© 2006 Heron Publishing—Victoria, Canada
Influences of canopy photosynthesis and summer rain pulses on root dynamics and soil respiration in a young ponderosa pine
forest
Laurent Misson (1, 2), Alexander Gershenson (3), Jianwu Tang (4), Megan McKay (1), Weixin Cheng (3) and Allen Goldstein (1)
1. Department of Environmental Science, Policy and Management, 151 Hilgard Hall, University of California, Berkeley, Berkeley,
CA 94720-3110, USA / 2. Corresponding author (lmisson@nature.berkeley.edu) / 3. Department of Environmental Studies, UC Santa Cruz, Santa Cruz, CA 95064, USA / 4. Department of Forest Resources, University of Minnesota, 1530 Cleveland Ave N, St. Paul, MN 55108, USA / Received June 30, 2005; accepted October 7, 2005; published online April 3, 2006
Summary
Our first objective was to link the seasonality of fine root dynamics with soil respiration in a ponderosa pine (Pinus ponderosa P. & C. Lawson) plantation located in the Sierra Nevada of California. The second objective was to examine how canopy photosynthesis
influences fine root initiation, growth and mortality in this ecosystem. We compared CO2 flux measurements with aboveground and belowground root dynamics. Initiation of fine root growth coincided with tree stem
thickening and shoot elongation, preceding new needle growth. In the spring, root, shoot and stem growth occurred simultaneously
with the increase in canopy photosynthesis. Compared with the other tree components, initial growth rate of fine roots was
the highest and their growing period was the shortest. Both above and belowground components completed 90% of their growth
by the end of July and the growing season lasted ~80 days. The period for optimal growth is short at the study site because
of low soil temperatures during winter and low soil water content during summer. High photosynthetic rates were observed following
unusual late-summer rains, but tree growth did not resume. The autotrophic contribution to soil respiration was 49% over the
whole season, with daily contributions ranging between 18 and 87%. Increases in soil and ecosystem respiration were observed
during spring growth; however, the largest variation in soil respiration occurred during summer rain events when no growth
was observed. Both the magnitude and persistence of the soil respiration pulses were positively correlated with the amount
of rain. These pulses accounted for 16.5% of soil respiration between Days 130 and 329.
Keywords:
fine root, minirhizotron, photosynthesis, plant-microbes interactions, rhizosphere, soil processes.
