The Study Of Exogenous Glucose Incorporates Into Soil Carbon Components Of Rooting Zone And The Responds Of Malus Baccata (L.) Borkh.

In China,apple orchards often build on hill with restricted soil organic matter?SOM?content and poor fertilizer condition.SOM is the main source of soil organic carbon?SOC?and other mineral nutrition.The active organic carbon is part of SOC,which were usually used as indexes of soil SOM turnover in responds to tillage managements.Exogenous organic matter input could regulats SOC level,promotes soil quality and plant growth.Soil suppied with exogenous organic matter is one of the efficient ways to achieve apple production with high quality and efficent.However,the distribution of exogenous organic matter in soil active SOC pools of apple orchards soil ecological system,and the mechanism of regulation on plant are until unclea.For these,in this study,the low molecular weight organic substances-glucose as organic carbon source instead of the high molecular weight organic substances that is difficultly isotope labelled,the seedlings of Malus baccata?L.?Borkh.were selected as material,gravel soil with 0.78%SOM was acted as culture substrate,in order to assessing the main fate of exogenous glucose in soil active carbon pools of rooting zone of Malus baccata?L.?Borkh.and evaluating the role of exogenous glucose for plant metabolism and growth.The main results are as follow:1.The ¹³C-glucose isotope labelling results showed that both the SOC,DOC,MBC and POC conten and?¹³C valus were significantly increased by ¹³C-glucose treatments,which mostly peaked at 7 d,and generally decreased.In the whole period,the contribution of glucose-C to SOC,DOC and MBC was always higher than native SOC,except POC.The mean residence times?MRT?of SOC,DOC,POC and MBC under glucose treatments were generally increased along with treatment times.On the whole,the MRT of SOC,DOC,MBC and POC under glucose-C that equal to native MBC content?GLC1?were significantly higher than glucose-C that 5 times higher than soil native MBCcontent?GLC2?.At the end of treatments,there were 79.81%,5.73%,9.41%,5.03%of GLC1,and 85.05%,5.77%,4.72%,4.46%of GLC2-C incorporated into SOC,POC,DOC and MBC,respectively.The contribution of glucose-C to SOC,DOC,POC and MBC,and the residual rate of total SOC were exhibited GLC1 was marked higher than GLC2,while the ¹³CO₂ vaalue and MRT were exhibited opposite trends.Therefore,GLC1 is better for promoting SOC content in gravel soil,and maintain the level of SOC,while the GLC2 lead to resources waste.2.The root activity and root respiration rate of Malus baccata?L.?Borkh.were significantly increased by exogenous glucose.Exogenous glucose also promoted the percentage of glycolysis,phosphopentose and tricarboxylic acid cycle pathways on the total respiration.The activities of key enzymes of glycolysis and tricarboxylic acid cycle pathways were enhanced,when exposed to exogenous glucose.The intermediate products-organic acids of glycolysis and tricarboxylic acid cycle were also increased,especially under GLC1.Malus baccata?L.?Borkh.feed with glucose lead to the ATP,ADP and energy charge in root were promoted.For the nitrogen metabolism,exogenous glucose increased the NO₃^--N and NO₂^—N content in root,while reduced the NH₄⁺-N content.The activities of key enzymes involved in nitrogen embolism of NR,GS,NADH-GDH,NADH-GOGAT,GOT and GPT were promoted in root of Malus baccata?L.?Borkh.feed with glucose,especially under GLC1.The ultimate products of nitrogen metabolism,the content of 17 free amino acids in root were pronouncedly increased.Also,exogenous glucose increased the IAA and ZT content,decreased the ABA content in root,especially under GLC1.The increased degree of IAA content was higher than ZT content in root under GLC1 treatment.Exogenous glucose induced the chlorophyll?a+b?content increased and promoted photosynthetic capacity of Malus baccata?L.?Borkh.The plant height and whole biomss were also promoted by exogenous glucose,especially under GLC1,while the stem diameter was not significantly affectd by external glucose.On the whole,GLC1 treatments exhibited higher promotion for carbon-nitrogen metabolism in root and growth of Malus baccata?L.?Borkh.,when compared with GLC2 treatments.Otherwise,according to the correlationanalisis,there was postive correlation was found between SOC,DOC,MBC,POC content and key enzymes involved in carbon-nitrogen metabolism in root of Malus baccata?L.?Borkh.by exogenous glucose treatments.Thus,exogenous glucose promoted the nitrogen absorb and metabolic capability in root,increased hormone contentin root,enhanced photosynthetic capacity and accumulated biomass by promoting soil organic carbon pools level,accelerating SOC turnover and increasing soil available nutrition contents.3.Malus baccata?L.?Borkh.seedlings were exposure to GLC1?GLC?,0.09 g·kg^-1indoleacetic acid?IAA?,0.06 g·kg^-1 triiodobenzoic acid?TIBA?,GLC+IAA and GLC+TIBA.Results showed that the mRNA expressions of SHY2,LBD11 and ALF4 in root development were significantly up-regulated in root under GLC,IAA and GLC+IAA treatments,while the SHR mRNA level was down-regulated.Total root length,superficial area and root volume were marked increased,root tended to be dichotomous branching structure,when Malus baccata?L.?Borkh.treated with GLC,IAA and GLC+IAA.GLC,IAA and GLC+IAA induced the gene expression of auxin biosynthesis?YUCCA8,TAR2 and TAA1?and auxin polar transport?LAX2,PIN1 and AUX1?in root,and then the endogenesis indoleacetic acid content in root was increased.GLC,IAA and GLC+IAA treatments promoted the root activity and respiration rate,increased the activities and genes expression of key enzymes involved in carbon-nitrogen metabolism?PEPC,NADP-ME,NADP-ICDH,NR,GS,NADH-GDH and NADH-GOGAT?.Also,the organic acids and free amino acid content in root were increased by GLC,IAA and GLC+IAA treatments.In the end,GLC,IAA and GLC+IAA treatments promoted the photosynthetic capacity and biomass accumulation.There was no significantly difference was found between IAA and GLC treatmetns for physiological metabolism and growth indexes in generally.On the contrary,although TIBA up-regulated the mRNA expression in auxin biosynthesis,but down-regulated genes expression in auxin polar transport,reduced endogenesis indoleacetic acid content in root.The mRNA levels of genes in root development were not notablely regulated,but root morphology and topological structure were restricted,carbon-nitrogen metabolism in root and growth were also inhibited by TIBA.Which negative effects could be alleviated by exogenous glucose?GLC+TIBA?.The improved SOC and available nutrition content in soil by GLC,GLC+IAA and GLC+TIBA treatments,not in IAA and TIBA treatments indicated that exogenous glucose plays a more important role than IAA for metabolism and growth of plant cultured in SOC-restricted condition.Therefore,exogenous glucose changed endogenesis indoleacetic acid content in root by regulating the biosynthesis and polar transportof auxin,and then regulated gene expression in root development,promoted root elongation and C-N metabolic capacity,benifited for growth and biomass accumulation.In conclusion,exogenous glucose was mainly inccorperated into SOC.Glucose-C that equal to native MBC was more stabilization and efficiency than glucose-C that 5 times higher than native MBC,and are preferentially involved in the formation of stable SOC,improved the level of SOC in gravel soil.Which were provided better microenvironments for root growth and development of Malus baccata?L.?Borkh..Otherwise,exogenous glucose induced turnover of soil organic carbon pools,and increased available nutrition content in soil for root.Also,the increased indoleacetic acid content in root due to the auxin biosynthesis and polar transport were regulated by exogenous glucose.Then root tends to dichotomous and benifited for improving efficiency of N absorb and metabolism in root.