沿干旱梯度小叶锦鸡儿灌丛化对草本植物叶片矿质元素浓度及地上生物量累积的影响

草原灌丛化通过改变物种之间的相互作用深刻影响着群落的结构和功能。然而,当前有关灌木如何影响不同功能群草本植物对矿质元素吸收和累积的研究仍明显不足。在内蒙古草原沿干旱梯度选取了4个研究地点,对比分析了小叶锦鸡儿(Caragana microphylla)灌丛斑块内和斑块外群落中禾草和非禾草功能群植物叶中矿质元素浓度以及地上生物量生产的差异,旨在阐明干旱和灌木对群落草本植物叶元素累积的影响,揭示灌草间相互作用的元素利用特征及其随干旱梯度的变化。结果显示：1)随干旱加剧,灌丛斑块内的非禾草功能群植物地上生物量保持恒定,但叶中的K、Ca、Mg、Fe、Mn和Cu元素浓度显著增加(P<0.05)。该结果表明群落中的非禾草功能群植物通过提高叶中的矿质元素水平来抵御和适应干旱胁迫。2)随干旱加剧,灌丛对非禾草功能群植物地上生物量,叶中Ca、Fe、Cu和Zn,禾草功能群植物叶中的P的累积影响从负(RII<0)或中性(RII=0)转变为正效应(RII>0)。该结果与胁迫梯度假说相符,表明灌木对草本植物的促进效应随干旱胁迫加剧而增加。3)灌丛的“沃岛”效应是驱动灌木对草本植物元素累积正效应...

Effects of Caragana microphylla encroachment on mineral element concentrations in leaves and aboveground biomass accumulation of herbaceous plants along an aridity gradient

Shrub encroachment in grasslands profoundly affects the structure and function of communities by altering species interactions. However, current research about the influences of shrubs on the uptake and accumulation of the mineral elements in herbaceous vegetation is still obviously insufficient. We selected four study sites along an aridity gradient in the Inner Mongolia grassland, and compared and analyzed the differences in leaf mineral element concentrations and aboveground biomass production of grasses and forbs outside and inside canopies of Caragana microphylla shrub patches. We aimed to clarify the effects of drought and shrubs on leaf element accumulation of herbaceous plants in communities, and revealed the interactions between shrubs and herbs with respect to utilization characteristics and corresponding variations along the aridity gradient. The results showed that:1) with the increasing aridity, the aboveground biomass of the forbs inside canopies of shrub patches remained constant, but the K, Ca, Mg, Fe, Mn and Cu concentrations in their leaves increased significantly (P<0.05). The results indicated that forbs in communities resisted and adapted to drought stress by increasing the levels of mineral elements in their leaves. 2) With the increasing aridity, the effects of shrubs on biomass, leaf Ca, Fe, Cu and Zn accumulation of forbs as well as on leaf P accumulation of herbs shifted from negative (RII<0) and neutral (RII=0) to positive (RII>0). The results were consistent with the stress-gradient hypothesis, suggesting that the facilitation effect of shrubs on herbaceous plants increased with drought stress. 3) The "fertile islands" effect was the main mechanism driving the positive impact of shrubs on the accumulation of elements in herbaceous plants. Our results reveal the importance of the facilitation effect of Caragana shrubs in maintaining vegetation species coexistence and ecosystem functioning stability in arid and semiarid grasslands of the Inner Mongolia.