Impact of land‐use intensity on the relationships between vegetation indices,photosynthesis and biomass of intensively and extensively managed grassland fens

Vegetation indices are widely used as model inputs and for non‐destructive estimation of biomass and photosynthesis, but there have been few validation studies of the underlying relationships. To test their applicability on temperate fens and the impact of management intensity, we investigated the relationships between normalized difference vegetation index (NDVI), leaf area index (LAI), brown and green above‐ground biomass and photosynthesis potential (PP). Only the linear relationship between NDVI and PP was management independent (R² = 0·53). LAI to PP was described by a site‐specific and negative logarithmic function (R² = 0·07–0·68). The hyperbolic relationship of LAI versus NDVI showed a high residual standard error (s.e.) of 1·71–1·84 and differed between extensive and intensive meadows. Biomass and LAI correlated poorly (R² = 0·30), with high species‐specific variability. Intensive meadows had a higher ratio of LAI to biomass than extensive grasslands. The fraction of green to total biomass versus NDVI showed considerable noise (s.e. = 0·13). These relationships were relatively weak compared with results from other ecosystems. A likely explanation could be the high amount of standing litter, which was unevenly distributed within the vegetation canopy depending on the season and on the timing of cutting events. Our results show there is high uncertainty in the application of the relationships on temperate fen meadows. For reliable estimations, management intensity needs to be taken into account and several direct measurements throughout the year are required for site‐specific correction of the relationships, especially under extensive management. Using NDVI instead of LAI could reduce uncertainty in photosynthesis models.     

Temporal trends in bromide release following rewetting of a naturally drained gully mire

Abstract. Recently, there has been interest in the occurrence of bromide (Br^-) in natural waters since it has been demonstrated that Br^-, in association with humic substances in raw waters, is readily incorporated into haloacetic acids in the form of organically bound bromine (Br) during water chlorination. We report results of the effects of experimentally rewetting a naturally drained gully mire on the hydrochemistry of Br^-, iron (Fe) and dissolved organic carbon (DOC) in the peat water. Results obtained over a three year period showed that rewetting substantially increased the concentrations of these solutes in the pore water, with peak values of 1 mg dm^-3 (Br^-), > 60 mg dm^-3 (Fe) and > 300 mg dm^-3 (DOC) detected in some samples after rewetting, compared with typical values < 0.05 mg dm^-3 (Br^-), < 1 mg dm^-3 (Fe) and < 15 mg dm^-3 (DOC) under the drained conditions. Bromide, Fe and DOC release were highly seasonal, with the largest concentrations observed in late-summer to autumn. However, whereas seasonal peak concentrations of Fe and DOC have since remained at these higher levels, seasonal peak concentrations of Br^- were progressively attenuated over time, suggesting the latter phenomenon is a flush effect, with no longer-term consequences for water quality.     

Spatial variability of surface peat properties and carbon emissions in a tropical peatland oil palm monoculture during a dry season

The expansion of oil palm monocultures into globally important Southeast Asian tropical peatlands has caused severe environmental damage. Despite much of the current focus of environmental impacts being directed at industrial scale plantations, over half of oil palm land-use cover in Southeast Asia is from smallholder plantations. We differentiated a first generation smallholder oil palm monoculture into 8 different sampling zones, and further divided the 8 sampling zones into oil palm root influenced (Proximal) and reduced root influence (Distal) areas, to assess how peat properties regulate in situ carbon dioxide (CO₂) and methane (CH₄) fluxes. We found that all the physico-chemical properties and nutrient concentrations except sulphur varied significantly among sampling zones. All physico-chemical properties except electrical conductivity, and all nutrient content except nitrogen and potassium varied significantly between Proximal and Distal areas. Mean CO₂ fluxes (ranged between 382 and 1191 mg m⁻² h⁻¹) varied significantly among sampling zones, and between Proximal and Distal areas, with notably high emissions in Dead Wood and Path zones, and consistently higher emissions in Proximal areas compared to Distal areas within almost all the zones. CH₄ fluxes (ranged between −32 and 243 µg m⁻² h⁻¹) did not significantly vary between Proximal and Distal areas, however significantly varied amongst sampling zones. CH₄ flux was notably high in Canal Edge and Understorey Ferns zones, and negative in Dead Wood zone. The results demonstrate the high heterogeneity of peat properties within oil palm monoculture, strengthening the need for intensive sampling to characterize a land use in the tropical peatlands.     

Is the decline of soil microbial biomass in late winter coupled to changes in the physical state of cold soils?

During winter when the active layer of Arctic and alpine soils is below 0 °C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles.Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks, in turn, could affect herbivory and production at higher trophic levels.     

香格里拉市泥炭沼泽生态系统服务功能价值评估

香格里拉市高寒地区分布有众多泥炭沼泽生态系统,在云南省具有典型性、代表性,在湿地生态系统功能调节过程中具有不可估量的作用。根据《云南省泥炭沼泽碳库调查报告》,结合香格里拉市泥炭沼泽生态系统特点,构建了泥炭沼泽生态系统服务功能价值评估指标体系,评估了支持功能、调节功能和文化功能3项服务功能价值,包括8个具体评价指标。估算结果表明,香格里拉市泥炭沼泽生态系统服务功能总价值为5.99亿元/a,单位面积价值为110.86元/(m²·a),其中：间接价值占总价值的95.32%,蓄水调洪、固氮释氧以及气候调节价值最显著。     

杉木采伐迹地鹅掌楸和杉木生长特性的研究

[目的]揭示引种鹅掌楸和杉木人工林在广西自治区融水县的生长特性,为杉木连栽迹地造林树种的选择提供科学依据。[方法]对广西自治区融水苗族自治县杉木采伐迹地的鹅掌楸和杉木人工林的生长特性进行了5年的定位监测,并进行了比较研究。[结果]在相似立地条件下,1～5年生鹅掌楸人工林的平均树高、平均胸径和平均蓄积量均明显高于杉木人工林,其中,5年生杉木人工林年均胸径生长量为1.43 cm,年均树高生长量为1.23 m,年平均蓄积量为17.02 m3/hm2,而5年生鹅掌楸人工林的上述3个数据分别为2.19 cm、1.78 m和31.80 m3/hm2,是杉木人工林的1.53、1.45和1.87倍。[结论]鹅掌楸是一种早期速生树种,其生长速度比杉木快,成材比杉木早,可以作为杉木的替代轮作树种进行推广。     

Methane suppression by iron and humic acids in soils of the Arctic Coastal Plain

Methane–climate interactions are reasonably well understood; the biogeochemical controls on net methane fluxes are less so. Within anoxic soils, alternative electron acceptors such as iron and humic substances influence microbial metabolic function, and thus affect the amount of carbon lost as methane (CH₄). We present three years of data from wet sedge tundra landscapes near Barrow, Alaska that show an inverse relationship between dissolved iron and CH₄ concentrations. We found increasing organic layer thickness related to increases in active layer organic matter content, and decreases in both bulk density and extractable iron. Organic layer depth was also a good proxy for carbon dioxide (CO₂) and CH₄ dynamics, with increasing organic layer depths relating to lower dissolved iron, higher amounts of dissolved CH₄, and lower CO₂:CH₄ ratios in the upper active layer. Net CH₄ fluxes were also significantly suppressed following the experimental addition of iron and humic acids. Iron and humic acid treatment effects were indistinguishable for CH₄ net flux; in contrast, post-treatment CH₄ fluxes were an average of 0.74-fold the control treatment flux rates. These results suggest that in-situ CH₄ production is tied to alternative electron acceptor availability, and that organic layer thickness is a good predictor of biogeochemical controls on CH₄ fluxes in wet-sedge Arctic Alaskan tundra.     

广义模糊综合决策方法选择杉木采伐迹地更新类型

本文应用广义模糊综合决策方法,B=A*R公式,建立各因素的函数式,计算彼此间的隶属程度,并经归一化计算各因素的综合决断,为杉木采伐迹地更新类型的选择,提供可比较的数量值.     

Multiyear greenhouse gas flux measurements on a temperate fen soil used for cropland or grassland

To date there is still a lack of reliable data on greenhouse gas emissions from drained fens needed to determine the climatic relevance of land use and land use change on peatlands and to supply the National Inventory Report for the German Greenhouse Gas Inventory. In this study we present the results of monthly‐based multiyear measurements of CO₂, N₂O and CH₄ flux rates in two drained agriculturally used fen ecosystems in NW Germany (cropland and grassland) over a period of 4.5 y using transparent and opaque closed chambers. CO₂ exchange was modelled at high resolution with temperature and photosynthetic active radiation. The measured and modelled values fit very well (R² ≥ 0.93). Annual GHG and Global Warming Potential (GWP) balances were determined. Net CO₂ emissions at the cropland and grassland sites were similarly high, taking into account changes in management; net ecosystem C balance amounted to about 4.0 to 5.0 Mg C ha^?1 y^?1. Emissions of N₂O and CH₄ were low at both sites. The mean GWP balance for a time frame of 100 y (GWP100) amounted to about 17.0 to 19.0 Mg CO₂‐eq. ha^?1 y^?1. The unexpectedly low greenhouse gas emissions from the cropland site are attributed to the high water table and a change in crop management. The change from corn for silage to corn‐cob mix lead transiently to rather small greenhouse gas emissions. The study confirms the need for multiyear measurements taking climatic and management variation into account.     

STUDY ON THE CUTOVER LAND OF THE HARDWOODKOREAN PINE FOREST FOR REPRODUCTION IN THE XIAOXINGAN MOUNTAINS OF NORTHEAST CHINA

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