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2 Urn Forestry & Urn Greening 3 (204) Contents lists ville t SieneDiret Urn Forestry & Urn Greening journl homepge: Importne of different omponents of green roof sustrte on plnt growth nd physiologil performne Thoms Young,, Dunn D. Cmeron,, Jeff Sorrill,2, Tim Edwrds,3, Greth K. Phoenix,4 Deprtment of Animl nd Plnt Sienes, University of Sheffield, Western Bnk, Sheffield S0 2TN, UK Green Roof Centre, Deprtment of Lndspe, University of Sheffield, Sheffield S0 2TN, UK Boningle Limited, Holyhed Rd, Alrighton, Wolverhmpton WV7 3AT, UK rtile info Keywords: Evpotrnspirtion Optimistion Polyrylmide gel Servie provision Sustrte omponents Wter holding pity strt Green roof sustrte is rguly the most importnt element of green roof, providing wter, nutrients nd physil support to plnts. Despite this there hs een lk of reserh into the role tht different sustrte omponents hve on green roof plnt growth nd physiologil performne. To ddress this, we ssessed the importne of three green roof sustrte omponents (orgni mtter type, rik prtile size nd wter sorent dditive) for plnt growth nd plnt physiologil performne. Lolium perenne (Ryegrss) ws grown in eight sustrtes in ontrolled greenhouse environment with ftoril design in omposition of (i) smll or lrge rik, (ii) onifer rk or green wste ompost orgni mtter, nd (iii) presene/sene of polyrylmide wter sorent gel ( SwellGel TM ). We found tht lrge rik sustrtes hd lower wter holding pity thn smll rik ( 35%), whih led to deresed shoot growth ( 7%) nd inresed root:shoot rtio (+6%). Green wste ompost inresed shoot nd root growth (+32% nd +3%) shoot nitrogen onentrtion nd hlorophyll ontent (20% nd 57%), nd deresed root:shoot rtio ( 5%) ompred to rk. The ddition of swell gel inresed sustrte wter holding pity (+24%), whih inresed shoot growth (+8%). Totl evpotrnspirtion ( proxy for potentil ooling) ws inresed y greter shoot iomss nd sustrte wter holding pity. Overll, this study provides one of the first quntittive ssessments of the reltive importne of ommonly used green roof sustrte omponents. It is ler tht sustrte omposition should e onsidered refully when designing green roofs, nd sustrte omposition n e tilored for green roof servie provision. 204 The Authors. Pulished y Elsevier GmH. This is n open ess rtile under the CC BY liense ( Introdution Green roofs n hve signifint enefiil impts in urn res inluding storm wter ttenution, urn het islnd redution, pssive individul uilding ooling nd provision of urn green spe for reretionl nd estheti use (Oerndorfer et l., 2007). Due to these environmentl enefits, the green roof Corresponding uthor. Tel.: E-mil ddresses: thoms.young@sheffield..uk (T. Young), d.meron@sheffield..uk (D.D. Cmeron), J.Sorrill@sheffield..uk (J. Sorrill), tim.edwrds@oningle.o.uk (T. Edwrds), g.phoenix@sheffield..uk (G.K. Phoenix). Tel.: Tel.: Tel.: Tel.: industry hs experiened rpid expnsion in the lst twenty yers nd green roofs re now ommon feture in most western urn res (Oerndorfer et l., 2007). The mount of empiril green roof reserh onduted in the lst ten yers hs lso expnded, however mny spets of green roof tehnology nd design hve still not een fully investigted or optimised, in prtiulr green roof sustrte whih is rguly the most importnt omponent of green roof. The sustrte usully hs to perform the role of n rtifiil soil for plnt growth nd therefore must provide moisture, nutrients nd physil support to plnts, whilst lso eing lightweight, hemilly stle, ertle, nd le to drin wter freely (Ampin et l., 200; Friedrih, 2008). These hrteristis re vitl for the long term survivl of green roof vegettion nd provision of the enefits (servies) tht green roofs provide. To dte however, there hs een little empiril reserh into the role of sustrte on provision of green roof servies (Ampin et l., 200; Olszewski nd Young, 20; Roth-Kleyer, 2005), into new sustrte mterils (Molineux / 204 The Authors. Pulished y Elsevier GmH. This is n open ess rtile under the CC BY liense (

3 508 T. Young et l. / Urn Forestry & Urn Greening 3 (204) et l., 2009; Solno et l., 202), iologil properties of sustrte (Kol et l., 982) or the influene of sustrtes on green roof vegettion growth (Emilsson, 2008; Frrell et l., 202; Kotsiris et l., 202; Ngse nd Dunnett, 20; Rowe et l., 2006). There hs lso een lk of reserh into the effet tht eh individul sustrte omponent (e.g. minerl ontent, type of orgni mtter, rtifiil dditives, mixing rtios) hs upon the growth nd physiologil performne of the vegettion it supports nd ultimtely the servies tht it provides (Dvork nd Volder, 200; Ouldoukhitine et l., 202). Most previous green roof sustrte reserh hs foused on the effet tht sustrte depth hs on plnt estlishment, growth nd long term survivl (Durhmn et l., 2007; Getter nd Rowe, 2007, 2008; Rowe et l., 202; Thuring et l., 200). It is generlly greed tht plnt growth nd physiologil performne inreses with sustrte depth, lthough sustrte depth is not lwys limiting growth ftor for some green roof speies, most notly for hrdy suulents (Getter nd Rowe, 2008). Inresed depth protets plnts from temperture extremes nd lso inreses the potentil reservoir of wter ville for plnts, reduing the hne of plnts experiening drought stress (Dunnett nd Kingsury, 200; Thuring et l., 200). However inresing sustrte depth omes t n eonomi ost (greter volume of sustrte required) nd lso my not e vile due to indequte strength in the roof to support the greter sustrte weight. An lterntive is to design sustrtes to e more effiient nd tilored towrds speifi or multiple servies y modifying individul omponents in order to hnge sustrte properties (e.g. inrese wter holding pity or nutrient provision). However in order for this to our, full understnding of the effet tht ll omponents of green roof sustrte hve on plnt growth nd performne must first e gined (Dvork nd Volder, 200). Due to the reltively shllow depth nd free drining nture of green roof sustrtes, wter stress is one of the most ommon limittions for plnt growth on green roofs (Rowe et l., 202; Thuring et l., 200). The wter holding pity of sustrtes n e inresed y deresing prtile size whih inreses the mount of inner prtile pore spe, lthough this n inrese the potentil of wter logging (Greson et l., 203; Olszewski nd Young, 20). It hs een shown tht inresed sustrte wter holding pity n inrese survivl of five different suulents during n extreme drought in Austrli (Frrell et l., 202), however it is not fully known how hnge in green roof sustrte prtile size nd therefore wter holding pity impts upon non suulent plnt growth nd performne during typil growing onditions (Olszewski nd Young, 20). An lterntive to inresing the mount of smller prtiles in sustrte, whih n hve negtive effetives on dringe nd wter logging, is the use of rtifiil wter retention gels. These re often used in hortiulture nd regenertion of degrded lnd to inrese soil/sustrte s wter holding pity nd redue plnt exposure to wter stress without the need for lrge mounts of extr growing medi (Ag et l., 200; Hüttermnn et l., 2009; Kiri et l., 20; Willimson et l., 20). Two previous trils hve reported tht similr enefits my e possile for green roof vegettion (Sedum) y providing longer term storge of wter in the sustrte (Olszewski et l., 200; Sutton, 2008). It hs lso een shown tht wter retention gels n inrese the wter holding pity of green roof sustrte, lthough this does not neessrily trnslte into enefits for plnts during periods of drought s this wter my not e ville or essile to plnts, nd the effetiveness of the gel my e speies dependent or vry depending on sustrte omposition (Frrell et l., 203). The type of orgni mtter used in green roof sustrte n lso ffet wter holding pity due to different sorption properties. However sutle hnges to its omposition or quntity my hve muh lrger effets on the sustrtes moisture dynmis due to its impt upon the estlishment nd long term survivl of green roof vegettion (Emilsson, 2008; Ngse nd Dunnett, 20). The vegettion present lters the rte t whih sustrte s wter reservoir is depleted, s the mount nd type of green roof vegettion plys key role in determining evpotrnspirtion rtes (Berghge et l., 2007; Wolf nd Lundholm, 2008). Therefore ltering orgni mtter type nd mount in sustrte will lso lter green roof performne through influening plnt growth, rte of wter use nd mount of trnspirtion. Despite the potentil for sustrte omposition to hevily influene green roof vegettion nd therefore green roof servie performne, the extent to whih sustrte omponents nd their rtios influene green roof vegettion remins unknown. Without this knowledge it is hllenging to engineer sustrtes tht re tilored towrds providing speifi servie nd therefore provide n optimised performne e.g. storm wter retention t ll times of the yer. With these onerns in mind, pot experiment ws estlished where the growth nd physiologil performne of the grss Lolium perenne (ryegrss) ws ssessed in ontrolled environment greenhouse trils. L. perenne ws grown on green roof sustrtes omposed of ftoril omintions of ommonly used green roof omponents of (i) smll or lrge rik, (ii) orgni mtter s rk or green wste ompost, nd (iii) presene/sene of polyrylmide gel (SwellGel TM ). Trils were lso undertken using two sustrte depths of 80 nd 20 mm. It ws hypothesised tht;. Smll rik would inrese the wter holding pity of green roof sustrte ompred to lrge rik, inresing evpotrnspirtion nd improving L. perenne shoot growth nd physiologil performne. 2. Green wste ompost would inrese nutrient vilility of the sustrte, leding to improved L. perenne nutrient sttus, shoot growth, physiologil performne nd inreses in evpotrnspirtion. 3. Polyrylmide gel (SwellGel) would inrese wter holding pity of the sustrte, leding to greter L. perenne shoot growth nd physiologil performne. 4. In light of these hypotheses, the est performing green roof sustrte in terms of L. perenne shoot iomss prodution, evpotrnspirtion nd plnt physiologil ondition would ontin smll rik, green wste ompost nd SwellGel. Methods Experimentl design The study ws undertken in temperture ontrolled greenhouse in dy/night regime of 6 h 20 C/8 h 5 C from to Where neessry, supplementry lighting ws used to ensure the required dy length (Helle Lmps, IR 400 HPS, 400 W). The eight sustrtes hd three omponent vriles: (i) rik size (smll rik t 2 5 mm prtile dimeter; lrge rik of 4 5 mm dimeter), (ii) orgni mtter type (rk or green wste ompost) nd (iii) presene or sene of polyrylmide gel SwellGel TM ( (Tle ). Brik ws rushed wste red rik, sieved to ensure rik frgments were within the size limits set. Green wste ompost (Green Estte, Sheffield, UK) ws omposed of omposted grden wste olleted in Sheffield, whilst rk ws soured s ommon grden mixed onifer rk mulh. SwellGel TM ( is soil dditive mde of ross linked polyrylmide whih is designed to expnd nd store

4 T. Young et l. / Urn Forestry & Urn Greening 3 (204) Tle Sustrte mixes used in the growth tril. Two sustrte depths were used (80 mm nd 20 mm) nd N =8. Sustrte numer Compost type 20% y volume Brik size Smll = 2 5 mm Lrge = 4 5 mm SwellGel % y volume Brk Smll Yes 2 Green Smll Yes wste 3 Brk Lrge Yes 4 Green Lrge Yes wste 5 Brk Smll No 6 Green Smll No wste 7 Brk Lrge No 8 Green wste Lrge No wter during high moisture levels nd relese it slowly k to the plnt s moisture levels deline. The sustrte ws mde up of 20% of either orgni mtter type (no extr fertilistion ws dded), with the remining 80% mde up from one of the two rushed rik size tegories. Dry SwellGel ws then dded s % of the totl sustrte volume s per mnuftures instrutions. Sustrte ws dded to pots (2 m m m) with two depths of sustrte (80 mm nd 20 mm), oth of whih re ommonly used depths on extensive green roofs. The experiment therefore hd fully ftoril design of rik size (2 5 mm/4 5 mm), orgni mtter type (green wste ompost/rk), SwellGel (presene/sene) nd sustrte depth (80 mm/20 mm) (Tle ). Eight replites of eh sustrte type nd depth were used to give totl of 28 pots. Plnt speies nd wter regime Although not ommonly found on green roofs in the UK, L. perenne (Hithok nd Green, 929) ws used s phytometer speies due to its lower stress tolerne thn hrdier green roof grsses, nd its reltively high growth rte. This ws desirle given the primry ims of this projet ws to detet effets of sustrte omposition nd differenes in plnt physiologil performne etween sustrtes, whih would e more redily quntifile with L. perenne thn with slow growing green roof speies over the durtion of the experiment. g of seed (Emorsgte Seeds, Kings Lynn, UK) per pot (pproximtely 500 seeds) were sown uniformly onto sturted sustrte nd then wtered to sturtion every dy until two weeks following germintion. After this point eh pot ws sujeted to wtering regime of 50 ml per week, spilt over two dys (with eh dy eing two wtering events of 37.5 ml) in order to mke the wtering event less intense nd to prevent exessive lehing. As perentge of totl pot wter holding pity the weekly wtering totl ws equivlent to 59 22% t 80 mm nd 45 95% t 20 mm. This is the equivlent to 50 mm month whih is verge for London, UK during winter months (Met Offie, 200). Sustrte wter holding pity nd evpotrnspirtion Unplnted sustrtes were ir dried in the greenhouse for three weeks nd weighed to quntify sustrte dry weight. They were then sturted (in stnding wter for two dys) nd llowed to drin for 5 min to reh field pity, fter whih they were weighed nd the differene in weights given s wter holding pity. During the experiment, pots were weighed dily s well s 5 min fter eh wtering event. Any redution in pot weight over time or etween wtering events ws ttriuted to evpotrnspirtion (following 5 min drining there ws never evidene of further lehed losses). Totl evpotrnspirtion of eh pot over the durtion of the experiment ws lulted s the sum of ll the weight differenes over ll time periods. We did not orret for plnt iomss in this weight sine we did not wnt to destrutively hrvest mid-wy through the experiment, nd plnt iomss ws less thn /500th the mss of the evpotrnspirtion mss. Plnt iomss nd shoot nitrogen ontent After 6 weeks growth following germintion, ll ove ground iomss ws hrvested, oven dried t 80 C for two dys nd weighed to otin dry weight. To determine root iomss, mteril ws wshed in wter to remove ll tres of rik nd ompost. After lening, roots with SwellGel still tthed were then soked in wter overnight to expnd the gel, whih ws then mnully removed using slpel. All root mteril ws dried (80 C for two dys) efore weighing. Lef tissue nitrogen (N) ontent ws determined on oven-dried ground smples from the finl iomss hrvest, following Kjeldhl digestion (Allen et l., 974). For this pproximtely 50 mg dry plnt iomss ws digested in ml onentrted sulphuri id with mirosptulr of tlyst (:0 CuSO 4 :LiSO 4 ) for 7 h t 375 C. After dilution (N = :00 dh 2 O) totl nitrogen ws determined y Flow Injetion Anlysis (Burkrd FIA Flo2, Burkrd Sientifi, Uxridge, UK). Chlorophyll ontent Biomss prodution nd shoot nitrogen ontent were supported y physiologil inditors of plnt helth. Men lef hlorophyll ontent for eh pot ws determined through etone extrtion (Cmeron et l., 2009). After the lst wtering event, five grss shoots ( g fresh weight) from different prts of the pot were hrvested nd kept on ie in the drk until extrtion of hlorophyll (within h to prevent degrdtion). The grss shoots were ground in pestle nd mortr with id wshed snd to form pste. 5 ml of ie old 80% etone ws dded nd the mixture further ground then trnsferred to 25 ml entrifuge tue. The pestle nd mortr were rinsed twie with 2 ml ie old 80% etone nd trnsferred to the sme entrifuge tue then diluted to 0 ml with ie old 80% etone. Smples were entrifuged t 8000 g for 5 min nd sorne of the superntnt mesured t 645 nd 663 nm using Ceil Ce 020 spetrophotometer (Ceil Instruments Ltd., Cmridge, UK). Chlorophyll ontent ws lulted using the following equtions ording to (Arnon, 949)), nd re-expressed s mg hlorophyll per dry shoot weight. Chl (mg l ) = (2.7 OD 663 ) (2.69 OD 645 ) Chl (mg l ) = (22.9 OD 645 ) (4.68 OD 663 ) Sttistil nlyses To determine the min ftoril effets nd intertions of the sustrte omponents (rik size, orgni mtter type, SwellGel nd sustrte depth), four-wy ANOVAs were performed. Tukey HSD tests were used to determine differenes etween eh individul sustrte. All sttistil nlyses were rried out in R Studio version 2.5. ( ), (R Development Core Tem, 20). Results Wter holding pity of sustrtes The presene of SwellGel inresed wter holding pity y 24% (p < 00), whilst lrge rik redued wter holding pity

5 50 T. Young et l. / Urn Forestry & Urn Greening 3 (204) () Totl Wter Holding Cpity (ml per L sustrte) , d d () Totl Wter Holding Cpity (ml per L sustrte) Brk Green Wste Compost d,d () Totl Evpotrnspirtion (ml per pot) ,,,, (d) Totl Evpotrnspirtion (ml per pot) ,,,d d Smll Brik Lrge Brik Sustrte Composition (80mm) 0 Smll Brik Lrge Brik Sustrte Composition (20mm) Fig.. () Wter holding pity (ml per L sustrte) of eh sustrte t 80 mm sustrte depth, () wter holding pity (ml per L sustrte) of eh sustrte t 20 mm sustrte depth, () men totl evpotrnspirtion (ml per pot) t 80 mm sustrte depth, (d) men totl evpotrnspirtion (ml per pot) of t 20 mm sustrte depth. Error rs re ± one stndrd error. Mens with sme letter do not signifintly differ from eh other within the sme su-figure (Tukey HSD, p < 5). Arevitions re s follows, SG, Swell Gel present; No SG, Swell Gel not present. Tle 2 Min ftor effets (four-wy ANOVA) for () sustrte wter holding pity (ml per L sustrte) nd () totl evpotrnspirtion of Lolium perenne grown for 3.5 months in eight different green roof sustrtes. Min ftors re rik size (smll vs. lrge), orgni mtter (rk vs. green wste ompost) nd SwellGel (sene vs. presene). Min ftor mens re shown with the % hnge lso shown etween the two levels within tht ftor (e.g. sene vs. presene of SwellGel). Ftor Df F-vlue P-vlue Brik Size Orgni SwellGel Depth % Chnge (±SE, n = 64) Smll Lrge Brk GW No Yes 80 mm 20 mm () Min ftor mens of wter holding pity (ml per L sustrte) *** Brik ±.9 Orgni ± 3.7 *** SwellGel ± 3.8 *** Depth ± 4.0 Sw.G:Org Brik:Depth Sw.G:Org:Brik Sw.G:Org:Brik:Depth * ** * * () Min ftor mens of totl pot evpotrnspirtion (ml) *** Brik ±.2 *** Orgni ±.4 *** SwellGel ±. *** Depth ±.3 Sw.G:Brik 7.8 *** Signifint ftoril intertions re lso shown. Sttistil signifines were lulted from four-wy ANOVA. Arevitions for eh ftor re s follows, Org, orgni mtter type; GW, green wste orgni mtter; Sw.G, SwellGel. * Sttistil signifine of p <. ** Sttistil signifine of p < 0. *** Sttistil signifine of p < 00.

6 T. Young et l. / Urn Forestry & Urn Greening 3 (204) y pproximtely 35% ompred to smll rik (p < 00) (Fig. nd, Tle 2). Orgni mtter type (rk or green wste) did not signifintly ffet wter holding pity (Tle 2). Inresing the sustrte depth from 80 mm to 20 mm signifintly inresed wter holding pity y 28% (p < 00) (Fig. nd, Tle 2). Overll sustrtes ontining smll rik nd SwellGel lwys hd signifintly higher wter holding pity thn sustrtes ontining lrge rik nd no SwellGel t oth depths regrdless of orgni mtter ontent (Tukey HSD, p < 5). Evpotrnspirtion SwellGel nd green wste orgni mtter oth signifintly inresed evpotrnspirtion y 4% nd 7% respetively ompred to no SwellGel (p < 00) nd rk (p < 00). Lrge rik signifintly deresed evpotrnspirtion y 2% ompred to smll rik (p < 00) (Fig. nd d, Tle 2). Sustrte depth hd signifint effet on totl evpotrnspirtion, with evpotrnspirtion % greter from 20 mm depth sustrte (p < 00) (Fig. nd d, Tle 2). At oth sustrte depths, smll rik with green wste orgni mtter hd greter evpotrnspirtion thn lrge rik with rk orgni mtter (Tukey HSD, p < 5). Shoot iomss Orgni mtter type hd the lrgest effet on shoot iomss, with this eing 32% greter on green wste thn rk sustrtes (p < 00) (Fig. 2 nd, Tle 3). The presene of SwellGel more modestly inresed dry shoot iomss y 8% (p < 00), nd lrge rik size deresed shoot iomss y 7% (p < 00) (Fig. 2 nd, Tle 3). Overll this ment tht sustrtes ontining green wste with either rik size or SwellGel presene hd signifintly greter iomss prodution thn ll rk sed sustrtes t oth 80 nd 20 mm depths (Tukey HSD, p < 5). Shoot iomss did not differ signifintly etween 80 nd 20 mm sustrte depth (Tle 3). Root iomss Orgni mtter type hd the gretest effet on root iomss prodution. Overll green wste signifintly inresed root iomss y 3% ompred to rk (p < 00). SwellGel hd the next gretest effet on root iomss, deresing this y 7% overll (p < 0) (Fig. 2 nd d, Tle 3). There ws signifint intertion etween SwellGel nd orgni mtter type (p < 0), with rk sustrtes produing signifintly greter levels of root growth when SwellGel ws not present. The sme intertion ourred etween SwellGel nd rik size (p < 00), with SwellGel signifintly deresing root iomss on smll rik, ut not on lrge rik (Fig. 2 nd d, Tle 3). Inresing the depth of sustrte from 80 mm to 20 mm signifintly inresed root iomss y 22% (p < 00) (Fig. 2 nd d, Tle 3). Brik size did not hve signifint effet on root iomss. Root:shoot rtio Root:shoot rtios with green wste orgni mtter ws signifintly redued y 5% ompred to rk (p < 00), while lrge rik signifintly inresed root:shoot rtios y 6% ompred to smll rik (p < 00) (Fig. 2e nd f, Tle 3). The presene of SwellGel redued root:shoot rtios y 5% (p < 00) (Fig. 2e nd f, Tle 3). The sme ftoril intertions oserved for root iomss were oserved for root:shoot rtios lso, with SwellGel reduing root:shoot rtios more when the orgni mtter ws rk rther thn green wste (p < 00), or smll rther thn lrge rik (p < ) (Fig. 2e nd f). Root:shoot rtios t 20 mm depth were 7% higher thn t 80 mm depth t 20 mm depth (p < 00) (Fig. 2e nd f, Tle 3). Shoot nitrogen onentrtion Green wste, SwellGel nd lrge rik hd very similr effets on shoot nitrogen onentrtion, inresing this y 2%, 20% nd 22% ompred to rk, no SwellGel nd smll rik respetively (p < 00) (Fig. 3 nd, Tle 4). A signifint intertion showed tht the inrese in shoot nitrogen onentrtion due to SwellGel ws muh lrger when it ws present with green wste rther thn rk, lthough this effet only ourred in smll rik (p < 0) (Tle 4). Sustrtes ontining SwellGel nd green wste hd signifintly higher shoot nitrogen onentrtions thn sustrtes without SwellGel nd rk sed t 80 mm depth (Tukey HSD, p < 5) nd prtly t 20 mm. Sustrte depth did not signifintly ffet shoot nitrogen onentrtion (Tle 4). Chlorophyll ontent Shoot hlorophyll ontent ws most signifintly ffeted y orgni mtter type nd sustrte depth, with green wste inresing hlorophyll ontent y 57% ompred to rk, nd 20 mm sustrte depth inresing hlorophyll ontent y 40% ompred to 80 mm (p < 00) (Fig. 3 nd d, Tle 4). Inresing rik size from smll to lrge used derese in hlorophyll ( 4%) ontent (p < ) (Tle 4). A signifint intertion etween SwellGel nd orgni ontent ourred with lrge rik only (p < 00), with SwellGel inresing hlorophyll ontent in rk sed sustrtes ut deresing hlorophyll ontent in green wste sustrtes (Tle 4). Disussion This study is one of the first systemti investigtions to quntify the importne of widely used green roof omponents for plnt growth nd physiologil performne. It is ler tht ltering the omposition/type of the omponent prts of green roof sustrte n hve sustntil effets on plnt physiologil performne nd wter lne. All three sustrte omposition ftors studied (presene of polyrymide gel (SwellGel), orgni mtter nd rik size) hd signifint effets on L. perenne, whih were lrgely onsistent ross oth sustrte depths, nd indeed often hd lrger effets thn the often previously studied sustrte depth. Although this tril only ssessed initil plnt estlishment, these findings n therefore egin to inform sustrte omposition hoie depending on plnt growth requirements (fst growing/high mintenne/lower drought tolerne vs. slow growing/low mintenne/higher drought tolerne). Wter holding pity & evpotrnspirtion SwellGel inresed the wter holding pity of green roof sustrtes, whih explins its enefit to shoot growth nd evpotrnspirtion. In this tril its effet on wter holding pity is less thn tht of rik size (smll rik inresed wter holding pity 50% more ompred to dding SwellGel). This does not men tht SwellGel hs limited impt on wter holding pity sine it onstituted only % volume in our sustrtes ompred to 80% rik. Indeed, greter impt of SwellGel ould e hieved y inresing the mount used, lthough there re limittions in the mount tht n dded due to sustrte disturne from onstnt expnsion nd ontrtion during wetting nd drying yles, physil limittions nd negtive effets on iomss yield (Frrell et l., 203). In ft, SwellGel my e more importnt in times of drought s wter stored in it my e relesed muh more slowly to

7 52 T. Young et l. / Urn Forestry & Urn Greening 3 (204) () Shoot iomss (g per pot) ().8.8 Brk.6 Green Wste Compost.6,.4,.4,.2.2.0,.0,, Shoot iomss (g per pot) () Root iomss (g per pot) ,,,, (d) Root iomss (g per pot) ,,,, (e) Root:shoot iomss rtio ,,,,, (f) Root:shoot iomss rtio ,,, Smll Brik Lrge Brik Sustrte Composition (80mm) Smll Brik Lrge Brik Sustrte Composition (20mm) Fig. 2. () shoot iomss on 80 mm sustrte depth, () shoot iomss on 20 mm sustrte depth, () root iomss on 80 mm sustrte depth, (d) root iomss on 20 mm sustrte depth, (e) root:shoot rtios on 80 mm sustrte depth, nd (f) root:shoot rtio on 20 mm sustrte depth. Error rs re ± one stndrd error. Mens with sme letter do not signifintly differ from eh other within the sme su-figure (Tukey HSD, p < 5). Arevitions re s follows, SG, Swell Gel present; No SG, Swell Gel not present. plnts thn wter stored in inner prtile pore spe (Ag et l., 200; Hüttermnn et l., 2009). However it should e noted tht this tril did not ssess the effet of SwellGel on plnt ville wter whih does not lwys inrese with greter sustrte wter holding pity nd n e speies dependent (Frrell et l., 203). Where sustrtes re used in regions with prolonged periods of low rinfll, or where greter frequeny of drought events re predited from limte hnge (Coumou nd Rhmstorf, 202), then SwellGel is likely to e n importnt nd enefiil omponent of sustrtes. None-the-less, using smll insted of lrge rik size ppers to e the simplest (nd likely most ost effetive) wy of improving sustrte wter holding pity. Vegettion plys mjor role in inresing evpotrnspirtion rtes from green roofs (Metselr, 202; Voyde et l., 200; Wolf nd Lundholm, 2008), nd in this tril the presene of L. perenne inresed totl evpotrnspirtion y etween 3 nd 57%

8 T. Young et l. / Urn Forestry & Urn Greening 3 (204) Tle 3 Min ftor effets (four-wy ANOVA) for () shoot iomss, () root iomss nd () root:shoot rtios of Lolium perenne grown in eight different green roof sustrtes. Min ftors re rik size (smll vs. lrge), orgni mtter (rk vs. green wste ompost) nd SwellGel (sene vs. presene). Min ftor mens re shown with the % hnge lso shown etween the two levels within tht ftor (e.g. sene vs. presene SwellGel). Ftor Df F-vlue P-vlue Brik Size Orgni SwellGel Depth % Chnge (±SE, n = 64) Smll Lrge N Y No Yes 80 mm 20 mm () Min ftor mens of dry shoot iomss (g) *** Brik ± 2.0 *** Orgni ± 2.7 *** SwellGel ± 2.6 Depth ± 2.6 Sw.G:Org:Depth 4.3 * () Min ftor mens of dry root iomss (g) Brik ± 2. *** Orgni ± 2.6 ** SwellGel ± 2.3 *** Depth ± 2.6 Sw.G:Org 7.3 ** Sw.G:Brik 2. *** () Min ftor mens of root:shoot rtios *** Brik ± 2.8 *** Orgni ±.8 *** SwellGel ± 2. *** Depth ± 3.2 Sw.G:Org 22.5 *** Sw.G:Brik 5.0 * Signifint ftoril intertions re lso shown. Sttistil signifines were lulted from four-wy ANOVA. Arevitions for eh ftor re s follows, Org, orgni mtter type; GW, green wste orgni mtter; Sw.G, SwellGel. * Sttistil signifine of p <. ** Sttistil signifine of p < 0. *** Sttistil signifine of p < 00. ompred to non vegetted sustrte (dt not shown). The mount of trnspirtion tht L. perenne ontriuted to the totl evpotrnspirtion mount is dependent on the totl mount of iomss produed (evpotrnspirtion nd L. perenne iomss were signifintly orrelted; r 2 = 0.482, p < 00), whih in turn is dependent on the nutrient ontent nd wter storge pity of the sustrte. Orgni mtter type did not ffet the wter holding pity of the sustrte ut did indiretly ffet the rte t whih wter ws lost from the sustrte y influening iomss prodution nd therefore trnspirtion. This highlights tht wter holding pity should not e the only sustrte property tht is onsidered when seleting sustrte for its influene on wter dynmis, s vegettion growth lso hs onsiderle influene on this. Limited evpotrnspirtion, however, my not lwys e desirle sine this n ply n importnt role in temperture regultion of host uildings (Blnus et l., 203; Cstleton et l., 200). Similrly, when designing green roof sustrte to promote greter plnt growth in order to inrese ooling from evpotrnspirtion, one hs to onsider the effet tht higher evpotrnspirtion rtes my hve upon the sustrte wter reservoir during times of drought. If this is depleted too quikly, leding to wter stress nd stomtl losure, plnts no longer trnspire t the sme rte, mortlity my our nd the net ooling effet of the green roof ould e redued. In ddition, y developing green roof solely for one servie, for exmple uilding ooling, other green roof servies my e ompromised, suh s iodiversity provision or estheti qulities. Therefore suh trde-offs must e tken into ount when optimising green roof sustrte (Ampin et l., 200; Lundholm et l., 200). Plnt growth Plnt iomss ws sustntilly inresed when green wste ompost ws used s the orgni mtter omponent insted of rk. Green wste ompost will hve more nutrients ville to plnts due to its preonditioned stte (omposted) nd greter diversity of soure mteril. It hs een shown previously tht inresing the orgni frtion of green roof sustrte inreses plnt growth (Ngse nd Dunnett, 20), lthough to our knowledge this is the first time tht it hs een demonstrted tht different orgni mtter types hve signifint effet on green roof plnt growth. Agin, inresed plnt growth my not lwys e desirle sine it n e detrimentl to long term plnt survivl s plnts with more luxurint growth n e more suseptile to the drought stresses ommon to green roofs (Btes et l., 203), nd will lso require more mintenne ompred to slower growing overge (Ngse nd Dunnett, 20). None-the-less, higher nutrient ontent (through inresed orgni frtion or different orgni mtter type) of green roof sustrtes inreses plnt growth (Ngse nd Dunnett, 20; Olszewski et l., 200) nd n improve long term sustrte development due to lrger uild up of ded iomss, whih n lso help prevent nutrients from eing lehed out of the system (Emilsson, 2008). The greter fund of nutrients in green wste is lso onsistent with the lower root:shoot rtios found in green wste ompost sustrte ompred to rk sustrtes. This indites less need for plnts to llote resoures to nutrient pturing roots in green wste sed sustrtes, nd greter llotion to the photosynthesising shoots (Hermns et l., 2006). The sme response in root:shoot rtios ws oserved for SwellGel nd smll rik,

9 54 T. Young et l. / Urn Forestry & Urn Greening 3 (204) () Shoot N onentrtion (mg N mg - iomss) ,,,, () Shoot N onentrtion (mg N mg - iomss) ,,, Brk Green Wste Compost,, () (d) Chlorophyll ontent (mg dry shoot weight g - ) ,,,,,,, Chlorophyll ontent (mg dry shoot weight g - ) , Smll Brik Lrge Brik Sustrte Composition (80mm) 0 Smll Brik Lrge Brik Sustrte Composition (20mm) Fig. 3. () Shoot nitrogen onentrtion (mg N mg dry iomss) on 80 mm sustrte depth, () shoot nitrogen onentrtion (mg N mg dry iomss) on 20 mm sustrte depth, () shoot hlorophyll onentrtion (mg g dry iomss) on 80 mm sustrte depth, (d) shoot hlorophyll onentrtion (mg g dry iomss) on 20 mm sustrte depth. Error rs re ± one stndrd error. Mens with sme letter do not signifintly differ from eh other within the sme su-figure (Tukey HSD, p < 5). Arevitions re s follows, SG, Swell Gel present; No SG, Swell Gel not present. likely due to the inresed vilility of wter whih redued the need for wter pturing root iomss. However sustrtes tht do the opposite nd promote higher root:shoot rtio (i.e. promote resoure llotion to roots) my tully e more desirle for green roofs during the estlishment phse of plnts, espeilly in res sujet to low preipittion nd high tempertures, where greter wter pture pity (roots) nd less surfe for trnspirtion (shoots) is desirle (Grossnikle, 2005; Ngse nd Dunnett, 20). Plnt growth ws signifintly deresed when rik prtile size ws inresed from 2 5 mm to 4 5 mm. This my e due to the poorer wter holding pity of the lrge rik sustrtes, s lrger prtile sizes redues inter-prtile pore spe nd therefore redues wter holding pity (Frrell et l., 202; Greson et l., 203). This effet my lso e due to the higher mounts of nitrogen lehed from lrge rik sustrtes throughout the tril, whih ould hve depleted nitrogen stoks in the sustrte t fster rte (see online supporting mteril). SwellGel hd reltively smll effet on plnt growth, lthough this my e due to the regulr wtering regime not resulting in gret enough wter stress for the enefits of SwellGel to e relised. Muh lrger inreses in Sedum shoot iomss with polyrylmide gel mendment hs previously een demonstrted, lthough higher temperture nd less frequent wtering regime were used in tht study (Olszewski et l., 200). However different types of wter retention mendment seem to differ in their ility to influene green roof plnt growth (Frrell et l., 203). Depth of sustrte hd no effet on plnt growth, whih ontrsts with mny other studies tht hve stted this to e mjor ftor in green roof plnt estlishment nd growth (Durhmn et l., 2007; Getter nd Rowe, 2007, 2008; Thuring et l., 200). Pst studies hve onluded tht inresed wter vilility in deeper sustrte is one of the most importnt ftors for plnt growth (Rowe et l., 202), ut wter vilility my not hve een mjor limiting ftor in this tril. Inresed depth lso protets plnts from frost dmge (Boivin et l., 200), s well s reduing extreme temperture flututions from solr rdition (Butler nd Orins, 20), oth of whih were not present in the ontrolled temperture environment of the greenhouse. These enefits of deeper sustrte would therefore not hve eome fully pprent in our study. Shoot nitrogen nd hlorophyll onentrtion Shoot N onentrtion ws inresed y SwellGel, however the mehnism ehind this is unler. It my e due to the SwellGel degrding to form rylmide nd then mmonium or nitrogen oxides (Hollimn et l., 2005; Smith et l., 997), or y Swell- Gel soring nitrogen from the sustrte. Alterntively it ould e due to inresed miroil tivity round the moisture pokets reted y the SwellGel s it hs een shown tht fungi nd teri n redily olonise polyrylmide gel nd utilise the nitrogen held within it (Hollimn et l., 2005; Ky-Shoemke et l., 998). As hlorophyll ontent ws not signifintly ffeted y

10 T. Young et l. / Urn Forestry & Urn Greening 3 (204) Tle 4 Min ftor effets (four-wy ANOVA) for () men shoot nitrogen onentrtion (mg g shoot iomss), () men hlorophyll ontent (mg g dry shoot iomss) of Lolium perenne grown in eight different green roof sustrtes. Min ftors re rik size (smll vs. lrge), orgni mtter (rk vs. green wste ompost) nd SwellGel (sene vs. presene). Min ftor mens re shown with the % hnge lso shown etween the two levels within tht ftor (e.g. sene vs. presene SwellGel). Ftor Df F-vlue P-vlue Brik Size Orgni SwellGel Depth % Chnge (±SE, n = 64) Smll Lrge Brk GW No Yes 80 mm 20 mm () Min ftor mens of totl nitrogen shoot onentrtion (mg g shoot iomss) *** Brik ± 2.8 *** Orgni ± 3. *** SwellGel ± 3.4 Depth ± 3.0 Sw.G:Org Org:Depth Sw.G:Org:Brik Sw.G:Org:Depth ** * ** * () Min ftor mens men hlorophyll ontent (mg g dry shoot iomss) * Brik ± 5.7 *** Orgni ± 8.9 SwellGel ± 5.8 *** Depth ± 8.0 Sw.G:Org.7 *** Org:Brik 6.7 * Sw.G:Org:Brik 2.9 *** Sw.G:Org:Brik:Depth 6. * Signifint ftoril intertions re lso shown. Sttistil signifines were lulted from four-wy ANOVA. Arevitions for eh ftor re s follows, Org, orgni mtter type; GW, green wste orgni mtter; Sw.G, SwellGel. * Sttistil signifine of p <. ** Sttistil signifine of p < 0. *** Sttistil signifine of p < 00. SwellGel ut did show signifintly higher levels in plnts grown in green wste ompost sustrtes, it ould indite tht ny dditionl nitrogen supplied through the presene of SwellGel ws not signifint ftor in hlorophyll prodution. Green wste ompost inresed shoot nitrogen onentrtion, proly y inresing the mount of nitrogen ville for plnt uptke (supported y KCl plnt ville nitrogen nlysis of sustrtes, see online supporting mteril). This is lso the likely reson for signifintly higher hlorophyll ontent on green wste s it hs lso previously een shown tht higher hlorophyll ontent in temperte grsses is orrelted with high shoot nitrogen onentrtion (Gáorčík, 2003). The higher onentrtion of shoot N in lrge rik is, in ontrst, likely to e used y negtive growth dilution s rik size did not hve signifint effet on totl tissue nitrogen stoks (dt not shown), ut did redue shoot growth, nd so potentilly onentrting the nitrogen in the smller shoot iomss. Depth of sustrte Inresing the depth of green roof sustrte generlly improves green roof plnt growth nd survivl y inresing wter nd nutrient vilility, espeilly during times of drought (Durhmn et l., 2007; Getter nd Rowe, 2007, 2008; Thuring et l., 200). Although this tril did not show suh drmti improvements to plnt growth nd physiologil performne with depth s previous trils, it ws onduted under ontrolled temperture onditions nd therefore plnts did not experiene some of the environmentl extremes tht roof top trils enounter. Conlusions This study hs shown tht ltering the hrteristis of ommonly used green roof sustrte omponents n signifintly lter the initil growth nd physiologil performne of the plnts grown upon them. This is espeilly importnt for green roofs euse vegettion plys ore role in provision of green roof servies (Oerndorfer et l., 2007). All four hypothesises were supported y the experimentl dt. By looking t eh sustrte omponent in turn it is ler tht orgni mtter type ws found to hve the most influene on plnt growth nd helth. Inresing plnt ville nutrients y swithing from rk to green wste ompost signifintly inresed L. perenne shoot N onentrtion, hlorophyll ontent nd shoot nd root iomss, whih in turn inresed totl evpotrnspirtion. However y lso reduing L. perenne root:shoot rtio, green wste ompost potentilly redued this plnt s ility to survive drought stress. The effetiveness of SwellGel to provide wter storge during drought ws not thoroughly tested in this tril due to the sene of drought onditions. However, SwellGel still improved plnt growth nd sustrte wter holding pity. Brik size hd lrger effet thn SwellGel on shoot growth nd wter holding pity, however SwellGel my e more effetive t providing wter to plnts during drought stress, lthough more studies on the plnt vilility of wter stored in SwellGel must e onduted. Therefore our fourth hypothesis whih predited tht sustrtes ontining smll rik, green wste ompost nd SwellGel would e the est performing sustrte in terms of shoot iomss prodution, evpotrnspirtion nd plnt physiologil ondition ws orret. However this does not neessry men tht this mixture of sustrte omponents will e the optimum for every green roof, with designers needing to onsider the prtiulr environmentl stresses t tht lotion nd the ore reson why tht green roof is eing uilt (e.g. high rinfll res will not need high wter retention for plnt growth, ut my need it for storm wter mitigtion). Clerly, ompositionl hnges in green roof sustrtes even mong ommonly used sustrte mterils n hve lrge influenes on the properties nd physiologil performne

11 56 T. Young et l. / Urn Forestry & Urn Greening 3 (204) of the vegettive omponent of the roof, nd emphsises the ft tht sustrte omposition should e onsidered refully when designing green roofs for optiml provision of prtiulr green roof servie. Appendix A. Supplementry dt Supplementry dt ssoited with this rtile n e found, in the online version, t Referenes Ag, H., Bgum Orikiriz, L.J., Osoto Esegu, J.F., Ou, J., Ks, J.D., Hüttermnn, A., 200. Effets of hydrogel mendment to different soils on plnt ville wter nd survivl of trees under drought onditions. CLEAN Soil Air Wter 38, Allen, S.E., Grimshw, H.M., Prkinson, J.A., Qurmy, C., 974. Chemil Anlysis of Eologil Mterils. Blkwell Sientifi, Oxford. Ampin, P., Slon, J., Crer, R., Hrp, D., Jer, F., 200. Green roof growing sustrtes: types, ingredients, omposition nd properties. J. Environ. Hortiult. 28, Arnon, D.I., 949. Copper enzymes in isolted hloroplsts. Polyphenoloxidse in Bet vulgris. Plnt Physiol. 24, 5. Btes, A.J., Sdler, J.P., Mky, R., 203. Vegettion development over four yers on two green roofs in the UK. Urn Forest. Urn Green. 2, Berghge, R., Bettie, D., Kelley, K., Husin, S., Rezi, F., Long, B., Negssi, A., Cmeron, R., Hunt, W., Quntifying evportion nd trnspirtionl wter losses from green roofs nd green roof medi pity for neutrlizing id rin. In: Ntionl Deentrlized Wter Resoures Cpity Development Projet (NDWRCP). Blnus, T., Vz Monteiro, M.M., Fntozzi, F., Vysini, E., Li, Y., Cmeron, R.W.F., 203. Alterntives to Sedum on green roofs: n rod lef perennil plnts offer etter ooling servie? Build. Environ. 59, Boivin, M.-A., Lmy, M.-P., Gosselin, A., Dnsereu, B., 200. Effet of rtifiil sustrte depth on freezing injury of six hereous perennils grown in green roof system. HortTehnology, Butler, C., Orins, C.M., 20. Sedum ools soil nd n improve neighoring plnt performne during wter defiit on green roof. Eol. Eng. 37, Cmeron, D.D., Preiss, K., Geuer, G., Red, D.J., The hlorophyll-ontining orhid Corllorhiz trifid derives little ron through photosynthesis. New Phytol. 83, Cstleton, H.F., Stovin, V., Bek, S.B.M., Dvison, J.B., 200. Green roofs; uilding energy svings nd the potentil for retrofit. Energy Build. 42, Coumou, D., Rhmstorf, S., 202. A dede of wether extremes. Nt. Clim. Chnge 2, Dunnett, Kingsury, 200. Plnting Green Roofs nd Living Wlls, 2nd ed. Timer Press, Portlnd, Oregon. Durhmn, A.K., Rowe, D.B., Rugh, C.L., Effet of sustrte depth on initil growth, overge, nd survivl of 25 suulent green roof plnt tx. HortSiene 42, Dvork, B., Volder, A., 200. Green roof vegettion for North Amerin eoregions: literture review. Lnds. Urn Pln. 96, Emilsson, T., Vegettion development on extensive vegetted green roofs: influene of sustrte omposition, estlishment method nd speies mix. Eol. Eng. 33, Frrell, C., Mithell, R.E., Szot, C., Ryner, J.P., Willims, N.S.G., 202. Green roofs for hot nd dry limtes: interting effets of plnt wter use, suulene nd sustrte. Eol. Eng. 49, Frrell, C., Ang, X.Q., Ryner, J., 203. Wter-retention dditives inrese plnt ville wter in green roof sustrtes. Eol. Eng. 52, 2 8. Friedrih, C., Low Impt Development: Seleting the Proper Components for Green Roof Growing Medi. Amerin Soiety of Civil Engineers, Reston, USA, pp Gáorčík, N., Reltionship etween ontents of Chlorophyll (+) (SPAD vlues) nd nitrogen of some temperte grsses. Photosyntheti 4, Getter, K., Rowe, B., Effet of sustrte depth nd plnting seson on Sedum plug survivl on green roofs. J. Environ. Hortiult. 25, Getter, K.L., Rowe, D.B., Medi depth influenes Sedum green roof estlishment. Urn Eosyst., Greson, A., Hre, M., Monghn, J., Hll, N., 203. The wter retention pilities of growing medi for green roofs. Eol. Eng. 6 (Prt A), Grossnikle, S.C., Importne of root growth in overoming plnting stress. New Forests 30, Hermns, C., Hmmond, J.P., White, P.J., Verruggen, N., How do plnts respond to nutrient shortge y iomss llotion? Trends Plnt Si., Hithok, A., Green, A., 929. Stndrd-speies of Linneus gener of Phnerogme ( ), in: Interntionl Botnil Congress, Cmridge (Englnd), 930: Nomenlture. Proposls y British Botnists. His Mjesty s Sttionery Offie., pp Hollimn, P.J., Clrk, J.A., Willimson, J.C., Jones, D.L., Model nd field studies of the degrdtion of ross-linked polyrylmide gels used during the revegettion of slte wste. Si. Totl Environ. 336, Hüttermnn, A., Orikiriz, L.J.B., Ag, H., Applition of supersorent polymers for improving the eologil hemistry of degrded or polluted lnds. CLEAN Soil Air Wter 37, Kiri, K., Omidin, H., Zohurin-Mehr, M.J., Doroudini, S., 20. Supersorent hydrogel omposites nd nnoomposites: review. Polym. Composites 32, Ky-Shoemke, J.L., Wtwood, M.E., Lentz, R.D., Sojk, R.E., 998. Polyrylmide s n orgni nitrogen soure for soil miroorgnisms with potentil effets on inorgni soil nitrogen in griulturl soil. Soil Biol. Biohem. 30, Kol, W., Shwrz, T., Mnsourie, P., 982. Extensive plnting of roof res vegettionl properties nd ost of 0 different sustrtes. Zeitshrift für Vegettionstehnik 5, Kotsiris, G., Nektrios, P.A., Prskevopoulou, A.T., 202. Lvndul ngustifoli growth nd physiology is ffeted y sustrte type nd depth when grown under Mediterrnen semi-intensive green roof onditions. HortSiene 47, Lundholm, J., MIvor, J.S., MDougll, Z., Rnlli, M., 200. Plnt speies nd funtionl group omintions ffet green roof eosystem funtions. PLoS ONE 5, e9677. Met Offie, 200. Greenwih Prk Averge Climti Dt: Metselr, K., 202. Wter retention nd evpotrnspirtion of green roofs nd possile nturl vegettion types. Resour. Conserv. Reyl. 64, Molineux, C.J., Fentimn, C.H., Gnge, A.C., Chrterising lterntive reyled wste mterils for use s green roof growing medi in the UK. Eol. Eng. 35, Ngse, A., Dunnett, N., 20. The reltionship etween perentge of orgni mtter in sustrte nd plnt growth in extensive green roofs. Lnds. Urn Pln. 03, Oerndorfer, E., Lundholm, J., Bss, B., Coffmn, R., Doshi, H., Dunnett, N., Gffin, S., Köhler, M., Liu, K., Rowe, B., Green roofs s urn eosystems: eologil strutures, funtions, nd servies. BioSiene 57 (0), Olszewski, M., Young, C., 20. Physil nd hemil properties of green roof medi nd their effet on plnt estlishment. J. Environ. Hortiult. 29, Olszewski, M.W., Holmes, M.H., Young, C.A., 200. Assessment of physil properties nd stonerop growth in green roof sustrtes mended with ompost nd hydrogel. HortTehnology 20, Ouldoukhitine, S.-E., Belri, R., Djedjig, R., 202. Chrteriztion of green roof omponents: mesurements of therml nd hydrologil properties. Build. Environ. 56, R Development Core Tem, 20. R: A Lnguge nd Environment for Sttistil Computing. R Foundtion for Sttistil Computing, Vienn, Austri, ISBN: , URL: Roth-Kleyer, S., Wter lne nd runoff retention of green roofs. In: Presented t the World Green Roof Congress, Bsel, Switzerlnd, pp Rowe, D.B., Monterusso, M.A., Rugh, C.L., Assessment of het-expnded slte nd fertility requirements in green roof sustrtes. HortTehnology 6, Rowe, D.B., Getter, K.L., Durhmn, A.K., 202. Effet of green roof medi depth on Crssulen plnt suession over seven yers. Lnds. Urn Pln. 04, Smith, E.A., Prues, S.L., Oehme, F.W., 997. Environmentl degrdtion of polyrylmides. II. Effets of environmentl (outdoor) exposure. Eotoxiol. Environ. Sf. 37, Solno, L., Ristvey, A.G., Le-Cox, J., Cohn, S.M., 202. Sequestering zin from reyled rum ruer in extensive green roof medi. Eol. Eng. 47, Sutton, R.K., Medi modifitions for ntive plnt ssemlges on green roofs. In: Proeedings of Greening Rooftops for Sustinle Communities, Bltimore, Mrylnd. Thuring, C.E., Berghge, R.D., Bettie, D.J., 200. Green roof plnt responses to different sustrte types nd depths under vrious drought onditions. Hort- Tehnology 20, Voyde, E., Fssmn, E., Simok, R., Wells, J., 200. Quntifying evpotrnspirtion rtes for New Zelnd green roofs. J. Hydrol. Eng. 5, Willimson, J.C., Rowe, E.C., Hill, P.W., Nson, M.A., Jones, D.L., Heley, J.R., 20. Allevition of oth wter nd nutrient limittions is neessry to elerte eologil restortion of wste rok tips. Restor. Eol. 9, Wolf, D., Lundholm, J.T., Wter uptke in green roof miroosms: effets of plnt speies nd wter vilility. Eol. Eng. 33,