Allelopathic Interference of Black Walnut Trees with Nitrogen-Fixing

C h a p t e r 18

Allelopathic Interference of Black Walnut Trees with Nitrogen-Fixing Plants in Mixed Plantings Felix Ponder, Jr.

Downloaded by MONASH UNIV on April 10, 2016 | http://pubs.acs.org Publication Date: January 8, 1987 | doi: 10.1021/bk-1987-0330.ch018

Forestry Sciences Laboratory, North Central Forest Experiment Station, U.S. Department of Agriculture Forest Service, Carbondale, IL 62901

The concentration of juglone (5-hydroxy-l, 4naphthoquinone), an allelopathic chemical produced by black walnut (Juglans nigra L.), was significantly lower in soil beneath plots of walnut trees mixed with autumn-olive (Elaeagnus umbellata Thunb.) than beneath plots of walnuts mixed with European alder (Alnus glutinosa (L.) Gaertn.) or walnuts alone. The number of nitrifying bacteria varied among treatments. Significantly more Nitrobacter inhabited the soil in plots of walnut mixed with European alder than in plots of walnut mixed with autumn-olive or walnut alone. Apparently juglone concentrations were not sufficient to inhibit populations of these nitrifying microorganisms. A tree incorporates nutrients, water, light, and metabolites to control its health and growth. Additionally, the tree must adapt to the presence of other organisms and to its environment. The direct or indirect inhibitory or stimulatory effect of one plant (including microorganisms) on another through the production of chemical compounds that escape into the environment is termed allelopathy (I) . One of the most prominent allelopathic responses in forestry is the effect of juglone from black walnut (Juglans nigra L.) on associated vegetation. The implications of juglone in black walnut management are of interest because black walnut has a high timber value and because some of the fastest-growing, plantation, black walnuts are planted in mixtures with nitrogen-fixing species such as autumnolive (Elaeagnus umbellata Thunb.), European alder (Ainus glutinosa (L.) Gaertn.), or herbaceous legumes. Therefore, interference may affect the growth of walnut. The term "interference" includes the overall deleterious effects of both competition and allelopathy in interplant relationships (2^) . Early evidence of black walnut allelopathy. As early as 77 A.D., the Juglans genus was cited as having a poisonous effect on other plants. An even earlier account was recorded by Pliny the Elder in This chapter not subject to U.S. copyright. Published 1987 American Chemical Society

Waller; Allelochemicals: Role in Agriculture and Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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ALLELOCHEMICALS: ROLE IN AGRICULTURE AND FORESTRY

h i s N a t u r a l i s H i s t o r i a about 1 A . D . , when he w r o t e : " t h e shade o f the walnut even caused headaches i n man and i n j u r y t o a n y t h i n g planted i n the v i c i n i t y " (3). J u g l o n e , a pigment i n b l a c k w a l n u t , was f i r s t s u g g e s t e d t o be t h e p h y t o t o x i c agent by Massey ( 4 ) ; t h i s was l a t e r c o n f i r m e d by D a v i s ( 5 ) . Chemically, the a c t i v e i n g r e d i e n t i s a p h e n o l i c compound t h a t h a s t h e c h e m i c a l f o r m u l a 5 - h y d r o x y - l , 4 naphthoquinone. J u g l o n e and/or i t s immediate p r e c u r s o r s a r e p r e s e n t i n t h e g r e e n l e a v e s , g r e e n h u l l s , b a r k , bud s c a l e s , f l o w e r s , phloem, and r o o t s of t r e e s i n t h e walnut f a m i l y . The degree o f j u g l o n e t o x i c i t y d i f f e r s g r e a t l y depending upon the i n t e r c e p t i n g s p e c i e s . F o r example, under f i e l d c o n d i t i o n s , j u g l o n e i s h i g h l y t o x i c t o tomato ( L y c o p e r s i c o n s p p . ) ( 6 ) , b u t beans ( P h a s e o l u s s p p . ) may (7_) o r may n o t be a f f e c t e d ( 8 ) . But when i n j e c t e d , j u g l o n e a f f e c t s bean and tomatoes s i m i l a r l y , by r e d u c i n g their respiration rates. The d i f f e r e n t i a l t o x i c i t y o f walnut t r e e s on o t h e r v e g e t a t i o n i n t h e f i e l d may be due t o d i f f e r e n c e s i n t h e a b i l i t y of p l a n t s t o r e l e a s e j u g l o n e from t h e g l u c o s i d e form i n which i t n o r m a l l y o c c u r s i n walnut t i s s u e ( 9 ) . Some p l a n t s may a v o i d exposure t o j u g l o n e because t h e i r r o o t systems a r e t o o s h a l l o w t o come i n t o c o n t a c t w i t h w a l n u t r o o t s ; o t h e r s may be a b l e t o w i t h s t a n d the s t r o n g o x i d i z i n g e f f e c t o f t h e p h y t o t o x i n ( 1 0 ) . T o x i c e f f e c t s due t o j u g l o n e p e r s i s t i n n a t u r e even a f t e r t h e w a l n u t t r e e s a r e dead (11) . J u g l o n e i s r e l e a s e d e i t h e r by l e a c h i n g and e x u d a t i o n from f o l i a g e , t h e f r u i t s , t h e b a r k , and t h e r o o t s o r by decomposition. I n t h e s o i l , j u g l o n e may be decomposed by m i c r o organisms o r adsorbed onto c l a y s o r o r g a n i c m a t t e r . Thus, t h e s o i l i s an i m p o r t a n t f a c t o r i n t h e a l l e l o p a t h i c i n t e r a c t i o n s caused by juglone (12). A l l e l o p a t h i c e f f e c t s o f j u g l o n e on n i t r o g e n - f i x i n g m i c r o o r g a n i s m s . Growth of b l a c k w a l n u t i n c r e a s e s when p l a n t e d w i t h t r e e s such as b l a c k l o c u s t ( R o b i n i a p s e u d o a c a c i a L . ) ( 1 3 ) , European b l a c k a l d e r ( 1 4 ) , and t h e shrub a u t u m n - o l i v e ( 1 5 ) , which form a s y m b i o t i c a s s o c i a t i o n with s o i l microorganisms to f i x n i t r o g e n . Although black w a l nut i s known t o i n h i b i t t h e growth o f a s s o c i a t e d p l a n t s , t h e e f f e c t s of j u g l o n e on s y m b i o t i c n i t r o g e n - f i x i n g s o i l m i c r o o r g a n i s m s have n o t been i n v e s t i g a t e d e x t e n s i v e l y . The n i t r o g e n - f i x i n g m i c r o o r g a n i s m s a s s o c i a t e d w i t h t h e r o o t s o f a u t u m n - o l i v e and European a l d e r b e l o n g t o t h e genus F r a n k i a . Dawson e_t a l . (16) r e p o r t e d t h a t t h e growth of F r a n k i a c u l t u r e s d e c r e a s e d as t h e j u g l o n e c o n c e n t r a t i o n i n c r e a s e d . V o g e l and Dawson (17) a l s o s t u d i e d t h e e f f e c t s o f j u g l o n e on F r a n k i a i s o l a t e s i n c u l t u r e and on t h e n o d u l a t i o n o f European a l d e r i n s o i l . They r e p o r t e d t h a t t h e t o t a l p r o t e i n c o n t e n t of t h e i s o l a t e s was reduced s i g n i f i c a n t l y by j u g l o n e a t 1 0 " ^ M c o n c e n t r a t i o n , b u t the degree o f growth i n h i b i t i o n v a r i e d w i t h F r a n k i a i s o l a t e s . Nodulation of b l a c k a l d e r i n p r a i r i e s o i l i n o c u l a t e d w i t h a F r a n k i a i s o l a t e from r e d a l d e r (A. r u b r a Bong.) was s i g n i f i c a n t l y d e c r e a s e d at j u g l o n e c o n c e n t r a t i o n s o f 10~3 and 10~4 M . A l l e l o p a t h i c e f f e c t s o f j u g l o n e on n i t r i f y i n g b a c t e r i a . I am unaware of any r e p o r t s d e a l i n g s p e c i f i c a l l y w i t h j u g l o n e as an i n h i b i t o r of n i t r i f i c a t i o n , b u t t h e r e have been s e v e r a l r e p o r t s o f i n h i b i t i o n o f n i t r i f i c a t i o n i n g r a s s l a n d and a few r e p o r t s i n d i c a t i n g i n h i b i t i o n i n forest s o i l . The c a u s a l agents i n b o t h s i t u a t i o n s have been


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i d e n t i f i e d as phenolic acids or phenolic glycosides (18-20). These aromatic compounds completely i n h i b i t e d the oxidation of ammoniumnitrogen to n i t r i t e - n i t r o g e n by Nitrosomonas at concentrations as low as 10" to 10~ M (20) . Oxidation of n i t r i t e - n i t r o g e n to n i t r a t e nitrogen by Nitrobacter required much higher concentrations of the inhibitors. Changes i n Nitrosomonas and Nitrobacter populations have been documented with changes i n the successional development of old f i e l d s to climax vegetation (20,21). The number of n i t r i f y e r s was high i n the f i r s t successional stage and decreased to a very low number i n the climax. It appears that i n h i b i t i o n of n i t r i f i c a t i o n s t a r t s during o l d - f i e l d succession and increases i n i n t e n s i t y as succession proceeds towards climax. Rice (22,23) found that many plants important i n o l d - f i e l d succession are very i n h i b i t o r y to selected strains of nitrogen-fixing and n i t r i f y i n g bacteria and concluded that most i n h i b i t o r s i d e n t i f i e d were phenolics. Thus, juglone might a f f e c t the growth of higher plants through i t s influence on s o i l microorganisms i n addition to i t s d i r e c t e f f e c t on the plants. 6


Allelopathic

8

A l l e l o p a t h i c e f f e c t s of juglone on young seedlings. Juglone may retard growth and i n h i b i t seed germination by disrupting c e l l d i v i s i o n . Rietveld (24) conducted experiments to determine juglone s e n s i t i v i t y of 16 plant species that were among those being considered for interplanting with black walnut as nurse species. He reported that seed germination and r a d i c l e elongation were affected by juglone i n 6 and 11 species, respectively, mainly by the higher concentrations (10""3 and 10"^ M). Of the species tested, European alder and autumn-olive were most s e n s i t i v e . European alder has been observed to decline at age 8 years i n plantings when mixed with black walnut. It has been surmised that black walnut allelopathy was the most l i k e l y cause for the black alder decline (25). To gain more understanding of the European alder decline and because of our concern about the future growth of black walnut planted with nitrogen-fixing species, a study was i n i t i a t e d to measure s o i l juglone concentration and to estimate the number of Nitrobacter and Nitrosomonas bacteria i n a black walnut plantation containing plots of black walnut alone and i n mixture with European alder and autumn-olive. Methods and Materials The absence of data at planting for parameters to be measured i n the study l i m i t s comparisons to current conditions i n the plantation. The study was conducted on s o i l of a 15-year-old bottomland forest planting i n southern I l l i n o i s containing plots of walnut planted alone and mixed with either European alder or autumn-olive. European alder decline and mortality were already evident. Rows within the 29.6-x38.4-m plots were 3.7 m apart. Trees within the rows of walnut-alone plots were 4.9 m apart. In mixed p l o t s , the walnut trees and autumn-olive or European alder were spaced 2.4 m apart, thus achieving a 1:1 mixture of walnut to nitrogen-fixer. The height of walnut trees ranged from 1.5 m i n walnut-alone plots to 5.5 m i n mixed p l o t s . The height of autumn-olive and European alder averaged 5 and 7 m, respectively.



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S o i l samples were collected i n mid-November at a distance of 0.9 m from each walnut tree at depths of 0-8, 8-16, and 16-30 cm for juglone estimates. Special e f f o r t was taken to avoid locating sample plots near dead or declining European alder trees. Another set of samples was collected at 0.9 m from walnut trees i n the same plots at depths of 0-4, 4-8, 8-16, and 16-24 cm for Nitrobacter and Nitrosomonas counts. To determine juglone, s o i l was sieved through a 40-mesh sieve and dried for 24 h at 40° C. S o i l was leached with chloroform and the leachate was banded on s i l i c a gel G TLC plates and chromatographed with a solvent mixture of cyclohexane, chloroform, and g l a c i a l acetic acid (70:20:10) (26). Juglone was observed as a v i s i b l e yellow-orange band at Rf = 0.40 (27). The band was scraped from the plate, the juglone eluted from the gel with chloroform, and the solution f i l t e r e d , Juglone concentrations were measured spectrophotometrically with a Bausch and Lomb Spectronic 20 at 420 nm. The most probable number technique (MPN) was used to estimate the number of Nitrosomonas and Nitrobacter i n samples (28). Counts were made after inoculated tubes were incubated for 3 weeks at 28° C. Total and n i t r a t e nitrogen were determined by Kjeldahl and colorimetric methods, respectively (29,30). Organic matter was determined by the wet oxidation method of Walkley (31) . S o i l pH was determined with a glass electrode i n a 2:1 mixture of water and s o i l . Results The mean juglone concentration i n s o i l beneath plots of autumn-olive/ black walnut was s i g n i f i c a n t l y lower than i n s o i l beneath European alder/black walnut and black walnut-alone plots (Table I ) . Juglone concentrations also d i f f e r e d with sampled depth (Table I ) . S i g n i f i cantly higher concentrations were present at the 0-8 cm depth than at lower depths. Although the number of Nitrosomonas bacteria was greater than the number of Nitrobacter i n each treatment p l o t s , only Nitrobacter d i f f e r e d s i g n i f i c a n t l y among treatments (Table I I ) . Both Nitrosomonas and Nitrobacter counts decreased s i g n i f i c a n t l y with sampled depths. S o i l beneath European alder/black walnut plots had higher n i t r a t e nitrogen levels than s o i l s beneath autumn-olive/black walnut or walnut-alone plots (Table I I I ) . Mean t o t a l nitrogen did not d i f fer s i g n i f i c a n t l y between treatments. Mean organic matter was greatest i n the European alder/black walnut treatment, followed by the walnut-alone and autumn-olive/black walnut treatments (Table I I I ) . The mean pH was lowest i n the autumno l i v e /black walnut treatment, followed by the European alder/black walnut and walnut-alone treatments. Discussion The higher juglone concentrations i n the surface s o i l and within a few centimeters of the s o i l surface beneath the walnut was due to the presence of leaves, f r u i t , and roots. Juglone concentrations i n this bottomland plantation followed a pattern similar to treatment differences reported for a companion upland mixed planting (26). However, results from the present investigation showed juglone


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Table I. Juglone Concentration i n S o i l According to Depth and Treatment i n a Mixed Planting of Black Walnut and Nitrogen-fixing Species


Depth (cm)

Juglone concentration (yg/g s o i l ) Walnut Autumn-olive European alder alone and walnut and walnut

0- 8 8-16 16-30

3.72 a 0.85 b 0.65 b

2.25 a 0.50 b 0.25 b

3.65 a 0.95 b 0.55 b

Mean

1.74 a

1.00 b

1.72 a

Means followed by the same l e t t e r are not s i g n i f i c a n t l y d i f ferent at the 0.05 l e v e l according to Scheffe s method of contrast. T

Table I I . Mean Number of Nitrosomonas and Nitrobacter i n S o i l i n a Mixed Planting of Black Walnut and Nitrogen-fixing Species According to Depth and Treatment

Treatment

S o i l Depth (cm)

Nitrosomonas (MPN/g s o i l )

Nitrobacter (MPN/g s o i l )

European alder and walnut

0- 4 4- 8 8-16 16-24 Mean

2880 1460 793 495 1407 a

2325 235 85 20 666 a

Autumn-olive and walnut

0- 4 4- 8 8-16 16-24 Mean

2108 1735 478 205 1131 a

606 42 13 3 166 b

2028 1223 683 322 1064 a

429 29 10 4 118 b

Walnut alone

0- 4 4- 8 8-16 16-24 Mean

Means followed by the same l e t t e r are not s i g n i f i c a n t l y d i f ferent at the 0.05 l e v e l according to Scheffe's method of contrast.


200

Table


III. Mean T o t a l and N i t r a t e N i t r o g e n , O r g a n i c M a t t e r , i n S o i l Beneath B l a c k Walnut P l a n t e d i n M i x t u r e w i t h N i t r o g e n - f i x i n g Species


Depth (cm)

European a l d e r and walnut

0- 8 8-16 16-30 52-61 Mean

0.18 0.09 0.09 0.07 0.11 a

0- 8 8-16 16-30 52-61 Mean

3.1 2.9 2.4 1.8 2.6 a

0- 4 4- 8 8-16 16-24 Mean

3.50 2.00 1.59 1.40 2.12 a

0- 4 4- 8 8-16 16-24 Mean

4.60 4.73 4.87 5.03 4.81 a

Autumn-olive and walnut

T o t a l N i t r o g e n (%) 0.14 0.10 0.09 0.07 0.10 a N i t r a t e N i t r o g e m (ppm) 2.5 2.0 1.6 1.3 1.8 b O r g a n i c M a t t e r (%) 2.07 0.75 0.74 0.80 1.09 c

and pH

Walnut alone

0.15 0.10 0.09 0.08 0.11 a

2.1 1.5 1.5 1.3 1.6 b

2.51 1.29 1.24 1.16 1.55 b

PH 4.27 4.60 4.80 4.90 4.64 b

4.53 4.77 5.03 5.20 4.88 a

Means f o l l o w e d by t h e same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t the 0 . 0 5 l e v e l a c c o r d i n g t o S c h e f f e ' s method of c o n t r a s t .



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c o n c e n t r a t i o n s to be h i g h e r i n the 0-8 cm s o i l l a y e r f o r the autumno l i v e / w a l n u t t r e a t m e n t than i n the u p l a n d p l a n t a t i o n . The l o w e r mean j u g l o n e c o n c e n t r a t i o n i n s o i l under a u t u m n - o l i v e ( T a b l e I ) , when compared w i t h European a l d e r , i s p r o b a b l y a s s o c i a t e d w i t h m i c r o e n v i r o n m e n t a l c o n d i t i o n s t h a t enhance the breakdown of p l a n t organs and r e s u l t i n o x i d a t i o n o f j u g l o n e i n the s o i l . The canopy i n p l o t s mixed w i t h European a l d e r was more open t h a n i n p l o t s mixed w i t h a u t u m n - o l i v e , and more herbaceous v e g e t a t i o n was p r e s e n t i n t h e s e p l o t s than i n a u t u m n - o l i v e p l o t s . European a l d e r / b l a c k w a l nut p l o t s c o n t a i n e d clumps o f f e s c u e ( F e s t u c a a r u n d i n a c e a S c h r e b . ) , b l a c k b e r r y (Rubus s p p . ) , s c a t t e r e d g r a s s e s , and b r o a d l e a f weeds. Ground c o v e r i n a u t u m n - o l i v e p l o t s c o n s i s t e d o f s m a l l herbaceous p l a n t s and a 2 - t o 3 - c m - t h i c k l e a f l i t t e r l a y e r . The shade and c l o s e d canopy p r o v i d e d by a u t u m n - o l i v e r e d u c e d water l o s s due t o t r a n s p i r a t i o n and e v a p o r a t i o n i m m e d i a t e l y above the s o i l , k e e p i n g t e m p e r a t u r e s about 2° C lower i n the summer and about 3° C warmer i n the w i n t e r ( 15). A l l these d i f f e r e n c e s i n p l o t c o n d i t i o n s a s s o c i a t e d with treatments are b e l i e v e d to account for d i f f e r e n c e s i n s o i l j u g l o n e c o n c e n t r a t i o n s t h a t are r e f l e c t e d i n the m o r t a l i t y of the European a l d e r (25). The h i g h e r n i t r i f y i n g b a c t e r i a p o p u l a t i o n s i n the European a l d e r / b l a c k walnut p l o t s compared t o a u t u m n - o l i v e / b l a c k walnut and w a l n u t - a l o n e p l o t s s u g g e s t t h a t more j u g l o n e s h o u l d be m e t a b o l i z e d . However, t h i s does not appear t o be the c a s e . A p p a r e n t l y , the d i f f e r e n c e i n b a c t e r i a l p o p u l a t i o n s i s not r e l a t e d to any d i r e c t d e t r i mental e f f e c t of j u g l o n e on the b a c t e r i a because r e l a t i v e N i t r o b a c t e r c o u n t s were h i g h e s t i n European a l d e r / b l a c k walnut p l o t s where the j u g l o n e c o n c e n t r a t i o n was a l s o h i g h e s t . Treatment means f o r pH and o r g a n i c m a t t e r v a r i e d s i g n i f i c a n t l y between t r e a t m e n t s , e x c e p t f o r the pH between European a l d e r / b l a c k walnut and w a l n u t - a l o n e . A c c o r d i n g to A l e x a n d e r ( 3 2 ) , nitrification i s almost n e g l i g i b l e a t pH 5 . 0 . N i t r i f i c a t i o n i n s o i l beneath r e d a l d e r (Alnus r u b r a Bong.) was r e p o r t e d a t a pH as low as 3.5 (33). O b v i o u s l y n i t r i f i c a t i o n has not been e l i m i n a t e d i n s o i l beneath t r e a t m e n t p l o t s i n our s t u d y . The h i g h e r n i t r a t e - n i t r o g e n c o n c e n t r a t i o n i n European a l d e r / b l a c k walnut p l o t s ( T a b l e I I I ) appears t o be c o n s i s t e n t w i t h the h i g h e r n i t r a t e - n i t r o g e n and n i t r i f y i n g c a p a c i t y of r e d a l d e r i n mixed p l a n t i n g s or a l o n e ( 3 4 , 3 5 ) . These a u t h o r s c o n c l u d e d t h a t n i t r i f i c a t i o n was b e t t e r i n s o i l s beneath r e d a l d e r because of b e t t e r s o i l f e r t i l i t y , e s p e c i a l l y higher nitrogen content. However, we found t h a t a l t h o u g h n i t r a t e - n i t r o g e n was h i g h e s t i n European a l d e r / b l a c k walnut p l o t s , t o t a l s o i l n i t r o g e n d i d not d i f f e r s i g n i f i c a n t l y between t r e a t m e n t s . T h e r e f o r e , s o i l f e r t i l i t y a l o n e , as s u g g e s t e d by t o t a l n i t r o g e n , does not appear t o be r e s p o n s i b l e f o r t h e h i g h e r N i t r o b a c t e r c o u n t s i n European a l d e r / b l a c k walnut p l o t s t h a n i n o t h e r treatments. I t seems t h a t the h i g h n i t r a t e - n i t r o g e n c o n c e n t r a t i o n i n the European a l d e r / b l a c k walnut p l o t s i s the r e s u l t of a h i g h n i t r i f y i n g b a c t e r i a l p o p u l a t i o n t h a t can be a t t r i b u t e d t o u n d e r s t o r y v e g e t a t i o n d i f f e r e n c e s between t r e a t m e n t s . L o d h i (34) r e p o r t e d t h a t the number of Nitrosomonas and N i t r o b a c t e r showed a d i r e c t r e l a t i o n s h i p w i t h amounts o f n i t r a t e - n i t r o g e n but an i n v e r s e r e l a t i o n s h i p w i t h ammoni u m - n i t r o g e n , and t h e r e l a t i v e amounts of ammonium and n i t r a t e n i t r o gen a r e i n f l u e n c e d by the s u c c e s s i o n a l s t a g e o f the v e g e t a t i o n on t h e



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site. Rice and Pancholy (36) reported that the numbers of Nitrobacter per gram of soil were generally highest in the first successional stage, intermediate in the second successional stage, and lowest in the climax. The dominant vegetation in walnut-alone plots was broomsedge (Andropogon virginicus L.). Several plants of this genus inhabit old fields and have been shown to be very inhibitory to Nitrobacter and Nitrosomonas (37). The almost bare to sparsely covered understory under autumnolive in autumn-olive/black walnut plots has been attributed to reduced light intensity caused by the dense shade. The understory conditions rapidly approach those of a hardwood "forest" compared to the open European alder/black walnut and walnut-alone plots (38) . Thus, the autumn-olive shorten the time i t would normally take oldfield conditions to disappear (37). The overall height of autumnolive and the understory plot conditions have not changed in the last 4 or 5 years, while growth of the black walnut has continued at an improved rate (39). European alder/black walnut plots, compared to the other treatments, are undergoing vegetational disturbances due to the decline and death of European alder. The disturbance is probably responsible for the overall higher number of Nitrosomonas and significantly higher Nitrobacter counts. The number of nitrifiers and rate of nitrification increase with disturbance in the ecosystem (V) . Nitrosomonas and Nitrobacter increased by 18 and 34 times, respectively, after a forest clearcut in Connecticut (40). It appears quite likely that, in our study, vegetational disturbance has eliminated or prevented the establishment of plant species that may be inhibitory to nitrifying bacteria. Also, the larger nitrifying population in European alder/black walnut plots is consistent with the higher nitrate-nitrogen concentration in the same plots compared to autumn-olive/black walnut or walnut alone. In summary, there is l i t t l e reason to be concerned about allelopathy in mixed plantations where walnut is grown for timber as the harvested crop. Allelopathy does appear to be a factor to consider before planting European alder as a nurse crop with black walnut. Black walnut has had no apparent effect on the autumn-olive but is probably responsible for the decline and mortality of the European alder. These results present interesting possibilities for future research on the plant/soil/microbial relationships related to the metabolism of aromatics. Acknowledgment s I am grateful to Drs. Shawky and Mahasin Tadros of Alabama A&M University, Normal, AL, for their assistance in determining juglone concentrations and nitrifying bacteria, respectively. Literature Cited 1. Rice, E. L. "Allelopathy"; Academic Press: New York, 1984; pp. 1, 247-265. 2. Muller, C. H. Vegetatio 1969, 18, 348-57.



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3. Southern Illinois University Press. "Selections From the History of the World, By Plinius (Pliny) Secundus, C. 1 A.D."; English translation by P. Holland (selected and introduced by P. Turner); Southern Illinois University: Carbondale, 1964; p. 194-5. 4. Massey, A. B. Phytopathology 1925, 15, 773-84. 5. Davis, E. F. Am. J. Bot. 1928, 15, 620. 6. Brooks, M. G. "Effects of Black Walnut Trees and Their Products on Other Vegetation"; West Va. Univ. Agric. Exp. Stn. Bull. 347, 1951, p. 31. 7. Perry, S. F. Bull. Torrey Bot. Club 1967, 94, 26-30. 8. Strong, M. C. "Walnut Wilt of Tomato"; Mich. Agric. Exp. Stn. Quart. Bull. 1944, 26, 194-5. 9. Daglish, C. J. Pharm. Pharmacol. 1952, 4, 539-46. 10. Gries, G. A. North. Nut Grow. Assoc. Annu. Rep. 1943, 32, 52-5. 11. Gabriel, W. J. J. For. 1965, 73, 234-37. 12. Fisher, R. F. J. Soil Sci. Soc. Am. 1978, 42, 801-3. 13. Finn, R. F. J. For. 1953, 51, 31-3. 14. Plass, W. T. "Growth and Survival of Hardwoods and Pine Interplanted with European Alder"; USDA For. Serv. Res. Pap. 1977, NE-376. 15. Funk, D. T.; Schlesinger, R. C.; Ponder, F., Jr. Bot. Gaz. 1979, 140 (Suppl.), 110-14. 16. Dawson, J. O.; Knowlton, S.; Sun, S. H. "The Effect of Juglone Concentration on the Growth of Frankia in vitro"; For. Res. Pap. 81-2, Dep. For., Univ. Ill.: Champaign-Urbana, 1981. 17. Vogel, C. S.; Dawson, J. O. Plant and Soil 1985, 87, 79-89. 18. Lodhi, Μ. A. K. Am. J. Bot. 1976, 63, 1-8. 19. Lodhi, Μ. A. K. Am. J. Bot. 1977, 64, 260-4. 20. Rice, E. L.; Pancholy, S. K. Am. J. Bot. 1974, 61, 1090-1103. 21. Rice, E. L.; Pancholy, S. K. Am. J. Bot. 1962, 59, 1033-40. 22. Rice, E. L. Ecology 1964, 45, 824-37. 23. Rice, E. L. Physiol. Plant. 1965, 18, 255-68. 24. Rietveld, W. J. J. Chem. Ecol. 1983, 9, 295-308. 25. Rietveld, W. J.; Schlesinger, R. C.; Kessler, K. J. J. Chem. Ecol. 1983, 9, 1119-33. 26. Ponder, F., Jr.; Tadros, S. H. J. Chem. Ecol. 1985, 11, 937-42. 27. Hedin, P. Α.; Langhans, V. E.; Graves, C. H. J. Agric. Food Chem. 1979, 27, 92-4. 28. Alexander, M.; Clark, F. E. In "Methods of Soil Analysis, Part 2"; Black, C. Α., Ed.; Agronomy Monograph No. 9. Am. Soc. Agron.: Madison, WI, 1965; p. 1467-72. 29. Bremner, J. M. In "Methods of Soil Analysis, Part 2"; Black, C. Α., Ed.; Agronomy Monograph No. 9. Am. Soc. Agron.: Madison, WI, 1965; p. 1449-64. 30. Carson, P. L. In "Recommended Chemical Soil Test Procedures for the North Central Region"; North Dakota Agric. Exp. Stn. Bull. 499, 1964, 13-5. 31. Walkley, A. Soil Sci. 1947, 63, 251-64. 32. Alexander, M. "Introduction to Soil Microbiology"; Wiley and Sons: New York, 1961; p. 273-75. 33. Bollen, W. B.; Lu, Κ. C. In "Biology of Alder"; Trappe, J. M.; Franklin, J. F.; Tarrant, R. F.; Hansen, G. Μ., Eds.; Pac. Northwest For. Range Exp. Stn.: Portland, OR, 1968; p. 141-48.


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34. 35. 36. 37.

Bollen, W. B.; Wright, E. Can. J. Microbiol. 1961, 7, 785-92. Lodhi, Μ. A. K. Am. J. Bot. 1978, 65, 340-4. Rice, E. L.; Pancholy, S. K. Am. J. Bot. 1963, 40, 691-702. Rice, E. L. In "The Grasses and Grasslands of Oklahoma"; Estes, J. R.; Tyrl, R. J., Eds.; Noble Foundation, Ardmore, OK, 1976; p. 90-111. 38. Spurr, S. H. "Forest Ecology"; Ronald Press Company: New York, 1964; p. 179. 39. Schlesinger, R. C.; Williams, R. D. For. Ecol. Manage. 1984, 235-43. 40. Smith, W. H.; Bormann, F. H.; Likens, G. E. Soil Sci. 1968, 106, 472-3.


RECEIVED January 21, 1986


Allelopathic Interference of Black Walnut Trees with Nitrogen-Fixing

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