温度升高对长江口芦苇湿地细根形态和生长的影响

Effects of experimental warming on the morphological and growth traits of fine roots in a Phragmites wetland of the Yangtze River Estuary

全球变暖对滨海湿地植物细根的影响目前尚不十分清楚。以长江口崇明东滩芦苇(Phragmites australis)湿地为对象,利用开顶式生长箱法进行模拟升温。于2019年5—10月,结合微根管法和根钻法,对0—40 cm土层细根(直径≤2 mm芦苇须根)的总根长、总表面积、比根长、比表面积、平均直径和生物量等指标开展连续观测,并计算其净生长速率和周转速率,分析气温升高对芦苇湿地细根形态特征和生长动态的影响。结果表明:在整个生长季,升温显著提高了0—40 cm土层细根的总根长、总表面积和总生物量,且主要表现在0—20 cm土层,而对比根长、比表面积无显著影响。升温显著增强了0—40 cm土层细根的净生长速率,且使其季节变异性加大。升温显著提高了10—40 cm土层细根的周转速率,但在0—10 cm土层影响不显著。总之,升温显著提高了芦苇湿地细根的总量和生长速率,改变其在土壤中的垂直分布格局,但对其水分和养分吸收效率无显著影响。升温使细根周转速率加快,同时使参与周转的细根总量增加,导致各土层特别是0—20 cm土层根源有机碳输入显著增加,这可能会深刻影响芦苇湿地的土壤碳平衡。

As the components having the highest biological activity and fastest turnover rate in the plant root system,fine roots(≤2mm)are very sensitive to global climate change and significantly affect the carbon balance and nutrient cycling in the belowground part of the terrestrial ecosystem.Coastal wetlands are among the ecosystems with significant carbon sink functions in the earth,where the belowground part plays a vital role.Up to date,several studies have revealed the influence mechanism of global warming on the above-ground part of coastal wetlands,however,relatively few studies were conducted to investigate the influence of global warming on the underground part of coastal wetlands.Particularly,until now,how will the fine roots of coastal wetland plantsl respond to warming conditions is unclear.This study was conducted to examine the potential effects of climate warming on fine roots in the Phragmites australis wetland in Chongming Dongtan of the Yangtze River Estuary.The open-top chamber(OTC)method was used to simulate a warming climate.From May to October 2019,the methods of minirhizotron and soil auger were used to determine the total length,total surface area,specific root length,specific root surface area,average root diameter,and biomass of the fine roots in the 0—40 cm soil layer(i.e.,the fibrous roots of P.australis with the diameter≤2 mm).The net growth rate and turnover rate of the fine roots were also calculated.The results showed that,during the entire growing season,warming significantly increased the total length,total surface area,and total biomass of the fine roots.The increases of the above indicators were more apparent in the 0—20 cm soil layer compared to the 20—40 cm soil layer.Warming did not have a significant impact on the specific root length and specific root surface area.Significant enhancement of the net growth rate of the fine roots caused by warming occurred in the entire 0—40 cm soil layer,with increased seasonal variability.Warming significantly increased the turnover rate of the fine roots in the 10—40 cm soil layer,whereas it didn′t change their turnover rate in the 0—10 cm soil layer.In summary,in the Phragmites australis wetland,warming significantly increased the quantity and growth rate of the fine roots,changed their distribution pattern in the 0—40 cm soil layer,but it did not affect the efficiency of the fine roots to absorb soil water and nutrients.The increase in the turnover rate and the biomass of the fine roots might lead to significantly increased root-derived organic carbon input,especially in the 0—20 cm soil layer,which might profoundly affect the soil carbon balance of the Phragmites australis wetland.Our results indicated that the potential changes of plant fine root-related carbon processes under warming conditions should be fully considered in the simulation and prediction of soil carbon balance in coastal wetlands.