Abstract:
Abstract: The demand for soilless substrates is on the rise, while simultaneously, countries across the world are reducing, restricting, and even banning the extraction and horticultural use of peat moss. Conifer wood fiber substrates have emerged as the most promising solution to fill the void left by the reduction in peat usage. However, freshly harvested trees, when chipped and milled for use as wood fiber in horticultural substrates, may contain chemicals that are harmful to young plants grown in them. Initial research has revealed that aging the wood fiber is an effective method to mitigate these phytotoxins, ensuring their safe use as a growing medium.

My research objectives can be summarized as follows:

1. To gain an understanding of the phytotoxic characteristics of substrates derived from different conifer tree species.
2. To investigate how the season (e.g. winter and summer) of tree harvest and wood fiber aging affect phytotoxic potential and severity.
3. To assess the phytotoxic potential of the four main morphological parts found in pine trees (Pinus taeda): bark, heartwood, sapwood, and needles.

To facilitate the study of phytotoxic responses in wood substrates, we have developed two rapid plant growth bioassays: plant sand culture and seed germination. Leachate extracted from processed wood fiber was used to irrigate tomatoes in sand culture and to germinate lettuce and tomato seeds, allowing us to illustrate the biocidal properties of the substrate itself. In addition to bioassays and other plant culture studies, we are seeking methodologies and procedures to analyze and quantify wood extractives responsible for phytotoxicity.

In our first study, we hypothesize that different coniferous tree species will exhibit varying levels of toxicity on floricultural crops and that phytotoxicity will decrease over time as the wood substrates age. The second study postulates that trees harvested in the summer will have higher phytotoxicity than those harvested in the winter, but wood fiber aged during the summer will volatilize chemicals more quickly compared to winter-aged wood. Finally, the third study hypothesizes that the bark and needles will cause more phytotoxic damage than the heartwood or sapwood.

Preliminary results confirm that phytotoxicity does indeed differ between tree species and diminishes as the wood ages. Subsequent studies will explore additional methods for alleviating phytotoxicity, by way of additives or other cultural practices.