Plant Functional Groups Structure And Nutrient Characteristics In The Process Of Vegetation Restoration In The Karst Plateau Rocky Desertification

Karst rocky desertification is the most serious ecological and environmental problem in the Southwest China,which severely restricts economic and social development,vegetation restoration and reconstruction is the fundamental way to solve this problem.In this study,the different natural restoration stages of degraded vegetation?grasslands stand phase,grass-shrubs stand phase,shrubs stand phase,tree-shrubs stand phase,tree stand phase?in the karst plateau rocky desertification area was selected as the research object.Taking plant functional groups structure and nutrient characteristics as research clues,the communities of different restoration phase were identified on the plant functional groups structure,C,N,P contents,C/N,C/P,N/P ratio,C,N,P storage,NUEN,NUEP,REN and REP.The aims of present study are to reveal the replacement laws of plant functional groups and the nutrient allocation strategies during the process of vegetation restoration,to deepen the understanding of the vegetation restoration process and provide a theoretical basis for plant configuration technology in karst rocky desertification area.The result obtained as the follows:?1?Dividing plant functional groups according to life forms?Herbal,Nanophaenerophyte,Microphaenerophyte,Mesophaenerophyte?,growth form?Grass,Shrub,Tree,Vine?,leaf habit?Evergreen plants,Deciduous plants?and adaptation level species?Pioneer species,Sub-pioneer species,Transitional species,Sub-climax species,Climax species?.Deciduous plants dominate throughout the whole restoration phase?54%?70%?.In the grasslands stand phase,Herbal?57%?,Grass?50%?and Pioneer species?90%?had an absolute advantage,Nanophaenerophyte and Microphaenerophyte?43%?,Shrub?42%?,Sub-pioneer species?10%?also had a certainly proportion,no Mesophaenerophyte,Tree,Transitional species,Sub-climax species,Climax species,namely,its a Grass and Pioneer species community?referred to as G-PS?;in the grass-shrubs stand phase,the proportion of Herbal?34%?,Grass?33%?,Pioneer species?64%?decreased,while Nanophaenerophyte and Microphaenerophyte?58%?,Shrub?51%?,Sub-pioneer species?21%?increased,and there were Mesophaenerophyte?8%?,Tree?7%?,Transitional species and above?15%?first time,namely,its a Grass,Shrub and Pioneer species community?referred to as G-S-PS?;in the shrubs stand phase,the proportion of Microphaenerophyte?27%?and Sub-pioneer species?36%?further increased,implied that was a Shrub-Grass layer,Microphaenerophyte and Sub-pioneer species community?referred to as Ph?Mi?-SPS?;in the tree-shrubs stand phase,the proportion of Microphaenerophyte?26%?,Grass?25%?,Shrub?35%?,Pioneer species?38%?declined,Mesophaenerophyte?17%?,Tree?21%?,Transitional species and above?36%?increased,which suggested that its a Tree-Shrub-Gress layer,Mesophaenerophyte and Transitional species community?referred to as Ph?Me?-SPS?;in the tree stand phase,the number of Mesophaenerophyte,Tree,Sub-climax species and Climax species increased further,forming a Tree-Shrub-Grass three layers,Mesophaenerophyte and Sub-climax species community?referred to as Ph?Me?-SCS?.The replacement of plant functional groups at different vegetation restoration phase made the community finally formed a stable vertical structure.?2?Leaf C(446.34?476.41g.kg^-1),N(10.10?17.65g.kg^-1),P(0.97?1.73g.kg^-1),C/N?27.20?48.45?,and C/P?287.62?487.66?basically increased with the progress of restoration,the mount of existing litters?1.32?13.22t.hm-2?,litter N?10.75?17.82g.kg-1?,P?0.57?0.80g.kg-1?,C/N?22.23?38.58?,C/P?520.39?745.80?,soil C(77.13?108.68g.kg^-1),N(2.86?8.71g.kg^-1),P(0.95?1.16g.kg^-1),N/P?2.63?7.45?showed a consistent change trend with the restoration phase,which were presented a trend of increasing first and then decreasing,soil C/N?10.95?42.56?and C/P?49.46?92.37?were rather higher in the late restoration phase.The N/P values?10.39-12.75?of different restoration phase were less than 14,which demonstrated the growth of plant in Karst Plateau rocky desertification regions mainly limited by N.These findings showed that,in the G-PS and G-S-PS communities phase,plant communities had lower plant growth rate,litter decomposition rate and higher soil available nutrient levels,in the Ph?Mi?-SPS and Ph?Me?-TS communities phase,plant communities had medium plant growth rate,higher litter decomposition rate and soil organic matter mineralization rate,in Ph?Me?-SCS communities phase,plant communities had higher plant growth rate,medium litter decomposition rate and lower soil available nutrient levels.Above results reflected that the distribution of C,N,P contents and C/N,C/P,N/P ratio in the vegetation-litter-soil continuum of communities at different restoration phase.?3?Compared with non-karst areas,leaf C and N contents of the Karst Plateau rocky desertification area is medium,while P and N/P is lower,suggested vegetation growth here is mainly restricted by N,the contents of litter C and P is lower,while N is higher,a lower litter C/N value means that litter here decomposed very quickly,the C,N,P contents of soil top 0-10cm layer are roughly higher,soil C/N is higher while C/P and N/P are lower,indicated that P regression is sufficient in the soil and N regression in insufficient,present as N-restricted type.?4?The biomass of community vegetation at different restoration phase was 9.95?132.32t.hm^-2,the vegetation-litter-soil?0-10cm?continuum C storage in turn were 3.86?65.13t.hm^-2,0.55?4.82t.hm^-2,25.18?45.93t.hm^-2,N storage were 0.09?0.83t.hm-2,0.02?0.21t.hm^-2,1.51?2.54t.hm^-2,and P storage were 9.13?84.75kg.hm^-2,0.88?9.31kg.hm^-2,379.88-609.21kg.hm^-2,the C,N,and P storage were ranked as soil layer>vegetation layer>litter layer.As the restoration progressed,the proportion of nutrient storage increased gradually?12%?55%?in vegetation,increased first and then decreased?2%?8%?4%?in litters,and decreased gradually?86%?40%?in top 0-10cm layer soil.From the perspective of storage oranges,in the G-PS and G-S-PS communities phase,C,N,and P nutrients were mainly stored in leaves?52%?68%?,in the Ph?Mi?-SPS and Ph?Me?-TS communities phase,they were mainly stored in branches?51%?75%?,in the Ph?Me?-SCS communities phase,C was mainly stored in stem?54%?,the storage amounts of N,P in leaves,branches,stems,and roots were not presented significant difference?21%?28%?.Above results reflected the distribution of total nutrients in the vegetation-litter-soil continuum and organs of communities at different restoration phase.?5?NUEN was in the order of Ph?Me?-SCS community?96.60g.g-1?>Ph?Mi?-SPS community?95.51g.g-1?>Ph?Me?-TS community?69.79g.g-1?,while NUEP was Ph?Mi?-SPS community(1208.97g.g^-1)>Ph?Me?-SCS community(1072.12g.g^-1)>Ph?Me?-TS community(1000.95g.g^-1).REN followed the order of Ph?Me?-SCS community?38.03%?>Ph?Mi?-SPS community?19.64%?>Ph?Me?-TS community?9.69%?,whlie REP was Ph?Me?-SCS community?43.72%?>Ph?Me?-TS community?39.22%?>Ph?Mi?-SPS community?36.75%?,and REP>REN,which indicated that N-restricted communities do not necessarily have high REN.NUEN and NUEP showed significant positive correlation with N and P?P<0.05?,respectively.REN and REP were significantly negatively related to soil N content?P<0.05?,but not significantly related to soil P content?P<0.05?,which showed that the REN and REP in the Karst plateau rocky desertification areas may depend on changes in soil N contents.?6?The nutrient utilization conefficients in the different restoration phase changed in the order of Ph?Mi?-SPS?0.58?>Ph?Mi?-TS?0.46?>Ph?Me?-SCS?0.44?,while the order was the reverse for the cycling coefficients.The recycling periods changed in the order Ph?Me?-SCS?24.51?>Ph?Mi?-SPS?13.52?>>Ph?Mi?-TS?12.90?.These results revealed that the nutrient storage rate decreased,the nutrient cycle accelerated with the restoration of vagetation,and the cycling periods took longest time in the Ph?Me?-SCS phase community.