ABSTRACT
Forest type and stand age are important biological factors affecting soil enzyme activities. However, the changes in soil enzyme activities across stand ages and underlying mechanisms under the two forest restoration strate-gies of plantations and natural secondary forests remain elusive. In this study, we investigated the variations of four soil enzyme activities including cello-biohydrolase (CBH), ß-1,4-glucosidase (ßG), acid phosphatase (AP) and ß-1,4-N-acetylglucosaminidase (NAG), which were closely associated with soil carbon, nitrogen, and phosphorus cycling, across Cunninghamia lanceolata plantations and natural secondary forests (5, 8, 21, 27 and 40 years old). The results showed that soil enzyme activities showed different patterns across different forest types. The acti-vities of AP, ßG and CBH in the C. lanceolata plantations were significantly higher than those in the natural secon-dary forests, and there was no significant difference in the NAG activity. In the plantations, AP activity showed a decreasing tendency with the increasing stand ages, with the AP activity in the 5-year-old plantations significantly higher than other stand ages by more than 62.3%. The activities of NAG and CBH decreased first and then increased, and ßG enzyme activity fluctuated with the increasing stand age. In the natural secondary forests, NAG enzyme activity fluctuated with the increasing stand age, with that in the 8-year-old and 27-year-old stand ages being significantly higher than the other stand ages by more than 14.9%. ßG and CBH enzyme activities increased first and then decreased, and no significant difference was observed in the AP activity. Results of the stepwise regression analyses showed that soil predictors explained more than 34% of the variation in the best-fitting models predicting soil enzyme activities in the C. lanceolata plantations and natural secondary forests. In conclusion, there would be a risk of soil fertility degradation C. lanceolata plantations with the increasing stand age, while natural secondary forests were more conducive to maintaining soil fertility.
Subject(s)
Cunninghamia , Humans , Adult , Child, Preschool , Child , Soil , Forests , Nitrogen/analysis , Phosphorus/analysis , Carbon/analysis , Soil Microbiology , ChinaABSTRACT
Soil respiration is a key process in forest biogeochemical cycling. Exploring the relationship between plant functional traits and soil respiration can help understand the effects of tree species conversion on soil carbon cycling. In this study, we selected 15 common subtropical tree species planted in the logging site of second-generation Chinese fir forest to measure soil CO2 emission fluxes, soil physicochemical properties, leaf and root functional traits of each species, and explored the effects of plant functional traits on soil respiration. The results showed that the annual flux of soil CO2 emissions varied from 7.93 to 22.52 Mg CO2·hm-2, with the highest value under Castanopsis carlesii (22.52 Mg CO2·hm-2) and the lowest value under Taxus wallichiana (7.93 Mg CO2·hm-2). Results of stepwise regression analysis showed that the annual flux of soil CO2 emission decreased with the increases of leaf nitrogen content and fine root diameter, and increased with increasing leaf non-structural carbohydrate. In the structural equation model, leaf non-structural carbohydrate had a direct and significant positive effect on soil CO2 emission fluxes, while leaf nitrogen content and fine root diameter had a direct negative effect by decreasing soil pH and soluble organic nitrogen content. Plantations of different tree species would affect soil CO2 emission directly by changing functional traits related to water and nutrient acquisition or indirectly through soil properties. When creating plantations, we should select tree species based on the relationship between plant functional traits and ecosystem functions, with a view to improving forest productivity and soil carbon sequestration potential.
Subject(s)
Ecosystem , Soil , Soil/chemistry , Carbon Dioxide/analysis , Forests , Trees , Nitrogen/analysis , CarbohydratesABSTRACT
We investigated soil C:N:P stoichiometry and nutrient dynamics of Cunninghamia lanceolata plantations at different stand ages (5, 8, 21, 27 and 40 years old) in Fujian Baisha Fores-try Farm. We measured the concentrations of soil total carbon (TC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), total calcium (Ca), total magnesium (Mg), and soil C:N:P stoichiometry at 0-10, 10-20, and 20-40 cm soil layers during different growth stages. The results showed that soil TC and TN concentrations and C:N remained unchanged during stand development. Soil TP content showed an increase-decrease-increase trend with increasing stand ages. Soil TP content was lowest, whereas C:P and N:P were highest at the mature stage of C. lanceolate plantation in the 0-10 and 10-20 cm soil layers. However, soil TP content showed no significant differences in all stand ages at the 20-40 cm soil layer. The contents of Ca and Mg were lowest at the mature stage of C. lanceolata stand. The TC was positively correlated with soil C:N, C:P and N:P. The TP was significantly and negatively correlated with soil C:P and N:P. Soil TP was a key factor regulating soil C:P and N:P stoichiometry. The development of mature plantation was mainly limited by soil P availability. To sustain the development of C. lanceolata plantations and improve nutrient cycling, phosphorus fertilizer could be applied during the rapid growth period of C. lanceolata. In addition, an appropriate extension of the rotation period of C. lanceolata plantation could facilitate soil nutrient restoration.
Subject(s)
Cunninghamia , Nitrogen/analysis , Nutrients , Phosphorus , SoilABSTRACT
Investigating the response of soil microbial biomass and ecological stoichiometry to tree species transition is of great significance for understanding soil nutrient cycling and availability in forest ecosystems. We measured soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP) and their stoichiometry across 0-40 cm soil depth between Mytilaria laosensis and Cunninghamia lanceolata plantations by the chloroform fumigation extraction method, which were replanted after the harvest of C. lanceolata plantation. The results showed that soil MBC in the 0-10 cm layer and soil MBN and MBP in the 0-20 cm layer under the M. laosensis were significantly higher than those under the C. lanceolata. The MBC/MBP in the 0-20 cm layer and MBN/MBP in the 10-20 cm layer were significantly lower under the M. laosensis plantation. The MBC/MBN showed no significant differences between the two forests. Soil moisture, organic carbon, total nitrogen, total phosphorus, available phosphorus were positively correlated with MBC, MBN and MBP, but negatively correlated with MBC/MBP and MBN/MBP. Results of stepwise linear regression analysis showed that MBN and MBP were mainly affected by soil total nitrogen and available phosphorus, while MBC/MBP and MBN/MBP were mainly driven by available phosphorus and organic carbon, respectively. Our results indicated that tree species transition from C. lanceolata to M. laosensis could increase soil microbial biomass in the surface layers, accelerate soil nutrients turnover and enhance soil nutrient supply. The increases of MBP under M. laosensis indicate alleviation of soil phosphorus limitation for tree growth.
Subject(s)
Cunninghamia , Ecosystem , Soil , Soil Microbiology , TreesABSTRACT
Phosphorus (P) limitation is one of the major issues for the management of subtropical plantations. Understanding the effects of tree species transition from conifer to broadleaved trees on soil P fraction and availability in different soil layers are of great significance for the sustainable development of subtropical forests. We compared changes in soil chemical properties, P fraction and availability across 0-100 cm soil profile between Mytilaria laosensis and Cunninghamia lanceolata plantations, which were initially reforested from C. lanceolata plantation in the spring of 1993. The results showed that soil organic P content in both plantations decreased significantly with soil depth. Compared with C. lanceolata, the M. laosensis plantation significantly increased soil available P content by 35.7% and 86.2% in the 0-10 and 10-20 cm, respectively. The contents of soil labile P and moderately labile P decreased significantly with soil depth in both plantations. The contents of labile P and moderately labile P were significantly higher in the surface soil (0-20 cm), while the non-labile P in the 80-100 cm was increased by 13.6%, and the free iron content in the 20-80 cm significantly decreased. Results of redundancy analysis showed that dissolved organic carbon and free iron were the most important factors influencing P fraction in those plantations. Tree species transition from C. lanceolata to M. laosensis could change the pattern of soil P fraction in soil profile, and greatly enhance soil P availability.
