土壤增温、隔离降水及其交互作用对杉木细根呼吸、形态及二者关系的影响

Effects of soil warming,precipitation exclusion,and their interaction on fine root respiration and its relationship with fine root morphology in Chinese fir

杉木根系呼吸(特别是细根呼吸)能表征根组织新陈代谢水平,为根养分吸收提供能量(如ATP),对亚热带森林生态系统碳平衡有重要作用,但其对全球变暖、降水减少及其交互作用的响应则尚不清楚.在福建三明森林生态系统国家野外科学观测研究站对杉木(Cunninghamia lanceolata)幼苗开展土壤增温和隔离降水双因子控制试验,包括对照(CT)、土壤增温5℃(W)、隔离降水50%(P)和土壤增温+隔离降水(WP),采用Oxytherm液相氧电极测定不同径级(0-1 mm、1-2 mm)细根比根呼吸速率,并同时测定根系形态指标,研究土壤增温、隔离降水及两者交互作用对杉木幼苗比根呼吸速率及其与细根形态特征相关关系的影响.结果表明:(1)土壤增温和隔离降水间交互作用对细根比表面积和组织密度均有显著影响,WP处理细根比表面积平均比W处理低31.2%,WP处理细根组织密度平均比CT高26.4%;WP处理细根组织密度平均比W处理高60.9%.此外,P处理1-2 mm细根的组织密度显著高于未进行P处理.(2)增温和降水减少对比根呼吸速率的影响并不存在交互作用;P处理1-2 mm的比根呼吸速率显著低于未进行P处理,但P处理对0-1mm细根比根呼吸速率无显著影响;(3)细根比根呼吸速率与比根长呈显著的正相关关系,且这种相关关系不受土壤增温、隔离降水及两者交互作用的影响.由此可见,1-2 mm细根比根呼吸速率主要受降水减少的影响而降低,这主要与降水减少导致1-2 mm细根组织密度增加以提高水分运输能力有关.此外,土壤增温、隔离降水及其交互作用并不会改变细根比根呼吸速率与细根形态特征间关系,细根比根呼吸速率与细根形态特征间稳定的相关关系可用于预测气候变化下根系呼吸速率的变化.(图5表3参63)

Plant root respiration,especially fine root respiration,indicates the level of root tissue metabolism,supplying energy,such as ATP,crucial for root nutrient uptake and contributing significantly to the carbon balance of forest ecosystems.Despite its pivotal role,the response of root respiration to the combined effects of global warming and reduced precipitation remains unclear.This study conducted a two-factor manipulative experiment involving soil warming and precipitation exclusion.The treatments included control(CT),soil warming by 5℃(W),precipitation exclusion by 50%(P),and soil warming+precipitation exclusion(WP).We utilized Chinese fir(Cunninghamia lanceolata)seedlings at Sanming Forest Ecosystem National Field Scientific Observation and Research Station in Sanming,Fujian,China.The specific respiration rate of fine roots(0-1 mm and 1-2 mm diameter class)of Chinese fir seedlings was measured using Oxytherm liquid-phase oxygen electrodes,with the morphological characteristics of fine roots determined simultaneously.The effects of soil warming,precipitation exclusion,and their interactions on specific respiration rate and its correlation with root morphological characteristics were analyzed.The results showed that:(1)the interaction between soil warming and precipitation exclusion had a significant effect on the specific surface area and tissue density of fine roots,with the average specific surface area of fine roots in the WP treatment being 31.2%lower than that in the W treatment and the average tissue density of fine roots in the WP treatment being 26.4%higher than that in the CT treatment.The average tissue density of fine roots in the WP treatment was 60.9%higher than that in the W treatment.In addition,the tissue density of the 1-2 mm roots under the P treatment was significantly higher than that under the non-P treatment.(2)No interaction was observed between increased temperature and reduced precipitation on the specific respiration rate of fine roots.The specific respiration rate of 1-2 mm roots under P treatment was significantly lower than that under non-P treatment;however,P treatment had no significant effect on the specific respiration rate of 0-1 mm fine roots.This could be attributed to the precipitation exclusion treatment,increased tissue density of transported roots,and improved water security.(3)A significant positive correlation was found between fine root specific respiration rate and specific root length,which was not affected by soil warming,precipitation exclusion,or their interaction.Notably,the specific root respiration rate of 1-2 mm fine roots was mainly reduced by precipitation exclusion.This reduction was attributable to the increase in the tissue density of 1-2 mm fine roots,a response to decreased precipitation aimed at improving water transport capacity.In addition,soil warming,precipitation exclusion,and their interactions did not change the relationship between specific root respiration rates and the morphological characteristics of fine roots.The stable correlation between fine root respiration rate and fine root morphological characteristics can be used to predict changes in root respiration rate under climate change.