石漠化裸岩引发环境异质响应及其对植被恢复的影响

Karst rocky desertification zone is a typical fragile eco-zone in china. And widely distributed bare rocks are the representative characteristic in these regions. Spatial heterogeneity is one of the important properties of soil, and it occurs on various scales in all types of soil environments. The moisture of surface soil layer has a significant role in the microenvironment and is a key parameter in soil surface modeling. Soil moisture is also an essential condition for normal plant growth, affecting both quality and survival. The variability and pattern of soil surface moisture is receiving increased attention from local to continental scales. Little attention has been paid to surface soil moisture variability, specifically in fragile ecosystems or in the context of vegetation restoration efforts in the karst region of subtropical China. To the bare rocks, we assuming there have three actions: ①shade, which intensifies soil moisture heterogeneity, ②heat, soil moisture affected by heated rocks, and ③enrichment, affected soil moisture, nutrition, soil seed banks, and the vegetations around them by intercept rain, seeds and litters spread in air. All of these actions affect soil moisture and nutrition directly or indirectly, while, soil moisture and nutrition are the restricted conditions for vegetations restoration in Karst rocky desertification area. So we try to test and verify the actions by long term auto-test in typical middle KRD areas. And can quantify the small-scale heterogeneities caused by bare rocks, analyse the response mechanism and scale of soil moisture, nutrition and seed banks around the bare rocks, search the relatively profitable locations for vegetations restoration in stress conditions. The results would enrich the vegetations restoration theories, and could provide scientific direct for vegetation recovery in these areas.

我国西南石漠化地区是典型生态脆弱区，岩石大面积出露地表是石漠化的典型特征之一。针对斑块分布的裸岩，设想其具有三种作用：①"遮荫作用"，岩石遮荫并强化了土壤水分的异质性；②"加热作用"，岩石加热升温影响周围土壤水分保持能力；③"富集作用"，岩石拦截富集并导致其周围土壤水分、养分、土壤中种子及地上植被产生小尺度的异质性。在典型中等强度石漠化地区，围绕出露岩石这一典型特征，针对植被恢复中土壤水分、养分两个主要限制性因子，采取长期定位自动观测技术，验证裸岩的"加热"、"遮荫"与"富集"作用，定量分析土壤水分、养分及土壤种子库对裸岩的异质响应，总结裸岩对植被恢复的影响及规律，综合分析"遮荫"、"加热"与"富集"作用的形成机制与尺度，探寻逆境背景下相对有利的人工恢复植被位点，丰富石漠化植被恢复理论体系，具有重要的理论与实践意义，能够为石漠化地区人工植被恢复工作提供理论参考和科学指导。

石漠化地区是典型的生态脆弱区。项目在典型石漠化地区，围绕石漠化出露岩石这一典型特征，通过原位阶段观测结合模拟岩石定位观测方法，收集到岩石周围土壤水分、养分、岩石表面温度及空气温湿度、地表植物生物量及土壤种子库的季节动态变化等大量科学数据，验证并明确了裸岩的“遮荫”、“加热”与“富集”作用及影响尺度。石漠化地区裸岩存在遮荫作用，且干旱季节强于湿润季节，岩石北侧土壤水分优于其他方面，遮荫作用受到岩石形状的影响。裸岩表面增温快、降温较慢，岩石具有显著的加热效应，岩石表层20cm 以内的空气相对湿度较小，岩石的加热效应导致石漠化地区小气候趋于干热化。裸岩对于其周围土壤养分及枯落物表现出富集效应，裸岩未对土壤种子库表现出收集作用。距离裸岩近处土壤养分优于较远处，以裸岩北侧对养分的富集作用较强，岩石北侧留存枯落物能力最强，在距离岩石25c m处留存量最大，为2.32 kg•m-2。自然状态下，裸岩周围种子发芽率极低，仅达6.8%，表明石漠化地区乔木植被的自然恢复能力差。种子在距离岩石15cm处萌发存活数量最多，达到11株。一年生裸根苗成活率为42.80%，在距离岩石15cm处存活量最大，为24株。种子的萌发存活率低于一年生裸根苗的存活率，表明石漠化地区人工促进植被恢复方式快于植被的自然恢复。通过综合分析，在裸岩北侧15cm处发现了植被恢复的有利位点。项目实施过程所获得的数据及阶段结果，可以进一步解释出露岩石对石漠化逆境的影响机制，促进对石漠化地区逆境环境特征及季节动态变化规律的理解，可以为石漠化地区生态治理过程中人工植被恢复造林位点的选择提供理论参考，丰富了石漠化植被恢复理论体系，对石漠化地区植被恢复和生态环境建设具有重要的参考价值，具有重要的理论与实践意义。