[Variations of water use efficiency and foliar nutrient concentrations in Cunninghamia lanceolata plantations at different ages]. / ä¸åŒæž—é¾„æ‰æœ¨äººå·¥æž—çš„æ°´åˆ†åˆ©ç”¨æ•ˆçŽ‡ä¸Žå¶ç‰‡å »åˆ†æµ“åº¦.

We studied water use efficiency (WUEi), nitrogen (N) and phosphorus (P) status of leaves at different leaf ages (current year, 1-, 2-, and 3-year-old foliage) as well as their relationships in a subtropical chronosequence of Chinese fir (Cunninghamia lanceolata) forests (3-, 8-, 14-, 21- and 46-year-old). The results showed that foliar WUEi varied significantly with foliar age in the order of current year foliage > 1-year-old foliage > 2-year-old foliage > 3-year-old foliage, while stand age had no significant impact on foliar WUEi. Foliar N/P ranged from 11.4 to 19.6 and was higher in younger and older stands than in stands at the fast-growing stage. The foliar N and P concentrations tended to display similar trends with foliar ages in the order of current year foliage>1-year-old foliage>2-year-old foliage>3-year-old foliage. WUEi did not change significantly with stand ages, probably because the photosynthetic rates and stomatal conductance decreased simultaneously with stand age. There was no relationship between WUEi and foliar N. WUEi had significant positive correlation with foliar P and significant negative correlation with foliar N/P. It is indicated that foliar P concentration would be a key factor affecting WUEi with increasing atmospheric N deposition in subtropical forests.

[Effects of tree species transfer on soil dissolved organic matter pools in a reforested Chinese fir (Cunninghamia lanceolata) woodland].

Based on the comparison between reforested 19-year-old Mytilaria laosensis and Cunninghamia lanceolata plantations on cut-over land of C. lanceolata, effects of tree species transfer on soil dissolved organic matter were investigated. Cold water, hot water and 2 mol x L(-1) KCl solution were used to extract soil dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) from 0-5, 5-10 and 10-20 cm soil layers. In M. laosensis plantaion, the concentrations of soil DOC extracted by cold water, hot water and 2 mol L(-1) KCl solutions were significantly higher than that in C. lanceolata plantation. In the 0-5 and 5-10 cm layers, the concentrations of soil DON extracted by cold water and hot water in M. laosensis plantation were significantly higher than that in C. lanceolata plantation. The extracted efficiencies for DOC and DON were both in order of KCl solution > hot water > cold water. In the 0-5 cm layers, soil microbial biomass carbon (MBC) under M. laosensis was averagely 76.3% greater than under C. lanceolata. Correlation analysis showed that there were significant positive relationships between hot water extractable organic matter and soil MBC. Differences in the sizes of soil DOC and DON pools between the M. laosensis and C. lanceolata forests might be attributed to the quality and quantity of organic matter input. The transfer from C. lanceolata to M. laosensis could improve soil fertility in the plantation.

[Effects of broadleaf plantation and Chinese fir (Cunninghamia lanceolata) plantation on soil carbon and nitrogen pools].

A comparative study was conducted on the soil C and N pools in a 19-year-old broadleaf plantation and a Chinese fir (Cunninghamia lanceolata) plantation in subtropical China, aimed to understand the effects of tree species on the soil C and N pools. In the broadleaf plantation, the C and N stocks in 0-40 cm soil layer were 99.41 Mg.hm-2 and 6. 18 Mg.hm-2, being 33.1 % and 22. 6 % larger than those in Chinese fir plantation, respectively. The standing biomass and the C and N stocks of forest floor in the broadleaf plantation were 1.60, 1.49, and 1.52 times of those in Chinese fir plantation, respectively, and the differences were statistically significant. There was a significant negative relationship between the forest floor C/N ratio and the soil C and N stocks. In the broadleaf plantation, the fine root biomass in 0-80 cm soil layer was 1.28 times of that in the Chinese fir plantation, and the fine root biomass in 0-10 cm soil layer accounted for 48. 2 % of the total fine root biomass. The C and N stocks in the fine roots in the broadleaf plantation were also higher than those in the Chinese fir plantation. In 0-10 cm soil layer, its C stock had a significant positive relationship with the fine root C stock. It was suggested that as compared with Chinese fir plantation, the soil in broadleaf plantation had a greater potential to accumulate organic carbon.