Survival of Poria Weirii on Paired Plots in Alder and Conifer Stands Poria
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Survival of Poria weirii on paired plots in alder and conifer stands Earl E. Nelson Pacific Northwest Forest and Range Experiment Station. Forest Service, United States Department of Agriculture, Forestry Sciences Laboratory, Corvallis. Oregon 97331, U.S.A. Abstract Cubes of Douglas-fir wood decayed by Poria weirii (Murr.) Murr. were buried for 12 months on paired plots in red alder and in conifer soils on the Cascade Head Experimental Forest. Survival of the fungus was not significantly different in the two soils, although pH was significantly lower and nitrate content significantly higher in alder soils. Even though effects on fungus survival were nil, red alder, for other reasons, might still be used to reduce damage caused by P. weirii root rot on areas of heavy infestation. Introduction Poria weirii (Murr.) Mum extensively damages stands of Douglas-fir (Pseudo- tsuga menziesii (Mirb.) Franco) and other conifers in the Pacific Northwest. The fungus spreads from stumps of trees infected in the previous rotation to roots of regeneration and along them, through root contacts, to adjacent trees. Spread of the disease in stands established in cutover infested sites might be reduced by interplanting species resistant to P. weirii attack. For example, western redcedar ( Thujaplicata Donn) or highly resistant native hardwood might be used with more susceptible but more valuable conifers such as Douglas-fir. Even though P. weirii would infect some of the planted conifers, spread would be greatly reduced by fewer root contacts between highly susceptible species. Similarly, a system of crop rotation using hardwoods to regenerate cutover infested sites might allow time for much of the P. weirii in stumps to die out before the next rotation of susceptible species. Red alder (Alnus rubra Bong.) is a promising candidate for interplanting or crop rotation where it is suited to the site. Soil enriched through nitrogen fixa- tion by red alder nodules may stimulate growth of adjacent or ensuing conifers and at the same time discourage development of P. weirii. Nitrate cannot be utilized by P. weirii but is used by competitive micro-organisms (Li et al., 1967). In addition, phenolic compounds present in alder litter and roots may restrict development of F. weirii as has been demonstrated in vitro (Li et al., 1969). Nelson (1968) reported reduced survival of P. weirii in alder as compared to conifer stands, but data supporting this conclusion could not be statistically analysed. To further examine possible effects of alder on P. weirii survival on the Cascade Head Experimental Forest, a similar study suited for statistical analysis was designed. Materials and methods Paired plots were established on the Cascade Head Experimental Forest near the Oregon coast. Twelve pairs were referenced to a trail beginning about elevation 30o ft (91 m) and ending at 800 ft (244 m) at points where patches of 155 Microbios 1975 12 155-158 75 ALDER CONIFER 5 10 11 12 PLOT PAIR Figure 1 Survival of P. weiriiin cubes buried 1 year in alder and in conifer soils. Table 1 Poria weiriisurvival and chemical and biological soil factors on 12 plot pairs Alder Conifer soil soil F Poria weirii survival (%) 2200 2400 029 Soil acidity (pH) 481 524 3767 Total nitrogen (%) 037 033 1.46 Noa nitrogen (ppm) 019 0 25 431 NO3 nitrogen (ppm) 1.07 073 8.33" NH ,t nitrogen (ppm) 1175 900 1-67 Bacteria/g soil ( x 10,000) 4410 6214 067 Actinomycetes/g soil ( 10,000) 704 638 028 Fungi/g soil ( x 10,000) 603 810 110 Results in all columns are mean values. Significant at 0 . 95 level. • • Significant at 0-99 level. 156 Microbios E. E. Nelson pure alder and pure conifer were easily accessible. One plot of each pair was in alder, the other in conifer (Douglas-fir; western hemlock, Tsuga heterophylla (Raf.) Sarg.; and Sitka spruce, Picea sitchensis (Bong.) Carr) type. Twelve 2 in (5 cm) wood cubes decayed by P. weirii had been cut earlier from one of three naturally infected Douglas-firs and were buried 8 in (20 cm) on each 3 ft X 4 ft (91 x 122 cm) plot. All 24 cubes buried on a plot pair were sawn from a single tree and appeared identical. Burial entailed (1) driving a 3-1- in (8 .g cm) stainless steel tube 8 in (20 cm) into the soil at the centre of each square foot of plot surface, (2) removing the core, (3) placing a cube in the hole, and (4) replacing the extracted soil core and lightly tamping it in place. Twenty-four representative cubes sampled for presence of the fungus before the experiment all contained viable P. weirii. Twelve months after burial, soil subsamples were taken with a i in (2 . 5 cm) sampling tube between the buried cubes at 6-8 in (15-2o cm) depth and combined into a single sample for each plot. Cubes were then removed with a shovel. Soil samples were partially air dried, screened through a 2 mm sieve, and split for analysis of pH, nitrogen (total, NH4, NO3, and NO2), and populations of bacteria, actinomycetes, and fungi. Cubes were brushed in running tap water to remove adhering soil, split on a radial or near radial plane, and chips cut from four points — centre, midway between centre and right, left, and lower edges of the split face — and trans- ferred onto malt agar slants. P. weirii could be identified in 10-r4 days by gross colony characteristics and presence of distinctive setal hyphae. Analysis of variance was used to test differences in soil properties and P. weirii survival between alder and conifer plots. Results Survival of P. weirii did not differ significantly between alder and conifer plots (Figure ). Survival rates of 24% in conifer soils and 22 % in alder compare with 22 % and o %, respectively, after 12 months in an earlier study (Nelson, 1968). Significant differences in pH and NO3 content did appear between alder and conifer soils (Table 1). Discussion Under conditions of this experiment, red alder did not reduce survival of P. weirii. However, lower pH and higher NO3 content of alder soils and perhaps other factors might affect other aspects of P. weirii disease development. For example, microbial competition on the surface of host roots might well be greater in the presence of the additional NO3 found in alder soils. Increased competition could then slow spread of the disease along an infected root and from infected to adjacent healthy roots. Certainly, red alder is itself highly resistant to infection and provides a barrier to disease spread by occupying the site, thus, separating roots of susceptible conifers. It has also been shown that nitrogen fixed in alder soils is beneficial to growth of associated conifers (Tar- rant, 1961). 157 Poria weirii survival Because of its soil-improving ability, initial rapid growth, and high resis- tance to P. warn, red alder might be considcied abovt (Abet species (either in mixture or by itself) in regenerating clearcuts containing numerous root rot centres. Silvicultural problems are inevitable but could be less troublesome than those confronted in trying to bring another rotation of Douglas-fir to commercial maturity on soils heavily infested with P. weirii. Before any silvicultural control measure can be explicitly recommended, however, research is needed on control of P. weirii using crop rotation or inter- planted resistant species and on the silviculture of resulting forests. References Li C. Y., Lu K. C., Trappe J. M., and Bollen W. B. 1967. Selective nitrogen assimilation by Poria Nature 213 814. Li C. Y., Lu K. C., Nelson E. E., Bollen W. B. and Trappe J. M. 1969. Effect of phenolic and other com- pounds on growth of Pona weir, in vitro. Microbios 3 305-11. Nelson E. E. 1968. Survival of Poria weirii in conifers, alder, and mixed conifer-alder stands. Res. Notes Pacif. N.W. Forest Range Expt Stn PNW-83. Tarrant R. F. 1961. Stand development and soil fertility in a Douglas-fir-red alder plantation. Forest Sci. 7 238— 45. Accepted 10 October 1974 158 Microbios E. E. Nelson News to Authors We can process your manuscripts for CYTOBIOS and MICROBIOS rapidly providing the typescript and illustrations have been carefully prepared in the correct style. Papers for MICROBIOS LETTERS will be published very swiftly indeed, and in many instances take only about EIGHT WEEKS from acceptance to publication. 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