Shallow Rooting Depth Research Articles

Chromosome groups 5, 6 and 7 harbor major quantitative trait loci controlling root traits in bread wheat (Triticum aestivum L.).

Identifying genomic regions for root traits in bread wheat can help breeders develop climate-resilient and high-yielding wheat varieties with desirable root traits. This study used the recombinant inbred line (RIL) population of Synthetic W7984 × Opata M85 to identify quantitative trait loci (QTL) for different root traits such as rooting depth (RD), root dry mass (RM), total root length (RL), root diameter (Rdia) and root surface areas (RSA1 for coarse roots and RSA2 for fine roots) under controlled conditions in a semi-hydroponic system. We detected 14 QTL for eight root traits on nine wheat chromosomes; we discovered three QTL each for RD and RSA1, two QTL each for RM and RSA2, and one QTL each for RL, Rdia, specific root length and nodal root number per plant. The detected QTL were concentrated on chromosome groups 5, 6 and 7. The QTL for shallow RD (Q.rd.uwa.7BL: Xbarc50) and high RM (Q.rm.uwa.6AS: Xgwm334) were validated in two independent F2 populations of Synthetic W7984 × Chara and Opata M85 × Cascade, respectively. Genotypes containing negative alleles for Q.rd.uwa.7BL had 52% shallower RD than other Synthetic W7984 × Chara population lines. Genotypes with the positive alleles for Q.rm.uwa.6AS had 31.58% higher RM than other Opata M85 × Cascade population lines. Further, we identified 21 putative candidate genes for RD (Q.rd.uwa.7BL) and 13 for RM (Q.rm.uwa.6AS); TraesCS6A01G020400, TraesCS6A01G024400 and TraesCS6A01G021000 identified from Q.rm.uwa.6AS, and TraesCS7B01G404000, TraesCS7B01G254900 and TraesCS7B01G446200 identified from Q.rd.uwa.7BL encoded important proteins for root traits. We found germin-like protein encoding genes in both Q.rd.uwa.7BL and Q.rm.uwa.6AS regions. These genes may play an important role in RM and RD improvement. The identified QTL, especially the validated QTL and putative candidate genes are valuable genetic resources for future root trait improvement in wheat.

Managing Sands of the Lower Mekong Basin to Limit Land Degradation: A Review of Properties and Limitations for Crop and Forage Production

Land development is rapidly occurring on sand-dominant soils that cover substantial areas of the Lower Mekong Basin (LMB). Sands are at risk of degradation on sloping uplands where agriculture is expanding and on lowland landscapes where intensification of cropping is occurring. Sandstone and granitic geology explain the prevalence of sand-dominant textures of profiles in the LMB. However, the sand terrains in uplands of Cambodia and Southern Laos mostly have not been mapped in detail and the diversity of their edaphic properties is poorly understood. On high-permeability sands, lowland rainfed rice crops are drought-prone, while nutrient losses from leaching are also a risk. Furthermore, waterlogging, inundation and subsoil hardpans are significant hazards that influence the choice of crops and forages for lowland soils. Soil acidity, low nutrient status, hard-setting and shallow rooting depth are significant constraints for crops and forages on sands in the lowlands. Land use change in the lowlands to alternative field crops and forages on sands is contingent on their profitability relative to rice, the amounts and reliability of early wet season rainfall, and the amounts of stored water available after harvesting rice. Low soil fertility and soil acidity are limitations to the productivity of farming systems on the sand profiles in uplands, while erosion, low soil organic matter levels and water balance are concerns for their sustainable use. Site-/soil-specific fertilizer and lime management, land suitability assessment and the use of conservation agriculture principles (minimum tillage and crop residue retention) can overcome some of these constraints.

The other side of tropical forest drought: do shallow water table regions of Amazonia act as large-scale hydrological refugia from drought?

Tropical forest function is of global significance to climate change responses, and critically determined by water availability patterns. Groundwater is tightly related to soil water through the water table depth (WT), but historically neglected in ecological studies. Shallow WT forests (WT < 5 m) are underrepresented in forest research networks and absent in eddy flux measurements, although they represent c. 50% of the Amazon and are expected to respond differently to global-change-related droughts. We review WT patterns and consequences for plants, emerging results, and advance a conceptual model integrating environment and trait distributions to predict climate change effects. Shallow WT forests have a distinct species composition, with more resource-acquisitive and hydrologically vulnerable trees, shorter canopies and lower biomass than deep WT forests. During 'normal' climatic years, shallow WT forests have higher mortality and lower productivity than deep WT forests, but during moderate droughts mortality is buffered and productivity increases. However, during severe drought, shallow WT forests may be more sensitive due to shallow roots and drought-intolerant traits. Our evidence supports the hypothesis of neglected shallow WT forests being resilient to moderate drought, challenging the prevailing view of widespread negative effects of climate change on Amazonian forests that ignores WT gradients, but predicts they could collapse under very strong droughts.

Vegetation and hydrology stratification as proxies to estimate methane emission from tidal marshes

Direct measurement of methane emissions is cost-prohibitive for greenhouse gas offset projects, necessitating the development of alternative accounting methods such as proxies. Salinity is a useful proxy for tidal marsh CH4 emissions when comparing across a wide range of salinity regimes but does not adequately explain variation in brackish and freshwater regimes, where variation in emissions is large. We sought to improve upon the salinity proxy in a marsh complex on Deal Island Peninsula, Maryland, USA by comparing emissions from four strata differing in hydrology and plant community composition. Mean CH4 chamber-collected emissions measured as mg CH4 m−2 h−1 ranked as S. alterniflora (1.2 ± 0.3) ≫ High-elevation J. roemerianus (0.4 ± 0.06) > Low-elevation J. roemerianus (0.3 ± 0.07) = S. patens (0.1 ± 0.01). Sulfate depletion generally reflected the same pattern with significantly greater depletion in the S. alterniflora stratum (61 ± 4%) than in the S. patens stratum (1 ± 9%) with the J. roemerianus strata falling in between. We attribute the high CH4 emissions in the S. alterniflora stratum to sulfate depletion likely driven by limited connectivity to tidal waters. Low CH4 emissions in the S. patens stratum are attributed to lower water levels, higher levels of ferric iron, and shallow rooting depth. Moderate CH4 emissions from the J. roemerianus strata were likely due to plant traits that favor CH4 oxidation over CH4 production. Hydrology and plant community composition have significant potential as proxies to estimate CH4 emissions at the site scale.

The impact of land use on future water balance - A simple approach for analysing climate change effects

Regional climate change projections for Europe agree in predicting a statistically significant warming in all seasons. The most significant climate change effect is its impact on water cycle through altering precipitation patterns and evapotranspiration processes at multiple scales. The anticipated changes in the distribution and precipitation amounts together with continuously increasing temperatures may induce a higher rate of water consumption in plants, which can generate changes in soil moisture, groundwater, and the water cycle. Thus, climate change can cause changes in the water balance equations structure. A Thornthwaite-type monthly step water balance model was established to compare the water balance in three different surface land cover types: (i) a natural forested area; (ii) a parcel with mixed surface cover; (iii) an agricultural area. The key parameter of the model is the water storage capacity of the soil. Maximal rooting depth of the given area is also determinable during the calibration process using actual evapotranspiration (AET) and soil physical data. The locally calibrated model was employed for assessing future AET and soil moisture of selected land cover types using data from four bias-corrected regional climate models. The projections demonstrate increasing actual evapotranspiration values in each surface cover type at the end of the 21st century. Regarding the 10th percentile minimum soil moisture values, the forested area displayed an increasing trend, while the agricultural field and mixed parcel showed a strong decrease. The 30-year monthly means of evapotranspiration shows the maximum values in June and July, while the minimum soil moisture in September. Water stress analysis indicates water stress is expected to occur only in the agricultural field during the 21st century. The comparison of the three surface covers reveals that forest has the greatest soil water storage capacity due to the highest rooting depth. Thus, according to the projections for 21st century, less water stress is predicted to occur at the forested area compared to the other two surface covers which shows shallow rooting depth.

Modelling the Interactions of Soils, Climate, and Management for Grass Production in England and Wales

This study examines the effectiveness of a model called LINGRA-N-Plus to simulate the interaction of climate, soil and management on the green leaf and total dry matter yields of ryegrass in England and Wales. The LINGRA-N-Plus model includes modifications of the LINGRA-N model such as temperature- and moisture-dependent soil nitrogen mineralization and differential partitioning to leaves and stems with thermal time from the last harvest. The resulting model was calibrated against the green leaf and total grass yields from a harvest interval x nitrogen application experiment described by Wilman et al. (1976). When the LINGRA-N-Plus model was validated against total grass yields from nitrogen experiments at ten sites described by Morrison et al. (1980), its modelling efficiency improved greatly compared to the original LINGRA-N. High predicted yields, at zero nitrogen application, were related to soils with a high initial nitrogen content. The lowest predicted yields occurred at sites with low rainfall and shallow rooting depth; mitigating the effect of drought at such sites increased yields by up to 4 t ha−1. The results highlight the usefulness of grass models, such as LINGRA-N-Plus, to explore the combined effects of climate, soil, and management, like nitrogen application, and harvest intervals on grass productivity.

Agricultural drainage increases the photosynthetic capacity of boreal peatlands

A drained boreal bog with active drainage ditches and the introduction of forage grass was compared with a natural bog site to assess the effect of agricultural drainage on the photosynthetic capacity of boreal peatlands. In this study, the net carbon dioxide uptake and the ecosystem respiration were measured using a pair of clear and dark chambers, connected to a greenhouse gas analyzer in order to estimate the gross primary production (GPP). Environmental factors, including photosynthetically active radiation (PAR), peat soil temperature, soil moisture, electrical conductivity and water table depth (WTD), and dissolved organic carbon (DOC) in the soil pore water were also investigated at each site. Our results confirmed a correlation between water table depth, peat soil temperature, electrical conductivity and peatland productivity. Changes in electrical conductivity, water table depth, and peat soil temperature together explained 61% of gross primary productivity variance at our drained peatland pasture site. In general, plant functional types/growth forms did not have any significant difference in their GPP at the drained site except shrubs which had a significantly higher GPP at PAR level greater than 1000 μmol/m2/s (F(3,30.84) = 11.64, p < 0.001). At the natural site, GPP was significantly higher at the hollow (0.168 ± 0.02 mg/m2/s) compared to the hummock (0.098 ± 0.01 mg/m2/s) where relatively the higher WTD was recorded. We therefore concluded that water shortage to the shallow rooting depth of shrubs on our hummock subplots may be the cause of the low productivity. At PAR greater than 1000 μmol/m2/s, productivity at the hollow was still significantly higher (0.17 ± 0.002 mg/m2/s) compared to the hummock (0.10 ± 0.00 mg/m2/s). This suggests that, for ecosystem carbon modelling, the minimum PAR level at which the GPP is estimated is very crucial. All the growth forms at the drained site recorded a significantly higher GPP than the microforms at the natural site. We speculate that not only hydrological changes via agricultural drainage can affect the carbon balance of boreal peatland ecosystem through photosynthesis, but also the hydrological changes in the peat due to the differences in peat soil makeup, structure and density. We, therefore, conclude that differences in microtopography and the corresponding changes in vegetation, land-use practice and its effects on peat soil properties and hydrology should be taken into account when modelling the gross primary production in a peatland ecosystem.

The importance of physiological, structural and trait responses to drought stress in driving spatial and temporal variation in GPP across Amazon forests

Abstract. The capacity of Amazon forests to sequester carbon is threatened by climate-change-induced shifts in precipitation patterns. However, the relative importance of plant physiology, ecosystem structure and trait composition responses in determining variation in gross primary productivity (GPP) remain largely unquantified and vary among models. We evaluate the relative importance of key climate constraints to GPP, comparing direct plant physiological responses to water availability and indirect structural and trait responses (via changes to leaf area index (LAI), roots and photosynthetic capacity). To separate these factors we combined the soil–plant–atmosphere model with forcing and observational data from seven intensively studied forest plots along an Amazon drought stress gradient. We also used machine learning to evaluate the relative importance of individual climate factors across sites. Our model experiments showed that variation in LAI was the principal driver of differences in GPP across the gradient, accounting for 33 % of observed variation. Differences in photosynthetic capacity (Vcmax and Jmax) accounted for 21 % of variance, and climate (which included physiological responses) accounted for 16 %. Sensitivity to differences in climate was highest where a shallow rooting depth was coupled with a high LAI. On sub-annual timescales, the relative importance of LAI in driving GPP increased with drought stress (R2=0.72), coincident with the decreased importance of solar radiation (R2=0.90). Given the role of LAI in driving GPP across Amazon forests, improved mapping of canopy dynamics is critical, opportunities for which are offered by new satellite-based remote sensing missions such as GEDI, Sentinel and FLEX.

Land Evaluation for Alternate Land Use Planning of Soils in Tatrakallu Village of Anantapuramu District, Andhra Pradesh

Twenty-two typical pedons (14 soil series- TTK1 to TTK-14) representing major landforms of Tatrakallu village of Ananatapuramu district of Andhra Pradesh were evaluated by using qualitative and quantitative methods. Three major land capability classes (III, IV and VI) were identified with two sub classes (erosion and wetness). Crop suitability analysis revealed that the village falls under marginally suitable (S3) with limitations of soil fertility, wetness and sodicity and not suitable (N) with limitations of slope, texture shallow rooting depth, sodicity and poor nutrient status. Riquier’s parametric approach was found to be good indicator for identification of production potential. The land evaluation revealed that, suitability and productivity of these soils were highly variable, and hence their management must be site-specific. The suggestion including the crop residue retention, nutrient recycling, minimum tillage, crop rotation, cover crops and intercropping not only helps to conserve soil and water more effectively in soils but also increase organic matter content and improve fertilizer use efficiency. Farmers continued to grow groundnut, pigeonpea, chickpea and castor for many years on marginally suitable as they are not aware of suitable soils for a particular crop. Adoption of suggested ameliorative measures and land use not only improve the yield but also sustain the soil productivity.

Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest

AbstractThe relationship between rooting depth and above‐ground hydraulic traits can potentially define drought resistance strategies that are important in determining species distribution and coexistence in seasonal tropical forests, and understanding this is important for predicting the effects of future climate change in these ecosystems.We assessed the rooting depth of 12 dominant tree species (representingc. 42% of the forest basal area) in a seasonal Amazon forest using the stable isotope ratios (δ18O and δ2H) of water collected from tree xylem and soils from a range of depths. We took advantage of a major ENSO‐related drought in 2015/2016 that caused substantial evaporative isotope enrichment in the soil and revealed water use strategies of each species under extreme conditions. We measured the minimum dry season leaf water potential both in a normal year (2014; Ψnon‐ENSO) and in an extreme drought year (2015; ΨENSO). Furthermore, we measured xylem hydraulic traits that indicate water potential thresholds trees tolerate without risking hydraulic failure (P50and P88).We demonstrate that coexisting trees are largely segregated along a single hydrological niche axis defined by root depth differences, access to light and tolerance of low water potential. These differences in rooting depth were strongly related to tree size; diameter at breast height (DBH) explained 72% of the variation in the δ18Oxylem. Additionally, δ18Oxylemexplained 49% of the variation in P50and 70% of P88, with shallow‐rooted species more tolerant of low water potentials, while δ18O of xylem water explained 47% and 77% of the variation of minimum Ψnon‐ENSOand ΨENSO.We propose a new formulation to estimate an effective functional rooting depth, i.e. the likely soil depth from which roots can sustain water uptake for physiological functions, using DBH as predictor of root depth at this site. Based on these estimates, we conclude that rooting depth varies systematically across the most abundant families, genera and species at the Tapajós forest, and that understorey species in particular are limited to shallow rooting depths.Our results support the theory of hydrological niche segregation and its underlying trade‐off related to drought resistance, which also affect the dominance structure of trees in this seasonal eastern Amazon forest.Synthesis. Our results support the theory of hydrological niche segregation and demonstrate its underlying trade‐off related to drought resistance (access to deep water vs. tolerance of very low water potentials). We found that the single hydrological axis defining water use traits was strongly related to tree size, and infer that periodic extreme droughts influence community composition and the dominance structure of trees in this seasonal eastern Amazon forest.

Effects of soil erosion on agro-ecosystem services and soil functions: A multidisciplinary study in nineteen organically farmed European and Turkish vineyards

This multidisciplinary research work evaluated the effects of soil erosion on grape yield and quality and on different soil functions, namely water and nutrient supply, carbon sequestration, organic matter recycling, and soil biodiversity, with the aim to understand the causes of soil malfunctioning and work out a proper strategy of soil remediation.Degraded areas in nineteen organically farmed European and Turkish vineyards resulted in producing significantly lower amounts of grapes and excessive concentrations of sugar. Plants suffered from decreased water nutrition, due to shallower rooting depth, compaction, and reduced available water capacity, lower chemical fertility, as total nitrogen and cation exchange capacity, and higher concentration of carbonates. Carbon storage and organic matter recycling were also depressed. The general trend of soil enzyme activity mainly followed organic matter stock. Specific enzymatic activities suggested that in degraded soils, alongside a general slowdown in organic matter cycling, there was a greater reduction in decomposition capacity of the most recalcitrant forms. The abundance of Acari Oribatida and Collembola resulted the most sensitive indicator of soil degradation among the considered microarthropods. No clear difference in overall microbial richness and evenness were observed. All indices were relatively high and indicative of rich occurrence of many and rare microbial species. Dice cluster analyses indicated slight qualitative differences in Eubacterial and fungal community compositions in rhizosphere soil and roots in degraded soils.This multidisciplinary study indicates that the loss of soil fertility caused by excessive earth movement before planting, or accelerated erosion, mainly affects water nutrition and chemical fertility. Biological soil fertility is also reduced, in particular the ability of biota to decompose organic matter, while biodiversity is less affected, probably because of the organic management. Therefore, the restoration of the eroded soils requires site-specific and intensive treatments, including accurately chosen organic matrices for fertilization, privileging the most easily decomposable. Restoring soil fertility in depth, however, remain an open question, which needs further investigation.

Large Crown Root Number Improves Topsoil Foraging and Phosphorus Acquisition.

Suboptimal phosphorus (P) availability is a primary constraint to plant growth on Earth. We tested the hypothesis that maize (Zea mays) genotypes with large crown root number (CN) will have shallower rooting depth and improved P acquisition from low-P soils. Maize recombinant inbred lines with contrasting CN were evaluated under suboptimal P availability in greenhouse mesocosms and the field. Under P stress in mesocosms, the large-CN phenotype had 48% greater root respiration, 24% shallower rooting depth, 32% greater root length density in the topsoil, 37% greater leaf P concentration, 48% greater leaf photosynthesis, 33% greater stomatal conductance, and 44% greater shoot biomass than the small-CN phenotype. Under P stress in the field, the large-CN phenotype had 32% shallower rooting depth, 51% greater root length density in the topsoil, 44% greater leaf P concentration, 18% greater leaf photosynthesis, 21% greater stomatal conductance, 23% greater shoot biomass at anthesis, and 28% greater yield than the small-CN phenotype. These results support the hypothesis that large CN improves plant P acquisition from low-P soils by reducing rooting depth and increasing topsoil foraging. The large-CN phenotype merits consideration as a selection target to improve P capture in maize and possibly other cereal crops.

Low densities in white pine stands reduce risk of drought-incited decline

White pine (Pinus strobus) is commonly found in naturally regenerated even-aged stands on former agricultural lands throughout its range. These stands can be managed for rapid production of high-quality sawtimber, and are thus a valuable timber resource. Yet, periodic growth decline and mortality events have occurred, such as that observed in the late 1990s in southern Maine, USA. The present study uses increment measurements from white pine tree cores collected in the early 2000s to compare increment chronologies in high- and low-mortality stands in southern Maine. Periods and severity of decline were quantified, revealing a growth decline and mortality event that began in 1996 following a late-summer drought in 1995. Further, the sites on which mortality was most pronounced were observed to have soil restrictions resulting in shallow rooting depth, ranging from 19 cm to 32 cm deep. Restrictions included bedrock, lithological discontinuity (loamy cap overlaying sand), and plow pans. Stand stocking was also a predisposing factor; on average, stands that experienced greater mortality during the decline event had higher stocking than those that experienced less mortality. As a consequence, stand densities in declining stands were reduced through mortality to levels more common in nearby non-decline stands; those densities correspond to recommendations for low-density management of white pine (i.e., 330–540 trees ha−1 and 17–25 m2 ha−1 of basal area at 20–30 cm DBH). The smaller diameters of the affected trees indicate the need to give priority to retention of large-diameter trees when thinning pole- and small sawtimber-sized (20–30 cm DBH) white pine stands. This and other studies demonstrate the need for low-density management of pole-size white pine stands to not only maximize growth and value but also reduce the risk of drought-incited decline and mortality on sites with rooting restrictions.

Transplanting Following Non-Native Plant Control in Rocky Mountain Foothills Fescue Grassland Restoration

Disturbed areas within national parks, resulting from historic and current land use activities, can harbor large and diverse populations of non-native plant species. These species must be controlled to prevent their spread and to restore native grassland. Research on alternative revegetation methods is urgently needed since seed based grassland restoration is often unsuccessful. The effectiveness of transplanting to restore foothills fescue grassland following implementation of non-native plant management was investigated at three disturbed sites in Waterton Lakes National Park, Alberta, Canada. Non-native plant abundance was reduced by cutting, glyphosate application, and steaming. Greenhouse grown seedlings of native fescue grassland species (13 forbs, five grasses, two shrubs) were outplanted into plots following management treatments, as three different sizes of container stock. The effects of prior non-native plant management and container size on transplant survival and growth were assessed over two growing seasons. Rhizomatous forbs and bunchgrasses with well-developed root systems had highest survival ( 50% over 14 months). Transplants with 10- to 15-cm rooting depth in cones and root trainers had significantly higher within-year survival than tray transplants with a shallow rooting depth. Transplant survival was improved by glyphosate application to control non-native plants prior to planting. Transplanting was effective for increasing native cover and species richness although high winter mortality reduced this effect. Key species for fescue grassland function were introduced at all sites and persisted for two growing seasons.

Characterising preferential flow and its interaction with the soil matrix using dye tracing in the Three Gorges Reservoir Area of China

Dye tracing experiments provide direct visual evidence of preferential flow in the soil. In this study, we applied the Brilliant Blue tracer across three forest sites (high-mountain forest, HF; middle-mountain forest, MF; and low-mountain forest, LF) and one cultivated field (CL) in the Three Gorges Reservoir Area of China to visualise preferential flow and characterise its interaction with the surrounding soil matrix. A set of parameters was extracted from photographs of dye-stained soil profiles to measure preferential flow, including (1) the ratio of the stained area to the total area of a soil section (SAR), (2) the degree of lateral water mixing of preferential flow into the soil matrix (LWM), (3) the greatest stained depth (SD), and (4) the stained path width (SPW). The highest SAR of all of the stained areas (i.e. a measure of the degree of preferential flow) was for MF (80%), followed by LF (68%), CL (48%), and HF (30%). The higher SAR in MF and LF was likely associated with more abundant and interconnected void spaces created by roots and soil fissures. The shallower rooting depth together with the higher content of clay and soil organic matter might lead to the lowest SAR in HF, suggesting a higher likelihood of soil erosion due to surface runoff. The relatively lower SAR in CL could be a result of soil compaction after tillage destroyed soil macropores. Moreover, the spatial distribution of preferential flow with soil depth varied among slope positions. In HF and MF, macropore flow dominated the A horizon with limited lateral diffusion. However, in the subsoil, although the SAR of all of the stained areas declined, the LWM (quantified as the SAR of yellow and green patches that have a lower concentration of the dye tracer) intensified. In the sandy soils at the LF site, macropore flow via soil fissures was the major type of preferential flow that showed a limited lateral diffusion. In CL, the degree of preferential flow (mainly as finger flows) decreased with soil depth. Based on the SPW profile, flow patterns were classified along soil depth at each site. The lower degree of preferential flow and the reduced SD in agricultural soils demonstrated the substantial impact of soil management on preferential flow and thereby infiltration. Therefore, current agricultural management exacerbates surface runoff and soil erosion and causes ecological degradation and sediment deposition in the Three Gorges Reservoir Area of China.

水分条件变化对哀牢山亚热带常绿阔叶林林下幼苗死亡率的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 水分条件变化对哀牢山亚热带常绿阔叶林林下幼苗死亡率的影响 DOI: 10.5846/stxb201306101572 作者: 作者单位: 中国科学院西双版纳热带植物园;中国科学院哀牢山亚热带森林生态系统研站,中国科学院西双版纳热带植物园;哈佛大学,中国科学院西双版纳热带植物园,中国科学院西双版纳热带植物园;中国科学院哀牢山亚热带森林生态系统研站,中国科学院西双版纳热带植物园;中国科学院哀牢山亚热带森林生态系统研站,中国科学院西双版纳热带植物园;中国科学院哀牢山亚热带森林生态系统研站,中国科学院西双版纳热带植物园;中国科学院哀牢山亚热带森林生态系统研站 作者简介: 通讯作者: 中图分类号: 基金项目: 中国科学院哀牢山亚热带森林生态系统研究站研究基金 The influence of changes in water availability on seedling mortality of a subtropical evergreen broadleaf forest on Ailao Mountain Author: Affiliation: Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences; Ailaoshan Station for Subtropical Forest Ecosystem Studies, Chinese Academy of Sciences,Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences; Harvard University,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探讨环境水分条件变化对亚热带森林林下乔木幼苗动态的影响,以及木材密度和幼苗在干旱中死亡率的关系,研究了哀牢山常绿阔叶林2005-2011年的总体和主要树种幼苗(黄心树、多果新木姜子、多花山矾、鸭公树和大花八角)的死亡率,并分析了幼苗死亡率和旱季幼苗根系所在土层土壤质量含水量、旱季降水量、旱季降水日数以及木材密度的关系。结果表明:1)幼苗死亡率与旱季降水日数、旱季浅层土壤平均质量含水量有显著的负相关关系,和旱季降水量无显著相关性;2)总幼苗及5种乔木幼苗的死亡率均在2010年(西南干旱)达到有观测以来最高,是2009年的2-10倍,其中多花山矾、黄心树幼苗的死亡率最高,大花八角幼苗的死亡率最低;3)在种间,幼苗2010年干旱中的死亡率和木材密度显著正相关,即木材密度较大的物种幼苗死亡率更高。研究表明林下幼苗由于根系较浅,对降雨变化较为敏感,因而受到了这次干旱的较大影响。由于木材密度较低的树种在干旱中有较低的死亡率,干旱频度和强度的增加可能使低木材密度幼苗的丰富度增加,森林的组成也将受到影响。 Abstract:In order to understand the influence of changes in water availability on the seedling dynamics of subtropical forests and the relationship between wood density and seedling mortality during a prolonged drought period, we studied seedling mortality patterns across all species and of 5 common tree species from an evergreen broadleaf forest on Ailao Mountain, southwest (SW) China from 2005 to 2011. The five tree species studied were Machilus bombycina, Neolitsea polycarpa, Symplocos ramosissima, Neolitsea chuii, and Illicium macranthum. The relationships between seedling mortality and rainy days, rainfall, soil water mass content (0-20 cm) during the dry season, and wood density were also analyzed. Our results showed that 1) Seedling mortality was negatively correlated with number of rainy days in the dry season and dry season soil water mass content, but not with total dry season rainfall; 2) The seedling mortalities of all species as a whole and of each of the 5 species studied reached a historical maximum in the 2010 SW China extreme drought, which were 2 to 10 times more intense than for 2009 (Machilus bombycina and Symplocos ramosissima had the highest seedling mortalities while Illicium macranthum had the lowest in 2010); 3) Across species, the seedling mortality in the 2010 drought was positively correlated with species-specific wood densities; species with higher wood densities had higher seedling mortalities. Previous studies have shown that trees in this forest did not experience severe drought stress during the 2010 SW China drought. However, the present study suggests that the seedlings were severely influenced by the rainfall anomaly during the 2010 dry season, probably owing to their shallow rooting depths and consequently high sensitivities to changes in rainfall. Additionally, because of the lower seedling mortalities in lower wood density species, the potential increase in drought frequency and severity in the future may increase the relative abundance of low wood density species, which may potentially lead to changes in forest species composition. 参考文献 相似文献 引证文献

Climate–growth relationships of relict Picea jezoensis at Mt. Gyebang, South Korea

A study was conducted to evaluate climatic variation at Mt. Gyebang, South Korea, and its influence on the modelled and observed growth of its relict Picea jezoensis population. Using the MT-CLIM and Biome-BGC models, year-to-year meteorological variation and subsequent changes in growing season, primary productivity and water balance were simulated. These were compared with the observed growth of sample P. jezoensis trees at the site. According to weather data and model calculations, the P. jezoensis stand at Mt. Gyebang was exposed to significant climate variations affecting growing season, carbon balance, and water balance. Although the length of growing season showed an increasing trend over time, the observed growth of P. jezoensis was unaffected by the length of growing season. Probably due to the site's shallow soil depths and species’ shallow rooting depth, the modelled increase in productivity caused by climate variation was not manifested in an increase in growth of P. jezoensis. These findings imply that the competitiveness of P. jezoensis at this site has declined over time and that an active approach to conservation planning for this species and site is warranted.

White spruce (Picea glauca) structural root system development and symmetry influenced by disc trenching site preparation

Mounding site preparation is normally required prior to planting seedlings for sites with understory competition and cold and wet soils in order to increase seedling establishment and survival in the boreal forest. Concern has been raised that planting seedlings on mounded microsites may influence the spatial distribution of lateral roots and lead to potential windthrow. The objective of this study was to examine root symmetry for container white spruce (Picea glauca) seedlings planted on disc trenched berms and no disc trenched sites compared to naturally regenerated seedlings in mixedwood forest of Saskatchewan. No significant differences were found between treatments for root cross sectional area index (CSAI) at radii of 25, 50 and 100cm from the stem center. Values of CSAI for planted seedlings on disc trenching, no disc trenching and natural regeneration sites all exhibited a degree of root asymmetry (range of 0.63–0.92) rather than being symmetrical (0.25) for all three radii. Disc trenching site preparation only impacted the direction of root development on <50% of planted container white spruce seedlings, for which the center of diameter (COD) positions were located on the berm side leading to a potential root asymmetry. However, the magnitude of this potential asymmetry was within the range observed on no disc trenching and natural regeneration sites. Rooting depth at 25–100cm radii from the stem, was significantly shallower in planted container seedlings (<6cm) compared to naturally regenerated white spruce seedlings (>38cm). Container seedlings exhibiting both shallow rooting depth and root asymmetry on disc trenched microsites suggests an increased risk for potential windthrow as the trees mature.

Blow me down: A new perspective on Aloe dichotoma mortality from windthrow

BackgroundWindthrow, the uprooting of trees during storms associated with strong winds, is a well-established cause of mortality in temperate regions of the world, often with large ecological consequences. However, this phenomenon has received little attention within arid regions and is not well documented in southern Africa. Slow rates of post-disturbance recovery and projected increases in extreme weather events in arid areas mean that windthrow could be more common and have bigger impacts on these ecosystems in the future. This is of concern due to slow rates of post-disturbance recovery in arid systems and projected increases in extreme weather events in these areas. This study investigated the spatial pattern, magnitude and likely causes of windthrown mortality in relation to other forms of mortality in Aloe dichotoma, an iconic arid-adapted arborescent succulent and southern Africa climate change indicator species.ResultsWe found that windthrown mortality was greatest within the equatorward summer rainfall zone (SRZ) of its distribution (mean = 31%, n = 11), and was derived almost exclusively from the larger adult age class. A logistic modelling exercise indicated that windthrown mortality was strongly associated with greater amounts of warm season (summer) rainfall in the SRZ, higher wind speeds, and leptosols. A statistically significant interaction term between higher summer rainfall and wind speeds further increased the odds of being windthrown. While these results would benefit from improvements in the resolution of wind and substrate data, they do support the hypothesised mechanism for windthrow in A. dichotoma. This involves powerful storm gusts associated with either the current or subsequent rainfall event, heavy convective rainfall, and an associated increase in soil malleability. Shallow rooting depths in gravel-rich soils and an inflexible, top-heavy canopy structure make individuals especially prone to windthrown mortality during storms.ConclusionsResults highlight the importance of this previously unrecognised form of mortality in A. dichotoma, especially since it seems to disproportionately affect reproductively mature adult individuals in an infrequently recruiting species. Smaller, more geographically isolated and adult dominated populations in the summer rainfall zone are likely to be more vulnerable to localised extinction due to windthrow events.

Soil degradation processes in the Italian agricultural and forest ecosystems

A number of processes of degradation threaten soil functions. Ten of them are acknowledged by the European Union and fifteen by the Organisation for Economic Co-operation and Development (OECD), but at least another seven have been indicated by different authors in Italy and in other parts of the world. This short review paper summarizes the nature, economic relevance, and territorial impact of soil degradation in Italy, and with reference to Europe as a whole, and highlights the most relevant research needs in soil conservation. The direct annual costs of the main soil degradation processes are estimated to be over 38,000,000,000 euro per year in Europe as a whole, while in Italy, only for landslides, floods, and soil erosion, costs amount to 900,000,000 euro. Loss of the ability to produce food commodities because of soil degradation is particularly important in Italy, since selfsufficiency in food has recently decreased to less than 80% and Italian agricultural soils are hit by several problems, such as limited soil drainage, unfavorable texture and stoniness, shallow rooting depth, and poor chemical properties. On average, soil sealing, reduction in organic matter, and soil compaction in Italy are comparable with those of many other countries, but the occurrence of soil erosion, floods, and landslides is more widespread than in most parts of Europe, and also the presence of salt-affected soils is becoming a major worry. The fight against soil degradation in Italy is certainly more difficult than in other countries because of the high environmental variability. However, according to the current trends, Italy is mostly probably destined not to achieve the European objective to significantly reduce main soil degradation processes by the year 2020. There are several research needs in the field of soil conservation in Italy. These include: i) a better basic knowledge about many soil degradation processes and of pedodiversity; ii) reliable, sensitive, and locally validated models for main degradation processes; iii) assessment of resilience of different soils against degradation processes, as well as of their reaction to the measures foreseen in the current European agricultural policy.