Allocation to growth and defense in Hevea

Plants allocate resources to growth, defense, and stress resistance, and resource availability can affect the balance between these allocations. We measured growth and defense in a provenance trial of rubber trees (Hevea brasiliensis) with clones originating from the Amazon basin. To test hypotheses on the allocation to growth vs. defense, we relate biomass growth and latex production to wood and leaf traits, to climate and soil variables from the original location, and to the genetic relatedness of the Hevea clones. Growth was weakly correlated with leaf traits, such as leaf mass per area, intrinsic water use efficiency, and leaf nitrogen content, but the relative investment in growth vs. defense was not associated with specific traits or environmental variables. Wood and leaf traits showed clinal correlations to rainfall and soil variables of the original location. These traits exhibited strong phylogenetic signals, highlighting the role of genetic factors in trait variation and adaptation. Contrary to expectations, there was no trade-off between growth and defense, but latex yield and biomass growth were positively correlated, and both increased with tree size. The absence of a trade-off may be attributed to high resource availability in the plantation, allowing trees to allocate resources to both growth and defense. The study provides insights into the interplay between resource allocation, environmental adaptations, and genetic factors in trees. While latex production (but not growth) also had strong phylogenetic signal, the underlying drivers for high variation of latex production in one of the commercially most important tree species remains unexplained. 

Methods
The study utilized Brazilian rubber trees, originally sampled from wild populations in the Amazon basin. Trees were planted in a provenance trial in Thailand with replicates per clone. Latex yield and growth data were collected over several years, while leaf and wood traits were measured from leaf and wood samples collected from various clones. Traits related to growth, defense, leaf, and wood traits were analyzed to explore potential trade-offs among these categories. Additionally, environmental variables from the original locations of the clones were considered in the analysis.