温带草原7种针茅植物根系特征及其对环境因子变化的适应

为比较针茅(Stipa)植物适应策略，以大尺度梯度下(>1600 km)温带草原主要针茅植物为对象，系统研究了8个样点7种针茅根系生物量、根冠比、解剖结构和生理调节物质的差异及其对环境因子的适应。在由东北至西南的区域上，随降水量下降针茅植物根系的抗旱特征增强或适应策略趋于复杂，不同针茅植物根系对水分变化(或旱季和雨季)有着不同的适应策略。综合分析表明贝加尔针茅(S.baicalensis)、大针茅(S.grandis)及克氏针茅(S.krylovii)(多伦样点)的生长受干旱制约，对降水高度敏感，雨季降水促进其生物量快速积累。沙生针茅(S.glareosa)、短花针茅(S.breviflora)、戈壁针茅(S.gobica)、本氏针茅(S.bungeana)等通过增大根冠比和渗透调节物质累积等途径提高根系吸水和保水能力，抵御干旱胁迫。偏相关分析显示实验区域针茅植物根系性状与降水量和海拔高度存在显著的相关性。

Root traits of seven Stipa species and their relations with environmental factors in temperate grasslands

In order to compare the adaptive strategies of Stipa species,divergences of root traits and their relationships with the environmental factors were addressed along a large-scale gradient (>1600 km) in temperate grasslands from northeast Inner Mongolia to central Ningxia (106.88°-120.12° E,38.02°-49.35° N). Root traits (e.g. root biomass,root shoot ratio (R/S),anatomical structures and physiological adjustments) of seven Stipa species were measured twice over the growing season (dry season and rainy season) in eight sites along the gradient. Root drought resistance traits for Stipa species were enhanced or complicated with the decrease of precipitation along the gradient from northeast to southwest,resulting in divergence of adaptive strategies to moisture changes (or dry season and rainy season) for these Stipa species. In general,root biomass of Stipa species exhibited fluctuating growth trend among the eight sites,reflecting both interspecific differences and convergent adaptability to drought. R/S of Stipa species were greater in dry season than in rainy season,but its changing trend was not inconformity in the two seasons. The variations of root epidermal thickness (E_pt) and cortical thickness (C_ort) for Stipa species were consistent with root diameter (R_d) in the eight sites,but differed between dry and rainy seasons. E_pt and C_ort become thinner with the decrease of precipitation in dry season,this was in favour of water absorption and horizontal transportation. Thickening E_pt and C_ort in rainy season prevented water flowing back from stele to C_ort and enhanced water retention. Root proline (Pro) and soluble sugar (SS) contents of Stipa species in deep soil layer were significantly higher than those in the surface soil,mainly because the deep roots were newborn absorbing roots with strong physiological activity and the main participants in osmotic regulation. The comprehensive analysis showed that the growths of Stipa baicalensis,S. grandis and S. krylovii (in Duolun site) were restricted by the seasonal drought,and these species were highly sensitive to moisture with rapid biomass accumulation in rainy season. Drought resistances for some species (e.g. S. glareosa,S. breviflora,S. gobica,S. bungeana) was raised by increasing R/S,water retention and absorption capacities and accumulation of osmotic adjustments. Partial regressions exhibited that the root traits were related significantly with precipitation and altitude in the grassland region. The distribution ranges of Stipa species with complex adaptability,such as S. glareosa and S. krylovii,may expand,if the drought in the region intensified in the future as IPCC predicted.