Microbial Ecological And Crop Effects And Diagnostic Index Of Copper Pollution In Grain-Vegetable Rotation Ecosystems

Three paddy soils namely yellowish red soil(YRS),purplish clayey soil(PCS) and silt loam soil(SLS)within 'rice-Chinese cabbage' rotation system were collected from Jiaxin county,Deqing County,and Xiasha District of Hangzhou City,Zhejiang province.Laboratory and greenhouse pot experiments combined with soil biochemical measurements,Biolog and Phospholipids fatty acids analysis were adopted to investigate the toxic effects of copper on both rice and cabbage growth. The research also focus on studying the toxic effects of Cu²⁺on soil microbial biological characteristics such as soil microbial biomass,soil basal respiration,soil enzyme activities,and soil microbial community structures.The results are summarized as follows:1.Toxic effect of Cu on plant growth depends on either vegetative types or soil basic physical-chemical characteristics.Lower Cu loading(50 mg kg^-1)promote cabbage growth except SLS.100 mg kg^-1Cu loading promote rice yield mainly because the increase of root length,tillers,spike length,as well as the number of total stems.Yet higher concentration of Cu has restrictive effect.The lethal concentration of Cu is 1200 mg kg^-1and 1600 mg kg^-1for YRS and PCS respectively,whereas it is 50 mg kg^-1for SLS under rice planting system.However,the lethal concentration is 800 mg kg^-1for all the three paddy soils under cabbage growing system.There are some physiological differences of Cu toxicity between rice and cabbage.50 mg kg^-1Cu loading boost root volume,root diameter,SPAD value,root length,and root surface area.Yet higher Cu loading restrict SPAD and photosynthesis, superoxide dismutase(SOD)activity,Malondialdehyde(MDA)levels,and proline content.The result is cabbage yield declined.Yet 50 mg kg^-1Cu loading prominently boost total stems and spikes,which increase the grain yield.However,higher Cu loading(＞400 mg kg^-1)extremely restrict chlorophyll synthesis,decrease spikes, grain number per panicle,as well as 1000-grain weight,led to grain yield dropped.2 The absorption of Cu by rice stalks and leafs is exponentially promoted along with the increased Cu loading.Cu content in rice roots and seeds is extremely enhanced along with the increased Cu loading.Cu absorption order within different rice organs is:roots＞stalks and leafs＞seeds.Cu accumulative amount both in cabbage upper and under ground part is rise along with increased Cu loading.Cu content in roots of cabbage is 77.77%-80.41%.Much more Cu was stored in roots than in leafs, which is benefit to reduce Cu accumulation in edible part of cabbage.3.The main fractionated Cu conponent in three soils were Fe-Mn oxide-fraction. The amount of available Cu²⁺was notably positive correlated with extracted Cu²⁺by four extractants(water,0.1 mol L^-1HCl,0.5 mol L^-1DTPA,and 1 mol L^-1NH₄OAc (pH7.0).All kind of extracted Cu was prominently negative correlated with rice yield, fresh cabbage leaf weight,fresh cabbage root weight,and dry leaf weight,but notably positive correlated with accumulated Cu within rice and cabbage organs.The quantity of 0.5 mol L^-1DTPA extracted Cu has the highest correlations shown that it is the best extractant for available Cu extraction.4.Both soil microbial biomass carbon,basal respiration and microbial quotient (MQ)was decreased along with prolonged incubation time mainly because easy usable available C resource provided by organic C mineralization was decreased. However,they were increased because root residual and its exudation provide available C resource for microbial biomass usage when soil planting rice and cabbage. The dose-effect of Cu on microbial biomass C is notably increased less than 400 mg kg^-1Cu loading.Yet higher Cu loading lead to extremely restriction effect on it.Soil microbial metabolic quotient(MMQ)was increased along with increased Cu loading and prolonged incubation time for rice growth.Yet it was decreased in all three paddy soils when planting cabbage.5.Catalase,urease,invertase,and phosphatase activities were notably promoted when Cu loading less than 100 mg kg^-1.Yet restrict effect were observed when Cu loading higher than 100 mg kg^-1.Sensitivity of the four enzymes to Cu contamination is urease＞invertase＞phophatase＞catalase.Enzymes activities were remarkable increased by planting rice and cabbage by decomposition of residual rice root and their exudation.6.Total microorganism was increased along with enhanced Cu loading less than 400 mg kg^-1.Yet extremely restriction effect were observed for PCS and SLS when Cu loading higher than 400 mg kg^-1.Total microorganism was reduced along with incubation time for fertile YRS and PCS.However,opposite effect was observed for SLS.Microorganism structures were also changed under Cu pollution.Bacteria ratio was notably increased along with enhanced Cu loading which may caused by the appearance of endurance bacteria.Fungal ratio was augmented because it's high resistance capability for threatening environment.Actinomycete ratio was decreased along with increased Cu loading.7.Cu contamination leads to the changes of both microbial biological structures and functions.Notable differences of C₁₂-C₂₀phospholipids fatty acid(PLFA)were measured among three paddy soils and within each of them.The first difference was measurable types of PLFA.In 8^thweek incubation time under 100-400 mg kg^-1Cu loading,the types of PLFA were.However,800 mg kg^-1Cu loading prominently restricted the PLFA types especially for SLS.But in 52^thweek incubation time,the types of PLFA were increased.Great changes were happened not only caused by increased Cu loading,but also caused by prolonged incubation time.The second changes were the ratios of main microorganisms.Bacteria account for absolutely most of the microorganism,whereas quite low percentage of fungal and actinomycetes in YRS and PCS.The result is coincides with the traditional culture method.Very simple PLFA structure was measured for non polluted SLS at 8^thweek incubation time which fungal account for 58.58%of total PLFA,bacteria account for 27.51%,0%for actinomycetes.But the percentage is changed to 6.85%,69.50%,and 0.69%in 52th week incubation time which shown that Cu loading is not the only factor to affect microorganism structure.The ratio of bacteria/total PLFA, actinomycetes/total PLFA were promoted,while the ratio of fungal/total PLFA and fungal/bacteria was decreased along with enhanced Cu loading.In addition,Cu pollution causes flexible or forbearing reaction of microorganisms.Some indicative PLFAs were appeared or disappeared.For example, Cu loading causes methane nourish bacteria-16:1w5c,aerobiosis bacteria-15:0 3OH, 16:0 2OH,and sulphatedeoxidize bacteria-17:1 w8c totally vanish,whereas anaerobicbacteria-17:0 ISO 3OH,and fungal-20:2W6,9C emergence as new PLFA types by Cu pollution inspiring in YRS.The G-bacteria(17:0 CYCLO and 19:0CYCLO w8c)and G⁺-bacteria(4:0 iso,15:0 anteiso,15:0 iso,15:0 iso 3OH,16:0 iso,17:0 anteiso,17:0 iso)was increased greatly.8.Cu pollution decreased microbial community metabolic profile(AWCD).No linear relationship exists between AWCD and test time.Some differences were observed for carbon resource utility by microorganisms under different Cu loading. 100 mg kg^-1Cu loading promotes AWCD,yet further increased Cu loading to 800 mg kg^-1cause decrease of AWCD.Main components analysis showed that AWCD among 31 carbon resource utilization rate were distribute widely which indicate the sensibility of microbial community structures to Cu contamination.Differences also exist among soil microbial functional diversities under changed Cu loading levels.Shannon index,Shannon Richness and Evenness of microbial community were decreased under higher Cu loading(＞800 mg kg^-1)indicated that the microbial community structure trends to singularity.The usage ability of C resource by microbial community in all three paddy soils was affected by Cu loading rate.100-400 mg kg^-1Cu loading promote C resource utility,but 800 mg kg^-1Cu loading notably restrict microbial community metabolic activity as their structures were simplified.These results demonstrated that both microbial community structure and microbial functional diversity can be used as sensitive bio-indicator for reflecting heavy metal caused environment changes.9.According to the restriction effect of Cu pollution to rice and cabbage growth, and to soil microbial ecological characteristics,we were modeling regression equations to calculate the critical concentration for these three paddy soils by using 10%yield reduction,food security sanitary criteria,and ecological dose as indexes. The critical levels of Cu are 198,185,and 71 mg kg^-1for YRS,PCS and SLS respectively.