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Harvard Forest Symposium Abstract 2020

• Title: Differences in water-use strategies between two coexisting conifer trees in an alpine habitat
• Primary Author: Yiping Zhang (Not Specified)
• Additional Authors: Neil Pederson (Harvard Forest)
• Abstract:

  Understanding tree water use and their interspecific differences will aid in the assessment of tree-level physiological adaptation and the prediction of forest stand structure dynamics. We investigated the seasonal variation of water sources between two co-occurring trees representing different life forms, the deciduous Larix principis-rupprechtii Mayr. and the evergreen Picea meyeri Rehd. et Wils., in an alpine habitat, Luya Mountain (North-Central China).
  From September 2013 to October 2014, we collected approximately 2400 samples at weekly/biweekly intervals, and analyzed the water isotopes (δD and δ18O) of tree xylem water and its potential water sources (precipitation, snow water, soil water) and the contribution of soil water at different depths. Concurrently, we monitored leaf phenology by direct observations and intra-annual stem xylem formation by the microcores method, which the latter was to identify the specific dates of the tree’s growth (i.e., onset, end, and maximum growth rate).
  The results indicated winter snowmelt water seemed to be the source water for growth onset, of which larch relied upon more than spruce. During the growing season (June through August), both larch and spruce mainly absorbed water from the same soil layer of 10-20 cm (averagely 38.9% and 37.5%, respectively). However, the potential inter-specific water competition was reduced at the accelerated growth stage when the earlywood were formed.
  Unlike deeper-rooting larch, shallower-rooting spruce showed higher ability to shift water sources among various soil layers, accompanied by the tighter stomata regulation, which expected to be more sensitive to water availability. Thus, if an increasing short-term water stress occurs under projected future warming, the spruce with water-saving strategy (isohydric behavior) may have a selective advantage against the anisohydric larch due to its higher effective water-use efficiency. Such diverging species-specific water use strategies improve our knowledge on tree-level ecophysiological mechanisms, with the implications for understanding ecosystem-level alpine forest structure dynamics and theirs resilience to environmental stress.

• Research Category: Physiological Ecology, Population Dynamics, and Species Interactions


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