Responses Of Soil Enzyme Activities And Their Stoichiometric Characteristics To Vegetation Restoration In The Karst Rocky Desertification Ecosystem,SW China

Soil enzymes are key influencing factors of soil nutrient cycling,and can reflect changes in soil fertility and ecosystem functions.However,for a long time,there has been a lack of research on soil enzyme activities and their stoichiometric characteristics in the karst rocky desertification ecosystem in southwest China,especially its responses to vegetation restoration,which obviously limits the in-depth understanding of the internal mechanism of soil quality evolution in the karst rocky desertification ecosystem in southwest China,and seriously affects the effectiveness of rocky desertification control.Therefore,in this study,the typical control area of karst rocky desertification in southwest China—Huajiang karst plateau canyon in Guanling county,Anshun city,Guizhou province was used as the research area,bare land was used as the control sample,aiming at seven vegetation restoration measures of Zanthoxylum bungeanum,Amomum villosum,Cupressus funebris,Tectona grandis,Pennisetum sinese,Lonicera japonica and Hylocereus undatus,study on the responses of soil enzyme activities,soil enzyme stoichiometric characteristics to vegetation restoration and its influencing factors,so that provide a theoretical basis for land management and regulation,restoration and reconstruction of degraded vegetation andsustainable development in the karst rocky desertification ecosystem in southwest China.The main research results are as follows:（1）URE activities showed P.sinese>T.grandis>bare land>L.japonica>C.funebris>H.undatus>Z.bungeanum=A.villosum.SUC activities showed L.japonica>Z.bungeanum>H.undatus>C.funebris>bare land>T.grandis>P.sinese>A.villosum.CAT activities showed H.undatus>T.grandis>bare land>P.sinese>L.japonica>Z.bungeanum>A.villosum>C.funebris.BG activities showed T.grandis>L.japonica>Z.bungeanum>H.undatus>A.villosum>bare land>P.sinese>C.funebris,there were significant differences among different soil layers of T.grandis in BG activities.In the soil depth of 0～15cm,there was no significant differences between seven vegetation restoration measures and bare land in soil CBH activities,CBH activities basically concentrated at40000 nmol·g^-1·h^-1.NAG activities showed T.grandis>H.undatus>A.villosum>P.sinese>C.funebris>L.japonica>bare land>Z.bungeanum,there were significant differences among different soil layers of L.japonica in NAG activities.LAP activities showed L.japonica>C.funebris>T.grandis>bare land>A.villosum>P.sinese>Z.bungeanum>H.undatus.AP activities showed bare land>T.grandis>L.japonica>C.funebris>Z.bungeanum>H.undatus>A.villosum>P.sinese.On the soil vertical profile,URE activities and SUC activities decreased in bare land and seven vegetation restoration measures with the increased of soil depth,while CAT activities showed a relatively stable changes with the increased of soil depth.soil CBH activities in C.funebris and L.japonica,soil NAG activities in Z.bungeanum and C.funebris,soil LAP activities in T.grandis and H.undatus,soil AP activities in seven vegetation restoration measures and bare land showed a decreasing trend with the increased of soil depth.Correlation analysis showed that there were significant or extremely significant correlations between different soil enzyme activities.On the whole,increasing the planting area of T.grandis,L.japonica and H.undatus as much as possible in the future will be more conducive to the ecological restoration in the karst rocky desertification ecosystem in Southwest China.（2）Soil enzyme carbon:nitrogen showed H.undatus>Z.bungeanum>P.sinese>A.villosum>bare land>T.grandis>C.funebris>L.japonica.Soil enzyme carbon:phosphorus showed P.sinese>A.villosum>H.undatus>C.funebris>Z.bungeanum>L.japonica>T.grandis>bare land.Except for A.villosum,soil enzyme carbon:phosphorus in the three soil layers in P.sinese was significantly different from other vegetation restoration measures and bare land.Soil enzyme nitrogen:phosphorus exhibited P.sinese>A.villosum>C.funebris>H.undatus>L.japonica>Z.bungeanum>T.grandis>bare land.Soil enzyme vector lengths were relatively concentrated ranging from 1.35 to 1.40,showed the distribution characteristics of the highest in P.sinese and the lowest in bare land.Soil enzyme vector angles were all greater than 45°,indicating that soil nutrients in the study area were limited by P,and soil enzyme vector angles were the largest in the three soil layers in bare land,which were significantly different from Z.bungeanum,A.villosum,C.funebris,P.sinese,L.japonica and H.undatus.Soil enzyme vector angles are all smaller than bare land in seven vegetation restoration measures,indicating that vegetation restoration has slowed down the limiting effect of P on soil nutrients in the karst rocky desertification ecosystem in southwest China.On the soil vertical profile,soil enzyme carbon:nitrogen decreased in C.funebris and L.japonica with the increased of soil depth,while soil enzyme carbon:nitrogen,soil enzyme carbon:phosphorus,soil enzyme nitrogen:phosphorus were no uniform changes in the remaining vegetation restoration measures and bare land with the increased of soil depth.Correlation analysis showed that soil enzyme vector lengths and vector angles were significantly correlated or extremely significantly correlated with soil enzyme activities and soil enzyme stoichiometric ratios.From the perspective of soil enzyme stoichiometry,not only the rational application of P fertilizer and the input of exogenous P should be considered in the future in the karst rocky desertification area in southwest China,but also vegetation restoration type with less human disturbance and rich species should be selected to improve the ecology environment.（3）Correlation analysis showed that except for activities of URE and CBH,the other soil enzyme activities and enzyme stoichiometric ratios had significant or extremely significant correlations of different degrees with soil physicochemical factors.Redundancy analysis showed that soil enzyme activities and soil enzyme stoichiometric ratios accounted for 34.98%and 7.87%in the first axis and the second axis respectively,that is to say,eight soil physicochemical factors in the first two ranking axes of RDA explained the cumulative effect of soil enzyme activities and soil enzyme stoichiometric ratio characteristics accounted for 42.85%,and the cumulative explanation for the relationship between the two was as high as 90.29%.Among the eight soil physicochemical factors,the explanatory amounts of bulk density and SOC to soil enzyme activities and enzyme stoichiometric ratios were 29.8%and 25.1%respectively,indicating that bulk density and SOC were the main factors affecting soil enzymes.The ranking results of individual effects showed that the effects of soil physicochemical factors on soil enzyme activities and enzyme stoichiometric ratios were ranked in descending order of importance:bulk density>SOC>TN>TP>pH>SOC:TN>TN:TP>SOC:TP.Except for TN:TP and SOC:TP,the other six soil physicochemical factors had significant effects on soil enzyme activities and enzyme stoichiometric ratios.In the future,we should pay attention to the research on the regulation of SOC on soil enzymes in the karst rocky desertification ecosystem in southwest China,while effectively protecting the soil structure and reducing the damage to the soil structure caused by human factors.