Project

Broadleaf temperate trees growth pattern response to increasing the frequency of freeze-thaw cycles

The future of temperate forests is highly uncertain because we do not know how different species will respond to ongoing climate change. One of the understudied climate change factors is the effect of freeze-thaw cycle frequency on the growth and survival of trees. Freeze-thaw cycles are known to disturb the plant hydraulic system, but the implications of this for the future of different tree species – following different strategies in hydraulic recovery from such disturbances – remains to be understood, and is required to better predict the future of temperate forests with climate change.

Objectives

In this project we will first detect how different hydraulic charasteristics relate to their resistance and recovery from freeze-thaw cycles by studying their stem growth dynamics in response to annual freeze-thaw cycle frequency. Second, we will demonstrate the possible negative implications of sugar consumption by hydraulic blockage repair for growth. Thirdly, we will compare species for their phenology in stem cambial activity and leaf expansion to show how these physiological mechanisms can cause divergence in phenology across species. 

Methodology

The study will be carried out in the Northeast Asia Botanical Garden (128°28′E, 42°24’N; 736 m altitudes), China. The study site enjoys a typical temperate continental climate influenced by monsoon with long, cold winter. We will select 12 common broad-leaved tree species co-occurring in the study site. The trees are growing in a common garden so as to guarantee that interspecific differences can truly reflect genetic differences. 

For tree-ring analyses two increment cores per tree will be collected from 15 trees per species at DBH (1.3 m). Ring width are measured with 1/100mm accuracy using a LINTAB measuring table in combination with the Time Series Analysis Program (TSAPWin). After cross-dating to correct for potential double or absent rings, the basal area increment (BAI) then will be calculated based on the measured ring widths. Growth responses to freeze-thaw cycles were computed through a bootstrapped principal component regression (PCR). 

For hydraulic characteristics measurement, segments for measuring hydraulic conductivity will be used and percent loss of hydraulic conductivity will be quantified by measuring the increase in hydraulic conductivity after removal of xylem embolism by high-pressure flushes. 

For measuring non-structural carbohydrates concentrations, samples will be collected in the period of repair embolism in April, and in July. The dried and ultra-fine powdered plant materials will be used for extracting NSC. The method for measuring non-structural carbohydrate concentrations is sulfuric acid-anthrone colorimetric method with some modifications. 

Leaf phenology will be recorded for individual sample trees every week. Observations will be made by screening buds of main shoots in the upper crown, and leaf phenophases will be classified as different stage. As for the detection of stem cambium activity, micro-samples will be collected every week to detect start of cambium activity. Since cambium becomes active, afterwards samples will be collected every 2nd week. Permanent cross-sections will be made to examine the wood formation process by using the paraffin embedding method.