The Earths Eldest at the Frontier of Change: Annual resolution climate and meteorological signals in Bristlecone Pine Needles

Annual resolution needle length and cuticle property data have been obtained from needles of bristlecone pine, Pinus longaeva, from the White Mountains, California, USA. The bristlecone pine, living at the tree line in extreme alpine conditions is known for its longevity, some individuals are the world’s oldest non-clonal organisms. The bristlecone pine’s suitability for annual resolution studies is unique because the tree holds on to the needles longer than any other plant and the needles grow in annual fascicles that are clearly distinguishable. In the present study a continuous 44 years long series of annual needle-length and structural stomatal conductance have been analyzed from individual trees in extreme low P[CO2]-conditions and are compared to long and short term climate variability as well as global atmospheric P[CO2] change. Distinct annual needle-length variations corresponded highly among eight different individual trees that were sampled. In this data-set, two signals are distinguished, an overall declining trend in needle length and an annual variability. The declining long-term trend provides evidence for a negative correlation between atmospheric P[CO2] concentration and needle-length. The annual variation relates to summer temperature and reflects the dominant climate system in the area, the PDO (Pacific Decadal Oscillation) which describes humidity and temperature regimes in the northern Pacific region. Our results for the first time demonstrate needle-length dependence on P[CO2] and temperature. A strong decline in structural stomatal conductance shows a strong response to changes in atmospheric P[CO2] and quantifies stomatal plasticity under near glacial P[CO2] not studied in-situ so far.