Seed productivity and dynamics of germination of Ziziphora L . species in the Pamir-Alay

Seed productivity of 4 Ziziphora species: Z. pamiroalaica, Z. interrupta, Z. brevicalyx, and Z. suffruticosa growing in the Pamir-Alay Mountains was studied. It was revealed that the indicator of real seed productivity did not exceed 40 %. Seed viability and character of germination were studied. It was established that seeds of all species did not have a dormancy period, had high viability, up to 95 % and high germination energy.


Introduction
Seed productivity is one of the important indicators of species vitality in different living conditions [1].It governs a species role in the phytocoenosis and expresses plant adaptation to environment conditions [2,3].Study of seed productivity is widely considered in modern literature [4][5][6].
Ziziphora representatives dominate in the plant cover of the Pamir-Alay and form in the high mountains the florocoenotype "thyme communities" characteristic of Central Asia, they grow on stony-cobble slopes and screes from the low to the high mountains [7,8].The species are widely used as medicinal plants [9] and are overharvested in the wild, which leads to population depletion.Study of seed productivity and seed germination will allow to reveal mechanisms of adaptation and sustainable development of species in various communities of the montane belt Pamir-Alay.In this regard the aim of the paper was study of seed productivity and seed germination of 4 Ziziphora species growing in the Pamir-Alay Mountains.

Material and methods
The material on seed productivity of 4 Ziziphora species was collected in 2016-2017 in the territory of Mogoltavsky and Gissaro-Darvazsky floristic regions of the Pamir-Alay (Tajikistan): Generally accepted procedure [10,11] was used for determination of potential (PSP) and real (RSP) seed productivities and productivity coefficient (C) for a shoot in 50 mature generative individuals.Seeds were germinated in Petri dishes, 100 pieces each, in 3-fold replication at room temperature 20-24 о С for 10 days.Germination rate was expressed by the number of seeds germinated per day as a percentage of the total number of seeds germinated for 10 days.Data were treated with the use of STATISTICA 10.

Results and discussion
The species are similar in inflorescence structure -this is a capitate thyrse consisting of numerous opposite-arranged dichasia.A flower gynecium contains 4 ovules.Ziziphora flowers are entomophilous, their efflorescence is acropetal (from the flowers in the lower part of the inflorescence to the flowers in the upper part).In this regard seed ripening in inflorescences is stretched in time.Z. interrupta has a many-flowered inflorescence, the number of flowers in it is 1.5-2 times greater compared to the other species (Table 1), in this regard its PSP is also higher.Despite growth in different ecological-phytocoenotic conditions, the index of seed setting of the species does not differ and averages 1.4-1.6 seeds per fruit.Real seed productivity ranges from 31 to 71 seeds per inflorescence.However, the coefficient of productivity, an indicator of species reliability and wellbeing, does not exceed 40% in the species under study.A fruit of the species under study -coenobium represents a fractional box in which there are 4 seeds.At disintegration of the box, erems in which there is one seed are formed.An erem coat grows together with that of a seed [12].Seeds are ovate, oblong-ovate, glabrous or tubercular.Erem colour (seed) is light brown, greyish-brown, seldom brown.The largest seeds are noted in Z. pamiroalaica, mass of 1000 seeds is almost 1.5 times greater than in the other species.Distinctions are also observed in size, values of length and width of Z. pamiroalaica and Z. brevicalyx seeds differ significantly from those of the other two species (Table 2).Seeds in the experiment swell very well and germinate better at the light than in the dark.Swelling process does not depend practically on the temperature of the germination medium and completely comes to an end in 1-2,5 days since the moment of moistening.Good water permeability of seed coats of Ziziphora species indicates absence of physiological dormancy and excludes necessity of scarification.Laboratory germinating ability of seeds of three species amounts to 93-95%, it is somewhat lower in Z. Conferences 11, 00006 (2018) https://doi.org/10.1051/bioconf/20181100006Prospects of Development and Challenges of Modern Botany pamiroalaica -88%.On the whole, germination percentage is very high (Fig. 1), which indicates superior quality of the species seed.Single-vertex curve of seed emergence rate (Fig. 2) with the maximum on the 3-d and 4th days of the experiment is typical of the species.Z. interrapta seeds germinate faster all, 68 % of seeds germinated already on the 3-rd day, the main quantity of Z. suffruticosa and Z. brevicalyx seeds emerged for 2 days and accounted for 91 и 90 %, respectively.Extended germination during 7 days was noted only in Z. pamiroalaica.Such a character of seed germination is connected with growth conditions of the species.The first three species grew in the lower and middle belts of the mountains at an altitude of 800-2200 m above sea level in the arider conditions in the shibliak belt, аnd Z. pamiroalaica -at an altitude of 2800 m and higher above sea level in more humid conditions in the belt of semisavanna tall herbage.

BIO Web of
High germinating ability and multiplicity of generative shoots compensate a low figure of the coefficient of inflorescence seed productivity.This makes it possible to maintain stability of populations in different montane belts of the Pamir-Alay.However, a short period from swelling to beginning of germination and high seed emergence rate at sharp fluctuations of weather conditions may adversely affect further existence and development of young plants.
The work was carried out within the framework of the projects of State Assignments ГР № 01011ТД065 (Tajikistan) and № АААА-А17-117012610053-9 (CSBG SB RAS, Russia).

Table 2 .
Morphometric indices of Ziziphora species seeds