoacacia L.) in the Georgia Pied- Forestry Research 2014, Article ID 821891, pp. d take of nutrients in comparison to other mont. Forest Ecology and Management 55(1): 11. - doi: 10.1155/2014/821891 n a broad leaf trees because of its capability to 315-331. - doi: 10.1016/0378-1127(92)90108-L Mantovani D, Veste M, Freese D (2014b). Black s fix biological nitrogen even under extreme Bréda N, Huc R, Granier A, Dreyer E (2006). Tem- locust (Robinia pseudoacacia L.) ecophysiologi- e c

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2013, Wurzburger & Miniat 2014). Never- sequences. Annals of Forest Science 63 (6): of Forestry 44: 29. [online] URL: http://www. o e theless, Kanzler et al. (2015) has observed 625-644. - doi: 10.1051/forest:2006042 biomedcentral.com/content/pdf/s40490-014- g o for Robinia an increase of the growth rates Bungart R, Bens O, Hüttl RF (2000). Production 0029-0.pdf i B after phosphate fertilization in Welzow- of bioenergy in post-mining landscapes in Lusa- Ritchie GA, Hinckley TM (1975). The pressure – Süd. The fact that limited phosphate, in tia: perspectives and challenges for alternative chamber as an instrument for ecological re- t combination with low Molybdenum availa- land use systems. Ecological Engineering 16: 5- search. Advances in Ecological Research 9: 165- s e bility in the soil, has an impact on the bio- 16. - doi: 10.1016/S0925-8574(00)00046-X 254. - doi: 10.1016/S0065-2504(08)60290-1 r o

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