Brown, A. H. F.

Howson, G.

English

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   Chapter (non-refereed)    Brown, A. H. F.; Howson, G.. 1988 Changes in tensile strength loss of cotton strips with season and soil depths under 4 tree species. In: Harrison, A. F.; Latter, P. M.; Walton, D. W. H., (eds.) Cotton strip assay: an index of decomposition in soils. Grange-over-Sands, NERC/ITE, 86-89. (ITE Symposium, 24).   Copyright © 1988 NERC  This version available at http://nora.nerc.ac.uk/5038/   NERC has developed NORA to enable users to access research outputs wholly or partially funded by NERC. Copyright and other rights for material on this site are retained by the authors and/or other rights owners. Users should read the terms and conditions of use of this material at http://nora.nerc.ac.uk/policies.html#access    This document is extracted from the publisher’s version of the volume. If you wish to cite this item please use the reference above or cite the NORA entry                           Contact CEH NORA team at  nora@ceh.ac.uk 86Changes in tensile strength loss of cotton strips withseason and soil depth under 4 tree speciesA H F BROWN and G HOWSONInstitute of Terrestrial Ecology, Merlewood Research Station, Grange-over-Sands1 SummarySeasonal changes in tensile strength loss of cottonstrips (CTSL), used as an index of potential organicmatter breakdown, were determined in stands of 4tree species at Gisburn (Bow land Forest), Lancashire.In general, decomposer potential is greater underalder (Alnusspp.) and pine (Pinus spp.) than under oak(Quercusspp.) and spruce (Piceaspp.). The seasonalpattern under oak (with a mid-season decline in ac-tivity) is very different from the seasonal curves forthe other species. CTSL also declines rapidly withdepth under oak and spruce, remaining relatively highat all depths under the alder and pine. This higherpotential for decomposition at depth under alder andpine is possibly related to the appreciable populationsof earthworms (Lumbricidae) under these 2 tree spe-cies; conversely, earthworms are rare in oak andspruce stands.It has also been observed that feeding roots of oakand spruce tend to proliferate near the surface, butare distributed more evenly with depth in alder andpine, these patterns being related to those for CTSL.2 BackgroundThe background to the study and a description of thesite are given by Brown and Harrison (1983) and Brown(1988). Briefly, the Gisburn study area consists of anexperimental planting of 4 tree species planted in0.2 ha plots, both as monoculture stands and in allpossible combinations of 2-species mixtures. These10 treatments are replicated in 3 blocks. The fourspecies are Scots pine (Pinus sylvestris), Norwayspruce (Picea abies),alder (Alnus glutinosa)and sess-ile oak (Quercus petraea).The aim of the study wasto use the cotton strip assay to test the hypothesisthat the 4 monoculture stands were altering the poten-tial for cellulose decomposer activity in the soils inwhich the biomass of earthworms and the distributionof fine roots were also found to differ.3 MethodOrganic matter decomposer activity is known to varywith both soil depth and season (Swift et al. 1979). Inusing the cotton strip assay under the different treespecies, we wished to determine whether there wasalso any species interaction in cellulose decompo-sition with either of these sources of variation. Al-though the standard cotton strip assay givesinformation on depth differences, it is necessary torepeat the assay at intervals to provide seasonal infor-mation. To this end, assays were repeated on 9 oc-casions, at 6-weekly intervals (ie for just over a year)in the monoculture plots of pine, spruce, alder andoak for each of the 3 replicate blocks. Assay periodsof 12 weeks were used, thus leading to an overlappingtime series of assays. Ten strips per plot were usedfor each test on each occasion, distributed on a sys-tematic basis throughout each tree plot. The ShirleySoil Burial Test Fabric (1976 batch) was used, the firstassay period starting on 5 January 1978, the lastfinishing on 26 February 1979. The methodology ofLatter and Howson (1977) was used throughout, pro-viding tensile strength loss (CTSL) data for 5 depthsat 4 cm intervals down the soil profiles. The data werealso calculated as cotton rotting rate (CRR), after Hillet al. (1988).Cloth control tensile strength was 47.4 kg for thebatch of cloth used on occasions 1-4 and 54.4 kg forthe subsequent batch used on occasions 5-9.To provide comparisons between cotton assay dataand other site parameters for the different tree stands,data on earthworm populations and the standing cropof fine roots are also presented. The earthwormswere sampled during 1981 using a dung bait method(Brown & Harrison 1983) for 2 of the 3 blocks, butexcluding oak stands. Some preliminary data on distri-bution of live roots one mm were obtained during1983 by hand-sorting replicate soil cores from the pineand spruce stands only.4 Results and discussionThe results from the cotton strip assay indicated thatthere were clear seasonal patterns of cellulose de-composer activity associated with the different treespecies plots (also discussed by French 1988). Be-cause these results were consistent between theseparate blocks, the data have been combined fromthe 3 blocks to give means based on 30 strips per treespecies. CTSL or CRR averaged for all 5 depths, ierepresenting whole strips, provides a summary Of thechanges in decomposer activity with time in eachforest stand (Figure 1).Statistically significant differences for CTSL (P<0.001on first, second, fifth, sixth occasions, and P<0.01 forthe other 4 occasions) occurred on all except the lastsampling occasion of the series. It is evident that,overall, cellulose decomposer activity was in the se-quence alder = pine>oak>spruce. Activity rose to apeak in late summer/early autumn in alder, pine andspruce stands, but with the pattern under oak beingvery different. Because the successive assay periodsTon July  Ton1978 1979were of identical length, the seasonal curves for CTSLand CRR are essentially similar. Only alder shows aslight discrepancy, when TS values were excessivelylow in summer (cf Walton 1988).The seasonal patterns for the separate depths undereach tree species (Figure 2) show that the differentpattern for oak became more accentuated with depth,being similar to those for other species only at thesurface. At 16-20 cm, the oak curve was clearly bimo-dal, with a secondary minimum at the time at whichthe other species reached their seasonal maxima.Inspection of the 4 sets of seasonal curves also re-veals that the decline in CTSL with depth, during theseason of high activity at least, was slight in alder andpine stands, but very marked under oak and spruce.This contrast between alder and pine, on the onehand, and oak and spruce, on the other, is possiblylinked with differences in both earthworm populationsand the distribution of the fine (ie the main feeding)roots. Figure 3 shows that alder and pine not only hadrelatively high numbers of earthworms, but that manyof them were  Lumbricus rubellus,  a partially burrow-ing species. The remainder consisted of surface-dwell-ing species (Brown & Harrison 1983). In contrast, thespruce stands had very few earthworms and negligibleLumbricus rubellus.  From observation, populations ofearthworms in the oak plots were judged to be at leastas low as those of spruce. It is, therefore, possiblethat there has been more transport both of organicmatter and of its decomposer organisms into the soilprofiles of alder and pine stands through earthwormactivity; and that this is reflected in the relatively highlevels of CTSL at all sampled depths.Yon July Ton1978 197987Figure 1. Changes with season in tensile strength loss of cotton strips, CTSL and CRR, following insertion under4 tree species, at Gisburn, 1978-79. Nine overlapping burial periods, each of 12 weeks; means of all depths(ie whole strip averages) for 3 blocks combined, points being placed on the retrieval date (for a 3D presentationof the oak data, see Walton 1988)Conversely, where the possibility of such mixing andtransport down the profile has only been slight, as inspruce (and oak) stands, there has been a concomitantrapid fall-off Of cellulose decomposer activity downthe profile.Similar reasoning could also explain the contrast infine root distribution between pine and spruce (Figure4). Under pine, with little reduction in cellulose decom-poser activity (and concomitant nutrient release) withdepth, feeding roots likewise tend to occur at alldepths, with least at the surface where other environ-mental conditions, such as susceptibility to droughtand temperature fluctuations, are likely to be leastsuitable for root activity. In contrast, because cellulosedecomposer activity in the spruce stands was verymuch greater at the surface than at depth, the feedingroots were concentrated at the main source of nutri-ents made available. Because of the resulting surface-rooting of spruce under such conditions, this speciesis typically more prone to drought than the deeper-rooting pine.It must be emphasized, however, that these interpret-ations now require testing in order to distinguish causefrom effect.5  AcknowledgementsMany people assisted in the field work, laboratorytesting and data handling involved in this study, includ-ing S H Atkinson, A E Elliott, C L Gardener, S Gardener,and R W Hollstein.88101978 1979 1978 1979Figure 2. Changes with depth of the seasonal curves for tensile strength loss under 4 tree species20 10ET] All  speciesm L.  rubellus151050 0P 1 ne A I der Spruce Oak* P 1 ne A I der Spruce Oak*Figure 3. Mean numbers and biomass (preserved tresh weight) of earthworms per trap under 4 tree species.Two trapping periods and 2 blocks, combined, at Gisburn, 1981 (*oak estimated from observation)LFH0-5 cm5-10 cm10-15 cm15-20 cmED  Pineall Spruce0 50 100 150 200Root length (cm core-1)Figure 4. Mean lengths of live roots mm) in soilcores of 24 mm diameter at 5 depths under Norwayspruce (n = 12) and Scots pine (n = 20), at Gisburn,1983 (source: J M Sykes & S M C Robertson unpub-lished data)896  ReferencesBrown, A.H.F.  1988. Discrimination between the effects on soilsof 4 tree species in pure and mixed stands using cotton strip assay.In:  Cotton strip assay. an index of decomposition in soils,  editedby A.F. Harrison, P.M. Latter & D.W.H. Walton, 80-85. (ITE sym-posium no. 24.) Grange-over-Sands: Institute of Terrestrial Ecology.Brown, A.H.F.  &  Harrison, A.F.  1983. Effects of tree mixtureson earthworm populations and nitrogen and phosphorus status inNorway spruce  (Picea abies) stands. In:  New trends in soil biology,edited by Ph. Lebrun, H.M. Andre, A. De Medts, C. Grégoire-Wibo &G. Wauthy, 101-108. Ottignies-Louvain-la-Neuve: Dieu-Brichart.French, D.D.  1988. Seasonal patterns in cotton strip decompositionin soils. In:  Cotton strip assay an index of decomposition in soils,edited by A.F. Harrison, P.M. Latter & D.W.H. Walton, 46-49. (ITEsymposium no. 24.) Grange-over-Sands: Institute of TerrestrialEcology.Hill, M.O., Latter, P.M.  & Bancroft, G. 1988. Standardization ofrotting rates by a linearizing transformation. In:  Cotton strip assayan index of decomposition in soils,  edited by A.F. Harrison, P.M.Latter & D.W.H. Walton, 21-24. (ITE symposium no. 24.) Grange-over-Sands: Institute of Terrestrial Ecology.Latter, P.M.  &  Howson, G.  1977. The use of cotton strips toindicate cellulose decomposition in the field.  Pedobiologia, 17, 145-155.Swift, M.J., Heal, 0.W.  &  Anderson,  J.M. 1979.  Decompositionin terrestrial ecosystems.  Oxford: Blackwell Scientific.Walton, D.W.H.  1988. The presentation of cotton strip assay re-sults. In:  Cotton strip assay. an index of decomposition in soils,edited by A.F. Harrison, P.M. Latter & D.W.H. Walton, 28-31. CITEsymposium no. 24.) Grange-over-Sands: Institute of TerrestrialEcology.

Changes in tensile strength loss of cotton strips with season and soil depths under 4 tree species

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Changes in tensile strength loss of cotton strips with season and soil depths under 4 tree species

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