Biomass And Nutrient Cycling Of Rocky Dersertification Shrubs In Southwestern Hunan

Vegetation restoration in southwest Hunan has received widespread attention. This research was conducted at light (LRD), moderate (MRD, abandoned land) and intense (IRD) rocky desertification shrub ecosystems in Shaoyang, Hunan province. We have collected plant and soil (at 3 layers,0-15,15-30,30-45 cm) samples. The harvest method was used for acquire the shrub biomass data and laboratory analysis for soil physical and chemical properties, plant nutrients. We compared the distribution patterns of biomass, soil and plant nutrients and biological cycling characteristics among three shrub ecosystems. Exploring a realization approach to build a high qualified ecosystem which containing the vegetation, soil and bedrock. Our results provide the basic data for material circulation and energy flow in rocky desertification ecosystem research. The result provided scientific therories and technical supports for vegetation restoration and sustainable development in karst rocky desertification areas. Our main results as follows:(1) The biomass of shrub ecosystems:①The average biomass distribution for different organs in shrub layers was root> stem> leaf biomass; the average biomass distribution for different parts in herb layers was:aboveground> underground biomass. For a same plot, the biomass in different vegetation layers were significantly difference (p<0.05), and the ranking list was:shrub layer> herb layer> litter layer. ② The biomass distribution for different layers in shrub and litter layers was LRD> MRD> IRD while it was MRD> LRD> IRD in herb layers. The total biomass was decreased with the deterioration of rocky desertification.(2) The soil physical and chemical properties:① With the deterioration of rocky desertification, soil bulk density increased significantly while soil porosity and capillary moisture capacity decreased. The pH value indicated the weak acidity of the soil. Soil capillary moisture capacity decreased with soil depth in each plot.② The contents of soil organic carbon (SOC) and total N in different soil layers were various (p<0.05) and decreased with soil depth, while the contents of total P, K, Ca and Mg had no obvious variation among the different soil layers (p>0.05). The average contents of total N, P, Ca and Mg in soils were significantly different in 3 rocky desertification grades, and the SOC, total N and P in MRD were relatively higher than others.③ The rank of macroelement contents in soils for LRD and IRD was SOC> total K> total Ca> total Mg> total N> total P while it was SOC> total K> total Ca> total N> total Mg> total P for MRD. The rank of macroelement contents in plants for 3 rocky desertification grades was total Ca> total N> total K> total Mg> total P. The content of SOC was significantly correlated with the contents of total N, K and Mg in soils (p<0.05); the content of total N was significantly correlated with the contents of total Ca and Mg; the content of total Mg was significantly correlated with the contents of P and Ca. There were no significant correlations among other nutrient elements (p>0.05).(3) The contents and distributions in plants:①The rank of average content for layer average and each organ in shrub layers was C>Ca>N>K> Mg> P; while it was C>Ca>K>N> Mg> P for layer average and aboveground part and it was C> Ca> N> K> Mg> P for underground part in herb layers; the rank of average content in litter layers was C>Ca>N>K> Mg> P.②Compared the nutrient average contents in different vegetation layers, the rank of SOC was litter layers> shrub layers> herb layers, while those were shrub layers> herb layers> litter layers for N, P, Ca, Mg and herb layers> shrub layers> litter layers for K, respectively.(4) The relationship between soil and plant nutrient:The content of total K in plants was significantly correlated with the corresponding contents in soils for shrub layers, and the contents of total N and Ca in herb layers were significantly correlated with the corresponding contents of N and Ca in soils, while the contents of total N, P, K and Mg in litter layers were significantly correlated with the corresponding contents in soils. Soil nutrients were closely related to vegetation growth.(5) Nutrient cycling in shrub ecosystems: ①Among three rocky desertifivation plots, the rank of nutrient accumulation was Ca> N> K> Mg> P. The rank of nutrient accumulation for different vegetation layers was shrub layers> herb layers> litter layers. The rank of nutrient annual retention and nutrient annual returns was Ca> N> K> Mg> P. The rank of nutrient annual uptake and nutrient annual returns in different plots was MRD> LRD> IRD.② The rank of nutrient utilization coefficient for Karst shrubs in southwest Hunan was MRD (0.723)> IRD (0.681)> LRD (0.619). The rank of utilization coefficient for different elements in LRD was K> Mg> N> P> Ca, while it was K> N> Mg> P> Ca in MRD and IRD, the utilization coefficient for Ca was the lowest. The rank of nutrient turnover period for different plots was LRD (3.430a)> IRD (3.052a)> MRD (2.763a), and K was the most fast in nutrient turnover for LRD and MRD, while N was the most fast in nutrient turnover for IRD, and Ca was the lowest in nutrient turnover for each plot.