Phosphorous fertilization and soil pH affect the growth of deciduous trees in a temperate hardwood forest

Abstract

Forest ecosystems with altered nutrient limitations are a common legacy of acidic deposition in North America. Continued acidic deposition has lowered soil pH and revealed phosphorus (P) limitations in many temperate forest ecosystems. Previous studies exploring P limitations or co-limitations are often short term, and thus may potentially show a response to limitation that is not sustained over time. To better understand how a forest's response to P limitation and acidic deposition can change over time, we added P, limestone to raise pH, and a cross-treatment where both P and limestone were added to 3 different northeastern Ohio forest stands over a 12-year period. We tracked diameter at breast height of the trees annually, conducted foliar nutrient analyses, and collected tree roots to assess treatment impacts on mycorrhizal colonization. We analyzed our dataset in three sections: the first 6 years after manipulation, the latter 6 years, and the entire 12-year period. These sections allowed us to compare differences between early responses to manipulation and later responses. Here, we found that P additions increased basal area growth across multiple species and throughout the entire study, confirming that our forest trees are P-limited. Cross-treatments similarly increased basal area growth, but not as much as P additions alone. Some species saw waning effects of treatment in the second half of the study. This could be due to changes in weather patterns, an adjustment of the study system's equilibrium, or the emergence of beech leaf disease in 2014, which has led to the decline of Fagus grandifolia. Early successional species such as Acer rubrum began to benefit from treatments after beech leaf disease killed canopy F. grandifolia trees, perhaps first being light-limited, but later able to take advantage of the nutrient additions and pH alteration of their soils. Our results suggest that in forests subject to acidic deposition, soil P may co-limit tree growth, but responses are species dependent.