Abundance and distribution of species in relation to soil properties in sedge-dominated habitats in Uyo Metropolis, Southern Nigeria

Cyperaceae is one large family amongst the Monocotyledons comprising up to 104 genera and about 5000 species [1]. Though most members of the Cyperaceae are considered serious weeds, they have a wide cosmopolitan distribution, with a dense concentration in the tropics. Despite this, relevant data on these plants are scanty going through literature and herbarium specimens [2]. The wide occurrence of these species enforces the need to intensify research efforts on the economic values and niche preferences of these individual belonging to taxonomically diffi cult but highly interesting plant family. Pedology is the scientifi c study of soil properties. Studies have revealed that most often than not, Soil and vegetation is interlocked in a series of intricate relationships which can never be taken for granted. Superfi cially, it is known that while plants serve as protective coverings for soil and as anchorage against erosion and other physical agents of destruction, it is also major plant nutrient reservoir and home to several benefi cial microbes. Hence, from the foregoing it worthy to note that vegetation cover affect the characteristics of soil including pH, nutrient concentrations, texture etc and vice versa. This phenomenon has led to varied impact on vegetation assemblages thus shaping its composition and structure [3,4].


Introduction
Cyperaceae is one large family amongst the Monocotyledons comprising up to 104 genera and about 5000 species [1].
Though most members of the Cyperaceae are considered serious weeds, they have a wide cosmopolitan distribution, with a dense concentration in the tropics. Despite this, relevant data on these plants are scanty going through literature and herbarium specimens [2]. The wide occurrence of these species enforces the need to intensify research efforts on the economic values and niche preferences of these individual belonging to taxonomically diffi cult but highly interesting plant family.
Pedology is the scientifi c study of soil properties. Studies have revealed that most often than not, Soil and vegetation is interlocked in a series of intricate relationships which can never be taken for granted. Superfi cially, it is known that while plants serve as protective coverings for soil and as anchorage against erosion and other physical agents of destruction, it is also major plant nutrient reservoir and home to several benefi cial microbes. Hence, from the foregoing it worthy to note that vegetation cover affect the characteristics of soil including pH, nutrient concentrations, texture etc and vice versa. This phenomenon has led to varied impact on vegetation assemblages thus shaping its composition and structure [3,4].
Knowledge of the niche concept theory further applauds this idea that vegetation communities are inevitably mingle in a web of unique connections with incumbent abiotic factors Abstract in their environment leading to individualistic and communal responses from plants due to these infl uences [5,6]. In line with the fore going, several erudite scholars have probed this notion supporting the nexus between the vegetation distribution and its soil environment in diverse natural and created ecosystems.
The roles of these omnipresent soil variations govern the dynamics of plant communities both in terms of numeric abundance and fl oristic attributes [4,10]. These natural interactions may be especially important from micro to ultra-scales especially in this current era of plant resource conservation and in the wake of climate uncertainties. To this end, this study seeks to reveal knowledge on the infl uence of pedo-ecological properties on four common Cyperaceae plants found in our immediate environment. This may give birth to management clues useful for their conservation in our clime.

Vegetation and soil sampling
Species were sampled in 10m x 10m quadrats, spaced at regular intervals of 20m according to the methods of Ubom (1996) and Greig-Smith [11]. In each quadrat, plants were enumerated and species were properly identifi ed to the species level. Voucher specimens of unknown species were collected for proper identifi cation at the Botany and Ecological Studies Departmental Herbarium, University of Uyo, Akwa Ibom State.
Frequency of occurrence and density of the species encountered were estimated according to the methods of Ubom, et al. [3].
Also within each quadrat, two soil samples were obtained at the depths of 0-15 cm respectively which was later bulked to form a composite sample according to Mbong and Ogbemudia [12]. The soil samples were air-dried and preserved for laboratory analysis. Soil pH was determined using Hanna hand held pH meter. Available phosphorus, Exchangeable Ca and Organic matter were determined using standard methods [13].

Statistical analysis
Mean and standard error were computed from triplicate values obtained from the determination of soil physico- Fisher least signifi cant different (LSD) test were employed to ascertain signifi cant differences between the means of the physicochemical properties of the studied soils. Pearson's correlation computed through SPSS was employed to ascertain the nature and strength of association existing between soil properties and density values of sedges in the study area according to the methods of Mbong, et al. [10]. In order to probe the infl uence of soil properties on the distribution of sedges, bivariate regression (logarithmic) was employed. Only sedges with moderate to high signifi cant Carl Pearson association coeffi cient were adopted for this protocol Ubom [14].

Result
The distribution of sedges and associated species found in the study area is shown in Table   The correlation matrix (Table 4) (Table 5).

Discussion
The vegetation physiognomy of the study area shows a total of four sedges with other associated species. This occurrence agrees with the principles of Mbong et. al. [12], that plant do not grow in isolation and that different species growing together in the same habitat under similar environmental conditions will differ in their tolerance or response to environmental gradient.
This justifi es the variability recorded in the patchy occurence and density of the species encountered. This was noted by earlier researchers [15].The numeric gaps as judged from the density values of the Cyperaceae species and other plants underscores the variability in species response to the soil

Sida acuta Malvaceae 900
Eleusine indica Gramineae 400 The density values noted for Ludwigia decurrens compares with those of the Cyperaceae species in this study [17]. This is justifi ed in that it can be interpreted to mean that these species may share similar environmental and nutrient requirements and this phenomenon is suggestive of a considerable level of competition in these habitats. Agreeing with this, Verma and Agrawal [18] noted that density estimates give information on the degree of competition in within a particular habitat. This is evident in this study in that, there is a visible but short- The suitability of correlation analysis in ascertaining the nature and strength of relationships existing between pairs of variables and the role of regression analyses in predicting the infl uence of associated variables on each other as found in this research is well documented by previous researchers [3,14,19,20]. Currently the high signifi cant correlation coeffi cient obtained between C. diff ormis and C rotundus in the matrix cannot be ignored because it hints that both sedges share similar soil nutrient preferences. Also, the matrix indicated that Cyperus iria showed strong affi nity for alkaline soils while Cyperus diff ormis and Cyperus rotundus showed high preference for acidic soils with increased organic matter content. This pattern of relationship exhibited by Cyperus diff ormis and Cyperus rotundus refl ects that habitats dominated by them witnessed continuous decomposition of dead plant materials (litter) giving rise to soil organic matter which on deposition is constantly associated with the addition of reasonable amounts of organic acids to the soil which keeps reducing the amount of calcium in the habitats. This is in tandem with Stevenson [21].
Specifi cally, Cyperus iria showed negative moderate association with the amounts of available phosphorus in the soil which explains that high density of this plant were observed in sites with low available phosphorus. In line with this trend, the regression model bears a negative slope. This is not unmatched. Here the relationship is understood in that this fast growing sedge persistently keeps drawing reasonable amounts of phosphorus from the soil stock, leaving room for defi cits with little or slow compensative replacement since this much needed macro nutrient is necessary to maintain its existing colonies and facilitate the establishment of new ones. On a general note, phosphorus is required by plants for the synthesis of ATP, constitution of plant nucleic structure and in the maintenance of plant health and vigor from seedling stage to maturity [18].  On the contrary, the regression model relating C. iria with soil pH and exchangeable Ca both carry positive slopes which bear evidence that C. iria bloom is favored with an increasing pH.
This not novel but in this account it authenticates the fact that increased calcium concentration in these sites foster enhanced values of soil pH and this observation tallies with Gould and Harper [23][24][25][26], view that these enhance pH increases the availability of nutrients to plants giving rise to a high dense cover of C. Iria in almost all the sites. Again, the increased pH facilitates microbial decomposition of plant debris giving rise to rapid nitrogen release into the soil.

Conclusion
This research concluded that, the study area is endowed The interactions existing between plant species with soil properties thus indicate their importance in this ecosystem.
The information obtained from this study could be useful in the management and conservation of lawns and (or) other sedgedominated habitats.