Tuesday, June 19, 2007 - 8:40 AM
Douglas Firs (Boise Centre on the Grove)

Using Organic Mulches to Manipulate Tree Growth and Secondary Compounds in Ponderosa Pine

Javier Lugo-Pérez and John E. Lloyd. University of Idaho, Moscow, ID

Mulching around trees can improve edaphic conditions that benefit tree establishment and development. The carbon and nitrogen ratio (C:N) of organic mulches can influence soil nitrogen availability through promoting nitrogen mineralization or immobilization. According to plant defense hypotheses, resource availability (e.g. nitrogen) may influence plant carbon allocation to growth and secondary metabolism. In our study, we used ponderosa pine (Pinus ponderosa) to measure the impact of organic mulch C:N ratio on growth and monoterpene production. Using the growth differentiation balance (GDB) hypothesis as a model, we predicted that under similar assimilation rate there will be a trade-off between growing rate and foliar monoterpene content. To test this prediction, we planted 25 large trees (~2.5m height) and 50 small trees (~0.30m height) in 50 cells isolated peripherally with landfill liner. The soil inside the cells was covered with one of the following five compost to bark mulch proportions: 1:0, 1:1, 1:2, 1:4 and 0:1, corresponding to the following C:N proportions: 10:1, 30:1, 45:1, 70:1 and 130:1. The experimental design was a randomized complete block design-split-plot in time with five blocks and one replicate per block. For both tree size categories, assimilation rate, relative growth rate and foliar monoterpene content were not different among treatments within year 2005 and 2006. Between years, we detect an increment in growth and reduction on foliar monoterpenes which support the predicted trade-off proposed by the GDB hypothesis. Inconsistent correlations between growth rate and monoterpene content within years suggest that this relationship is highly variable among individuals.