Exploring Diverse Conducting Elements with Habit Preference in Some Acrocarpous and Pleurocarpous Mosses: a Comparative Analysis
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International Journal of Research on Social and Natural Sciences Vol. I Issue 1 June 2016 ISSN (Online) 2455-5916 Journal Homepage: www.katwacollegejournal.com Exploring diverse conducting elements with habit preference in some acrocarpous and pleurocarpous mosses: A comparative analysis Shelly Sinha, Botany, Rabindra Mahavidyalaya, Hooghly, India Article Record: Received March 30 2016, Revised paper received May 21 2016, Final Acceptance June 3 2016 Available Online June 7 2016 Abstract Mosses are very successful flora with cosmopolitan distribution and harbour certain needs in respect to their niche constraints such as varied growth forms, diverse leaf cell configuration and systematic placement. Existence of a specific taxon reveals the detailed habit of an explicit area. This is mainly due to compact growth form, ability to retain moisture, endohydric or ectohydric type. The present study mainly focuses on fabrication of different conducting elements within two major orders of pleurocarpic mosses and acrocarpous mosses respectively, each showing wide occurrence in that specific selected area. Comparative studies elucidate that development and organisation of unspecialised water conducting cells manifest unique epiphytic habit dominance within the particular moss taxa whether being acrocarpic or pleurocarpic. Acrocarpous mosses with stable conducting components mostly confer either as terrestrial or lithophytes with turf or dendroid growth patterns. Paradoxically, one with less conducting elements shows epiphytic type being the pendants. Whereas, pleurocarpic mosses are mostly prostrate or creeping plants, dwell on wood with epiphytic selection. And those on rock and ground add new intertwining or overlaid growth each year to form mats. Therefore the habit preference is significantly correlated with wide distribution or formation of conducting elements both in leaves as well as in central axis. Key words: Habitat, epiphytic, leaf cell pattern, central strand 1. Introduction Incessant need for water manifest the drift of plants gradually from aquatic to terrestrial platform (Glime, 2015). Evolutionary lineage clarified that the movement onto land is conceded with their gametophytic dominance still acquired within some plant group members. Plants with advanced vascular tissues eventually been developed and gametophytes in these highly vascularised tracheophytes unravel water complications by being confined within the protection of sporophytic tissues. Parallely, diminution of the gametophyte might necessarily foster reduction in conducting tissues as the contiguous sporophytic tissue reduced available space and made gametophytic vascularisation less relevant (Raven, 2002). Sequentially, the gametophyte-dominant mosses inhabited on land for retrieving water and essential nutrients. Ironically, growth potential in this group is not as highly polarized as vascular plants; yet they are remarkably successful colonizers and significant in ecosystem dynamics (Vanderpoorten & Goffinet, 2009). In spite of being foremost terrestrial flora, a "top-down" view of land plants, seemingly expecting the bryophytes to be their simpler version and termed precisely as desiccation-tolerant tracheophytes (Raven, 2002).They obtain nutrients directly from substances dissolved in ambient moisture. However, they play a significant role in nutrient cycling, soil formation, providing microhabitat for other plants and animals, promote seed germination and fill gaps in the habitat (Glime, 2015). They exhibit extensive cover on the substrate and provide microenvironment for the activity of numerous microorganisms, constituting a kind of specific bryo-system.The division Bryophyta comprise of 13,700 species and form second largest group among terrestrial plants (Govindapyariet al., 2012). Interestingly, on one side, vascular plants signify the strategy of adaptation to irregular and inconsistent source of water on land. While, desiccation tolerant group of bryophytes represent an alternative, photosynthesising and growing when water is freely available and suspending metabolism when it is not (Proctor, 2000a). Mosses are different from stereotype tracheophytes by being ectohydric, (carrying external capillary water which can vary widely in quantity without affecting the water status of the cells). In spite of this, typical terrestrial plants use two major adapting approaches towards water economy, termed as homoiohydry and 1 International Journal of Research on Social and Natural Sciences Vol. I Issue 1 June 2016 ISSN (Online) 2455-5916 poikilohydry (Proctor, 2000b). The former one endeavours to maintain a high water potential under water limiting conditions, whereas, the latter may be defined as the incompetent to control water loss to the environment with the result that cellular water content fluctuates in concert with external water availability (Wood, 2007). Progressively, mosses have evolved a unique physiological adaptation which allow suspension of metabolism during periods of drought and its resumption when water is once available, well known as poikilohydry (Oliver, 2009). Implementing the alternative strategy of evolving desiccation tolerance, growing during moist period and suspending metabolism during drought revealed the uniqueness of this group.Despite the typical relegation of bryophytes to the category of non-vascular, conduction has played a major role in the phylogenetic history of acrocarpous mosses (Sinha et al., 2009; Govindapyariet al., 2012). Whereas, evolutionary path elucidated that they survived both during gradual water loss and prolonged periods of drought (Proctor, 2000a). Studies explored that they have perfected physiological mechanisms that outdistance those of their tracheophyte counterparts (Oliver et al. 2000). This ability has led plant physiologists to use bryophytes as model systems for the study of desiccation tolerance physiology, even to the extent of attempting to introduce those genes to crop plants (Comis 1992; Oliver et al., 2000), and this use has made it into the agricultural literature with articles such as "Miracle Moss" (Comis, 1992). Mosses have undergone repeated morphological reduction and simplification often as a result of colonizing specialized and particularly xeric or ephemeral habitats (Vitt, 1981). Hedenäs (1999) examined the importance of various character states on the phylogenetic history of pleurocarpous mosses (typically the ones that grow horizontally) and determined that, based on redundancy analysis, gametophyte variance relates to characters associated with water conduction. Furthermore, one of the most important environmental variables in this phylogeny was the non-wetland to wetland gradient. Adaptation and structural modification caused regular speciation and resulted high species richness. However, the water conducting cell study was mainly focussed on acrocarpous mosses that exhibit turf pattern. The families Polytrichaceae and Mniaceae represent the well-developed endohydric groups (Proctor, 2000b) which has stereome, leptome and a central strand. On the other hand, some acrocarpous mosses also show ectohydric pathway, as they absorb water rapidly into the cells by small capillary systems (Buch, 1947). Hébant (1973) describes the living parenchyma cells around the central strand in the Polytrichaceaeto be a hydrome sheath, a term originated by Tansley and Chick (1901). Among different mosses, Sphagnum has the most unusual water system in its leaves of any bryophyte. Its leaves have two types of cells, and rarely a border in addition. These two types are the water-holding, colourless, dead hyaline cells and the green chlorophyllose(photosynthetic) cells. The hyaline cells serve as water reservoirs for the photosynthetic cells. Their walls have true perforations and are strengthened by spiral thickenings, suggesting the structure of tracheophyte vessels (Hébant 1977; Sinha et al., 2009).Further studies done by Ron & Kawai (1991) described the moss stem as having a basic structure much like that of tracheophytes with an epidermis surrounding the cortex. This basic structure describes most of the pleurocarpous mosses that move internal substances mostly horizontally. Eventually, the water conduction studies steadily moved to desiccation tolerance capacity of individual members. Unfortunately, comprehensive survey of mosses of a particular area in respect to their conducting elements with their habit constitution needs to be much more explored. Therefore, the present study mainly focuses on fabrication of different conducting elements within two major orders of pleurocarpic mosses and acrocarpous mosses respectively, each showing wide occurrence in that specific selected area. 2. Materials and methods Mosses from Uttarakhand (mainly Mukteshwar, Uttarakhandand its adjoining areas) were collected in polythene bags during the month of November. They were air dried by spreading out on the blotting sheets for 3 - 4 days and stored in labelled standard sized (10x15 cm) paper packets. Date of collection, locality and habitat along with the substratum type etc. were recorded in the field note-book and also on the packets containing the material. For the study the dried material is soaked in water with 0.1% safranine solution for a few minutes in Petridish. The different parts of the samples were taken out with the help of needles, brush and forceps and were carefully observed under the binocular microscope and compound microscope. Transverse and longitudinal sections of the central axis