POTENTIAL FOR CONTROLLING THE SPREAD OF CENTAUREA MACULOSA WITH GRASS COMPETITION

5 Pages·1996·2.4 MB·English

by  John L Lindquist

GreatBasin Naturalist56(3), © 1996,pp.267-271
POTENTIAL FOR CONTROLLING THE SPREAD OF
CENTAUREA MACULOSA WITH GRASS COMPEL ITION
John L. Liiul<iiiist'-, Bnitc I). Maxwell', and'!'. WeavcM-'
—
Ab.str.\(:t. Spottetl kiiapwt'fd (Ccntaurcd inaculosd Lam.) is a major raiigclaiul and roadsidt' wi'cd oftlic uortlic-ni
Rock>' Mountains. It is oiten found in plant communities dominatedbyPsc'uchmn'pu-riaspicatum orFcstuca idahoeims,
hutitrareK invadesroadsidesdominated!)>•Bnnniisbiennis Leyss.Ahove^roundhiomassofthe3j^rassspeciesj^rownin
nii.xturewith Cciitaiirea was compared togrowdi in monocultureatarangeofnitrogen input levels. The results suggest
thatBrointi.s iscapableofsuppressingthegnw'thofCentaurca withthedegreeofsui:)pression increasingwith increasing
nitrogen lexels. The 2 nati\e grasses had no impact on Centaurca under tlie controlled en\ironment conditions ofthis
study.
Keijwords:annpctition, weedcontrol. Centaurcamaculosa, Bromus inermis, Agropyron spicatimi, Festuca idahoen-
sis,exoticplants.
Centaurca maculosa Lam. (spotted knap- Our objective was to measure the competi-
weed) is a major weed associated with spring tive ability of3 grass species against Centaurca
wet-simimer diy areas of the northern Rocky in 2-way interaction experiments in sand cul-
Mountains (Forcella and Harvey 198L Tyser ture. Mixture and monoculture treatments
and Key 1988, Weaver et al 1989). Centaurca were tested for 12 wk at 5 positions on a nitro-
dominates waste places, invades disturbed gen gradient to determine whether competi-
rangeland, and sometimes invades undisturbed tive relations were influenced by differences in
range (Tyserand Key 1988). In contrast, itrarely nitrogen availability. A plant's ability to com-
invades roadsides dominatedbyBromusinermis pete is related to its growth rate or ability to
Leyss. (Weaver et ak 1989). This suggests that gain biomass relative to associated species
it may be exchided fi-om waste pkices that are (Haiper 1977). We compared aboveground bio-
planted to Bromus before Centaurca invades. mass of each species grown in mixture with
Alternatively, because planting exotics violates Centaurca to its growth in monoculture.
the charge ofnational park managers, one may
ask whether Centaurca might also be excluded Materials and Methods
from disturbed areas by planting native grasses
that naturally dominate either relatively dry The rhizomatous exoticpasture grass Bromus
{Pseudorocgneria spicatum [Pursh] Scribnerand inermis Leyss. and 2 native bunchgrasses nor-
Smith = Agropyron spicatum) or more moist mally dominating relatively diy foothills {Pseu-
{Festuca idahoensis Elmer) foothill habitats. dorocgneria spicatum) or moister grasslands
Weed suppression may be accomplished by immediately above and below the conifer zone
(1) preempting resources with more competi- {Festuca idahoensis) were grown in 2-species
tive plant species or (2) using biocontrols or mixtures (replacement series)with C. maculosa.
herbicides that selectively increase weed mor- Experiments consistedof3competition treat-
talit\', decrease vigor, or prevent reproduction ments (monocultures ofboth grass and Centau-
(Lindquist et al. 1995). This study considers rca, and 50:50 mixture) combined with 5 nitro-
managementofCentaurca maculosa bycompe- gen addition treatments. Each treatment com-
tition rather than by common herbicide and bination had 10 replicates. Within each experi-
biocontrol methods. This approach deserves ment, pots were arranged in a completely ran-
attention because it may be less expensive and domized design on a greenhouse bench and
more effective than herbicides in the long rotated weekly to minimize position effects.
term. Each experiment was subject to different light
'DepartmentofBiologyandDepartmentotPlant,Soil,andEnvironmentalSciences,MontanaStateUniversity,Bozeman,MT.5971"
-Presentaddres.s:DepartmentofAgronomy,Universit\'ofNebraska.Lincoln,NE68.58.3-091.'5.
267
268 Great Basin Naturalist [Volume 56
conditions because ofits position in the green- calculated to determine whether competitive
house. A square planting pattern was used relationships varied across relative nitrogen
with 4 plants spaced 5 cm apart. In each pot in levels. RCI is calculated as
the mixture treatments, plants of the same
specieswere locatedon the diagonal. RGI = (B, I^mix)/B, [2]
Seeds were planted at a depth of 1.0 cm in
1000-cm'^ pots filled with coarse washed sand. where B,^^,^,-,^ and B,^^j^ are the aboveground diy
Pots were watered daily for 1 wk to allow biomass (gplant"^) foraspecies grown inmono-
seedling establishment. Excess seedlings were culture and mixture, respectively. A negative
thinned and remaining seedlings allowed to RCI value indicates that the species performs
grow for an additional week prior to the addi- betterin mixture than inmonoculture. RCI may
tion of nutrients. The basic nutrient solution be the best measure for determining species
was balancedwith respect to all essential nutri- displacement under competitive conditions
ents but could be varied to allow the establish- across a resource gradient (Grace 1995). Analy-
ment of nitrogen levels from 0%, 1%, 10%, sis ofvariance was used to test for differences
30%, and 100% ofa standard level (Machlis and in RCI within a species across nitrogen treat-
Torrey 1956). Sufficient nutrient solution (200 ments. Student's t was used to compare RCI
ml) was applied to satinate the pot twiceweekly between speciesateach nitrogenadditionlevel.
and water (200 ml) was added once each week.
Regular watering with nutrient solution and Results
alternate washing with tap water held the soil
solution near the applied level and pre\'ented A hvperbolic relationship between individ-
any concentration of the soil solution due to ual plant biomass and relative nitrogen level
evapoti-anspiration. Experimentswereconducted was found in all mixtures and monocultures
during March, April, and May 1988, when (Figs, la-f). Estimates of /,• (biomass at inter-
greenhouse temperatures ranged from 14° to cept) differed between mixtures and monocul-
32° C (25° C mean). tures only for Centaurea grown in mixturewith
Twelve weeks after emergence, plants in Broiniis (Table 1). Estimates ofA,- (maximum
each pot were clipped at the soil surface, sepa- biomass) differed for Bronuis and Centaurea
rated by species, dried at 45° C for 5 d, and (Tiible 1).
weighed. Relative competition intensity was signifi-
Nonlinear regression procedin-es (SAS 1988, cantly negative for Broimis at all nitrogen addi-
Gauss-Newton least squares estimation method) tion levels; it varied from negati\'e values at
were used to fit a rectangular hyperbola equa- low nitrogen to positixe \'alues at higher nitro-
tion [1] (Cousens 1985) to mixture and mono- gen levels for Centaurea in competition with
culture dataforeach species: Bronius (Fig. 2). However, RCI did not differ
from zero in the experiments where P. spiea-
N
/, • tum and E idahoensis were in competition with
N [1] Centaurea (data not shown).
/. •
+
;i
A, Discussion
where B — aboveground dry biomass (g Growth response ofBromus to nitrogen was
plant~l), Aj = maximum aboveground biomass greater in mixture with Centaurea than in
of species / (g plant"^), N = relative nitrogen monoculture, as indicated by the regression
addition level, and /, = biomass ofspecies / as lines (Fig. la) and the negative RCI values
relative nitrogen addition level approaches zero. across all nitrogen addition levels (Fig. 2). In
To determine the relative success ofCentau- contrast, growth response of Centaurea was
rea in competition with each grass species, lower in mixtme with Bromus than in mono-
estimates ol A,- and Ij were compared between culture (Fig. 1). The increase in Centaurea RCI
mixtures and monocultures using the extra at high relative nitrogen le\el indicates that
sum of sc^uares procedure (Ratkowsky 1983, Bronuis is a better competitor in the high
Lindcjuist et al. 1996). In addition, relative^ nitiogen treatments (Fig. 2). Results suggest
competition intensity (RCI; Grace 1995) was that Bnnnus is capable of suppressing the
1996] CoMFEiiTivE Suppression of Centaurea 269
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CQ 0.0 0.2 0.4 0.6 0.8 1.0 d 0.0 0.2 0.4 0.6 0.8 1.0
270 Great Basin Naturalist [Volume 56
Table 1. Estimatesofparametervaluesfollowedbyasymptoticstandarderrorsformaximumabovegroundbiomass(g
plant~l) (A), biomass as relative nitrogen level approaches zero (/), and the coefficient ofdetermination (r-) obtained
from fitting equation [1] to monoculture and mixture data ofeach species. Variation in / andA between competition
treatments was tested using the extra sum ofsquares principle, with P value indicating the significance level for the
comparisonofparameter(Coeff)valuesfromthemonocultureandmixtureregressions.
Species Coeff Competitiontreatment Pvalue
Monoculture Mixture
Broiiius
1996] CoMiuniTivK Sli'I'hkssion of Cemavrea 271
-1.5
0.01 0.1 0.3 1.0
Relative Nitrogen Addition Level
Fig. 2. Relative competition intensity (RCI) ofBroinii.s and Ccntawea across 5 relative nitrogen addition levels. Let-
ters above bars indicate whether RCI varies (Duncan's multiple range test, F < 0.05) within species across nitrogen
le\el.Anasteriskindicatesthat RCI differs(P < 0.05)amongspeciesatthatnitrogenlevel.
Pseiidoroegneria and Festuca, probably would control in a com {Zea //ia|/.s)-soybean (Glycine max)
not sufficienth' suppress Centaiirea to decrease rotation.WeedScience43:269-275.
theApdovtaennttiaaglesforofintvhaesicoonm.petitive method over LlNDQUJo.IfJS.Tco,KreJnl.-lLvs.e,,lDvK.e.tAlH.eoaMwfoatRitnTt,EeNraSfnEedNre,RncSW.eeAsr.telCral\ta.iyo,n1s9Rh9.i6pS.sc.ShtmaWbeienleiktd,y
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