基于控水试验的喀斯特出露基岩生境植物水分来源分析
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摘要
裂隙发育的喀斯特出露基岩生境,虽无土层覆盖却能维持不同生活型植物的水分消耗.然而目前对该类生境植物的水分来源缺乏清晰认识.本研究以植物潜在水分来源相对简单的孤立出露基岩为例,聚焦遮雨(即剔除雨水对浅层水源的补给)1年后仍然生长旺盛的代表性植物种,同时以无遮雨处理样地(即始终接受降雨补给)的同种植物为对照,运用稳定性氢氧同位素技术,结合对植物水势的测定,综合分析了3种典型植物(落叶乔木菜豆树、落叶乔木紫弹树、常绿灌木四子海桐)的水分来源.结果表明:在降水充沛的雨季,遮雨条件下3种植物均依赖与泉水同位素比率相近的深层水源,这是植物在遮雨1年后仍能正常生长的根本原因;遮雨菜豆树和四子海桐凌晨水势与自然植株无显著差异,表明植物未受水分胁迫,而紫弹树凌晨水势显著低于自然植株,表明其受一定程度的水分胁迫;自然条件下,3种植物茎水同位素比率均显著低于遮雨植株,且处于近期雨水同位素比率波动范围内,表明植物均依赖受近期雨水主导的浅层水源.遮雨和自然条件下,四子海桐正午水势与凌晨水势始终无明显差异,表现出较为保守的水分利用策略;另外2种植物正午水势显著低于凌晨水势,属于偏挥霍型水分利用策略.具备利用浅层和深层水源的能力是喀斯特无土覆盖出露基岩生境植物适应不同水分环境和维持多样化水分利用策略的关键.
Although lack of soil coverage, rock outcrops with developed fractures in karst region can maintain water consumption of plants with different life forms. Water sources for plants on these habi-tats are unclear. Isolated rocky outcrop with relatively simple sources of water was selected for this study. We focused on typical plant species that still thrived after excluding rainfall(removing the water supply to the shallow water) over one year, compared with the same plant species living without rain shelter(always receiving rainfall supplies). Water sources of three representative tree species(Radermachera sinica, Celtis biondii, and Pittosporum tonkinense) were analyzed by using stable isotope techniques and combining with the measurement of plant water potential. The results showed that all the three species depended on deep water sources with similar isotopic values to spring water under rain-sheltered condition, during the rainy season, which explained why plants could still grow normally after rainfall-exclusion over one year. The predawn water potential of R. sinica and P. tonkinense under rain-sheltered condition was not significantly different from those living in natural conditions, which indicated both species were not under water stress. The predawn water potential of C. biondii under rain-sheltered condition was significantly lower than individuals living in natural conditions, which indicated it was under water stress. Under natural condition, water isotope values of stems of all the three species were significantly lower than that under rain-sheltered condition and were within the range of fluctuation of recent rainwater isotope values, indicating that these plants relied on shallow water sources that dominated by recent rainfall. Under both rain-sheltered and natural conditions, there was no obvious difference between the predawn water potential and the midday water potential of P. tonkinense, showing a conservative water use strategy. The midday water potential of other two species was significantly lower than the predawn water potential, showing a profligate/opportunistic water use strategy. Our results indicated that the ability to utilize shallow and deep water sources is key for the plants growing on the habitat of Karst rock outcrops where they could adapt different water environments and maintain diversified water use strategies under the condition with no soil coverage.
Although lack of soil coverage, rock outcrops with developed fractures in karst region can maintain water consumption of plants with different life forms. Water sources for plants on these habi-tats are unclear. Isolated rocky outcrop with relatively simple sources of water was selected for this study. We focused on typical plant species that still thrived after excluding rainfall(removing the water supply to the shallow water) over one year, compared with the same plant species living without rain shelter(always receiving rainfall supplies). Water sources of three representative tree species(Radermachera sinica, Celtis biondii, and Pittosporum tonkinense) were analyzed by using stable isotope techniques and combining with the measurement of plant water potential. The results showed that all the three species depended on deep water sources with similar isotopic values to spring water under rain-sheltered condition, during the rainy season, which explained why plants could still grow normally after rainfall-exclusion over one year. The predawn water potential of R. sinica and P. tonkinense under rain-sheltered condition was not significantly different from those living in natural conditions, which indicated both species were not under water stress. The predawn water potential of C. biondii under rain-sheltered condition was significantly lower than individuals living in natural conditions, which indicated it was under water stress. Under natural condition, water isotope values of stems of all the three species were significantly lower than that under rain-sheltered condition and were within the range of fluctuation of recent rainwater isotope values, indicating that these plants relied on shallow water sources that dominated by recent rainfall. Under both rain-sheltered and natural conditions, there was no obvious difference between the predawn water potential and the midday water potential of P. tonkinense, showing a conservative water use strategy. The midday water potential of other two species was significantly lower than the predawn water potential, showing a profligate/opportunistic water use strategy. Our results indicated that the ability to utilize shallow and deep water sources is key for the plants growing on the habitat of Karst rock outcrops where they could adapt different water environments and maintain diversified water use strategies under the condition with no soil coverage.
引文
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[12] Kulmatiski A, Adler PB, Stark JM, et al. Water and nitrogen uptake are better associated with resource availa-bility than root biomass. Ecosphere, 2017, 8(3): e01738, doi: 10.1002/ecs2.1738
[13] Sobrado MA, Turner NC. A comparison of the water relations characteristics of Helianthus annuus and Helian-thus petiolaris when subjected to water deficits. Oecologia, 1983, 58: 309-313
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[15] Zeng F-J (曾凡江), Zhang X-M (张希明), Li X-Y (李向义), et al. Seasonal variation of Tamarix ramosissima and Populus euphratica water potentials in southern fringe of Taklamakan Desert. Chinese Journal of Applied Ecology (应用生态学报), 2005, 16(8): 1389-1393 (in Chinese)
[16] Franks PJ, Drake PL, Froend RH. Anisohydric but isohydrodynamic: Seasonally constant plant water potential gradient explained by a stomatal control mechanism incorporating variable plant hydraulic conductance. Plant, Cell & Environment, 2007, 30: 19-30
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[18] Nie Y-P (聂云鹏), Chen H-S (陈洪松), Wang K-L (王克林). Methods for determining plant water source in thin soil region: A review. Chinese Journal of Applied Ecology (应用生态学报), 2010, 21(9): 2427-2433 (in Chinese)
[19] McCole AA, Stern LA. Seasonal water use patterns of Juniperus asheion the Edwards Plateau, Texas, based on stable isotopes in water. Journal of Hydrology, 2007, 342: 238-248
[20] Nie Y-P (聂云鹏), Chen H-S (陈洪松), Wang K-L (王克林), et al. Challenges and probable solutions for using stable isotope techniques to identify plant water sources in karst regions: A review. Chinese Journal of Applied Ecology (应用生态学报), 2017, 28(7): 2361-2368 (in Chinese)
[21] Schwinning S. The water relations of two evergreen tree species in a karst savanna. Oecologia, 2008, 158: 373-383
[22] Dammeyer HC, Schwinning S, Schwartz BF, et al. Effects of juniper removal and rainfall variation on tree transpiration in a semi-arid karst: Evidence of complex water storage dynamics. Hydrological Processes, 2016, 30: 4568-4581
[23] Eggemeyer KD, Schwinning S. Biogeography of woody encroachment: Why is mesquite excluded from shallow soils? Ecohydrology, 2009, 2: 81-87
[24] Kukowski KR, Schwinning S, Schwartz BF. Hydraulic responses to extreme drought conditions in three codominant tree species in shallow soil over bedrock. Oecologia, 2013, 171: 819-830
[25] Ford D, Williams P. Karst Hydrogeology and Geomorphology. Chichester, England: John Wiley & Sons, 2007
[26] Hanson CT, Blevins RL. Soil water in coarse fragments. Soil Science Society of America Journal, 1979, 43: 819-820
[27] Poot P, Lambers H. Shallow soil endemics: Adaptive advantages and constraints of a specialized root-system morphology. New Phytologist, 2008, 178: 371-381
[28] Nie Y-P (聂云鹏), Chen H-S (陈洪松), Wang K-L (王克林). Seasonal variation of water sources for plants growing on continuous rock outcrops in limestone area of Southwest China. Chinese Journal of Plant Ecology (植物生态学报), 2011, 35(10): 1029-1037 (in Chinese)
[29] McCole AA, Stern LA. Seasonal water use patterns of Juniperus ashei on the Edwards Plateau, Texas, based on stable isotopes in water. Journal of Hydrology, 2007, 342: 238-248
[30] Hubbert KR, Beyers JL, Graham RC. Roles of weathe-red bedrock and soil in seasonal water relations of Pinus jeffreyi and Arctostaphylos patula. Canadian Journal of Forest Research, 2001, 31: 1947-1957
[31] Donovan LA, Ehleringer JR. Water stress and use of summer precipitation in a great basin shrub community. Functional Ecology, 1994, 8: 289-297
[32] Bucci SJ, Scholz F, Goldstein G, et al. Processes preventing nocturnal equilibration between leaf and soil water potential in tropical savanna tree species. Tree Physiology, 2004, 24: 1119-1127
[33] West AG, Dawson TE, February EC, et al. Diverse functional responses to drought in a Mediterranean-type shrubland in South Africa. New Phytologist, 2012, 195: 396-407
[2] Chen H-S (陈洪松), Fu W (傅伟), Wang K-L (王克林), et al. Dynamic change of soil water in Peak-Cluster depression areas of karst mountainous region in northwest Guangxi. Journal of Soil and Water Conservation (水土保持学报), 2006, 20(4):136-139 (in Chinese)
[3] May LH, Milthorpe FL. Drought resistance of crop plants. Field Crop Abstracts, 1962, 15: 171-179
[4] White JWC, Cook ER, Lawrence JR, et al. The D/H ratio of sap in trees: Implications for water resources and tree D/H ratios. Geochimica et Cosmochimica Acta, 1985, 49: 237-246
[5] Flanagan LB, Ehleringer JR, Marshall JD, et al. Diffe-rential uptake of summer precipitation among co-occurring trees and shrubs in a pinyon-juniper woodland. Plant, Cell and Environment, 1992, 15: 831-836
[6] Ehleringer JR, Roden J, Dawson TE. Assessing ecosystem-level water relations through stable isotope ratio analyses// Sala OE, Jackson RB, Mooney HA, eds. Metho-ds in Ecosystem Science. New York: Springer, 2000:181-214
[7] Dawson TE, Mambelli S, Plamboeck AH, et al. Stable isotopes in plant ecology. Annual Review of Ecology, Evolution, and Systematics, 2002, 33: 507-559
[8] Querejeta JI, Estrada-Medina H, Allen MF, et al. Water source partitioning among trees growing on shallow karst soils in a seasonally dry tropical climate. Oecologia, 2007, 152: 26-36
[9] Liu B-Q (刘保清), Liu Z-M (刘志民), Qian J-Q (钱建强), et al. Water sources of dominant sand-binding plants in dry season in southern Horqin Sandy Land, China. Chinese Journal of Applied Ecology (应用生态学报), 2017, 28(7): 2093-2101 (in Chinese)
[10] Fu A-H (付爱红), Chen Y-L (陈亚宁), Chen Y-P (陈亚鹏). Changes of stem water potential of Tamarix ramosissima under drought stress in lower reaches of Tarim River. Chinese Journal of Ecology (生态学杂志), 2008,27(4): 532-538 (in Chinese)
[11] Cheng X-F (成雪峰), Zhang F-Y (张凤云), Chai S-X (柴守玺). Stomatal response of spring wheat and related affecting factors under different irrigation treatment. Chinese Journal of Applied Ecology (应用生态学报), 2010, 21(1): 36-40 (in Chinese)
[12] Kulmatiski A, Adler PB, Stark JM, et al. Water and nitrogen uptake are better associated with resource availa-bility than root biomass. Ecosphere, 2017, 8(3): e01738, doi: 10.1002/ecs2.1738
[13] Sobrado MA, Turner NC. A comparison of the water relations characteristics of Helianthus annuus and Helian-thus petiolaris when subjected to water deficits. Oecologia, 1983, 58: 309-313
[14] Kukowski KR, Schwinning S, Schwartz BF. Hydraulic responses to extreme drought conditions in three co-domi-nant tree species in shallow soil over bedrock. Oecologia, 2013, 171: 819-830
[15] Zeng F-J (曾凡江), Zhang X-M (张希明), Li X-Y (李向义), et al. Seasonal variation of Tamarix ramosissima and Populus euphratica water potentials in southern fringe of Taklamakan Desert. Chinese Journal of Applied Ecology (应用生态学报), 2005, 16(8): 1389-1393 (in Chinese)
[16] Franks PJ, Drake PL, Froend RH. Anisohydric but isohydrodynamic: Seasonally constant plant water potential gradient explained by a stomatal control mechanism incorporating variable plant hydraulic conductance. Plant, Cell & Environment, 2007, 30: 19-30
[17] Wang H-Z (王海珍), Han L (韩路), Zhou Z-L (周正立), et al. Dynamic response of water potential of Populus pruinosa to different underground water level. Agricultural Research in the Arid Areas (干旱地区农业研究), 2007, 25(5): 125-129 (in Chinese)
[18] Nie Y-P (聂云鹏), Chen H-S (陈洪松), Wang K-L (王克林). Methods for determining plant water source in thin soil region: A review. Chinese Journal of Applied Ecology (应用生态学报), 2010, 21(9): 2427-2433 (in Chinese)
[19] McCole AA, Stern LA. Seasonal water use patterns of Juniperus asheion the Edwards Plateau, Texas, based on stable isotopes in water. Journal of Hydrology, 2007, 342: 238-248
[20] Nie Y-P (聂云鹏), Chen H-S (陈洪松), Wang K-L (王克林), et al. Challenges and probable solutions for using stable isotope techniques to identify plant water sources in karst regions: A review. Chinese Journal of Applied Ecology (应用生态学报), 2017, 28(7): 2361-2368 (in Chinese)
[21] Schwinning S. The water relations of two evergreen tree species in a karst savanna. Oecologia, 2008, 158: 373-383
[22] Dammeyer HC, Schwinning S, Schwartz BF, et al. Effects of juniper removal and rainfall variation on tree transpiration in a semi-arid karst: Evidence of complex water storage dynamics. Hydrological Processes, 2016, 30: 4568-4581
[23] Eggemeyer KD, Schwinning S. Biogeography of woody encroachment: Why is mesquite excluded from shallow soils? Ecohydrology, 2009, 2: 81-87
[24] Kukowski KR, Schwinning S, Schwartz BF. Hydraulic responses to extreme drought conditions in three codominant tree species in shallow soil over bedrock. Oecologia, 2013, 171: 819-830
[25] Ford D, Williams P. Karst Hydrogeology and Geomorphology. Chichester, England: John Wiley & Sons, 2007
[26] Hanson CT, Blevins RL. Soil water in coarse fragments. Soil Science Society of America Journal, 1979, 43: 819-820
[27] Poot P, Lambers H. Shallow soil endemics: Adaptive advantages and constraints of a specialized root-system morphology. New Phytologist, 2008, 178: 371-381
[28] Nie Y-P (聂云鹏), Chen H-S (陈洪松), Wang K-L (王克林). Seasonal variation of water sources for plants growing on continuous rock outcrops in limestone area of Southwest China. Chinese Journal of Plant Ecology (植物生态学报), 2011, 35(10): 1029-1037 (in Chinese)
[29] McCole AA, Stern LA. Seasonal water use patterns of Juniperus ashei on the Edwards Plateau, Texas, based on stable isotopes in water. Journal of Hydrology, 2007, 342: 238-248
[30] Hubbert KR, Beyers JL, Graham RC. Roles of weathe-red bedrock and soil in seasonal water relations of Pinus jeffreyi and Arctostaphylos patula. Canadian Journal of Forest Research, 2001, 31: 1947-1957
[31] Donovan LA, Ehleringer JR. Water stress and use of summer precipitation in a great basin shrub community. Functional Ecology, 1994, 8: 289-297
[32] Bucci SJ, Scholz F, Goldstein G, et al. Processes preventing nocturnal equilibration between leaf and soil water potential in tropical savanna tree species. Tree Physiology, 2004, 24: 1119-1127
[33] West AG, Dawson TE, February EC, et al. Diverse functional responses to drought in a Mediterranean-type shrubland in South Africa. New Phytologist, 2012, 195: 396-407