Nutrient uptake by mulberry and Chinese prickly ash associated with arbuscular mycorrhizal fungi

Hechun Piao·Siliang Li·Shijie Wang



Nutrient uptake by mulberry and Chinese prickly ash associated with arbuscular mycorrhizal fungi

Hechun Piao1·Siliang Li1·Shijie Wang1

Understanding how nutrient absorption processes in plants are related to arbuscular mycorrhizal（AM）association is critical for predicting the effects of AM symbiosis on elemental cycling for plants.Both mulberry（Morus alba）and Chinese prickly ash（Zanthoxylum bungeanum）are AM-associated plants，widely distributed in southwest China.It was hypothesized that if the nutrient absorption processes were efficiently associated with AM symbiosis in both mulberry and Chinese prickly ash，foliar nutrient concentrations-especially calcium（Ca）-would be primarily determined by the soil conditions in different regions.To investigate this，AM colonization levels of soils，nutrient levels in soils and leaves，and δ13C values of leaves were analyzed for mulberry and Chinese prickly ash. In this study，spore density in soils with low pH was higher than that in soils with high pH.The average concentrations of sugar delivered to roots in both mulberry and Chinese prickly ash in soil with relatively low pH and soil extractable cations were higher than those in other areas. The values of foliar δ13C in both mulberry and Chinese prickly ash in low soil-pH and soil extractable cations were lower than those in contrast areas，indicating that water availability was impacted by soil characteristics.The efficiency in AM-mediated processes might play an important role in translocation between soil nutrients and plant tissue. The results suggest uptake and translocation of nutrients，especially Ca，in AM-associated plants may be affected by an efficiency of AM-mediated processes.Since Sr does not appear to be similarly affected，expressing Ca and other nutrient concentrations relative to Sr could be used to evaluate whether the uptake and translocation of Ca and other nutrients are affected by AM-mediated processes.

Arbuscular mycorrhizal fungi·Elemental

ratio·Carbon isotopes·Mulberry·Chinese prickly ash

上文已经界定了定义，为什么还要谈概念的现代诠释呢？这是因为目前各类学者及组织的定义和内涵阐述多数体现在标准化对于商业贸易、产业发展、科技进步、社会治理四个方面的作用，缺乏现代内涵的延伸。而与此同时，标准化活动的范围和内容正在不断的丰富与扩展，这也赋予了标准化基本概念的新内涵，需要对标准化给出新的诠释[6]。

1 Introduction

A number of laboratory and field studies indicated that arbuscular mycorrhizal（AM）fungi was important in the uptake of nutrients，such as calcium （Ca），magnesium（Mg），potassium（K），nitrogen（N），and phosphorus（P），resulting in high levels of foliar nutrients in AM-associated plants（George et al.1992；Taylor and Harrier 2001；Veresoglou et al.2011；Doubkova´et al.2012；Mu¨ller et al. 2013；Khabou et al.2014；Xiao et al.2014）.Mulberry（Morus alba）and Chinese prickly ash（Zanthoxylum bungeanum）both provide economic benefits and ecosystem services in southwest China.Mulberry is a fast-growing species，while Chinese prickly ash is a slow-growing species；both easily adapt to calcareous and some loam soils and are able to form associations with AM fungi.Both mulberry and Chinese prickly ash possess natural defenses and characteristics that enable them to survive and even flourish under systems with anthropogenic disturbance，such as karst areas that have experienced environmental degradation.AM fungi contribute to plant adaptation and ecosystem sustainability by promoting a closed nutrient cycle（Rillig 2004；van der Heijden et al.2008）.AM fungi can also improve the water absorption capacity of plants（Evelin et al.2009）.The importance of AM fungi inenhancing host plant growth is well known（Smith and Read 1997；Gosling et al.2006），and has been explained by the ability of the fungal extraradical hyphae to spread in soil and take up nutrients and water that are spatially unavailable to roots（Doubkova´et al.2012）.

✉ Siliang Li lisiliang@vip.skleg.cn

1The State Key Laboratory of Environmental Geochemistry，Institute of Geochemistry，Chinese Academy of Sciences，Guiyang 55002，People’s Republic of China

Soil conditions can affect the response of plants to inoculation with AM fungi and influence the development of mycorrhizal associations（Orozco-Patin˜o and Medina-Sierra 2013）.Soil pH has a significant effect on organisms and processes in the soil（Olsson et al.2010），and plays an important role in AM growth；in turn，AM symbiosis regulates soil pH（Orozco-Patin˜o and Medina-Sierra 2013）. Ma°rtensson et al.（2012）found AM fungal hyphae decrease in the soil with increasing soil pH.Furthermore，fungal growth is favored at low pH，while bacteria growth is favored at high pH（Ba´rcenas-Moreno et al.2011）.Soil acidity can directly affect AM fungal distribution，and in some cases soil acidification may restrict some fungal species in the soil（Guo et al.2012）.Base cation concentration and organic matter can also affect fungal distribution（Olsson et al.2010）.An et al.（2008）found that soil chemical properties，especially soil pH，are the major driving force for AM fungi communities in acid soils. Plants can acidify or alkalinize the soil medium（Moody and Aitken 1997）thus affecting the optimal pH needed by AM species for proliferation in the roots（Orozco-Patin˜o and Medina-Sierra 2013）.Mycorrhizal colonies can form and excrete organic substances by the extraradical hyphae and/or the roots of host plants，which can solubilize nonavailable nutrients，resulting in a strong capacity to mobilize nutrients absorbed by the host plant（Theuerl and Buscot 2010；Piao and Liu 2011）.

Calcium and strontium （Sr）ions have many similar properties，including the same ionic charge，similar ionic radii，and the ability to form complexes and chelates of varying levels of solubility（Shtangeeva et al.2011）.Strontium istaken up by plants in similar ways toCa；however，Sr and Ca accumulations in plants cannot be predicted simply from the behavior of Ca because Ca and Sr can interact competitively for uptake into biological systems（Shtangeeva et al.2011）.Because of the marked immobility of Ca2+and Sr2+within plants（Caines and Shennan 1999；Sua´rez 2010），root morphological features should be responsible for variations in Ca2+and Sr2+acquisition. Since plant-mycorrhiza associations are common，AM fungi’seffectsonplantnutrientavailabilityshouldbetakeninto account in interpreting differences between Ca and Sr uptake.Mycorrhizal symbiosis does not modify Sr accumulation or transfer to host plants（Ladeyn et al.2008）.Van der Heijden et al.（2015）showed that the internal pool of Ca in trees is more active than previously thought based on Ca isotopic data.On acid soils a preferential uptake of Ca over Sr occurs，while on calcareous soils a preferential uptake of Sr over Ca occurs（Poszwa et al.2000），implying that the foliar Ca and Sr concentrations should differ in different regions for the same plant species.Soils with a high concentration of CaCO3significantly decrease root growth and alter the symbiosis development steps of the AM fungus（Labidietal.2012）.Therefore，arelativelyhighefficiencyin an AM-mediated process should be responsible for high foliarCaandothernutrientconcentrations，whilearelatively low efficiency should be responsible for low Ca and other foliar nutrient contents（Piao and Liu 2011）.The value of δ13C is often increased when water availability is limited，as a result of stomatal closure and hence reduced transpiration（Grant et al.2012）.Limited transpiration rates result in low Ca and Sr concentrations in plant tissues（Funk and Amatangelo 2013）.Therefore，Ca uptake and translocation byplantsisdrivenbythetranspirationstream（Clarholmand Skyllberg 2013）.The ratios of foliar Ca/Sr versus soil Ca/Sr can express the degree to which Ca concentrations in plants have been discriminated over Sr relative to their soil resources（Blum et al.2012）.It was hypothesized that the differences in ratios of foliar Ca/Sr versus soil Ca/Sr in differentregionsshouldbedeterminedbysoilconditions.Thus，the objective of this study was to use measurements of stable carbon isotopes，and nutrient and sugar concentrations，to identify the parameters causing different foliar Ca andothernutrientconcentrationsinAM-associatedplantsof different regions.

2 Materials and methods

2.1 Research site

The study area is located in a transitional zone between lowland and hills in the mountainous terrain of the Guizhou Province of southwest China.Soil samples were collected in karst areas，where the geological environment is extremely fragile，the area overpopulated，and the economy backward，leadingtoseriouslanddegradationintheformofkarstrocky desertification and extensive exposure of basement rocks in some regions（Wang et al.2004；Liu 2007；Li et al.2013）. Mulberry is a perennial tree，which is widely cultivated in China for leaves，fruit，medicine，and sericulture purposes. Chinese prickly ash is a shrub species that is also widely cultivatedinChinaasacondimentandasmedicine.Because of their high drought resistance，both mulberry and Chinese prickly ash have played an important role in economic development and adapting fragile ecosystem restoration.

The samples were divided into two groups for both mulberry and Chinese prickly ash.For mulberry，the first group included the samples collected from Libo soils（17 sites）and the second group samples collected from Huangpingsoils（16 sites）.For Chinese prickly ash，sampleswere collected from Zunyi soils（22 sites）and from Huajiang soils（22 sites）.The sites were located in areas where soils developed in mixed terrains，except for the soils at Huajiang where the parent material was primarily limestone.The soil type was yellow Ultisols in all sampling areas，havingalongland-usehistoryasmaizefields.Sample locations and environmental parameters for sampling sites are listed in Table 1.Soil samples were taken from 0 to 15 cm depth to provide an indication of available nutrients，with at least six replicated plots for each soil sample. Nurseries growing Chinese prickly ash seedlings varied in size from～10 to 100 m2.Under normal conditions，the farmers sow seeds in September and remove weeds at regular intervals.A chemical fertilizer was not added to any of the nursery soils after sowing seed.Belowground parts of mulberry trees grown on the sampling sites for less than 4 years were used in this study.All shoots（aboveground parts）were developed every year in the mulberry plantation for sericultural purposes.The leaf samples were collected in late May for mulberry，while the seedlings were collected in early September for Chinese prickly ash.Detailed samples of leaves and roots were taken.

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2.2 Laboratory analysis

The average concentrations of extractable Ca in Libo soils growing mulberry was lower than that in Huangping soils，but the difference was not significant.The concentration of extractable Sr in Libo soils was slightly higher（not significantly）than that in Huangping soils（Table 2）.

2.3 Statistical analyses

Statistical analysis was conducted using SPSS 12.0 software（SPSS Science，Chicago，USA）.Differences between mean values of nutrient concentrations in samples between Libo and Huangping soils for mulberry，and between Zunyi and Huajiang soils for Chinese prickly ash were determined by a t test.Pearson correlation coefficients were performed to assess relationships between each plant tissue and soil parameters，and linear regression was used to assess relationships between foliar Ca/Sr ratios versus soil Ca/Sr ratios.For all statistical tests，differences were considered significant at P＜0.05.

Table 1 Sampling locations and environmental conditions

3 Results

3.1 AM colonization level and number of spores

In this study，six samples were used for determining AM colonization levels for each plant species.Colonization levelsofAMfungiformulberrywere16，13，and12%inLibosoils；and16，32，and9%inHuangpingsoils.Colonizationlevelsof AM fungi for Chinese prickly ash were 50，82，and 86%in Zunyi soils；and 17，20，and 31%in Huajiang soils.Six samples were used for determining AM spores for mulberry soils.Thenumbersofsporesin20 gdrysoilswere33，11，and 19 in Libo soils；and 16，15，and 13 in Huangping soils.

3.2 Total carbon and sugar concentrations in plant tissues

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The average concentration of foliar sugar in mulberry in Libo soils（340±138 mmol kg-1）was significantly lower than that in Huangping soils（530±285 mmol kg-1）（P＜0.05）.However，the average concentration of root sugar in mulberry in Libo soils（628±217 mmol kg-1）was significantly higher than that in Huangping soils（458±219 mmol kg-1）（P＜0.05）.For Chinese prickly ash，the average concentration of foliar sugar in Zunyi soils（226±39 mmol kg-1）was slightly lower than that in Huajiangsoils（242±90 mmol kg-1）.Theaverage concentrationofrootsugarinZunyisoils（262±115 mmol kg-1）was slightly higher than that in Huajiang soils（250±125 mmol kg-1）（Fig.1b）.

3.3 Soil pH and soil extractable nutrients

Table 2 shows that the mean soil pH in Libo soils was significantly lower than that in Huangping soils.In the Chinese prickly ash plots，pH ranged from 5.49 to 8.12 in Zunyi soils，and from 6.79 to 8.10 in Huajiang soils.The mean soil pH in Zunyi soils was significantly lower than that in Huajiang soils（Table 3）.

Plant samples for laboratory analysis were dried for 48 h at 60°C and ground with a mortar and pestle.Total carbon（C）and N were determined with a CHNS autoanalyzer（PE 2400-ll，Norwalk，CT，USA）.Plant P was digested using nitric-perchloric acid and analyzed by the vanadomolybdate colorimetric method.Olsen extractable P（Olsen P）was measured by 0.5 M NaHCO3extraction（adjusted to pH 8.5 with NaOH）（Olsen et al.1954）.Total soil P was determined after combustion of 1 g soil for 2 h at 550°C followed by digestion with 6 M HCl（Graetz et al.1999）.Standard soil analysis methods were used to measure soil extractable Ca，Mg，K，and Sr with 1 M NH4OAC（Thomas 1982）.The samples of both mulberry and Chinese prickly ash were sent to the Key Laboratory for Conservation and Utilization of Bio-resources of Yunnan University and examined for mycorrhizal colonization following the method of Li et al.（2005）.Briefly，afterclearingtherootswith10%KOH，they were acidified in lactic acid，stained with acid fuchsin，and subsequentlyexaminedfortheirlevelofcolonizationundera compound-light microscope（OLYMPUS-BX51，Japan）at magnification×200 according to the method of McGonigle et al.（1990）.For soluble sugar determination，0.25 g of airdriedmaterialwasextractedfourtimeswithdistilledwaterat 75°C，modified from the method of Chinnasamy and Bal（2003）wherebywater was usedinsteadof 80%ethanol，and the water temperate was 75°C rather than boiling.After each extraction，samples were filtered，and the filtrates were used to determine soluble sugar colorimetrically through anthrone reaction（Piao and Liu 2011）.The δ13C values of leaves were measured by combustion of～2 mg C mixed withCuOat850°Cina vacuum-combustionsystemfor2 h. Carbon dioxide generated in the combustion tubes was separated by cryogenic distillation，then collected in breakseals and analyzed on a mass spectrometer（MAT 252 Finnigan，Bremen，Germany）.Thedata are expressedrelative to the international standard PDB as‰.The precision for sample repeats was better than 0.2‰for δ13C.

On average，the concentrations of extractable Ca in Zunyi soils growing Chinese prickly ash were lower than that in Huajiang soils，and the concentration of extractable Sr in ZunyisoilswassignificantlyhigherthanthatinHuajiangsoils（Table 3）.

Fig.1 a Carbon concentrations in leaves and roots of mulberry and Chinese prickly ash，and b sugar concentrations in leaves and roots of mulberry and Chinese prickly ash.LB Libo，HP Huangping，ZY Zunyi，HJ Huajiang（*P＜0.05）

3.4 Tissue chemistry and carbon isotopic compositions of leaves

作为近代著名的文学大家，鲁迅不仅对当时的种种社会问题给予了高度关注，同时对女性问题作出了深刻的思考。在他的作品当中，不乏女性人物形象，比如《明天》中的单四嫂、《子夜》中的子君等，但无论是什么样的女性角色，都一定程度受到封建思想的侵害。任何人都不可能脱离社会而存在，个人的命运很大程度上会受社会种种弊端影响，而《祝福》中的祥林嫂则是一个典型的代表。

4.3 Relationship between water availability and Ca uptake and translocation

Anti-corrosion Design of Concrete Structure in Sulfate Strong Corrosive Environment in Saline Soil in Plateau Area LI Yuting,ZHANG Xiaofeng,YE Sheng(102)

首先，中小企业管理制度内容不能全面化地涵盖企业管理中的日常工作。制定制度的管理者由于自身知识的缺乏，对岗位要求和内容等认识不清，因而不能很好地完善制度政策。如管理思想的偏差或管理细节的缺失导致企业管理效能不均衡。其次，管理制度内容缺乏针对性，容易在执行时产生监管不力的情况，制度较难以落实，对管理形式和管理方式提出了很大的挑战。最后，管理制度内容不能及时更迭。在当前经济时代发展迅速的时代，管理模式和管理方法及管理思想一定要紧跟时代潮流，但中小企业管理者在制定和修改制度的时候没有很好地结合当前的经济形势对管理制度进行修改。

The average concentration of foliar N in mulberry grown on Libo soils was significantly lower than that in Huangping soils，but little difference of foliar Mg，K，and P concentrations was found between Libo and Huangping soils（Table 4）.The concentrations of foliar N and K in Chinese prickly ash grown on Zunyi soils were significantly lower than those in Huajiang soils（Table 5）.Except for Ca，Mg，and Sr，the average concentrations of root nutrients in mulberry（K，N，and P）did not differ between Libo and Huangping soils（Table 4）.Except for N，theaverage concentrations of root nutrients in Chinese prickly ash（Ca，Mg，K，Sr，and P）returned little difference between Zunyi and Huajiang soils（Table 5）.

用矢量网络分析仪分析超声换能器阻抗匹配电路的阻抗曲线变化趋势,并不断地优化修改高低频段中心频率处的匹配阻抗值及LC参数值,调整阻抗曲线的位置,使S11与S22的轨迹压缩在Smith Chart中心点附近,如图5所示,AOTF光谱衍射效率达到最高,此时高低超声换能器优化后的匹配阻抗值为15-j*10 Ω和20-j*15 Ω。在AOTF衍射效率最佳的情况下,优化后的高低频段换能器匹配电路的S11参数在-30 dB～-20 dB之间,满足回波损耗小于-10 dB的参数指标[7],双路超声换能器阻抗匹配电路输入回波损耗测试结果如图6所示。

Soil microorganisms，especially fungi，may contribute significantly to the long-term retention of elements in organic layers of forest soils，excepting Sr（Parekh et al. 2008）.If the amounts of nutrients acquired by AM fungi are low，AM fungi have only a relatively minor impact on reducing nutrient leaching（van der Heijden et al.2008）. Using two-chambered pots where only AM fungal hyphae connected the chambers，Meding and Zasoski（2008）examined nutrient transfer between native plant species of grasses and forbs，and suggest that there is no evidence of significant Sr transfer between experimental plants via extraradical hyphae.However their results could be attributed to immobilization of Sr within plant tissues.It seems that the more severe leaching losses of Sr relative to other nutrients should be attributed to Sr acquisition and retention and not related to AM symbiosis.

Table 2 Mean values for soil pH；total N；P and Olsen P；organic C；and soil extractable Ca，Mg，K，and Sr concentrations in mulberry soils

Table 3 Mean values for soil pH；total N；P and Olsen P；organic C；and soil extractable Ca，Mg，K and Sr concentrations in Chinese prickly ash soils

Table 4 Mean values for foliar and root Ca，Mg，K，Sr，P，and N in mulberry plants

3.5 The ratios of foliar nutrient/Sr versus soil nutrient/Sr

The ratios of foliar nutrient/Sr versus soil nutrient/Sr are listed for mulberry and Chinese prickly ash in Table 6. Significant differences were found in the ratios for foliar Ca/Sr，Mg/Sr，and K/Sr between Libo and Huangping soils and between Zunyi and Huajiang soils.The ratios of foliar P/Sr and foliar N/Sr were similar between Libo and Huangping soils and between Zunyi and Huajiang soils.The ratios of foliar and soil Ca/Sr，Mg/Sr，and K/Sr were generally higher than 1.The ratios for Ca/Sr of mulberry were higher in Libo soils（with mean soil pH value of 4.92）when compared to Huangping soils，which had a relatively high soil pH（P＜0.05）.Similarly，the ratios for Ca/Sr of Chinese prickly ash were somewhat higher in Zunyi soils（with relatively low soil pH）than in Huajiang soils with a mean soil pH 7.68（P＜0.05）.

Table 5 Mean values for foliar and root Ca，Mg，K，Sr，P，and N in Chinese prickly ash

4 Discussion

4.1 Ca behavior differs from Sr in soils

林区郁闭度低主要是指该区域中的林木郁闭度低于0.7的人工林或郁闭度低于0.6的天然林，管理人员也要分情况落实森林抚育管理工作[3]。如果郁闭度较低，幼龄木生长易受到其他植物的抑制，但情况较好的林区，管理人员需要重点调节幼龄木与其他植物的营养，帮助幼龄木获取更多的生长营养元素，帮助其快速成长。具体可通过伐除其他植株，移栽生长密集的幼苗来实现。

The limestone of the study area has a high concentration of Sr relative to aluminosilicate minerals（Jiang and Ji 2011）. However，the concentrations of Sr in extractable fractions were lower in Huajiang soils developed from limestone than in the Zunyi soils developed on mixed terrains，indicating the intensive leaching of Sr relative to other nutrients during carbonate weathering and soil development in the karst area（Jiang and Ji 2011）.Sr concentration in plants is maximized in soils with a low pH（Karpova and Gomonova 2006）.Increasing soil pH with CaCO3，especially in combination with application of organic fertilizers，can lead to changes in the soil chemical properties controlling Sr mobility，which results in a lower uptake of Sr by plants（Karpova and Gomonova 2006）.Previous studies have indicated that soil nutrient availability is limited in high soil pH（Kerley 2000；Al-Karaki and Al-Omoush 2002）.However，Stark et al.（2011）found that high soil pH usually parallels high soil extractable nutrient concentration，with important consequences for plants and chemical quality of soil organic matter.This finding was supported，especially for Ca，by a study in southwest China（Piao and Liu 2012）.While an acid condition might produce more soil nutrient availability，it might also lead to more soil nutrient loss through leaching.This is likely to be the main reason why the Sr leaching loss was more severe than that of other nutrients in both Libo and Huangping soils.Most soil nutrients in this study were relatively high in Zunyi and Huajiang-both soils with higher pH values. Soil organic C did not show a difference between the two soil groups in this study.In ion exchange on clays，Ca and Sr behave almost identically owing to the divalent charge and similar hydrated radius（Blum et al.2008）.In ion exchange on soil organic matter，Ca may be retained preferentially over Sr to a small degree（Baes and Bloom 1988；Blum et al.2008），and the presence of soil microorganisms does not significantly enhance the retention of Sr in the organic system the way it does other elements（Parekh et al.2008）.

Fig.2 Average foliar δ13C in Chinese prickly ash grown on Huajiang and Zunyi soils，and in mulberry grown on Huangping and Libo soils（**P＜0.01）

4.2 Relationship between AM fungi and nutrients distribution

Foliar δ13C in mulberry in Libo soils（-30.0±0.5‰）was significantly lower than that in Huangping soils（-29.3±0.7‰）（P＜0.01）.For Chinese prickly ash，foliar δ13C in Zunyi soils（-28.5±1.4‰）was similar to that in Huajiang soils（-28.0±0.8‰）（Fig.2）.

Table 6 Ratios of foliar nutrient/Sr versus soil nutrient/Sr（mean±standard deviations）

There was little difference in AM colonization levels between mulberry and Chinese prickly ash.This supports previous research conclusions that there is no significant relationship between AM colonization levels and nutrient acquisition（Piao and Liu 2011；Piao et al.2012）.In this study，spore density in the Libo soils（with a relatively low soil pH and some soil nutrients）was higher than that in Huangping soils，which is consistent with the results of Aliasgharzadeh et al.（2001），who have reported a negative correlation between spore density and available soil Mg and Ca（Evelin et al.2009）.Guo et al.（2012）have found that high soil pH with CaCO3treatment significantly decreases root growth and alters the symbiosis development steps of the AM fungus Rhizophagus irregularis，such as germination，hypha elongation，root colonization rate，extraradical hyphal development，and sporulation.However the fungus is able to completely fulfill its life cycle（Labidi et al.2012），which might influence the distribution of nutrients between soil and plants.

The AM fungal community structure is significantly influenced by environmental factors，especially soil moisture，pH，available N，and P（Wang et al.2013；De Beenhouwer et al.2015）.The present data show that the average concentrations of sugar delivered to roots in both mulberry and Chinese prickly ash with relatively low soil pH and soil extractable N and P were higher than values in contrast areas.AM symbiosis depends on the host sugars for the formation，maintenance，and function of fungal structures（Zhu and Miller 2003）.Root turnover can account for up to 40%of the C input into soil and is clearly the major driver for soil microbiological processes（Richardson et al.2009）. The fungi are obligate symbionts and cannot survive without a photosynthate supply from the host plant（Smith et al.2010）.Therefore，acquisition of nutrients and growth responses depend on soluble photosynthate production and its concentration in the soil（Orozco-Patin˜o and Medina-Sierra 2013）.Meanwhile，root exudates not only influence nutrient availability but also interact with soil microorganisms（Richardson et al.2009）.The amount of C allocated to AM processes is estimated to range from 4 to 20% of a plant’s total C budget（Smith and Read 1997）. M°rtensson et al.（2012）reported that the allocation of C to the extraradical AM hyphae decreases with increasing pH，ranging from not detectable to 1.2 μg13C g-1dry soil in the pH range of 5.5-8.5.CaCO3treatment of soil decreases chicory root growth（Labidi et al.2012）.This effect is more drastic in mycorrhizal roots than in non-mycorrhizal ones，which may be related to the allocation of a considerable portion of C by mycorrhizal roots to maintain fungal metabolism（Labidi et al.2012）.Mycorrhizal colonization can result in the excretion of organic substances by extraradical hyphae and/or roots of host plants，which can solubilize non-available forms of nutrients，resulting in a strong capacity to mobilize nutrients absorbed by the host plant（Theuerl and Buscot 2010；Piao and Liu 2011）.Differences in sugar levels of plant tissues were found between Libo and Huangping soils，and between Zunyi and Huajiang soils.A key feature of AM-mediated processes is the transfer of photosynthate from the host plant to the AM fungal hyphae（Zhu and Miller 2003；Richardson et al. 2009；Piao and Liu 2011）.For example，there is significantly less sucrose in both shoots and roots of summer wheat with AM fungus compared with summer wheat without AM fungus（Hawkins and George 2001）.The efficiency of the AM-mediated processes was higher in both Libo and Zunyi soils than those in Huangping and Huajiang soils.

The average concentration of foliar Ca in mulberry in Libo soils was relatively higher than that in Huangping soils（Table 4）.For Chinese prickly ash，the mean value of foliar Ca in plants grown in Zunyi soils was higher than for those in Huajiang soils（Table 5）.The average concentration of foliar Sr in mulberry in Libo soils was significantly higher compared to that found in Huangping soils（Table 4）.The average concentration of foliar Sr in Chinese prickly ash in Zunyi soils was significantly higher than concentrations found in Huajiang soils（Table 5）.

Arbuscular mycorrhizal symbiosis is beneficial in providing host plants with water，thus enhancing the tolerance of the host plants to water deficit（Ba´rzana et al.2012）.The value of δ13C is often increased when water availability is limited，as a result of stomatal closure and hence reduced transpiration（Grant et al.2012）.Previous results show that plants under water stress increase their foliar δ13C relative to those without water stress（Hubick et al.1986；Farquhar et al.1988）.Values of δ13C are not affected by irrigation or N treatments（Pascual et al.2013）.Both mulberry and Chinese prickly ash have the capacity to grow in a widerange of environments.Under drought stress，the growth of mulberry is inhibited，but the trees are known to respond to the stress by increasing the root absorptive area and enhancing capacity for water retention（Huang et al.2013）. Mulberry trees have a high water demand owing to their fast growth rate and high metabolism（Guha et al.2012），resulting in large biomass.The present results show that the values of foliar δ13C in both mulberry and Chinese prickly ash in Libo and Zunyi soils，respectively，were relatively lower than those in Huangping and Huajiang soils.This indicates that water availability in both mulberry on Libo soils and Chinese prickly ash on Zunyi soils was higher than on Huangping and Huajiang soils，which would attribute to the higher efficiency of AM-mediated processes in the Libo and Zunyi soils due to different environmental characteristics，such as pH and soil nutrient distribution.

During water transport from root to leaf，divalent cations such as Ca and Sr undergo a series of exchange reactions at negatively charged sites on cell walls（Funk and Amatangelo 2013）.Both Ca and Sr are immobile elements，meaning that they are not resorbed from a leaf once they have been assimilated（Karley et al.2000），and therefore foliar Ca and Sr concentrations should be correlated with how much water is taken up over a leaf’s lifetime（Funk and Amatangelo 2013）.Low transpiration rates result in a small quantity of Ca and Sr in plant tissues，with implications for the nutritional quality of plants and for rates of biochemical cycling（Funk and Amatangelo 2013）.Clarholm and Skyllberg（2013）reported that actual evapotranspiration is in control of the cycling of base cations，such as Ca and Mg，between soil and trees.Therefore，Ca uptake by tree roots is by passive movement in the mass flow of soil water driven by the transpiration stream.

4.4 The ratios of foliar nutrient/Sr versus soil nutrient/Sr

The ratios of foliar Ca/Sr versus soil Ca/Sr measure the degree to which Ca has been incorporated preferentially over Sr in plants relative to their soil presence（Blum et al. 2012）.However，the bias toward Ca over Sr depends on soil conditions.The current data show that both mulberry grown at Libo and Chinese prickly ash at Zunyi had a relatively preferential uptake of Ca over Sr compared with contrast areas.Differences between Ca and Sr behavior were found during uptake of nutrients from soils，and might be caused by ion exchange processes during ascent in the xylem （Clarkson 1984）.Our results show the ratios of foliar Ca/Sr versus soil Ca/Sr for both mulberry and Chinese prickly ash were higher on soils with relatively low pH and soil extractable cations，where the efficiency of AM-mediated processes would increase.This suggests that relatively high efficiencies in the AM-mediated processes might be responsible for the high ratios of foliar Ca/Sr versus soil Ca/Sr in both Libo and Zunyi soils relative to the Huangping and Huajiang soils.Meanwhile，Sr is retained by cation exchange sites in stems to a greater extent than Ca，resulting in increased translocation of Ca relative to Sr in the leaves of plants（Poszwa et al.2000；Dasch et al.2006；Funk and Amatangelo 2013），which might be another cause for the difference of translocation.

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The ratios of foliar Mg/Sr versus soil Mg/Sr and the ratios of foliar K/Sr versus soil K/Sr were also higher for soils with lower pH than for soils with higher pH for both mulberry and Chinese prickly ash（Tables 2，6），a pattern repeated with the ratios of foliar Ca/Sr versus soil Ca/Sr. These results also indicate that both mulberry at Libo and Chinese prickly ash at Zunyi had a preferential uptake of Mg and K over Sr compared with contrast areas.As for the ratios of foliar P/Sr versus soil P/Sr and the ratios of foliar N/Sr versus soil N/Sr，there were no differences among regions，so these nutrients may be not suitable for assessing the effects of AM-mediated processes on uptake by mulberry and Chinese prickly ash.

The average concentration of foliar C in mulberry on Libo soils（33.5±1.2 mol kg-1）wassimilartothaton Huangping soils（33.4±0.9 mol kg-1），but the average concentration of root C in mulberry of Libo soils（36.6±1.3 mol kg-1）was significantly higher than that of Huangping soils（35.0±2.7 mol kg-1）（P=0.038）.For Chinese prickly ash，the average concentration of foliar C in Zunyi soils（35.2±0.6 mol kg-1）was significantly lower than that in Huajiang soils（36.5±0.6 mol kg-1）（P=0.000），but the average concentration of root C in Zunyi soils（36.5±0.7 mol kg-1）was similar to that in Huajiang soils（36.7±0.7 mol kg-1）（Fig.1a）.

5 Conclusion

Mulberry（Morus alba）and Chinese prickly ash（Zanthoxylum bungeanum）are important economic plants widely distributed in southwest China.In this study，the nutrients and AM-colonization level of soils as well as carbon isotopic compositions of leaves were investigated for mulberry and Chinese prickly ash growing in varied environmental conditions.The results suggested that the high efficiency in AM-mediated processes was responsible for the relatively high levels of foliar Ca，Mg，and K relative to Sr absorbed by mulberry and Chinese prickly ash grown on Libo and Zunyi soils，respectively，while the relatively low efficiency in AM-mediated processes was responsible for the low amount of foliar Ca，Mg，and K relative to Sr in others areas.Water availability also affects ratios of foliar Ca/Sr versus soil Ca/Sr.Since uptake and translocation of Ca and Sr in AM plants might be influencedbyanefficiencyofAM-mediatedprocesses，expressing Ca concentration relative to Sr could be used to evaluate whether the nutrient could be affected by AM-mediated processes.However the ratios of foliar Ca/Sr versus soil Ca/Sr could vary with species and environmental conditions，including temperature and precipitation. More research on these processes in the future will improve the interpretation of foliar elemental ratios as an index for evaluating AM-mediated processes and elemental cycling on the Earth’s surface.

AcknowledgmentsThe authors wish to thank Dr.Z.W.Zhao，from the Key Laboratory for Conservation and Utilization of Bio-resources of Yunnan University for assistance in determining arbuscular mycorrhizal colonization levels.This study was financially supported by the National Natural Science Foundation of China（Grant no. 4121004），and water project of MEP（2012ZX07503003001）.

Aliasgharzadeh N，Rastin NS，Towfighi H，Alizadeh A （2001）Occurrence of arbuscular mycorrhizal fungi in saline soils of the Tabriz Plain of Iran in relation to some physical and chemical properties of soil.Mycorrhiza 11：119-122

Al-Karaki GN，Al-Omoush M（2002）Wheat response to phosphogypsum and mycorrhizal fungi in alkaline soil.J Plant Nutr 25（4）：873-883

An G-H，Miyakawa S，Kawahara A，Osaki M，Ezawa T（2008）Community structure of arbuscular mycorrhizal fungi associated with pioneer grass species Miscanthus sinensis in acid sulfate soils：habitat segregation along pH gradients.Soil Sci Plant Nutr 54：517-528

Baes AU，Bloom PR（1988）Exchange of alkaline earth cations in soil organic matter.Soil Sci 146：6-14

Ba´rcenas-Moreno G，Rousk J，Ba°a°th E（2011）Fungal and bacterial recolonisation of acid and alkaline forest soils following artificial heat treatments.Soil Biol Biochem 43：1023-1033

Ba´rzana G，Aroca R，Paz JA，Chaumont F，Martinez-Ballesta MC，Carvajal M，Ruiz-Lozano JM （2012）Arbuscular mycorrhizal symbiosis increases relative apoplastic water flow in roots of the host plant under both well-watered and drought stress conditions. Ann Bot 109：1009-1017

Blum JD，Dasch AA，Hamburg SP，Yanai RD，Arthur MA（2008）Use of foliar Ca/Sr discrimination and87Sr/86Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest.Biogeochemistry 87：287-296

Blum JD，Hamburg SP，Yanai RD，Arthur MA（2012）Determination of foliar Ca/Sr discrimination factors for six tree species and implications for Ca sources in northern hardwood forests.Plant Soil 356：303-314

Caines AM，Shennan C（1999）Growth and nutrient composition of Ca2+use efficient and Ca2+use inefficient genotypes of tomato. Plant Physiol Biochem 37：559-567

Chinnasamy G，Bal AK（2003）Seasonal changes in carbohydrates of perennial root nodules of beach pea.J Plant Physiol 160：1185-1192

Clarholm M，Skyllberg U（2013）Translocation of metals by trees and fungi regulates pH，soil organic matter turnover and nitrogen availability in acidic forest soils.Soil Biol Biochem 63：142-153

Clarkson DT（1984）Calcium transport between tissues and its distribution in the plant.Plant Cell Environ 7：449-456

个例库以文档形式存于省台分布式服务器中,其中资料可手动添加,随时更新,并确保查询的快捷高效和资料的安全。

Dasch AA，Blum JD，Eagar C，Fahey TJ，Driscoll CT，Siccama TG（2006）The relative uptake of Ca and Sr into tree foliage using a whole-watershed calcium addition.Biogeochemistry 80：21-41

De Beenhouwer M，Van Geel M，Ceulemans T，Muleta D，Lievens B，Honnay O（2015）Changing soil characteristics alter arbuscular mycorrhizal fungi communities of Arabica coffee（Coffea Arabica）in Ethiopia across a management gradient.Soil Biol Biochem 91：133-139

Doubkova´P，Suda J，Sudova´R（2012）Arbuscular mycorrhizal symbiosis on serpentine soils：the effect of native fungal communities on different Knautia arvensis ecotypes.Plant Soil 345：325-338

Evelin H，Kapoor R，Giri B（2009）Arbuscular mycorrhizal fungi in alleviation of salt stress：a review.Ann Bot 104：1263-1280

Farquhar GD，Hubick KT，Condon AG，Richards RA（1988）Carbon isotope fractionation and plant water-use efficiency.Ecol Stud 68：21-40

Funk JL，Amatangelo KL（2013）Physiological mechanisms drive differing foliar calcium content in ferns and angiosperms. Oecologia 173：23-32

George E，Haussler K，Vetterlein G，Gorgus E，Marschner H（1992）Water and nutrient translocation by hyphae of Glomus mosseae. Can J Bot 70：2130-2137

Gosling P，Hodge A，Goodlass G，Bending GD（2006）Arbuscular mycorrhizal fungi and organic farming.Agric Ecosyst Environ 113：17-35

Graetz DA，Nair VD，Portier KM，Voss RL（1999）Phosphorus accumulation in manure-impacted Spodosols of Florida.Agric Ecosyst Environ 75：31-40

采用了微波消解-电感耦合等离子体质谱法同时测定卷烟烟丝中K、Ca和Mg的含量。经方法精密度和回收率试验证明，该方法具有操作简单、分析快速、重复性好等优点，适合卷烟烟丝中K、Ca和Mg含量的同时测定。

Guha A，Sengupta D，Rasineni GK，Reddy AR（2012）Non-enzymatic antioxidative defence in drought-stressed mulberry（Morus indica L.）genotypes.Trees 26：903-918

Guo YJ，Ni Y，Raman H，Wilson AL，Ash GJ，Wang AS，Li GD（2012）Arbuscular mycorrhizal fungal diversity in perennial pastures；responses to long-term lime application.Plant Soil 351：389-403

Hawkins H-J，George E （2001）Reduced15N-nitrogen transport through arbuscular mycorrhizal hyphae to Triticum aestivum L. supplied with ammonium vs.nitrate nutrition.Ann Bot 87：303-311

Grant OM，Davies MJ，James CM，Johnson AW，Leinonen I，Simpson DW（2012）Thermal imaging and carbon isotope composition indicate variation amongst strawberry（Fragaria x ananassa）cultivars in stomatal conductance and water use efficiency. Environ Exp Bot 76：7-15

Huang XH，Liu Y，Li JX，Xiong XZ，Chen Y，Yin XH，Feng DL（2013）The response of mulberry trees after seedling hardening to summer drought in the hydro-fluctuation belt of three Gorges reservoir areas.Environ Sci Pollut Res 20：7103-7111

用水效率方面，全市万元GDP用水量由2011年的17.0 m3下降到2013年的13.15 m3，万元工业增加值用水量由2011年的11.61 m3下降到9.33 m3，在全国大城市中处于领先水平。工业用水重复利用率为88%，城镇供水管网漏损（失）率为12.72%。

Hubick KT，Farquhar GD，Shorter R（1986）Correlation between water-use efficiency and carbon isotope discrimination in diverse peanut（Arachis）germplasm.Aust J Plant Physiol 13：803-816

Jiang YB，Ji HB（2011）Sr fluxes and87Sr/86Sr characterization of river waters from a karstic versus granitic watershed in the Yangtze River.J Geochem Explor 110：202-215

Karley AJ，Leigh RA，Sanders D（2000）Where do all the ions go？The cellular basis of differential ion accumulation in leaf cells. Trends Plant Sci 5：465-470

Karpova EA，Gomonova NF（2006）Strontium in an agrocenosis on a soddy-podzolic soil under conditions of the long-term effect and aftereffect of fertilizers.Eur J Soil Sci 39：779-784

区块链面向的也是高价值数据，但针对的是数据机构或数据管理员，以及可能造假的问题。区块链不信任数据机构和数据管理员，不信任他/她写入的数据，除非多个相关方能够根据事先达成的协议（共识机制），集体同意录入。传统数据库为追求一致性而牺牲了效率，大数据为追求效率而牺牲了一致性，而区块链为追求更高的一致性而牺牲了更多的效率。

Kerley SJ（2000）Changes in root morphology of white lupin（Lupinus albus L.）and its adaptation to soils with heterogeneous alkaline/acid profiles.Plant Soil 218（1-2）：197-205

Khabou W，Hajji B，Zouari M，Rigane H，Abdallah FB（2014）Arbuscular mycorrhizal fungi improve growth and mineral uptake of olive tree under gypsum substrate.EcolEng 73：290-296

Labidi S，Jeddi FB，Tisserant B，Debiane D，Rezgui S，Grandmougin-Ferjani A，Sahraoui AL-H（2012）Role of arbuscular mycorrhizal symbiosis in root mineral uptake under CaCO3stress.Mycorrhiza 22：337-345

Ladeyn I，Plassard C，Staunton S（2008）Mycorrhizal association of maritime pine，Pinus pinaster，with Rhizopogon roseolus has contrasting effects on the uptake from soil and root-to-shoot trasfer of137Cs，85Sr and95mTc.J Environ Radioact 99：853-863

Li LF，Yang AN，Zhao ZW （2005）Seasonality of arbuscular mycorrhizal symbiosis and dark septate endophytes in a grassland site in southwest China.FEMS Microbiol Ecol 54：367-373

Li S-L，Liu C-Q，Li J，Xue Z，Guan J，Lang Y，Ding H，Li L（2013）Evaluation of nitrate source in surface water of southwestern China based on stable isotopes.Environ Earth Sci 68：219-228

Liu C-Q（2007）Biogeochemical processes and cycling of nutrients in the Earth’s surface：chemical erosion and nutrient cycling in Karstic catchments，Southwest China.Science Press，Beijing，p 608

Ma°rtensson L-M，Schnoor TK，Olsson PA （2012）Allocation of carbon to mycorrhiza in the grasses Koeleria glauca and Corynephorus canescens in sandy grasslands.Appl Soil Ecol 54：55-62

McGonigle TP，Miller MH，Evans DG，Fairchild GL，Swan JA（1990）A new method which gives an objective measure of colonization of roots by vesicular-arbuscular mycorrhizal fungi.New Phytol 115：495-501

Meding SM，Zasoski RJ（2008）Hyphal-mediated transfer of nitrate，arsenic，cesium，rubidium，and strontium between arbuscular mycorrhizal forbs and grasses from a California oak woodland. Soil Biol Biochem 40：126-134

Moody PW，Aitken RL（1997）Soil acidification under some tropical agricultural systems：rates of acidification and contributing factors.Aust J Soil Res 35：163-173

Mu¨ller A，George E，Gabriel-Neumann E（2013）The symbiotic recapture of nitrogen from dead mycorrhizal and non-mycorrhizal roots of tomato plants.Plant Soil 364：341-355

Olsen SR，Cole CV，Watanabe FS，Dean LA（1954）Estimation of available phosphorus in soils by extraction with sodium bicarbonate.USDA Circ.939，Washington

Olsson PA，Schnoor TK，Hanson S-A（2010）pH preferences of redlisted gasteromycetes in calcareous sandy grasslands：implications for conservation and restoration.Fungal Ecol 3：357-365

Orozco-Patin˜o F，Medina-Sierra M （2013）Effects of arbuscular mycorrhizal fungal species and the medium pH on the growth of Pueraria phaseoloides（Roxb.）Benth.Symbiosis 60：65-71

Parekh NR，Poskitt JM，Dodd BA，Potter ED，Sanchez A（2008）Soil microorganisms determine the sorption of radionuclides within organic soil systems.J Environ Radioact 99：841-852

Pascual M，Lordan J，Villar JM，Fonseca F，Rufat J（2013）Stable carbon and nitrogen isotope ratios as indicators of water status and nitrogen effects on peach trees.Sci Hortic 157：99-107

Piao H-C，Liu C-Q（2011）Variations in nitrogen，zinc and sugar concentrations in Chinese fir seedlings grown on shrubland and ploughed soils in response to arbuscular mycorrhizae-mediated process.Biol Fertil Soils 47：721-727

Piao H-C，Liu C-Q（2012）Response of biomass accumulation and nodulation by Vicia villosa to soil conditions：evidence from δ13C and δ15N isotopes.Chin J Geochem 31：119

Piao H-C，Liu C-Q，Wang S-J（2012）Isotopic evaluation of the role of arbuscular mycorrhizae in the nitrogen preference in Chinese fir seedlings.Pedobiologia 55：167-174

Poszwa A，Dambrine E，Pollier B，Atteia O（2000）A comparison between Ca and Sr cycling in forest ecosystems.Plant Soil 225：299-310

Richardson AE，Barea J-M，McNeill AM，Prigent-Combaret C（2009）Acquisition of phosphorus and nitrogen in the rhizosphere and plantgrowthpromotionbymicroorganisms.PlantSoil 321：305-339

Rillig MC（2004）Arbuscular mycorrhizae and terrestrial ecosystem processes.Ecol Lett 7：740-754

Shtangeeva I，Steinnes E，Lierhagen S（2011）Macronutrients and trace elements in rye and wheat：similarities and differences in uptake and relationships between elements.Environ Exp Bot 70：259-265

Smith SE，Read DJ（1997）Mycorrhizal symbiosis，2nd edn. Academic Press，San Diego

Smith SE，Facelli E，Pope S，Smith FA（2010）Plant performance in stressful environments：interpreting new and established knowledge of the roles of arbuscular mycorrhizas.Plant Soil 326：3-20 Stark S，EsKelinen A，Ma¨nnisto¨MK（2011）Regulation of microbial community composition and activity by soil nutrient availability，soil pH，and herbivory in the tundra.Ecosystems 15：18-33

Sua´rez N（2010）Leaf lifetime photosynthetic rate and leaf demography in whole plants of Ipomoea pes-caprae growing with a low supply of calcium，a‘non-mobile’nutrient.J Exp Bot 61：843-855

Taylor J，Harrier LA（2001）A comparison of development and mineral nutrition of micropropagated Fragaria X ananassa cv. Elvira（strawberry）when colonised by nine species of arbuscular mycorrhizal fungi.Appl Soil Ecol 18：205-215

Theuerl S，Buscot F（2010）Laccases：toward disentangling their diversity and functions in relation to soil organic mater cycling. Biol Fertil Soils 46：215-225

Thomas GW（1982）Exchangeable cations.In：Page AL，Miller RH，Keeney（eds）Methods of soil analysis，Part 2.Chemical and microbiological properties-agronomy monograph no.9，2nd edn. ASA-SSSA，Madison，pp 159-165

Van der Heijden MGA，Bardgett RD，van Straalen NM （2008）The unseen majority：soil microbes as drivers of plant diversity and productivity in terrestrial ecosystems.Ecol Lett 11：296-310

Van der Heijden G，Dambrine E，Pollier B，Zeller B，Ranger J，Legout A（2015）Mg and Ca uptake by roots in relation to depth and allocation to aboveground tissues：results from an isotopic labeling study in a beech forest on base-poor soil.Biogeochemistry 122：375-393

Veresoglou SD，Shaw LJ，Sen RB（2011）Glomus intraradices and Gigaspora margarita arbuscular mycorrhizal associations differentially affect nitrogen and potassium nutrition of Plantago lanceolata in a low fertility dune soil.Plant Soil 340：481-490

Wang S-J，Liu Q-M，Zhang D-F（2004）Karst rocky desertification in southwestern China：geomorphology，landuse，impact and rehabilitation.Land Degrad Dev 15：115-121

Wang P，Shu B，Wang Y，Zhang DJ，Liu JF，Xia JF（2013）Diversity of arbuscular mycorrhizal fungi in red tangerine（Citrus reticulate Blanco）rootstock rhizospheric soils from hillside citrus orchads.Pedobiologia 56：161-167

Xiao JX，Hu CY，Chen YY，Yang B，Hua J（2014）Effects of low magnesium and an arbuscular mycorrhizal fungus on the growth，magnesium distribution and photosynthesis of two citrus cultivars.Sci Hortic 177：14-20

Zhu Y-G，Miller RM（2003）Carbon cycling by arbuscular mycorrhizal fungi in soil-plant systems.Trends Plant Sci 8：407-409

14 October 2015/Revised：17 December 2015/Accepted：25 January 2016/Published online：23 March 2016ⒸScience Press，Institute of Geochemistry，CAS and Springer-Verlag Berlin Heidelberg 2016