模拟不同降雨时间格局下喀斯特垂直异质生境对桢楠幼苗光合和生长的影响

由于岩石裸露、地表破碎、坡度陡峻、洼地土壤堆积等因素的共同作用，喀斯特区域土壤具有明显的不连续性和高度异质性，土壤侵蚀往往较为严重。喀斯特地区高度异质性的生境为植物提供了不同的水分、肥料、空气和空间，对植物的生长和生理具有显著影响。在全球气候变化下，降雨时间格局的改变可能将进一步加剧喀斯特的生境异质性。桢楠是我国特有的国家二级保护树种，虽然它只零星分布在喀斯特地区，但由于它能在岩石间生长得很好，仍被认为是一种可能的适宜树种。以二年生桢楠（Phoebe zhennan S.Lee）幼苗为研究对象，研究总降水量相同条件下两种降雨时间格局（I_2d：2 d降雨间隔；I_19d：：19 d降雨间隔处理）和三种垂直异质小生境（S₀：无石全土，S_1/2：半石半土，S_3/4：多石少土）对其光合生理和生长的影响。结果显示：（1）在I_2d条件下，桢楠幼苗的光合速率在半石半土生境（S_1/2）下最大，且有较大的地径和株高；而在I_19d条件下，桢楠的光合和生长（株高和地径）均随着岩溶裂隙层的增厚逐渐减小。（2）在全土生境（S₀）下，降雨时间格局的改变并不影响桢楠的光合和株高，而在有岩溶裂隙层的生境下（S_1/2和S_3/4），降雨时间间隔的延长会抑制桢楠的光合和株高及地径的生长，提高气孔密度，且这种抑制或促进作用会随着岩溶裂隙层的增厚而加剧。研究表明，在降雨间隔时间短，降雨均匀充足时，有少量的岩溶裂隙能够促进桢楠的生长和光合，但降雨间隔时间延长后，这种作用丧失。另一方面，在土壤相对较厚时，降雨时间间隔的改变对桢楠的光合和生长影响不显著，但岩溶裂隙层的增加，加剧了降雨时间间隔增大对桢楠光合的负面影响。

Effects of simulated karst vertical heterogeneous habitat on photosynthesis and growth of Phoebe zhennan S.Lee seedlings under different rainfall temporal pattern

Karst regions represent a unique ecosystem, with its obviously discontinuous and highly heterogeneous limestone soil due to the combination of exposed rocks, tattered land surface, steep slopes, soil accumulation in depressions, and often severe soil erosion. Highly heterogeneous habitats in karst areas provide different water, fertilizer, air and space for plants, which have a significant impact on plant growth and physiology. Under the global climate change, variation in rainfall temporal pattern may further exacerbate habitat heterogeneity in karst regions. Phoebe zhennan S.Lee is an endemic, national second-class protective tree species in China. Even it only distributes in karst regions sporadically, it is still considered to be a probable suitable tree there since it can grow well between the rocks. In this study with P. zhennan seedlings as the research object, we selected two kinds of rainfall temporal pattern (I_2d :The rainfall interval is 2 days, I_19d:The rainfall interval is 19 days) and three kinds of heterogeneous habitats (S₀:all soil, S_1/2:half stone and half soil, S_3/4:more stones and less soil), to investigate the response to photosynthesis and growth. The main results are as follows:(1) under the condition of I_2d, the photosynthetic rate of P. zhennan was the largest in the half stone and half soil habitat (S_1/2), and had larger ground diameter and plant height; while under the condition of I_19d, the photosynthesis and growth (plant height and ground diameter) of P. zhennan decreased gradually with the thickening of karst fissure layer. (2) In the soil habitat (S₀), the change of rainfall pattern did not affect the photosynthesis and plant height of P. zhennan, however, in the habitat with karst fissure layer (S_1/2 and S_3/4), the extension of the rainfall interval inhibited the photosynthesis and the growth of plant height and ground diameter of, but increase the density of stomata, This inhibition or promotion increased with the thickening of the karst fissure layer. The above results show that:when the rainfall interval is short and the rainfall is relatively uniform and sufficient, a small number of karst fissures can promote the growth and photosynthesis of P. zhennan, but this effect is lost when the rainfall interval is extended. On the other hand, under the condition that the soil is thick enough, the change of rainfall time interval has no significant effect on the photosynthesis and growth of P. zhennan, but the increase of the karst fissure layer exacerbates the negative impact of the increase of the rainfall interval on the photosynthesis of P. zhennan.