Assistant Professor University of Texas Rio Grande Valley, Texas, United States
Abstract: Reforestation attempts in semi-arid regions are often plagued with seedling mortality due to high temperatures and drought even in drought-tolerant species. Seedling growth post-planting, particularly of roots to more stable deep soil moisture, is therefore a crucial determinant of survival. Though roots are a strong determinant of drought tolerance, blanket approaches in soil creation for seedlings grown in plant bands do not take this into account. To better understand the effects of soil aeration and texture has on root development in addition to how root traits affect drought survivability, we conducted a study to better understand these influences. Border palo verde, Cercidium macrum (I.M. Johnst.), seedlings were grown in different sized (8” and 4”) plant bands to produce seedlings of different root length densities using three soil types: a standard mix used by the US Fish and Wildlife involving a 50-50 vermiculite-topsoil mix including osmocote, and field-collected a fine sandy loam and sandy clay loam soil where vermiculite was excluded, creating a total of 6 different treatments. We assessed stem diameter, plant height, and root biomass and length using a flatbed scanner and image digitizer (WinRhizo, Regent Instruments, Canada) device. Our findings suggest that soil texture and lack of vermiculite does not inhibit stem diameter or height growth. However, we found that clay soils negatively affected root development and smaller plant bands (higher root densities) promoted higher root length densities. Therefore, our results suggest that it may be possible to propagate seedlings using soils matched to the site where they will be planted, which may enhance their drought resilience and overall success. However, it may be necessary to avoid clay soils, but more research is needed to determine whether clay soils are inherently difficult due to texture or some other aspect of chemistry. A more comprehensive assessment of soil mixture practices may produce more fruitful rehabilitation and plantings.
