Pedrero L Pez Et Al 2015 Restoration Ecology

R E S E A R C H A R T I C L E

Effects of hydropriming treatments on the invigorationof aged Dodonaea viscosa seeds and water-holdingpolymer on the improvement of seedling growthin a lava fieldLuis V. Pedrero-López1, Alejandra Rosete-Rodríguez1, Maria E. Sánchez-Coronado1,Pedro E. Mendoza-Hernández1,2, Alma Orozco-Segovia1,3

Restoration requires techniques similar to those used in agriculture to improve germination and seedling vigor. We treated6-year-old (collected in 2003, S-2003) and 1-month-old (S-2009) seeds of Dodonaea viscosa with hydropriming (HP). Seeds weremade permeable with hot water prior to hydration for 24 or 48 hours (HP-24 and HP-48, respectively) followed by dehydration.The resulting seedlings exposed to both HP treatments were sown in a lava field in soil mixed with hydrogel (HG) under theshade projected by five vegetation patches. The effects of these treatments on germination, seedling field survival, and growthwere assessed. HP-24 in S-2009 and HP-48 in S-2003 increased the germination percentage from 22.5 and 31.7% in controlseeds (permeable seeds) to 63.3 and 98.3%, respectively. The seedlings-2009 (from S-2009) with HG maintained high survivalin all vegetation patches. Seedlings-2003, however, had low survival. The lack of HG was negatively related to the photon fluxin each patch. Survival of seedlings-2009 increased with HG of up to 398.41𝛍mol m−2 s−1; after which survival decreased.During the rainy season, HP enhanced seedling growth, except the basal diameters and number of leaves in the seedlings-2003with HP-24. During the dry season, the effects of HG and HP were similar for all the seedlings. In the following rainy season,the priming effect was lost while HG continued to promote seedling growth. The combined use of HP and HG and the shadeprojected by the patches resulted in a successful vegetation recovery strategy.

Key words: field seedling survival, hydrogel, restoration ecology, seed germination, shade of vegetation patches

Implications for Practice

• During restoration, it is important to use the shade pro-jected by vegetation patches and forest borders to improveseedling establishment in the field.

• Knowledge of the variability and quality of the shade pro-vided by vegetation might improve establishment, par-ticularly when combined with other techniques such ashydropriming (HP) and the use of hydrogel.

• HP was an efficient strategy for reviving an aged seedsupply and will aid in the recovery of vegetation.

• Hydrogel promoted seedling growth over at least 8 monthsin the field.

• Seedlings from old and new seeds performed well inthe field after HP treatment and when sown with hydro-gel. Thus, this restoration intervention is potentiallycost-effective and efficient.

Introduction

Global deforestation rates (approximately 5.2× 106 ha/yearfrom 2000 to 2010) continue to cause substantial land degra-dation (FAO 2010). To revert the effects of deforestation,

restoration of ecosystems, with local native species, is neces-sary. An integral component of restoration is the effective use ofnative seed as the most important tool for achieving large-scalerestoration (Merritt & Dixon 2011). Restoration is limitedby the fact that the seeds available for restoration programshave frequently been stored for several months or years undersuboptimal conditions (e.g. in uncontrolled environments suchas in paper bags or containers). These conditions may reduceseed vigor and consequently decrease germination percentageand seedling vigor (Vázquez-Yanes & Orozco-Segovia 1993).Seedling survival in the field requires vigorous seedlings that

Author contributions: LVPL, AOS, PEMH conceived and designed the research;LVPL, ARR, PEMH performed the experiments; MESC, LVPL analyzed the data;AOS, MESC contributed reagents, materials, and analysis tools; LVPL, AOS, MESCwrote and edited the manuscript.

1Departamento de Ecología Funcional, Instituto de Ecología, Universidad NacionalAutónoma de Mexico, Avenue Universidad 3000, Ciudad Universitaria, Coyoacán,Mexico, DF 04510, Mexico2Facultad de Ciencias, Universidad Nacional Autónoma de Mexico, Avenue Universi-dad 3000, Ciudad Universitaria, Coyoacán, Mexico, DF 04510, Mexico3Address correspondence to A. Orozco-Segovia, email [email protected]

© 2015 Society for Ecological Restorationdoi: 10.1111/rec.12283Supporting information at:http://onlinelibrary.wiley.com/doi/10.1111/rec.12283/suppinfo

Restoration Ecology 1

Invigoration of Dodonaea seeds and seedlings

have the ability to cope with the environmental stresses causedby deforestation (Merritt & Dixon 2014), such as soil erosion,increases in temperature, and subsequent loss of soil moisture(Orsenigo et al. 2014). For these reasons, it is crucial to increaseboth seed and seedling vigor and to search for ecologicallybased solutions, such as water-holding polymers (Vallejo et al.2012; Piñeiro et al. 2013), which increase the probability ofseedling survival of native species in the field.

Some priming strategies used in the biotechnology industryto produce improved seeds for culture have been successfullyapplied to agriculture. Priming treatments (sensu Heydeckeret al. 1975) are based on the tolerance of seed embryos tohydration and dehydration without viability loss, even whenthe radicle has only just protruded (Bruggink & van der Toorn1995). Priming consists of hydrating seeds in water or osmoticsolutions (e.g. PEG and NaCl) while avoiding radicle emer-gence; the seeds are then dehydrated to their original watercontent. After drying, these seeds can be stored while maintain-ing the germination advantages acquired during the primingtreatment (i.e. mobilization of reserves, cell membrane repair,DNA and RNA repair, and de novo synthesis of proteins; Bray1995; Halmer 2004; Rajjou et al. 2012). In general, primingincreases seed germination rates (i.e. velocity) and synchrony,reduces lag time, and increases seedling vigor, tolerance todrought and crop yield. In addition, priming treatments havebeen successfully used to invigorate old seeds or artificiallyaged seeds (Sánchez et al. 2001).

In trees, priming effects have primarily been tested in speciesfrom temperate forests, such as Pinus spp. (Wang & Downie1995). Only a few studies have been conducted in trees fromother ecosystems, including Callitris spp. (Adams 1999),Wigandia urens (González-Zertuche et al. 2001), Cecropiaschreberiana (Sánchez et al. 2003), Mimosa bimucronata,Guazuma ulmifolia (Brancalion et al. 2008, 2010, respec-tively), Parkia multijuga (Calvi et al. 2008), Albizia julibrissin(Sedghi et al. 2011), Quercus rugosa (Castro-Colina et al.2012), Aegle marmelos (Venudevan & Srimathi 2013), andGmelina arborea (Moruf et al. 2013), among others.

The main purpose of these studies was to invigorate seeds,enhance seed germination, and produce healthy and vigorousseedlings for restoration. With this purpose, we examinedseed germination and seedling growth and establishment ofDodonaea viscosa Jacq. (Sapindaceae, hopbush), which isa useful (medicinal, ornamental, and horticultural) nativepioneer species distributed worldwide (Camacho 2000; Har-rington & Gadek 2009; Baptista et al. 2013). Dodonaea viscosacommonly grows in disturbed oak and pine forests, tropicaldeciduous forests, and xerophylous shrublands (Rzedowski& Rzedowski 2001). It is able to grow on eroded soils andsteep slopes in lava rock and clay soils (PRONARE 1998).Because D. viscosa has a high tolerance to light, water, anddisturbance stress, this species has been proposed for use inprimary stabilization for restoration of deforested arid androcky areas (Mendoza-Hernández et al. 2013; Junyan et al.2014). This species is able to stabilize lava field by aiding insoil stabilization as well as providing organic matter to the soil,thereby contributing to litter accumulation, soil retention, and

microclimatic amelioration (Martínez-Pérez et al. 2006;Monroy-Ata et al. 2007).

The urban, protected natural area Parque Ecológico de laCiudad de Mexico (PECM) is located in a lava field south ofMexico City. The area is worthy of protection and restorationbecause it provides important ecosystem services, mainly filtra-tion and storage of water and recharging of aquifers (Vitousek2006; Mendoza-Hernández et al. 2013). Basaltic areas are alsoa source of medicinal plants, firewood, building materials, andother products for local inhabitant (Velázquez et al. 2001; Allenet al. 2010). Lava fields are harsh environments, in which the useof polymers (hydrogel, HG) might increase water collection andretention (Shooshtarian et al. 2011; Vallejo et al. 2012).

In this study, we compared the effect of hydropriming (HP)on germination and seedling production of 6-year-old seedsand 1-month-old seeds of D. viscosa (i.e. long-lived, orthodoxseeds; RBGK 2015) to determine if seed storage age influencesgermination and seedling establishment. This species was usedas a study species to determine the effect of HG, HP, and theshade projected by five small vegetation fragments (i.e. patches)on the recuperation of an aged seed lot and assessed the efficacyof these strategies to aid in vegetation recovery.

Methods

The Species

The dry winged papery capsules of Dodonaea viscosa haveanemochorous dispersal, although secondary dispersal may behydrochorous due to the high floatability of the capsules (Har-rington & Gadek 2009). One to three seeds are produced percapsule (most commonly two). Seeds of D. viscosa are lenticu-lar (2.93± 0.32× 2.2± 0.12 in size). The seeds exhibit physicaldormancy, which is broken by acid scarification or immersion inhot water (Baskin et al. 2004; Benítez-Rodríguez et al. 2014).Germination percentages after treatments may be high, but inthe nursery there may be high seedling mortality caused bydamping-off (Camacho 2000). Seedling establishment percent-ages are relatively high in deep soils (Camacho 2003), but inundeveloped soils, such as that found in lava fields, survival ofD. viscosa is scant (Mendoza-Hernández et al. 2013).

Study Site

The “PECM” is located in the southern part of Mexico City(19∘15′32′′N, 99∘12′1.9′′W, 2,400–2,850 m asl). At this eleva-tion, the climate is temperate with a long subhumid fresh sum-mer Cb′(w2)(w). The mean annual temperature is 11∘C, and themean annual precipitation is 1,100 mm; 80% of the precipita-tion occurs between June and October (González-Hidalgo et al.2002). A large proportion of the protected area is a lava field thatis approximately 1,650–2,000 years old (Siebe 2000). The lavafields in the southern part of Mexico City provide the city withimportant ecosystem services, among which the most valuedare climate regulation and the recharge (water infiltration 40%,DGCOH 1986) and purification of aquifers (Cano-Santana et al.2006). The lava field exhibits edaphic aridity as a result of high

2 Restoration Ecology


Figure 1. (A) Intact and (B) denuded soil after disturbance in the lava fieldin the “PECM.”

rates of water percolation and decreased water retention in theshallow soil (Vaughan et al. 2011; Mendoza-Hernández et al.2014). The vegetation in the PECM is xerophylous shrublandsurrounded by an oak forest that grows in shallow and deep soils(Fig. 1A). Parts of the shrubland and oak forest were disturbed tovarying degrees by illegal settlements between 1980 and 1989.This resulted in a wide matrix that was deprived of vegetationand from which the lava rock was removed, fragmented, andused to level the area (Fig. 1B; Mendoza-Hernández et al. 2013).Immersed in this matrix are small fragments of disturbed oakforest; some of these forests were used to test the effect of shadeon the establishment of pioneer D. viscosa seedlings. Dodonaeaviscosa has a density of 188 individuals per hectare within thedisturbed matrix.

General Procedures

Approximately 4,000 seeds per year were collected fromat least 20 individuals in the PECM during the years 2003(S-2003, dry weight= 0.011± 0.001 g, water content drybasis= 9.6± 1.8%, S-2003 viability was 78%, and the remain-ing seeds had rotted during incubation) and 2009 (S-2009, dryweight= 0.0107± 0.001, water content dry basis= 8.6± 1.3%,and seed viability 96%). In the laboratory, seeds of all individ-uals were manually separated from fruits, mixed, and storedin glass containers under laboratory conditions (21.6± 1.8∘C,relative humidity [RH]= 38.7%). In all cases, seeds were ger-minated at 25∘C in closed plastic boxes (15× 18× 6 cm) filledwith moist silica sand. The boxes were placed inside germina-tion chambers (Lab-Line Instruments, Inc., 844, Melrose Park,IL, U.S.A.) equipped with cool white fluorescent (F20T12/CW,Sylvania, 20 W, Danvers, MA, U.S.A.) and incandescent lamps(Solar, 25 W, Tultitlan, Edo.Mex., Mexico). The photoperiodwas 12/12 hours (light/darkness). The experimental designincluded five replicates of 25 seeds per box per treatment. Overthe course of 30 days, the presence of radicle protrusion (i.e.germination) was recorded every second day.

Germination Pre-Treatments

Seeds from both the 2003 and 2009 collections were madepermeable by immersion in hot water. A total of 15 nylonmesh bags with 25 seeds each were placed in a 1-L glassbeaker containing 600 mL of water at 96∘C. After the bags wereimmersed in the water, the temperature was lowered to 80∘C;seeds remained in the water for 5 minutes. The temperaturewas then lowered to 75∘C, and the seeds were immediatelydried under laboratory conditions. To test the rejuvenating andinvigorating effects of priming, seeds were exposed to HP(hydration in water) in a dark room (21.6± 1.8∘C, RH= 38.7%).For the HP procedure, five replicates of 25 seeds were placedin Petri dishes that were 15 cm in diameter and covered withtap water for 24 hours (HP-24). Five additional replicates werecovered with water for 48 hours (HP-48). At the end of eachtreatment, seeds were dried for 2 days in the same dark room,sown in plastic boxes with moist sand, and placed in germinationchambers. After 2 days of drying, the seeds had returned to theirinitial water content (indicated previously). The experimentaldesign consisted of 2 seed collections× 3 treatments (HP-24,HP-48, and hot water treated control seeds)× 5 replicates.

Planting Areas and Seedling Growth Evaluation

When the cotyledons were open and green, the seedlings weretransplanted to 1-L black plastic bags filled with organic soil andsilica sand (1:1) and placed in a greenhouse for 6 months. Sub-sequently, seedlings were planting in a lava field (PECM) withunderdeveloped soils and low water retention, near five vege-tation patches located between 2,600 and 2,650 m asl inside a25 ha area. Because vegetation edges may be suitable micrositesfor reintroducing individuals to plant communities (Temperton& Zirr 2004; Mendoza-Hernández et al. 2014), we constructeda model of shade dynamics throughout the year for each of thefive vegetation patches. The planting areas were located underthe shade provided by each patch, which was in the North West(NW) sector of each patch during the dry season and lasted from8 to 12 hours per day. In the NW section of each patch (i.e. theplanting area), a minimum of 10 measurements of photosyn-thetic photon flux density (400–700 nm, PPFD) were taken eachhour from 09:00 to 18:00 hours at different locations within theplanting area using a quantum meter (MQ-200 Apogee Instru-ments, Logan, UT, U.S.A.). Patch sizes were as follows: 329 m2

(patch 1), 260 m2 (patch 2), 396 m2 (patch 3), 350 m2 (patch 4),and 508 m2 (patch 5) (see Mendoza-Hernández et al. 2014).

Twenty seedlings from each priming treatment were sown inthe shaded area of each patch (Fig. 2). Control seedlings wereeliminated due to low germination and low seedling survival(<27%). At the time of transplanting, seedling growth variablesvaried widely between individuals within each treatment, thusseedlings were not the same size. The seedlings from S-2003and treated with HP-24 were significantly smaller than seedlingsof the other treatments (p< 0.05, Fig. 3).

During the sowing process, we dug 20 holes of approx-imately 10 cm in depth and 20 cm in diameter; 10 holeswere filled with a mixture of the local substrate (i.e. frag-mented lava rock and soil) and 1 L of hydrated HG (4 g/L,



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Figure 2. Diagram of one of the patches showing the shaded area whereseedlings of Dodonaea viscosa were planted and its orientation withrespect to the vegetation patch. Circles represent planted seedlings.

Stockosorb, Aqua-gel, GM, 1–2 mm, Comercializadora Inter-nacional, Mexico, DF, Mexico). The total volume of the mixturein each hole was approximately 3 L. The microsites (i.e. thespecific locations where the holes were dug) were selectedaccording to the conditions of the substrate. Sites with remov-able fragmented rock and soil instead of continuous rock werechosen. Over the course of a year (i.e. August 2009 to July2010), monthly measurements were taken regarding seedlingsurvival, height, crown cover area (CCA= (D1/2)× (D2/2)×𝝅),basal diameter (BD), and leaf number. When analyzing plant

growth, we took into account only the data from seedlingsthat survived the entire measurement period. Because a severedry season affected seedling growth, the observation periodwas divided into three growth periods: August–November,December–March, and April–July. Seedlings originating fromprimed S-2003 and S-2009 are termed seedlings-2003 andseedlings-2009.

Statistical Analysis

Germination percentages were arcsine transformed. Final per-centages were analyzed using a two-way analysis of variance(ANOVA). Agreement with the assumptions of the parametrictests was assessed. Post hoc comparisons were completed witha Tukey test. The germination data were fitted using exponen-tial sigmoid curves of the form y= a/[1+ b(−cx)] implementedin TableCurve 2D, v3 (AISN Software, Chicago, IL, U.S.A.).The survival of the seedlings at the end of the experiment wasanalyzed with a logistic regression using the software packageJMP (ver. 8.0 SAS Institute Inc., Cary, NC, U.S.A.). Seedlingsurvival in each patch was related to the values calculated duringJuly (when measurements were completed) for species richness,H′, J, plant cover, and mean PPFD under the shade projected byeach patch in which the seedlings were planted. The growth vari-ables were compared with two-way ANOVA tests. The crowncover data were natural log transformed to meet the ANOVAassumptions.

Figure 3. Initial growth of Dodonaea viscosa seedlings before transplanting to the field. Seedlings were obtained from seeds collected in 2003 and 2009.Mean values+SD are shown. Lowercase letters indicate significant differences. Prior to germination, the seeds of both collections were treated with HP for24 hours (white bars) or 48 hours (gray bars).



Table 1. Effect of the variables tested with a two-way ANOVA on the finalgermination percentage of the seeds of Dodonaea viscosa collected in 2003or in 2009 in the PECM lava field. df , degrees of freedom.

Source of Variation F df p

Hydropriming 60.82 2, 23 0.0001Year of collection 37.00 1, 23 0.0001Hydropriming× year of collection 28.90 2, 23 0.0001

Results

Germination

The collection year, HP, and their interactions significantlyaffected the germination of Dodonaea viscosa. Control seedsfrom both collections (28 and 34% for S-2003 and S-2009,respectively) had germination percentages significantly lowerthan HP-treated seeds. The germination percentage was highestin S-2009 treated with HP-24 (98.3%). Within the S-2003 group,the highest germination percentages were found in the HP-48treatment (63.3); however, this germination percentage wassignificantly lower than in the S-2009 group (Table 1; Fig. 4).

Survival

The seedlings-2009 with HG showed the highest survivalprobability, and this probability was high in all fragments(Table 2; Fig. 5). The final survival probabilities, recorded inJuly 2010, were significantly affected by HG, the collectionyear of the seeds, the planting area, and the interactions amongthese three factors. The survival probabilities were lowest forthe seedlings-2003 planted without HG (0.02–0.29, Fig. 5B),whereas the highest survival probabilities were observed forthe seedlings-2009 planted with HG (0.63–0.78, Fig. 5C).These results were independent of planting area. For the sur-vival of the seedlings-2003 planted with HG (Fig. 5A) and theseedlings-2009 planted without HG (Fig. 5D), significant dif-ferences were observed among planting areas.

The PPFD throughout the study period ranged from 6–478,48–1198.7, 15–740.7, 30–1,461 to 48–371 μmol m−2 s−1

Table 2. Effect of the variables tested with the logistic regression analysison the final survival of the seedlings of Dodonaea viscosa growing indifferent areas in the PECM lava field.

Source of Variation X2 df p

Hydrogel 70.62 1 0.0001Year of collection 23.52 1 0.0001Planting area 14.97 4 0.0001Hydrogel× year of

collection× planting area14.59 4 0.0001

for patches 1, 2, 3, 4, and 5, respectively. Survival of theseedlings-2003 without HG was inversely related to themean PPFD according to an exponential function y= a+ b/x2

(r2 = 0.93, F = 42.29, p= 0.007). Survival of the seedlings-2009without HG was related to the mean PPFD via a logistic doseresponse function y= 4ax−c−1bc+1c2/(c− 1+ cx−cbc + x−cbc)2

(r2 = 0.99, F = 1,187.92, p= 0.0008), where a= amplitude,b= x at y max, and c is a form parameter. That is, as PPFDincreased, the survival first increased and then decreased.

In the rainy season of 2009, the seedling height, crown cover,BD, and the number of leaves were significantly affected by HP,HG, and the interaction between HG and the year of collection(Table S1, Supporting Information). For the seedlings-2003,the growth in height, BD, and number of leaves was generallyenhanced by the HP-48 treatment. The lowest values for crowncover were found in the HP-24 treatment without HG. For theseedlings-2009, the presence of HG tended to increase growthvariables. In these seedlings, the highest values for all thevariables were found in the HP-48 treatment with the presenceof HG (Fig. 6).

In the dry season of the year 2010, the results were similarto those found in the previous season. However, the significantinteraction between HG and the year of seed collection was notobserved (Table S1) because in both years the HP-48 treatmentand the presence of HG resulted in an increase of growth vari-ables (Fig. 6). By contrast, in the rainy season of 2010, the effectof the HP treatment was not observed, while the effect of HG

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Figure 4. Germination of Dodonaea viscosa seeds collected in 2003 (old) (A) and in 2009 (recently collected) (B), pretreated with 24 hours of HP ( ),48 hours of HP ( ) or untreated (control, ). Mean values±SD are shown. Lowercase letters indicate significant differences. Both HP treatments ended witha drying period.



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Figure 5. Probabilities of field survival of the seedlings obtained from the preconditioned seeds of Dodonaea viscosa collected in the years 2003 and 2009.The seedlings were planted with (A, C) or without (B, D) HG beneath the NW shade projected by five vegetation patches in the PECM; Patch 1 ( ),Patch 2 ( ), Patch 3 ( ), Patch 4 ( ), and Patch 5 ( ).

and the interaction between HG and the year of seed collectionwas maintained (Table S1). Thus, values for all growth variableswere significantly higher for the seedlings-2009 with the pres-ence of HG (Fig. 6). Furthermore, the seedling height, BD, andnumber of leaves showed higher values than in the 2009 dry sea-son, but the crown cover showed lower values than in the twoprevious seasons (Fig. 6D–F).

Discussion

HP was an efficient tool to increase the germination percentagein both scarified seed lots, both for the older S-2003 and for therecently collected S-2009. The percentage of seeds that germi-nated due to the priming treatment depended on the duration ofthe treatment and seed age. For the S-2003 lot, an HP-48 treat-ment was required, whereas for S-2009, an HP-24 treatmentwas more than sufficient. In both seed lots, control seeds had alow germination percentage, but after the best priming treatmentfor each collection was applied, S-2003 reached 63.3± 8.6%germination and S-2009 reached 98.3± 1.9%. The germinationpercentage of S-2003 in the year of collection was reportedto be greater than 80% after scarification (Benítez-Rodríguezet al. 2014). The effect of priming in each seed lot differed. Inaddition to their physical dormancy, Dodonaea viscosa seedsmay be physiologically dormant (Camacho 2000; Baskin et al.2004). Thus, in the S-2009 group, priming alleviated dormancy.The low germination of D. viscosa in the S-2003 group maybe a result of seed aging under suboptimal storage conditions

(i.e. uncontrolled temperature and RH). These conditions, incombination with the seeds’ lipid content (15%), might haveaccelerated seed aging (Shaban 2013). In spite of the lipidcontent, this species cannot be considered an oily species(Caddick 2004). During storage, seed membrane integrity andmitochondrial enzymatic activity decline and DNA degrades.These factors, and others, affect seed physiology (McDonald2004; Shaban 2013). It is well known that priming repairsdamage occurring in naturally and artificially aged seeds, asdemonstrated for Oryza sativa, Poaceae (Lee & Kim 2000),Agropyron elongatum (Akbarpour et al. 2014), and other plantssuch as onion, corn, leek, and tomato (McDonald 2004; Wagneret al. 2011).

Several shrubs and trees, such as Abelmoschus esculentusand Albizia julibrissin, have been treated with hormone-primingagents (i.e. gibberellins added to the water). Others, such asLeucaena leucocephala, have been hydroprimed to improve thegermination of aged seeds (Sánchez et al. 2005; Sedghi et al.2011; Raj et al. 2013). The improvement of germination in agedseeds by HP alone, as accomplished here with the D. viscosatree, is a novel tool that can be used by farmers during restorationprograms.

An interesting result obtained with the priming treatmentswas that the few seedlings obtained from the control seeds ofboth seed lots underwent high mortality due to damping-off; asimilar result was observed by Benítez-Rodríguez et al. (2014).By contrast, the primed seedlings had high survival, most likelybecause priming induces resistance to seedling diseases orantipathogenic effects (Mondal & Bose 2014).



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Figure 6. Field growth of the Dodonaea viscosa seedlings from seeds collected in 2003 and 2009. The mean values+SD are shown. Lowercase lettersindicate significant differences. Growth in the rainy season of 2009 (August–November), the dry season of 2009–2010 (December–March), and the rainyseason of 2010 (April–July), in the PECM. Prior to germination, the seeds of both collections were treated with HP for 24 or 48 hours. The seedlings weresown without (white bars) or with (gray bars) the presence of HG in the soil.

Survival is a crucial step for recruitment. In this study, we didnot have sufficient seedlings from the control seeds (<27%),due to low germination and low survival in the shade house, tobe transplanted to the field. Low survival (32%) of control seedshas also been reported in previous studies (Benítez-Rodríguezet al. 2014). However, the seedlings-2003 and seedlings-2009subjected to the HP-24 and HP-48 treatments had high survival

in the field for a 5-month period, August–December, whichincluded parts of both the rainy and dry seasons. These resultssuggest that HG delayed drought stress in the PECM; otherstudies found similar results with Citrus spp., Prosopis laevi-gata, and other trees (Arbona et al. 2005; Shooshtarian et al.2011; Ríos-Saucedo et al. 2012). Relatively high survival (i.e.50%) for 10 months has been reported for Quercus suber



(Chirino et al. 2011); a similar result was observed for theseedlings-2009 with HG. However, the seedlings of Q. suberwere 11 months old when they were planted in the field,whereas the seedlings of D. viscosa were only 6 months old. Atthe end of the study, we found that the survival of the seedlingssown without HG was related to the mean PPFD in each patch.The probability of survival of the older seeds declined as PPFDincreased. By contrast, the recently collected seeds exhibitedincreased survival until an PPFD of 398.41 μmol m−2 s−1 wasreached, after which survival decreased. This outcome suggeststhat PPFD affected the availability of water in the micrositeswithout HG via soil water evaporation due to the degree ofexposure to light. By contrast, survival of the seedlings grownwith HG was not affected by the mean PPFD. The HG polymerprolongs the survival of horticultural and forest species (Hüt-termann et al. 1999; Silva et al. 2012), and indeed high survivalfor the seedlings-2009 was maintained by HG in all vegetationpatches. This result was in contrast to the low survival of theseedlings-2003 growing without HG. For other treatmentswithout HG, field survival differed after the first 5 monthsdepending on the vegetation type that created the shade, butthere was no clear pattern. The largest difference betweenpatches was observed in the seedlings-2003 growing with HGand the seedlings-2009 growing without HG. In addition tothe presence of HG, the heterogeneity at a small scale betweenindividual planting sites played an important role in maintaininghigh survival probabilities. The shade produced for isolatedtrees, fragments, or vegetation borders was not homogeneousin space and time; at small scales, this creates safe and unsafesites for seedling survival and growth (Maestre et al. 2003;Oliet & Jacobs 2007; Mendoza-Hernández et al. 2014). For thisreason, the use of adequate scales is necessary for the studyof different plant processes in the field (Orozco-Segovia &Sánchez-Coronado 2009; Longepierre et al. 2014).

The effect of seed age, HP, and HG varied between thegrowth periods. S-2003 required a longer period of seedpriming (48 hours) to produce invigorated seedlings duringthe first months of planting. In the rainy season of 2009(August–November 2009), all growth variables were enhancedfor the HP group, in particular seedling height and BD, andthe number of leaves were affected. However, the presence ofHG was also important, particularly for the seedlings-2009.Notably in the seedlings-2003, BD and the number of leaveswere lowest with the HP-24 treatment. In the dry season(December–March 2009–2010), HG was approximately asimportant as HP, and its effects were independent of seed age.HP for 48 hours and HG enhanced seedling growth accordingto all metrics except crown cover. During the rainy season, HGwas the unique determining factor for higher seedling growthfor the seedlings-2009. Priming invigorated the seedlings andmade plants more resistant to water stress. However, this effectwas lost after 8 months of planting, at which time seedlingsrequired only a reliable source of moisture, which was providedby the addition of HG to the soil.

Seedling survival and growth in the field requires vigor-ous seedlings with the ability to cope with the environmen-tal stresses caused by deforestation (Mendoza-Hernández et al.

2014) and global climatic change (Abeli et al. 2014). In thisstudy, we were able to demonstrate that seedlings from S-2003performed well in the field after HP treatment and when sownwith HG, as assessed at the end of this study. Despite the uncer-tainty regarding these techniques (Cortina et al. 2011) and thechallenges present for plants accessing water in lava fields, ourresults in the PECM demonstrated a successful restoration inter-vention. Seed HP is an inexpensive and easily applied techniquethat can be applied and tested in any species by any farmeror land manager, ensuring better environmental outcomes forrestoration.

Acknowledgments

This study was supported by the Grant Programa de Apoyo aProyectos de Investigación e Innovación Tecnológica (PAPIIT)IN202912. We thank to the Drs D. Eldridge, K. Dixon, andto one anonymous reviewer for the critical review of themanuscript and grammar improvement. Also to Dr G. G.Guzmán for the determination of seedling disease and to A. G.Ponce, D. V. Vidal, I. A. Calixto, and R. Graniel for technicalsupport.

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Supporting InformationThe following information may be found in the online version of this article:

Table S1. Effect of the variables tested with three-way ANOVAs on the growthresponse of the seedlings of Dodonaea viscosa in different planting areas of the ParqueEcológico de la Ciudad de México lava field. ns, nonsignificant.

Coordinating Editor: David Eldridge Received: 1 July, 2015; First decision: 5 August, 2015; Revised: 14 August, 2015;Accepted: 15 August, 2015


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Pedrero L Pez Et Al 2015 Restoration Ecology