Histological 

 Differentiation 

 Among Abiotic 

 Causes of Conifer 

 Needle Necrosis 



Clinton E. Carlson 

 Carma J. Gilligan 



INTRODUCTION 



Conifer needle necrosis and chlorosis can be induced by 

 several agents including salt (Spotts and others 1972); winter 

 drought (Carlson and Meyer 1973); air pollutants including 

 fluoride, sulfur oxides, reduced sulfurs (Treshow and Pack 1970; 

 Carlson and others 1974; Weinstein 1977); and presumably other 

 causes. Field studies of air pollution-related injury and damage 

 to conifers near emitting sources involve a great deal of subjec- 

 tivity in the identification of cause. Even though foliar chemical 

 analyses may indicate accumulation of a pollutant in a forest, 

 relationships of needle abnormalities to the contaminant may re- 

 main obscure (Treshow 1969). Solberg and Adams (1956), 

 Carlson and Dewey (1971), and Gordon (1972) suggested that 

 light microscopy of sections of affected needles may be diag- 

 nostic. Sections were made in a transition zone defined as a 

 ca. 0.08 in (2 mm) needle segment that includes healthy, chlo- 

 rotic, and necrotic tissue. However, Stewart and others (1973) 

 claimed that fluoride, salt, and winter damage caused virtually 

 identical histological changes within symptomatic needles. 



The purpose of this research was to determine whether abiotic 

 causes of necrosis induce differential symptomatology in conifer 

 needle tissue; the work involved laboratory and field studies. 



METHODS 

 Laboratory Study 



Two-year-old Pseudotsuga menziesii and Pinus ponderosa 

 seedlings were obtained in late winter from the Forest Service 

 nursery at Coeur d'Alene, Idaho, transplanted while dormant 

 to 8-inch clay pots, and placed in a greenhouse. The potting 

 medium was 70 percent nursery soil and 30 percent composted 

 sawdust. No fertilizer was added, and pots were watered evenly 

 every 3 or 4 days. Greenhouse temperature and humidity were 

 recorded on a hygrothermograph throughout the experiment. 

 The first 2 weeks following transplanting, greenhouse temper- 

 ature was kept at ca. 50° F (10° C) and photoperiod at 16 hours 



with 550 fc (foot-candles) to minimize transplant shock. Tem- 

 perature then was increased to 70° F (21 ° C) during the day and 

 was allowed to drop to 50° F (10° C) at night. Bud break oc- 

 curred ca. 3 weeks after transplanting. Needle development ap- 

 peared normal and there was no visible evidence of transplant 

 shock. Four months after transplanting, new foliage was fully 

 elongated and the seedlings were physiologically active. By this 

 time, temperature fluctuated diurnally between 50° to 91° F (10° 

 to 33° C) and light intensity varied between 500 and 6,000 fc, 

 depending on cloud cover. Relative humidity varied from 45 to 

 85 percent, averaging ca. 65 percent. Seedlings did not exhibit 

 adverse effects due to greenhouse environmental conditions. 



Several phytotoxic gases commonly emitted from industrial 

 sources located near coniferous forests and other abiotic stresses 

 often suggested as alternative causes of foliar injury were selected 

 as treatments. Seedlings of each species were randomly segre- 

 gated into eight groups of ten each. Each group of ten seedlings 

 was subjected to one of the following randomly assigned treat- 

 ments: control, excessive salt, drought, simulated winter drying, 

 sulfur dioxide (S0 2 ), hydrogen sulfide (H 2 S), ethyl mercaptan 

 (C 2 H 6 S), and hydrogen fluoride (HF). All treatments except 

 controls were administered specifically to develop foliar injury; 

 when injury was noted seedlings were removed to the normal 

 greenhouse environment. Treatments are detailed below. 



CONTROL 



Seedlings were placed in a stainless steel chamber of 18 ft 3 

 (.51 m 3 ) internal volume with plexiglass roof and windows. The 

 chamber was refrigerated to maintain relatively constant temper- 

 atures and light was provided with a bank of fluorescent and in- 

 candescent lights emitting about 1,500 fc at tree level. Temper- 

 ature was maintained at 68° to 77° F (20°to 25° C) and relative 

 humidity at 50 to 60 percent. 



Charcoal-filtered air was supplied to the chamber through a 

 Worthington air compressor at ca. 1 .77 ftVmin (50 1/min) for 72 

 hours. Seedlings were then removed to the normal greenhouse 

 environment. 



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