Submitted to: Scientia Horticulturae
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/15/2010
Publication Date: 4/23/2011
Citation: Glenn, D.M., Campostrini, E. 2011. Girdling and summer pruning in apple increase soil respiration. Scientia Horticultureae. DOI: 10.1016/j.scienta.2011.04.023. Interpretive Summary: When the canopy of trees is pruned or restricted by damage or girdling, the effect on the root system is unclear. In field studies, we cut a spiral around the trunks of apple trees, girdling, and summer pruned approximately 30% of the canopy from apple trees; both common horticultural practices in apple production. We measured the carbon dioxide emissions from the soil beneath the trees as an indication of biological activity. We found that both summer pruning and trunk girdling caused root death, and soil microbes used the dead roots as food to increase soil microbial respiration and emission of carbon dioxide from the soil. The period of time for root death was short and likely did not have a chronic effect on the root system. This work demonstrated that summer pruning and trunk girdling, while temporarily affecting the root system, does not appear to decrease overall productivity in apple production.
Technical Abstract: The root system of plants derives all its energy from photosynthate translocated from the canopy to the root system. Canopy manipulations that alter either the rate of canopy photosynthesis or the translocation of photosynthate are expected to alter dry matter partitioning to the root system. Field studies were conducted to evaluate the effect of trunk girdling (2008 and 2009) and summer pruning (2009) on root/soil respiration, photochemical efficiency and leaf carbohydrate content. In apple trees, within 3 days of girdling the trunk, root/soil respiration rate increased more than 2X suggesting rapid root die-off and microbial decomposition of the dead root tissue that required 30 days to return to control levels. Photoinhibition (PI) was increased by girdling when crop load was low and PI was not related to leaf carbohydrate levels. Girdling reduced sucrose and sorbitol levels in both years, however, total leaf carbohydrates were not affected by girdling. Summer pruning demonstrated a significant increase in root/soil respiration within 2 weeks of treatment, also suggesting root die-off and microbial decomposition of the tissue. These data demonstrate that common canopy cultural techniques may result in reduced root biomass due to reduced carbon partitioning to the root system that is necessary to maintain a given level of root biomass.