吕梁山森林群落草本层植物物种多样性的空间格局及其对模拟增温的响应

Spatial pattern of herbaceous plant species diversity and its changes due to simulated warming in the forest community of the Luliang Mountains

为研究气候变暖背景下森林群落草本层植物物种多样性对温度升高的响应及其随海拔、纬度的空间分布格局,按照纬度梯度选择吕梁山系北段的管涔山和南段的五鹿山为研究区,并在每个山地的不同海拔梯度(高、中、低)分别设置对照(CK)、低度增温(OTC1)和高度增温(OTC2) 3种试验样地。于2017年植被生长季对植物多度、频度、盖度、高度进行调查,计算物种多样性指数(Simpson指数、Shannon指数、Pielou指数、Patrick指数)。结果表明:(1)吕梁山森林群落草本层植物物种多样性随海拔呈"v型"变化格局,即在中间海拔梯度处最低,且海拔梯度对各多样性指数的影响均达到极显著水平(P<0.01)。(2)物种多样性随纬度升高呈递增趋势(P>0.05),即较高纬度山地具有较高的物种多样性。(3)物种多样性随温度升高整体呈递减趋势(P>0.05),即温度升高可抑制林下草本层植物物种多样性。(4)在增温处理下,五鹿山草本植物的Simpson指数、Shannon指数和Patrick指数呈递减趋势,Pielou指数先降低后升高;管涔山草本植物的Simpson指数、Shannon指数和Pielou指数先增加后减小,Patrick指数呈递增趋势。整体来说,在吕梁山较低海拔,持续增温会使物种多样性降低;在中等海拔,物种多样性随温度升高呈现先下降后上升的变化趋势;在较高海拔,适度增温可提高物种多样性,持续增温则抑制多样性。因此,增温对吕梁山森林群落草本植物物种多样性的影响随海拔升高整体呈下降趋势。

The objective of this study was to investigate the species diversity of herbaceous plant communities in forests regarding changes due to temperature increases, and the spatial distribution pattern at varying elevations and latitudes in a warming climate. Adhering to a latitudinal gradient, Guancen Mountain in the northern section of the Luliang Mountains and Wulu Mountain in the southern section of the Luliang Mountains were selected as study areas. Three plot categories [ control, low temperature increase （OTC1）, and high temperature increase （OTC2） ] were set at different altitudes （high, medium, and low） in each of the study areas. During the vegetation growth season in 2017, plant diversity, frequency, coverage, and height were investigated to calculate species diversity indices （ Simpson index, Shannon index, Pielou index, and Patrick index）. An S-THB-M008 air temperature probe with an RS3-B radiation shield was set up at a height of＇ 20 cm above ground level to measure ambient temperature. Our data revealed that the herbaceous species diversity in the forest community of the Luliang Mountains exhibited a ＂v-shaped＂ pattern depending on elevation （i.e., the lowest species diversity was found in the middle elevation）. Altitude effects were most strongly correlated with the Simpson index （R2= 0.1711）, and the effects of the altitude gradient on diversity indices were highly significant （P 〈 0.01 ）. Additionally, species diversity increased with latitude, and latitude effects were most correlated with the Simpson index （R2= 0.1221, P〉 0.05）. This is followed by the Shannon index （R2 =0.0807）, the Pielou index （R~= 0.0785） , and the Patrick index （R2= 0.0382）. In response to increasing temperatures, each diversity index initially decreased, but then increased, with an overall downward trend （P〉0.05）. Thus, increasing temperatures may decrease the plant species diversity of herbaceous layers under the forest canopy. Among species diversity indices, the Simpson index produced the strongest correlation of temperature effects （R2 = 0.3374, P 〉 0.05）. Moreover, under simulated warming conditions, the Simpson index, Shannon index, and Patrick index of herbaceous species in Wulu Mountain exhibited a decreasing trend. In contrast, the Pielou index increases first and then decreases. In comparison, the Simpson index, Shannon index, and Pielou index of herbaceous plants in Guancen Mountain increased at first and then decreased, whereas the Patrick index increased. Overall, continued warming will decrease species diversity at lower altitudes of the Luliang Mountains. At moderate altitudes, species diversity will first decrease and then increase with rising temperatures. At relatively high altitudes, moderate warming will increase species diversity, but continued warming will negatively affect species diversity. Moreover, the effect of the altitude gradient on plant species diversity in the understory herbaceous layer was highly significant （P 〈 0.01 ）. In Guancen Mountain, different treatments showed a significant effect on the Pielou Index （P〈0.05）. However, in other plots, different treatments did not significantly affect plant species diversity. The diversity of plant species was least affected by the combination of high gradients and different treatments. Therefore, the effects of warming on the diversity of herbaceous species in the forest community of the Luliang Mountains exhibit a decreasing trend with elevation.