Spatial variation in plant nutrient composition on Marion Island

Rossouw, Marius Wilhelmus (2014-04)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: To estimate nutrient budgets and model nutrient cycling at a whole ecosystem level on sub-Antarctic Marion Island requires information on the spatial variability of plant nutrient concentrations on the island. The complexity of constructing budgets and models will also be reduced if, instead of considering each plant species individually, the species can be grouped on the basis of their similarities/differences in nutrient concentrations. This thesis presents the results of an investigation into both these aspects. Altitude and distance from the sea are highly correlated with each other and thus influence the concentrations of all the nutrients considered (N, P, K, Ca, Mg and Na) very similarly. Concentrations of N, P and Na in living leaves, dead leaves, stems and roots decrease going inland, due to a decline in the influence of animal manuring and of sea spray. Ca concentration increases going inland, away from the organic peats characteristic of the lowland regions toward the mineral rawmark inland soils. Declining sea spray and increasing soil minerality going inland both affect plant Mg concentration; the net effect is a slight decrease in Mg concentration going away from the coast. K concentration in living leaves and roots did not change going inland; dead leaf and stem K concentrations showed a weak decline. Bryophyte shoot nutrient concentrations do not show such marked patterns of change going inland. Considering the bryophyte species as a whole, the only significant effect is that shoot Na concentration decreases, and Ca concentration increases, going inland. Although information on nutrient concentrations in all plant organs from all four (N, E, W and S) sides of the island was available for only a few species, and in many instances the between-side effect was not significant for individual species, the pattern of between-side differences is quite clear. Living leaf N, P and Mg concentrations are higher in west side than east side plants, with south and north side plants having intermediate concentrations. Leaf K concentrations are highest on the north and lowest on the west side, with east and south side concentrations being intermediate. Leaf Ca concentrations are highest on the south side and lowest on the north side, with east and west side Ca concentrations being intermediate. Leaf Na concentration declines more sharply with distance inland on the island's western and southern sides than on its eastern and northern sides, so that closer than 450 m from the shore leaf Na concentration is higher on the west and south than on the east or north sides, but further inland than that the difference lessens. There was sufficient information for dead leaf, stem and root nutrient concentrations only for the west and east sides of the island. West-east differences in nutrient concentrations of dead leaves are the same as for living leaves. Stem and root west-east concentration differences are also similar to those for living leaves, except for P and Mg concentrations, which were similar on the two sides. All organs showed the same steeper decline in Na concentration on the west than on the east side of the island. Bryophytes show somewhat different between-side nutrient concentration patterns to the vascular plants. South side (not west) bryophytes have highest N and P concentrations but, like for the vascular plants, east side bryophytes have the lowest N and P concentrations. Also similar to the vascular plants, bryophyte K concentration is highest on the north side and lowest on the west side, although south side concentrations are nearly as high as the north side ones. Unlike the vascular plant leaves, bryophyte Mg concentration is highest on the south (not west) side and lowest on the north (not east) side, with east and west side concentrations being intermediate. South side bryophytes have highest Ca and Na concentrations, similar to the vascular plant pattern. Ordination and clustering analyses of leaf nutrient concentrations suggested five nutrient type clusters amongst the island's plant species. The clusters differ in the amount (low, moderate or high) of N, P, K and Na versus the amount of Ca and Mg. Species membership of the clusters is strongly related to what major taxonomic group (bryophyte, pteridophyte, monocot or dicot) the species belongs to, but habitat factors, especially the intensity of animal manuring, also play a role. Plant guilds compiled previously for the island and which have been suggested might prove useful for modeling nutrient standing stocks on a whole island basis associate poorly with the clusters. Where a particular guild does associate closely with a cluster it is mostly an effect of taxonomic group (the guild members are all from a single taxonomic group) or habitat (the guild members are typical for a particular habitat). It is suggested that in order to reduce the complexity and arduousness of constructing whole island plant nutrient standing stock budgets, the species should be grouped according to their taxonomy – as bryophytes, dicots, monocots, club mosses or pteridophytes (the ferns proper). Subgroups of these taxonomic groups can be constructed on the basis of habitat. Mostly, this will be necessary to distinguish plants from manured habitats from plants of the same species from unmanured ones.

AFRIKAANSE OPSOMMING: Ten einde die voedingstofvoorrade en modelvoedingstofsiklus op die sub-Antarktiese Marioneiland op 'n algehele ekosisteemvlak te raam, word inligting oor die ruimtelike variasie in plantvoedingstofkonsentrasies op die eiland benodig. Die raming van voorrade en die konstruksie van modelle sal ook minder ingewikkeld wees indien plantspesies op grond van hul ooreenkomste/verskille in voedingstofkonsentrasies gegroepeer word eerder as om elke spesie individueel te beskou. Hierdie tesis bied 'n uiteensetting van die ruimtelike variasie (hoogte, afstand van die see én kant van die eiland) in die chemiese samestelling (N, P, K, Ca, Mg en Na) van plante, en probeer die plantspesies op grond daarvan in voedingstoftipes klassifiseer. Hoogte en afstand van die see is nou verwant en beïnvloed dus voedingstofkonsentrasies op feitlik dieselfde manier. N-, P- en Na-konsentrasies in lewende blare, dooie blare, stingels en wortels neem af in die rigting van die binneland weens 'n afname in die invloed van dierebemesting en seesproei. Ca-konsentrasies styg weer namate daar vanaf die organiese veengrondkenmerke van die laagliggende streke na die mineraalryke binnelandse grond beweeg word. Sowel die afname in seesproei as die toename in grondmineraalgehalte in die rigting van die binneland beïnvloed die Mg-konsentrasie in plante; die netto uitwerking is 'n effense afname in Mg-konsentrasie namate daar wegbeweeg word van die kus. Die K-konsentrasie in lewende blare en wortels verander nie in die rigting van die binneland nie, terwyl dié in dooie blare en stingels 'n geringe afname toon. Die voedingstofkonsentrasies in briofietspruite toon egter nie dieselfde merkbare veranderingspatrone in die rigting van die binneland nie. Wat die briofietspesie in die geheel betref, is die enigste beduidende uitwerking dat die Na-konsentrasie in spruite afneem en die Ca-konsentrasie toeneem namate daar na die binneland beweeg word. Die N-, P- en Mg-konsentrasies in lewende blare is hoër by plante in die weste as in die ooste van die eiland, en plante in die suide en noorde toon tussenkonsentrasies. K-konsentrasies in blare is die hoogste in die noorde en die laagste in die weste, met tussenkonsentrasies in die ooste en suide. Ca-konsentrasies in blare is weer die hoogste in die suide en die laagste in die noorde, met tussenkonsentrasies in die ooste en weste. Aan die weste- en suidekant van die eiland toon Na-konsentrasies in blare 'n skerper afname namate daar verder van die see beweeg word as aan die ooste- en noordekant. Verskille in die voedingstofkonsentrasies van dooie blare in die weste en ooste is dieselfde as vir lewende blare. Konsentrasieverskille in stingels en wortels in die weste en ooste is ook soortgelyk aan dié in lewende blare, buiten P- en Mg-konsentrasies, wat dieselfde was aan albei kante. Alle plantorgane toon dieselfde skerper afname in Na-konsentrasies in die weste as in die ooste van die eiland. Die voedingstofkonsentrasiepatrone tussen die verskillende kante van die eiland was ietwat anders vir briofiete as vir vaatplante. Briofiete in die suide (nie die weste nie) het die hoogste N- en P-konsentrasies. Soos die vaatplante, het die briofiete in die ooste die laagste N- en P-konsentrasies. Óók soortgelyk aan die vaatplante, is die K-konsentrasie van briofiete die hoogste in die noorde en die laagste in die weste, hoewel konsentrasies in die suide bykans so hoog is as dié in die noorde. In teenstelling met die blare van vaatplante, is die Mg-konsentrasie van briofiete die hoogste in die suide (nie die weste nie) en die laagste in die noorde (nie die ooste nie), met tussenkonsentrasies in die ooste en weste. Briofiete in die suide het die hoogste Ca- en Na-konsentrasies, wat weer ooreenstem met die vaatplantpatroon. Ordinasie- en trosvormingsontledings van voedingstofkonsentrasies in blare dui op vyf voedingstoftipes onder die plantspesies op die eiland, op grond van die (klein, matige of groot) hoeveelheid N, P, K en Na teenoor die hoeveelheid Ca en Mg. Die klas waartoe 'n spesie behoort, hou sterk verband met sy hoof- taksonomiese groep (briofiet, pteridofiet, monokotiel of dikotiel), hoewel habitatfaktore (veral die intensiteit van dierebemesting) ook 'n rol speel. Die plantgildes wat voorheen vir die eiland opgestel is, toon weinig ooreenkoms met die klasse wat uit hierdie studie na vore kom.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/86405
This item appears in the following collections: