Ecological Archives E096-064-A4
Xubing Liu, Rampal S. Etienne, Minxia Liang, Yongfan Wang, Shixiao Yu. 2015. Experimental evidence for an intraspecific Janzen-Connell effect mediated by soil biota. Ecology 96:662–671. http://dx.doi.org/10.1890/14-0014.1
Appendix D. Detailed descriptions on how each trait was measured.
Specific leaf area (SLA) is the ratio of projected leaf area to dry weight expressed in mm²/mg. We randomly selected 10 relatively young, fully expanded leaves without symptoms of pathogen or herbivore attack from each adult for this measurement. Leaves were immediately stored in wet PVC bags and taken to the field lab for weighting and measuring. We determined leaf area within 3 h of harvesting using the LI-3000C portable leaf area meter (Li-Cor, Lincoln, Nebraska, USA). We calculated SLA after oven-drying (at 60 °C for 72 h) of the fresh leaves as leaf area divided by leaf dry mass. We then used these oven-dried leaves for leaf nitrogen concentration (LNC) analysis, after removing any petiole or rachis. LNC is the total amount of N per unit of dry leaf mass (mg/g) and was measured using the Kjeldahl method by a Foss KjeltecTM 2300Autoanalyzer (Foss Tecator AB, Hoganas, Sweden).
Wood density is the ratio of oven-dry mass to fresh volume of a section of a plant's main stem, expressed in mg/mm3. We used an increment borer to extract one core at breast height (1.3-m) from the focal individual of each population. We took the cores from bark to pith (center) of the stems, and determined fresh volume of the cores by the volume replacement method (Cornelissen et al. 2003). We dried the samples in the oven at 60 °C for 96 h and then weighed them.
We determined seed mass from 100 randomly selected seeds (mature and alive) under the canopy of each population. We removed any accessories such as fruit flesh (but not the testa), oven-dried the seeds until equilibrium mass at 80 °C for 48 h and weighed them.
We measured photosynthetic rate by using the LI-6400 portable photosynthesis system (Li-Cor, Lincoln, Nebraska, USA). We chose two to four newly formed mature leaves experiencing full sunlight per upper canopy branch (20 leaves per population) and measured the photosynthetic rates between 0800 and 1100 hours.
For each population, we set up a circular plot in spring 2011, with a radius of 50 m and the focal individual that provided seeds and soil as the center. DBH was recorded for all conspecific individuals ≥ 5 cm DBH in each plot. As a measure of mean local abundance, we calculated the total basal area of all conspecific individuals within each plot (log-transformed). We used the maximal DBH as an estimate of the maximal individual size for each population. We defined spatial distance between each pair of populations as the projector distance between two focal individuals and assessed it with a portable GPS with an accuracy of 5 m.
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