[Relationships between tree functional traits and leaf nitrogen and phosphorus resorption efficiencies in subtropical young plantations]. / äºšçƒ­å¸¦å¹¼æž—æ ‘æœ¨åŠŸèƒ½æ€§çŠ¶ä¸Žå¶ç‰‡æ°®ç£·é‡å¸æ”¶çŽ‡çš„å ³ç³».

We examined the relationship between tree functional traits and leaf nitrogen and phosphorus resorption efficiencies across 29 species in 3-year-old pure plantations in subtropical China. The results showed that the average nitrogen (NRE) and phosphorus (PRE) resorption efficiencies in 29 young plantations were 50.5% and 57.3%, respectively. The average NRE of 22 arbuscular mycorrhizal (AM) tree species was 52.7%, significantly higher than that of the seven ectomycorrhizal (EM) tree species (45.1%). NRE was positively correlated with fine root tissue density across the 29 tree species. PRE was positively correlated with root diameter in the seven EM tree species. Functional traits of 22 AM tree species were not associated with NRE and PRE. Among all of the 29 tree species, mycorrhizal type, specific leaf area, fine root tissue density, leaf thickness, and the interaction effects of mycorrhizal type with leaf thickness explained 27% variation in NRE. Specific root length, fine root carbon content, fine root carbon to nitrogen ratio, mycorrhizal type, leaf carbon content, and the interaction effects of mycorrhizal type with leaf carbon content explained 35% variation in PRE. Root functional trait of subtropical species could predict nitrogen and phosphorus resorption efficiencies. The model with multiple functional traits could better reveal the relative importance of different biological factors on nutrient resorption efficiency.

[Effects of broadleaved tree species on soil microbial stoichiometry in clear-cut patches of Cunninghamia lanceolata plantation]. / æ‰æœ¨é‡‡ä¼è¿¹åœ°è¥é€ é˜”å¶æ ‘ç§å¯¹åœŸå£¤å¾®ç”Ÿç‰©ç”Ÿæ€åŒ–å­¦è®¡é‡ç‰¹å¾çš„å½±å“.

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.

[Dynamics of nutrient concentration and microbial community composition during fine root decomposition in subtropical Mytilaria laosensis and Cunninghamia lanceolata plantations.] / äºšçƒ­å¸¦ç±³è€æŽ’å’Œæ‰æœ¨ç»†æ ¹åˆ†è§£è¿‡ç¨‹ä¸­å »åˆ†ä¸Žå¾®ç”Ÿç‰©ç¾¤è½ç»„æˆçš„å˜åŒ–.

We conducted a 12-month fine root decomposition experiment under 19-year-old Mytilaria laosensis and Cunninghamia lanceolate plantations to explore the dynamics of nutrient concentration and microbial community composition. The aim of this study was to provide insights into nutrient cycling under plantations with different tree species. Our results showed that the initial concentrations of phosphorus (P) and potassium (K) were significantly higher in the fine root of M. laosensis than those in C. lanceolata, which significantly decreased with decomposition. Nitrogen (N) concentration in fine roots of both species increased with decay time. The variation of N concentration in fine root of C. lanceolata lagged behind that in M. laosensis. During the decomposition, magnesium (Mg) concentration in fine root of C. lanceolata showed no significant changes, but that of M. laosensis decreased at the initial decay stage and increased thereafter and was significantly lower than that of C. lanceolata at the 8th month. The ratio of fungi to bacteria (F/B) of both species decreased at the initial stage and then increased, with significantly higher F/B in fine root of M. laosensis than that of C. lanceolate after one-year decay. Redundancy analysis (RDA) showed that changes in N and K concentrations and C/N ratio explained 37.2%, 14.5% and 14.8% of the variations in microbial community composition of C. lanceolata fine root respectively. However, during the decay of M. laosensis fine root, concentrations of Mg and K were key factors, accounting for 35.9% and 17.6% of the variations in microbial community composition, respectively. We concluded that other nutrients beyond N, such as Mg, might also be an important factor affecting root decomposition in different tree species.

[Seasonal dynamics of soil mineral nitrogen pools and nitrogen mineralization rate in different forests in subtropical China]. / 亚热带不同林分土壤矿质氮库及氮矿化速率的季节动态.

We conducted an in situ incubation experiment to determine soil mineral N (NH4+-N and NO3--N) concentrations and soil net N mineralization rates (net ammonification rate and net nitrification rate) using close-top PVC tubes in three adjacent forests (natural forest, Castanopsis kawakamii and Cunninghamia lanceolata plantation) from September 2014 to August 2015 in subtropical China, investigating the effects of forest type and season on soil inorganic N concentrations and soil net N mineralization rates. Results showed that soil NO3--N was the dominant form in mi-neral N pool in all three forests, and the proportion of NO3--N to soil inorganic N content ranged from 55.1% to 87.5% and from 56.1% to 79.1% in natural forest and Cunninghamia lanceolata plantation, respectively. The effects of forest types on soil mineral N pool were only significant on soil NO3--N, and the concentration of NO3--N in Castanopsis kawakamii was significantly lower than in the other two forests. The NO3--N and mineral N pool varied seasonally in all forests, and were higher in dormant season (October to February) than in growing season (March to September). Soil nitrification rate was very low in the whole year in all three forests and soil net ammonification was the major process of soil net mineralization. Tree species significantly affected soil net ammonification rate, and the value under Chinese fir was significantly lower than the other two fore-sts. The seasonal patterns of the soil net ammonification rate were not similar in all the three forests, but with the lowest value occurring in November and February in the following year. Analysis using variance of repeated measures indicated that soil mineral N concentrations and soil N mineralization rates were significantly affected by forest type and season, and correlation analysis showed that soil mineral N and soil N mineralization rate were significantly affected by water moisture and temperature, and the effects of litter on soil N mineralization rate were mainly through quality control, ra-ther than the quantity control.

[Variations of water use efficiency and its relationship with leaf nutrients of different altitudes of Wuyi Mountains, China]. / æ­¦å¤·å±±ä¸åŒæµ·æ‹”æ¤ç‰©æ°´åˆ†åˆ©ç”¨æ•ˆçŽ‡çš„å˜åŒ–åŠå ¶ä¸Žå »åˆ†å˜åŒ–çš„å ³ç³».

We determined the water use efficiency and nitrogen and phosphorus concentrations of plants at different altitudes (600, 900, 1300, 1500, 1800, 2000, 2100 m) in Wuyi Mountains to understand the relationship of water use efficiency with foliar nutrients. The results showed that plant water use efficiency increased with altitude, and the leaf δ18O of tree showed no significant variance with altitude. On the whole, leaf nitrogen concentration showed no obvious trend, while leaf phosphorus concentration at high altitude was significantly higher than that at low altitude. No significant relationship between water use efficiency and foliar nitrogen concentration was found in this study, but water use efficiency had a positive correlation with foliar phosphorus concentration. In conclusion, the change of water use efficiency was mainly caused by the difference in photosynthetic rate. The effect of water status on plant water use efficiency was not significant. The variances of leaf phosphorus concentrations along the altitudinal gradient may affect photosynthetic rate and in turn the water use efficiency of plant in this area.

[Effects of litter and root exclusion on soil microbial community composition and function of four plantations in subtropical sandy coastal plain area, China]. / å‡‹è½ç‰©å’Œæ ¹ç³»åŽ»é™¤å¯¹æ»¨æµ·æ²™åœ°åœŸå£¤å¾®ç”Ÿç‰©ç¾¤è½ç»„æˆå’ŒåŠŸèƒ½çš„å½±å“.

We conducted detritus input and removal treatment (DIRT) to examine the effects of shifting above- and belowground carbon (C) inputs on soil microbial biomass, community composition and function in subtropical Pinus elliottii, Eucalyptus urophylla × Eucalyptus grandis, Acacia aulacocarpa and Casuarina equisetifolia coastal sandy plain forests, and the treatments included: root trenching, litter removal and control. Up to September 2015, one year after the experiment began, we collected the 0-10 cm soil samples from each plot. Phospholipid fatty acid (PLFA) analysis was used to characterize the microbial community composition, and micro-hole enzymatic detection technology was utilized to determine the activity of six kinds of soil enzymes. Results showed that changes in microbial biomass induced by the C input manipulations differed among tree species, and mainly affected by litter and root qualily. In E. urophylla × E. grandis stands, root trenching significantly decreased the contents of total PLFAs, Gram-positive bacteria, Gram-negative bacteria, fungi and actinomycetes by 31%, 30%, 32%, 36% and 26%, respectively. Litter removal reduced the contents of Gram-positive bacteria, fungi and actinomycetes by 24%, 27% and 24%, respectively. However, C input manipulations had no significant effect on soil microbial biomassunder other three plantations. According to the effect of C input manipulations on soil microbial community structure, litter and root exclusion decreased fungi abundance and increased actinomycetes abundance. Different treatments under different plantations resulted in various soil enzyme activities. Litter removal significantly decreased the activities of cellobiohydrolase, ß-glucosidase, acid phosphatase and N-acetyl-ß-d-glucosaminidase of P. elliottii, A. aulacocarpa and C. equisetifolia, root exclusion only decreased and increased the activities of ß-glucosidase in P. elliottii and A. aulacocarpa forest soils, respectively. Litter removal also decreased the activities of polyphenol oxidase (PPO) and peroxidase (PER) in P. elliottii and C. equisetifolia forest soils, while root trenching had no significant effect on the activities of PPO and PER under all plantations. The properties of litter and root were the important factors in determining the soil microbial community and enzyme activity, and the change of soil microenvironment, such as temperature and moisture, caused by C input manipulations was also the important driver for the change of soil microbial property.

[Effects of forest types on soil dissolved organic carbon and nitrogen in surface and deep la-yers in subtropical region, China.] / äºšçƒ­å¸¦å ¸åž‹æž—åˆ†å¯¹è¡¨å±‚å’Œæ·±å±‚åœŸå£¤å¯æº¶æ€§æœ‰æœºç¢³ã€æ°®çš„å½±å“.

Forest types have significant effects on the availability and dynamics of soil dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). By now the impacts of forest types on soil DOC and DON were mainly focused on surface soil (0-10 cm). Based on the comparisons between natural forest, Phyllostachys pubescens, Castanopsis kawakamii and Cunninghamia lanceolata plantations, we investigated the effects of forest types on soil DOC and DON pools in top (0-10 cm) and deep soils (40-60 cm). Cold water, hot water and KCl solutions were used to extract soil DOC and DON from surface and deep soils. Results showed that the effects of forest types on soil DOC, DOC/TOC, DON and soil microbial biomass carbon were only significant in the surface soil. The concentrations of DOC and DON varied with extract methods and hot water extracted the largest amounts of DOC and DON, and cold water the least. Correlations among hot water, KCl and cold water extracted DOC and DON were significant, suggesting that the organic C and N released by these three solutions might be at least partly from similar pools. The concentrations of DOC and DON and DOC/TOC in surface soil under natural forest and P. pubescens were greater than under C. kawakamii and C. lanceolata. It indicated that the concentrations of DOC and DON were greater under the natural forest and P. pubescens than under the C. kawakamii and C. Lanceolata, and more beneficial to improve soil fertility.

[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.