Biologia 66/2: 275—281, 2011Section BotanyDOI: 10.2478/s11756-011-0001-x

Effect of nitrogen addition and drought on above-ground biomassof expanding tall grasses Calamagrostis epigejosand Arrhenatherum elatius

Karel Fiala1, Ivan Tůma1,2 & Petr Holub1,3

1Department of Vegetation Ecology, Institute of Botany, Academy of Sciences of the Czech Republic, Lidická 25/27, CZ-60200 Brno, Czech Republic2Department of Agrochemistry, Soil Science, Microbiology and Plant Nutrition, Faculty of Agronomy, Mendel Universityin Brno, Zemědělská 1, CZ-61300 Brno, Czech Republic,3Institute of Systems Biology and Ecology, Academy of Sciences of the Czech Republic, (Global Change Research Centre –CzechGlobe), Poříčí 3b, CZ-60300 Brno, Czech Republic

Abstract: Tall expansive grasses act as serious weeds since they spread intensively and are a important threat to biodiversityof various plant communities. A field experiment was set up based on three sets of paired plots, where Calamagrostis epigejosand Arrhenatherum elatius dominated and a mixture of both these tall grasses occurred. Parallel plots were treated byadditional amounts of nitrogen (50 kg N ha−1) for six years (2002–2007). Above-ground biomass was harvested in bothwet (2004) and dry (2007) years, separated in individual fractions, and weighed to determine the above-ground biomass.We wanted to know if a higher nitrogen availability in dry year can support above-ground growth of expansive tall grassesC. epigejos and A. elatius and what their competitive ability of these tall grasses in mixture is in dry conditions. Droughtresulted in a decrease in above-ground biomass production of studied tall expansive grasses, and, in a relative increase inmortality of A. elatius shoots in comparison with C. epigejos. Drought can substantially reduce the effect of applied nitrogenon above-ground growth of expansive tall grasses. However, A. elatius appears to be producing more above-ground biomassafter application of N even in relatively dry conditions.

Key words: dicotyledonous; dieback; litter; mixtures of tall grasses; other grasses

Introduction

Biological invasions by alien plant species are large-scale phenomena of widespread importance and repre-sent one of the major treats to European biodiversity(Lambdon et al. 2008). A similar behaviour is also typ-ical for several native European perennial C-3 plantssuch as for tall grasses Calamagrostis epigejos (L.)Roth and Arrhenatherum elatius (L.) J. Presl et C.Presl.C. epigejos, a rhizomatous perennial grass, toler-

ates most often dry sites on soils with a very low con-tent of organic matter and low to very low contents ofN; however both the growth and reproduction are en-hanced under open, moist and nutrient (especially N)rich conditions (e.g., Rebele & Lehmann 2001; Fiala etal. 2003). C. epigejos exhibits extremely broad ecolog-ical amplitude, growing from littoral zones of aquatichabitats to dry steppe sites. It can be considered asthe most expansive species in the landscape of theCzech Republic. Nowadays, C. epgejos is dominant inthe majority of disturbed habitats from lowland to sub-montane zone. A conspicuous further expansion of thisspecies is expected (Prach & Wade 1992).A. elatius, a tuft forming perennial tall grass, is

commonly found on well-aerated, moderately deep neu-tral or nearly neutral soils of high to moderate fertility(Pfitzenmeyer 1962). A. elatius is a fast-growing grassand early-successional species, that dominates nutrient-rich communities (Fraser & Grime 1998; Tůma et al.2005).Expansive grasses are a serious threat to biodiver-

sity. Negative correlations were found between increas-ing dominance of A. elatius and C. epigejos and speciesrichness (Sedláková & Fiala 2001; Fiala et al. 2004).The competitive grasses can arrest succession for a longtime forming a dense, compact sward (Prach & Pyšek2001). In this respect, C. epigejos plays a prominentrole in the present Central European landscape. Thusboth mentioned tall grasses represent plant species ofglobal importance due to their intensive expansion intovarious ecosystems and to recent spreading in large ar-eas in Europe and North America (e.g., ten Harkel &van der Meulen 1996; Rebele & Lehmann 2001; Wilson& Clark 2001; Fiala et al. 2003).Grass species especially often increase markedly as

a result of eutrofication. Increased nitrogen (N) avail-ability is obviously of major importance in Europeangrasslands and is indicated by enhanced growth of sometall grasses (Bobbing & Roelofs 1995). Calamagrostis

c©2011 Institute of Botany, Slovak Academy of Sciences

276 K. Fiala et al.

epigejos and Arrhenatherum elatius, not excepted, in-crease strongly as a result of enhanced nutrients avail-ability, especially of N (Oomes & Mooi 1981; Berendseet al. 1992; Fiala et al., 2003, 2004; Liancourt et al.2009).The earlier our results concerning competitive abil-

ity studied tall grasses obtained in cultivation experi-ments suggest that the competitive ability of Calama-grostis relative to Arrhenatherum declined in the het-erogeneous soil environment when compared to homo-geneous treatments (Tůma et al. 2009). Thus nutrientheterogeneity can enhance the competitive ability ofArrhenatherum relative to Calamagrostis. The greatestsignificant increases in relative yield of Arrhenatherumgrowing in mixtures with Calamagrostis occurred inboth unfertilized and fertilized unclipped treatments(Tůma et al. 2005). Intensive allocation of nitrogen tothe aboveground biomass of Arrhenatherum and Cala-magrostis as a response to clipping contributed to thehigh losses of nitrogen from these species, which wereassociated with a decrease of competitive ability.Climate change models forecast a reduction in

annual precipitation and more extreme events (lessrainy days and longer drought period between rain-fall events), which may have profound effects on ter-restrial ecosystems. Plant growth and community dy-namics are likely to be affected by these changes sinceproductivity is limited by water availability. Climatechange may affect ecosystem functioning through in-creased temperature or changes in precipitation pat-terns (Stemberg et al. 1999; Fay et al. 2008). Droughtimposed on the earlier growth stages, most drasticallyinfluenced plant growth and final yield (e.g., Stampfli1992; Holub 2002). Such changes may affect numeroussoil, plant, and ecosystem properties in grasslands andultimately affect their productivity and biological di-versity. In order to understand the probable changes ingrowth and production of tall expanding grasses, it isessential to analyse also their adaptation to differentrainfall conditions.Grasslands in the Podyjí National Park (South

Moravia, the Czech Republic) are a highly diversecommunity with many characteristic species. A greatpart of the area was covered with a dry acidophilousshort grass vegetation represented by the plant com-munity Potentillo- arenariae-Agrostidetum vienalis (seeSedláková & Fiala 2001). Since 1995, however, a largeincrease of tall grasses A. elatius and C. epigejos hasbeen observed in these communities. Great areas oforiginal short grass communities have been alreadyreplaced by nearly monospecific stands of these tallgrasses.We set up a field experiment to study the effect

of N addition on formation of above-ground biomass ofexpanding tall grasses Calamagrostis epigejos and Ar-rhenatherum elatius. Substantial differences in amountof precipitation recorded in individual years enable usto study the effect of both N addition and droughton expanding tall grasses, especially on formation theirabove-ground biomass. We wanted to know and com-

pare the extent of their above-ground biomass reductionin dry conditions, i.e., their drought tolerance and thecompetitive ability of these grasses.The following hypotheses were tested:i) The effect of additional N supply will be greater

on the increase of above-ground biomass of the tall grassA. elatius in wet year than on C. epigejos, becauseA. elatius is considered as a fast-growing, mesophilicspecies, whose biomass responds dramatically to a highsoil fertility treatment.ii) In a mixture of both tall grasses, the above-

ground biomass of C. epigejos will increase in wetyear after N application, due to an extensive system ofbelow-ground organs which can take up nutrients moreeasily.iii) The effect of additional N on an increase of

above-ground biomass of tall grasses will be eliminatedin dry year, because droughts can reduce nutrient avail-ability.iv) Formation of above-ground biomass of C. epige-

jos will be less affected by dry conditions compared toA. elatius, due to an extensive system of below-groundorgans.

Material and methods

Study sitesOur studies were carried out in the Podyjí National Parknear the town of Znojmo (the Czech Republic). Studiedstands were located near the village Havraníky (48◦49′ N,16◦01′ E). A great part of the area is covered with dry aci-dophilous short grass vegetation represented by the plantcommunity Potentillo-Agrostidetum (see Introduction). Thebedrock is formed by granite, with a nutrient-poor shallowsoils of Ranker type (Table 1). The studied locality (altitudearound 320 m) was characterized by annual mean air tem-perature 9.0◦C and 587 mm of yearly sum of precipitation.The amount of precipitation water was collected monthlyat studied locality. Changes in above-ground plant biomasswere determined in relatively wet (2004) and dry (2007)years. During the growing seasons 2004 and 2007, the pre-cipitation was 391 and only 258 mm, respectively (Fig. 1).At the beginning of the growing season 2007, study sites re-ceived lower amount of precipitation (−12% of the long-termaverage) than was recorded in 2004 (+10%). A one-monthperiod completely without any rain turned up at the begin-ning of the growing season 2007. In addition, only 38 mm ofprecipitation fell in a 99-day drought from the second halfof August to November in the previous year 2006 (Fig. 1).The growing season of the year 2003 was also dry, never-theless about 190 mm of precipitation was recorded duringthree autumn months (September to November). Thus thebeginning of the 2007 was drier than that of 2004 year.

Vegetation analysesCommon species in the intact acidophilous dry grass-land were, beside the dominant Festuca ovina, graminoidsAvenula pratensis, Phepum phleoides, Avenella flexuosa, An-thoxanthum odoratum, Poa pratensis, Carex humilis anddicots Pimpinella saxifraga, Potentilla arenaria, Thymuspraecox, Genista pillosa, Achilea collina, Hieratium pi-losella, Rumex acetosella.

Stands characterized by considerable dominance of A.elatius and/or C. epigejos (mostly nearly monospecific), as

Effect of nitrogen and drought on above-ground biomass of C. epigejos and A. elatius 277

Table 1. Soil features of studied grass stands recorded at the beginning of the field experiment (April 2002) in individual plots (soillayer 0–10 cm).

Type of stands Arrhenatherum Calamagrostis Arrhenatherum + Calamagrostis stands

Treatments N 0 +N N 0 +N N 0 +N

pH-H2o 4.33 ± 0.12 4.58 ± 0.18 4.70 ± 0.25 4.78 ± 0.13 4.38 ± 0.08 4.85 ± 0.13pH-KCl 3.95 ± 0.20 4.23 ± 0.19 4.33 ± 0.33 4.55 ± 0.15 3.90 ± 0.10 4.55 ± 0.13Org. matter (%) 12.9 ± 1.8 12.2 ± 3.4 9.3 ± 0.39 8.9 ± 0.89 15.9 ± 3.22 9.9 ± 1.14Ca (mg 1 kg−1) 745 ± 121 842 ± 86 684 ± 226 858 ± 160 644 ± 77 975 ± 46Mg (mg 1 kg−1) 124 ± 30 107 ± 11 116 ± 22 110 ± 27 79 ± 14 121 ± 2.0P (mg 1 kg−1) 10.7 ± 1.7 36.3 ± 14 20.3 ± 2.9 8.5 ± 1.0 10.0 ± 0.5 15.7 ± 2.1K (mg 1 kg−1) 191 ± 52 324 ± 65 264 ± 17 199 ± 55 168 ± 40 230 ± 55Ntot (%) 0.39 ± 0.06 0.38 ± 0.13 0.28 ± 0.01 0.28 ± 0.08 0.49 ± 0.01 0.33 ± 0.05

Data are means ± SE (n = 4)

0

20

40

60

80

100

120

140

160

180

50 100 150 200 250 300 35

Time [months]

Pre

cip

itat

ion

[m

m]

III IV V VI VIII IX XIXVII

2007

2004

2006

391 mm

446 mm

258 mm

Fig. 1. Changes in pattern of precipitation recorded at studied locality in the course of the 2004, 2006 and 2007 growing seasons. Thesums of precipitation recorded during growing seasons are shown.

well as a mixture of both tall grass species were studied indescribed region. Increasing dominance of both tall grasseswas strongly negatively correlated with the species rich-ness. In these stands the number of species decreased to lessthan 63% and 44% of the original number in the dry grass-land (Fiala et al. 2004). The forbs especially disappearedalmost completely in Calamagrostis. They recorded 5.0 and3.5 plant species in A. elatius and C. epigejos stands on theaverage.

On the area of approximately five hectares, four 2 ×2 m plots were laid out in stands dominated by both A.elatius and C. epigejos (further referred as Arrhenatherumand Calamagrostis stands). Four plots were placed on theboundary between both tall grasses, i.e., characterized bymixture of both tall grasses. Stands in other twelve par-allel plots of the same size, situated closely to the firstset of plots, were treated by additional amounts of N (50kg N ha−1, i.e., 5 × 10 kg N ha−1 during growing seasons)for six years (2002–2007) in order to study the above-groundbiomass production of studied grasses affected by additionalN. Above-ground plant parts were collected from area 20 ×

40 cm (one replication in each of four 2 × 2 m plots) in Au-gust 31, 2004 and August 15, 2007 (placed in different partsof 2 × 2 m plots). Samples were sorted into the followinggroups: above-ground parts of A. elatius, C. epigejos, othergraminoids (grasses, Carex sp.) and dicotyledons. In addi-tion, living and dead above-ground parts of both tall grassesand a great amount of undecomposed plant litter were sep-arated in the dry 2007 year. After drying (at 60◦C for threedays) the plant material was weighed.

Statistical analysisObtained data were evaluated by means of the analysis ofvariance, using statistical package STATISTICA 7.0. Three-way ANOVA analysis was used to test the effect of N fer-tilization, plant species and years, as independent variables,on the above-ground biomass of C. epigejos, A. elatius,other grasses, dicotyledons and above-ground biomass asdependent variables. F-value and resulting P level were de-termined. Significant differences among means were tested(LSD test (P < 0.05) after ANOVA).

278 K. Fiala et al.

Table 2. The effect of plant species, N fertilization and year, on total above-ground biomass of stands of tall grasses Arrhenatherumelatius and Calamagrostis epigejos.

A. elatius C. epigejos Other grasses Dicotyledons TotalEffects

df F df F df F df F df F

Species (S) 2 71.8 *** 2 41.9 *** 2 23.1 *** 2 3.3 * 2 0.97 NSFertilization (N) 1 14.8 *** 1 7.7 ** 1 0.3 NS 1 0.25 NS 1 21.9 ***Year (Y) 1 22.7 *** 1 18.2 *** 1 49.2 *** 1 8.3 ** 1 101.7 ***SxN 2 8.9 *** 2 3.7 * 2 3.8 * 2 0.99 NS 2 0.77 NSYxS 2 6.8 *** 2 6.5 ** 2 22.3 *** 2 0.07 NS 2 0.41 NSYxN 1 1.2 NS 1 2.6 NS 1 0.3 NS 1 0.19 NS 1 4.6 *YxSxN 2 2.9 NS 2 0.3 NS 2 4.0 * 2 0.85 NS 2 0.32 NS

F values; NS non significant; * P < 0.05, ** P < 0.01, *** P < 0.001

Table 3. Effect of nitrogen fertilization (+N) on the above-ground biomass (in g m−2) of stands of tall grasses Arrhenatherum elatiusand Calamagrostis epigejos and mixtures of both tall grasses recorded in dry 2007 year.

Type of stands Arrhenatherum Calamagrostis Arrhenatherum + Calamagrostis stands

Treatments N 0 +N N 0 +N N 0 +N

A. elatiusLiving 59 ± 15a 121 ± 38b 11 ± 4a 18 ± 14a 43 ± 15a 47 ± 13aDead 137 ± 23bc 182 ± 38c 26 ± 14a 16 ± 12a 85 ± 12ab 133 ± 31bcTotal 196 ± 20b 303 ± 43c 37 ± 17a 34 ± 26a 128 ± 27b 180 ± 24b

C. epigejosLiving 26a 5.4a 123 ± 47bc 170 ± 44c 41 ± 13ab 31 ± 12aDead 4a 0.5a 42 ± 12ab 112 ± 44b 26 ± 16a 51 ± 44abTotal 30 ± 17a 5.9a 165 ± 56bc 282 ± 70c 67 ± 28ab 81 ± 55ab

Other grasses 1.3ab 3.4b 0.9ab 0.6a 0a 0.4aDicotyledons 8.5 3.8 7.6 3.4 1.3 7Above-ground 237 ± 28a 316 ± 44b 211 ± 45ab 320 ± 54b 197 ± 24a 268 ± 77bLitter 228 ± 33ab 305 ± 15b 422 ± 40c 330 ± 36bc 262 ± 51ab 196 ± 25aAbove-ground + litter 465 ± 38 621 ± 56 633 ± 81 650 ± 75 459 ± 61 464 ± 97

Data are means ±SE. Different letters denote significantly different values (LSD test (P < 0.05) after ANOVA)

Results

Effect of nitrogen addition on above-ground biomassThree-way ANOVA analysis, evaluating all data ob-tained in two years, has shown that the amountof above-ground biomass of individual plant species,biomass of other present grasses, and dicotyledons (ex-cept total above-ground dry mass) differed significantlyby species (Table 2). Application of additional N af-fected significantly the biomass of both tall grasses,A. elatius particularly, and the above-ground biomassof whole stands as well. Fertilization did not influ-ence significantly the biomass of dicotyledons and othergraminoids. The analysis of variance also confirmed theeffect of different years on biomass of both tall grassesand separated fractions of above-ground plant parts.Concerning interactions, the above-ground biomass wasaffected by species and fertilization, as well as by speciesand year (Table 2).In the wet year, higher inputs of N in grass stands

affected significantly above-ground biomass of both tallgrasses, as well as the total above-ground biomassof whole Calamagrostis stands (Fig. 2). Dry mass ofabove-ground biomass of A. elatius increased by 123%and C. epigejos by 77% and they reached after N fer-

tilization, respectively, 477 ± 51 (mean ±SE) and 627± 117 g m−2 on the average. In Arrhenatherum stands,on the contrary, the application of N resulted in signif-icant reduction of the amount and proportion of otherpresent grasses from 299 ± 35 g m−2 (53% of totalabove-ground biomass) down to 177 ± 62 g m−2 (24%)(Fig. 2).In comparison with unfertilized stands, additional

amount of N applied to mixtures of both tall grasses in-creased twofold the above-ground biomass of C. epige-jos in the wet year (up to 272 ± 65 g m−2 on the aver-age). However, biomass of A. elatius was not changedhere, ranging in both treatments around 325 g m−2

on the average. Nevertheless, the amount of dry massof other grasses increased (Fig. 2). However, all thesechanges were not significant.

Effect of drought on above-ground biomassIn the dry year 2007, the production of above-ground biomass was markedly lower in all treat-ments (by 50–60 %) (Fig. 2). Nevertheless, an in-crease in above-ground biomass of both tall grassesremained, due to application of N. In comparisonwith unfertilized stands, above-ground biomass of A.elatius was after N fertilization higher by 35% (statis-

Effect of nitrogen and drought on above-ground biomass of C. epigejos and A. elatius 279

0

100

200

300

400

500

600

700

800

Calamagrostis Calamagrostis +N Calamagrostis Calamagrostis +N

Ab

ove

gro

un

d d

ry m

ass

[g m

-2]

A. elatius

C. epigejos

Grasses

Dicotyledons

Drought2004 2007

A

C

A

A

a

bc

ab a

a

c

a ab

a

c

aa

a

d

aba

0

100

200

300

400

500

600

700

800

Arrhenatherum xCalamagrostis

Arrhenatherum xCalamagrostis +N

Arrhenatherum xCalamagrostis

Arrhenatherum xCalamagrostis +N

Type of stand / Treatments

Ab

ove

gro

un

d d

ry m

ass

[g m

-2]

AB

BC

AAB

c

ab

a a

bc

bc

ab

ab

b

ab aba

b

a

2004 2004Drought

0

100

200

300

400

500

600

700

800

Arrhenatherum Arrhenatherum +N Arrhenatherum Arrhenatherum +N

Ab

ove

-gro

un

d d

ry m

ass

[g m

-2]

20072004Drought

ABC

C

A

AB

b

aba aa

c

b

a

c

ab

a

b

b

d

Fig. 2. Effect of nitrogen fertilization (+N) on the above-ground biomass (in g m−2) of stands of tall grasses dominated by Arrhen-atherum elatius and Calamagrostis epigejos and mixtures of both tall grasses recorded in wet 2004 and dry 2007 years. Mean values ofA. elatius, C. epigejos, other grasses and dicotyledons are also given. Values denoted different small (capital) letters show significantlydifferent values (LSD test (P < 0.05) after ANOVA) between individual fractions (between total above-ground biomass).

tically significant difference) and that of C. epigejos by41%.The proportion of A. elatius in above-ground

biomass of a mixture of both tall grasses prevailedin both treatments, although not significantly. After

N applications it represented 67% of all above-groundbiomass of stands in the dry year and the dry mass ofthis plant species attained 180 ± 24 g m−2.In comparison with C. epigejos, the above-ground

biomass of A. elatius was mostly formed by dead parts

280 K. Fiala et al.

in the middle of August of the dry year, when sam-ples were collected. The proportion of living plant mat-ter was nearly two times lower in A. elatius (35.6%)than that in C. epigejos (68.6%) (Table 3). Drymass of mostly dead biomass of dicotyledons (mostlyPimpinella saxifraga L., Veronica officinalis L., Galiumverum L.) was extremely low (ranging between 1.3 and8.5 g m−2) and other grasses practically disappeared inthe dry year due to both competition of tall grasses andreduced water availability.The greatest accumulation of plant litter was found

in unfertilized stands of C. epigejos (422 ± 40 g m−2)and the lowest values characterized fertilized standswith a mixture of both tall grasses (196 ± 25 g m−2)(Table 3). The highest values of total above-groundbiomass, comprising both dry mass of above-groundbiomass and litter, were found in fertilized stands ofboth tall grasses (621 ± 56 g m−2 – A. elatius, 650± 75 g m−2 – C. epigejos).

Discussion

Effect of nitrogen addition on above-ground biomassThe effect of N supply upon the above-ground biomassof studied tall grasses was quite evident in wet yearand was in accordance with results obtained by sev-eral authors (e.g., Oomes & Mooi 1981; Berendse etal. 1992; Brunn 1999; Liancourt et al. 2009). Arrhen-atherum elatius produced 2.2 times more above-groundbiomass whereas C. epigejos only 1.8 times more intheir stands, due to a greater N availability, as our firsthypothesis also expected. Nevertheless, above-groundbiomass of C. epigejos attained 627 g m−2 after N ap-plication in contrast to studied unfertilized stands (355g m−2) where this species dominated.Plant species from nutrient-poor habitats, like C.

epigejos, have an advantage by being better able toretain captured nutrients due to a longer life span oftissues (e.g., Diemer et al. 1992; Schlapfer & Ryser1996). Both A. elatius and C. epigejos are highly ef-ficient systems of nutrient retranslocation due to theirwell-developed rhizomes and shoot bases (Holub 2002;Fiala et al. 2004). As a consequence of these features,C. epigejos and A. elatius can benefit more from avail-able N than other plant species. These features of bothtall grass species, among others, can be reflected in sub-stantial increase of their above-ground biomass underan enhanced N availability.In the mixture of both tall grasses, the amount

of above-ground biomass of C. epigejos was doubled(not significantly) after N addition, as expected in oursecond assumption. However, no reduction of above-ground biomass of A. elatius was observed and the pro-portion of its biomass in total above-ground biomassof fertilized stands was higher (A. elatius reached 46%,C. epigejos 39%). The greatest significant increases inrelative yield of A. elatius growing in mixtures with C.epigejos for one year occurred in both unfertilized andfertilized unclipped treatments (Tůma et al. 2005). Inearly-successional phases, heterogeneous soil environ-

ment may enhance competitive ability of tuft formingA. elatius with the phalanx type of growth (Tůma etal. 2009). Calamagrostis epigejos, a guerilla grass, isconsidered as a species with greater ability to acquirenutrients from soils being characterized by an extensivesystem of below-ground organs and able to use rhizomesin the selective placement of ramets into high resourcepatches (de Kroon & Hutchings 1995). Competitiveability of C. epigejos can obviously increase with time,i.e., with the formation of large below-ground plantsystems, rhizomes in particular. Calamagrostis epige-jos was able to spread into stands formed by A. elatiustufts and to replaceA. elatius (Fiala et al. 2004). On thecontrary, fast growing species, such as A. elatius, maylose their initial advantage of fast growth because ofnutrient losses due to a short organ life span (Schlapfer& Ryser 1996). Thus C. epigejos, the guerrilla growthstrategy, could further cause competitive exclusion ofA. elatius (Fiala et al. 2004). The competitive superi-ority of C. epigejos was evident on the most productivesubstrate in the long run (Rebele 2000). Thus, specieslike C. epigejos, capable of the guerrilla type growthare often more successful later in succession than thoseof phalanx type growth like A. elatius (Prach & Pyšek1994).

Effect of drought on above-ground biomassEffect of different years (wet and dry) on above-groundbiomass of studied tall grass species was confirmed bythe analysis of variance. Above-ground biomass of stud-ied stands attained in dry year only 40 to 50% of valuesrecorded in wet 2004 year. Above-ground biomass andplant abundance in grasslands mostly decreased withdecreasing rainfall (e.g., Stampfli 1992; Silvertown et al.1994; Holub 2002). In contrast to the C-4 drought toler-ance grasses, the abundance of C-3 grasses can usuallyvaried significantly in native grassland among differentyears (Wilson 2007). This nature is also reflected in ourobtained results.The trend indicating an increase of above-ground

biomass (mostly not significant), due to N application,was also noticed in dry year although the increase of val-ues of above-ground dry mass was substantially lowerthan recorded in wet year. Thus our third assumptionthat the effect of additional N on an increase of above-ground biomass of tall grasses will be eliminated in dryyear was not confirmed. The growth and the relativeabundance of A. elatius can be primarily stimulated bynutrient addition than water addition (Liancourt et al.2005). Nevertheless, competition intensity increased forthis species with both watering and fertilization. Brunn(1999) reported a relatively smaller biomass incrementof C. epigejos for dry sites after N fertilization (50 kg Nha−1 yr−1). However, in our experiments it appears,that above-ground biomass of A. elatius can signifi-cantly increase after fertilization even in unfavourablydry soil. Although not significant, the increase of its to-tal biomass was also recorded in studied mixture of bothtall grasses. Thus our fourth assumption, that biomassproduction of C. epigejos will be less affected by dry

Effect of nitrogen and drought on above-ground biomass of C. epigejos and A. elatius 281

conditions, was not fully confirmed. Our results showrather the opposite relation than we expected, i.e., A.elatius produced probably more aboveground dry mass.Calamagrostis epigejos is unable to spread if the stressfactors nutrient deficiency and drought are combined(Suss et al. 2004). However, in contrast to A. elatius,the above-ground biomass of C. epigejos was mostlyformed by living parts of studied stands in the middleof August of the dry year.In conclusion we can state that obtained results in-

dicate that drought can substantially change the above-ground biomass production of tall expanding grasses,reduce the effect of additional N and increase thedieback of above-ground parts of A. elatius due to a lowamount of precipitation. However, the above-groundbiomass production ofA. elatius was in its stands signif-icantly higher after application of N either in relativelywet or dry conditions.

Acknowledgements

The authors are greatly indebted to Dr. J. Úlehla for lin-guistic assistance. This research was supported by GrantAgency of the Czech Republic (Project No. 526/06/0556)and by projects AV0Z 60050516 and AV0Z 60870520.

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Received December 6, 2009Accepted February 26, 2010