Measuring dry weight biomass

Protocol

 

Author

Amy Davidson

Definition

Dry weight biomass measurements with electronic balance

Overview

Total dry mass is often used as an indication of plant fitness. In particular, dry vegetative mass is generally correlated to reproductive mass. In addition, the plant samples may be split into leaves, stems and roots. This enables calculation of the root to shoot ratio, and leaf to stem ratio which may provide information on adaptation to different water or nutrient levels. Further leaf dry weight can be coupled with measurements of leaf area to calculate Specific Leaf Area (SLA). SLA is often correlated with relative growth and may also indicate adaption to shade conditions (shade adapted plants generally have higher SLA than sun adapted plants).

Materials/Equipment

  • Drying oven (60oC)
  • Paper bags
  • Electronic balance
  • Cardboard or other non-static platform

Units, terms, definitions

  • g = grams
  • dry mass = oven dried weight
  • oC = degrees Celsius

Procedure

Step 1 Preparation:
You will need to place harvested material into labelled paper bags. Place these in a 60oC oven for approximately three days or until weight has stabilised. Remove from oven and place ags into ziplock plastic bags, you can place more than one paper bag into a ziplock bag as long as the ziplock bag can still be sealed. Place a small amount of silica gel (approx 1 tablespoon per large zip lock bag) into each ziplock bag.
Step 2 Measurement:

  1. Turn electronic balance on, open one side of balance cabinet and place cardboard or other non-static platform on balance.
  2. Zero the scales using an empty bag that is otherwise identical to those your dried samples are stored in (e.g. bag also has been oven dried for same time period, and if your samples are stapled in the bags put a staple in the empty bag). Place the empty bag on the scales and press the “zero button”. The scale should now read zero and is ready for measurements.
  3. Place your first sample on the scales, ensure it is not resting anywhere other than the measuring balance plate or cardboard platform on the measuring balance. Wait at least 30 seconds until the scale has stabilized, record the value and remove the sample carefully.
  4. Repeat step 3 for all samples.

NOTE: Keep plastic bags sealed between measurements to avoid entry of moisture. Place weighed bags in a fresh plastic bag with silica gel.

Notes

Preparation time: 3 days (for drying)
Measurement time: ~3 min per sample + 3 min to zero scale at start of measurement session

Troubleshooting tips

If the sample will not stabilize ensure it is not touching the sides of the balance cage anywhere, if it still does not stabilize, remove the sample and re-zero the scales then repeat the measurement.