| Drought stress is the most serious constraint on plant growth and production,which severely limits the primary productivity of plants,mainly manifesting in the effects of water absorption,growth morphology,biomass accumulation,and stoichiometric cycling.Karst ecosystem is a very special ecological landform on the earth where drought occurs frequently,leading that water has become the most important factor limiting plant growth here.Coupled with the long-term unreasonable human interference in social and economic activities,a series of rocky desertification phenomena have occurred in the karst landforms of Southwest China.Vegetation restoration is the fundamental way to repair the stability of karst ecosystems and solve environmental problems.Screening plant species suitable for karst areas for drought resistance technology research is the key and prerequisite for vegetation restoration in karst ecosystems.In this study,a pot experiment and a field experiment were conducted meanwhile to investigate the dynamical effects of individual inoculation and co-inoculation of different arbuscular mycorrhizal fungi（AMF）,F.mosseae and C.etunicatum on the growth,water status,photosynthesis,drought resistance and soil microecology of Cinnamomum migao H.W.Li（C.migao）seedlings.The mechanism of AMF promoting the growth and drought resistance of C.migao seedlings under drought stress was discussed.The main results are as follows:1.Effects of AMF on the water physiology of C.migao seedlings under different water conditionsIn the pot experiment,the RWC of AMF seedlings was almost 90%,which was significantly higher than that of CK treatment（72%）.In terms of water potential,in the SS stage,drought stress significantly reduced the water potential,with CK treatment decreasing the most（114.62%）and C.etunicatum treatment decreasing the least（32.56%）.In the REC stage,the water potential of all treatments recovered,and the AMF plants recovered faster than CK.In the PS stage,the WUE of C.etunicatum plants were significantly higher than other treatments.In the SS stage,drought stress decreased the WUE of CK treatment significantly.Otherwise,AMF inoculation increased the WUE under drought stress.The WUE of C.etunicatum plants was still the highest（123.70%）among all treatments.The results of each treatment on the water physiology of C.migao seedlings in field experiment was almost consistent with that in pot experiment,only some differences in the degree of influence.2.Effects of AMF on the growth and photosynthesis of C.migao seedlings under different water conditionsIn pot experiment,AMF significantly increased plant height,stem diameter and leaf area of C.migao seedlings.The plant height of C.etunicatum,F.mosseae and Mixed was higher than that of CK by 94.08%,71.42%and 55.73%,respectively.The stem diameter was also obviously higher than CK at 60.95%,48.08%and 28.55%,respectively.Compared with the CK treatment,the leaf area of C.etunicatum,F.mosseae and Mixed plants was increased by 27.83%,9.14%and 24.23%,respectively.AMF also had a significant effect on root length,root surface area and root mean diameter of C.migao seedlings during the experimental period.The root length of C.etunicatum,F.mosseae and Mixed was 339.97%,96.84%and 56.70%higher than that of CK,respectively.The root surface area of C.etunicatum,F.mosseae and Mixed was higher by 527.04%,148.41%and 77.01%than that of CK,respectively.The root mean diameter of C.etunicatum,F.mosseae and Mixed was higher by 171.54%,23.08%and1.54%than that of CK,respectively.The effects of C.etunicatum on growth were most.In the PS stage,AMF inoculation significantly increased the net photosynthetic rate（Pn）of C.migao seedlings.Which increased most in C.etunicatum plants by61.43%.In the SS stage,drought stress significantly declined the Pn,CK decreased most by 71.97%.During the experimental stage,the Tr of AMF plants was significantly higher than that of CK treatment.In the PS stage,there was no obvious difference between all AMF seedlings,F.mosseae was the highest（4.95）,significantly higher than CK by 60.71%.In the SS stage,the Tr of each treatment under drought stress was significantly lower than that under well-watered,and the CK treatment was decreased by 67.63%.And the Tr of C.etunicatum,F.mosseae and Mixed was higher than CK by83.21%,82.85%and 90.51%,respectively,indicating that the effect of drought stress on Tr of CK plants was significantly greater than that of AMF plants.AMF significantly increased the stomatal conductance（gs）of C.migao seedlings.The gs of C.etunicatum,F.mosseae and Mixed was higher than that of CK by 320.12%,252.36%and 260.25%under well-watered condition,respectively.Under drought stress condition,it was higher than CK by 80.02%,160.28%and 20.23%respectively.It shows that under well-watered condition,AMF has a more significant effect on gs of C.migao seedlings.AMF,especially C.etunicatum,reduced the intercellular CO2 concentration（Ci）of C.migao seedlings significantly.The effects of AMF on the growth and photosynthesis of C.migao seedlings under different water conditions in field experiment were basically same as those of pot experiment.3.Effects of AMF on the osmotic regulation,antioxidant capacity and endogenous hormones of C.migao seedlings under different water conditionsIn the pot experiment,the S-sugar content of C.etunicatum,F.mosseae and Mixed was higher than that of CK under well-watered condition by 125.71%,97.86%and66.43%respectively.And it was higher than CK by 210.84%,177.11%and 171.08%under drought stress condition,respectively.In terms of the S-starch content,only C.etunicatum was significantly higher than that of CK（46.97%）under well-watered condition,while under drought stress,C.etunicatum,F.mosseae and Mixed was higher than CK by 72.56%,35.68%and 27.10%,respectively.Similarly,AMF increased the SP content of C.migao seedlings,with the strongest increase in C.etunicatum significantly.The effects of AMF on the osmotic regulation of C.migao seedlings under different water conditions of field experiments were basically same as those of pot experiment.In both two experiments,AMF had no significant effect on the Pro content of C.migao seedlings under well-watered.Drought stress significantly increased the Pro content of each treatment.The Pro content of AMF plants were significantly lower than that of CK（35%～44%）,showing that AMF can offset parts of the accumulation of Pro caused by drought stress.Under both water conditions,AMF significantly reduced the content of MDA（20.95%～61.4%）,and decreased more obviously under well-watered than that under drought stress,indicating that AMF can protect the cell membrane of C.migao seedlings from damage whether the seedlings are under drought or well-watered.Improving the antioxidant enzyme activity is also a major mechanism for AMF to improve the drought resistance of host plants.In both two experiments,AMF had no effect on SOD activity of C.migao seedlings under well-watered condition.Under drought stress,AMF increased the SOD activity of seedlings（20.18%～68.67%）,and C.etunicatum increased most.Under both water conditions,AMF significantly increased the POD and CAT activities of C.migao seedlings.In the pot experiment,the POD and CAT activity of C.etunicatum was significantly higher than CK by 84.18%and 99.59%,respectively.In the field experiment,the POD activity of F.mosseae was the highest,which was higher than CK by 80.72%,and the CAT activity of C.etunicatum was the highest,which was higher than CK by 83.16%,indicating that AMF,especially C.etunicatum,could protect the host plants and promote the growth regardless of whether the plants grow under well-watered or stress.AMF can also help C.migao seedlings to resist and adapt to drought by regulating the endogenous hormones concentration.In both two experiments,AMF had no significant effect on SA and JA contents of C.migao seedlings under well-watered condition.When drought stress induced SA and JA accumulation in C.migao seedlings,AMF could reduce the accumulation of SA（17.76%～20%）and JA（14.27%～22%）in C.migao seedlings,offsetting some of the damage caused by drought.Under both two water conditions,AMF significantly reduced the ABA content of C.migao seedlings.It can be seen that AMF regulates plant growth under drought and improves its drought resistance in many ways.4.Effects of AMF on C,N and P concentration in C.migao seedlings and soil under different water conditionsIn the pot experiment,AMF had a significant effect on the contents of SOM,total nitrogen（TN）and total phosphorus（TP）in C.migao seedlings during the whole experiment,and drought stress also had significant effects on SOM and TN in leaves and roots of C.migao seedlings.Under the two water conditions,AMF significantly increased the SOM and TN contents in leaves and roots of C.etunicatum seedlings and the TP contents in leaves,stems and roots of C.etunicatum seedlings.AMF surprisingly increased C:N in the leaves of C.migao seedlings but decreased C:N in stems and roots.AMF significantly reduced C:P and N:P in various organs of C.migao seedlings.AMF surprisingly increased soil SOM and TN contents in root compartment（RC）and hyphal compartment（HC）,but had no significant effect on soil TP content in RC.Significantly reduced soil TP content in HC.AMF except for C.etunicatum,reduced the soil C:N in RC and HC.But AMF surprisingly increased soil C:P and N:P in RC and HC.In the field experiment,AMF significantly increased SOM content in leaves and roots of C.migao seedlings,but decreased SOM content in stems.AMF especially C.etunicatum surprisingly increased the content of TN and TP in C.migao seedlings,but reduced the C:N,C:P and N:P of C.migao seedlings.AMF significantly increased soil SOM and TN content,had no significant effect on TP content.In SS and REC stages,C.etunicatum reduced soil C:N obviously.AMF surprisingly increased soil C:P but had little effect on soil N:P.It can be seen that in the two experiments,the effects of AMF on the nutrient of C.migao seedlings and soil were basically same.5.Effects of AMF on soil enzyme activities under different water conditionsIn the pot experiment,AMF had a significant positive effect on soil catalase activity（S-CAT）in RC and HC under both water conditions.C.etunicatum increased highest,which was higher than CK by 89.37%and 99.58%,respectively.AMF also had a positive effect on soil urease activity（S-UE）in RC and HC.Under well-watered condition,the S-UE activity of C.etunicatum and F.mosseae were both decidedly higher than that of CK.Under drought stress,only the S-UE activity of C.etunicatum was obviously higher than that of CK.In the HC,there was no significant difference in soil S-UE activity under well-watered condition.Under drought stress,the soil S-UE activity of C.etunicatum was surprisingly higher than that of CK.Under well-watered condition,the soil S-ACP activity of C.etunicatum was strongest in RC,but there was no difference in the soil S-ACP activity among all treatments under drought stress.Under both two water conditions,only C.etunicatum significantly increased the soil S-ACP activity in HC.On the whole,C.etunicatum had a more significant effect on soil S-ACP activity regardless of water conditions.The S-SC activity of C.etunicatum and F.mosseae treatments were absolutely higher than that of CK under well-watered condition,under drought stress,only C.etunicatum increased markedly soil S-SC activity than CK,indicating that C.etunicatum could significantly increase soil S-SC activity regardless of water conditions.The changes of soil total glomalin（T-GRSP）content and easily extractable glomalin（EE-GRSP）content in RC and HC were almost consistent.Under two water conditions,the contents of soil T-GRSP and EE-GRSP of AMF in RC and HC both were noteworthy higher than those of CK,and the content of C.etunicatum was the highest.The effects of AMF on soil enzyme activities under different water conditions of field experiments were basically same as those of pot experiment.6.Effects of AMF on rhizosphere microorganisms under different water conditionsIn the pot experiment,AMF significantly increased the bacterial community composition in the roots of C.migao seedlings under both water conditions,and recruited the species and proportion of rhizosphere bacteria in RC and HC.C.etunicatum had the most obvious effect on bacterial community composition and abundance.AMF significantly increased the community composition and abundance of fungi in the roots,rhizosphere of C.migao seedlings in RC and HC.The effects of AMF status were markedly different,and the effect of C.etunicatum treatment on fungal community composition and abundance was the most.Overall,the effect of AMF on fungi is far more obvious than that of bacteria.In conclusion,drought stress significantly inhibited the growth of C.migao seedlings by limiting the physiological and biochemical processes of water physiology,photosynthetic physiology and nutrient absorption.Otherwise,Arbuscular mycorrhiza fungi promoted the growth and biomass accumulation of C.migao seedlings and the resistance to drought significantly by increasing the water content,nutrient absorption and photosynthesis of C.migao seedlings,enhancing the antioxidant enzyme activity and the accumulation of osmotic adjustment substances,and improving the physical and chemical properties and enzyme activity of soil microecology and the composition of microbial community.Among all treatments,C.etunicatum inoculation treatment had the best effect,and which would be selected for large-scale breeding and afforestation in the later stage. |
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