| The resolution adopted by the Sixth Plenary Session of the 19th Central Committee of the Party pointed out that"protecting the ecological environment is to protect productive forces,and improving the ecological environment is to develop productive forces.We must adhere to the concept that green water and green mountains are the silver mountain of gold,and more consciously promote green development,circular development and low-carbon development."Southern China’s karst,centred on the Guizhou plateau,is one of the three major contiguous distribution areas of karst in the world,and also one of the most typical and complex karst developments and the richest landscape types,while rocky desertification is the most serious ecological,environmental and social development problem facing this area,and must be controlled.Walnut（Juglans regia L）,as the top four nuts in the world,is an important economic forest tree species,and has become a countermeasure tree species for ecological restoration and industrial adjustment in rocky desertification mountainous areas due to its high habitability and economic benefits.The plantation production of walnut and other economic forests is an effective way to balance ecological control,economic development and social benefits in karst rocky desertification area.Based on the theories of physical geography,ecology,plant functional traits,soil science,plant nutrition and ecological chemometrics,In response to the problem of less research on the status and changing characteristics of nutrients in walnut forest soil,apoplastic,leaves and fruits in karst areas,and the nutrient limitation of walnut cannot be revealed from the nutrient studies of soil-plant continuum.Combining the theories of spatial variation of nutrients,fruit quality,and coupling of soil-apoplastic-leaf systems,in the two selected study areas（salaxi study area and Huajiang study area）.a total of 21 standard sample plots of walnuts of different grades of rocky desertification were selected on the basis of field treks and background surveys in the study area,using analytical methods such as principal component analysis,redundancy analysis and nutrient diagnosis.A positioning observation study was conducted from July 2020 to October 2021,and the sample plots were surveyed for basic environmental information,soil,apoplastic matter,leaf and fruit samples were collected and measured.To investigate the correlation between soil,litter and leaf nutrients and fruit quality,elucidate the role of plant functional traits in indicating fruit quality and nutrients in walnuts,integration and demonstration of optimal control techniques for walnuts,and to provide scientific references for the sustainable development of walnut economic forests in rocky desertification areas.（1）To reveal the variability of walnut soil-leaf-apoptotic nutrients,functional plant traits and limiting factors for different classes of walnut nutrients.Total nitrogen TN,total carbon TC and fast-acting phosphorus AP indicators of karst plateau canyon soils decrease with increasing stone desertification,and total phosphorus TP,organic carbon TOC,TC and TN of karst plateau mountains soils decrease with increasing stone desertification grade.Soil-foliage ecological stoichiometry N:P<14 in both study areas,indicating that walnut growth is mainly limited by nitrogen.A total of 16 fruit amino acid species were detected,and the content of most species decreased with increasing stone desertification grade.TN（potential1.817>mild1.733>moderate1.625>intensity 1.592g/kg）and TC（potential2.723>mild2.588>moderate2.571>intensity2.533g/kg）indicators of karst plateau canyon soils decreased with increasing stone desertification.TP（no2.842>potential2.758>light2.183 g/kg）,TOC（no9.246>potential8.345>light 8.255 g/kg）,TC（no2.516>potential2.415>light 2.349 g/kg）,TN（no1.627>potential 1.600>light1.313 g/kg）of karst plateau mountains soils were correlated with stone desertification grade were negatively correlated with rocky desertification grade.Leaf nutrients in karst plateau mountains decreased and then increased with increasing rocky desertification.Soil TN,TC and AP indicators in karst plateau canyon decreased with increasing rocky desertification.Soil TP,TOC,TC and TN of karst plateau mountains are negatively correlated with rocky desertification grade.Apoplastic nutrients differed significantly（P<0.05）among rocky desertification classes.Soil-leaf ecological stoichiometry in both study areas indicated that plant growth was mainly N-limited,with C and N utilisation decreasing with increasing rocky desertification.Karst plateau canyon apoplastic N:P is limited by N in areas of slight and moderate rocky desertification areas,by both N and P in areas of intensive rocky desertification area,and mainly by P in areas of potential rocky desertification.Walnut leaf Tr,Ci,Gs and LUE in karst plateau canyon showed a trend of decreasing and then increasing with increasing rocky desertification,and leaf dry weight,leaf saturated fresh weight and leaf area all showed a decreasing trend with increasing rocky desertification grade,and an increasing trend of leaf fresh weight,leaf saturated fresh weight,leaf area and leaf thickness of karst plateau mountain walnuts with increasing rocky desertification grade.soil capacitance in karst plateau canyon showed slight>potential>intensive>moderate rocky desertification areas,and soil capacitance in karst plateau mountains increased with increasing rocky desertification grade;a total of 16 species of amino acids were detected in fruits of the two demonstration areas,and the content changes of most species decreased with increasing rocky desertification grade.The functional traits of walnut are indicative of nutrient abundance and fruit quality,which is a feasible way to conduct future research on walnut nutrients and fruit quality.The nutrient limitation of walnuts in different rocky desertification of karst is different,it is to develop improvement solutions based on the findings,which is important for guiding ecological restoration and sustainable development of walnut forests in karst areas and enriching walnut research in karst areas.（2）The coupling relationship between soil-leaf-apoptotic nutrients,plant functional traits and fruit quality was explored.Redundancy analysis showed that soil chemical indicators explained 31.1%and76.0%of the variation in fruit appearance and quality in the plateau canyon and plateau mountains areas respectively,with higher contributions from p H（19.7%）,N:P（16.2%）,NH4+-N（10.6%）and AP（11.0%）.Soil nutrients in the karst plateau canyon explained 37.4%of the variation in photosynthetic traits,and soil nutrients explained 50.2%of the variation in photosynthetic traits.Soil nutrients AN and AP contribute most to variation in leaf functional traits in karst plateau mountains,respectively.The overall scores of soil quality evaluation in both study areas were negatively correlated with the grade of rock desertification.Karstplateaucanyon（potential1.833>slight-0.213>moderate-0.697>intensity-0.927）,karst plateau mountains（no1.160>potential0.183>light-1.343）.The overall score of walnut fruit in karst plateau mountains decreases with increasing rocky desertification grade,（no2.493>potential-0.777>slight-1.703）.Ten amino acid fractions,including TAA,EAA and MAA,increased with increasing soil TC and TN content in Plateau Canyon;EAA,BAA and UAA increased with increasing soil TK content in plateau mountains;MAA,UAA and IAA decreased with increasing p H.Leaf nutrient indicators in plateau canyon and plateau mountains explained only 8.3%and 31.2%of the variation in fruit appearance and quality,with TN,TP,C:N and TC being the most significant contributors;the content of 5amino acid fractions,including TAA,EAA and SAA,in plateau canyon fruits decreased with increasing leaf TC and Ca.;leaf TP was significantly positively correlated with UAA and IAA in plateau mountain;and plateau canyon apoplastic TN had significant positive correlations with all amino acids except for Asp,Glu,Arg and Cys,which had no correlation;N:P was positively correlated with all measured species of amino acids except Cys and Lys.The content of eight types of amino acids,including Lys,TAA and ESS,decreased with the increase of apoplastic Ca;the content of 10 types of amino acids,including Asp,Glu,TAA and EAA,increased with the increase of apoplastic TN in highland mountain fruits.Soil moisture content of karst plateau canyon was significantly and positively correlated with 11 categories of amino acids such as Ser and Gly;soil capacitance of karst plateau mountain area was significantly and negatively correlated with 17 categories of fruit indicators such as green skin rate,Glu,Ser and TAA.total soil porosity was significantly and positively correlated with fruit shape index,Glu,Ser,His,Val and Ile.Fruit diameter was highly significantly and positively correlated with kernel weight in the plateau canyon,in addition,fruit diameter was significantly and positively correlated with 10 types of amino acid fractions such as TAA and EAA;fruit diameter was significantly and positively correlated with shell thickness,fruit shape index,crude protein and dry fruit weight in the karst plateau mountains.The overall score of karst plateau canyon walnut fruits showed that intensity（3.107）>potential（1.207）>slight（-1.603）>moderate（-2.710）rocky desertification.The overall score of walnut fruit quality in karst plateau mountains decreased with increasing rocky desertification grade,indicating that the higher the degree of rocky desertification,the poorer the quality of walnut fruit.The correlation between soil quality and fruit quality conditions in karst rocky desertification areas,as well as between walnut nutrients and fruit quality,and functional traits and fruit quality were revealed,providing scientific reference for scientific management of walnut economic forests in rocky desertification areas,such as soil fertilization.（3）Key technologies for quality and efficiency improvement of walnuts were integrated and demonstrated.After the implementation of key technical measures of mulch improvement,soil fertilization and pruning,the soil bulk weight of each stone desertification grade in the two demonstration areas was reduced and the total soil porosity increased.The soil capacity of the two demonstration areas was decreased and the total soil porosity was increased after the control.Based on the actual environmental conditions and management conditions of walnut planting in the demonstration areas,soil fertilisation,understorey mulch improvement and pruning and shaping techniques for walnuts were implemented based on the determination of functional characteristics of walnut leaves,fruit quality and leaf-soil-apoplastic nutrient content in the demonstration areas,based on the actual environmental conditions and management conditions of walnut cultivation,soil physical properties differed before and after the implementation of the technology,with fluctuations in soil water content,soil capillary water holding capacity and soil capillary porosity,a decrease in soil bulk density and an increase in total soil porosity in the two demonstration areas.The combination of soil fertilization,mulch improvement and pruning and shaping techniques helped to improve the ground strength of walnut stands and increase the quality and efficiency of walnuts.A site-specific management model of investigation followed by treatment should be implemented in the study of walnut nutrients and quality to avoid blind measures,thereby promoting scientific management of the walnut forest industry,which is important for karst ecological restoration and sustainable economic development. |
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