| Moso bamboo(Phyllostachys heterocycla(Carr.)Mitford cv.Pubescens)is a typical asexual reproduction plant,characterized by fast growth and strong sustainability.It is the most widely distributed and planted bamboo species in China with high economic and ecological benefits.In order to pursue higher resource revenues,the area of bamboo forests continues to expand in some areas and the management is enhanced.By the rapid propagation of rhizome,Moso bamboo forests can extend to the broadleaf forests,coniferous forests,and even abandoned agricultural lands,which is one of the main ways for the increase in Moso bamboo forest area.The expansion of Moso bamboo forests improves the resource supply capacity,but also causes a decrease in biodiversity and a series of other negative impacts.Revealing the interaction of vegetation and soil during the expansion is an effectively theoretical foundation of scientific and reasonable controlling the expansion of Moso bamboo forests.In this paper,the horizontal and continuous expansion interface of Moso bamboo forests to broadleaf forests,Chinese fir forests,and wastelands were selected as research objects,and observation sample areas of three expansion interfaces: bamboo –broadleaf,bamboo-coniferous,and bamboo-wasteland were set.Each sample area was divided into 3-4 quadrats,including pure Moso bamboo forests,mixed bamboo-broadleaf forests,broadleaf forests,conifer forests and wastelands,which covered the different states of Moso bamboo expansion.Through the research on evolution of characteristics and the interaction between aboveground(communities,leaves)and belowground(root,soil)in different stages of expansion,growing adaption strategies of Moso bamboo during its expansion was revealed,which provided a theoretical basis for effectively controlling the Moso bamboo expansion to surrounding forests in a sustainable health management.The main conclusions were as follows:1.The expansion of Moso bamboo forests to Chinese fir forests was the most adaptable.Along with the expansion,diameter at breast height(DBH)and biomass showed an increasingtrend,and litter N:P was more suitable to Moso bamboo growth.With the extending of Moso bamboo to broadleaf forests and wastelands,the competition among different species increased that Moso bamboo adapted to the new growth environment.DBH and biomass first decreased and litter N:P gradually shifted the mean N:P of Moso bamboo in China.With the adaptability increasing,DBH and biomass increase.With the expansion of Moso bamboo to Chinese fir forests,mean DBH and productivity in expansion interface to broadleaf forests increased by4.3% and 14.1%,and 13.8% and 21.3% in expansion interface to Chinese fir forests.During expansion to broadleaf and coniferous forests,its leaf area index increased significantly along with the expansion of Moso bamboo.Compared to pure Moso bamboo forest,leaf area index in expansion interface to pure broadleaf forest increased by 21.1%,and 47.9% for pure Chinese fir forests.While leaf area index decreased by 2.3% in expansion of Moso bamboo forests to wastelands.2.During the expansion of Moso bamboo forests to broadleaf forests,Chinese fir forests and wastelands,the adaptability of leaf characteristics and leaf nutrient content occurred.Specific leaf area of Moso bamboo forest showed a decreasing trend with the expansion of Moso bamboo forests to Chinese fir forests,ranging from 2.56-2.13.Leaf N:P were 16.49,17.61,16.63 and 18.82,respectively,and P limitation was decreased,which was good for the growth of Moso bamboo forests.Specific leaf area first decreased and then increased with 2.36,2.17,2.20 and 2.42 for the expansion of Moso bamboo forests to broadleaf forests.N:P were17.47,17.80,17.62 and 16.55,respectively.N:P of pure Moso bamboo forests and mixed Moso bamboo and broadleaf forests were lower than those of pure broadleaf forests,which was obviously limited by N.Specific leaf area first increased and decreased for the expansion of Moso bamboo forests to wastelands with the values of 1.70,2.30 and 2.02,respectively.Specific leaf area of the interface of Moso bamboo forests and wasteland was highest.N:P were 16.45,12.93 and 13.91,which was obviously limited by N element.3.During the expansions,Moso bamboo forests adjusted the spatial distribution of fine roots,the distribution of different diameters of fine roots,root length density,fine root nutrients and stoichiometric ratios to adapt the competitive environment.(1)Fine roots of Moso bamboo was mainly distributed in the 0-20 cm soil layer.Biomass of 0-1mm fine roots was significantly higher than that of 1-2mm fine roots with higher variability.This distribution of fine roots was good for the expansion of Moso bamboo forests for the better competitive advantages.In horizontal expansion direction,fine root biomass decreases with the expansion of Moso bamboo forests while root length density gradually increased,which reflected that Moso bamboo Moso enhanced its competitiveness by absorbing more nutrients and water with minimal roots in the expansion process.Compared to pure Moso bamboo forests,in 0-10 soil layer,diameter 0-1mm fine root biomass decreased by 27.32% and root length density increased to 60.01% in bamboo-broadleaf interface.Fine root biomass decreased by 43.34% and root length density increased by 19.58% in bamboo-fir interface,compared to 57.84% and 6.23% in bamboo-wasteland interface.After analyzing trends of nutrients,such as C,N,P,K and fine root distribution patterns of all expansion interfaces,results suggested that in each interface Moso bamboo could build up a high nutrient content in internal environment to adapt to external competition,showing better adaptability.(2)Moso bamboo forests adjusted the nutrient contents and stoichiometric ratios to adapt new competitive environments.In the bamboo-broadleaf surface,the stoichiometric ratios of main nutrients of fine roots showed an increasing trend with its expansion.N:P were 19.04,21.03,21.50,21.00,indicting in the expansion of Moso bamboo forests to broadleaf forests,the competition of N and P between Moso bamboo to broadleaf trees increased,especially for P.For the expansion of Moso bamboo forests to Chinese fir forests,C contents decreased and N showed an increasing trend,while P content first decreased and increased.C:P and C:P showed a decreasing trend,and N:P showed a decreasing trend with 16.86,18.97,17.81 and 20.67.This indicated a sufficient soil N and P supply,and N supply was more sufficient than P after the expansion of Moso bamboo forests to Chinese fir forests.The competition between Moso bamboo forests and Chinese fir forests was relatively weak,promoting the growth of Moso bamboo forests.Fine root C content showed a decline trend and N decreased first and then increased,while P contents showed an increased trend,compared to the decrease trend for C:N,C:P and N:P.N:P were 17.270,12.504 and 8.267.This indicated that the decreasing in Ccontent of fine roots was good for Moso bamboo growth when the expansion of Moso bamboo forest to wasteland.P content was higher,but obviously limited by N.4.The expansion of Moso bamboo forests increased the variability of soil nutrients.Soil organic matter content increased by 7.57% in bamboo-broadleaf interface than pure Moso bamboo forests,but still lower than pure broadleaf forest.Soil organic matter content increased by 9.58% and 13.08% in bamboo-fir interface compared to pure Moso bamboo forests and pure Chinese fir forests.Meanwhile,total N,P,and K contents in both bamboo-broadleaf and bamboo-Chinese fir interfaces were on the rise with different change patterns.This may be related to different nutrients from different species composition of litter,and may be also related different needs of nutrients of different vegetation.The expansion of Moso bamboo to wasteland led to a decrease in soil organic matter,total N and hydrolysis N,but total P and effective P content increases gradually.5.The soil-vegetation contained complex internal response and adaptation mechanisms.The expansion of Moso bamboo was a result of the comprehensive effects of leaf,fine root and litter and soil nutrients and other factors,as well as the comprehensive effects of vegetation composition,fine root,leaf and litter return.This led strong adaptive functional traits of Moso bamboo forests in a dominant position in the expansion process.Among the three expansions,there were strong relationships between leaf,fine root,litter and soil available nutrients and their stoichiometric ratios.Leaf N contents and fine root K contents was positively related in bamboo-broadleaf and bamboo-wasteland surfaces.In bamboo-broadleaf interface,C content of litter and soil p H value was significantly negatively correlated.Litter N was significantly positively related to soil hydrolysis N and available K in in bamboo-Chinese fir interface.In bamboo-broadleaf and bamboo-fir interfaces N content of fine root and soil p H value and soil hydrolysis N were significantly positively correlated.Above all,during expansion to broadleaf,Chinese fir forest and wasteland,the community structure,leaf and fine root traits of Moso bamboo forests made adaptive adjustments to enhance the competitiveness of growth in new environment.Compared to other expansions,the expansion of Moso bamboo forests to Chinese fir forests was the best.Meanwhile,the expansion of Moso bamboo forests increased the soil nutrients variability,which could promote the further expansion of Moso bamboo forests. |
