Effects of starch-based superabsorbent polymer on survival and physiology of Pinus ponderosa seedlings exposed to severe drought stress

Planting nursery-grown trees has become necessary to reach reforestation goals to promote forest recovery; however, these young transplants are vulnerable to drought-related stress and mortality. Land managers may want to consider implementing silvicultural applications, such amending the soil water holding capacity, to reduce drought stress in plants. We applied a superabsorbent polymer in three different ways as a soil amendment for ponderosa pine seedlings in a greenhouse drought trial. We watered the seedlings for 12 weeks and then initiated a severe drought by completely cutting off water. We measured the effect of the polymer treatment on seedling survival, height relative growth rate, stomatal conductance (g _s ), and chlorophyll fluorescence (ФPSII and F _v /F _m ), and compared a null treatment model to test models for each response, using time, treatment, and an interacting time-treatment effect as covariates. We found that the polymer did improve survival probability and median time to death in treatments that distributed the polymer throughout the soil, but was unable to influence the seedlings’ drought-avoidant strategy of early stomatal closure and cessation of growth. However, the addition of the polymer may buffer the seedling against photoinhibition, which may increase drought recovery capacity and thus has the potential to increase seedling survival in a reforestation setting. This experiment serves as a proof of concept that water-retaining soil amendments may be beneficial for conifer seedlings in severe drought, but more research must be done to understand the efficacy of using these in a reforestation project.