Ozone and/or Water Stresses Could have Influenced the Betula ermanii Cham. Forest Decline Observed at Oku-Nikko, Japan

Abstract

A serious forest decline of Betula ermanii Cham. has been observed at Mt. Mae-Shirane, Oku-Nikko, Japan, where high ozone (O3) concentration and severe water deficiency have been measured. In order to consider the possibility whether O3 and/or water stresses could have been the causes of the forest decline of B. ermanii, plant growth experiments were conducted in environment-controlled growth cabinets. Two-year-old seedlings of B. ermanii were exposed to either charcoal-filtered air (O3 concentration <5 ppb) or 50 ppb O3 (daily average, ranging between 20-100 ppb) for 123 days at 20.0/12.5 +/- 1.0 degrees C (day/night) and 70/80 +/- 7% relative humidity (day/night). Simultaneously, seedlings were treated with three watering regime: 1.0 < pF < 1.8 (no water stress), 1.8 < pF < 2.5 (mild water stress) or 2.5 < pF < 3.0 (severe water stress). O3 exposure significantly reduced the dry weights of leaf, root and the whole plant, while water stress significantly reduced the dry weights of each organ and the whole plant. Significant reductions of net photosynthesis, transpiration and stomatal conductance were also observed under O3 and/or water deficiency treatments, while contents of RuBP carboxylase/oxygenase (Rubisco), chlorophyll( a+b ) and some essential nutrient elements (N, P, K, Mg and Ca) were not markedly changed. It was suggested that the decrease in net photosynthetic rate induced mainly by stomatal closure was the major cause of the growth reduction under O3 and/or water stresses. No significant interactions between O3 and water stresses were observed in terms of the depression of dry matter production, which suggested that simultaneous stress treatments of O3 exposure and water deficiency could affect the tree growth of B. ermanii additively.

Ecophysiological Responses of Northern Birch Forests to the Changing Atmospheric CO2 and O3 Concentrations

“…We believe that the allocation pattern of N in a leaf changes and much N is needed for repair of damaged tissue, resulting in impaired photosynthesis. Some other researchers did not observe decreases in chlorophyll or Rubisco (Shimizu and Feng, 2007;Saleem et al, 2001) despite decreases in the photosynthetic rate (Shimizu and Feng, 2007). It is possible that the slower photosynthetic rate is due to a decrease in stomatal conductance as a result from exclusion of O 3 from leaves (Shimizu and Feng, 2007).…”

“…Although N concentration in green leaf is not affected by O 3 so much Shimizu and Feng, 2007;Karlsson et al, 2003;Oksanen and Rousi, 2001;Saleem et al, 2001;Oksanen and Saleem, 1999;Pääkkönen et al, 1998), N concentration in leaf litter (fallen leaves) increased by O 3 treatment, suggesting the impaired capacity of trans-locating N from senescent leaves to tree body (Uddling et al, 2005). This may lead increased N loss at the whole tree level.…”

“…High O 3 damages chloroplasts (Prozherina et al, 2003;Pääkkönen et al, 1998) and reduces the photosynthetic rate (Mäenpää et al, 2011;Shimizu and Feng, 2007;Uddling et al, 2005;Shavnin et al, 1999). This can be reflected in changes in chlorophyll fluorescence that reveals O 3 stress in photosynthetic pathways (Mao et al, 2012;Wittmann et al, 2007;Shavnin et al, 1999).…”

“…In terms of the reason why stomatal conductance does not increase despite increased density of stomata under elevated O 3 , the effectiveness of low stomatal aperture against O 3 stress, or impaired photosynthetic pathway by O 3 seems to be a good answer (Paoletti and Grulke, 2005). There are cases where stomatal conductance decreased by O 3 (Shimizu and Feng, 2007;Oksanen et al, 2005a;. Above-mentioned inhibition of photosynthesis caused by O 3 , or exacerbation by other stresses (Oksanen et al, 2005a; might cause the decrease in stomatal conductance.…”

“…Moreover, ozone stress also reduces the chance of C acquisition, with shorter leaf longevity (Oksanen, 2005;Uddling et al, 2005;Prozherina et al, 2003;, or with decreased leaf biomass Shimizu and Feng, 2007;Oksanen, 2001;Oksanen and Rousi, 2001), leaf area (Oksanen, 2001;Saleem et al, 2001;Oksanen and Saleem, 1999;Pääkkönen et al, 1998), and leaf number (Oksanen and Rousi, 2001;Pääkkönen et al, 1998) per tree, in addition to impaired photosynthesis. Such C deficiency may lead to the reduction in tree growth at elevated O 3 Shimizu and Feng, 2007;Karlsson et al, 2003;Oksanen, 2001;, which in turn reflects in the growth of tree organ.…”