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Soil respiration in a tropical grassland
0038-0717/81/04026108102.oo/o Copyright 0 1981 Pergamon Press Ltd
Soil Bin/. Biorhrm. Vol. 13. pp. 261 to 268. 1981 Printed in Great Britain. All rights reserved
SOIL
RESPIRATION IN A TROPICAL GRASSLAND S. R. GUPTA and J. S. SXNGH*
Department of Botany, Kurukshetra University, Kurukshetra-132 119, India (Accepted 20 December 1980) Summary-Soil respiration throughout an annual cycle was measured at three different stands in a tropical grassland situated at Kurukshetra at 29”58’ N lat. and 76”51’ E long. Rates of CO* evolution were measured by alkali absorption using 13 cm dia x 23 cm aluminium cylinders inserted 10 cm into the ground. Both movable and permanently-fixed cylinders were used. The COs evolution rates for the three stands were: Stand I (dominated by Sesbaniabispinosa)49-358 mg CO2 m-’ h- ‘; Stand II (mixed grasses) 55-378 mg CO2 m-’ h-i; and Stand III (dominated by Desmosrachyo bipinnata) 55-448 mg CO2 m-* h-‘. A positive significant relation existed between rate of CO2 evolution and soil water content (r = 0.59-0.74), and between soil respiration and temperature (r = 0.58-0.69). A statistical model developed on the basis of the relationship between CO2 evolution rates and certain abiotic environmental factors showed 69% comparability between the calculated and .observed values of soil respiration. The contribution of root and root-associated microorganisms to total soil respiration was estimated at 42% using the relationship between root biomass and COs output from movable cylinders.
INTRODUCTION
LundegFtrdh (1927) defined soil respiration as the sum
total of all soil metabolic functions in which CO2 is produced. It includes three biological processes, namely, microbial respiration, root respiration and fauna1 respiration and a non-biological process, i.e. chemical oxidation which may be particularly pronounced at high temperatures (Bunt and Rovira, 1954). Soil microorganisms such as bacteria and fungi play a major role in releasing CO2 by metabolizing organic debris. In a mesic deciduous forest in Eastern Tennessee, Reichle et al. (1975) have reported that the microflora contributes over 99% of the decomposer CO,. The soil fauna also has a marked effect on total soil metabolism and is responsible for about 20% of energy release from organic matter within the soil decomposer community (Macfadyen, 1963). The contribution of root respiration to total soil respiration is often estimated at 50% (Macfadyen, 1970). Most reports on soil respiration (Singh and Gupta, 1977) are from temperate countries with only a few from the tropics (Bal, 1926; Schulze, 1967; Wanner, 1970; Medina and Zelwer, 1972; Wanner et al., 1973; Lamotte, 1975; Gupta and Singh, 1977). We determined the seasonal variation in rates of CO2 evolution, the effect of vegetation and time of enclosure of ground area on the rate of soil respiration, the relationship of soil respiration to certain weather variables and the contribution of root respiration to total soil respiration in a tropical grassland. MATERIAL
AND
METHODS
The study site is situated at Kurukshetra (29’58’ N lat. and 7651’ E long.), approximately 250m above sea level. The alluvial soil is slightly calcareous in
* Present address: Department of Botany, Kumauo University, Naioi Tal-263 002, India.
nature with a pH of 8.8 + 0.11. The organic C, poro-
sity and water holding capacity of soil were 0.55 f 0.060/, 49.0 + 3.61% and 51.06 + 1.33%, respectively in the month of June, 1976. The climate is tropical monsoonal (Singh and Yadava, 1974) with a warm wet period (June-Septernbet), a cool dry period (October-February) and a hot dry period (March-May), see Fig. 1. The vegetation of the study site is composed of three stands. Stand I is dominated by Sebania bispinosa (Jacq.) W. F. Wight; stand II is represented by a mixture of grasses such as, Aristida adscensionis Linn., Bothriochloa pertusa (L.) A. Camus, Cenchrus setigerus Vahl, Chloris barbata (L.) SW., Dichanthium annulatum (Forsk.) Stapf., Sporobolus coromendelianus (Retz.) Kunth, Sporobolus diander (Retz.) Beauv.; and stand III is dominated by Desmostachya bipinnata (L.) Stapf. The areas occupied by the different stands were determined by running a number of line transects. Thus stands I, II and III accounted for 24, 36 and 40% of the total study area, respectively. Soil respiration was measured in each stand throughout 14 months. The soil respiration rate for the grassland as a whole was calculated as an area weighted mean from the results for each stand. Soil respiration was measured using an alkali absorption method (Gupta and Singh, 1977) using 13 cm dia x 23 cm tall aluminium cylinders inserted 10 cm deep into the ground. Ten cylinders (three each in stands I and III, and four in stand II) were fixed in the ground at randomly-determined locations in the grassland in the first week of July 1975. These cylinders were left in place and CO1 evolution was determined every l-3 weeks from July 1975 to August, 1976. The first determinations of COz production were made 1 week after the cylinders had been inserted in the soil. A second set of ten cylinders (three each on stands I and III, and four on stand II) were also installed at randomly-determined locations in the fields in the 261
S.
262 400 -
-
zoo-
!
= e E cr
R.
GUPTA and
J. S.
SINGH
Ramfall
----
Temperature
-.-.-
So11 water
200-
100 -
0’
Jul 1975
Sep
Aug
Ott
Dee
Nov
Jan 1976
Feb
Mar
Apr
Jun
May
0
Jul
Aug
Fig. 1. Soil water content, mean of preceding total daily air temperature and preceding total rainfall data for the dates during which soil respiration was measured.
first week of July. 1975. These cylinders were moved to new but comparable locations every month from July to October. 1975 to determine the effect to the time of enclosure on CO, production. During the post-monsoon period, the soil became relatively hard and it was not possible to move the cylinders to new locations without major disturbance of the enclosed area. Therefore, the cylinders were moved again only in the last week of February, 1976 and then in the first week of June, 1976. On each date of measurement. soil water content was determined by taking three 5 x 1Ocm deep soil cores from areas adjacent to the cylinders. Weighed soil samples from these cores were dried at 105’C to constant weight and the percentage soil water content was calculated on a dry weight basis (Fig. 1). With the second set of cylinders, the soil was excavated each time after the cylinders were moved to new locations, while from the first set of cylinders (permanently-fixed), the soil was excavated when the experi-
ments were completed in August, 1976. The excavated soil was analysed for root biomass (g m-‘). RESULTS
Soil respirafion
AND DISCUSSION
rates
It was evident that the seasonal
trend of CO1 evolution from permanently-fixed cylinders and from movable cylinders was similar, Fig. 2 (stand I). Fig. 3 (stand II). and Fig. 4 (stand III). But differences did occur in the magnitude of soil respiration in the two sets of cylinder sampled on similar days. These differences will be discussed later. The soil respiration for the entire grassland was calculated as an area-weighted mean for each date using soil respiration values from permanently-fixed cylinders of the three stands from July 1975 to January 1976, and from movable cylinders from February to- August 1976 (Fig. 5). The values for movable cylinders were higher than those for permanently-
p-4
(a)
{--+
(b)
r
I.
0
July 1975
A
S
0
I
N
I
D
I
Jan I976
I
F
t
1
M
A
r
I
M
I
J
I
J
I
A
Months
Fig. 2. Seasonal variation in soil respiration on Stand I from 18 July 1975 to 31 August 1976 (a) permanently-fixed cylinder, (b) movable cylinder.
263
Soil respiration 500-
400
-
k ?
E 8 N
300 -
iz s i_ .-e
200
f l
% cn
100 -
I
0
July
S
A
,
I
Jan 1976
D
N
0
197’5
I
F
M
I
I
A
M
I
J
J
J
A
MOfhS
Fig. 3. Seasonal variation in soil respiration on Stand II from 18 July 1975 to 31 August 1976. (a) permanently-fixed cylinder, (b) movable cylinder.
effect of soil moisture and moderate temperatures on microbial activity and root metabolism. During the summer months, low soil moisture contents became a factor limiting soil heterotroph and root metabolism. The combined effect of low soil moisture content and low temperature resulted in decreased soil metabolic activities during the winter months.
fixed cylinders during the period February to August, 1976; therefore, the results from movable cylinders were used for this period. The seasonal pattern of soil respiration showed that the rates of CO2 evolution were maximum during the rainy season, except for the periods when the soil became saturated with water; this was followed by the summer months and was lowest during the winter. Analysis of variance indicated a significant difference in the rate of soil respiration among different sampling dates (P < 0.001) for all three stands. The higher rates during the rainy season reflect the favourable
Effect of vegetation on soil respiration rates
The CO2 output from permanent cylinders showed differences in the magnitude of soil respiration between the three stands. The soil respiration
600 i
&$ &--[
500 t
I= r
(a) (bl
400-
E N
8
F
300-
i-5 .-i
200 -
.% cn 100 -
0'
I
I
July 1975
A
S
0
I
t
I
N
D
Jan
I
I
F
M
I
,
A
M
J'J
I
,
A
1976
Months Fig. 4. Seasonal variation in soil respiration on Stand III from 18 July 1975 to 31 August 1976. (a) permanently-fixed cylinder, (b) movable cylinder.
S.
264 Calculated
o---o
R.
GLPTA
and J. S. SINGH
soil metabolism was probably more controlled by adverse climatic conditions than by the vegetation. Similarly, the insignificant differences in the values for 12-28 July, 1976 were due to depressed rates of COz evolution because the soils were waterlogged.
soil restitution
-$
‘E
3 0’
a
’
18July A 1975
S
a
h
0
N
D Jan F 1976
c
h
M
A
J
M
Months
Fig. 5. Seasonal trends in soil respiration from July 1975 to May 1976. The actual rates are compared to calculated values from a statistical model for all sites of grassland.
(mgCOz me2 hh’) values varied from 49 + 5.2 to 358 li: 22.0 on stand I. from 55 i 8.5 to 378 _t 16.2 on stand II. and from 55 + 5.7 to 448 * 35.1 on stand III. Thus. soil respiration seems to be htghest in stand III. This may be due to a higher root biomass in stand III (Table 1). The values of soil respiration for different dates were subjected to an analysis of variance to test for the differences in the rates among the three stands. No significant difference was found for the values from the three stands for all dates from July 1975 to August 1976. Nevertheless, on 13 out of 43 sampling dates. the differences were significant. From soil respiration values plotted Figs 2. 3 and 4, it is clear that for those dates when the soil respiration values were low, the differences between the stands were not significant. For example. from 30 October, 1975 to 8 March, 1976. CO* evolution rates were low with insignificant differences between the stands. This period was characterized by low soil water contents and cool temperatures. Thus,
Table
1. Root biomass
Date cylinders were installed
from movable
The effect of time of enclosure on the measurement of soil respiration was determined by comparing the CO2 evolution rates from permanently-fixed cylinders with those from movable cylinders. There was no appreciable difference between the CO2 outputs of the two series of cylinders from July. 1975 to January 1976 (Figs 2, 3 and 4). From 3 February, 1976 to 16 May, 1976. the CO: evolution rates were higher from movable cylinders at all of the stands. However. the outputs when compared by t-test for difference of means indicate that there was no significant difference in soil respiration between two series of cylinders on most of the dates during this period. From 9 June to 31 August, 1976. soil respiration rates were significantly different between two sets of cylinders in stands I and III, whereas in stand II the rates differed significantly on eight dates out of a total of 13. From the preceding discussion it is evident that there was no short-term effect of time of enclosure on CO-, output rates. But when the cylinders were moved to new locations about 6 months later than the installation of permanent-cylinders, the rates of CO2 evolution were highest from the movable-cylinders. The root biomass in the individual stands did not vary appreciably from July to October, 1975 but the root biomass was highest in stand III (Table 1). The root biomass decreased substantially from February to June. 1976. A comparison of root biomass in permanent cylinders (excavated on 4 September. 1976) with that in movable cylinders (excavated in last week of July. 1975) showed a 87”, decrease in the permanent cylinders on stand I. while on stands II and III the root material decrease in these cylinders amounted to 84 and 56”“. respectively. It was observed that there were no fragments of litter left in the permanent cylinders, From the effect of enclosure on the measurement of soil respiration. it can be concluded that the movable cylinders gave a more accurate estimate of the CO2
and permanent cylinders” (Mean f 1 SE)
Date cylinders were removed
Root biomass Stand
on the three stands
on the date of removal tg me21 Stand II
1
of cylinders Stand
III
Movable
6 July 1975 8 Aug. 1975 18 Sept. 1975 6 Oct. 1975 26 Nov. 1975 26 Feb. 1976 1 June 1976
20 July 1975 30 Sept. 1975 2 Oct. 1975 5 Nov. 1975 25 Feb. 1976 1 June 1976 4 Sept. 1976
6 July 1975
4 Sept. 1976
“Cylinders
used for measurement
452 454 577 592 307 181 500
+ 38.9 + 88.4 + 152.0 + 145.0 + 31.3 &- 17.4 + 33.1
56 + 8.7 of CO,
evolution
cylinders 701 + 101.7 504 & 81.8 559 2 89.1 576 + 116.5 469 + 74.1 331 * 24.3 501 + 72.1 Permanent cylinders . 111 k23.2
of vegetation
from soil.
924 738 575 749 836 712 786
_t + + + _t + k
96.4 72.5 75.5 92.8 98.6 81.3 100.1
410 + 15.9
Soil respiration
output, particularly in long-term experiments, because the movable cylinders would contain approximately the same quantity of root and litter material as is present under field conditions. Thus, it is advisable to move the cylinders every few months to maintain as natural an amount of root and litter material as possible. Soil respiration and weather variables The total CO2 output from the soil-litter system is governed directly or indirectly by two major environmental factors, namely, temperature and moisture (Singh and Gupta, 1977). According to Kucera and Kirkham (1971), a major portion of the variability in soil respiration on a tall grass prairie could be explained in terms of such variables. In our work, the soil respiration values measured from 18 July, 1975 to 28 May, 1976 for the three stands and the calculated values of soil respiration for the grassland as a whole have been used in regression analysis to evaluate the relationship of soil water, air temperature, and precipitation with soil respiration. Precipitation has been included because it is possible that it could have effects not completely linked to soil moisture conditions, such as washing standing dead material into the litter layer (affecting availability of substrate), whereas soil water has a direct influence on root metabolism and microorganism activity. Regression equations showing the relationship between CO2 evolution rates and the weather variables are given in Table 2. Soil water and COz evolution rates. It is evident from Table 2 that for stand I (Fig. 6a) and stand II (Fig. 6b) a positive significant correlation explains about 49-S% of the variability in soil respiration due to variability in soil water. For stand III (Fig. 6c) there was no significant relationship between soil moisture contents and CO1 output. This is because stand III was located in a low lying area where accumulation of water created temporary waterlogging which is inhibitory to soil respiration. Under water-
logged conditions, some of the COz produced as a
265
result of microbial activity and root metabolism gets dissolved in water and may not be measured by alkali absorption. Additionally, in waterlogged soil, the microbial activity may be depressed by a decrease in O2 concentrations in the soil atmosphere. For the grassland as a whole, second and third degree polynomial equations explain 57% of the variability in soil respiration as against 34% variability by simple regression due to variations in soil moisture (Table 2). Rainfall and CO2 evolution rates. The preceding total rainfall (rainfall between two dates of soil respiration measurements i.e. tl and tz) had a positive significant relationship with CO2 evolution rates for stands I and II and for the grassland as a whole. These regressions explain 21% (stand II) to 28% (stand I) variability in the soil respiration due to rainfall, only 12% variability was explained for the grassland as a whole. The lower correlation on the grassland as a whole was certainly due to the insignificant relation for stand III. Thus it may be argued that in our study, soil water explains a greater amount of variability in soil respiration than the rainfall. The rainfall relations would be subjected to factors infiltration, runoff, and evapotranspiration, while soil water is a resultant of all these factors. Temperature and CO2 evolution rates. For the three stands and for the grassland as a whole the mean air temperature had a positive significant relation with rates of COz evolution. A variability of 3247% in soil respiration was explained by the variability in air temperature. Witkamp (1966), Kucera and Kirkham (1971) and Anderson (1973) have shown that temperature exerts a decisive influence on CO2 metabolism of the soil when there is sufficient water supply. In our work a slightly better relationship with soil water could be due to the fact that the system remains water limited during a longer period each year. Tesgrovh and Gloser (1976) have also shown soil water to be of greater significance than temperature in controlling the output of COz from soil. The soil respiration results for the grassland as a whole have been used in a multiple regression analy-
Table 2. Regression equations showing the relationships between soil respiration (Y) and soil water (W), Rainfall (R) and Temperature (T) Equation
Vegetation Stand I Stand II Stand III Grassland as a whole Stand I Stand II Stand III Grassland as a whole Stand I Stand II Stand III Grassland as a whole
“r”
P= f= ?= ?= ?= ?= ?= ?= P= ?=
70.12 + 9.51 W 72.11 + 10.55 W 173.32 + 3.01 W 111.15 + 6.35 W 25.37 + 21.16 W’ - 0.44 W” 51.62 + 13.60 W’ - 0.06 Wz - 0.009 W’ 159.29 + 1.15R 156.89 + 0.96 R 214.47 + 0.19 R 176.34 + 0.69R
0.74** 0.70** 0.31NS 0.59** o.57a** 0 57*** 0:53** 0.46** 0.19NS 0.35*
P= ?= P= f=
3.80 + 8.30 T -30.14 + 9.02 T 20.72 + 8.55 T -7.80+8.77T
0.58** 0.66** 0.64** 0.69**
Degrees of freedom for all the above equations = 28. r = Correlation coefficient; a = multiple correlation; **P < 0.01; NsNot significant; *P i 0.05.
S. R. GUPTA
and J. S. SINGH
Fig. 6a-c Relationship between soil water (“,) and soil respiration (mg CO2 mm2 h- ‘) on Stand I (a). Stand II (b) and Stand III (c).
sis to statistically evaluate the combined effect of temperature and soil water. The resulting regression equation is : Y = 39.42 + 1.45 X, + 5.05 X1 (R2 = 0.66 d.f. = 29, P < 0.01) where, Y = CO2 output (mgCOz me2 h-l), X1 = mean air temperature (‘C) and X2 = soil water (“6). .The multiple R2 is found to be significant at a 0.01 level of probability and explains 66”, of the variation in soil respiration which is a considerable improvement over the single factor analyses. SfatisticL11 model of soil respiration A statistical model based on the relationship between soil respiration and abiotic environmental factors viz. mean daily air temperature (T’C). soil water (IV”,) and rainfall (R mm. total rainfall between soil respiration measurement dates tl and t2) shows that a linear combination of above three abiotic variables explained 69” 0 of the variability in soil respiration of the grassland as a whole according to the following regression: p= 61.17 + 1.78 T + 1.11 M’ - 0.54 R(R’ = 0.69. d.f. = 29. P < 0.01) output (mg COZ m-’ h-l). where, P= co2 T = temperature ( C). W = soil water (“,). and R = rainfall (mm). Output of the above model for those dates for which soil respiration measurements were taken are plotted together with observed soil respiration values in Fig. 5. The calculated values of soil respiration simulate our results in most important respects. The re-
lationship between observed and calculated (model output) soil respiration is positive and significant and shows at least 69% comparability between the two. Root respiration Attempts have been made to assess the contribution of root metabolism to total soil respiration and we (Singh and Gupta, 1977) have discussed the various methods used to determine root respiration and the factors affecting it. In this study, root respiration was evaluated indirectly by relating the amount of root biomass to rates of CO2 evolution. In a tall grass prairie, Kucera and Kirkham (1971) have used this method to separate microbial activity and root metabolism. A total of 19 cylinders (six each in stands II and III. and seven in stand I) were fixed in the experimental areas on 15 September, 1976 in such a way that they contained varying amounts of root biomass. The soil respiration rates were measured on 16 September. Then the soil cores were excavated from each experim”;ntal cylinder to a depth of 1Ocm and the root biomass was determined on an oven-dry weight basis m-2. When the CO2 evolution rates were related to root biomass, the following regression is obtained (Fig. 7): ?= 223.l_7 + 0.198X (r = 0.65, d.f. = 18, P < 0.01) where, Y = CO* output (mgC0, m-2 h-‘) and X = root biomass (dry wt g mm2). The relationship explains 42:; of the variability in soil respiration due to the variability in root biomass,
Soil respiration
480
?= 223,17+Q20
O’C
200
x (r.0.65, d.f.*lB, PQOI)
400
600
800
1000
Root biomaqgm-*
Fig. 7. relationship between root biomass and soil respiration rate for all sites of the grassland. in other words the contribution of roots and rootassociated micro-organisms to total respiration averages at 42%. From Fig. 7, it is obvious that the rate of CO* evolution increases with increase in root biomass. Crapo and Coleman (1972) while studying the broom-sedge old field community in South Carolina, suggested that the contribution of root respiration is in proportion to biomass present. For any one sampling date, it could be assumed that the rate of respiration me2 holds a positive relation with the root biomass present. But the same quantity of root biomass may respire at different rates under varying sets of environmental conditions and therefore, the 42% contribution estimated for roots may not hold true for the entire year. Additionally, the proportions of functional and non-functional root biomass may affect the rate and it is not easy to separate these two components (Singh and Coleman, 1973, 1974). Comparison
with
other
studies
Within the tropical savanna ecosystems, the maximum soil respiration rates vary from 329 to 532mg COZ m-‘h-t (Singh and Gupta, 1977), whereas, at our study site the maximum rates ranged from 358 to 389mg CO2 me2h-t from July 1975 to May 1976 and from 364 to 475 mg COZ me2 h-’ during the months of June-August, 1976. Thus our values are comparable to those reported for tropical savannas. The values (329 and 330mg COzm*’ h-t) reported for savanna in Costa Rica (Schulze, 1967) and Bor~SSUS palm savanna (Lamotte, 1975) are lower than those of our study site, while the value of 532mg COZ mm2 h-’ reported by Medina and Zelwer (1972) is slightly higher. We (Singh and Gupta, 1977) have stated that the temperate grasslands show a great variability in the rates of COZ output from the soil. The method used may account for some of the variability. The highest rates of soil respiration may be in the range of 2300-2700 mg CO2 m-’ h-t (Yastrebov, 1953; Makarov, 1958; de Jong and Schappert, 1972) whereas most of studies indicate a value in the range of 200-889mg CO2 me2 h-t. The maximum rates (450-869 mg CO* m-’ h-t) reported in most of tem-
267
perate studies exceed that of the grassland we studied. However, the studies of Coleman (1973) Redmann (1978) and Wildung et at. (1975) indicate tower rates (N-332 mg COZ m-* h-t) than those we observed. An examination of reported values of soil respiration shows that with the exception of too high values which may be due to methodological differences, the temperate and tropical systems do not appear to show markedly different rates of soil respiration. On the basis of higher primary production in tropical grasslands (Singh, 1968; Bourliere and Hadley, 1970; Singh and Yadava, 19741, one would except higher soil respiration rates in tropical situations. However, although the soil resphation rates may be similar or higher, the total annual integrated soil respiration in tropical systems may be higher compared to temperate systems because of the longer thermal growing season. Coleman (1973) reported the values of annual soil respiration as 1309 g CO, m-* and 1546g CO1 mm2 during 1970 and 1971, respectively for a successional grassland. For a short grass prairie, Coleman et al. (1976) have reported a value of 830g COz m-‘. For the grassland we studied, the annual CO, output amounts to 1725 g CO, me2 for the year 1975-76. Thus, the tropical systems often are water limited for a considerable period during each year, their total respiration need not always exceed that in temperate systems. Acknowledgements-We thank Dr David C. Coleman for helpful suggestions. Financial assistance from the Council of Scientific and ~nd~trial Research, New Delhi. is gratefully acknowledged. Thanks are due to Professor R. S. Mehrotra, Head of the Botany Department. Kurukshetra University, for providing facilities. REFERENCES ANDERSON J.M. (1973) Carbon dioxide evoiution from two
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119-124.
REICHLE D. E.. MCBRAYER J. F. and AUSM~S B. S. (1975) Ecological energetics of decomposer invertebrates in a deciduous forest and total respiration budget. In Proyrrss in Soil Zooloy~. (J. Vanek, Ed.). pp. 283-292. Academic Publishing House of Czechoslovak Academy of Sciences. Prague. SCHULZE E. D. (1967) Soil respiration of tropical vegetation types. Ecology 48, 652-653. SINCH J. S. (1968) Net above ground community productivity in the grasslands at Varanasi. In Proceedings of the Symposium on Recent Adwncrs in Tropical Ecology.
(R. Misra and B. Gopal. Edsl. pp. 631-654. International Society for Tropical Ecology, Varanasi. SINGH J. S. and COLEMAN D. C. (1973) A techmque for evaluating functional root biomass in grassland ecosystems. Cunadiun Journul of Botany 31, 1867-70. SINGH J. S. and COLEMAN D. C. (1974) Distribution of photo-assimilated Idcarbon in the root system of a short grass prairie. Journal of Ecology 62, 359-365. SINGH J. S. and GUPTA S. R. (1977) Plant decomposition and soil respiration in terrestrial ecosystems. Botunicul Reciew 43, 449-528. SINGH J. S. and YADAVA P. S. (1974) Seasonal variation in composition plant biomass and net primary productivity of a tropical grassland at Kurukshetra. India. Ecologicul Monographs 44, 351-376. TESXROVAM. and GLOSER J. (1976) Total CO, output from alluvial soils with two types of grassland communities. Pedobiologiu 16. 364-372. WANNER H. (1970) Soil respiration, litter fall and productivity of tropical rain forest. Journul of Ecology 58, 543-547. WANNER H.. SOEROHALDOKO S., SANTOSA, N. P. D., PANGGABEAN G., YINGCHOT P. and NGUYEN-THI-TUYET-HOA (1973) Die Bodenatmung in tropischen Regen Waldern Sudost-Asien s. Oecologia 12, 289-302. WILDUNG R. E.. GARLAND T. R. and BUSCHBOM R. L. (1975) The interdependent effects of soil temperature and water content on soil respiration rate and plant root decomposition in arid grassland soils. Soil Bioloyy & Biochemistry 7, 373-378. WITKAMP M. (1966) Rates of carbon dioxide evolution from the forest Boor. Ecology 47, 492494. YASTEREBOV M. T. (1958) Effect of the major biological factors on air composition of Alluvial Soils in the Klyazma river flood plain. Soviet Soil Science 10, 1155-1162.
Soil Bin/. Biorhrm. Vol. 13. pp. 261 to 268. 1981 Printed in Great Britain. All rights reserved
SOIL
RESPIRATION IN A TROPICAL GRASSLAND S. R. GUPTA and J. S. SXNGH*
Department of Botany, Kurukshetra University, Kurukshetra-132 119, India (Accepted 20 December 1980) Summary-Soil respiration throughout an annual cycle was measured at three different stands in a tropical grassland situated at Kurukshetra at 29”58’ N lat. and 76”51’ E long. Rates of CO* evolution were measured by alkali absorption using 13 cm dia x 23 cm aluminium cylinders inserted 10 cm into the ground. Both movable and permanently-fixed cylinders were used. The COs evolution rates for the three stands were: Stand I (dominated by Sesbaniabispinosa)49-358 mg CO2 m-’ h- ‘; Stand II (mixed grasses) 55-378 mg CO2 m-’ h-i; and Stand III (dominated by Desmosrachyo bipinnata) 55-448 mg CO2 m-* h-‘. A positive significant relation existed between rate of CO2 evolution and soil water content (r = 0.59-0.74), and between soil respiration and temperature (r = 0.58-0.69). A statistical model developed on the basis of the relationship between CO2 evolution rates and certain abiotic environmental factors showed 69% comparability between the calculated and .observed values of soil respiration. The contribution of root and root-associated microorganisms to total soil respiration was estimated at 42% using the relationship between root biomass and COs output from movable cylinders.
INTRODUCTION
LundegFtrdh (1927) defined soil respiration as the sum
total of all soil metabolic functions in which CO2 is produced. It includes three biological processes, namely, microbial respiration, root respiration and fauna1 respiration and a non-biological process, i.e. chemical oxidation which may be particularly pronounced at high temperatures (Bunt and Rovira, 1954). Soil microorganisms such as bacteria and fungi play a major role in releasing CO2 by metabolizing organic debris. In a mesic deciduous forest in Eastern Tennessee, Reichle et al. (1975) have reported that the microflora contributes over 99% of the decomposer CO,. The soil fauna also has a marked effect on total soil metabolism and is responsible for about 20% of energy release from organic matter within the soil decomposer community (Macfadyen, 1963). The contribution of root respiration to total soil respiration is often estimated at 50% (Macfadyen, 1970). Most reports on soil respiration (Singh and Gupta, 1977) are from temperate countries with only a few from the tropics (Bal, 1926; Schulze, 1967; Wanner, 1970; Medina and Zelwer, 1972; Wanner et al., 1973; Lamotte, 1975; Gupta and Singh, 1977). We determined the seasonal variation in rates of CO2 evolution, the effect of vegetation and time of enclosure of ground area on the rate of soil respiration, the relationship of soil respiration to certain weather variables and the contribution of root respiration to total soil respiration in a tropical grassland. MATERIAL
AND
METHODS
The study site is situated at Kurukshetra (29’58’ N lat. and 7651’ E long.), approximately 250m above sea level. The alluvial soil is slightly calcareous in
* Present address: Department of Botany, Kumauo University, Naioi Tal-263 002, India.
nature with a pH of 8.8 + 0.11. The organic C, poro-
sity and water holding capacity of soil were 0.55 f 0.060/, 49.0 + 3.61% and 51.06 + 1.33%, respectively in the month of June, 1976. The climate is tropical monsoonal (Singh and Yadava, 1974) with a warm wet period (June-Septernbet), a cool dry period (October-February) and a hot dry period (March-May), see Fig. 1. The vegetation of the study site is composed of three stands. Stand I is dominated by Sebania bispinosa (Jacq.) W. F. Wight; stand II is represented by a mixture of grasses such as, Aristida adscensionis Linn., Bothriochloa pertusa (L.) A. Camus, Cenchrus setigerus Vahl, Chloris barbata (L.) SW., Dichanthium annulatum (Forsk.) Stapf., Sporobolus coromendelianus (Retz.) Kunth, Sporobolus diander (Retz.) Beauv.; and stand III is dominated by Desmostachya bipinnata (L.) Stapf. The areas occupied by the different stands were determined by running a number of line transects. Thus stands I, II and III accounted for 24, 36 and 40% of the total study area, respectively. Soil respiration was measured in each stand throughout 14 months. The soil respiration rate for the grassland as a whole was calculated as an area weighted mean from the results for each stand. Soil respiration was measured using an alkali absorption method (Gupta and Singh, 1977) using 13 cm dia x 23 cm tall aluminium cylinders inserted 10 cm deep into the ground. Ten cylinders (three each in stands I and III, and four in stand II) were fixed in the ground at randomly-determined locations in the grassland in the first week of July 1975. These cylinders were left in place and CO1 evolution was determined every l-3 weeks from July 1975 to August, 1976. The first determinations of COz production were made 1 week after the cylinders had been inserted in the soil. A second set of ten cylinders (three each on stands I and III, and four on stand II) were also installed at randomly-determined locations in the fields in the 261
S.
262 400 -
-
zoo-
!
= e E cr
R.
GUPTA and
J. S.
SINGH
Ramfall
----
Temperature
-.-.-
So11 water
200-
100 -
0’
Jul 1975
Sep
Aug
Ott
Dee
Nov
Jan 1976
Feb
Mar
Apr
Jun
May
0
Jul
Aug
Fig. 1. Soil water content, mean of preceding total daily air temperature and preceding total rainfall data for the dates during which soil respiration was measured.
first week of July. 1975. These cylinders were moved to new but comparable locations every month from July to October. 1975 to determine the effect to the time of enclosure on CO, production. During the post-monsoon period, the soil became relatively hard and it was not possible to move the cylinders to new locations without major disturbance of the enclosed area. Therefore, the cylinders were moved again only in the last week of February, 1976 and then in the first week of June, 1976. On each date of measurement. soil water content was determined by taking three 5 x 1Ocm deep soil cores from areas adjacent to the cylinders. Weighed soil samples from these cores were dried at 105’C to constant weight and the percentage soil water content was calculated on a dry weight basis (Fig. 1). With the second set of cylinders, the soil was excavated each time after the cylinders were moved to new locations, while from the first set of cylinders (permanently-fixed), the soil was excavated when the experi-
ments were completed in August, 1976. The excavated soil was analysed for root biomass (g m-‘). RESULTS
Soil respirafion
AND DISCUSSION
rates
It was evident that the seasonal
trend of CO1 evolution from permanently-fixed cylinders and from movable cylinders was similar, Fig. 2 (stand I). Fig. 3 (stand II). and Fig. 4 (stand III). But differences did occur in the magnitude of soil respiration in the two sets of cylinder sampled on similar days. These differences will be discussed later. The soil respiration for the entire grassland was calculated as an area-weighted mean for each date using soil respiration values from permanently-fixed cylinders of the three stands from July 1975 to January 1976, and from movable cylinders from February to- August 1976 (Fig. 5). The values for movable cylinders were higher than those for permanently-
p-4
(a)
{--+
(b)
r
I.
0
July 1975
A
S
0
I
N
I
D
I
Jan I976
I
F
t
1
M
A
r
I
M
I
J
I
J
I
A
Months
Fig. 2. Seasonal variation in soil respiration on Stand I from 18 July 1975 to 31 August 1976 (a) permanently-fixed cylinder, (b) movable cylinder.
263
Soil respiration 500-
400
-
k ?
E 8 N
300 -
iz s i_ .-e
200
f l
% cn
100 -
I
0
July
S
A
,
I
Jan 1976
D
N
0
197’5
I
F
M
I
I
A
M
I
J
J
J
A
MOfhS
Fig. 3. Seasonal variation in soil respiration on Stand II from 18 July 1975 to 31 August 1976. (a) permanently-fixed cylinder, (b) movable cylinder.
effect of soil moisture and moderate temperatures on microbial activity and root metabolism. During the summer months, low soil moisture contents became a factor limiting soil heterotroph and root metabolism. The combined effect of low soil moisture content and low temperature resulted in decreased soil metabolic activities during the winter months.
fixed cylinders during the period February to August, 1976; therefore, the results from movable cylinders were used for this period. The seasonal pattern of soil respiration showed that the rates of CO2 evolution were maximum during the rainy season, except for the periods when the soil became saturated with water; this was followed by the summer months and was lowest during the winter. Analysis of variance indicated a significant difference in the rate of soil respiration among different sampling dates (P < 0.001) for all three stands. The higher rates during the rainy season reflect the favourable
Effect of vegetation on soil respiration rates
The CO2 output from permanent cylinders showed differences in the magnitude of soil respiration between the three stands. The soil respiration
600 i
&$ &--[
500 t
I= r
(a) (bl
400-
E N
8
F
300-
i-5 .-i
200 -
.% cn 100 -
0'
I
I
July 1975
A
S
0
I
t
I
N
D
Jan
I
I
F
M
I
,
A
M
J'J
I
,
A
1976
Months Fig. 4. Seasonal variation in soil respiration on Stand III from 18 July 1975 to 31 August 1976. (a) permanently-fixed cylinder, (b) movable cylinder.
S.
264 Calculated
o---o
R.
GLPTA
and J. S. SINGH
soil metabolism was probably more controlled by adverse climatic conditions than by the vegetation. Similarly, the insignificant differences in the values for 12-28 July, 1976 were due to depressed rates of COz evolution because the soils were waterlogged.
soil restitution
-$
‘E
3 0’
a
’
18July A 1975
S
a
h
0
N
D Jan F 1976
c
h
M
A
J
M
Months
Fig. 5. Seasonal trends in soil respiration from July 1975 to May 1976. The actual rates are compared to calculated values from a statistical model for all sites of grassland.
(mgCOz me2 hh’) values varied from 49 + 5.2 to 358 li: 22.0 on stand I. from 55 i 8.5 to 378 _t 16.2 on stand II. and from 55 + 5.7 to 448 * 35.1 on stand III. Thus. soil respiration seems to be htghest in stand III. This may be due to a higher root biomass in stand III (Table 1). The values of soil respiration for different dates were subjected to an analysis of variance to test for the differences in the rates among the three stands. No significant difference was found for the values from the three stands for all dates from July 1975 to August 1976. Nevertheless, on 13 out of 43 sampling dates. the differences were significant. From soil respiration values plotted Figs 2. 3 and 4, it is clear that for those dates when the soil respiration values were low, the differences between the stands were not significant. For example. from 30 October, 1975 to 8 March, 1976. CO* evolution rates were low with insignificant differences between the stands. This period was characterized by low soil water contents and cool temperatures. Thus,
Table
1. Root biomass
Date cylinders were installed
from movable
The effect of time of enclosure on the measurement of soil respiration was determined by comparing the CO2 evolution rates from permanently-fixed cylinders with those from movable cylinders. There was no appreciable difference between the CO2 outputs of the two series of cylinders from July. 1975 to January 1976 (Figs 2, 3 and 4). From 3 February, 1976 to 16 May, 1976. the CO: evolution rates were higher from movable cylinders at all of the stands. However. the outputs when compared by t-test for difference of means indicate that there was no significant difference in soil respiration between two series of cylinders on most of the dates during this period. From 9 June to 31 August, 1976. soil respiration rates were significantly different between two sets of cylinders in stands I and III, whereas in stand II the rates differed significantly on eight dates out of a total of 13. From the preceding discussion it is evident that there was no short-term effect of time of enclosure on CO-, output rates. But when the cylinders were moved to new locations about 6 months later than the installation of permanent-cylinders, the rates of CO2 evolution were highest from the movable-cylinders. The root biomass in the individual stands did not vary appreciably from July to October, 1975 but the root biomass was highest in stand III (Table 1). The root biomass decreased substantially from February to June. 1976. A comparison of root biomass in permanent cylinders (excavated on 4 September. 1976) with that in movable cylinders (excavated in last week of July. 1975) showed a 87”, decrease in the permanent cylinders on stand I. while on stands II and III the root material decrease in these cylinders amounted to 84 and 56”“. respectively. It was observed that there were no fragments of litter left in the permanent cylinders, From the effect of enclosure on the measurement of soil respiration. it can be concluded that the movable cylinders gave a more accurate estimate of the CO2
and permanent cylinders” (Mean f 1 SE)
Date cylinders were removed
Root biomass Stand
on the three stands
on the date of removal tg me21 Stand II
1
of cylinders Stand
III
Movable
6 July 1975 8 Aug. 1975 18 Sept. 1975 6 Oct. 1975 26 Nov. 1975 26 Feb. 1976 1 June 1976
20 July 1975 30 Sept. 1975 2 Oct. 1975 5 Nov. 1975 25 Feb. 1976 1 June 1976 4 Sept. 1976
6 July 1975
4 Sept. 1976
“Cylinders
used for measurement
452 454 577 592 307 181 500
+ 38.9 + 88.4 + 152.0 + 145.0 + 31.3 &- 17.4 + 33.1
56 + 8.7 of CO,
evolution
cylinders 701 + 101.7 504 & 81.8 559 2 89.1 576 + 116.5 469 + 74.1 331 * 24.3 501 + 72.1 Permanent cylinders . 111 k23.2
of vegetation
from soil.
924 738 575 749 836 712 786
_t + + + _t + k
96.4 72.5 75.5 92.8 98.6 81.3 100.1
410 + 15.9
Soil respiration
output, particularly in long-term experiments, because the movable cylinders would contain approximately the same quantity of root and litter material as is present under field conditions. Thus, it is advisable to move the cylinders every few months to maintain as natural an amount of root and litter material as possible. Soil respiration and weather variables The total CO2 output from the soil-litter system is governed directly or indirectly by two major environmental factors, namely, temperature and moisture (Singh and Gupta, 1977). According to Kucera and Kirkham (1971), a major portion of the variability in soil respiration on a tall grass prairie could be explained in terms of such variables. In our work, the soil respiration values measured from 18 July, 1975 to 28 May, 1976 for the three stands and the calculated values of soil respiration for the grassland as a whole have been used in regression analysis to evaluate the relationship of soil water, air temperature, and precipitation with soil respiration. Precipitation has been included because it is possible that it could have effects not completely linked to soil moisture conditions, such as washing standing dead material into the litter layer (affecting availability of substrate), whereas soil water has a direct influence on root metabolism and microorganism activity. Regression equations showing the relationship between CO2 evolution rates and the weather variables are given in Table 2. Soil water and COz evolution rates. It is evident from Table 2 that for stand I (Fig. 6a) and stand II (Fig. 6b) a positive significant correlation explains about 49-S% of the variability in soil respiration due to variability in soil water. For stand III (Fig. 6c) there was no significant relationship between soil moisture contents and CO1 output. This is because stand III was located in a low lying area where accumulation of water created temporary waterlogging which is inhibitory to soil respiration. Under water-
logged conditions, some of the COz produced as a
265
result of microbial activity and root metabolism gets dissolved in water and may not be measured by alkali absorption. Additionally, in waterlogged soil, the microbial activity may be depressed by a decrease in O2 concentrations in the soil atmosphere. For the grassland as a whole, second and third degree polynomial equations explain 57% of the variability in soil respiration as against 34% variability by simple regression due to variations in soil moisture (Table 2). Rainfall and CO2 evolution rates. The preceding total rainfall (rainfall between two dates of soil respiration measurements i.e. tl and tz) had a positive significant relationship with CO2 evolution rates for stands I and II and for the grassland as a whole. These regressions explain 21% (stand II) to 28% (stand I) variability in the soil respiration due to rainfall, only 12% variability was explained for the grassland as a whole. The lower correlation on the grassland as a whole was certainly due to the insignificant relation for stand III. Thus it may be argued that in our study, soil water explains a greater amount of variability in soil respiration than the rainfall. The rainfall relations would be subjected to factors infiltration, runoff, and evapotranspiration, while soil water is a resultant of all these factors. Temperature and CO2 evolution rates. For the three stands and for the grassland as a whole the mean air temperature had a positive significant relation with rates of COz evolution. A variability of 3247% in soil respiration was explained by the variability in air temperature. Witkamp (1966), Kucera and Kirkham (1971) and Anderson (1973) have shown that temperature exerts a decisive influence on CO2 metabolism of the soil when there is sufficient water supply. In our work a slightly better relationship with soil water could be due to the fact that the system remains water limited during a longer period each year. Tesgrovh and Gloser (1976) have also shown soil water to be of greater significance than temperature in controlling the output of COz from soil. The soil respiration results for the grassland as a whole have been used in a multiple regression analy-
Table 2. Regression equations showing the relationships between soil respiration (Y) and soil water (W), Rainfall (R) and Temperature (T) Equation
Vegetation Stand I Stand II Stand III Grassland as a whole Stand I Stand II Stand III Grassland as a whole Stand I Stand II Stand III Grassland as a whole
“r”
P= f= ?= ?= ?= ?= ?= ?= P= ?=
70.12 + 9.51 W 72.11 + 10.55 W 173.32 + 3.01 W 111.15 + 6.35 W 25.37 + 21.16 W’ - 0.44 W” 51.62 + 13.60 W’ - 0.06 Wz - 0.009 W’ 159.29 + 1.15R 156.89 + 0.96 R 214.47 + 0.19 R 176.34 + 0.69R
0.74** 0.70** 0.31NS 0.59** o.57a** 0 57*** 0:53** 0.46** 0.19NS 0.35*
P= ?= P= f=
3.80 + 8.30 T -30.14 + 9.02 T 20.72 + 8.55 T -7.80+8.77T
0.58** 0.66** 0.64** 0.69**
Degrees of freedom for all the above equations = 28. r = Correlation coefficient; a = multiple correlation; **P < 0.01; NsNot significant; *P i 0.05.
S. R. GUPTA
and J. S. SINGH
Fig. 6a-c Relationship between soil water (“,) and soil respiration (mg CO2 mm2 h- ‘) on Stand I (a). Stand II (b) and Stand III (c).
sis to statistically evaluate the combined effect of temperature and soil water. The resulting regression equation is : Y = 39.42 + 1.45 X, + 5.05 X1 (R2 = 0.66 d.f. = 29, P < 0.01) where, Y = CO2 output (mgCOz me2 h-l), X1 = mean air temperature (‘C) and X2 = soil water (“6). .The multiple R2 is found to be significant at a 0.01 level of probability and explains 66”, of the variation in soil respiration which is a considerable improvement over the single factor analyses. SfatisticL11 model of soil respiration A statistical model based on the relationship between soil respiration and abiotic environmental factors viz. mean daily air temperature (T’C). soil water (IV”,) and rainfall (R mm. total rainfall between soil respiration measurement dates tl and t2) shows that a linear combination of above three abiotic variables explained 69” 0 of the variability in soil respiration of the grassland as a whole according to the following regression: p= 61.17 + 1.78 T + 1.11 M’ - 0.54 R(R’ = 0.69. d.f. = 29. P < 0.01) output (mg COZ m-’ h-l). where, P= co2 T = temperature ( C). W = soil water (“,). and R = rainfall (mm). Output of the above model for those dates for which soil respiration measurements were taken are plotted together with observed soil respiration values in Fig. 5. The calculated values of soil respiration simulate our results in most important respects. The re-
lationship between observed and calculated (model output) soil respiration is positive and significant and shows at least 69% comparability between the two. Root respiration Attempts have been made to assess the contribution of root metabolism to total soil respiration and we (Singh and Gupta, 1977) have discussed the various methods used to determine root respiration and the factors affecting it. In this study, root respiration was evaluated indirectly by relating the amount of root biomass to rates of CO2 evolution. In a tall grass prairie, Kucera and Kirkham (1971) have used this method to separate microbial activity and root metabolism. A total of 19 cylinders (six each in stands II and III. and seven in stand I) were fixed in the experimental areas on 15 September, 1976 in such a way that they contained varying amounts of root biomass. The soil respiration rates were measured on 16 September. Then the soil cores were excavated from each experim”;ntal cylinder to a depth of 1Ocm and the root biomass was determined on an oven-dry weight basis m-2. When the CO2 evolution rates were related to root biomass, the following regression is obtained (Fig. 7): ?= 223.l_7 + 0.198X (r = 0.65, d.f. = 18, P < 0.01) where, Y = CO* output (mgC0, m-2 h-‘) and X = root biomass (dry wt g mm2). The relationship explains 42:; of the variability in soil respiration due to the variability in root biomass,
Soil respiration
480
?= 223,17+Q20
O’C
200
x (r.0.65, d.f.*lB, PQOI)
400
600
800
1000
Root biomaqgm-*
Fig. 7. relationship between root biomass and soil respiration rate for all sites of the grassland. in other words the contribution of roots and rootassociated micro-organisms to total respiration averages at 42%. From Fig. 7, it is obvious that the rate of CO* evolution increases with increase in root biomass. Crapo and Coleman (1972) while studying the broom-sedge old field community in South Carolina, suggested that the contribution of root respiration is in proportion to biomass present. For any one sampling date, it could be assumed that the rate of respiration me2 holds a positive relation with the root biomass present. But the same quantity of root biomass may respire at different rates under varying sets of environmental conditions and therefore, the 42% contribution estimated for roots may not hold true for the entire year. Additionally, the proportions of functional and non-functional root biomass may affect the rate and it is not easy to separate these two components (Singh and Coleman, 1973, 1974). Comparison
with
other
studies
Within the tropical savanna ecosystems, the maximum soil respiration rates vary from 329 to 532mg COZ m-‘h-t (Singh and Gupta, 1977), whereas, at our study site the maximum rates ranged from 358 to 389mg CO2 me2h-t from July 1975 to May 1976 and from 364 to 475 mg COZ me2 h-’ during the months of June-August, 1976. Thus our values are comparable to those reported for tropical savannas. The values (329 and 330mg COzm*’ h-t) reported for savanna in Costa Rica (Schulze, 1967) and Bor~SSUS palm savanna (Lamotte, 1975) are lower than those of our study site, while the value of 532mg COZ mm2 h-’ reported by Medina and Zelwer (1972) is slightly higher. We (Singh and Gupta, 1977) have stated that the temperate grasslands show a great variability in the rates of COZ output from the soil. The method used may account for some of the variability. The highest rates of soil respiration may be in the range of 2300-2700 mg CO2 m-’ h-t (Yastrebov, 1953; Makarov, 1958; de Jong and Schappert, 1972) whereas most of studies indicate a value in the range of 200-889mg CO2 me2 h-t. The maximum rates (450-869 mg CO* m-’ h-t) reported in most of tem-
267
perate studies exceed that of the grassland we studied. However, the studies of Coleman (1973) Redmann (1978) and Wildung et at. (1975) indicate tower rates (N-332 mg COZ m-* h-t) than those we observed. An examination of reported values of soil respiration shows that with the exception of too high values which may be due to methodological differences, the temperate and tropical systems do not appear to show markedly different rates of soil respiration. On the basis of higher primary production in tropical grasslands (Singh, 1968; Bourliere and Hadley, 1970; Singh and Yadava, 19741, one would except higher soil respiration rates in tropical situations. However, although the soil resphation rates may be similar or higher, the total annual integrated soil respiration in tropical systems may be higher compared to temperate systems because of the longer thermal growing season. Coleman (1973) reported the values of annual soil respiration as 1309 g CO, m-* and 1546g CO1 mm2 during 1970 and 1971, respectively for a successional grassland. For a short grass prairie, Coleman et al. (1976) have reported a value of 830g COz m-‘. For the grassland we studied, the annual CO, output amounts to 1725 g CO, me2 for the year 1975-76. Thus, the tropical systems often are water limited for a considerable period during each year, their total respiration need not always exceed that in temperate systems. Acknowledgements-We thank Dr David C. Coleman for helpful suggestions. Financial assistance from the Council of Scientific and ~nd~trial Research, New Delhi. is gratefully acknowledged. Thanks are due to Professor R. S. Mehrotra, Head of the Botany Department. Kurukshetra University, for providing facilities. REFERENCES ANDERSON J.M. (1973) Carbon dioxide evoiution from two
temperate deciduous woodland soils. ~o~r~i of _ Applied ._ Ecoiogy 10.361-378.
BAL D. V. (1926) Studies on carbon dioxide oroduction in soil and Holutibn. Anna/s of Applied &log{ 13, 23 l-243. B~URLIEREF. and HADLEYM. (1970) The ecology of tropical Savannas. Annual Review of Ecology & Systematics 1, 125-152.
BUNTJ. S. and ROVIRA A. D. (1954) Oxygen uptake and carbon dioxide evolution of heat sterilized soil. Nature 173, 1242. COLEMAND. C. (1973) Soil carbon balance in a successional grassland. Oikos 24, 195-199. COLEMAND. C., ANDREWSR.,ELLIS J. E. and SINGHJ. S. (1976) Energy flow and partitioning in selected and manmanaged and natural ecosystems. Agroecosystems 3, 45-54.
CRAPON. L. and COLEMAND. C. (1972) Root distribution and respiration in Carolina old field. Oikos 23, 137-139. DE JONG E. and SCHAPPERTH. J. V. (1972) Calculation of soil respiration and activity from CO, profiles in the soil. Soil Science 113, 328-333. GUPTAS. R. and SINGHJ. S. (1977) Effect of alkali concentration volume and absorption area on the measurement of soil respiration in a tropical sward. ~e~ob~o~og~u17, 233-239. KIR~TAH. (1971) Studies of soil respiration in warm-temperate evergreen broad leaf forests of South Western Japan. Japanese Journal of Ecology 21, 23@-244. KUCERAC. L. and KIRKHAMD. R. (1971) Soil respiration studies in tafl grass prairie in Missouri. Ecotogy 52, 912-915.
‘68
S. R. GUPTA and J. S. SIN~;H
LAMOTTEM. (1975) The structure
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