Soil C, N and P stoichiometry in different forest stand types in the middle and lower reaches of the Beijiang River, China

We examined the vertical distribution characteristics of soil organic carbon (C), total nitrogen (N), total phosphorus (P) and their ecological stoichiometric ratios in 0-80 cm soil profile under three forest stand types in the middle and lower reaches of the Beijiang River, including broad-leaved forest, coniferous forest, and mixed coniferous and broad-leaved forest. The results showed that soil C, N and P contents of the three forest stand types were 12.17-14.25, 1.14-1.31, and 0.27-0.30 g·kg^-1, respectively. The contents of C and N decreased with the increases of soil depth. The content of C and N in each soil layer showed that coniferous and broad-leaved mixed forest > coniferous forest > broad-leaved forest. There was no significant difference in P content among the three stand types, and there was no obvious variation in the vertical profile. The soil C/N, C/P, and N/P of the three forest types were 11.2-11.3, 49.0-60.3, and 4.5-5.7, respectively. There was no significant difference in soil C/N among the three stand types. The highest soil C/P and N/P were found in the mixed forest. There was no interaction between soil depth and stand type in affecting soil C, N, P contents and their stoichiometric ratios. There was significant positive correlation between C and N, and between N and C/P in each stand type and soil layer. Soil C/P and N/P had stronger ecological indicating effects on stand types. The coniferous and broad-leaved mixed forest was strongly limited by P availability.

[Hydrological functions of litters under five typical plantations in southern and northern mountains of Lanzhou City, Northwest China]

Combined with field observation and indoor water immersion test, water holding characteristics of litters from five typical plantations (Platycladus orientalis, Robinia pseudoacacia, Populus alba var. pyramidalis, P. orientalis+R. pseudoacacia, P. alba var. pyramidalis+R. pseudoacacia) in southern and northern mountains of Lanzhou City were examined. Results showed that litter mass under the plantations ranged from 13.50 to 47.01 t·hm^-2, with an order of P. alba var. pyramidalis+R. pseudoacacia＞P. orientalis+R. pseudoacacia＞P. orientalis＞R. pseudoacacia＞P. alba var. pyramidalis. The percentage of un-decomposed litters was greater than that of semi-decomposed litters in all plantations except for P. orientalis plantations. The maximum water-holding rate of litters ranged from 190.8% to 262.7%, with the greatest value in the P. alba var. pyramidalis+R. pseudoa-cacia and the lowest in P. orientalis plantations. The maximum water-holding capacity of litters was 35.29-123.59 t·hm^-2, with an order of P. alba var. pyramidalis+R. pseudoacacia＞P. orientalis+R. pseudoacacia＞R. pseudoacacia＞P. orientalis＞P. alba var. pyramidalis. Litter water absorption rate declined linearly within the first hour, and then decreased slowly. Semi-decomposed litters had a higher water-absorption rate than un-decomposed litters. The maximum water retaining amount and effective retaining amount of the litters were P. alba var. pyramidalis+R. pseudoacacia＞P. orientalis+R. pseudoacacia＞P. orientalis＞R. pseudoacacia＞P. alba var. pyramidalis. P. alba var. pyramidalis+R. pseudoacacia had the highest effective retaining rate. P. alba var. pyramidalis+R. pseudoacacia plantation had highest capacity for soil and water conservation in southern and northern mountains of Lanzhou City.

[Distribution of Organic Carbon in Soil Aggregates from Four Kinds of Forest Vegetation on Jinyun Mountain]

This study was intended to explore the distribution and stability of soil aggregates and the organic carbon for different forest types and to provide a scientific basis for the efficient management of soil carbon pools in subtropical forest ecosystems. Four subtropical forest types, including bamboo forest, broad-leaf forest, coniferous forest, and a mixed coniferous and broad-leaf forest on Jinyun Mountain (Chongqing Municipality), were selected as research subjects to explore the distribution of soil aggregates and organic carbon in different layers (depths of 0-20, 20-40, 40-60, and 60-100 cm). The results showed:The content of >2 mm aggregates and mean weight diameter (MWD), geometric mean diameter (GMD), and >0.25 mm aggregate content (R_0.25) in broad-leaf forests decreased with soil depth, while other forests did not have a similar distribution pattern. In each soil layer, bamboo forest soils were mainly composed of >2 mm fractions of aggregates, which made up 30.73%-53.08% of the total content; The content of 2-0.25 mm particle size aggregates of broad-leaf and mixed forest soils was higher than that for other sizes, and its content ranged from 36.27% to 44.67% and 48.69% to 52.44%, respectively. The 2-0.25 mm and <0.053 mm fractions of aggregates dominated conifer soils. In general, the MWD, GMD, and R_0.25 of bamboo aggregates were higher than for other stands in each soil layer, and the fractal dimension (D) was lower than for other stands. This indicated that the soil aggregates of bamboo forest have better stability. As the soil layer deepened, the organic carbon content of soil aggregates in forest types, except for coniferous forest, gradually decreased. Among them all, bamboo forest aggregates had the highest organic carbon content, and this was significantly higher than that of coniferous forest and mixed forest. In the whole soil profile, as far as different aggregate size is concerned, there was no obvious regularity about organic carbon in the four forest types soil aggregates; the organic carbon content of the 2-0.25 mm and <0.053 mm fractions of aggregates was high in every soil layer. There was a significant difference in the relative contribution of organic carbon in soil aggregates for different forest stands, among these contributions, the contribution rate of organic carbon in the <0.053 mm fraction of aggregates in the coniferous forest was the highest. The organic carbon contribution rate of the >2 mm fraction of bamboo forest aggregates was as high as 27.44%-53.47%. Broad-leaf forests and mixed forests had the highest contribution to the organic carbon of the 2-0.25 mm fractions of soil aggregates. Among the four forest types on Jinyun Mountain, the soil aggregates in bamboo forest have better stability, but the stability of aggregates in coniferous forests is poor. In each soil layer, the content of bamboo forest organic carbon in the various aggregates was the highest, and that of coniferous forest was the lowest.