桢楠幼苗适应喀斯特岩溶裂隙生境及降雨时间格局变化的方式

Phoebe zhennan S.Lee seedlings adjust the biomass allocation and root distribution to adapt to the karst fissure habitat and rainfall temporal pattern

喀斯特生态系统是全球陆地生态系统的重要组成部分,生态环境极为脆弱。由于碳酸盐岩长期强烈的化学溶蚀作用,其基本特征体现为地表土壤和地下岩溶裂隙及洞穴的二元结构。近年来,在全球气候变化下,我国西南地区降雨格局呈现降雨频次减少且单次降雨量增加的趋势。因此,岩溶裂隙和区域降雨时间格局改变将对喀斯特地区的植物生长产生重要影响。通过模拟不同岩溶裂隙生境(S_(0):24 cm土壤;S_(1/2):12 cm土壤层+12 cm裂隙层;S_(3/4):6 cm土壤层+18 cm裂隙层)和不同降雨时间格局(I_(2d):2 d降雨间隔;I_(19d):19 d降雨间隔),探究二年生桢楠(Phoebe zhennan S.Lee)幼苗是否通过生物量分配及根系分布的调整来适应变化环境。结果显示:(1)短时间降雨格局下,相比全土生境,少量岩溶裂隙存在并不影响桢楠幼苗生物量的积累,然而随着岩溶裂隙层进一步增厚和降雨时间间隔延长,桢楠降低了总生物量,减少了茎且增大了根和叶的生物量分配。(2)桢楠幼苗的根系垂直分布随着深度增加而下降,且无论在何种降雨时间格局下,两种岩溶裂隙生境下桢楠均增加了岩溶裂隙之上土壤层的根系生物量分配比例。研究表明:赋存有土壤的岩溶裂隙能成为植物幼苗赖以生存的生境,但这种提供生境的能力随岩溶裂隙层增厚以及降雨时间间隔延长而减弱。桢楠幼苗以牺牲对茎生物量的分配投资为代价,提高对根系或者叶片的生物量投资,同时增大界面土层中的根系分布,来保证最大化地利用有限的土壤资源,从而适应喀斯特的岩溶裂隙(及干旱)生境。

Karst is one of the most important fragile ecological environments in globally terrestrial ecosystems.It is basically characterized by the dual structure of surface soil and underground karst fissures and caves,due to the long-term strong chemical dissolution of carbonate rocks.In recent years,under global climate change,the rainfall pattern in southwestern China has shown a trend of decreasing rainfall frequency and greater sub-rainfall.The karst region in southwestern China,which belongs to the subtropical monsoon climate,often suffers from more obvious alternating wet and dry conditions.The underground karst fissures and variation in the temporal pattern of regional rainfall will have a significant impact on plant growth and development in this region.In this study,in order to explore whether the seedlings of Phoebe zhennan S.Lee adjust biomass allocation and root distribution to adapt to the changing environment,we simulated different karst fissure habitats(S_(0):24 cm soil;S_(1/2):12 cm soil layer+12 cm karst fractured layer;S_(3/4):6 cm soil layer+18 cm karst fractured layer)and different rainfall temporal patterns(I_(2d):rainfall interval of 2 days;I_(19d):rainfall interval of 19 days),and checked the plants biomass accumulation and allocation,root vertical distribution.The results showed that:(1)under the short-term rainfall pattern,compared with the whole soil habitat,the habitat with a small proportion of karst fissures did not affect the biomass accumulation of P.zhennan seedlings.With the thickening of karst fractured layer and the extension of the rainfall interval,P.zhennan reduced the total biomass,allocating less biomass to stems and more to roots and leaves.(2)The vertical distribution of root system of P.zhennan seedlings decreased with the deepen of soil layer,but increased the root biomass allocation ratio in the soil layer above the karst fissures,regardless of the rainfall temporal pattern.The results show that the fissures hosted soil can be a certain habitat for plants.However,with the thickening of fractured layer and extension of the rainfall interval,the fissures weaken the ability of the habitat.P.zhennan seedlings increase investment to root and leaf at the expense of stem biomass,and increase the root distribution in the interface soil layer above the fissures to ensure the maximum use of limited soil resources so as to adapt to the fissure(and arid)habitat in karst.