Anthropogenic Calcium Depletion: A Unique Threat to Forest Ecosystem Health?

Abstract

Numerous anthropogenic factors can deplete calcium (Ca) from forest ecosystems. Because an adequate supply of Ca is needed to support fundamental biological functions, including cell membrane stability and stress response, the potential for Ca deficiency following the individual, cumulative, or potentially synergistic, influences of anthropogenic factors raises important questions concerning organism and ecosystem health. Past work has shown that one Ca-depleting factor (foliar acid mist exposure) reduces concentrations of biologically important membrane-associated Ca (mCa) from red spruce foliar cells, destabilizes these cells, and results in their increased susceptibility to the freezing injury responsible for red spruce decline in northeastern U.S. montane eco-systems. Data presented here indicate that these same disruptions can occur for other tree species and that soilbased Ca manipulation can also alter critical mCa pools. Considering the unique role Ca plays in the physiological response of cells to environmental change and stress, we hypothesize that depletion of biologically available Ca (e.g., mCa) could result in a scenario similar to recognized immune deficiency syndromes in animals. A hypothetical pathway through which anthropogenically induced Ca deficiencies could predispose plants, and possibly animals, to exaggerated injury following exposure to environmental stress is presented, and the potential implications of this scenario to ecosystem health are discussed.

Calcium constrains plant control over forest ecosystem nitrogen cycling

“…In northeastern North America several decades of acid deposition depleted nutrient cations, especially Ca (Federer et al 1989, Likens et al 1996. Loss of Ca has been associated with declines in key tree species, e.g., sugar maple, and changes in both terrestrial and aquatic biodiversity and nutrient cycling (Driscoll et al 2001, Schaberg et al 2001). Concerns about soil Ca depletion have increased even more as legislation to reduce acid deposition has been passed and implemented.…”

Decreased water flowing from a forest amended with calcium silicate

“…The critical role of Ca in forests has highlighted the need to understand better the consequences of available soil Ca depletion. Acid deposition has caused rates of Ca leaching to far exceed rates of replenishment through weathering and atmospheric deposition, making soil Ca loss a threat to long-term forest vitality in regions prone to acid deposition (13,(16)(17)(18)(19)(20)(21).…”

Are Northeastern U.S. forests vulnerable to extreme drought?

“…Long-term acidic deposition in the Northeastern U.S. resulted in major losses of calcium and magnesium from soils (Likens et al 1996). Calcium plays an important role in many physiological processes in trees including signal transduction during periods of stress (i.e., temperature extremes, drought, and wounding), which is critical for acclimation to environmental stress and preventing mortality (Schaberg et al 2001). Acid rain can also directly leach calcium from Picea rubens leaves, which can lead to delayed responses in stomatal closure during drought (Borer et al 2005), potentially limiting mechanisms that prevent leaf desiccation.…”