Date of Award
Bachelor of Science
Steven K. Rice
carbon, plants, isotope, dry, wet, bulk
Bryophytes (mosses and their relatives) are a major carbon sink, and their productivity, is expected to be affected by climate change. Changes in plant productivity caused by changes in the climate can be tracked through stable carbon isotopes. This research aims to find a connection between stable carbon isotope signatures and water availability in bryophytes by examining the composition of 13C in soluble sugars and bulk tissue. Similar to trees, which leave rings of growth every year, mosses build up peat deposits, which can be used to gain information about the weather and water availability of a region. Information on weather can be determined by the stable carbon isotope composition of bryophytes. Atmospheric carbon exists in two isotopic forms: 12C (approximately 99% of the total CO2 in the atmosphere) and 13C (1%) and rubisco (the enzyme responsible for carbon fixation in photosynthesis) prefers the lighter isotope. Carbon dioxide diffuses 10,000 times slower in water than in air; consequently, when a water film forms on a plant leaf (particularly on moss leaves, which lack stomata) the plant will assimilate more 13C, as rubisco becomes less selective when CO2 becomes limiting. Differences in δ13C in plant tissues are caused by such discrimination processes. Studies have shown a link between carbon isotope signatures in bulk tissues and moisture over time periods of several weeks, but there is little correlation on shorter time scales. Soluble sugars are primarily the result of new photosynthesis and sugars that have yet to be 3 integrated into the bulk tissue of the bryophyte. The goal of this experiment is to explore the timing of carbon isotope discrimination in bryophytes and determine if a short--‐term link can be made between carbon isotope composition and moisture levels by examining δ13C at soluble sugars. Samples of Sphagnum papillosum were maintained in growth champers under two water conditions (dry and moist) over a time period of four weeks. Each week, a sample of plants (n=5) was collected and soluble sugars were extracted from their tissues. The carbon isotope composition of their bulk tissues was determined and a significant effect of both treatment and week was found. Over time, wet plants were less discriminating against 13C where drier plants maintained the same carbon isotope composition throughout the experiment. In addition, a control experiment was preformed to find the carbon isotope composition of the soluble sugars.
Williamson, Olivia Hope, "13C Composition in Bryophyte Primary Sugars as an Indicator of Water Availability" (2016). Honors Theses and Student Projects. 228.