4.8.1 Intraspecific variation of leaf attributes
Figure 4.34 visualizes the intraspecific variation of ten important leaf morphological and chemical parameters. The graphs show the maximum and minimum value, the upper and lower quartile and mean calculated from 10-individual samples for each of 19 species.
Following this first overview, the degree of variation was further analysed and quantified by the coefficient of variance.
Table 4.15 presents the coefficient of variance of chemical and morphological leaf traits within the 30 most frequent species in the random samples. For 19 of the species, the coefficient of variance was additionally listed for light-saturated net photosynthesis and maximum stomatal conductance.
It is obvious that some parameters show high intraspecific variance throughout the species, whereas others are constantly less variable in most species. Calcium concentration was the most variable parameter within many species. Leaf size was likewise very variable in most species, whereas SLA showed a universally low variance. P, N/P ratio and δ15N varied a lot within the species, while N or C/N ratio showed less variance (Figure 4.35).
Looking at the two gas exchange parameters included revealed that gsmax varied more
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within species than Amax, and that both were usually more variable among the individuals of natural forest species, than within the secondary forest, or the agroforestry system.
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system Natural forest Secondary forest Agroforestry system
Figure 4.34 Mean, lower and upper quartile, maximum and minimum values of 10 leaf traits in 19 species occurring in three different land use types. The calculations were based on 10 individuals per species, except for the Macaranga tanarius means, which were based on 4 individuals.
4 RESULTS
Table 4.15 The coefficient of variance (sd / mean (%)) calculated for 12 leaf traits and their intraspecific variation in the 30 most abundant species in the random samples (number of individuals underlying each species mean was 3 – 10). Parameters presented are leaf size (LS), length-width ratio (LW), specific leaf area (SLA), weight related concentration of calcium (Ca), phosphorus (P), nitrogen (N) and element ratios (C/N, N/P), as well as δ13C and δ15N. Additionally, the coefficient of variance for Amax and gsmax is presented for 19 of the species. The species are listed under the land use type where they were most frequent. (Ind – number of individuals underlying the coefficient of variance)
Ind LS LW SLA Ca P N C/N N/P δ13C δ15N Amax gsmax
Tabernamontana macrocarpa 4 19 22 11 23 22 7 11 20 6 25
Trema orientalis 10 39 11 17 32 24 28 38 36 4 60 9 28
Aglaia argentea, Bischofia javanica, Litsea sp.3 and Meliosma sumatrana were natural forest species with particularly high intraspecific variance for most leaf traits. The two species Litsea sp.1 and Siphonodon celastrineus showed the highest variance in the gas exchange parameters among the natural forest species. Generally, natural forest species
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showed a higher intraspecific variance in P and Ca and gas exchange parameters than the secondary forest species.
Among the secondary forest species, Trema orientalis had the highest intraspecific variance for most leaf traits, followed by Macaranga hispida, Homalanthus populneus and Acalypha caturus. Macaranga hispida was the secondary forest species with highest intraspecific variance in leaf gas exchange parameters.
Looking at the four agroforestry species revealed that Theobroma cacao was overall most variable among the four and that Gliricidia sepium and Erythrina sp. had strikingly similar coefficients of variance throughout the parameters and particularly low intraspecific variance in N.
Figure 4.35 Intraspecific coefficient of variance (sd / mean (%)) in 11 morphological and chemical leaf traits for eight natural forest species, eight secondary forest species and three agroforestry system species. (LS – Leaf size, LW – Length-width ratio, SLA – Specific leaf area)
4.8.2 Variation of leaf attributes within land use types
Studying the interspecific variance in normalized 18-species samples of the four land use types (four species in AF), the most important finding was that P was more variable than N among species in all land use types, except secondary forest. The variance of N among natural forest species was remarkably low, while the variance in P was much higher than among secondary forest species. Leaf size was the most variable parameter within all four land use types, followed by Ca and δ15N (Table 4.16).
4 RESULTS
Similar to the intraspecific variance, the interspecific variance of stomatal conductance was higher than that of Amax, and secondary forest was the least variable land use type concerning leaf gas exchange of its species.
As can be seen in Table 4.16, natural forest was the land use type with overall highest interspecific variance for leaf traits. Five of the 12 listed leaf traits showed their maximum value of the coefficient of variance for the natural forest, whereas the other three land use types had the highest interspecific variance of the four for one or two parameters. Secondary forest had the highest coefficient of variance among the four land use types only for δ15N.
Amax and SLA varied most among the agroforestry species.
Table 4.16 Coefficient of variance (sd / mean (%)) for morphological and chemical leaf traits in the normalized 18-species average samples of natural forest (NF), secondary forest (SF) and forest garden (FG), and in the species average of the four agroforestry system (AF) species. The coefficients for Amax and gsmax are calculated from eight-species samples for NF and SF, and from three species for AF. The coefficients of variance among the four land use types studied are listed in the fifth column. (n.d. – no data)
NF
(%) FG
(%) SF
(%) AF
(%)Variance between land use types
No. species 18 18 18 4 (%)
Leaf size 98 75 91 96 42
Length-width ratio 100 17 29 26 24
SLA 29 33 28 34 15
Ca 62 45 61 40 20
P 41 45 29 32 32
N 3 38 38 30 26
C/N 31 37 32 36 23
N/P 35 25 20 28 22
δ13C 4 4 2 4 4
δ15N 40 65 96 73 13
Amax 43 n.d. 22 47 44
gsmax 68 n.d. 17 53 36
4.8.3 Variation of leaf attributes among land use types
The coefficient of variance for 12 important morphological, chemical and physiological leaf traits among the four land use types studied is accounted in the very right column of Table 4.16. The largest difference between the land use types was found for Amax, followed by leaf size and thereafter gsmax and P, while the highest similarity was obtained for SLA
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(and δ15N and δ13C). The variance among land use types was analysed using means of the random sample, which is defined in Table 3.2.