REPRODUCTIVE EFFORT AS AN ELEMENT OF LIFE STRATEGY OF LYTHRUM SALICARIA L

The aim of the study was to compare some life strategy traits of individuals of Purple Loosestrife Lythrum salicaria within three meadow populations existing under various habitat conditions. The study attempted to answer the following questions: Do different habitat conditions affect the biomass allocation between particular organs of individuals? Can the individuals belonging to different populations of the same species realise their own unique reproductive strategy, in other words, can their reproductive effort represent various levels? In the case of L. salicaria the reproductive effort, measured by the participation of infl orescence biomass in the biomass of aboveground parts of genets, exhibits similar values (14.2-15.1%) in all the study populations, despite their habitat conditions. This fact proves that at the population level, the reproductive effort is relatively stable. Great differences are visible in the case of particular individuals within each of the populations. Specifi c genets in a population, depending on the habitat microstructure and the biotic relations with other individuals both of their own and other species, may realise their own reproductive strategies, being a part of their life strategies.


INTRODUCTION
Life history of a species, also referred to as its lifestyle, comprises the entire course of events in the life of an individual (genet) connected with successive stages of its development and growth, until its death (H a r p e r , 1977).The genet survival in a population, affected by a set of unique habitat conditions, is determined by a set of life history traits.Temporal pattern of its growth and reproduction is shaped by such features as, among others, growth rate, size, body mass, vegetative offspring and number of generative propagules produced per one generative episode, and the number of such episodes during the ontogeny (S t e a r n s , 1992).Each individual is affected by a different selection force, resulting from natural selection, both under the infl uence of habitat conditions, which change with different rate, and under the pressure of intra-and interspecifi c competition.These limitations condition the shaping of such a combination of life history traits which becomes a life strategy.At the level of an individual, a web of evolutionary trade-offs is formed, which is a result of the drive to reach maximum size and reproduction success on the one hand, and to adapt to the environment and last in time on the other (S i l v e r t o w n and L o v e t t D o u s t , 1993; C r a w l e y , 1997).
In clonal species of the iterative growth type which multiply their basic structures, i.e. shoots, rhizomes and roots, and thus expand the genet, a particularly important element of life strategy is the biomass allocation to vegetative and generative parts of plants.The part of the biomass (energy) used to produce generative organs, in relation to the total biomass (energy) of an individual, is defi ned as reproductive effort (H a r p e r and O g d e n , 1970).
The aim of the present study is to compare some life strategy traits of individuals of Purple Loosestrife Lythrum salicaria within three populations existing in different types of meadow vegetation occurring in habitats of various resource abundance.The study attempts to answer the following questions: Do different habitat conditions affect the division of energy between particular organs of individuals?Can the individuals belonging to different populations of the same species realise their own unique reproductive strategy, in other words, can their reproductive effort represent various levels?

MATERIALS AND METHODS
The study was carried out in the Szum river valley in the Central (Tomaszów) Roztocze region, near Górecko Kościelne.The study area comprised hydrogenic habitats, within the inundation terrace and occupied by communities of variously moist meadows of the Molinio-Arrhenatheretea class.Their vegetation was dominated, fi rst of all, by macroforbes: Filipendula ulmaria, Lythrum salicaria, Lysimachia vulgaris, Cirsium rivulare, C. oleraceum.
Purple Loosestrife Lythrum salicaria L. (Lythraceae) is a perennial clonal plant belonging to rhizocaulophytes (Ł u k a s i e w i c z , 1962).Genets of L. salicaria are compact and usually consist of several, maximum a dozen, of ramets.Therefore, the species takes part in the formation of both fi ne-grained and coarse-grained spatial mosaic.The calendar age of genets is estimated as exceeding 10 years.Strong, well-shaped underground organs enable the individuals to last long in the once occupied area.Therefore, L. salicaria realises its dynamics in time rather than in space, and belongs to the promoters of succession within meadow communities (F a l i ń s k a , 1991, 2003).
In order to conduct the biometrical analysis and to estimate the biomass, the total number of 90 generative individuals of L. salicaria were collected in the growing season of the year 2006.The genets came from three meadow patches (30 plants out of each), differing in habitat conditions, vegetation composition and population density.The patches of Cirsietum rivularis (A) and Lythro-Filipenduletum ulmariae (B) occupy eutrophic habitats on a fl at inundation terrace, supplied with highly mineralised waters (300-350 mg dm -3 ).The vegetation of the third of the analysed patches, Lysimachio vulgaris-Filipenduletum (C), occupies poorer soils, supplied with acidic, lowly mineralised (100-130 mg dm -3 ) seeping waters, typical of neighbouring mires; it is characteristic of a high participation of Carex acutiformis, too.Population density of L. salicaria in particular patches was as follows: patch A -1.00 genet m -2 , patch B -4.25 genets m -2 , and patch C -3.05 genets m -2 .Measurement comprised the following morphological features: stem height (1 cm accuracy), number of branches, leaves and infl orescences, and infl orescence length (0.5 cm accuracy).Aboveground parts of plants were subsequently divided into the stem, leaves and the infl orescence part.The material thus divided was dried and weighed with the 0.0001 g accuracy.In order to determine the reproductive effort, the participation of infl orescence biomass in the total biomass of an individual's aboveground parts was measured.The results were analysed statistically with the Shapiro-Wilk, Levene and Kruskal-Wallis tests.

RESULTS
The differences between the study populations of Lythrum salicaria were signifi cant (0.001< p <0.05) in case of all the features subjected to biometrical analy-sis.Most of them do not exhibit the Gaussian distribution, with the exception of stem height (all populations), number of shoot branches (patch A, i.e.Cirsietum rivularis population), and leaves (patch A and patch B -Lythro-Filipenduletum ulmariae).Genets from patch B are characteristic of the lowest mean height of ramets, while all the remaining analysed vegetative parameters reach their highest values here (Tab.1).The average number of leaves per individual is twice as high as in the case of patch C (Lysimachio vulgaris-Filipenduletum population).As far as the generative features are concerned, individuals from patch B have shown the highest number of infl orescences (Tab.2, Fig. 1).In all the populations, the infl orescence length is negatively correlated with their number; patch A: r = -0.33;patch B: r = -0.10;patch C: r = -0.29.The genets of L. salicaria occupying patch A exhibit the intermediate values of all the parameters in respect to the remaining populations.The only exception is the average infl orescence length which reaches its lowest value in this population.The lowest variability among all the analysed features was observed in patch B.
The comparison of the aboveground parts of plants additionally indicates the biggest size of genets in patch B (statistically signifi cant differences between the populations), and the smallest size in patch C (Fig. 2).The average percentage of biomass coming from particular aboveground parts of plants was similar in all the populations and was contained within the following ranges: stem − 49.8-52.1%,leaves − 33-36% and infl orescence −14.2-15.1%.The individuals of L. salicaria coming from the C population exhibit the lowest value of the coeffi cient of variation in the case of the stem and infl orescence biomass (Tab.3).The greatest variability in the biomass allocation was observed for the individuals of the A population.The reproductive effort of the B and C populations showed similar values (15.1 and 14.9%), while its slightly smaller value (14.2%) was noted in the population coming from the Cirsietum rivularis patch (Tab.4).Great differences are visible in particular individuals within each of the populations; population A: 8-times different, population B: ca.4-times, population C: ca 3-times.

DISCUSSION
One of the most important evolutionary tradeoffs undertaken by clonal species is the share of biomass spent on vegetative growth and generative reproduction.In the case of Lythrum salicaria, habitat differences are refl ected in the diverse size and genet architecture in particular populations, which further infl uence the biomass of an individual and its reproductive effort.Purple Loosestrife occurs in the patch of macroforbes Lythro-Filipenduletum ulmariae (patch B), where the individuals are frequently branched, and therefore producing the highest number of infl orescences.Despite its highest

Stem biomass
Leaf biomass Infl orescence biomass density among all three analysed populations, the infl orescence biomass in this patch is greater by 52% and 66% than in the remaining patches of Cirsietum rivularis (patch A) and Lysimachio vulgaris-Filipenduletum (patch C), respectively.In patch C, in turn, there occur individuals of the tallest stems.This fact is connected with the habitat conditions, that is, with considerable solum moisture and, fi rst of all, with a dense and tall herb layer, which reinforces the interspecifi c competition, particularly on the part of Carex acutiformis.Additionally, the shading caused by the entering of willowalder shrubs makes the individuals of L. salicaria 'run to the sun' (F a l i ń s k a , 1990).Tall ramets raise infl orescences above the herbaceous layer also because of pollinators, especially the Lepidoptera.Yet, despite the fact that in the patch of Lysimachio vulgaris-Filipenduletum generative ramets are the tallest and infl orescences the longest, their size does not affect the reproductive effort in this population.
The percentage of biomass spent on reproduction is different not merely across the individuals of different species, but often among the plants of the same one (H a r p e r , 1977).The reproductive effort may depend on genet age, size and sex, as well as on habitat conditions of a population, its density, the succession stage of a community, abundance of nutrient resources and light conditions, and on the infl uence of competition, although these relationships are not always unambiguous In the case of L. salicaria the reproductive effort measured by the participation of infl orescence biomass in the biomass of aboveground parts of genets, exhibits similar values (14.2-15.1%) in all the study populations, despite their habitat conditions.This fact proves that at the population level, the reproductive effort is relatively stable.In L. salicaria populations the biomass percentage spent on reproduction is not connected with the number of generative ramets, produced by a genet, similarly to other populations occurring in hydrogenic habitats, e.g.Caltha palustris (W e r p a c h o w s k i , 1989) and Senecio rivularis (C z a r n e c k a , 1995).
The study shows that, at the level of a whole population, different habitat conditions are not decisive for the differentiation of the matter and energy allocation pattern between vegetative and generative structures.However, particular genets in a population, depending on the habitat microstructure and the biotic relations with other individuals both of their own and other species, may realise their own reproductive strategies, being a part of their life strategies (H a r p e r , 1977; S o u t hw o o d , 1988; K o z ł o w s k i , 1992).Wysiłek reprodukcyjny jako element strategii życiowej populacji Lythrum salicaria L.
(H a r p e r and O g d e n , 1970; G a i n e s et al. 1974; v a n A n d e l and Ve r a , 1977; N e w e l l , 1978; S a m s o n and W e r k , 1986; W e r p a c h o w s k i , 1989; P o w e l s o n and L i e f f e r s , 1992; Ve r b u r g and G r a v a , 1998; H e m b o r g and K a r l s s o n , 1999; P i n o et al. 2002).
Ve r b u r g R., G r a v a D., 1998.Differences in allocation patterns in clonal and sexual offspring in a woodland pseudo-annual.Oecologia, 115: 472-477.We r p a c h o w s k i C., 1989.Reproductive strategies of Caltha palustris L. under various living conditions.Acta Soc.Bot.Pol.58: 423-437.

Table 1
Vegetative traits of individuals in the Lythrum salicaria populations.

Table 3
Biomass allocation in generative individuals of Lythrum salicaria populations (in g).