Transpiration Efficiency Calculator
Enter accumulated dry matter and transpired water to compute transpiration efficiency TE = dry matter ÷ transpiration, assessing how much dry matter a plant produces per unit water lost.
Input Data
Results
At a glance:Transpiration efficiency (TE) measures the physiological efficiency of 'using water to make dry matter', defined as accumulated dry matter over a period divided by water transpired in the same period: TE = dry matter ÷ transpired water, commonly g dry matter / kg water (equal to g/L since 1 kg water ≈ 1 L). It is closely related to the broader 'water-use efficiency (WUE)' but TE specifically focuses on the water truly transpired through leaf stomata, excluding non-productive losses like soil evaporation, thus more directly reflecting leaf and plant-level physiology. TE depends on several factors: stronger photosynthesis (more carbon fixed per stomatal opening), more conservative stomatal control (less water loss while maintaining photosynthesis), and water-saving pathways like C4 or CAM generally give higher TE. Therefore TE is an important selection trait for drought-tolerant, water-saving crop breeding — high-TE varieties maintain higher productivity under limited water. Note TE is strongly affected by atmospheric evaporative demand (expressed as vapor-pressure deficit, VPD): the drier the air (higher VPD), the more transpiration per unit carbon fixed, so TE falls. Rigorous comparisons across experiments or seasons often normalize TE to VPD (e.g. TE×VPD as a more stable varietal trait) or compare under similar climates. Carbon-isotope discrimination (δ¹³C) is also used as an indirect long-term TE indicator. Use consistent dry matter and transpired water corresponding to the same plant and period, with matching units (dry matter g, water kg gives g/kg).
Formula
Transpiration efficiency: TE = accumulated dry matter ÷ water transpired.
Units: g dry matter / kg water = g/L (1 kg water ≈ 1 L).
Environment: TE decreases as vapor-pressure deficit VPD rises.
$$TE = \frac{DM}{W_{transpired}}$$$$TE \propto \frac{1}{VPD}$$How to Use
- Measure the dry matter added over the period (dried to constant weight) and the transpired water (e.g. pot weighing for daily water loss).
- Enter dry matter and transpired water with matching units (dry matter g, water kg).
- The tool returns TE (dry-matter output per kg water); compare varieties under similar VPD.
Main factors affecting transpiration efficiency TE
| Factor | Effect on TE | Note |
|---|---|---|
| Photosynthetic pathway (C4 / CAM) | Increases | Fixes more carbon per water, usually higher than C3 |
| Conservative stomatal control | Increases | Less loss while maintaining photosynthesis, better water return |
| Dry air (high VPD) | Decreases | More transpiration per carbon fixed when air is drier |
| Stress / disease lowering photosynthesis | Decreases | Water use unchanged but dry-matter output drops |
Always consider VPD when comparing TE; often use TE×VPD or δ¹³C as a more stable varietal index.
Case Studies
TE from dry matter and water use
A potted crop added 500 g dry matter and transpired 100 kg water in one growth stage.
TE = 500 ÷ 100 = 5 g/kg.
Means 5 g dry matter per kg water — compare water-productivity with other varieties under similar climate.
Comparing two varieties at the same VPD
Variety A: 500 g dry matter, 100 kg water → TE = 5 g/kg.
Variety B: 480 g dry matter, 80 kg water → TE = 6 g/kg.
At similar VPD, variety B makes 1 g more dry matter per kg water, better water-saving productivity — a desirable parent for drought breeding; if VPD differs, correct first.
FAQ
How does TE differ from water-use efficiency (WUE)?
The concepts are close but at different levels. WUE usually means 'yield (or dry matter) ÷ total water use', where total water may include non-productive soil evaporation — a field/population-level metric. TE specifically means 'dry matter ÷ water transpired through leaves', excluding soil evaporation, a plant/leaf physiological-level efficiency. Field WUE decomposes into TE and 'fraction of transpired vs total water'; higher TE helps higher WUE.
Why must VPD be considered when comparing TE?
Because leaf transpiration rate is proportional to atmospheric vapor-pressure deficit (VPD): drier air means more water lost per stomatal opening, so more transpiration per unit carbon fixed and TE drops. Without VPD correction, 'very dry hot day' could be mistaken as 'low-efficiency variety'. Practice often uses TE×VPD or carbon-isotope discrimination (δ¹³C) as indices less affected by current weather.
How to measure transpired water?
Potted plants commonly use weighing (lysimetry): cover the soil surface to block soil evaporation, weigh the pot periodically, and the weight loss is transpired water. In the field use sap-flow meters, eddy covariance, or water-balance methods to estimate transpiration. The key is to separate 'transpiration' from 'soil evaporation', because TE targets only plant-lost water; if you measure total water including soil evaporation, you get something closer to WUE than pure TE.
Why is C4 plant TE higher?
C4 plants (e.g. maize, sugarcane) have a carbon-concentration mechanism that maintains high photosynthesis at lower intercellular CO₂, so they can keep stomata narrower, lose less water, yet fix carbon undiminished. Fixing more carbon per unit transpiration makes TE higher than most C3 plants. CAM plants are more extreme — open stomata at night to fix carbon, closed by day — usually the highest TE, an extreme water-saving strategy.
Can TE units be converted?
Yes. TE = dry matter ÷ water; if dry matter in g and water in kg, the result is g/kg; since 1 kg water ≈ 1 L, g/kg numerically equals g/L. Using mg with g, or kg with m³, just keep units consistent and apply the corresponding factor. Always unify units before comparing literature values.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.