喀斯特11种典型生态恢复树种凋落叶分解及其对土壤碳排放的激发效应

旨在探究喀斯特地区退化生态系统植被恢复树种凋落叶分解过程及其对土壤碳排放的激发效应,为选择合适的树种进行植被恢复提供数据支持。以中国林科院热带林业实验中心大青山石山树木园11种适应性强、耐干旱贫瘠的优良石山树种为研究对象,利用¹³C自然丰度法区分凋落叶和土壤来源CO₂并量化土壤激发效应,比较不同生态恢复树种凋落叶分解及其激发效应的差异,探讨凋落物分解及其激发效应与凋落物性状之间的关联。结果表明:(1)11个生态恢复树种凋落叶在碳相关化学性质(水溶性碳、半纤维素和单宁含量等)、养分含量(磷和镁含量等)及化学计量特征(碳磷比和氮磷比)等方面均表现出较高程度变异。(2)不同生态恢复树种凋落叶分解及其诱导的土壤激发效应具有极显著差异(P<0.001);在整个培养实验期间,11个生态恢复树种凋落叶平均分解了35.3%,其中海南椴分解最快,达到50%,而青冈栎分解最慢,仅分解16.5%。(3)总体上看,凋落叶处理的土壤呼吸速率(5.1 mg C kg^-1 土壤 d^-1)是对照土壤呼吸速率(2.3 mg C kg^-1土壤d^-1)的2.2倍,凋落叶添加显著促进土壤有机碳分解,平均达到37.6%;其中海南椴、割舌树和任豆凋落叶输入则抑制土壤有机碳分解(抑制程度分别为-13.2%、-6.9%和-22.5%),产生负激发效应。(4)凋落叶分解与非结构性碳(r=0.63,P=0.04)和水溶性碳(r=0.91,P<0.001)呈显著正相关,与叶干物质含量(r=0.64,P=0.03)、纤维素(r=0.62,P=0.04)和锰含量(r=-0.63,P=0.04)呈显著负相关。多元回归分析结果表明,水溶性碳、钾和钙含量相结合可以解释生态恢复树种凋落叶分解变异的98%;然而,凋落叶性状与土壤激发效应强度之间并没有显著相关性。从土壤养分归还角度考虑,喀斯特退化生态系统恢复树种可以选择光皮梾木、海南椴、顶果木和降香黄檀等凋落叶分解较快的树种,以促进土壤养分循环和植被恢复;另一方面,从土壤碳固持角度来看,海南椴、任豆和割舌树等凋落叶输入会抑制土壤有机碳分解,从而有利于提高退化生态系统土壤碳封存能力。

Leaf litter decomposition and its priming effect of eleven typical ecological restoration tree species in the karst area of China

The objective of this study is to provide data support for selecting ecological restoration tree species in degraded karst ecosystem. We studied the decomposition of leaf litter and its priming effect on soil organic carbon mineralization across eleven typical tree species in the karst area of China. Eleven typical ecological restoration tree species with strong adaptability and drought tolerance from Experimental Center of Tropical Forestry, Chinese Academy of Forestry were selected for the study. We used the natural abundance difference in δ¹³C values of C₃ plant leaf litters and C₄ soil to separate leaf-derived CO₂ from soil-derived CO₂ and quantified soil priming effect intensity, the difference of leaf litter decomposition and its priming effect among different ecological restoration tree species were compared to explore the relationship between leaf litter traits and its decomposition and soil priming effect intensity. (1) The 11 ecological restoration tree species used in the study exhibited a fair degree variation in carbon-related properties (water soluble carbon, hemicellulose and tannin), nutrient contents (phosphorus and magnesium), and stoichiometric characteristics (carbon to phosphorus ratio and nitrogen to phosphorus ratio). (2) Leaf litter decomposition and priming effect intensity were significantly different among different ecological restoration tree species (P<0.001). The fraction of added leaf litter decomposed over the entire incubation period was 35.3% averaged across all 11 species with the highest for Hainania trichosperma litter (50%) and the lowest for Cyclobalanopsis glauca (16.5%). (3) Over the 200-d incubation period, mean daily CO₂ production from the control soil was 2.3 mg C kg^-1 soil d^-1, but 5.1 mg C kg^-1 soil d^-1 from the soil with leaf litter. It ranged from 4.2 (Cyclobalanopsis glauca) to 6.2 mg C kg^-1 soil d^-1 (Dalbergia odorifera). Overall, the added leaf litters significantly stimulated the decomposition of soil organic carbon by 37.6% on average. The input of leaf litter from Hainania trichosperma,Walsura robusta and Zenia insignis inhibited the decomposition of soil organic carbon, i.e., it induced the negative priming effect (the intensity of priming effect was -13.2%, -6.9%, and -22.5%, respectively). (4) The decomposition of ecological tree species leaf litter related well to leaf litter traits, litter water soluble carbon and non-structure carbohydrates content were positively correlated with the decomposition of leaf litter, whereas leaf dry mass content, cellulose and manganese concentrations were negatively associated with leaf litter decomposition. Considering all litter traits together, the combination of water soluble carbon, potassium, and calcium concentrations presented most relevant to explain the decomposition of leaf litter (R²=0.98, P<0.0001). However, we found no relationship between leaf litter traits and the intensity of soil priming effect. From the perspective of soil nutrient return, tree species with relatively fast leaf litter decomposition, such as Cornus wilsoniana wanger, Hainania trichosperma, Acrocarpus fraxinifolius, and Dalbergia odorifera could be selected for ecological restoration in degraded karst ecosystems, which contributed to soil nutrient cycling and vegetation recovery and development. From the perspective of soil carbon sequestration, the input of leaf litters such as Hainania trichosperma, Zenia insignis and Walsura robusta can slow down the decomposition of soil organic carbon, which is beneficial to enhancing the potential of soil carbon stocks in degraded karst ecosystems.