坡向对青藏高原东北缘高寒草甸植被构成和养分特征的影响

摘要

坡向是重要地形因子之一，通过影响光照、温度及土壤养分等进而影响群落植物种的组成和分布。本研究通过对青藏高原东北缘不同坡向高寒草甸草地的植被构成和养分特征进行了分析，揭示坡向对植物群落组成和空间分布形成的影响。结果表明，1）草地群落优势种和亚优势种构成，阳坡以禾本科的赖草、西北针茅和洽草等为主，阴坡以莎草科的矮嵩草和线叶嵩草及豆科的阴山扁宿豆等为主；2）草层高度、植物物种数和α多样性指数为阴坡＞阳坡，β多样性指数在坡向之间无显著差异；3）阳坡和阴坡草地植物生活型以地面芽和地下芽为主，分别占草地群落总物种数的71．0％和89．0％，1／2年生及地上芽植物为阳坡＞阴坡，地面芽植物为阴坡＞阳坡，地下芽植物在坡向之间无显著差异；4）草地群落生物量构成，阳坡为禾本科（78．3％）＞莎草科（8．3％）＞菊科（6．4％）＞其他科（7％），阴坡为莎草科（54．3％）＞豆科（16．4％）和禾本科（14．8％）＞蓼科（5．3％）和菊科（4．6％）＞其他科（4．0％）；除菊科外，所有各科植物生物量在坡向之间均差异显著，地上总生物量在坡向之间无显著差异；5）0～20 cm 土壤 N 含量为阴坡＞阳坡，10～20 cm 土壤 P、K、Cu、Zn 含量为阳坡＞阴坡；6）0～30 cm 土温为阳坡＞阴坡，0～40 cm 土壤含水量阴坡＞阳坡。总之，坡向对高寒草甸草地群落植物种构成和土壤理化特性的变化起着重要作用。%Aspect is an important topographical factor that affects illumination,temperature,and soil nutri-ents,all of which affect the composition and distribution of plant species.In this study,we evaluated the effect of aspect on the soil nutrient characteristics and on the composition and spatial distribution of plant communi-ties in an alpine meadow in the northeast margin of the Qinghai-Tibet Plateau.The dominant and subdomi-nant species in grassland communities were Leymus secalinus ,Stipa krylovii ,and Koeloria cristata (Gra-mineae)on sunny slopes and Kobresia humilis and Kobresia capillifolia (Cyperaceae)and Melilotoids rutheni-ca var.inschanica (Leguminosae)on shady slopes.The herbage height,α-diversity index,and number of plant species in grasslands were greater on shady slopes than on sunny slopes,while theβ-diversity indexes of grasslands were similar between shady and sunny slopes.The plant life-form spectrum both on sunny and shad-y slopes mainly consisted of hemicryptophytes and geophytes,accounting for 89% and 71% of the total number of species,respectively.There were more annual and biennial plants and hemicryptophytes on sunny slopes than on shady slopes,but more hemicryptophytes on shady slopes than on sunny slopes.There were similar numbers of geophytes on sunny and shady slopes.The plant families contributing to total biomass in grassland communities on sunny slopes were Gramineae (78.3%)>Cyperaceae (8.3%)>Asteraceae (6.4%)>others (7%);and to grassland communities on shady slopes were Cyperaceae (54.3%)>Leguminosae (16.4%), Gramineae (14.8%)>Polygonaceae (5.3%),Asteraceae (4.6%),and others (4%).For all of the plant fami-lies except for the Asteraceae,the contribution to total biomass differed significantly between sunny and shady slopes,but the contribution to total aboveground biomass was similar between sunny and shady slopes.The ni-trogen content in the 0 -20 cm soil layer was higher on the shady slope than on the sunny slope,while the phosphorus,potassium,copper,and zinc contents in the 10-20 cm soil layer were higher on the sunny slope than on the shady slope.The soil temperature in the 0-30 cm layer was higher on the sunny slope than on the shady slope,whereas the water content in the 0-40 cm soil layer was higher on the shady slope than on the sunny slope.Together,these results show that aspect plays an important role in the composition of vegetation communities and in the physical and chemical properties of soil in alpine meadows.