An ecology student investigated the distribution of stinging nettles (Urtica dioica) across six distinct zones of a woodland edge.
The student measured the soil nitrate concentration and counted the number of nettles in several 1 m2 quadrats within each zone. The results are shown in the table below.
| Woodland zone | Mean soil nitrate concentration in mg⋅kg−1\text{mg}\cdot\text{kg}^{-1}mg⋅kg−1 | Mean number of nettles per m2\text{m}^2m2 |
|---|---|---|
| Zone 1 | 120 | 15.4 |
| Zone 2 | 95 | 11.2 |
| Zone 3 | 70 | 7.8 |
| Zone 4 | 45 | 4.1 |
| Zone 5 | 20 | 1.3 |
| Zone 6 | 5 | 0.2 |
Explain the effect of soil nitrate concentration on the number of stinging nettles per m2\text{m}^2m2.
