不同林龄尾巨桉人工林生态系统生物量的研究

对闽南山区不同林龄(2、3、4、5、6年生)尾巨桉人工林生态系统的生物量进行了研究,其中林木生物量采用标准木法,林下植被和地被物生物量采用样方收获法。结果表明:乔木层生物量随着林龄的增加而逐渐增加,分别为45.14、69.22、92.20、111.82、175.09t/hm2,其中树干占的比例最大(44.5%～60.4%),细根最小(0.2%～0.6%);各林龄尾巨桉生产力依次为22.86、26.07、32.63、32.70、46.69t/(hm2·a),叶的生产力随林龄增长呈现先增加后减少的趋势;林下植被生物量依次为5308.83、7201.62、5676.47、4033.42、9183.13kg/hm2,其中灌木生物量在3年生时最大,为2121.89kg/hm2,而草本生物量在6年生时最大,达到1062.19kg/hm2;不同年龄尾巨桉地被物现存量大小表现为6年生>3年生>5年生>2年生>4年生,2～5年生时未分解层现存量小于分解层,6年生时则是分解层现存量小于未分解层。

Biomass and Carbon Sequestration Potential of Poplar-Wheat Inter-cropping System in Irrigated Agro-ecosystem in India

An attempt has been made to assess the productivity as well as the carbon sequestration potential of this mixture. The grain as well as straw yields were significantly lower in poplar block plantations than in the open （14 to 64% and 13 to 66% grain and straw yield, respectively under one to six year plantation）. The annual productivity of poplars was recorded maximum after fourth year and later the annual wood increment decreased （42.4, 39.8 and 35.6 m^3/ha/yr after 4^th, 5^th and 6^th year, respectively）. The enrichment of soil through litter and roots enhanced the organic carbon in the surface layer of soil （0-15 cm） under poplar blocks as compared to open fields with wheat crop only. The carbon storage potential in agroforestry system was recorded very high in comparison to sole crop. The carbon storage in agroforestry system increased with the age of the plantation and the major contribution came from the timber, roots and litter （37.30 mg/ha after six years）. However, wheat crop yield decreased under poplar but this may be compensated by the poplar trees in terms of biomass, economic returns and the carbon sequestration potential.

Evaluation of the individual allocation scheme and its impacts in a dynamic global vegetation model

The strategies of plant growth play an important role not only in ecosystem structure,but also in global carbon and water cycles.In this work,the individual carbon allocation scheme of tree PFTs and its impacts were evaluated in China with Institute of Atmospheric Physics-Dynamic Global Vegetation Model,version 1.0（IAP-DGVM1.0）as a test-bed.The results showed that,as individual growth,the current scheme tended to allocate an increasing proportion of annual net primary productivity（NPP）to sapwood and decreasing proportions to leaf and root accordingly,which led to underestimated individual leaf biomass and overestimated individual stem biomass.Such biases resulted in an overestimation of total ecosystem biomass and recovery time of mature forests,and an underestimation of ecosystem NPP and tree leaf area index in China.

Distribution and Estimation of Aboveground Biomass of Alpine Shrubs along an Altitudinal Gradient in a Small Watershed of the Qilian Mountains, China

Shrublands serve as an important component of terrestrial ecosystems, and play an important role in structure and functions of alpine ecosystem.Accurate estimation of biomass is critical to examination of the productivity of alpine ecosystems, due to shrubification under climate change in past decades.In this study, 14 experimental plots and 42 quadrates of the shrubs Potentilla fruticosa and Caragana jubata were selected along altitudes gradients from 3220 to 3650 m a.s.l.(above sea level) on semi-sunny and semi-shady slope in Hulu watershed of Qilian Mountains, China.The foliage, woody component and total aboveground biomass per quadrate were examined using a selective destructive method, then the biomass were estimated via allometric equations based on measured parameters for two shrub species.The results showed that C.jubata accounted for 1–3 times more biomass(480.98 g/m2) than P.fruticosa(191.21 g/m2).The aboveground biomass of both the shrubs varied significantly with altitudinal gradient(P<0.05).Woody component accounted for the larger proportion than foliage component in the total aboveground biomass.The biomass on semi-sunnyslopes(200.27 g/m2 and 509.07 g/m2) was greater than on semi-shady slopes(182.14 g/m2 and 452.89g/m2) at the same altitude band for P.fruticosa and C.jubata.In contrast, the foliage biomass on semi-shady slopes(30.50 g/m2) was greater than on semi-sunny slopes(27.51 g/m2) for two shrubs.Biomass deceased with increasing altitude for P.fruticosa, whereas C.jubata showed a hump-shaped pattern with altitude.Allometric equations were obtained from the easily descriptive parameters of height(H), basal diameter(D) and crown area(C) for biomass of C.jubata and P.fruticosa.Although the equations type and variables comprising of the best model varied among the species, all equations related to biomass were significant(P < 0.005), with determination coefficients(R2) ranging from 0.81 to 0.96.The allometric equations satisfied the requirements of the model, and can be used to estimate the regional scale biomass of P.fruticosa and C.jubata in alpine ecosystems of the Qilian Mountains.

The Application of Ecosystem Dynamic Model in Xiamen Bay

This paper is to establish a nitrogen and phosphorus nutrients cycle-based numerical model of ecological dynamics for Xiamen Bay on the basis of the existing three-dimensional barocline hydrodynamic model. The calculation results show that the estuarine district of Jiulongjiang estuary has the highest inorganic nitrogen concentration followed by the West Harbor, which demonstrates that Jiulongjiang River is the main input source of inorganic nitrogen in Xiamen Bay. The West Harbor has relatively high concentration of nutrients caused by the huge land pollution emission and its own poor water exchange capacity; while the distribution rules of phytoplankton biomass correspond with those of phosphates, demonstrating Xiamen Bay＇s phytoplankton controlled by phosphorus; the haloplankton biomass differs slightly, presenting the gradual reduction from the interior part to the exterior part of the bay.

Life history, secondary production and trophic basis of two dominant mayflies in a subtropical stream of China

Mayflies constitute a major part of macroinvertebrate biomass and production in Iotic ecosystems, and play an important role in material cycle and energy flow. There are more than 250 species of mayflies in rivers and streams of China. In order to learn their ecological functions, an investigation on life cycle, production and trophic basis of dominant species of mayflies in a second-order branch of Hanjiang River basin, Hubei, China was carried out during June 2003 to June 2004. The results showed that the dominant mayfly species Epeorus sp. and Caenis sp. developed two generations per year; in term of Epeorus sp., pupation mainly occurred in spring and then from late summer to early autumn, while Caenis sp. pupated in spring and autumn. The abundance and biomass of the Epeorus sp. population peaked twice （1 226 ind/m^2, 3.142 5g/m^2） in April and June. Caenis sp. also had two peaks （307ind/m^2, 1.590 g/m^2）, but in February and June. Cohort production and cohort P/B ratio of Epeorus sp. were 161.009 g/m2 wet weight and 7.7, respectively, and annual production and P/B ratio were 267.46g/m^2.a wet weight and 15.4, respectively; cohort production and P/B ratio of Caenis sp. were 26.7995g/m^2 wet weight and 4.7, its annual production and P/B ratio were 53.60 g/m2.a wet weight and 9.4, respectively. For Epeorus sp., the proportions contributing to secondary production of the main food types were： amorphous detritus, 33.46%; fungi, 10.83%; vascular plant detritus, 1.80%; diatoms, 53.90%; for Caenis sp., the proportions were 70.79%, 6.90%, 3.52% and 18.77%, respectively.

Sustainable fisheries in shallow lakes:an independent empirical test of the Chinese mitten crab yield model

Next to excessive nutrient loading,intensive aquaculture is one of the major anthropogenic impacts threatening lake ecosystems.In China,particularly in the shallow lakes of mid-lower Changjiang(Yangtze) River,continuous overstocking of the Chinese mitten crab(Eriocheir sinensis) could deteriorate water quality and exhaust natural resources.A series of crab yield models and a general optimum-stocking rate model have been established,which seek to benefit both crab culture and the environment.In this research,independent investigations were carried out to evaluate the crab yield models and modify the optimum-stocking model.Low percentage errors(average 47%,median 36%) between observed and calculated crab yields were obtained.Specific values were defined for adult crab body mass(135 g/ind.) and recapture rate(18%and 30%in lakes with submerged macrophyte biomass above and below 1 000 g/m^2)to modify the optimum-stocking model.Analysis based on the modified optimum-stocking model indicated that the actual stocking rates in most lakes were much higher than the calculated optimum-stocking rates.This implies that,for most lakes,the current stocking rates should be greatly reduced to maintain healthy lake ecosystems.

Effects of Channelization on Fish Biomass in River Ecosystems

Channel straightening in a naturally meandering river is a common historical trigger of channel incision which typically results in stream bank destabilization. Several of the larger river systems in the upland portion of the Yazoo River Basin have subjected channelization resulting in profound changes in the physical and geomorphological characteristics of these systems. Fish were sampled using electroshocking gear and hoop nets to evaluate the impact of stream bank destabilization and loss of habitat heterogeneity resulting from channelization on fish communities. While distinct differences in the fish communities were evident, only the Skuna appeared to have characteristics of a damaged system. More than 95% of the biomass was comprised of species reaching an adult length of less than 300 mm. The lotic omnivorous fishes that dominated the biomass from Skuna are often associated with smaller streams rather than rivers. Furthermore, 72% of the catch consisted of fish preferring littoral zone habitats. The shallow depth and lack of woody debris in Skuna provided a selective advantage for smaller species of fish that could use shoreline habitats as protection from the current. Based on results from the Skuna River, channel straightening that leads to channel incision, bank failure and over widening provide habitats too shallow to support a community of fishes typical of northern Mississippi riverine system. This information may be useful in making comparison of damaged riverine ecosystems and assist managers in determining impairment and success in the TMDL （Total Maximum Daily Load） process.

Leaf and Ecosystem Gas Exchange Responses of Buffel Grass-Dominated Grassland to Summer Precipitation

Sporadic rain events that occur during summer play an important role in the initiation of biological activity of semi-arid grasslands.To understand how ecosystem processes of a buffel grass(Cenchrus ciliaris L.)-dominated grassland respond to summer rain events,an LI 6 400 gas exchange system was used to measure the leaf gas exchange and plant canopy chambers were used to measure net ecosystem CO2exchange(NEE) and ecosystem respiration(Reco), which were made sequentially during periods before rain(dry) and after rain(wet). Gross ecosystem photosynthesis(GEP) was estimated from NEE and Reco fluxes, and light use efficiency parameters were estimated using a rectangular hyperbola model. Prior to the monsoon rain, grassland biomass was non-green and dry exhibiting positive NEE(carbon source) and low GEP values during which the soil water became increasingly scarce. An initial rain pulse(60 mm) increased the NEE from pre-monsoon levels to negative NEE(carbon gain) with markedly higher GEP and increased green biomass. The leaf photosynthesis and leaf stomatal conductance were also improved substantially. The maximum net CO2uptake(i.e.,negative NEE) was sustained in the subsequent period due to multiple rain events. As a result, the grassland acted as a net carbon sink for 20 d after first rain. With cessation of rain(drying cycle), net CO2 uptake was reduced to lower values. High sensitivity of this grassland to rain suggests that any decrease in precipitation in summer may likely affect the carbon sequestration of the semiarid ecosystem.

Microbial Biomass Dynamics in a Tropical Agroecosystem： Influence of Herbicide and Soil Amendments

The influences of herbicide alone and in combination with the soil amendments with contrasting resource qualities on dynamics of soil microbial biomass C （MBC）, N （MBN）, and P （MBP） were studied through two annual cycles in rice-wheat-summer fallow crop sequence in a tropical dryland agroecosystem. The experiment included application of herbicide （butachlor） alone or in combination with various soil amendments having equivalent amount of N in the forms of chemical fertilizer, wheat straw, Sesbania aculeata, and farm yard manure （FYM）. Soil microbial biomass showed distinct temporal variations in both crop cycles, decreased from vegetative to grain-forming stage, and then increased to maximum at crop maturity stage. Soil MBC was the highest in herbicide ＋ Sesbania aculeata treatment followed by herbicide ＋ FYM, herbicide ＋ wheat straw, herbicide ＋ chemical fertilizer, and herbicide alone treatments in decreasing order during the rice-growing period. During wheat-growing period and summer fallow, soil MBC attained maximum for herbicide ＋ wheat straw treatment whereas herbicide ＋ FYM, herbicide ＋ Sesbania, and herbicide ＋ chemical fertilizer treatments showed similar levels. The overall trend of soil MBN was similar to those of soil MBC and MBP except that soil MBN was higher in herbicide ＋ chemical fertilizer treatment over the herbicide ＋ wheat straw treatment during rice-growing period. In spite of the addition of equivalent amount of N through exogenous soil amendments in combination with the herbicide, soil microbial biomass responded differentially to the treatments. The resource quality of the amendments had more pronounced impact on the dynamics of soil microbial biomass, which may have implications for long-term sustainability of rainfed agroecosystems in dry tropics.

Nitrogen addition affects plant biomass allocation but not allometric relationships among different organs across the globe

Aims Biomass allocation to different organs is a fundamental plant ecophysiological process to better respond to changing environments;yet,it remains poorly understood how patterns of biomass allocation respond to nitrogen(N)additions across terrestrial ecosystems worldwide.Methods We conducted a meta-analysis using 5474 pairwise observations from 333 articles to assess how N addition affected plant biomass and biomass allocation among different organs.We also tested the'ratio-based optimal partitioning'vs.the'isometric allocation,hypotheses to explain potential N addition effects on biomass allocation.Important Findings We found that(i)N addition significantly increased whole plant biomass and the biomass of different organs,but decreased rootrshoot ratio(RS)and root mass fraction(RMF)while no effects of N addition on leaf mass fraction and stem mass fraction at the global scale;(ii)the effects of N addition on ratio-based biomass allocation were mediated by individual or interactive effects of moderator variables such as experimental conditions,plant functional types,latitudes and rates of N addition and(iii)N addition did not affect allometric relationships among different organs,suggesting that decreases in RS and RMF may result from isometric allocation patterns following increases in whole plant biomass.Despite alteration of ratio-based biomass allocation between root and shoot by N addition,the unaffected allometric scaling relationships among different organs(including root vs.shoot)suggest that plant biomass allocation patterns are more appropriately explained by the isometric allocation hypothesis rather than the optimal partitioning hypothesis.Our findings contribute to better understand N-induced effects on allometric relationships of terrestrial plants,and suggest that these ecophysiological responses should be incorporated into models that aim to predict how terrestrial ecosystems may respond to enhanced N deposition under future global change scenarios.

Soil Microbial Responses to Experimental Warming and Nitrogen Addition in a Temperate Steppe of Northern China

The responses of soil microbes to global warming and nitrogen enrichment can profoundly affect terrestrial ecosystem functions and the ecosystem feedbacks to climate change.However,the interactive effect of warming and nitrogen enrichment on soil microbial community is unclear.In this study,individual and interactive effects of experimental warming and nitrogen addition on the soil microbial community were investigated in a long-term field experiment in a temperate steppe of northern China.The field experiment started in 2006 and soils were sampled in 2010 and analyzed for phospholipid fatty acids to characterize the soil microbial communities.Some soil chemical properties were also determined.Five-year experimental warming significantly increased soil total microbial biomass and the proportion of Gram-negative bacteria in the soils.Long-term nitrogen addition decreased soil microbial biomass at the 0-10 cm soil depth and the relative abundance of arbuscular mycorrhizal fungi in the soils.Little interactive effect on soil microbes was detected when experimental warming and nitrogen addition were combined.Soil microbial biomass positively correlated with soil total C and N,but basically did not relate to the soil C/N ratio and pH.Our results suggest that future global warming or nitrogen enrichment may significantly change the soil microbial communities in the temperate steppes in northern China.

Long-term variability of root production in bioenergy crops from ingrowth core measurements

Aims Long-term determination of root biomass production upon land-use conversion to biofuel crops is rare.To assess land-use legacy influences on belowground biomass accumulation,we converted 22-year-old Conservation Reserve Program(CRP)grasslands and 50+-year-old agricultural(AGR)lands to corn(C),switchgrass(Sw)and restored prairie(Pr)biofuel crops.We maintained one CRP grassland as a reference(Ref).We hypothesized that land-use history and crop type have significant effects on root density,with perennial crops on CRP grasslands having a higher root biomass productivity,while corn grown on former agricultural lands produce the lowest root biomass.Methods The ingrowth core method was used to determine in situ ingrowth root biomass,alongside measurements of aboveground net primary productivity(ANPP).Ancillary measurements,including air temperature,growing season length and precipitation were used to examine their influences on root biomass production.Important Findings Root biomass productivity was the highest in unconverted CRP grassland(1716 g m?2 yr?1)and lowest in corn fields(526 g m?2 yr?1).All perennial sites converted from CRP and AGR lands had lower root biomass and ANPP in the first year of planting but peaked in 2011 for switchgrass and a year later for restored prairies.Ecosystem stability was higher in restored prairies(AGR-Pr:4.3±0.11;CRP-Pr:4.1±0.10),with all monocultures exhibiting a lower stability.Root biomass production was positively related to ANPP(R2=0.40).Overall,attention should be given to root biomass accumulation in large-scale biofuel production as it is a major source of carbon sequestration.