Arthrocnemum Macrostachyum and Halimione Portulacoides in an Extensive Green Roof System Under Two Watering Regimes

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Agriculture and Agricultural Science Procedia 4 ( 2015 ) 242 – 249

IRLA2014. The Effects of Irrigation and Drainage on Rural and Urban Landscapes, Patras, Greece The growth of Arthrocnemum macrostachyum and Halimione portulacoides in an extensive green roof system under two watering regimes

Angeliki Paraskevopouloua*, Ilias Mitsiosa, Ioannis Fragkakisa, Panayiotis Nektariosa, Nikolaos Ntoulasa, Paraskevi Londrab and Maria Papafotioua

aLaboratory of Floriculture & Landscape Architecture, Department of Crop Science, School of Agriculture, Engineering and Environmental Sciences, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece bDepartment of Natural Resources Management and Agricultural Engineering, School of Agriculture, Engineering and Environmental Sciences, Agricultural University of Athens, 75, Iera Odos, 11855, Athens, Greece

Abstract

The marine halophytes Arthrocnemum macrostachyum and Halimione portulacoides are found growing naturally in saltmarshes within Greece creating an aesthetically pleasing groundcover that also reflects the changing of seasons. The potential use of these species in an extensive green roof system in coastal areas would lead to additional benefits such as preserving and enhancing the local landscape character and supporting biodiversity. The growth of Arthrocnemum macrostachyum and Halimione portulacoides in an extensive green roof system under two watering regimes (30% ET0 and 15% ET0) was investigated. The substrates used consisted of soil (S), pumice (Pum) and grape marc compost (C) or peat (P), at various volumetric proportions indicated by the subscripts: S15:Pum70:C15, S15:Pum70:P15 and S15:Pum70:P7.5:C7.5. Biometric measurements to determine plant growth included plant height and diameter, growth index, dry weights and ground cover. The growth of both plant species was similar under both watering regimes until elevated summer temperatures lead to plant loss in the reduced watering regime (15% ET0). Both shoot and root dry weights of both plant species at the end of the experiment were greater under the 30% ET0 watering regime. Results indicated that both watering regimes (30% ET0 and 15% ET0) studied could be applied initially in the early summer months followed by watering with 30% ET0 at increased summer temperatures.

© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). PeerPeer-review-review under responsibility ofof TechnologicalData Research Educational and Consulting Institute of Epirus, Hydroconcept R&D (www.hydroconcept.gr)

Keywords: pumice; grape marc compost; drought tolerance; Mediterranean species

1. Introduction

High building density and urban sprawl have generated urban environments containing limited in number and size green spaces. Green roofs could contribute to increasing the total amount of urban green spaces (Yuen and

* Corresponding author. Tel.: +30-210-529-4551; fax: +30-210-529-4552. E-mail address: [email protected].

2210-7843 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Data Research and Consulting doi: 10.1016/j.aaspro.2015.03.028 Angeliki Paraskevopoulou et al. / Agriculture and Agricultural Science Procedia 4 ( 2015 ) 242 – 249 243

Wong, 2005; Wolf and Lundholm, 2008; Benvenuti, 2014). However the load capacity of existing buildings could constitute a limiting factor in the development of a green roof system. In such cases extensive green roofs characterized by relatively lightweight substrates of small depth may constitute the only option for green roof installation. Green roofs in general are characterized by exposure to wind and solar radiation however the shallow substrate depth of extensive green roofs create further adverse plant growing conditions that include, wide temperature and moisture fluctuations (Wolf and Lundholm, 2008; Dunnett and Kingsbury, 2010). Overall a relatively small number of plant species are used in extensive green roofs. Most common plant groups used in extensive green roofs are forbs, sedums and grasses (Nagase and Dunnett, 2010). These are usually characterized by the formation of a low-growing green cover year round that is relatively easy to establish and reproduce. In areas of Mediterranean climatic conditions, especially in semiarid and arid locations limited water availability especially during the summer constitutes an additional adverse effect on plant growth of extensive green roofs. The ability of plants to withstand drought conditions especially where water availability is limited constitutes a decisive factor for plant selection (Dunnett and Kingsbury, 2010). More recent research has steered to study the growth of drought tolerant shrub species in extensive green roofs (Nektarios et al., 2011; Kotsiris et al., 2012; Papafotiou et al., 2013a). Dianthus fruticosus sub. fruticosus a native plant species of the Mediterranean grew successfully with limited irrigation (15% Epan) in a shallow substrate (7.5 cm depth) (Nektarios et al., 2011). Lavandula angustifolia grew successfully with limited irrigation at a substrate depth of 20 cm (Kotsiris et al., 2012). Similarly the Mediterranean species Artemisia absinthium, Helichrysum italicum, and Helichrysum orientale under limited irrigation and substrate depth (7.5 cm) were found suitable for growth in extensive Mediterranean green roofs (Papafotiou et al., 2013a). Native plant species capable to withstand normal environmental conditions encountered on a rooftop could offer additional benefits to green roof plantings such as the preservation of the local landscape character, the preservation of the local wildlife, habitat and diversity, the restoration of locally distinctive and/or culturally representative native plant species to an area, and the adaptation of native plant species to the local environmental conditions, pests and diseases (Getter and Rowe, 2006; Snodgrass and Snodgrass, 2006; Oberndorfer et al., 2007). Plants growing on roofs in coastal areas are further subjected to saline conditions whether in the form of deteriorated water-irrigation quality in coastal areas (Dazy, et al., 1997; Lambrakis and Kallergis, 2001) or sea spray (salt-spray) (Dazy, et al., 1997). Furthermore the increased interest and demand for the use of recycled water in landscape irrigation is often characterized by increased levels of salinity (Zollinger et al., 2007). In such cases plants tolerant to saline conditions such as halophytes could possibly be an option for green roof plantings. Current research into the use of halophytes in green roof systems is limited. This seems to be amongst the first papers to study the growth of halophytes in an extensive green roof system. Papafotiou et al. (2013b) showed Atriplex halimus a native halophyte of Greece to be a suitable plant species for extensive green roofs. We study the growth of two native halophytes of Greece Arthrocnemum macrostachyum and Halimione portulacoides in an extensive green roof in Athens.

2. Methods

2.1 Plant material

Two plant species were selected for study, Arthrocnemum macrostachyum and Halimione portulacoides. Both species are native halophytes of Greece often found in coastal areas forming an evergreen low-growing groundcover. A. macrostachyum is a stem-succulent perennial halophytic shrub typical of Mediterranean salt marshes found in the coasts of S. Europe (Flora Europaea, 2010; Vicente et al., 2009; Redondo-Gomez et al., 2010). In Greece this species is often found forming a low-growing cover with the foliage changing colour throughout the year between various shades of green, yellowish-green and red. H. portulacoides is a decumbent small shrub found on the coasts of S. & W. Europe, from Bulgaria to Denmark (Flora Europaea, 2010). In the coasts of Greece stems often root forming a low-growing cover of silvery farinose foliage. Five centimeter long stem cuttings with roots were taken from the base of the plants growing in the wetland of Oropos, in Attica Greece, and planted in small pots (sized width x length x depth, 5 cm x 5 cm x 10 cm) filled with 1:1 peat: perlite in Jan. 2011. The potted stem cuttings were placed in the greenhouse of the Laboratory of Floriculture and Landscape Architecture garden of the Agricultural University of Athens, Greece to establish and grow until needed. 244 Angeliki Paraskevopoulou et al. / Agriculture and Agricultural Science Procedia 4 ( 2015 ) 242 – 249

2.2 Experimental design

The experiment was conducted in plastic containers at the experimental plot of the Laboratory of Floriculture and Landscape Architecture garden of the Agricultural University of Athens, Greece (lat. 37o58΄57΄΄N and long. 23o42΄17΄΄E). Plastic rectangular shaped containers (Holiday Land A.E. Piraeus, Attiki) dimensioned 400 mm width by 600 mm length by 220 mm height were used to simulate the profile of an extensive green roof system. Holes drilled at the bottom of the container allowed for drainage. The interior of the containers simulated an extensive green roof system. Specific the interior of the containers were lined from the bottom up with a protection mat (3 mm thickness and a dry weight of 0.32 kg.m-2 retaining 3 L.m-2 of water; TSM32, Zinco, Egreen, Athens, 10672, Greece), drainage element (made of recycled polyethylene, 25 mm height, weight of 1.5 kg.m-2 and capacity to store 3 L.m-2 of water; FD25, Zinco, Egreen, Athens, 10672, Greece), and non-woven geotextile (made of thermally . -2 strengthened polypropylene, 600 μm in thickness, mass of 100 g m , apparent opening size of D90 = 110 μm and water flow rate of 155 L.m-2.s-1; SF, Zinco, Egreen, Athens, 10672, Greece); and subsequently filled with 100 mm in depth substrate. Uniform in size plants were selected from the plants propagated in the greenhouse (Jan. 2011) and transplanted, one each at the centre of the plastic rectangular shaped containers described above on 7 June 2011. The planted containers were placed on metal benches in the Laboratory’s garden mentioned above. The three substrates used in the study consisted of sandy loam soil (S), pumice (Pum), peat (P) or / and grape marc compost (C) in the following volume ratios: 15S:70Pum:15P (S15:Pum70:P15), 15S:70Pum:15C (S15:Pum70:C15) and 15S:70Pum:7.5C:7.5P (S15:Pum70:P7.5:C7.5). The pumice (LAVA, Mining & Quarrying A.D., Athens, 14123, Greece) had a particle-size distribution of 0.06-8 mm. The peat was white peat (Klasman Base Substrate 5 Plus, Germany) with a pH of 6 and no fertilisation. The grape marc compost was used as an alternative to peat in an effort to minimise or replace the use of white peat and develop a more economic and sustainable substrate from waste product of wine production, consisting of grape skins, seeds and stems. All plants were watered regularly every-other day for a month to allow them to establish. Two plastic containers identical to the planted containers were positioned randomly among the experimental plots and with water to the same level as the rim of the substrate surface of the planted containers. These containers were used to measure the daily ET0. The experiment began on 13 July 2011 and finished on 17 October 2011. The irrigation treatments included two levels, determined as 30% and 15% of evapotranspiration (ET0). Daily ET0 values were multiplied by the pan coefficient determined by the climatic conditions of the experimental location as defined in Table 5 of FAO’s Irrigation and Drainage paper 56 (1998) and the crop coefficient (0.30 or 0.15 for 30% and 15% ET0 respectively) in order to determine the amount of irrigation. Irrigation was performed manually with a watering can producing a fine spray, when the accumulated amount for irrigation reached 70 mm. The latter expressed the amount of water at saturation and was determined by the water retention curve of the substrate with the least water holding capacity. When increased summer temperatures lead to plant loss in the reduced watering regime (15% ET0) irrigation was performed daily as 30% and 15% of evapotranspiration.

2.4 Meteorological data The monthly average air temperature as well as the average maximum and minimum temperature, relative humidity and precipitation (Table 1) were recorded by the Laboratory of General and Agricultural Meteorology at the Agricultural University of Athens. Rainfall occurred mainly during plant establishment and in October near the end of the study period. Rainfall during the summer only occurred twice between 1.2 mm and 3.4 mm therefore it did not affect irrigation treatments.

Table 1. The average monthly air temperature, average monthly maximum and minimum temperature and relative humidity, total monthly rainfall and days of rainfall during the experimental period. avg. air temp. avg max temp avg min. temp. relative humidity total rainfall no. days of month 2011 (oC) (oC) (oC) (%) (mm) rainfall June 24.5 29.8 18.7 57.6 33.8 4 July 28.8 34.1 22.3 47.5 0 0 August 28.3 33.5 22.3 45.8 1.2 1 Angeliki Paraskevopoulou et al. / Agriculture and Agricultural Science Procedia 4 ( 2015 ) 242 – 249 245

September 25.5 31.5 19.0 49.1 3.4 1 October 16.7 21.7 12.0 64.9 48.4 6

2.5 Biometric measurements

Plant growth was measured fortnightly. Measurements included plant height (from the substrate surface) and diameter (average between the largest foliage diameter and its perpendicular) and growth index (GI) (average between plant height, largest foliage diameter and its perpendicular). Ground cover percentage (%) was determined monthly according to Richardson (2001) and Ntoulas et al. (2012) and amended further to meet the particular experimental needs. Uniform lighting conditions were created using a lightweight box made of MDF (dimensioned 400 mm width by 600 mm length by 1000 mm height) positioned on top of each individual container. Mounted on the interior top side of the box were two fluorescent lamps Starlicht (60W, 420 Lumen, 2700 Kelvin). Digital images were taken using a Panasonic Lumix, wide 25 mm, f/3.3 digital camera through a small hole centered on the top side of the box. Ground cover percentage was determined using Adobe Photoshop CS3 software (Adobe Systems Inc., USA) by dividing the number of pixels representing the ground cover of plant growth by the total pixel count of each image. At the end of the experiment (17 Oct. 2011) both shoot and root biomass dry weights were determined separately. The shoot biomass of each plant was harvested at the substrate surface and placed in a paper bag. The substrate was carefully washed off the root biomass under running tap water and over a fine mesh to collect possible roots that might break off during washing. Fine roots found growing under the geotextile were also collected, washed and added to the harvested main root biomass. After washing, excess water was removed and the total root biomass collected was placed in a paper bag. The paper bags containing the harvested plant biomass were placed in a drying oven at 75 oC for 5 d, after which the dry weight was determined.

2.6 Statistical analysis

The two factors were substrate type (S15:Pum70:P15, S15:Pum70:C15, S15:Pum70:P7.5:C7.5) and irrigation amount . (15% ET0 and 30% ET0). Hence six treatments were applied (3 substrates X2 irrigations) and 8 replicates for each treatment. The arrangement of the containers followed the randomized complete block design. Significance of results was determined by two-way analysis of variance (ANOVA). The treatment means were compared using Fisher’s least significant difference (LSD) at P < 0.05. The data were analysed using SPSS Statistical Software v. 17.0 (SPPS Inc. Chicago, USA).

3. Results and Discussion

The growth of both plant species was similar under both watering regimes until elevated summer temperatures lead to plant loss in the reduced watering regime (15% ET0). The reduced number of plants beyond the 7 September 2011 for A. macrostachyum and 24 August 2011 for H. portulacoides did not allow for statistical analyses. A. macrostachyum growing in substrate S15:Pum70:P15 irrespective of irrigation treatment was least tolerant to water stress and the number of plants lost from the elevated summer temperatures did not allow for statistical analyses beyond the 27 July 2011. The 70 mm benchmark originally set for irrigation was reached approximately every 11-13 days. This irrigation frequency did not seem to affect plant growth early in the summer. On the other hand this irrigation frequency was too sparse for both species to effectively withstand stress from the elevated summer temperatures that followed and which led to the death of several plants in both irrigation treatments (Figure 1). Papafotiou et al. (2013a) found that sparse irrigation (5-day intervals) became a limiting factor and affected negatively the shoot dry weight of Artemisia absinthium and Helichrysum orientale, as well as the height of H. orientale growing in compost amended substrate of 15 cm depth. Plants of Lavandula angustifolia growing in 20 cm depth substrates also showed increased summer stress (Kotsiris et al., 2012). The growth and ground coverage were also reduced for the Mediterranean species Centranthus ruber and Verbascum thapsus growing in a shallow substrate (15 cm) (Benvenuti and Bacci, 2010). Deeper substrates retain larger amounts of water that is available to plants during drought periods as they dry out more slowly compared to shallower substrates (VanWoert, 2005). 246 Angeliki Paraskevopoulou et al. / Agriculture and Agricultural Science Procedia 4 ( 2015 ) 242 – 249

VanWoert (2005) showed that Sedum species growing at 2-cm substrate depth required watering at 2-day intervals to support growth as opposed to 14-day intervals at a deeper 6-cm substrate depth. Possibly the studied species could have withstood the drought period at a deeper substrate depth. On the other hand plant responses to water and salt stress, share in common, the reduced ability of water uptake in plants. Razzaghi et al. (2014) showed that the halophyte Chenopodium guinoa Willd. was able to tolerate water stress under saline conditions, by reducing day respiration thus reducing stomatal opening and plant growth. Possibly salinity could condition the two halophytes studied (A. macrostachyum and H. portulacoides) to withstand water stress. More research is necessary to investigate the above. Two-way ANOVA showed that the interaction of the main factors, substrate type and irrigation, was not significant in both species. Therefore only the results of the irrigation treatments are presented here. Plant height and diameter and growth index of both A. macrostachyum and H. portulacoides did not differ in the two irrigation treatments (Figure 2). The growth of A. macrostachyum was more or less unaffected by the treatments as opposed to the growth of H. portulacoides which showed an overall increase throughout the duration of the experiment. Although not significant, the plant height and diameter and growth index of H. portulacoides watered with 30% ET0 were slightly greater than those of plants watered with 15% ET0. Under adverse environmental condition many wild plant species show cessation of growth (Chapin, 1983). More specific during drought stress plants often limit their growth to reduce their water requirements for the maintenance of high biomass (Schuppler et al., 1998). Similarly to the above, the ground cover percentages of both species studied were not significantly different between irrigation treatments (Figure 3). Results indicated that the groundcover percentage of the plants of both species watered with 30% ET0 were greater compared to plants watered with 15% ET0.

(a) A. macrostachyum (b) H. portulacoides

Fig. 1. Effect of irrigation (30% ET0 and 15% ET0) on survival percentage of (a) A. macrostachyum and (b) H. portulacoides growing under Mediterranean extensive green roof conditions. Angeliki Paraskevopoulou et al. / Agriculture and Agricultural Science Procedia 4 ( 2015 ) 242 – 249 247

(a) A. macrostachyum (b) H. portulacoides

Fig. 2. Effect of irrigation (30% ET0 and 15% ET0) on plant height and diameter and growth index of (a) A. macrostachyum and (b) H. portulacoides growing under Mediterranean extensive green roof conditions. Mean comparison at each date with Fisher’s least significant difference (LSD) at P < 0.05.

(a) A. macrostachyum (b) H. portulacoides

Fig. 3. Effect of irrigation (30% ET0 and 15% ET0) on ground cover percentage of (a) A. macrostachyum and (b) H. portulacoides growing under Mediterranean extensive green roof conditions. Mean comparison at each date with Fisher’s least significant difference (LSD) at P< 0.05.

(a) A. macrostachyum (b) H. portulacoides

Fig. 4. Effect of irrigation (30% ET0 and 15% ET0) on shoot and root biomass dry weight (g) of (a) A. macrostachyum and (b) H. portulacoides growing under Mediterranean extensive green roof conditions. Mean comparison at each date with Fisher’s least significant difference (LSD) at P < 0.05.

Although the effect of irrigation was not obvious for plant growth, as the result for plant height, diameter, growth index and ground cover percentage were not statistically significant, it had a significant effect on both shoot and root 248 Angeliki Paraskevopoulou et al. / Agriculture and Agricultural Science Procedia 4 ( 2015 ) 242 – 249

dry weights. It seems that plant height and diameter were less effective than shoot and root dry weights in determining differences between treatments due to limited plant growth under drought stress. Both shoot and root biomass dry weights of A. macrostachyum and H. portulacoides irrigated with 30% ET0 were significantly greater than plants irrigated with 15% ET0 (Figure 4). Though initially the irrigation treatments did not seem to have a significant effect on plant growth, it seems that the elevated summer temperatures influenced the effect of irrigation οn the surviving plants as plants watered with 30% ET0 showed greater biomass at the end of the experiment than plants watered with 15% ET0 (Figure 4). These results agree with the results shown above for the ground cover percentages.

4. Conclusions

In Mediterranean coastal areas both species studied have the potential to be used in extensive green roof systems. A. macrostachyum and H. portulacoides established successfully and were able to sustain growth at a shallow substrate depth (10 cm). Ground coverage as well as shoot and root dry weights of both plant species at the end of the experiment were greater under the 30% ET0 watering regime. Irrigation frequency had an important effect on plant survival. Results indicated that both watering regimes (30% ET0 and 15% ET0) studied could be applied initially in the early summer months. However during summer stress, sparse irrigation at 13-day intervals had a negative effect on plant growth in either the 30% or 15% ET0 irrigation treatment. More research is necessary to investigate whether watering with saline water could possibly counteract plant loss by sparse irrigation. Daily irrigation at 30% ET0 during increased summer stress was found to support the growth of both species without further plant loss. In conclusion, both species A. macrostachyum and H. portulacoides were found suitable for extensive Mediterranean green roofs of shallow depth (10 cm) with limited amount of irrigation water (30% ET0) provided that this is supplied on a more frequent basis.

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