Effects of root diameter,branch order,root depth,season and warming on root longevity in an alpine meadow

Fine root is of importance in biogeochemical cycles especially in terrestrial ecosystems. The lack of understanding of the factors controlling root lifespan has made accurate prediction of carbon flow and nutrient cycling difficult. A controlled warming experiment was performed in an alpine meadow on the northern Tibetan Plateau (near Nagchu Town). We used a minirhizotron technique to measure root dynamics in situ during the growing season of 2013 and 2014 and survival analyses to assess root lifespan and the effects of root diameter, branch order, birth season, root depth and warming on root lifespan. Root diameter, branch order and root depth were all positively correlated with root lifespan. With an increase in diameter of 0.1 mm, mortality hazard ratio of roots declined by 19.3 %. An increase in one level in branch order was associated with a decrease of 43.8 % in root death ratio. Compared with roots born in May–mid-July, the mortality hazard ratio of roots born in late July–August and September–October reduced by 26.8 and 56.5 %, respectively. In warming treatments, roots tended to be thinner, less branched and deeper, and there was a higher proportion of roots born in spring compared to ambient conditions. Warming shortened the median root lifespan 44 days. However, in single warming condition, root diameter had no significant influence on root lifespan. Root diameter, branch order, root depth and season of birth were all factors affecting root lifespan in the alpine meadow; however, root branch order was dominant.     

Interactive effects of soil warming and fertilization on root production, mortality, and longevity in a Norway spruce stand in Northern Sweden

The effects of soil warming and nitrogen availability on root production, longevity and mortality were studied using minirhizotrons in irrigation (C), fertilized (F), heated (H), and heated‐fertilized (HF) plots in a Norway spruce stand in northern Sweden from October 1996 to October 1997. Irrigation was included in all treatment plots. Heating cables were used to maintain the soil temperature in heated plots at 5°C above that in unheated plots during the growing season. A Kaplan–Meier approach was used to estimate the longevity of fine roots and Cox proportional hazards regression to analyze the effects of the H, F, and HF treatments on the risk of root mortality. The proportion of annual root length production contributed by winter–spring production amounted to 52% and 49% in heated plots and heated‐fertilized plots, respectively. The annual root length production in C plots was significantly higher than in other treatments, while the HF treatment gave significantly greater production compared with the F treatment. The risk of mortality (hazard ratio) relative to C plots was higher in H plots (358%) and F plots (191%). The interaction between heating and fertilizing was strongly significant. The increase in the risk of root mortality in combined fertilization and heating (103%) was lower than that in the H or F plots. The results show that nitrogen addition combined with warmer temperatures decreases the risk of root mortality, and fine root production is a function of the length of the growing season. In the future, fertilization combined with the warmer temperatures expected to follow predicted climatic change may increase root production in boreal forests at low fertility sites.     

Effects of Warming and Nitrogen Addition on Plant Photosynthate Partitioning in an Alpine Meadow on the Tibetan Plateau

Quantifying plant carbon (C) allocation among different pools is critical for understanding and predicting how C turnover responds to global climate change in terrestrial ecosystems. A field experiment with increasing warming and nitrogen (N) was established to investigate interactive effects on plant C allocation in alpine meadows. Open-top chambers (OTCs) were used to simulate warming. In OTCs, daytime air and soil temperature at 5 cm depth increased by 2.0 and 1.6 °C, respectively, compared with ambient conditions, but soil moisture at 5 cm depth decreased by 4.95% (v/v) from 2012 to 2014. Warming reduced aboveground biomass by 38, 36, and 43% in 2012, 2013, and 2014, respectively, and increased belowground biomass by 64% and 29% in 2013 and 2014, respectively, and the root-to-shoot ratio was significantly increased. Specifically, warming increased the proportion of plant roots in the deep layers (10–20 cm). Both N addition and its combination with warming substantially enhanced belowground biomass. Pulse-labeling experiments for ¹³C revealed that warming reduced the translocation of assimilated C to shoots by 8.8% (38.7% in warming, and 47.5% in the control [CK]), and increased the allocation to root by 12.2% (55.5% in warming, and 43.3% in CK) after 28 days labeling. However, N addition increased the proportion of assimilated C allocated to shoots by 6.5% (54.0% in N addition, and 47.5% in CK), whereas warming combined with N addition reduced this proportion by 10.9%. A decline in soil water content in the surface layer may be the main cause of plants allocating more newly fixed photosynthate to roots. Therefore, plants promoted root growth to draw water from deeper soil layers (10–20 cm). We concluded that climate warming will change the allocation patterns of plant photosynthates by affecting soil water availability, whereas N addition will increase plant photosynthates aboveground in alpine meadows and thus will significantly affect C turnover under future climate change scenarios.

     

Root size and soil environments determine root lifespan: evidence from an alpine meadow on the Tibetan Plateau

We used a minirhizotron system to investigate the influence of three major factors—root morphology, root depth, and season of root emergence—on root survivorship and longevity in a Kobresia humilis meadow on the Tibetan Plateau during the growing season of 2009. Root longevity was assessed by survival analysis, Kaplan–Meier analysis, and Cox proportional hazards regression. Root longevity was correlated positively with root diameter. A 17.5 % decrease in the risk of mortality was associated with a 0.1-mm increase in diameter. Roots distributed in the top 10 cm of the soil had significantly shorter longevities than roots at greater depths, with a 48 % decrease of mortality risk for each 10-cm increase in soil depth from the surface to 40 cm. Of all the factors examined, the season of root emergence had the strongest effect on root lifespan. Roots that emerged in May and June had shorter longevity than roots that emerged later in the year, and roots that emerged in September and October were more likely to survive over winter. Our findings indicated that life-history traits of roots in K. humilis meadows are highly heterogeneous, and this heterogeneity should be considered when modeling the contribution of roots to carbon and nitrogen fluxes in this type of meadow ecosystem. Moreover, temporal, spatial, and compositional variations in root longevity must be considered.     

青藏高原多年冻土区不同水分条件的高寒草甸根系功能性状对增温的响应

在青藏高原多年冻土广泛分布的风火山地区,选择小嵩草（Kobresia pygmea）草甸和藏嵩草（Kobresia tibetica）沼泽化草甸为研究对象,采用开顶增温室（Open top chambers, OTCs）模拟气候变暖,探讨模拟增温对土壤水分差异的两种草甸地下生物量及根系功能性状的影响。结果显示,（1）增温显著增加小嵩草草甸0—20 cm根系生物量,主要是由于表层（0—10 cm）根系生物量显著增加,而对藏嵩草沼泽化草甸根系生物量无影响。（2）增温显著增加了小嵩草草甸根组织密度,同时提高了藏嵩草沼泽化草甸10—20 cm的比根长和比根面积（3）增温降低了小嵩草草甸的根系碳含量及10—20 cm根系氮含量,增加了藏嵩草沼泽化草甸的碳含量及10—20 cm根系氮含量,显著提高了小嵩草草甸和藏嵩草沼泽化草甸深层（10—20 cm）根系碳氮比。这些结果预示着增温使得土壤水分较低的小嵩草草甸朝着资源保守的慢速生长型发展,以适应暖干化的环境;土壤水分较高的藏嵩草沼泽化草甸朝着资源获取的快速生长型发展,加速利用土壤中的养分满足植物生长需要。可见,土壤水分可以调节高寒草甸对气候变暖的演变趋势,强调了水分的重要性。     

模拟增温对青藏高原高寒草甸根系生物量的影响

在青藏高原高寒草甸布设模拟增温实验样地,采用土钻法于2012—2013年植被生长季获取5个土层的根系生物量,探讨增温处理下根系生物量在生长季不同月份、不同土壤深度的变化趋势及其与相应土层土壤水分、温度的关系。结果表明:(1)根系生物量在2012年随月份呈增加趋势,其中7—9月较大,其平均值在对照、增温处理下分别为3810.88 g/m~2和4468.08 g/m~2;在2013年随月份呈减小趋势,其中5—6月较大,其平均值在对照、增温处理下分别为4175.39 g/m~2和4141.6 g/m~2。增温处理下的总根系生物量高出对照处理293.97 g/m~2,而各月份总根系生物量在处理间的差值均未达到显著水平。表明在增温处理下根系生物量略有增加,但在生长季不同月份其增加的程度不同,致使年际间的增幅出现差异。(2)根系生物量主要分布在0—10 cm深度,所占百分比为50.61%。在增温处理下,0—10 cm深度的根系生物量减少,减幅为8.38%;10—50 cm深度的根系生物量增加,增幅为2.1%。相对于对照处理,增温处理下0—30 cm深度的根系生物量向深层增加,30—50 cm深度的根系生物量增加趋势略有减缓。可见,在增温处理下根系生物量的增幅趋向于土壤深层。(3)根系生物量与土壤水分呈极显著的递减关系,在增温处理下线性关系减弱;与土壤温度呈极显著的递增关系,在增温处理下线性关系增强。表明土壤水分、温度都可极显著影响根系生物量,但在增温处理下土壤温度对根系生物量的影响较土壤水分更为敏感而迅速。     

Interactive effects of soil warming and nitrogen addition on fine root production of Chinese fir seedlings

Aims There have been a large number of studies on the independent separate responses of fine roots to warming and nitrogen deposition, but with contradictory reporting. Fine root production plays a critical role in ecosystem carbon, nutrient and water cycling, yet how it responds to the interactive warming and nitrogen addition is not well understood. In the present study, we aimed to examine the interactive effects of soil warming and nitrogen addition on fine root growth of 1-year-old Chinese fir (Cunninghamia lanceolata) seedlings in subtropical China.
Methods A mesocosm experiment, with a factorial design of soil warming (ambient, +5 °C) and nitrogen addition (ambient, ambient + 40 kg·hm^-2·a^-1, ambient + 80 kg·hm^-2·a^-1), was carried out in the Chenda State-owned Forest Farm in Sanming City, Fujian Province, China. Fine root production (indexed by the number of fine roots emerged per tube of one year) was measured biweekly using minirhizotrons from March of 2014 to February of 2015.
Important findings (1) The two-way ANOVA showed that soil warming had a significant effect on fine root production, while nitrogen addition and soil warming × nitrogen addition had no effect. (2) The three-way ANOVA (soil warming, nitrogen addition and diameter class) showed that soil warming, diameter class and soil warming × diameter class had significant effects on fine root production, especially for the number of fine roots in 0-1 mm diameter class that had been significantly increased by soil warming. Compared with the 1-2 mm roots, the 0-1 mm roots seemed more flexible. (3) Repeated measures of ANOVA (soil warming, nitrogen addition and season) showed that soil warming, season, soil warming × season, and soil warming × nitrogen addition × season had significant effects on fine root production. In spring, the number of fine roots was significantly increased both by soil warming and soil warming × season, while soil warming, nitrogen addition, soil warming × nitrogen addition significantly decreased fine root production in the summer. (4) Soil warming, soil layer, soil warming × soil layer had significant effects on fine root production. The number of in-growth fine roots was significantly increased by soil warming at the 20-30 cm depth only. It seemed that warming forced fine roots to grow deeper in the soil. In conclusion, soil warming significantly increased fine root production, but they had different responses and were dependent of different diameter classes, seasons and soil layers. Nitrogen addition had no effect on fine root production. Only in spring and summer, soil warming and nitrogen addition had significant interactive effects.     

Climate warming alters the relative importance of plant root and microbial community in regulating the accumulation of soil microbial necromass carbon in a Tibetan alpine meadow

Climate warming is predicted to considerably affect variations in soil organic carbon (SOC), especially in alpine ecosystems. Microbial necromass carbon (MNC) is an important contributor to stable soil organic carbon pools. However, accumulation and persistence of soil MNC across a gradient of warming are still poorly understood. An 8-year field experiment with four levels of warming was conducted in a Tibetan meadow. We found that low-level (+0–1.5°C) warming mostly enhanced bacterial necromass carbon (BNC), fungal necromass carbon (FNC), and total MNC compared with control treatment across soil layers, while no significant effect was caused between high-level (+1.5–2.5°C) treatments and control treatments. The contributions of both MNC and BNC to soil organic carbon were not significantly affected by warming treatments across depths. Structural equation modeling analysis demonstrated that the effect of plant root traits on MNC persistence strengthened with warming intensity, while the influence of microbial community characteristics waned along strengthened warming. Overall, our study provides novel evidence that the major determinants of MNC production and stabilization may vary with warming magnitude in alpine meadows. This finding is critical for updating our knowledge on soil carbon storage in response to climate warming.     

Interactions between root growth, slope and soil detachment depending on land use: a case study in a small mountain catchment of Northern Laos

Roots modify the properties of soil in their immediate vicinity. Individually, fine roots (<1 mm in diameter) have little effect on soil properties, but this is offset by the fact that they make up most of a plant’s total root length. Roots growing near the soil surface may influence soil detachment. Slope conditions are also known to influence root growth. A field study conducted in a small watershed of Northern Lao People’s Democratic Republic (PDR) during the 2005 rainy season assessed putative interactions between shallow fine roots, slope angle and soil detachment under three land uses: shifting cultivation, fallow and tree plantations. We used auger sampling and root windows to measure root length density and 1-m² microplots to monitor water infiltration, runoff and soil detachment. Annual crops and plantation trees did not explore shallow soil horizons as thoroughly as fallow species. Under both crop and fallow, RLD in the top 5 cm decreased as slope increased. This pattern could be linked, either as a cause or a consequence, to slope-related changes in infiltration regimes. In contrast, no clear relation between fine root development and soil detachment was found.     

Long-term warming effects on root morphology, root mass distribution, and microbial activity in two dry tundra plant communities in northern Sweden

Effects of warming on root morphology, root mass distribution and microbial activity were studied in organic and mineral soil layers in two alpine ecosystems over>10 yr, using open-top chambers, in Swedish Lapland. Root mass was estimated using soil cores. Washed roots were scanned and sorted into four diameter classes, for which variables including root mass (g dry matter (g DM) m(-2)), root length density (RLD; cm cm(-3) soil), specific root length (SRL; m g DM(-1)), specific root area (SRA; m2 kg DM(-1)), and number of root tips m(-2) were determined. Nitrification (NEA) and denitrification enzyme activity (DEA) in the top 10 cm of soil were measured. Soil warming shifted the rooting zone towards the upper soil organic layer in both plant communities. In the dry heath, warming increased SRL and SRA of the finest roots in both soil layers, whereas the dry meadow was unaffected. Neither NEA nor DEA exhibited differences attributable to warming. Tundra plants may respond to climate change by altering their root morphology and mass while microbial activity may be unaffected. This suggests that carbon may be incorporated in tundra soils partly as a result of increases in the mass of the finer roots if temperatures rise.     

Soil warming and CO2 enrichment induce biomass shifts in alpine tree line vegetation

Responses of alpine tree line ecosystems to increasing atmospheric CO₂ concentrations and global warming are poorly understood. We used an experiment at the Swiss tree line to investigate changes in vegetation biomass after 9 years of free air CO₂ enrichment (+200 ppm; 2001–2009) and 6 years of soil warming (+4 °C; 2007–2012). The study contained two key tree line species, Larix decidua and Pinus uncinata, both approximately 40 years old, growing in heath vegetation dominated by dwarf shrubs. In 2012, we harvested and measured biomass of all trees (including root systems), above‐ground understorey vegetation and fine roots. Overall, soil warming had clearer effects on plant biomass than CO₂ enrichment, and there were no interactive effects between treatments. Total plant biomass increased in warmed plots containing Pinus but not in those with Larix. This response was driven by changes in tree mass (+50%), which contributed an average of 84% (5.7 kg m^?2) of total plant mass. Pinus coarse root mass was especially enhanced by warming (+100%), yielding an increased root mass fraction. Elevated CO₂ led to an increased relative growth rate of Larix stem basal area but no change in the final biomass of either tree species. Total understorey above‐ground mass was not altered by soil warming or elevated CO₂. However, Vaccinium myrtillus mass increased with both treatments, graminoid mass declined with warming, and forb and nonvascular plant (moss and lichen) mass decreased with both treatments. Fine roots showed a substantial reduction under soil warming (?40% for all roots <2 mm in diameter at 0–20 cm soil depth) but no change with CO₂ enrichment. Our findings suggest that enhanced overall productivity and shifts in biomass allocation will occur at the tree line, particularly with global warming. However, individual species and functional groups will respond differently to these environmental changes, with consequences for ecosystem structure and functioning.     

增温下土壤资源异质分布对杉木幼苗生长的影响

在福建三明森林生态系统与全球变化研究站陈大观测点开展大气温度控制、土壤温度控制和土壤资源分布3因子试验,探讨土壤资源异质分布和增温对杉木幼苗地下和地上生长的影响,以及增温是否能改变杉木幼苗细根对土壤资源异质分布的识别度,以明确杉木人工林在全球变暖背景下对土壤资源异质分布的响应.结果表明:杉木对土壤资源异质分布的识别度主要体现在吸收根(0~1 mm径级)上,而1~2 mm径级细根则不具有识别度.除了单独大气增温处理对杉木1~2 mm径级细根的避贫系数具有显著影响外,不同增温处理均未对杉木幼树细根的贫富比、趋富系数和避贫系数产生显著影响.与土壤资源均质分布相比,土壤资源异质分布增加了0~1 mm径级细根生物量,降低了树高.与无大气增温相比,大气增温降低了0~1和0~2 mm径级细根生物量,增加了树高.与无土壤增温相比,土壤增温降低了1~2 mm径级细根生物量,但增加了树高和侧枝长度.大气增温控制、土壤增温控制和土壤资源异质分布对杉木地下、地上生长都无显著交互作用.杉木幼苗吸收根本身对土壤资源异质分布具有识别度,但增温并不会改变杉木幼苗细根对土壤资源异质分布的识别度.     

土壤增温与氮添加对杉木幼苗细根径级根长分布的影响

通过在福建省三明市陈大林业国有林场内开展土壤增温(增温5 ℃、不增温)和氮添加(不添加、4、8 g N·m^-2·a^-1)的交互试验(共6个处理),研究土壤增温、氮添加及二者交互作用对杉木细根径级根长分布的影响,用扩展模型可很好地拟合6个处理的径级根长分布(R²=0.97).结果表明: 增温使杉木细根总根长变小,但对细根直径影响不显著;氮添加使杉木细根总根长和直径均变小;增温和氮添加的交互作用对细根总根长有显著影响,但对细根直径无显著影响.6个处理细根径级根长分布均能用极值函数模型较好地拟合(R²>0.98).相关分析显示,直径<1 mm细根的比根长与极值模型拟合参数c值呈显著负相关,实际总根长与极值模型拟合参数b呈显著正相关.增温和氮添加及其交互作用可以影响杉木细根形态特征;极值模型拟合各处理径级根长分布所得参数在一定程度上可以反映细根形态特征对环境条件变化的响应.     

植物残体对青藏高原高寒草甸土壤、微生物和胞外酶C∶N∶P化学计量特征的影响

植物残体是引起土壤、微生物和胞外酶C∶N∶P改变的关键因素,但是其作用机理尚不明确。本研究以青藏高原东缘高寒草甸为对象,通过测定土壤、微生物生物量和胞外酶活性等指标,探究移除地上植物或根系及植物残体添加对土壤、微生物和胞外酶C∶N∶P的影响。结果表明: 与无人为扰动草甸相比,移除地上植物显著降低了土壤C∶N(变幅为-23.7%,下同)、C∶P(-14.7%)、微生物生物生物量C∶P、N∶P,显著提高了微生物生物量C∶N、胞外酶C∶N∶P。与移除地上植物相比,移除地上植物和根系显著降低了土壤C∶N(-11.6%)、C∶P(-24.0%)、N∶P(-23.3%)和微生物生物量C∶N,显著提高了微生物生物量N∶P和胞外酶N∶P;移除地上植物后添加植物残体显著提高了微生物生物量C∶N、C∶P和胞外酶C∶N,显著降低了胞外酶N∶P。与移除地上植物和根系相比,移除地上植物和根系后添加植物残体显著降低了土壤C∶N(-16.4%)、微生物生物量C∶P、N∶P和胞外酶N∶P,显著提高了胞外酶C∶N。综上可知,去除植物显著影响土壤、微生物和胞外酶的C∶N∶P,微生物生物量和胞外酶C∶N∶P对植物残体的响应更为敏感。有无根系是添加植物残体时土壤、微生物和胞外酶的生态化学计量稳定性强弱的关键所在。添加植物残体的措施适用于植物根系尚且完好的草甸,有利于高寒草甸土壤碳固存,对没有根系的草甸土壤可能不适用,会增加土壤CO₂排放。     

Initial responses of soil CO2 efflux and C, N pools to experimental warming in two contrasting forest ecosystems, Eastern Tibetan Plateau, China

Alpine ecosystems are harsh environments where low temperatures are generally a limiting factor. Predicted global warming is thus expected to have a profound impact on alpine ecosystems in the future. This study was conducted to compare the effect of experimental warming on soils in two contrasting forest ecosystems (a dragon spruce plantation and a natural forest) using the open top chamber (OTC) method in the Eastern Tibetan Plateau of China. The OTC enhanced average daily mean soil temperatures by 0.61°C (plantation) and 0.55°C (natural forest), respectively, throughout the growing season. Conversely, soil volumetric moisture declined by 4.10% in the plantation and by 2.55% in the natural forest. Across all measuring dates, warming increased average soil CO₂ efflux by 10.6% in the plantation and by 15.4% in the natural forest. However, elevated temperatures did not affect the respiration quotient in either forest. Two-stage sulfuric acid hydrolysis was used to quantify labile and recalcitrant C and N fractions in the two contrasting soils. Warming significantly reduced labile C and N fractions in both ecosystems but did not influence the total, recalcitrant and microbial biomass C and N pools. Labile C, N and microbial biomass C showed significant interactions in warming × forest type × season. Irrespective of warming treatments, all measured pools were significantly larger in the natural forest compared to the plantation. Taken together, our results indicate that the lowered soil labile C and N pools may be induced by the increased soil CO₂ efflux. The responses of the natural forest soil were more sensitive to experimental warming than those of the plantation. We conclude that reforestation dramatically lowers soil C and N pools, further affecting the responses of forest soils to future global warming.     

Fine root biomass estimates from minirhizotron imagery in a shrub ecosystem exposed to elevated CO2

Fine root biomass and C content are critical components in ecosystem C models, but they cannot be directly determined by minirhizotron techniques, and indirect methods involve estimating 3-dimensional values (biomass/ soil volume) from 2-dimensional measurements. To estimate biomass from minirhizotron data, a conversion factor for length to biomass must be developed, and assumptions regarding depth of view must be made. In a scrub-oak ecosystem in central Florida, USA, root length density (RLD) was monitored for 10 years in a CO₂ manipulation experiment using minirhizotron tubes. In the seventh year of the study, soil cores were removed from both ambient and elevated CO₂ chambers. Roots from those cores were used to determine specific root length values (m/g) that were applied to the long-term RLD data for an estimation of root biomass over 10 years of CO₂ manipulation. Root length and biomass estimated from minirhizotron data were comparable to determinations from soil cores, suggesting that the minirhizotron biomass model is valid. Biomass estimates from minirhizotrons indicate the <0.25 mm diameter roots accounted for nearly 95% of the total root length in 2002. The long-term trends for this smallest size class (<0.25 mm diameter) mirrored the RLD trends closely, particularly in relation to suspected root closure in this system. Elevated CO₂ did not significantly affect specific root length as determined by the soil cores. A significant treatment effect indicated smallest diameter fine roots (<0.25 mm) were greater under elevated CO₂ during the early years of the study and the largest (2–10 mm) had greater biomass under elevated CO₂ during the later years of the study. Overall, this method permits long-term analysis of the effects of elevated CO₂ on fine root biomass accumulation and provides essential information for carbon models.     

高寒灌丛生长季土壤转化酶与脲酶活性对增温和植物去除的响应

对青藏高原东缘窄叶鲜卑花土壤转化酶与脲酶活性对增温(0.6～1.3 ℃)和植物去除的响应进行研究,以了解气候变暖和植被干扰对高寒灌丛生长季不同时期土壤生态过程的影响.结果表明: 增温在整个生长季节使去除/不去除植物处理土壤转化酶活性显著增加了3.7%～13.3%.增温除在生长季末期对不去除植物处理土壤脲酶活性影响不显著以外,在其他时期使去除/不去除植物处理土壤脲酶活性显著增加10.8%～56.3%.去除植物处理对土壤转化酶与脲酶活性的影响因增温与生长季节而存在显著差异.去除植物显著降低了不增温样方生长季初期和末期与增温样方整个生长季节土壤转化酶活性,而没有显著影响生长季中期不增温样方土壤转化酶活性.去除植物仅在生长季末期使不增温样方土壤脲酶活性显著降低了10.5%;而在增温样方,去除植物仅在生长季初期和中期使土壤脲酶活性显著降低16.0%～18.7%.以上结果有利于全面认识高寒灌丛生态系统土壤碳氮循环过程.     

疏叶骆驼刺根系对土壤异质性和种间竞争的响应

近年来, 植物根系对土壤异质性的响应和植物根系之间的相互作用一直是研究的热点。过去的研究主要是针对一年生短命植物进行的, 而且多是在人工控制的温室条件下进行的。而对于多年生植物根系对养分异质性和竞争的综合作用研究很少。该文对塔里木盆地南缘多年生植物疏叶骆驼刺(Alhagi sparsifolia)根系生长对养分异质性和竞争条件的响应途径与适应策略进行了研究, 结果表明: (1)在无竞争的条件下, 疏叶骆驼刺根系优先向空间大的地方生长, 即使另一侧有养分斑块存在, 其根系也向着空间大的一侧生长; (2)在有竞争的条件下, 疏叶骆驼刺根系生长依然是优先占领空间大的一侧, 但是竞争者的存在抑制了疏叶骆驼刺的生长, 导致其枝叶生物量和根系生物量都明显减少(p < 0.01), 而养分斑块的存在促进了疏叶骆驼刺根系的生长; (3)疏叶骆驼刺根系的生长不仅需要养分, 也需要足够的空间, 空间比养分更重要; (4)有竞争者存在的时候, 两株植物的根系都先长向靠近竞争者一侧的空间, 即先占据“共有空间”。研究结果对理解植物根系觅食行为和植物对环境的适应策略有重要意义。     

土壤增温对杉木幼苗细根呼吸和非结构性碳的影响

在福建省三明市陈大国有林场开展杉木幼苗土壤增温试验,采用内生长环法研究土壤增温(+5℃)对杉木幼苗细根比呼吸速率和非结构性碳的影响,分析杉木人工林对全球变暖的地下响应及其适应性.结果表明:增温第二年,土壤增温引起细根组织内非结构性碳水化合物(NSC)的较大变化,1月增温处理0~1 mm细根NSC和淀粉浓度下降,1~2 mm细根可溶性糖和NSC浓度下降;7月增温处理0~1 mm细根NSC、可溶性糖和淀粉浓度提高,使1~2mm细根淀粉浓度增加.增温第3年,土壤增温对细根NSC无显著影响.增温处理使0~1 mm细根比根呼吸速率在增温第二年7月增加,而在第三年7月下降;与0~1 mm细根相比,增温处理对1~2 mm细根比呼吸速率没有显著影响.细根呼吸对增温的响应与增温持续时间有关,随增温时间的延长,细根呼吸产生部分驯化,同时能够使细根NSC浓度保持稳定.     

Effects of field experimental warming on wheat root distribution under conventional tillage and no‐tillage systems

Despite the obvious importance of roots to agro‐ecosystem functioning, few studies have attempted to examine the effects of warming on root biomass and distribution, especially under different tillage systems. In this study, we performed a field warming experiment using infrared heaters on winter wheat, in long‐term conventional tillage and no‐tillage plots, to determine the responses of root biomass and distribution to warming. Soil monoliths were collected from three soil depths (0–10, 10–20, and 20–30 cm). Results showed that root biomass was noticeably increased under both till and no‐till tillage systems (12.1% and 12.9% in 2011, and 9.9% and 14.5% in 2013, in the two tillage systems, respectively) in the 0–30 cm depth, associated with a similar increase in shoot biomass. However, warming‐induced root biomass increases occurred in the deeper soil layers (i.e., 10–20 and 20–30 cm) in till, while the increase in no‐till was focused in the surface layer (0–10 cm). Differences in the warming‐induced increases in root biomass between till and no‐till were positively correlated with the differences in soil total nitrogen (R² = .863, p < .001) and soil bulk density (R² = .853, p < .001). Knowledge of the distribution of wheat root in response to warming should help manage nutrient application and cycling of soil C‐N pools under anticipated climate change conditions.