Plant functional types on Marion Island

Thesis (MSc)--Stellenbosch University, 2016.

ENGLISH ABSTRACT: A database was compiled of structural and physiological traits for 25 vascular species and 17 bryophyte species on Marion Island (sub-Antarctic). The structural traits included leaf, stem and root characteristics and the physiological traits are all associated with photosynthetic responses to light and were measured using chlorophyll fluorescence quenching analysis. The data were subjected to principal component analysis and clustering analysis to construct a suite of plant functional types (PFTs). The correspondences between the PFTs and plant habit/taxonomy (forb, graminoid, fern, moss and liverwort), status (native to the island or introduced alien) and habitat (oligotrophic, manured or saline) were investigated using correspondence analysis. There were significant differences in most of the structural traits, but in only one of the photosynthetic traits, between sites at the same altitude and between altitudes. The between-site differences could not be explained since site characteristics were not measured, but the between site differences were often species-dependent; a particular species might show its lowest value for a particular trait at the same site where another species showed the highest value for that trait. The between-altitude differences in structural trait values could be ascribed to the effect of greater wind speed at higher altitude (lower stature, tougher leaves and stems). High altitude plants have greater specific root length, probably a response to low soil nutrient status and hence a need for foraging roots. However, plants in saline coastal habitats also show a high specific root length, probably in response to the inhibitory effect of high salt concentration on nutrient and water uptake. All the species except Azorella selago, the archetypical vascular species of high altitude were more stunted and showed greater signs of stress at high altitude than at low altitude. Native species tend to show greater values for those traits indicative of structural strength (tough, thick leaves, strong stems), and allocate a greater proportion of their biomass aboveground, than human-introduced alien species. Alien graminoids also have higher stomatal densities (but lower chlorophyll concentrations on a leaf area basis) than native species. There are no consistent differences in photosynthetic capacity between natives and aliens, except that native species tend to show a sharper photosynthetic response to increasing light at low levels, possibly an adaptation to the consistently low light regime at the island. Maximum photosynthetic electron transport rate varies greatly (by an order of magnitude) between the island’s vascular species and by almost an order of magnitude between the bryophyte species. Species with high electron transport rate also tend to have a high effective quantum yield and show electron transport saturation at high light – all indicative of high photosynthetic capacity sun species, most of which are forbs. The shade-adapted, lowest photosynthetic capacity species are mostly ferns, mosses and liverworts. Graminoids tend to be moderate photosynthetic capacity species but some of the forb species also have moderate, and even low, photosynthetic capacity. Only two structural traits were measured on bryophytes so in grouping both the vascular and bryophyte species together into functional types only the photosynthetic traits were considered. This yielded eight photosynthetic functional groups, together representing three levels of photosynthetic capacity - high, moderate or low capacity. Forbs predominate in the two highest photosynthetic capacity groups, graminoids (with one hepatic) in the moderate to moderately high capacity groups, graminoids, ferns and some bryophytes in the low to moderate capacity groups and bryophytes and shade-adapted ferns in the very low to low capacity groups. Mosses tend to have a higher capacity than hepatics although four of the six species in the very lowest capacity group are mosses. At each level of photosynthetic capacity – the high, moderate or low capacity groups – the species are divided into subgroups based on their capability for photoprotection at high light and how sharply photosynthesis responds to increasing light at low levels. Previous studies at the island have unequivocally shown that habitats influenced by seal and seabird manuring have higher soil and plant nutrient status, greater plant vitality and higher productivity. It was expected that species restricted to, or that attain maximum cover in manured habitats would be in the group with highest photosynthetic capacity. However, a surprising finding of the study is that those species occur in all the photosynthetic capacity groups except the highest capacity one. Further research into plant functional traits and functional types at the island should consider phenological, reproductive, and a wider suite of physiological, traits, especially the temperature responses of, and desiccation effects on, photosynthesis, photorespiration and respiration. Since wind is such a dominant factor at the island, its effects on plant morphology, architecture, growth and physiology also need to be addressed.

AFRIKAANSE OPSOMMING: ‘n Databasis was saamgestel van strukturele en fotosintetiese eienskappe vir 25 vaatplantspesies en 17 briofietspesies op Marioneiland (sub-Antarkties). Die strukturele eienskappe het blaar, stingel en wortel eienskappe ingesluit en die fisiologiese eienskappe word geassosieer met die fotosintetiese reaksie op lig en was gemeet met behulp van chlorofilfluoressensie blussingontleding. Hierdie data was blootgestel aan beginsel komponentontledings en trosvormingsontledings om sodoende groeperings van plant funksionele tipes (PFT’s) te konstruktureer. Die ooreenkomste tussen die PFT’s en plant habitat/taksonomie (kruidagtig, grasplant, varing, mos en lewermos), status (inheems of uitheems) en habitat (oligotrofies, bioties of soutafsetting) was ondersoek deur middel van korrespondensie-ontleding. Daar was beduidende verskille vir meeste van die strukturele eienskappe, maar slegs vir een van die fotosintetiese eienskappe, tussen liggings op dieselfde hoogte bo seevlak asook tussen liggings op verskillende hoogtes. Hierdie verskynsel kan nie tans verduidelik word nie, aangesien daar geen ligging eienskappe gemeet is nie, maar die tussen-ligging verskil was soms spesie-afhanklik; ‘n spesifieke spesie kan die laagste waarde vir ‘n sekere eienskap toon by dieselfde ligging as waar ‘n ander spesie weer die hoogste waarde vir daardie eienskap toon. Die verskille in strukturele eienskappe by verskillende hoogtes bo seevlak kan toegeskryf word aan die effek van die hoër windspoed by die hoër liggings (wat lei tot korter plante en meer geharde blare en stingels). Plante by hoër liggings het groter spesifieke wortellengtes, wat waarskynlik ‘n reaksie is op lae grondnutriëntstatusse waar voedingswortels benodig word. Daarinteendeel het plante wat in die soutryke kusgebied voorkom ook ‘n hoër spesifieke wortellengte, wat waarskynlik ‘n reaksie is op die inhiberende effek van hoë soutkonsentrasies op die absorbering van nutriënte en water. Al die spesies by die hoër liggings behalwe Azorella selago, wat die tipiese verteenwoordiger is van vaatplante wat op hoër hoogtes bo seevlak kan voorkom, het meer onderdrukte groei en meer tekens van stres getoon. Inheemse spesies was geneig om groter waardes te toon vir daardie plant eienskappe wat strukturele gehardheid uitbeeld (sterk, dik blare, stingels en wotels) en wend ook proporsioneel meer biomassa bogronds aan as wat die uitheemse plante doen. Uitheemse grasplante het ook ‘n hoër huidmondjie digtheid (maar laer chlorofilkonsentrasies per blaaroppervlak) as die van inheemse spesies. Daar is geen beduidende verskille in die fotosintetiese kapasiteit tussen inheemse en uitheemse spesies nie, behalwe dat die inheemse spesies geneig is om ‘n skerper fotosintetiese reaksie teenoor toenemende lig van lae vlakke te toon, wat moontlik die plant se aanpassing tot die konstante lae lig toestande van die eiland is. Die maksimum fotosintetiese elektron vervoer tempo variëer grootliks tussen die eiland se vaatplantspesies en ook tussen die briofietspesies. Spesies met hoë elektron vervoer tempo’s het ook die neiging om ‘n hoër effektiewe kwantum opbrengs te hê en toon ‘n elektron vervoer versadigingspunt by hoë lig – wat ‘n aanduiding is dat hierdie spesies is met hoë fotosintetiese kapasiteit, waarvan meeste kruidagtige plante is. Spesies wat vir skadu aangepas is het die laagste fotosintetiese kapasiteit en is meestal varings, mosse en lewermosse. Die fotosintetiese kapasiteit van grasplante is oor die algemeen matig, maar sommige kruidagtige spesies het matig en selfs lae fotosintetiese kapasitiet. Vir die groepering van briofietspesies en vaatplantspesies tesame is slegs die fotosintetiese eienskappe gebruik, aangesien slegs twee strukturele eienskappe op die briofietspesies gemeet is. Agt fotosintetiese groepe is gevorm wat lae, matige en hoë fotosintetiese kapasiteite verteenwoordig. Kruidagtige plante kom meestal in die twee groepe voor met die hoogste fotosintetiese kapasiteite, grasplante (tesame met een lewermos) val onder die matig tot matige hoë fotosintetiese kapasiteit groepe, ander grasplante, varings en sommige van die briofiete val onder die lae tot matige kapasiteit groepe en die res van die briofiete en skadu-aangepaste varings kom voor in die lae tot baie lae kapasiteit groepe. Mosse het die neiging om hoër fotosintetiese kapasiteite te toon as lewermosse, hoewel vier van die ses spesies wat voorkom in die laagste kapasiteit groep mosse is. Op elke vlak van fotosintetiese kapasiteit – hoë, matige en lae fotosintetiese kapasiteit groepe – word die spesies verder verdeel in subgroepe wat gebasseer is op hul fotobeskermingskapasiteit by hoë lig en ook hoe skerp hul fotosintese kan reageer op die verhoging van lig by lae vlakke. Vorige studies op die eiland dui duidelik aan dat habitatte wat bemes word deur robbe en seevoëls het hoër grond-en plantnutriënt statusse, beter plant groeivermoëns en produktiwiteit. Daar was verwag dat plante wat beperk is tot, óf wat maksimum dekking bereik, in die bemesde habitatte in groepe sou voorkom wat die hoogste fotosintetiese kapasiteite besit. Inteendeel, ‘n verrassende bevinding van dié studie was dat hierdie spesies voorkom in al die fotosintetiese kapasiteit groepe behalwe die hoogste kapasiteit groep.

National Research Foundation (NRF)