The effects of pre-drying and fragmentation on the leaching on nutrient elements and organic matter from Phragmites australis (Cav.) Trin. Litter

Aquatic Botany, 14 (1982) 29--39

29

Elsevier Scientific Publishing Company, Amsterdam - - Printed in The Netherlands

THE EFFECTS OF PRE-DRYING AND FRAGMENTATION ON THE LEACHING OF NUTRIENT ELEMENTS AND ORGANIC MATTER FROM PHRA GMITES A USTRALIS (CAV.)TRIN. LITTER

VAGN J U H L LARSEN

Botanical Institute, University of Aarhus (Denmark) (Accepted for publication 16 December 1981)

ABSTRACT Larsen, V.J., 1982. The effects of pre-drying and fragmentation on the leaching of nutrient elements and organic matter from Phragmites australis (Car.) Trin. litter. Aquat. Bot., 14: 29--39. Leaching experiments with six differently treated types of Phragmites australis (Cav.) Trin. leaves and stems (fresh, air-dried, air-dried and fragmented, lyophilized, oven-dried at 70°C and 105 ° C) were carried out in the laboratory. It was found that larger amounts (actual and relative) of soluble components were leached from leaves than from stems. Average calculations show that between 75 and 124% of the initial content of Na ÷ and K ÷ were leached from leaves and 40--86% from stems. Sixty-four--l13% of Mg ÷÷and Ca ÷* were leached from leaves whereas 3--58% were lost from stems. It was further found that Na ÷ and K ÷ were leached from the litter at a rate greater than that of Mg** and Ca w. Pre-treatment significantly affected the leaching of ions and soluble organic matter from leaves and stems. Oven-drying of leaves decreased the initial leaching rate of Mg ~ and Ca +*, whereas fragmentation of stems resulted in an increased leaching of all ions. All types of pre-treatment significantly increased the leaching of soluble organic components from leaves and stems.

INTRODUCTION

Decomposition of dead organic matter has been a subject of study in the terrestrial as well as the aquatic environment. It has been f o u n d t h a t physical leaching is an important part of decomposition, and t h a t this process is largely responsible for the rapid initial loss of soluble components from decomposing litter. In decomposition experiments in woodland habitats Attiwill (1968), Gosz et al. (1973) and Strojan (1978) f o u n d that K ÷was almost entirely lost from the litter, whereas divalent ions such as Mg** and Ca ~ showed little or no change during decomposition. The behaviour of Na ÷ differs in the various studies. Attiwill (1968) f o u n d t h a t Na ÷ was lost from Eucalyptus litter, whereas an accumulation was observed in decomposing leaves from several species of deciduous trees by Gosz et al. (1973) and Strojan (1978). 0304-3770/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company

30 From the results of litterbag experiments, Boyd (1970) concluded that everything else being equal, leaching is much more intense in water than on land. Both field studies and laboratory experiments have shown that under aquatic conditions not only Na ÷ and K ÷, but also Mg~ and Ca ~* are lost during decomposition. It is usually found that Na ÷ and K ÷ are leached at higher rates than Mg~+ and Ca *+ (Latter and Cragg, 1967; Planter, 1970; Boyd, 1970, 1971; Mason and Bryant, 1975; Wohler et al., 1975), although deviations from this have been reported (McLachlan, 1971; Howard-Williams and Junk, 1976; Howard-Williams and Howard-Williams, 1978). Laboratory experiments by Planter (1970), McLachlan (1971) and Howard-Williams and Howard-Williams (1978) have shown that leaching is a very rapid process, most ions being leached from the litter in the first 24 h. Soluble organic substances are lost at a slower rate than ions, the leaching rate being largest during the first fourteen days to a month (Godshalk and Wetzel, 1978b; Howard-Williams and Junk, 1976; Wohler et al., 1975). The above results have been reached in studies in which a wide variety of species and differently pre-treated plant material were used. Fresh litter was used by Latter and Cragg (1967), Attiwill (1968), Gosz et al. (1973) and De la Cruz and Gabriel (1974). In the leaching experiments by McLachlan (1971) and Planter (1970) 'dry' grass (largely Eragrostis species) and air~lried, 0.5~cm segments of Phragmites stems were used. 'Oven
31

at 21--23°C. Material of this type is referred to as ADL (leaves) and ADS (stems). (d) Leaves and stems treated as in (c) b u t cut into 0.5-cm segments. Material of this t y p e is referred to as A D F L (leaves) and ADFS (stems). (e) Leaves and stems cut into 8-cm segments and oven
To find the initial content of mineral elements, ten samples of oven-dried (105°C) and ground leaves and stems (2 g) were digested in 20 ml of 4:1 concentrated HNO3 and HC104 and analyzed for Na ÷, K ÷, Mg++ and Ca ++. A conductivity meter CDM 3 (Radiometer, Copenhagen) was used for analyzing electrical conductivity. For the analysis of ions an atomic absorption spectrop h o t o m e t e r (Perkin-Elmer Model 503) with flame equipment was used. Prior to the Ca++ analysis 1% of lanthanum was added to all samples (Slavin et al., 1963). Results from the leaching experiments are given in ~S, p p m (mg 1"1 or mg kg -1) or % weight loss. To be able to convert the weight of pre-treated TABLE I Mean weight loss (in %) and standard error of the mean (in parentheses) of fresh, senescent leaves and stems of Phragmites after various_ treatments Material

Leaves Stems

AD*

6.82(0.36) 5.23(0.09)

Percent weight loss** AD+LY

D70

D105

11.95(0.15) 10.00(0.02)

12.30(0.08) 10.23(0.05)

13.78(0.73) 10.97(0.18)

*AD = air-drying (10 days). **AD + LY = air-drying and lyophilization (10 days); D70 = oven-drying at 70°C (3 days); D105 = oven-drying at 105°C (3 days).

32 material to fresh weight, the loss in weight of the different treatments of leaves and stems was determined. The results are given in Table I. Results from the different treatments were compared through a one-way analysis of variance in combination with pair-wise comparisons. R E S U L T S A N D DISCUSSION

Leaching of ions The initial c o n t e n t of ions in senescent Phragmites leaves is a b o u t 3--20 times greater than in dead standing stems (Table II). The contents of Na +, Mg`+ and Ca`+ (in stems) are comparable to those reported b y Seidel (1966), Riemer and Toth (1968) and Mason and Bryant (1975). The content of K ÷ is lower, however, and that of Ca`+ in leaves higher than found b y the above mentioned authors. TABLE

II

Mean concentration and range of Na ÷, K ÷, Mg** and Ca** (ppm dry weight) in leaves and stems of Phragmites (n=10) Ma~ri~

Leaves S~ms

Concen~ationin p p m Na +

Range

K ÷

Range

Mg ~

Range

Ca ~

Range

1254 141

1123--1412 98-- 170

1602 520

1446--1728 478-- 547

1612 121

1545--1695 107-- 127

9976 497

8372--10946 453-- 567

The initial difference in ion content b e t w e e n leaves and stems is also reflected in the amounts of ions leached from the t w o types of litter. The electrical conductivity increased to a b o u t 400--600/~S in the experiments with leaves, compared to only 25--35 pS for stems (Fig. 1). Figure 1 reveals other differences in the leaching of ions b e t w e e n leaves and stems. The most obvious difference is that an equilibrium seemed to be established after one to t w o days for leaves whereas the electrical conductivity increased continually in the experiments with stems. Figure 1, in combination with statistical analyses, shows that pre-treatment significantly affects the leaching of ions from b o t h types of litter (P < 0.05 during the first five days of the experimental period). Ions were eluted in lesser amounts from oven~iried than from fresh, air-dried and lyophilized leaves (P < 0.05 between Day 2 and Day 5), an effect that was n o t evident with stems. It can also be seen that fragmentation of air-dried stems resulted in a significantly increased leaching compared to all the other pre-treatments (P < 0.05 between min 30 and Day 5). Average calculations show that after 30 days of leaching 89--124% of the initial c o n t e n t of Na ÷, 65--93% of K ÷, 75--113% of Mg`+ and 64--104% of Ca `+ were lost from leaves. Na + and K ÷ were leached at rates greater than Mg`+

33 700

600

ADL

500

.~ . . / ~ /

.... .........

ADFL

400 300 >" 200 J

I00 a z I

10

50

100

1000 T iM£ (minutes]

STEMS

/

10.000

50.000

/~,,, /"

LYS

--

ADFS

> 20

,,l-"""

I

I0

1O0

% 000 TiME (minutes)

10.0O0

F i g . 1. C h a n g e s in t h e e l e c t r i c a l c o n d u c t i v i t y ( i n l e a v e s a n d s t e m s ( 3 . 0 g f r e s h w e i g h t 1" o f w a t e r ) • ..... • = LYL, LYS; a ~ = ADL, ADS; • .... • .... • = D105L, D105S. Bars indicate standard

I

50.000

~ S ) in d i s t i l l e d w a t e r in w h i c h Phragmites were immersed, o o = FRL, FRS; • = ADFL, ADFS; D ~ = D70L, D70S; error.

and Ca ~+ (Fig. 2). On average 76--80% of the total loss of Na ÷ and K + occurred during the first hour, and equilibrium was established soon afterwards. About 17 h were needed for a comparable leaching of Mg** and Ca +~ (62--85%) and equilibrium was established after about 2 days. Results for the leaching of K ÷ from lyophilized leaves (LYL in Fig. 2) have been omitted from these and future figures since it was found that significantly larger amounts of K ÷ were lost than were originally present in the leaves (P < 0.01). The differences observed between the leaching of Na ÷ and K ÷ compared to Mg ~ and Ca *+ are in agreement with results from Planter (1970), Boyd (1970) and Mason and Bryant (1975), and can be explained by the different mobilities of the ions in plants (Attiwill, 1968). Pre-treatment of leaves significantly affected the leaching of Mg** and Ca ~ (P < 0.05). The leaching of Na ÷ and K ÷ was not significantly affected.

34

20 LEAVES

/~\

o. 16 u. o 12 ~

"~

~

~

t~.~_ .t>,, .~.I~,~ t .T.. ~.

I~

. , . ~ , ' ~ ""

""

DIO5L ADLFRLO?0L ADFL

""

8

o c~

100

1000 10.000 TiME(minutes)

LEAVES

°I

501000

........

,,,~

.-''""

"~'t LYL t ......... t'""" AOFL

DT0 L

_.

B o

ltO

I00

t 1000

TiME

20

50.000

t 10.000

I

(minutes)

LEAVES

....

T ~"~I

. . . . . T''-.

.... ~

LYL

c~ 15 £

12

z zo ,j

I0

I00

I000 TiME (m;nutes)

120

.., LEAVES

I0.000

50.000

__..~...~I"-..I

100 o-80

u 60 ~0

z 20 .....,..--e "~ 1o

, 1oo

~ooo

TIME (minutes)

1o ooo

, 5o.00o

35

The loss of ions from either air
05

STEMS

.''~

~

jill'"

c~ 04 --

LYS AOFS ADS

FRS o

.-'''''''''

(~ 02

~

D105 -(

DTOS

~o~ 10

100

1000

10000

50000

TIME (m,nutes3

Fig. 3. Changes in c o n c e n t r a t i o n o f Mg++ (in p p m ) in d i s t i l l e d w a t e r in w h i c h Phragmites stems (3.0 g fresh w e i g h t 1"~ o f w a t e r ) were immersed, o o = FRL, FRS; • .... • = LYL, LYS; ~ A = ADL, ADS; • .... • = ADFL, ADFS; ~ D = D70L, D70S; • .... • = D105L, D105S. Bars indicate standard error. ~ indicate mean concentration (and range) if 1 0 0 % o f t h e i o n s h a d b e e n l e a c h e d .

F i g . 2. C h a n g e s i n c o n c e n t r a t i o n o f N a ÷, K ÷, Mg++ a n d C a ++ ( i n p p m ) i n d i s t i l l e d w a t e r i n w h i c h Phragmites l e a v e s ( 3 . 0 g f r e s h w e i g h t 1"~ o f w a t e r ) w e r e i m m e r s e d , o o = FRL; FRS; • .... • = LYL, LYS; a ~ = ADL, ADS; • .... • = ADFL, ADFS; D o = D70L, D70S; • ..... • = D105L, D105S. Bars indicate standard error.-~ indicate mean concentration (and range) if 100% of the ions had been leached.

36

Ca+* were lost from stems and no equilibrium was established at the end of the experimental period. The slower rate of leaching from stems than from leaves might be a result of the smaller diffusion gradients that will be established when the former type of litter is immersed in water. Another factor that may be of importance in this connection is the longer diffusion distance found in the thicker stems than in leaves. Unlike the above results, Planter (1970) found that K ÷ and Na ÷ were lost very rapidly from Phragmites stems, equilibrium being established after only 35--120 minutes. A possible explanation of this discrepancy is that Planter (1970) used cut, 0.5 cm stem segments which would result in lower diffusion distances, thus facilitating leaching. In the present study fragmentation of the stems actually resulted in an increased loss of ions (Figs. 1 and 3), and for Na÷ and K ÷ an equilibrium seemed to be established after about 17 h to 2 days.

Weight loss In addition to Na ÷, K ÷, Mg** and Ca**, other soluble components were also lost from the litter. According to Howard-Williams and Howard-Williams (1978) the loss can be attributed to leaching and decomposition of organic substances such as amino acids, aliphatic acids and sugars. The majority of soluble matter in Phragmites leaves was lost during the first 1--5 days (Table III), results comparable to those found by Kaushik and Hynes (1971) in leaching experiments with leaves of oak, elm, maple, beech and alder. After one month the leaching of both mineral elements and soluble organic compounds resulted in a weight loss that amounted to between 11.0 and 16.6% for leaves and 1.7--6.2% for stems (Table III). Some 85--98% of this weight loss can be attributed to the leaching of soluble matter other than Na ÷, K ÷, Mg** and Ca**. Pre-treatment of the litter significantly affected the loss of soluble components (P < 0.05 from Day 2 to Day 30). After 30 days the weight loss from all types of pre-treated/leaves and stems was significantly larger than that from fresh litter (P < 0!.05). A similar effect has been observed by Harrison and Mann (1975) and Godshalk and Wetzel (1978a) who found an increased leaching from pre
Laboratory experiments with leaves and stems of Phragmites australis (Cav.) Trin. have shown that leaching of ions and other soluble components differ for the two types of litter and that different types of pre-treatment significantly affect leaching. These findings indicate that, in order to be able to compare results, it is necessary to describe exactly not only the species, but also the plant part used, the type of pre-treatment and the exact conditions under which it was incubated.

FRL

*FR

= fresh; A D

S = stems.

= air-dried; A D F

3.1(0.3) 4.2(0.8) 1.6(0.9) 1.3(0.8) 1.6(0.2) 2.3(0.3) 1.8(0.6) 1.7(0.0)

FRS

P e r c e n t w e i g h t loss*

1 rain 1.6(1.1) 30 m i n 2.7(0.5) 60 m i n 4.7(0.6) 17 h o u r s 3.9(0.7) 2 days 8.9(0.3) 5 days 7.9(0.9) 15 d a y s 11.4(1.1) 30 d a y s 11.0(0.7)

Elapsed time

. ---1.7(0.1) 2.0(0.2) 2.8(0.2) 3.4(0.1)

ADS

---2.6(0.1) 1.8(0.1) 3.6(1.0) 3.5(0.2)

ADFS

= lyophilized, D 7 0

1.8(0.3) 1.8(0.4) 8.3(0.4) 10.1(0.3) 11.9(0.7) 11.4(1.1) 14.9(0.7)

.

ADFL

= air-dried a n d f r a g m e n t e d ; L Y

. . -1.1(0.5) 6.3(0.3) 10.6(0.7) 13.2(0.3) 13.9(0.3) 15.8(0.3)

ADL 2.9(0.0) 2.8(0.0) 2.0(0.2) 3.6(0.1) 4.5(0.1) 4.8(0.1) ---

LYS

0.8(0.1) 0.9(0.2) 0.8(0.0) 5.8(2.1) 2.0(0.2) 11.3(1.7) 2.8(0.1) 3.9(0.1)

D70S

--1.5(0.2) 8.3(0.3) 7.1(0.6) 12.7(0.7) 15.4(0.6) 16.6(1.9)

D105L

= o v e n - d r i e d at I 0 5 ° C ; L = leaves;

1.4(0.1) 2.0(0.2) 2.7(0.3) 12.2(1.0) 11.9(0.4) -13.6(0.2) 16.2(0.5)

D70L

= o v e n - d r i e d at 7 0 ° C , D I 0 5

4.4(0.1) 5.2(0.2) 4.0(0.3) 11.3(0.8) 15.1(0.2) 17.3(0.6) 13.5(0.1) 15.5(0.7)

LYL

4.1(0.2) 4.2(0.2) 4.1(0.2) 5.1(0.1) 4.1(0.1) 5.6(0.1) 6.3(0.3) 6.2(0.2)

D105S

Mean w e i g h t loss (in %) a n d s t a n d a r d e r r o r of t h e m e a n (in p a r e n t h e s e s ) of Phragmites l e a v e s a n d s t e m s a f t e r v a r i o u s p e r i o d s o f i m m e r s i o n in distilled water

T A B L E III

LO

38

The results reported in the present study do not give any definite answers as to which pre-treatment should be chosen in leaching/decomposition experiments. The use of fresh, senescent litter imitates what happens under natural conditions, but results in relatively large errors, during analysis. Often it is impossible to start all experiments immediately after collection of the material, and pre-drying is necessary to avoid uncontrolled decay. When storage is necessary a lenient pre-treatment should be adopted. The results of the present study indicate that air-drying and/or lyophilization are preferable to ovendrying and fragmentation. ACKNOWLEDGEMENTS

The author thanks Hans-Henrik Schierup for his critical reading of the manuscript, Else Brandt and Karin Bon~ for their technical assistance and David Clayre and Marianne Simonsen for their linguistic suggestions. REFERENCES Attiwill, P.M., 1968. The loss of elements from decomposing litter. Ecology, 49: 142--145. Boyd, C.E., 1970. Losses of mineral nutrients during decomposition of Typha latifolia. Arch. Hydrobiol., 66: 511--517. Boyd, C.E., 1971. The dynamics of dry matter and chemical substances in a Juncus effusus population. Am. Midl. Nat., 86: 28--45. De la Cruz, A.A. and Gabriel, B.C., 1974. Caloric, elemental, and nutritive changes in decomposing Juncus roemerianus leaves. Ecology, 55: 882--886. Godshalk, G.L. and Wetzel, R.G., 1978a. Decomposition of aquatic angiosperms. I. Dissolved components. Aquat. Bot., 5: 281--300. Godshalk, G.L. and Wetzel, R.G., 1978b. Decomposition of aquatic angiosperms. II. Particulate components. Aquat. Bot., 5: 301--327. Gosz, J.R., Likens, G.E. and Bormann, F.H., 1973. Nutrient release from decomposing leaf and branch litter in the Hubbard Brook Forest, New Hampshire. Ecol. Monogr., 43: 173--191. Harrison, P.G. and Mann, K.H., 1975. Detritus formation from eelgrass (Zostera marina L.): the relative effects of fragmentation, leaching, and decay. Limnol. Oceanogr., 20: 924-934. Hodkinson, I.D., 1975. Dry weight loss and chemical changes in vascular plant litter of terrestrial origin, occurring in a beaver pond ecosystem. J. Ecol., 63: 131--142. Howard-Williams, C. and Howard-Williams, W., 1978. Nutrient leaching from the swamp vegetation of Lake Chilwa, a shallow African lake. Aquat. Bot., 4: 257--267. Howard-Williams, C. and Junk, W.J., 1976. The decomposition of aquatic macrophytes in the floating meadows of a Central Amazonian Vgtrzea lake. Biogeographica, 7: 115--123. Kaushik, N.K. and Hynes, H.B.N., 1971. The fate of the dead leaves that fall into streams. Arch. Hydrobiol., 68: 465--515. Latter, P.M. and Cragg, J.B., 1967. The decomposition of Juncus squarrosus leaves and microbial changes in the profile of Juncus moor. J. Ecol., 55: 465--482. Mason, C.F. and Bryant, R.J., 1975. Production, nutrient content and decomposition of Phragmites communis Trin. and Typha angustifolia L. J. Ecol., 63: 71--95. McLachlan, S.M., 1971. The rate of nutrient release from grass and dung following immersion in lake water. Hydrobiologia, 37: 521--530. Planter, M., 1970. Elution of mineral components out of dead reed Phragmites communis Trin. Polsk. Arch. Hydrobiol., 17: 357--362.

39 Riemer, D.N. and Toth, S.J., 1968. A survey of the chemical composition of aquatic plants in New Jersey. New Jersey Agricultural Experiment Station, Bulletin 820, 14 pp. Schierup, H.-H. and Larsen, V.J., 1981. Macrophyte cycling of zinc, copper, lead and cadmium in the littoral zone of a polluted and a non-polluted lake. I. Availability, uptake and translocation of heavy metals in Phragmites australis (Cav.) Trin. Aquat. Bot., 11: 197--210. Seidel, K., 1966. Reinigung yon Gew~ssern durch hShere Pflanzen. Naturwissenschaften, 53: 289--297. Slavin, W., Spraque, S. and Manning, D.C., 1963. The determination of calcium by atomic absorption spectrophotometry. Perkin-Elmer Newsletter, 15: 49--56. Strojan, C.L., 1978. Forest leaf litter decomposition in the vicinity of a zinc smelter. Oecologia, 32: 203--212. Wohler, J.R., Robertson, D.B. and Laube, H.R., 1975. Studies on the decomposition of Potamogeton diversifolius. Bull. Torrey Bot. Club, 102: 76--78.