Year

2022

Degree Name

Doctor of Philosophy

Department

School of Earth, Atmospheric and Life Sciences

Abstract

There is a general lack of biologically relevant climate data to facilitate ecological research in Antarctica. Climate data that exist for Antarctic regions are derived from satellite and automated weather station observations. However, the climate conditions at ground level, where the bulk of Antarctica’s terrestrial biodiversity lives, often vary considerably from those at or above weather station height. Climate data at this finer scale at or beneath the ground surface in the thermal boundary layer (termed microclimate), are poorly represented by meteorological climate data. Currently, ground-level microclimate variation in Antarctic regions is extremely difficult to predict through modelling techniques. The dominant terrestrial plant life in Antarctica are mosses which form turfs that display highly variable micro-topography. Such turfs can play a large role in biogeochemical cycling and permafrost insulation with associated links to microclimate and moss health, however these links are poorly understood due to a lack of quantitative and spatially explicit data at a relevant scale. Furthermore, the soil insulation properties of moss cover in permafrost regions are poorly understood and often mis-represented in climate models, leading to erroneous predictions of soil temperatures and permafrost thaw rates for alpine, Arctic and Antarctic regions.

In this thesis, I address these knowledge and methodological gaps and present a range of novel fieldwork, modelling and experimental methodologies to quantify spatially explicit links between micro-topography, microclimate and moss health and physiology over centimetre scales for moss turfs in Maritime Antarctica. Additionally, I present a method for generating Antarctic ground surface/moss canopy microclimate data at a centimetre resolution without the need for empirical microclimate data to fit the model. Lastly, I use a novel experimental method to explore mechanisms involved in creating ground surface and soil microclimate variation in moss covered soils, specifically, how a decline in moss health and how water at the ground surface affect soil and surface microclimates.

Moss canopy (ground surface) temperatures differed significantly from weather station temperatures, and micro-topography drove considerable spatial variation in moss canopy temperatures, light intensity and moss turf water content among Antarctic moss turfs. Specifically, at centimetre scales, moss canopy temperatures differed up to 29 °C at a single point in time, maximum canopy temperature differed up to 15 °C, and light intensity differed up to 1000 μmol.m-2.s-1. Moss turf micro-topography was the predominant driver over landscape scale topography, while variation in moss turf water content was mostly driven by landscape scale topography but still influenced significantly by micro-topography. Mosses positioned on micro-topographic positions with a north-facing micro-aspect were warmer, drier and received more light than those on south-facing micro-topographic positions just centimetres away, and these differences translated to differences in moss physiology and investment in photoprotection by carotenoid pigments. Over this south-north gradient, concentrations of photoprotective carotenoid pigments increased in moss canopy tissue, while photosynthetic efficiency declined steeply, with micro-topographically driven differences in light intensity and turf water content being the biggest drivers. Much of the measured variation in microclimate temperatures over centimetre scales could be predicted using physical models that were previously untested at these scales. The model predicted moss canopy temperatures across gridded centimetre resolution micro-topographic spatial layers that covered the extent where moss canopy temperatures were measured. Predicted and measured temperatures at the same micro-topographic locations aligned with an RMSE of 1.89 °C and a correlation value up to 0.90. In addition to this, a decline in moss health resulted in warmer soil temperatures compared to healthy moss and the mechanisms driving this were illustrated from measured data. A decrease in water holding capacity of unhealthy moss resulted in excess water seepage into underlying soil, generating higher soil heat content and thermal conductivity, and thus, greater input of heat energy into the soil. This was reflected by measurements of thermal conduction through the soil. Consequently, soil temperature was significantly warmer when topped by unhealthy moss compared to healthy moss, revealing the role of water in driving processes of warming as well as cooling, and how moss health can govern these processes.

In conclusion, microclimate variation created by centimetre scale micro-topography is significant and biologically relevant for Antarctic moss turfs. In turn, moss health and water availability play a key role in driving soil microclimate variation. This thesis contributes to the subject area by providing spatially explicit links between micro-topography, microclimate and moss physiology in a polar context where moss turfs are important for both biodiversity and biogeochemical cycling. In addition, this thesis presents a method for generating biologically relevant ground-surface microclimate data in Antarctica where there is a current lack of such data to facilitate ecological research. By understanding the links between micro-topography, microclimate, moss physiology and moss health, these techniques form the building blocks required for continuous remote biological monitoring of Antarctic moss beds on a larger scale.

FoR codes (2008)

0102 APPLIED MATHEMATICS, 0103 NUMERICAL AND COMPUTATIONAL MATHEMATICS, 0607 PLANT BIOLOGY, 060704 Plant Pathology

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.