Skip to main content
NCBI home page
Annals of Botany logoLink to Annals of Botany
. 2006 May;97(5):813–817. doi: 10.1093/aob/mcl041

Comparison of Leaf Life Span, Photosynthesis and Defensive Traits Across Seven Species of Deciduous Broad-leaf Tree Seedlings

SAWAKO MATSUKI 1,*, TAKAYOSHI KOIKE 2
PMCID: PMC2803406  PMID: 16510512

Abstract

• Background and Aims Leaf life span, photosynthetic parameters and defensive traits were compared across seven species of deciduous broad-leaved tree seedlings native to northern Japan to test the ‘cost–benefit hypothesis’ that more productive leaves are more susceptible to herbivore attack than less productive leaves.

• Methods Studies were made on three early successional species, Alnus hirsuta, Betula maximowicziana and Betula platyphylla ‘japonica’; one mid-successional species, Ostrya japonica, and three late-successional species, Carpinus cordata, Quercus mongolica ‘grosseserrata’ and Acer mono. Photosynthetic parameters and defensive traits (total phenolics, condensed tannin and toughness) of leaves were measured for each species, and a bioassay test with Eri silkmoth larvae (Samia cynthia ricini) was undertaken to evaluate differences between species in susceptibility to herbivore attack.

• Key Results Early successional species have a shorter leaf life span (62–88 d) than late successional species (155–187 d). Leaf nitrogen content and light-saturated photosynthetic rate per unit leaf area (Psat-area) and per unit leaf mass (Psat-mass) were negatively correlated with leaf life span. The nitrogen content of early successional species was about 30 mg g−1 and that of late successional species was about 16 mg g−1. Leaf toughness and the C/N ratio were positively correlated with leaf life span, although condensed tannin was not correlated with leaf life span. The bioassay test showed that the number of days the larvae survived was negatively correlated with leaf life span. Average survival of larvae feeding on leaves of A. hirsuta, which has the shortest leaf life span, was 14·4 d and that of Q. mongolica, which has the longest leaf life span, was 6·6 d. The number of days of larval survival was positively correlated with leaf nitrogen content. There was no correlation between days of larval survival and defensive traits.

• Conclusions These results indicate that species with a shorter leaf life span have higher photosynthetic productivity and are more susceptible to herbivore attack than species with a longer leaf life span. This supports the ‘cost–benefit hypothesis’.

Keywords: Acer mono, Alnus hirsuta, Betula maximowicziana, Betula platyphylla ‘japonica’, Carpinus cordata, Ostrya japonica, Quercus mongolica ‘grosseserrata’, cost–benefit hypothesis, phenolic compounds, light-saturated photosynthetic rate, bioassay test, Samia cynthia ricini

INTRODUCTION

Several deciduous broad-leaved trees with differing photosynthetic capacities grow together in the cool temperate forests of northern Japan (Koike, 1988). In general, early successional species have a shorter leaf life span (Kikuzawa, 1986), higher photosynthetic rates (Bazzaz, 1979; Koike and Sakagami, 1985; Koike 1988) and greater shoot elongation (Kikuzawa, 1982; Koike, 1987) than late successional species. It has been suggested that heterogeneity of plant quality affects the pattern of feeding by insect herbivores (Pacala and Crawley, 1992; Hunter et al., 1999), encouraging the co-existence of species with different competitive abilities (Janzen, 1970; Augspurger, 1983; Pacala and Crawley, 1992).

Several studies have demonstrated a trade-off between foliar ability in production and maintenance, the existence of which is called the ‘cost–benefit hypothesis’ (Mooney and Gulmon, 1982). It asserts that long-lived leaves have higher cost (maintenance, defence) and less benefit (photosynthates) than short-lived leaves (Chapin et al., 1980; Coley, 1988; Reich et al., 1995). Kikuzawa (1991) explained this relationship using a simple model with only a few parameters: rate of photosynthesis, construction cost and maintenance costs of a leaf. Herms and Mattson (1992) also suggest that plants may face the dilemma of choosing between producing new leaves or defence with chemical compounds already laid down, because biosynthesis of secondary compounds is to be balanced against the cost of new growth (Riipi et al., 2002; Matsuki et al., 2004). The theoretical hypothesis has been confirmed, but there are few studies of the relationship between leaf life span and defensive cost (but see Coley, 1988).

Immobile defence chemicals such as phenolics, which are large molecular weight compounds, are major defensive components of tree leaves. They would be most cost-effective in long-lived leaves, because these compounds have high synthesis construction costs and cannot be recycled during leaf senescence (Coley et al., 1985; Coley, 1988). Quantification of phenolics in various species having differing leaf life spans would shed light on the cost–benefit hypothesis.

Defensive effects of phenolic compounds against herbivores have been demonstrated in several studies, but the pattern of grazing in natural forests and bioassay testing do not always reflect the amount of phenolic compounds present (Underwood et al., 2002). Bioassay testing is effective in demonstrating the capability for anti-herbivore defence. Larvae of the Eri silkmoth (Samia cynthia ricini Donovan) are good indicators of the capability of a species for foliar defence (Konno et al., 2004; Koike et al., 2006).

In this study, we examine the photosynthetic parameters (light-saturated photosynthetic rate, concentration of carbon and nitrogen), indexes of defence (leaf toughness, total phenolics and condensed tannin) and number of days of larval survival in seven woody species with varying leaf life spans, to test the ‘cost–benefit hypothesis’.

MATERIALS AND METHODS

Plant material

Seven species of 2-year-old deciduous broad-leaved tree plants (Acer mono Maxim, Alnus hirsuta Turcz, Betula maximowicziana Regel, Betula platyphylla ‘japonica’ Hara, Carpinus cordata Blume, Ostrya japonica Sarg and Quercus mongolica ‘grosseserrata’ Rehd) were obtained from Kuriyama, a town near Sapporo, and were planted at the experimental nursery of Hokkaido University Forests (43°4′N, 141°20′E) under full sunlight in April 2000. The maximum photosynthetic photon flux density (PPFD; 400–700 nm) at this open site ranged between 1500 and 2000 µmol m−2 s−1 on sunny days. The seedlings were watered regularly.

Alnus hirsuta is a typical succeeding leaf emergence species. Betula maximowicziana and B. platyphylla ‘japonica’ are heterophyllous type species, which flush their early leaves in spring and expand their late leaves successively with shoot elongation (Kikuzawa, 1982). These three species often appear in open sites and/or the edge of forests, and they are categorized as early successional species (Koike, 1988). Only A. hirsuta has a symbiotic nitrogen-fixing micro-organism in its root system (Kikuzawa, 1982). Ostrya japonica is a flush and succeeding type, and appears at the edges of forest and/or in relatively lighter underforest. It is categorized as a mid-successional species (Kikuzawa, 1982; Koike, 1988). Acer mono, C. cordata and Q. mongolica ‘grosseserrata’ are flush type species, and they can maintain growth in underforest. They are categorized as late successional species (Kikuzawa, 1982; Koike, 1988).

The leaf life span of each species was determined from almost daily counts of the number of leaves present on each of 20 plants per species, from leaf expansion (late in April) to leaf fall. The date when half the total number of leaves had fallen was defined as the end of the leaf life span (T. Koike, unpubl. res.).

Measurement of defensive characteristics

Three mature leaves per plant were sampled from six plants per species in late July 2001. Leaf toughness was measured at three points (avoiding the main vein) on each leaf, using a push–pull gauge (CPU gauge, AIKOH, Nagoya, Japan), and the mean value was determined; the unit is a Newton (kg m s−2). After measurement of leaf toughness, the leaves were immediately freeze-dried (FLEXI-DRY, FTS Systems, Stony Ridge NY, USA) and mill ground (TM10, Tescom, Tokyo, Japan) to a powder. The concentration of total phenolics in 20 mg of leaf powder was determined by the Folin–Ciocalteu method (Folin and Ciocalteu, 1927), as modified by Julkunen-Titto (1985). The concentration of condensed tannin was determined using the proanthocyanidin method (Bate-Smith, 1977).

Measurement of light-saturated photosynthetic rate

The light-saturated photosynthetic rate of plants was determined in mid-August 2001 by a portable system dedicated to the measurement of photosynthetic rates (LI-6400, Li-Cor, Lincoln, NE, USA) at a PPFD of 2000 µmol m−2 s−1 and a leaf temperature of 25 °C, with a CO2 concentration of 360 p.p.m. as chosen previously by Koike (1995). For these measurements, three plants were used per species. The plants were different individuals from those used for the measurement of defensive characteristics and photosynthetic rate and for the bioassay test. The light-saturated photosynthetic rate was measured on mature leaves for each species.

Measurement of nitrogen and carbon content and leaf mass per area

After measurement of the light-saturated photosynthetic rate, the leaves involved were harvested, and two circular leaf disks (diameter of leaf disk: 8 mm) were punched from the centre part of the leaf blade, avoiding the main vein, and were dried in an oven at 60 °C for 2 d. Dry masses of leaf disks were then measured to determine the leaf mass per unit area (LMA). The leaf disks were then used for measurement of nitrogen and carbon content by an NC analyser (NC-900, Shimadzu, Kyoto, Japan).

Bioassay test

A bioassay test was carried out with the larvae of the Eri silkmoth (Samia cynthia ricini Donovan), from July 5, 2001. This species originated from, and has been widely reared in, northern India to produce silk. The larvae are suitable for evaluating the level of plant defence against herbivorous insects, because their host range is wide (Fukui et al., 2002; Konno et al., 2004). A line of the Eri silkmoth is maintained in the laboratory, and egg masses were provided by Dr Kotaro Konno (National Institute of Agrobiological Science). Ten larvae were fed with leaves of one of the seven species from the first instar. Leaves for this bioassay were harvested from the same plants used for chemical analysis. In total, 70 larvae were grown in a feeding chamber at 25 °C and 16 h of light. An abundant quantity of fresh leaves was made available to the larvae. The number of days of larval survival is defined as the average of days of life (from first instar to death) of 10 larvae for each species.

Statistics

Correlations between two parameters were analysed using Pearson's correlation coefficient. Stepwise multiple regression analysis (forward) was done to test the contribution of several parameters [nitrogen content, C/N ratio, toughness, light-saturated photosynthetic rate per unit leaf mass (Psat-mass), total phenolics and condensed tannin] to the leaf life span. Stepwise multiple regression analysis (forward) was also done to test the contribution of several parameters (leaf life span, nitrogen content, C/N ratio, toughness, total phenolics and condensed tannin) to days of larval survival. All statistical analyses employed the Stat View statistical software (version 5·0.1 SAS Institute, Cary, NC, USA).

RESULTS

Correlation between photosynthetic parameters, defensive traits and leaf life span

Nitrogen content was strongly negatively correlated with leaf life span (P < 0·01, Fig. 1A). Early successional species (A. hirsuta, B. maximowicziana and B. platyphylla ‘japonica’), which have a shorter leaf life span, had approx. 30 mg g−1 nitrogen content, and late successional species (C. cordata, Q. mongolica ‘grosseserrata’ and A. mono), which have a longer leaf life span, had approx. 16 mg g−1 nitrogen content. In contrast, the C/N ratio of leaves was positively correlated with leaf life span (P < 0·01, Fig. 1B). The light-saturated photosynthetic rate per unit leaf area (Psat-area) and Psat-mass were both negatively correlated with leaf life span (Psat-area, P < 0·01; Psat-mass, P = 0·04, Fig. 1C).

Fig. 1.

Fig. 1.

Open in a new tab

Correlation between leaf life span and (A) nitrogen content, (B) C/N ratio and (C) light-saturated photosynthetic rate per leaf mass (Psat) of leaves. Ah = Alnus hirsuta, Bm = Betula maximowicziana, Bp = Betula platyphylla ‘japonica’, Oj = Ostrya japonica, Cc = Carpinus cordata, Qm = Quercus mongolica ‘grosseserrata’, Am = Acer mono.

There was a weak positive correlation between the concentration of total phenolics and leaf life span (P = 0·08, Fig. 2A). However, if A. hirsuta, which has less nitrogen limitation because of its symbiotic micro-organism, was removed from the statistical calculation, there was a significant positive correlation between total phenolics and leaf life span (P < 0·01). Condensed tannin was not correlated with leaf life span (P = 0·60, Fig. 2B). The concentration of condensed tannin was much higher in O. japonica than in the other species. Leaf toughness was positively correlated with leaf life span (P = 0·04, Fig. 2C). The leaf toughness of Q. mongolica was markedly greater than in the other species, and toughness in the early successional species was relatively low. LMA was also positively correlated with leaf life span, although this correlation was not statistically significant (P = 0·42). Betula platyphylla had the lowest LMA, 2·51 mg cm−2, and Q. mongolica had the highest LMA, 5·77 mg cm−2.

Fig. 2.

Fig. 2.

Open in a new tab

Correlation between leaf life span and (A) total phenolics, (B) condensed tannin and (C) toughness of leaves. See Fig. 1 for key to abbreviations.

Stepwise multiple regression analysis also indicated the strong correlation between leaf nitrogen content and leaf life span. Leaf life span was related primarily to nitrogen content (adjusted r2 = 0·849, F = 34·725, P = 0·002). Nitrogen content and leaf toughness explained 91 % of the leaf life span (adjusted r2 = 0·907, F = 30·314, P = 0·0038). Nitrogen content, leaf toughness and Psat-mass explained 97 % of the leaf life span (adjusted r2 = 0·972, F = 69·641, P = 0·0028). The contribution of chemical defences (total phenolics and condensed tannin) to the leaf life span was very weak and chemical defences were rejected from the stepwise multiple regression analysis.

Bioassay test

The number of days of survival of larvae was negatively correlated with leaf life span, although the effect was statistically marginal (P = 0·07, Fig. 3A). The number of days of larval survival was positively correlated with nitrogen content (P = 0·03, Fig. 3B). There was no relationship between days of larval survival and chemical defences (total phenolics, P = 0·60; condensed tannin, P = 0·51). Leaf toughness was also unrelated to days of larval survival (P = 0·52).

Fig. 3.

Fig. 3.

Open in a new tab

Correlation between days of larval survival and (A) leaf life span and (B) nitrogen content. See Fig. 1 for key to abbreviations.

Stepwise multiple regression analysis also indicated that the days of larval survival were explained only by the nitrogen content (adjusted r2 = 0·574, F = 9·073, P = 0·0297). Other parameters were rejected from the stepwise multiple regression analysis.

DISCUSSION

High nitrogen content (Fig. 1A) and/or Psat (Fig. 1C), implying high photosynthetic productivity in short-lived leaf species, and a high level of toughness (Fig. 2C), implying high physical strength in long-lived leaf species, support the cost–benefit hypothesis proposed by several authors (Mooney and Gulmon, 1982; Kikuzawa, 1991). With regard to chemical defences, these are also essential to maintain long-lived leaves, because long-lived leaves are at greater risk of herbivore attack over their life span than short-lived leaves. We found a significant correlation between total phenolics and leaf life span only if A. hirsuta was excluded from the statistical analysis (Fig. 2A). Why is the concentration of total phenolics of A. hirsuta relatively high, despite the fact that it has short-lived leaves? A possible reason is that A. hirsuta is less limited in its nitrogen supply and that this promotes the synthesis of phenolic compounds. Alnus hirsuta has symbiotic nitrogen-fixing micro-organisms in its root system (Kikuzawa, 1982). Phenolic metabolites are derived from the aromatic amino acid phenylalanine (Waterman and Mole, 1994), which of course contains nitrogen and must be synthesized from a nitrogen source.

The number of days of larval survival was explained well only by leaf nitrogen content (Fig. 3B). This indicates that the effect of leaf nitrogen content on the survival of S. cynthia ricini larvae is much stronger than the effect of defensive traits. It appears that the high palatability of short-lived leaf species is not always explained solely by the amount of phenolic compounds and toughness. Several studies of gypsy moths have also shown that larval survival and/or growth are not well explained solely by the amount of phenolic compounds (Hunter and Lechowicz, 1992; Traw et al., 1996; Lindroth and Kinney, 1998). Species-by-species characteristics of the leaf nitrogen content and other chemical compounds should be taken into account when estimating palatability to herbivores.

Acknowledgments

We thank Dr Konno Kotaro (National Institute of Agrobiological Science) who provided egg masses of the Eri silkmoth, and Tomohiro Abe and Takanori Shibata for help with bioassay testing. Financial support from the Japan Society of Promotion of Science of MEXT is acknowledged (Basic Research Type A to T.K. and Young Scientists to S.M.).

Present address: Hokkaido Forestry Research Institute, Bibai 079-0198, Japan.

LITERATURE CITED

  1. Augspurger CK. 1983. Offspring recruitment around tropical trees: changes in cohort distance with time. Oikos 40: 189–196. [Google Scholar]
  2. Bate-Smith EC. 1977. Astringent tannins of Acer species. Phytochemistry 16: 1421–1426. [Google Scholar]
  3. Bazzaz FA. 1979. The physiological ecology of plant succession. Annual Review of Ecology and Systematics 10: 351–371. [Google Scholar]
  4. Chapin FS III, Johnson DA, McKendrick JD. 1980. Seasonal movement of nutrients in plants of differing growth form in an Alaskan tundra ecosystem: implications for herbivory. Journal of Ecology 68: 189–209. [Google Scholar]
  5. Coley PD. 1988. Effects of plant growth rate and leaf lifetime on the amount and type of anti-herbivore defense. Oecologia 74: 531–536. [DOI] [PubMed] [Google Scholar]
  6. Coley PD, Bryant JP, Chapin FS. 1985. Resource availability and plant antiherbivore defense. Science 230: 895–899. [DOI] [PubMed] [Google Scholar]
  7. Folin O, Ciocalteu V. 1927. On tyrosine in proteins as determination in proteins. Journal of Biological Chemistry 27: 627–650. [Google Scholar]
  8. Fukui A, Murakami M, Konno K, Nakamura M, Ohgushi T. 2002. A leaf-rolling caterpillar improves leaf quality. Entomology Science 5: 263–266. [Google Scholar]
  9. Herms DA, Mattson WJ. 1992. The dilemma of plants: to grow or defend. Quarterly Review of Biology 67: 283–335. [Google Scholar]
  10. Hunter AF, Lechowicz MJ. 1992. Foliage quality change during canopy development of some northern hardwood trees. Oecologia 89: 316–323. [DOI] [PubMed] [Google Scholar]
  11. Hunter MD, Forkner RE, McNeil JN. 1999. Heterogeneity in plant quality and its impact on the population ecology of insect herbivores. In: Hutchings MJ, John EA, Stewart AJA, eds. The ecological consequences of environmental heterogeneity. Oxford: Blackwell Science, 155–179.
  12. Janzen DH. 1970. Herbivores and the number of tree species in tropical forests. American Naturalist 104: 501–528. [Google Scholar]
  13. Julkunen-Tiitto R. 1985. Phenolic constituents in the leaves of northern willows: methods for the analysis of certain phenolics. Journal of Agricultural and Food Chemistry 33: 213–217. [Google Scholar]
  14. Kikuzawa K. 1982. Leaf survival and evolution in Betulaceae. Annals of Botany 50: 345–353. [Google Scholar]
  15. Kikuzawa K. 1986. Leaf survival strategy of forest trees. Japanese Journal of Ecology 36: 131–136. [Google Scholar]
  16. Kikuzawa K. 1991. A cost–benefit analysis of leaf habit and leaf longevity of trees and their geographical pattern. American Naturalist 138: 1250–1263. [Google Scholar]
  17. Koike T. 1987. Photosynthesis and expansion in leaves of the early, mid, and late successional tree species, birch, ash and maple. Photosynthetica 21: 503–508. [Google Scholar]
  18. Koike T. 1988. Leaf structure and photosynthetic performance as related to the forest succession of deciduous broad-leaved trees. Plant Species Biology 3: 77–87. [Google Scholar]
  19. Koike T. 1995. Effects of CO2 in interaction with temperature and soil fertility on the foliar phenology of alder, birch, and maple seedlings. Canadian Journal Botany 73: 149–157. [Google Scholar]
  20. Koike T, Sakagami Y. 1985. Comparison of the photosynthetic responses to temperature and light of Betula maximowicziana and Betula platyphylla var. japonica. Canadian Journal of Forest Research 15: 631–635. [Google Scholar]
  21. Koike T, Tobita H, Shibata T, Mastuki S, Konno K, Kitao M, Yamashita N, Maruyama Y. 2006. Defense characteristics of seral deciduous broad-leaved tree seedlings grown under differing levels of CO2 and nitrogen. Population Ecology 48: 23–29. [Google Scholar]
  22. Konno K, Hirayama C, Nakamura M, Tateishi K, Tamura Y, Hattori M, Kohno K. 2004. Papain protects papaya trees from herbivorous insects: role of cysteine proteases in latex. The Plant Journal 37: 370–378. [DOI] [PubMed] [Google Scholar]
  23. Lindroth RL, Kinney KK. 1998. Consequences of enriched atmospheric CO2 and defoliation for foliar chemistry and gypsy moth performance. Journal of Chemical Ecology 24: 1677–1695. [Google Scholar]
  24. Matsuki S, Sano Y, Koike T. 2004. Chemical and physical defense in the early and late leaves in three heterophyllous birch species native to northern Japan. Annals of Botany 93: 141–147. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Mooney HA, Gulmon SL. 1982. Constraints on leaf structure and function in reference to herbivory. BioScience 32: 198–206. [Google Scholar]
  26. Pacala SW, Crawley MJ. 1992. Herbivores and plant diversity. American Naturalist 140: 243–260. [DOI] [PubMed] [Google Scholar]
  27. Reich PB, Koike T, Gower ST, Schoettle AW. 1995. Causes and consequences of variation in conifer leaf life-span. In: Smith WK, Hinckley TM, eds. Ecophysiology of coniferous forests. New York: Academic Press, 225–254.
  28. Riipi M, Ossipov V, Lempa K, Haukioja E, Koricheva J, Ossipova S, Pihlaja K. 2002. Seasonal changes in birch leaf chemistry: are there trade-offs between leaf growth and accumulation of phenolics? Oecologia 30: 380–390. [DOI] [PubMed] [Google Scholar]
  29. Traw MB, Lindroth RL, Bazzaz FA. 1996. Decline in gypsy moth (Lymantria dipar) performance in an elevated CO2 atmosphere depends upon host plant species. Oecologia 108: 113–120. [DOI] [PubMed] [Google Scholar]
  30. Underwood N, Rausher M, Cook W. 2002. Bioassay versus chemical assay: measuring the impact of induced and constitutive resistance on herbivores in the field. Oecologia 131: 211–219. [DOI] [PubMed] [Google Scholar]
  31. Waterman PG, Mole S. 1994. Analysis of Phenolic Plant Metabolites. London: Blackwell Science Publications.

Articles from Annals of Botany are provided here courtesy of Oxford University Press

RESOURCES