A global analysis of root distributions for terrestrial biomes

Understanding and predicting ecosystem functioning (e.g., carbon and water fluxes) and the role of soils in carbon storage requires an accurate assessment of plant rooting distributions. Here, in a comprehensive literature synthesis, we analyze rooting patterns for terrestrial biomes and compare distributions for various plant functional groups. We compiled a database of 250 root studies, subdividing suitable results into 11 biomes, and fitted the depth coefficient to the data for each biome (Gale and Grigal 1987). is a simple numerical index of rooting distribution based on the asymptotic equation Y=1-^d, where d = depth and Y = the proportion of roots from the surface to depth d. High values of correspond to a greater proportion of roots with depth. Tundra, boreal forest, and temperate grasslands showed the shallowest rooting profiles (=0.913, 0.943, and 0.943, respectively), with 80–90% of roots in the top 30 cm of soil; deserts and temperate coniferous forests showed the deepest profiles (=0.975 and 0.976, respectively) and had only 50% of their roots in the upper 30 cm. Standing root biomass varied by over an order of magnitude across biomes, from approximately 0.2 to 5 kg m^-2. Tropical evergreen forests had the highest root biomass (5 kg m^-2), but other forest biomes and sclerophyllous shrublands were of similar magnitude. Root biomass for croplands, deserts, tundra and grasslands was below 1.5 kg m^-2. Root/shoot (R/S) ratios were highest for tundra, grasslands, and cold deserts (ranging from 4 to 7); forest ecosystems and croplands had the lowest R/S ratios (approximately 0.1 to 0.5). Comparing data across biomes for plant functional groups, grasses had 44% of their roots in the top 10 cm of soil. (=0.952), while shrubs had only 21% in the same depth increment (=0.978). The rooting distribution of all temperate and tropical trees was =0.970 with 26% of roots in the top 10 cm and 60% in the top 30 cm. Overall, the globally averaged root distribution for all ecosystems was =0.966 (r ²=0.89) with approximately 30%, 50%, and 75% of roots in the top 10 cm, 20 cm, and 40 cm, respectively. We discuss the merits and possible shortcomings of our analysis in the context of root biomass and root functioning.     

Lidar remote sensing of above-ground biomass in three biomes

Estimation of the amount of carbon stored in forests is a key challenge for understanding the global carbon cycle, one which remote sensing is expected to help address. However, estimation of carbon storage in moderate to high biomass forests is difficult for conventional optical and radar sensors. Lidar (light detection and ranging) instruments measure the vertical structure of forests and thus hold great promise for remotely sensing the quantity and spatial organization of forest biomass. In this study, we compare the relationships between lidar‐measured canopy structure and coincident field measurements of above‐ground biomass at sites in the temperate deciduous, temperate coniferous, and boreal coniferous biomes. A single regression for all three sites is compared with equations derived for each site individually. The single equation explains 84% of variance in above‐ground biomass (P < 0.0001) and shows no statistically significant bias in its predictions for any individual site.     

Large altitudinal increase in tree root/shoot ratio in tropical mountain forests of Ecuador

Tropical rain forests decrease in tree height and aboveground biomass (AGB) with increasing elevation. The causes of this phenomenon remain insufficiently understood despite a number of explanations proposed including direct or indirect effects of low temperature on carbon acquisition and carbon investment, adverse soil conditions and impaired nutrient supply. For analysing altitudinal patterns of aboveground/belowground carbon partitioning, we measured fine (<2 mm in diameter) and coarse root (2–5 mm) biomass and necromass and leaf area index (LAI), and estimated AGB from stand structural parameters in five tropical mountain rain forests at 1050, 1540, 1890, 2380 and 3060 m along an altitudinal transect in the South Ecuadorian Andes. Average tree height and AGB were reduced to less than 50% between 1050 and 3060 m, LAI decreased from 5.1 to 2.9. The leaf area reduction must have resulted in a lowered canopy carbon gain and thus may partly explain the reduced tree growth in the high-elevation stands. In contrast, both fine and coarse root biomass significantly increased with elevation across this transect. The ratio of root biomass (fine and coarse) to AGB increased more than ten-fold from 0.04 at 1050 m to 0.43 at 3060 m. Under the assumption that fine root biomass does reflect root productivity, our data indicate a marked belowground shift in C allocation with increasing elevation. Possible explanations for this allocation shift are discussed including reduced N supply due to low temperatures, water logging or adverse soil chemical conditions. We conclude that the fine root system and its activity may hold the key for understanding the impressive reduction in tree size along tropical mountain slopes in Ecuador. Analyses of fine root turnover and longevity in relation to environmental factors along altitudinal transects in tropical mountains are urgently needed.     

Global response of terrestrial ecosystem structure and function to CO2 and climate change: results from six dynamic global vegetation models

The possible responses of ecosystem processes to rising atmospheric CO₂ concentration and climate change are illustrated using six dynamic global vegetation models that explicitly represent the interactions of ecosystem carbon and water exchanges with vegetation dynamics. The models are driven by the IPCC IS92a scenario of rising CO₂ ( Wigley et al. 1991 ), and by climate changes resulting from effective CO₂ concentrations corresponding to IS92a, simulated by the coupled ocean atmosphere model HadCM2‐SUL. Simulations with changing CO₂ alone show a widely distributed terrestrial carbon sink of 1.4–3.8 Pg C y^?1 during the 1990s, rising to 3.7–8.6 Pg C y^?1 a century later. Simulations including climate change show a reduced sink both today (0.6–3.0 Pg C y^?1) and a century later (0.3–6.6 Pg C y^?1) as a result of the impacts of climate change on NEP of tropical and southern hemisphere ecosystems. In all models, the rate of increase of NEP begins to level off around 2030 as a consequence of the ‘diminishing return’ of physiological CO₂ effects at high CO₂ concentrations. Four out of the six models show a further, climate‐induced decline in NEP resulting from increased heterotrophic respiration and declining tropical NPP after 2050. Changes in vegetation structure influence the magnitude and spatial pattern of the carbon sink and, in combination with changing climate, also freshwater availability (runoff). It is shown that these changes, once set in motion, would continue to evolve for at least a century even if atmospheric CO₂ concentration and climate could be instantaneously stabilized. The results should be considered illustrative in the sense that the choice of CO₂ concentration scenario was arbitrary and only one climate model scenario was used. However, the results serve to indicate a range of possible biospheric responses to CO₂ and climate change. They reveal major uncertainties about the response of NEP to climate change resulting, primarily, from differences in the way that modelled global NPP responds to a changing climate. The simulations illustrate, however, that the magnitude of possible biospheric influences on the carbon balance requires that this factor is taken into account for future scenarios of atmospheric CO₂ and climate change.     

Above‐ and Belowground Carbon Stocks in a Miombo Woodland Landscape of Mozambique

Quantifying ecosystem carbon stocks is vital for understanding the relationship between changes in land use and carbon dioxide emissions. Here, we estimate carbon stocks in an area of miombo woodland in Mozambique, by identifying the major carbon stocks and their variability. Data on the biomass of tree stems and roots, saplings, and soil carbon stocks are reported and compared with other savannas systems around the globe. A new allometric relationship between stem diameter and tree stem and root biomass is presented, based on the destructive harvest of 29 trees. These allometrics are combined with an inventory of 12,733 trees on 58 plots over an area of 27 ha. Ecosystem carbon stocks totaled 110 tC/ha, with 76 tC/ha in the soil carbon pool (to 50 cm depth), 21.2 tC/ha in tree stem biomass, 8.5 tC/ha in tree coarse root biomass, and 3.6 tC/ha in total sapling biomass. Plot‐level tree root:stem (R:S) ratio varied from 0.27 to 0.58, with a mean of 0.42, slightly higher than the mean reported for 18 other savanna sites with comparable aboveground biomass (R:S=0.35). Tree biomass (stem+root) ranged from 3.1 to 86.5 tC/ha, but the mean (32.1 tC/ha) was well constrained (95% CI 28–36.6). In contrast, soil carbon stocks were almost uniformly distributed and varied from 32 to 133 tC/ha. Soil carbon stocks are thus the major uncertainty in the carbon storage of these woodlands. Soil texture explained 53 percent of the variation in soil carbon content, but only 13 percent of the variation in woody carbon stocks. The history of disturbance (fire, elephants, logging/charcoal production, and shifting cultivation) is likely to decouple changes in woody carbon stocks from soil carbon stocks, mediated by tree–grass interactions. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .     

黄土高原退耕还草地植物群落动态对生态系统碳储量的影响

退化农地通过植被恢复能够提高生态系统的固碳能力,但是植被恢复中植物群落特征如何影响生态系统碳储量仍存在不确定性。以农田为对照,选取自然恢复8、15、25、35 a草地为对象,探讨退耕还草地植物群落特征对生态系统碳储量的影响。结果表明：群落盖度随着恢复年限的增加而显著增加,恢复35 a时达到最大值（64.0%）,优势种从达乌里胡枝子、赖草、茵陈蒿演变为长芒草、铁杆蒿;禾草类、多年生草本和灌木逐渐成为优势种。Shannon-Weiner指数、Patrick指数均呈先上升后下降的趋势,均在第15年达到最大值。地上植被碳储量和地下植被碳储量在恢复期间呈直线增加的趋势,且均在35 a达最大值,分别为0.83 Mg C/hm²、1.49 Mg C/hm²,而凋落物碳储量在第25年达到最大值,为0.40 Mg C/hm²。土壤碳储量与有机碳含量总体呈先下降后上升的趋势,在第8年达到最低值,在第35年恢复到农田水平之上,占生态系统碳储量的93.3%-99.6%;表层0-10 cm土壤碳储量占0-30 cm碳储量的38.9%-50.3%,呈表聚现象。生态系统碳储量与土壤碳储量趋势一致,即恢复到第8年最低,为24.32 Mg C/hm²,恢复到第35年最高,为43.70 Mg C/hm²。群落盖度、地上生物量、凋落物生物量、禾草、豆科以及多年生植物的重要值与生态系统碳储量呈显著正相关（P<0.05）,杂草和一年生植物重要值与生态系统碳储量呈显著负相关（P<0.05）。研究表明植被群落组成的动态变化通过增加植被碳储量和土壤碳储量实现生态系统碳储量的增加,而多年生植物、杂草与禾草的重要值和地下生物量与凋落物生物量是影响生态系统碳储量的重要植被因子。     

Root:shoot ratios of old and modern,tall and semi-dwarf wheats in a mediterranean environment

A field study tested the hypothesis that modern wheat varieties invest a lesser proportion of the total dry matter (root plus shoot) in the root system compared to old varieties. The study was carried out on a duplex soil (sand over clay) at Merredin, Western Australia in a Mediterranean type environment. We also compared the root:shoot dry matter ratios of near-isogenic lines for Rht dwarfing genes.Root:shoot ratios decreased with crop growth stage and were closely related to the developmental pattern of a variety. All varieties appeared to accumulate more dry matter into shoots after the terminal spikelet stage. For the modern variety Kulin this occurred as early as 55 days after sowing (DAS), but did not occur until 90 DAS in the old variety Purple Straw. For all varieties, root dry matter reached its maximum at anthesis, while shoot dry matter continued to increase till maturity. At anthesis there were no significant differences in shoot dry matter between varieties, but from Purple Straw to Kulin root dry matter and thus root:shoot ratio decreased.The tall and dwarf isogenic lines had similar developmental and root:shoot dry matter accumulation patterns.At anthesis, the old variety Purple Straw had significantly higher root dry matter and root length density in the top 40-cm of the profile than modern variety Kulin. There were no varietal differences in rooting depth, water extraction or water use. At maturity about 30% of the total dry matter was invested in the roots among wheat varieties. Grain yield, harvest index (HI) and water use efficiency of grain (WUE_gr) increased from old to modern varieties.The reduced investment of dry matter in the root system and thus the lower root:shoot ratio from early in the growing season may partly explain the increased HI and WUE_gr of modern compared to old varieties.     

Solar‐induced chlorophyll fluorescence is strongly correlated with terrestrial photosynthesis for a wide variety of biomes: First global analysis based on OCO‐2 and flux tower observations

Solar‐induced chlorophyll fluorescence (SIF) has been increasingly used as a proxy for terrestrial gross primary productivity (GPP). Previous work mainly evaluated the relationship between satellite‐observed SIF and gridded GPP products both based on coarse spatial resolutions. Finer resolution SIF (1.3 km × 2.25 km) measured from the Orbiting Carbon Observatory‐2 (OCO‐2) provides the first opportunity to examine the SIF–GPP relationship at the ecosystem scale using flux tower GPP data. However, it remains unclear how strong the relationship is for each biome and whether a robust, universal relationship exists across a variety of biomes. Here we conducted the first global analysis of the relationship between OCO‐2 SIF and tower GPP for a total of 64 flux sites across the globe encompassing eight major biomes. OCO‐2 SIF showed strong correlations with tower GPP at both midday and daily timescales, with the strongest relationship observed for daily SIF at the 757 nm (R² = 0.72, p < 0.0001). Strong linear relationships between SIF and GPP were consistently found for all biomes (R² = 0.57–0.79, p < 0.0001) except evergreen broadleaf forests (R² = 0.16, p < 0.05) at the daily timescale. A higher slope was found for C₄ grasslands and croplands than for C₃ ecosystems. The generally consistent slope of the relationship among biomes suggests a nearly universal rather than biome‐specific SIF–GPP relationship, and this finding is an important distinction and simplification compared to previous results. SIF was mainly driven by absorbed photosynthetically active radiation and was also influenced by environmental stresses (temperature and water stresses) that determine photosynthetic light use efficiency. OCO‐2 SIF generally had a better performance for predicting GPP than satellite‐derived vegetation indices and a light use efficiency model. The universal SIF–GPP relationship can potentially lead to more accurate GPP estimates regionally or globally. Our findings revealed the remarkable ability of finer resolution SIF observations from OCO‐2 and other new or future missions (e.g., TROPOMI, FLEX) for estimating terrestrial photosynthesis across a wide variety of biomes and identified their potential and limitations for ecosystem functioning and carbon cycle studies.     

Genetic variation in pea (Pisum sativum L.) demonstrates the importance of root but not shoot C/N ratios in the control of plant morphology and reveals a unique relationship between shoot length and nodulation intensity

Nodule numbers are regulated through systemic auto‐regulatory signals produced by shoots and roots. The relative effects of shoot and root genotype on nodule numbers together with relationships to organ biomass, carbon (C) and nitrogen (N) status, and related parameters were measured in pea (Pisum sativum) exploiting natural genetic variation in maturity and apparent nodulation intensity. Reciprocal grafting experiments between the early (Athos), intermediate (Phönix) and late (S00182) maturity phenotypes were performed and Pearson's correlation coefficients for the parameters were calculated. No significant correlations were found between shoot C/N ratios and plant morphology parameters, but the root C/N ratio showed a strong correlation with root fresh and dry weights as well as with shoot fresh weight with less significant interactions with leaf number. Hence, the root C/N ratio rather than shoot C/N had a predominant influence on plant morphology when pea plants are grown under conditions of symbiotic nitrogen supply. The only phenotypic characteristic that showed a statistically significant correlation with nodulation intensity was shoot length, which accounted for 68.5% of the variation. A strong linear relationship was demonstrated between shoot length and nodule numbers. Hence, pea nodule numbers are controlled by factors related to shoot extension, but not by shoot or root biomass accumulation, total C or total N. The relationship between shoot length and nodule numbers persisted under field conditions. These results suggest that stem height could be used as a breeding marker for the selection of pea cultivars with high nodule numbers and high seed N contents.     

陆生植物生物量分配对模拟氮沉降响应的Meta分析

分析了陆生植物地上、地下各组织中生物量分配对氮沉降的响应,为研究大气氮沉降背景下陆地生态系统的碳、氮循环过程及植物生物量分配、立木收获、定向培育等相关研究和实践提供参考依据。共收集整理了国内外63篇论文的原始数据资料进行Meta分析(Meta-analysis),用以定量评估氮沉降对植物生物量分配的影响,并通过亚组分析进一步探讨了不同生态系统类型、植物种类、氮肥形式、施氮水平和持续时间对生物量分配的影响。结果表明,总体来看施氮会显著促进植物地上部分生物量分配,植物叶生物量和茎生物量在施氮条件下均显著增加;然而地下生物量所受促进作用要低于地上部分,表现为植物细根生物量和粗根生物量在氮输入下并没有显著变化;植物根冠比在氮沉降下显著降低;叶重比、茎重比和根重比在氮沉降下没有显著变化。此外,亚组分析结果表明生态系统类型和植物类型会显著影响植物总生物量和根冠比对氮沉降的响应,草本植物在氮沉降下的生物量累积明显优于木本,这说明短期氮沉降可能会增加草本的覆盖面积;施肥形式对根冠比的影响存在明显差异,相比于尿素,硝酸铵对植物根冠比的作用更显著;不同施氮水平显著影响地上生物量分配,中氮水平(本研究为60—120 kg hm-2a-1)促进作用最大,高氮水平(本研究为≥120 kg hm-2a-1)促进作用明显减弱,这与总生物量的变化一致,表明过高的氮沉降量将抑制植物生长;氮沉降处理时间长短对植物地上生物量的影响也存在显著差异,当施氮时间高于3年,氮沉降对地上生物量的促进作用几乎消失。总之,短期氮沉降会使植物分配更多生物量给地上部分,且氮沉降对草本植物生物量的累积作用明显优于木本,这些发现可为未来大气氮沉降背景下植物地上、地下部分碳存储、植物群落结构、植被动态等相关研究提供科学依据。     

实验增温对陆地生态系统根系生物量的影响

根系是植物吸收土壤水分和养分的重要器官, 驱动着多个生态系统过程, 该研究揭示了实验增温对根系生物量的影响及机制, 可为气候变暖背景下土壤碳动态和生态系统过程的变化提供理论依据。该研究从已发表的151篇国内外研究论文中收集到611组数据, 通过整合分析(meta-analysis)方法研究了实验增温对根系生物量(根系总生物量、粗根生物量、细根生物量、根冠比)的影响, 并探讨了增温幅度、增温年限、增温方式的影响, 以及根系生物量对增温的响应与本底环境条件(生态系统类型、年平均气温、年降水量、干旱指数)的关系。结果表明: (1)模拟增温使细根生物量显著增加8.87%, 而对根系总生物量、粗根生物量、根冠比没有显著影响; (2)中等强度增温(1-2 ℃)使得细根生物量和根冠比分别提高14.57%和23.63%; 中短期增温实验(<5年)对细根生物量具有促进影响, 而长期增温实验(≥5年)使细根生物量有降低的趋势; 开顶箱增温和红外辐射增温分别使细根生物量显著提高了17.50%和12.16%, 而电缆加热增温使细根生物量和粗根生物量显著降低了23.44%和43.23%; (3)不同生态系统类型对于增温响应不一致, 模拟增温使苔原生态系统细根生物量显著提高了21.03%, 细根生物量对增温的响应与本底年平均气温、年降水量、干旱指数均呈显著负相关关系。     

Pollen-based reconstructions of Japanese biomes at 0, 6000 and 18,000 14C yr bp

A biomization method, which objectively assigns individual pollen assemblages to biomes ( Prentice et al., 1996 ), was tested using modern pollen data from Japan and applied to fossil pollen data to reconstruct palaeovegetation patterns 6000 and 18,000 ¹⁴C yr bp Biomization started with the assignment of 135 pollen taxa to plant functional types (PFTs), and nine possible biomes were defined by specific combinations of PFTs. Biomes were correctly assigned to 54% of the 94 modern sites. Incorrect assignments occur near the altitudinal limits of individual biomes, where pollen transport from lower altitudes blurs the local pollen signals or continuous changes in species composition characterizes the range limits of biomes. As a result, the reconstructed changes in the altitudinal limits of biomes at 6000 and 18,000 ¹⁴C yr bp are likely to be conservative estimates of the actual changes. The biome distribution at 6000 ¹⁴C yr bp was rather similar to today, suggesting that changes in the bioclimate of Japan have been small since the mid‐Holocene. At 18,000 ¹⁴C yr bp the Japanese lowlands were covered by taiga and cool mixed forests. The southward expansion of these forests and the absence of broadleaved evergreen/warm mixed forests reflect a pronounced year‐round cooling.     

Data gaps in anthropogenically driven local‐scale species richness change studies across the Earth's terrestrial biomes

There have been numerous attempts to synthesize the results of local‐scale biodiversity change studies, yet several geographic data gaps exist. These data gaps have hindered ecologist's ability to make strong conclusions about how local‐scale species richness is changing around the globe. Research on four of the major drivers of global change is unevenly distributed across the Earth's biomes. Here, we use a dataset of 638 anthropogenically driven species richness change studies to identify where data gaps exist across the Earth's terrestrial biomes based on land area, future change in drivers, and the impact of drivers on biodiversity, and make recommendations for where future studies should focus their efforts. Across all drivers of change, the temperate broadleaf and mixed forests and the tropical moist broadleaf forests are the best studied. The biome–driver combinations we have identified as most critical in terms of where local‐scale species richness change studies are lacking include the following: land‐use change studies in tropical and temperate coniferous forests, species invasion and nutrient addition studies in the boreal forest, and warming studies in the boreal forest and tropics. Gaining more information on the local‐scale effects of the specific human drivers of change in these biomes will allow for better predictions of how human activity impacts species richness around the globe.     

高寒草甸主要植物地上地下生物量分布及退化对根冠比和根系表面积的影响

研究高寒草甸主要植物地上地下生物量的分布及其对退化的响应有利于了解高寒草甸的退化过程。该研究首先在西藏那曲生态环境综合观测研究站小嵩草围栏内(2009年围封)选择原生植被较好的地点随机选择小嵩草(Kobresia pygmaea)、矮嵩草(K.humilis)、紫花针茅(Stipa purpurea)、二裂委陵菜(Potentila bifurca)和青藏苔草(Carex moorcroftii)等5种植物斑块,选择退化斑块上(与原生植被相比)的二裂委陵菜和青藏苔草;然后用烘箱烘至恒重并称重,用扫描仪对根系进行扫描用于估算根系表面积;最后利用2因子方差分析检验不同物种个体、不同取样层次对地上和地下生物量的影响,利用物种和退化状态2因子方差分析检验对地上生物量的影响,以及利用物种、取样层次和退化状态3因子方差分析检验对二裂委陵菜和青藏苔草地下生物量、根冠比和根系表面积的影响。结果表明:在未退化条件下,小嵩草、矮嵩草和紫花针茅0~10cml地下生物量占0~30cm地下生物量的70%以上,0~30cm地下生物量占其地上地下总生物量的96%以上;二裂委陵菜(Potentilla bifurca)和青藏苔草(Carex moorcroftii)0~10cm地下生物量占0~30cml地下生物量的50%以上,其中二裂委陵菜0~30cm地下生物量占其地上地下总生物量的57%,青藏苔草0~30cm地下生物量占其地上地下总生物量的87%;对于退化草甸的主要植物,退化显著降低了二裂委陵菜的地上生物量、地下生物量和根冠比,对其根系表面积影响不大,但显著增加了青藏苔草的地上生物量,降低了其根冠比,对其地下生物量和根系表面积影响不大。     

Loss of dry matter and cell contents from fibrous roots of sugar beet due to sampling,storage and washing

To obtain correction factors for estimating root dry weight from washed samples and to test the efficiency of various procedures for storing root samples, dry matter losses were determined by simulating root washing methods with roots obtained from a nutrient culture. For sugar beet dry matter losses were higher than values previously found for wheat and ryegrass: about 30% for the procedure normally used and about 40% for samples pretreated with sodium pyrophosphate. The largest share of water-soluble sugars was lost from root samples within one day of storing roots. The N content of roots expressed on the basis of remaining dry matter rose first during handling of the root samples and decreased in samples stored for a longer period. In most cases no cell wall material (cellulose and lignin) is lost from the root samples; expressed on the basis of remaining dry weight the contents consequently rose.Communication no. 2 of the Dutch Programme on Soil Ecology of Arable Farming Systems     

Nutrients associated with terrestrial dissolved organic matter drive changes in zooplankton:phytoplankton biomass ratios in an alpine lake

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Regulation of shoot/root ratio by cytokinins from roots inUrtica dioica: Opinion

According to current knowledge, cytokinins are predominantly root-born phytohormones which are transported into the shoot by the transpiration stream. In the hormone message concept they are considered the root signals, which mediate the flux of the photosynthates to the various sinks of the plant. In this review, experiments are assessed, in which changes of the shoot to root ratio of biomass, caused by different levels of nitrogen supply to a model plant,Urtica dioica, could be traced to the natural cytokinin relations of the plant. Disturbance of the internal cytokinin balance of the plant resulted in a disproportionate distribution of the assimilates in favour of the cytokinin-enriched shoot. Inspite of some shortcomings of the hormone message concept, the presented work corroborates the significance of root-sourced cytokinins in the regulation of biomass partitioning between shoot and root.     

Organic fertilizer applications influence on the shoot and root biomass production and plant nutrient of Calopogonium mucunoides from crude oil-contaminated soils

The impact of crude oil-contaminated soil on the shoot and root biomass yield and nutrients uptake of Calopogonium mucunoides Desv. using two types of composted manure (COM) as soil amendments were investigated. This was with a view to assessing the growth response of the test plant under different levels of crude oil soil contamination. Five levels [0, 2.5, 5, 10, and 20% (v/v)] of crude oil, each was replicated thrice to contaminate 3 kg of soil when 12 g pot^?1 COM; 12 g pot^?1 neem-fortified composted manure (NCM) and control, soil without manure application (C) were imposed as manure treatments. The mean fresh shoot biomass yield at zero crude oil soil contamination and with COM application was 2.67 g pot^?1. This value was significantly (p < 0.05) higher than 2.05 g pot^?1 for NCM and 1.67 g pot^?1 for the control. Also, the mean fresh root yield at zero crude oil soil contamination with COM application was 4.02 g pot^?1. This value was significantly (p < 0.05) higher than 2.41 g pot^?1 for NCM and 1.71 g pot^?1 for the control. The dry shoot and root biomass yield followed similar pattern. The shoot and root yield of C. mucunoides significantly (p < 0.05) reduced with increase in crude oil soil contamination. The nutrients uptake of C. mucunoides, particularly N, P, Ca, Mg, and Fe, were enhanced with COM fertilization having higher available P, K, and Na values; and by implication, suggesting the importance of adequately formulated composted manure usage in the rehabilitation studies of crude oil-contaminated soil.     

Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes

Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide. Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.