| In order to reveal the effects of global warming on the growth and functional traits of fine roots in natural and plantation forests in subtropical regions,field in situ soil warming experiments in Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation were carried out at the Fujian Sanming Forest Ecosystem National Observation and Research Station.The experiment adopted a randomized block design,two treatments of soil warming(W,+4°C)and control(CT,+0°C)were set,each treatment was set up with 5 replicates.In different seasons,the root in-growth core donut method was used to measure the fine root growth(0-20cm),morphological characteristics(diameter,root length,specific root length,specific root area and root tissue density),chemical elements and stoichiometric characteristics(carbon,nitrogen,phosphorus,potassium,calcium,magnesium,carbon nitrogen ratio,nitrogen phosphorus ratio and calcium magnesium ratio)and physiological metabolic characteristics(specific root respiration rate,soluble sugar,starch and non-structural carbohydrates).Compared with the control,the results of the warming treatment showed that:(1)Warming has a significant effect on the growth of fine roots in both Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation.In rainy season,the growth of 0-1mm fine roots in Castanopsis kawakamii natural forest decreased significantly by 41.2%,while that in Cunninghamia lanceolata plantation increased significantly by 109.9%;In dry season,the fine root growth of 0-1 and 1-2mm in Castanopsis kawakamii natural forest increased significantly,while that of Cunninghamia lanceolata plantation did not change significantly.In addition,the seasonal response patterns of total fine root growth(0-2mm)of Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation to warming are different.The total fine root growth of Castanopsis kawakamii natural forest increases significantly in dry season,while that of Cunninghamia lanceolata plantation increases significantly in rainy season.(2)The response of fine root morphological characteristics to warming is different between Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation.In rainy season,the diameter and length of 0-1 and 1-2mm fine roots in Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation have no significant change,but the specific root length and specific root area of 0-1mm fine roots in Castanopsis kawakamii natural forest have significantly decreased by 53.2% and 42.9%.In order to reduce the impact of warming on the absorption of fine root resources,the root tissue density of 0-1mm fine roots in Castanopsis kawakamii natural forest has significantly increased by 134.4%,but the specific root length of 0-1mm fine roots in Cunninghamia lanceolata plantation has significantly increased by 28.8%,there was no significant change in specific root area and root tissue density;In dry season,the 0-1 and1-2mm fine root length of Castanopsis kawakamii natural forest increased significantly by 38.5% and 33.5% respectively,but the 0-1 and 1-2mm fine root diameter,specific root length,specific root area and root tissue density of Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation did not change significantly.It may be that in dry season,the fine roots of Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation respond to warming more by adjusting growth or other functional traits.(3)In rainy season,warming only significantly increased the C/N of 1-2mm fine root and Ca/Mg of 0-1mm fine roots in Castanopsis kawakamii natural forest and significantly decreased the K and Mg contents of 1-2mm fine roots in Cunninghamia lanceolata plantation,which had no significant impact on other indexes.In dry season,the C,N and P contents of 0-1 and 1-2mm fine roots in Castanopsis kawakamii natural forest decreased significantly by 10.8% and 4.2%,34.8% and 27%,37.4% and 28.6%respectively,and the contents of K in 0-1mm fine roots and Mg in 1-2mm fine roots also decreased significantly by 58.9% and 20% respectively,the contents of C and N in1-2mm fine roots of Cunninghamia lanceolata plantation increased significantly by 9.6%and 48.3% respectively,and the content of Mg in 0-1mm fine roots decreased significantly by 30.3%,while there were no significant changes in Ca,N/P and Ca/Mg in fine roots of Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation.(4)In rainy season,the SRR of 0-1 and 1-2mm fine roots in Castanopsis kawakamii natural forest did not change significantly,while the SRR of 0-1mm fine roots in Cunninghamia lanceolata plantation decreased significantly by 64.1%,the soluble sugar and NSC contents of 0-1mm fine roots in Castanopsis kawakamii natural forest decreased significantly by 44.4% and 33.8% respectively,and the starch content did not change significantly,while the soluble sugar content of 0-1mm fine roots in Cunninghamia lanceolata plantation increased significantly by 41.5% and the starch content decreased significantly by 15.9%,but the NSC of fine roots did not change significantly;In the dry season,the SRR of 0-1mm fine roots of Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation decreased significantly by 66.2% and 60.7%respectively.Warming had no significant effect on the soluble sugar,starch and NSC of0-1 and 1-2mm fine roots of Castanopsis kawakamii natural forest,while the starch and NSC of 1-2mm fine roots of Cunninghamia lanceolata plantation decreased significantly by 43.9% and 14.2% respectively.In conclusion,warming had certain effects on the growth and functional traits of fine roots in both Castanopsis kawakamii natural forest and Cunninghamia lanceolata plantation,and there were seasonal differences,but different stands had different responses to warming.In rainy season,warming reduces SRL,SRA and growth of fine roots in Castanopsis kawakamii natural forest.Castanopsis kawakamii natural forest adopts the strategy of maintaining the stability of fine root chemical elements and SRR and increasing the consumption of NSC to reduce the impact of warming on fine root resource absorption and growth,while Cunninghamia lanceolata plantation responds to warming by increasing fine root SRL to absorb more water and nutrients and reducing SRR to reduce consumption to promote fine root growth.In dry season,the Castanopsis kawakamii natural forest can increase the fine root length,expand the resource absorption space,and make full use of the content of N,P,K and Mg stored in the fine root,so as to significantly increase the fine root growth in response to the warming.The strategy adopted by the Cunninghamia lanceolata plantation is to increase the fine root C investment and N absorption and consumption of NSC to maintain the fine root growth. |
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