Nutrient characteristics in rhizosphere of pure and mixed plantations of Manchur ian walnut and Dahurian larch

A comparison study was made for the characteristics of pH value, orga nic matter content, nutrient element N, P and K contents in rhizosphere soils of pure and mixed plantations of Manchurian walnut and Dahurian larch and in bulk soils. The results show that the pH values of rhizosphere soil for all the plant ations except the pure walnut stand, which was slightly higher, were lower than those of bulk soils, while the organic matter contents in the rhizosphere soil f or all the plantations except the mixed plantation, which was slightly lower, we re higher than that in bulk soil. There exists a relative nitrogen accumulation in the rhizosphere and the extent to which the nitrogen accumulates is closely r elated to tree species and mixed pattern. As far as the total P and K contents a re considered, there exists a deficient tendency in rhizosphere in comparison wi th bulk soil. The element N, P and K are all mobilized in the rhizosphere of the pure or mixed plantation, characterized by the higher contents of the available N, P and K in the rhizosphere. The available N content in the rhizosphere of th e larch in mixed plantation was obviously higher than that of its pure plantatio n, whereas the available P and K contents in the rhizosphere of walnut in the mi xed plantation, on the other hand, were significantly higher than those of its p ure plantation.

Spatial and Temporal Distributions of Soil Organic Matter in the Mixed Plantations of Alder and Cypress in the Hilly Areas of Central Sichuan Basin

The investigation was conducted on the spatial and temporal distributions of soil organic mater （SOM） in the mixed plantations of alder （Aluns crernastogyne） and cypress （Cupressus funebris ） （MPAC）, which distributed in the hilly areas of central Sichuan Basin （HACSB）. The results show that： （1） the spatial distribution of SOM among different sites at the same age are not significant before 15-year-old, but significant at 20-year-old, and not significant again after 25-year-old; （2） the SOM contents in 0-15 cm and 15-30 cm layers increase sharply from 10- to 15-year-old, and decline gradually from 15- to 30- year-old; the SOM contents of the 30-year-old PCP were 80. 38% and 78.42% higher than that of the 10-year-old, but 29.16% and 53.37% lower than that of 15-year-old in the 0-15 cm and 15-30 cm layers, respectively. The decrease of SOM contents would lead to the degradation of soil fertility and the decline of forest productivity.

Soil microbial properties and nutrients in pure and mixed Chinese fir plantations

An investigation on soil organic carbon, total N and P, NO3-N, available P, microbial biomass C, N and P, basal respiration and metabolic quotients （qCO2） was conducted to compare differences in soil microbial properties and nutrients between 15-year-old pure Chinese fir （Cunninghamia lanceolata） and two mixed Chinese fir plantations （mixed plantations with Alnus crernastogyne, mixed plantations with Kalopanax septemlobus） at Huitong Experimental Station of Forest Ecology （26°45′N latitude and 109°30′E longitude）, Chinese Academy of Sciences in May, 2005. Results showed that the concentrations of soil organic carbon, total N, NO3^--N, total P and available P in mixed plantations were higher than that in pure plantation. Soil microbial biomass N in two mixed plantations was averagely higher 69% and 61% than that in pure plantation at the 0-10 cm and 10-20 cm soil depth, respectively. Soil microbial biomass C, P and basal respiration in mixed plantations were higher 11%, 14% and 4% at the 0-10 cm soil depth and 6%, 3% and 3% at the 10-20 cm soil depth compared with pure plantation. However, soil microbial C： N ratio and qCO2 were averagely lower 34% and 4% in mixed plantations than pure plantation. Additionally, there was a closer relation between soil microbial biomass and soil nutrients than between basal respiration, microbial C： N ratio and qCO2 and soil nutrients. In conclusion, introduction of broad-leaved tree species into pure coniferous plantation improved soil microbial properties and soil fertility, and can be helpful to restore degraded forest soil.

The variation of nutrient concentration in the rhizosphere of larch and ash in mixed and monoculture stands

Soil samples were taken from rhizosphere zone and off-rhizosphere zone of ash (Fraxinus mandshurica Rupr.) and larch (Larix olgensis Henry) in mixed and monoculture stands, and the nutrient concentration of N, P, and K was analyzed to study the effect of nutrients variation on yield improvement in the mixed stand. The result showed that: 1) The stand level total soil N concentration and available N in the mixed stand was similar to that in the monoculture stand of ash, but higher than that in monoculture stand of larch. The total N and available N concentration in rhizosphere soil of ash in the mixed stand was similar to that in the monoculture stand of ash, but the available N concentration in rhizosphere of larch in mixed stand was much higher than in its monoculture. 2) The stand level total P, total K concentration in the mixed stand was similar to that in monocul-ture stands of both species, but available P and K was more concentrated in the mixed stand than in the monoculture stands of ash. The rhizosphere available P and K of ash in the mixed stand was 44.1% and 13.5% (for the 9-yr-old stands) and 79.6% and 25.6% (for the 21-yr-old stands) higher than that in its monoculture. The improvement of soil P and K availability in the mixed stand is concluded.

Functional diversity dominates positive species mixture effects on ecosystem multifunctionality in subtropical plantations

Mixed-species plantations generally exhibit higher ecosystem multifunctionality than monospecific plantations.However,it is unclear how tree species functional composition influences species mixture effects on ecosystem multifunctionality.We selected 171 monospecific and mixed-species plantations from nine regions across subtropical China,and quantified 13 key ecosystem functional properties to investigate how species mixture effects on ecosystem multifunctionality are modulated by functional diversity and identity.We found that ecosystem multifunctionality was significantly higher(p<0.05)in mixed tree plantations than in monospecific plantations except the mixed-conifer species plantations.Across all regions,ecosystem multifunctionality was significantly higher(p<0.05)in mixed conifer-broadleaf plantations than in monospecific plantations of the corresponding species,but not different between mixed and monospecific coniferous plantations.The magnitude of species mixture effects on ecosystem multifunctionality varied greatly with tree species compositions.Taking Cunninghamia lanceolata Lamb.as an example,the effects varied from a range of 2.0%–9.6%when mixed with a conifer species to 36%–87%when mixed with a broadleaf species.The functional diversity was the dominate driver shaping ecosystem multifunctionality,while functional identity,as expressed by community-weighted mean of specific leaf area,also had a positive effect on ecosystem multifunctionality through the increased below-ground nitrogen and phosphorus stocks regulated by specific leaf area of the mixing tree species.Our study highlights the important role of functional diversity in shaping ecosystem multifunctionality across region-wide environmental conditions.Mixed conifer-broadleaf tree plantations with distinct functional traits benefit the enhancement of ecosystem multifunctionality,and the magnitude of species mixture effects is modulated by the functional identity of tree species composition;those relationships deserve a special consideration in multifunctional management context of subtropical plantations.

Effects of Different Tree Species and Proportions on Soil Fertility Quality in Eucalyptus Mixed Plantation

In order to study the effects of Eucalyptus mixed plantation with different mixed tree species and mixed proportion on soil nutrient accumulation and fertility quality, Eucalyptus-Mytilaria laosensis and Eucalyptus-Magnolia sumatrana mixed plantations in Guangxi State-owned Qipo Forest Farm were selected as the research objects. Based on 15 conventional soil fertility indexes, the minimum data set and membership function method were used to evaluate the soil fertility quality of mixed plantations with different structures. The results showed that compared with pure forest, the soil organic matter, total nitrogen, total potassium, alkali hydrolyzable nitrogen, available phosphorus, available potassium and other nutrients of mixed plantations with different treatments were significantly increased, and the contents of Cu and Zn in trace elements were most significantly increased. Compared with pure forest, the soil fertility quality of mixed plantations with different structures was significantly improved. The treatment with the highest soil fertility quality was 25% of Eucalyptus-M. sumatrana mixed plantation. When formulating production and management strategies, it can refer to construction measures of the mixed plantation to ensure the sustainability of forest soil fertility, and promote the healthy and sustainable development of Eucalyptus plantation and downstream industries in Guangxi.

田林老山中山两类森林凋落物研究

田林老山中山两类森林凋落物研究梁宏温（广西农学院林学分院，南宁５３０００１）ＳｔｕｄｉｅｓｏｎｔｈｅＬｉｔｔｅｒｆａｌｌｏｆＴｗｏＦｏｒｅｓｔＴｙｐｃｓｉｎＭｉｄ—ＡｌｔｉｔｕｄｅｏｆＬａｏｓｈａｎＭｏｕｎｔａｉｎｉｎＴｉａｎｌｉｎＣｏｕｎｔｙ．￥Ｌ...

Allelopathic effects of leaf litters of Eucalyptus camaldulensis on some forest and agricultural crops

Allelopathic effects of different doses of Eucalyptus camaldulensis leaf litters were investigated through an experiment in the green house of Institute of Forestry and Environmental Sciences, Chittagong, Bangladesh. Three popular agricultural crops： Falen （Vigna unguiculata）, Chickpea （Cicer arietinum）, Arhor （Cajanus cajan） and two widely used plantation trees： Sada koroi （Albizia procera） and Ipil ipil （Leucaena leucocephala） were selected as bioassay species. Experiment was set on tray at room temperature 27℃. The effects of different doses of leaf litter extracts were compared to the control. Results suggest that leaf litters of E, camaldulesis induced inhibitory effects, It was also found that the effect depend on concentration of extract and litterfall, type of receiver species. Higher concentration of the materials had the higher effect and vice versa. Though all the bioassay species were suppressed some of them showed better performance. Vigna unguiculata, Cicer arietinum are recommended in agroforestry based on this present Experiment output. In mixed plantation, Leucaena leucochephala is a better choice while compared to Albizia procera.

Allelopathic effects of Leucaena leucocephala leaf litter on some forest and agricultural crops grown in nursery

An experiment was conducted to assess the effect of leaf litter of Leucaena leucocephala on two forest crops Sada koroi （Albizia procera）, Ipil ipil （L. leucocephala） and three agricultural crops Falen （Vigna unguiculata）, Chickpea （Citer arietinum） and Arhor （Cajanus cajan） in the nursery of the Institute of Forestry and Environmental Sciences, Chittagong University, Bangladesh, in a Randomized Block Design. Results suggested that leaf litters ofL. leucocephala induced inhibitory effects on germination and growth of bioassay. It was also found that the effect depended on concentration of extract and litterfall, type of receptor species. Higher concentration of the materials had the higher effect and vice versa. Growth response of receptor crops varied with the variation of leaf litter application. The study revealed that application of low-dose leaf litter specially litter of 10 g·m^-2 had stimulating effect on shoot growth of C. arietinum, Vunguiculata and A. procera. While in all other cases significant inhibitory effect was observed and it was significantly increased with the increase of leaf litter application. However, the trend of inhibition was uneven with treatments. Root growth was found to be more affected than shoot growth.

Tree diversity effects on forest productivity increase through time because of spatial partitioning

Background: Experimental manipulations of tree diversity have often found overyielding in mixed-species plantations. While most experiments are still in the early stages of stand development, the impacts of tree diversity are expected to accumulate over time. Here, I present findings from a 31-year-old tree diversity experiment(as of2018) in Japan.Results: I find that the net diversity effect on stand biomass increased linearly through time. The species mixture achieved 64% greater biomass than the average monoculture biomass 31 years after planting. The complementarity effect was positive and increased exponentially with time. The selection effect was negative and decreased exponentially with time. In the early stages(≤ 3 years), the positive complementarity effect was explained by enhanced growths of early-and mid-successional species in the mixture. Later on(≥ 15 years), it was explained by their increased survival rates owing to vertical spatial partitioning — i.e. alleviation of self-thinning via canopy stratification. The negative selection effect resulted from suppressed growths of late-successional species in the bottom layer.Conclusions: The experiment provides pioneering evidence that the positive impacts of diversity-driven spatial partitioning on forest biomass can accumulate over multiple decades. The results indicate that forest biomass production and carbon sequestration can be enhanced by multispecies afforestation strategies.

Impacts of competition and nitrogen addition on plant stoichiometry and non-structural carbohydrates in two larch species

Previous research has shown that competition between plants can have differential effects on leaf stoichiometry and non-structural carbohydrate(NSC)in different environments.However,little attention has been given to understanding these effects on non-photosynthetic organs,particularly of deciduous tree species.Here we assess the impact of competition on below and aboveground biomass,stoichiometry,nutrient composition and NSC in pure and mixed forests of two Larch species,Larix kaempferi and L.olgensis under nitrogen(N)addition.Nitrogen enrichment did not result in stronger intraspecific competition for both species and L.olgensis benefited from the presence of L.kaempferi under different N levels.Stems kept relatively stable C/N compared to roots and branches in response to competition,while N addition imposed stronger impacts on N/P of different organs rather than competition.In contrast to stable C concentrations,starch and soluble sugar concentrations were more easily impacted by competition and the addition of nitrogen.Competition forced L.kaempferi and L.olgensis to allocate more carbon into storage by increasing their starch concentration and starch/soluble sugar of stems under competition.However,no significant differences in stoichiometry and NSC concentration between intra-and interspecific competition were found.NSC and nutrient pools of L.kaempferi stems,branches and coarse roots consistently declined due to competition regardless of N addition.Coarse and fine roots of L.kaempferi accumulated more N when in competition with L.olgensis than with a conspecific neighbor under N addition.Our results show that NSC was more sensitive to competition relative to stoichiometric traits(N and P)of non-photosynthetic organs.