摘要
稀树草原是全球生态系统的重要组成部分,世界主要稀树草原生态系统具有不同的地貌特征和独立的演化历史。水分、养分、火烧和和放牧是稀树草原生态系统结构和功能特征的最重要影响因素,树种幼苗的补充和更新是影响稀树草原长期动态平衡的关键阶段。然而,前人的研究尚未阐明资源和干扰对树种幼苗生长的影响及相对重要性、树种适应模式的共性和特性、以及适应模式与树种起源的关系。
本研究选取热带亚热带地区非洲和澳大利亚的稀树干草原和稀树湿草原的代表性树种,进行树种幼苗的温室实验,观察水分、养分梯度和树草竞争对树种幼苗生长的影响,探讨主要的植物功能性状对树种起源和不同处理条件的响应,研究功能性状间的相关性,以发现树种的适应模式,并分析不同的适应模式是否能够反映不同大洲的地貌特征及稀树草原独立的演化进程。
研究发现:(1)植物通过调整自身的生长模式和资源分配格局来适应环境,树种在长期进化过程中发展出的不同适应模式反映了其生长地的气候和干扰特征。(2)植物体需要平衡相对生长速率与自我防卫和养分保有能力间的关系。二者的平衡态势随植物体生长发育的不同阶段而不同,并受环境条件的影响。(3)稀树草原树种的生长受水分、养分的促进和树草竞争的抑制。氮供应的增加促进了地上部的生长尤其是增加了茎部的生物量分配,提高了叶片的光合能力。土壤含水量主要影响根系的形态结构、生长模式和植物体内水分含量。树种幼苗与草在地下为获取更多的水分和养分的竞争和在地上为获取更多光能的竞争同样激烈。(4)植物对环境的适应具有趋同进化的特点;植物功能性状间相互关联,性状的组合决定着植物群落与生态系统功能之间的相互作用。这些研究结果提示,不同大陆的稀树草原树种对环境的适应性生长策略具有一致性,但受到自身独立演化进程的影响,种系发生可能对树种的响应模式有重要影响。
Savanna is an important ecosystem throughout the world, characterized by the co-occurrence of trees and grasses. Savanna vegetation has variable physiognomy and floristic composition, the result of independent evolution on different continents from a host of plant genera in response to local environmental conditions. Water, nutrient, fire and herbivory are key environmental determinants. Tree seedling recruitment and establishment is the critical stage to long-term balance and dynamics in savanna.
However, the questions of whether and how species have adapted to differences in environmental variables expressed at continental scales and whether these adaptations have affected their abilities to grow in competition with grasses remain elusive. In order to access this, I conducted a greenhouse pot trial experiment to test the effect of resource availability and competition with grass on the growth of tree seedlings of species that are dominant in semi-arid and humid savannas in Africa and Australia. Various plant functional traits in relation to treatments, continents and savanna types have been evaluated using General Linear Model; correlations between these traits are further calculated by Spearman’s correlation.
Main findings are: (1) Biomass allocation pattern is a major factor in the response of plants to limited resource supply and disturbance; (2) The trade-off between relative growth rate and nutrient acquisition and conservation is affected by plant developmental stage and environmental stress; (3) Seedling growth is positively correlated with water and nutrient availability and inhibited by tree-grass competition. Growing pattern reflects local environmental conditions and is modified by independent flora evolution across continents; (4) Species’seedlings show convergent traits for environmental conditions. The association of plant functional traits and trait-environment linkage affect and reflect the ecological interaction between plant community and their ecosystem.
引文
[1] Cole M M. The Savannas: Biogeography and Geobotany. London: Academic Press, Harcourt Brace Jovanovich Publishers, 1986. 111-298
[2] Sims P L. Grasslands. In: Barbour M G & Billings W D, eds. North American terrestrial vegetation. Cambridge: Cambridge University Press, 1988. 265-286
[3] Scholes R J. Savanna. In: Cowling R M, Richardson D M & Pierce S M, eds. Vegetation of Southern Africa. Cambridge: Cambridge University Press, 1997. 258-277
[4] Eva H D, Glinni A, Janvier P, et al. Vegetation map of tropical South America at 1:5 000 000. Germany: European Communities, 1998. 3-5
[5] Specht R L and Specht A. Australian plant communities: dynamics of structure, growth and biodiversity. Melbourne: Oxford University Press, 1999. 23-37
[6] Stibig H J and Beuchle R. Forest cover map of continental Southeast Asia at 1:4 000 000 derived from Spot4-vegetation satellite images. Germany: European Communities, 2003. 10-12
[7] Grime J P. Benefits of plant diversity to ecosystems: immediate, filter and founder effects. Journal of Ecology, 1993, 86: 902-910
[8]于顺利,陈宏伟.内蒙古高原温带稀树草原生态系统特征与成因.生态学杂志,2007,26(4):549-554
[9] San JoséJ J, Montes R, and Mazorra M. The nature of savanna heterogeneity in the Orinoco Basin. Global Ecology and Biogeography Letters, 1998, 7: 441-455
[10] Kottek M, Grieser J, Beck C, et al. World map of the K?ppen-Geiger climate classification updated. Meteorologische Zeitschrift, 2006, 15:259-263
[11]倪健.区域尺度的中国植物功能型与生物群区.植物学报,2001,43(4):419-425
[12] Larom D, Garstang M, Raspet R, et al. Abiotic controls on elephant communication. Acoustical Society of America, 1994, 96: 3297-3298
[13] Midgley J J and Lawes M J. Savanna woody plant dynamics: the role of fire and herbivory, separately and synergistically. Australian Journal of Botany, 2010, 58(1): 1-11
[14] Lavorel S and Chesson P L. How species with different regeneration niches coexist in patchy habitats with local disturbances. Oikos, 1995, 74: 103-114
[15] Toledo and Bush M B. A Holocene pollen record of savanna establishment in coastal Amapá. Anais Da Academia Brasileira De Ciências, 2008, 80(2): 341-351
[16] Overbeck G E and Pfadenhauer J. Adaptive strategies in burned subtropical grassland in southern Brazil Flora, 2007, 202(1): 27-49
[17] Archer S, Coughenour M, Dall'Aglio C, et al. Savanna biodiversity and ecosystem properties. Biodiversity and Savanna Ecosystem Processes-a Global Perspective. Berlin: Springer-Verlag, 1997. 207-215
[18] Grover H D and Musick H B. Shrubland encroachment in Southern New Mexico, U. S. A.: an analysis of desertification process in the American Southwest. Climatic Change, 1990, 17: 305-330
[19] Scholes R J and Archer S R. Tree-Grass interaction in savannas. Annual Review of Ecology and Systematics, 1997, 28: 517-544
[20] Illius A W and O’Connor T G. On the relevance of non-equilibrium concepts to arid and semiarid grazing systems. Ecological Application, 1999, 9: 798-813
[21] Higgins S I, Bond W J, and Trollope W S. Fire, resprouting and variability: a recipe for grass-tree coexistence in savanna. Journal of Ecology, 2000, 88, 213-229
[22] Jeltsch F, Weber G E, and Grimm V. Ecological buffering mechanisms in savannas: a unifying theory of long-term tree-grass coexistence. Plant Ecology, 2000, 161: 161-171.
[23] Sankaran M, Hanan N P, Scholes R J, et al. Determinants of woody cover in African savannas. Nature, 2005, 438: 846-849
[24] Kraaij J and Ward D. Effects of rain, nitrogen, fire and grazing on tree recruitment and early survival in bush-encroached savanna, South Africa. Plant Ecology, 2006, 186: 235-246.
[25] Koch J M, Richardson J, and Lamont B B. Grazing by kangaroos limits the establishment of the grass trees Xanthorrhoea gracilis and X. preissii in restored bauxite mines in Eucalypt forest of Southwestern Australia. Restoration Ecology, 2004, 12: 297-305
[26] Williams R J, Duff G A, Bowman D M J S, et al. Variation in the composition and structure of tropical savannas as a function of rainfall and soil texture along a large scale climatic gradient in the northern territory, Australia. Journal of Biogeography, 1996, 23: 747-756
[27] Henley W J, Levavasseur G, and Franklin L A. Photoacclimation and photoinhibition in Ulva rotundata as influenced by nitrogen availability. Planta, 1991, 184: 235-243.
[28] Bowman W D, Bahnj L, and Damm M. Alpine landscape variation in foliar nitrogen and phosphorus concentration and the relation to soil nitrogen and phosphorus availability. Arctic Antarctic and Alpine Research, 2003, 35(2): 144-149
[29] Aerts R. Nutrient resorption from senescing leaves of perennials: are there general patterns? Ecology, 1996, 84: 597-608
[30] Thompson K, Parkinson J A, Band S R, et al. A comparative study of leaf nutrient concentration in a regional herbaceous flora. New Phytologist, 1997, 136: 679-689
[31] Frost P G H and Robertson F. The ecological effects of fire in savannas. Determinants of Tropical Savannas. Paris: IRL Press, 1987. 93-140
[32] Frost P G H, Medina E, Menaut J C, et al. Responses of savannas to stress and disturbance. Biology International, 1985, 10: 1-82
[33] Hoffmann W A. The effects of fire and cover on seedling establishment in a neotropical savanna. Journal of Ecology, 1996, 84: 383-393
[34] Hoffmann W A. Post-burn reproduction of woody plants in a neotropical savanna: the relative importance of sexual and vegetative reproduction. Journal of Applied Ecology, 1998, 35: 422-433
[35] Olff H, Ritchie M E, and Prins H H T. Global environmental controls of diversity in large herbivores. Nature, 2002, 415: 901-904
[36] Digby P G N and Kempton R A. Multivariate Analysis of Ecological Communities. London: Chapman & Hall, 1987. 32-53
[37] Thomas C D, Cameron A, Green R E, et al. Extinction risk from climate change, Nature, 2004, 427(6970): 145-148
[38] Polis G A. Why are parts of the world green? Multiple factors control productivity and the distribution of biomes. Oikos, 1999, 86: 3-15
[39] Bond W J and Midgley J J. The evolutionary ecology of sprouting in woody plants. Int. J. Plant Sci. 2003, 164: S103-S114
[40] Loreau M, Naeem S, Inchausti P, et al. Biodiversity and ecosystem functioning: current knowledge and future challenges. Science, 2001, 294: 804-808
[41] Price G J and Webb G E. Late Pleistocene sedimentlogy, taphonomy and megafauna extinction on the Darling Downs, southeastern Queensland. Australian Journal of Earth Sciences, 2006, 53: 947-970
[42] Wroe S and Field J. A review of the evidence for a human role in the extinction of Australian megafauna and an alternative interpretation. Quaternary Science Reviews, 2006, 25: 2692-2703
[43] Sarmiento G. The Ecology of Neotropical Savannas. USA: Harvard University Press, 1984. 33-56
[44] Walker B H and Noy-Meir I. Aspects of the stability and resilience of savanna ecosystems. In: Huntly B J & Walker B H, eds. Ecology of tropical savannas. Berlin: Springer-Verlag, 1982. 556-590
[45] Menaut J C, Gignoux J, Prado C, et al. Tree community dynamics in a humid savanna of the Cote-d’Ivoire: modeling the effects of fire and competition with grass and neighbours. Journal of Biogeography, 1990, 17: 471-481
[46] Van Wijk M T and Rodriguez-Iturbe I. Tree-grass competition in space and time: Insights from a simple cellular automata model based on ecohydrological dynamics. Water Resources Research, 2002, 38: 1179-1193
[47] Rossiter N A, Setterfield S A, Douglas M M, et al. Testing the grass-fire cycle: alien grass invasion in the tropical savannas of northern Australia. Diversity and Distribution, 2003, 9: 169-176
[48] Williams D G and Baruch Z. African grass invasion in the Americas: ecosystem consequences and the role of ecophysiology. Biological Invasions, 2000, 2: 123-140.
[49] Davis M A, Wrage K J, and Reich P B. Competition between tree seedlings and herbaceous vegetation: support for a theory of resource supply and demand. Journal of Ecology, 1998, 86 :652-661
[50] Gordon D R and Rice K J. Competitive suppression of Quercus douglasii (Fagaceae) seedling emergence and growth. American Journal of Botany, 2000, 87: 986-994
[51] Dickie I A, Schnitzer S A, Reich P B, et al. Is oak establishment in old-fields and savanna openings context dependent? Journal of Ecology, 2007, 95: 309-320
[52] Brown J R and Archer S. Shrub invasion of grassland: recruitment is continuous and not regulated by herbaceous biomass or density. Ecology, 1999, 80: 2385-2396
[53] Bond W J, Smythe K A, and Balfour D A. Acacia species turnover in space and time in an African savanna. Journal of Biogeography, 2001, 28: 117-128
[54] Li J, Duggin J A, Grant C D, et al. Germination and early survival of Eucalyptus blakelyi in grasslands of the new England Tablelands, NSW, Australia. Forest Ecology and Management, 2003, 173: 319-334
[55] Barot S, Gignoux J, and Menaut J C. Demography of a savanna palm tree: prediction from comprehensive spatial pattern analysis. Ecology, 1999, 80: 1987-2005
[56] Goheen J R, Keesing F, Allan B F, et al. Net effects of large mammals on Acacia seedling survival in an African savanna. Ecology, 2004, 85: 1555-1561
[57] Khurana E and Singh J S. Influence of seed size on seedling growth of Albizia procera under different soil water levels. Annals of Botany, 2000, 86: 1185-1192
[58] Weltzin J F and McPherson G R. Facilitation of conspecific seeding recruitment and shifts in temperate savanna ecotones. Ecological Monographs, 1999, 69: 513-534
[59] Anderson L J, Brumbaugh M S, and Jackson R B. Water and tree-understory interaction: a natural experiment in a savanna with Oak Wilt. Ecology, 2001, 82: 33-49.
[60] Barnes P W and Archer S. Tree-shrub interaction in a subtropical savanna parkland: competition or facilitation? Journal of Vegetation Science, 1999, 10: 525-536
[61] Bauhus J, Van Winden A P, and Nicotra A B. Aboveground interaction and productivity in mixed-species plantations of Acacia mearnsii and Eucalyptus globulus. Canadian Journal of Forest Research, 2004, 34: 686-694
[62] Hoffmann W A and Franco A C. Comparative growth analysis of tropical forest and savanna woody plants using phylogenetically independent contrasts. Journal of Ecology, 2003, 91: 475-484
[63] Kanegae M F, Braz V, and Franco A C. Effects of seasonal drought and light availability on growth and survival of Bowdichia virgilioides in two characteristic savanna physiognomies of Central Brazil. Revista Brasileira de Botanica, 2000, 23: 457-466
[64] Sankaran M, Ratnam J, and Hanan N P. Tree-grass coexistence in savannas revisited- insights from an examination of assumption and mechanisms invoked in existing models. Ecology Letters, 2004, 7: 480-490
[65] Sarmiento G. Adaptive Strategies of Perennial Grasses in South American Savannas. Journal of Vegetation Science, 1992, 3: 325-336
[66] Tomlison K W, Van Langevelde F, Barbosa E R M, et al. Review: tree seedling recruitment in savannas (In prep.)
[67] Kelly R D and Walker B H. The effects of different forms of land use on the ecology of a semi-arid region in southeastern Rhodesia. Journal of Ecology, 1976, 64: 553-576
[68] Kress W J, Wurdack K J, Zimmer E A, et al. Use of DNA barcodes to identify flowering plants. PNAS 2005, 102: 8369-8374
[69] Shaw J, Lickey E B, Beck J T, et al. The tortoise and the hare II: relative utility of 21 noncoding chloroplast DNA sequences for phylogenetic analysis. American Journal of Botany, 2005, 92: 142-166
[70] Leigh J H. The relative palatability of various varieties of weeping lovegrass Eragrostis curvula. Grass and Forage Science, 1961, 16(2): 135-140
[71] Tilman D. Secondary succession and the pattern of plant dominance along experimental nitrogen gradients. Ecological Monographs, 1987, 57: 189-214
[72] Pant A P, Radovich T J K, Hue N V, et al. Vermicompost extracts influence growth, mineral nutrients, phytonutrients and antioxidant activity in pak choi (Brassica rapa cv. Bonsai, Chinensis group) grown under vermicompost and chemical fertiliser. Journal of the Science of Food and Agriculture 2009, 89(14): 2383-2392
[73] Damaraju L and Raghavarao D. Fractional plans to estimate main effects and two factor interactions inclusive of a specific factor. Biometrical Journal, 2002, 44(6): 780-785
[74] Miller M F. Acacia seed survival, seed germination and seedling growth following pod consumption by large herbivores and seed chewing by rodents. African Journal of Ecology, 1995, 33(3): 194-210
[75] Reisman-berman O, Kigel J, and Rubin B. Short soaking in water inhibits germination of Datura ferox L. and D. stramonium L. seeds. Weed Research, 1989, 29(5): 357-363
[76] Hsiao W F and Bidochka M J. Effect of temperature and relative humidity on the virulence of the entomopathogenic fungus, Verticillium lecanii, toward the oat-bird berry aphid, Rhopalosiphum padi (Hom., Aphididae). Journal of Applied Entomology, 1992, 114(1-5): 484-490
[77] Pavlik B M and Nickrent D L. The recovery of an endangered plant. I. creating a new population of Amsinckia grandiflora. Coervation Biology, 1993, 7(3): 510-526
[78] Landsberg J A. Comparison of methods for assessing defoliation, tested on eucalypt trees. Austral Ecology, 1989, 14(4): 423-440
[79] Rytter L and Ericsson T. Leaf nutrient analysis in Salix viminalis (L.) energy forest stands growing on agricultural land. Zeitschrift für Pflanzenern?hrung und Bodenkunde 1993, 156(4): 349-356
[80]纪佩吉,卓海燕,翁晓敏等.粤东地区重要外来有害植物叶蛋白含量的研究.中国野生植物资源,2005,24(6):48-50
[81] Baraloto C and Paine C E T. Functional trait variation and sampling strategies in species-rich plant communities. Functional Ecology, 2010, 24(1): 208-216
[82] Nguyen D V and ?entürk Damla. Covariate-adjusted regression for longitudinal data incorporating correlation between repeated measurements. Australian and New Zealand Journal of Statistics, 2009, 51(3): 319-333
[83] Brown P J and Vannucci M. Bayes model averaging with selection of regressors. Journal of the Royal Statistical Society: Series B (Statistical Methodology), 2002, 64(3): 519-536
[84] Kingman A and Zion G. Some power considerations when deciding to use transformations. Statistics in Medicine, 1994, 13(5-7): 769-783
[85] Schielzeth H. Simple means to improve the interpretability of regression coefficients. Methods in Ecology and Evolution, 2010, 1(2): 103-113
[86] Bakshi B R. Multiscale PCA with application to multivariate statistical process monitoring. AIChE Journal, 1998, 44(7): 1596-1610
[87]项文化,田大伦,闫文德.森林生物量与生产力研究综述.中南林业调查规划,2003,22(3):57-64
[88]任海彦,郑淑霞,白永飞.放牧对内蒙古锡林河流域草地群落植物茎叶生物量资源分配的影响.植物生态学报,2009,33(6):1065-1074
[89]王静,杨持,王铁娟.放牧退化群落中冷蒿种群生物量资源分配的变化.应用生态学报,2005,16(12):2316-2320
[90]田大栓,包祥,关其格等.内蒙古草原3种针茅属植物不同组织水平的生物量生殖分配.植物生态学报,2009,33(1):97-107
[91] Holechek J, Pieper R D, and Herbel C H. Range Management: Principles and Practices. Fifth edition. New Jersey: Pearson Prentice Hall, 2002, 71-93
[92] Schoener T. Field experiments on interspecific competition. American Naturalist, 1983, 122: 240-285
[93] Monk C D. An ecological significance of evergreenness. Ecology, 1966, 47: 504–505
[94] Oria G H and Solbrig O T. A cost-income model of leaves and roots with special reference to arid and semi-arid areas. American Naturalist, 1977, 111: 677–690
[95] Takashima T, Hikosake K, and Himse T. Photosynthesis or persistence: nitrogen allocation in leaves of evergreen and deciduous Quercus species. Plant, Cell and Environment, 2004, 27: 1047-1054
[96] Pooter H and Eva J R. Photosynthetic nitrogen-use efficiency of species that differ inherently in specific area. Oecologia, 1998, 116: 26-37
[97] Shangguan Z P, Shao M A, and Dyckma J. Effects of nitrogen nutrition and water deficit on net photosynthetic rate and chlorophyll fluorescence in winter wheat. Journal of Plant Physiology, 2000, 156: 46-51
[98] Shangguan Z P, Zheng S X, and Zhang L M. Effect of nitrogen fertilization on leaf chlorophyll fluorescence in field grown winter wheat under rained condition. Agricultural Sciences in China, 2005, 4(1): 15-20
[99] Taub D R and Lerdau M T. Relationship between leaf nitrogen and photosynthetic rate for three NAD-ME and three NADP-ME C4 grass. American Journal of Botany, 2000, 87: 412-417
[100] Shipley B and Thi-Tam Y. Dry matter content as a measure of dry matter concentration in plants and their parts. New Phytologist, 2002, 153: 359-364
[101] ReichP B, Ellsworth D S, Walters M B, et al. Generality of leaf trait relationships: a test across six biomes. Ecology, 1999, 80: 1955-1969
[102] Eviner V T and Chapin F S III. Functional matrix: a conceptual framework for predicting multiple plant effects on ecosystem processes. Annual Review of Ecology, Evolution and Systematics, 2003, 34: 455-485
[103] Tjoelker M G, Craine J M, Wedin D, et al. Linking leaf and root trait syndromes among 39 grassland and savannah species. New Phytologist, 2005, 167: 493-508
[104] Norby R J and Jackson R B. Root dynamics and global change: seeking an ecosystem perspective. New phytologist, 2000, 147: 3-12
[105] Reich P B, Tilman D, Craine J, et al. Do species and functional groups differ in acquisition and use of C, N and water under varying atmospheric CO2 and N availability regimes? A field test with 16 grassland species. New Phytologist, 2001, 150: 435-448
[106] Westoby M, Falster D S, Moles A T, et al. Plant ecological strategies: some leading dimensions of variation between species. Annual Review of Ecology and Systematics, 2002, 33: 125-15
[107] Reich P B, Walters M B, and Ellsworth D S. From tropics to tundra: global convergence in plant functioning. Proceedings of the National Academy of Sciences of the United States of America, 1997, 94: 13730-13734.
[108] Craine J M and Lee W G. Covariation in leaf and root traits for native and non-native grasses along an altitudinal gradient in New Zealand. Oecologia, 2003, 134: 471-478
[109] Kerkhoff A J, Fagan W F, Elser J J, et al. Phylogenetic and growth form variation in the scaling of nitrogen and phosphorus in the seed plants. American Naturalist, 2006, 168: E103-E122
[110] Craine J M, Froehle J, Tilman D G, et al. The relationships among root and leaf traits of 76 grassland species and relative abundance along fertility and disturbance gradients. Oikos, 2001, 93: 274-285
[111] Ryan M G. Effects of climate change on plant respiration. Ecological Applications, 1991, 1: 157-167
[112] Wright I J, Reich P B, Westoby M, et al. The worldwide leaf economics spectrum. Nature, 2004, 428: 821-827