n Southern African Forestry Journal - Effects of temperature on seedlings growing in pots in a controlled environment : scientific paper




The re-establishment of Pinus patula seedlings into sites with high harvesting residue (slash) loads can negatively affect the survival of these plants. Field trials have examined the role that insect pests and fungal diseases play in causing this phenomenon. Research has also indicated that temperatures at ground level tend to be higher in the slash during the day, compared to areas where slash had been removed. The current investigation aimed to determine whether the high temperatures experienced in the slash are likely to be the sole causal agent for the observed mortality. Pots containing P. patula seedlings were exposed to four different temperatures (26<sup>o</sup>, 32<sup>o</sup>, 38&lt;sup&gt;o&lt;/sup&gt; and 44&lt;sup&gt;o&lt;/sup&gt; C) in an illuminated growth chamber. The duration of exposure was 1, 2 or 3 hours. The exposure to the different temperatures was repeated on 7 days in a 10 day period. Respiration rates increased significantly at the high temperatures, while the chlorophyll a, b and total chlorophyll concentrations were significantly reduced at the highest temperature. Increasing temperature also significantly reduced both height and new root growth in the seedlings during the experiment. The results indicate that, although no mortality was observed during the experiment, continued exposure to high temperatures over an extended period has the potential to cause seedling mortality. However, it is hypothesised that high temperatures predispose the seedlings to attack by pests and pathogens on site.


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