Growth and Morphophysiological Responses of Protium heptaphyllum Seedlings to Root Deformation and Light Availability

Abstract

J-root deformation caused at the time of pricking out is highlighted in several forest nursery manuals, but there are few reports in the literature on the consequences of this type of root deformation on the physiology and growth of tree seedlings. Protium heptaphyllum is a tropical tree with potential for use in forest enrichment projects and agroforestry systems. This study aimed to evaluate the biomass allocation, root hydraulic conductivity and growth of P. heptaphyllum seedlings subjected to root deformation and three contrasting light levels (44%, 28%, and 2% of full sunlight) over a period of 155 days. Root deformation negatively affected the shoot to root dry mass ratio (S/R), the diameter to root volume ratio (D/RV), the height to root volume ratio (H/RV) and relative growth rate (RGR). Seedlings at 44% and 28% of full sunlight had lower S/R and higher hydraulic conductivity per unit of root volume (Kr/RV), net assimilation rate (NAR), and RGR when compared with seedlings at 2% of full sunlight. No significant interactions were observed between root deformation and light. Root deformation caused at the time of pricking out affects the quality of seedlings, decreasing growth rates and changing morphophysiological characteristics independently of light availability. Study Implications: Poor quality tree seedlings with J-root deformation is a problem frequently pointed out in forest nursery manuals. Despite this, there is scarce information in the literature on how errors in the pricking out process affect the morphology and physiology of tree seedlings. We demonstrated that this type of root deformation decreases the growth rate and changes important characteristics of Protium heptaphyllum seedlings regardless of light environment. We highlight important morphological and physiological effects of errors in the management of tree seedlings, which are frequently pointed out in forest nursery manuals but have not been demonstrated by experimental studies.