Changes In Root Biomass Research Articles

Tropical root responses to global changes: A synthesis.

Tropical ecosystems face escalating global change. These shifts can disrupt tropical forests' carbon (C) balance and impact root dynamics. Since roots perform essential functions such as resource acquisition and tissue protection, root responses can inform about the strategies and vulnerabilities of ecosystems facing present and future global changes. However, root trait dynamics are poorly understood, especially in tropical ecosystems. We analyzed existing research on tropical root responses to key global change drivers: warming, drought, flooding, cyclones, nitrogen (N) deposition, elevated (e) CO2, and fires. Based on tree species- and community-level literature, we obtained 266 root trait observations from 93 studies across 24 tropical countries. We found differences in the proportion of root responsiveness to global change among different global change drivers but not among root categories. In particular, we observed that tropical root systems responded to warming and eCO2 by increasing root biomass in species-scale studies. Drought increased the root: shoot ratio with no change in root biomass, indicating a decline in aboveground biomass. Despite N deposition being the most studied global change driver, it had some of the most variable effects on root characteristics, with few predictable responses. Episodic disturbances such as cyclones, fires, and flooding consistently resulted in a change in root trait expressions, with cyclones and fires increasing root production, potentially due to shifts in plant community and nutrient inputs, while flooding changed plant regulatory metabolisms due to low oxygen conditions. The data available to date clearly show that tropical forest root characteristics and dynamics are responding to global change, although in ways that are not always predictable. This synthesis indicates the need for replicated studies across root characteristics at species and community scales under different global change factors.

Impact of changes in root biomass on the occurrence of internal browning in radish root

The purpose of this study was to investigate the effects of root biomass during the later stage of growth on fatty acid composition and lipid peroxidation, and to clarify the physiological mechanisms by which these differences affect internal browning (IB) development in radish roots. Therefore, we controlled the enlargement of roots by changing the thinning period and generated plots composed of roots with different biomass in the latter half of growth. The earlier the radish seedlings were thinned, the more vigorous the root growth from an earlier stage was achieved. Earlier thinning caused IB from the early stage of root maturation, and IB severity progressed with subsequent age progression; however, IB damage did not occur when root size during the later growth stage was kept small by later thinning. Higher levels of hydrogen peroxide, peroxidase activity, NADPH-dependent reactive oxygen species (ROS) burst-related genes, and carbonyl compounds were detected in earlier-thinned large-sized roots compared to later-thinned small-sized ones. Compared with the latter small-sized roots, the former large-sized roots had a lower ratio of linoleic acid (18:2) and a higher ratio of α-linolenic acid (α-18:3). Furthermore, in earlier-thinned large-sized roots, higher levels of phospholipase- and/or lipoxygenase-related genes were detected compared to later-thinned small-sized ones. These facts suggest the possibility that root biomass in the later stage of growth affects the desaturation of membrane fatty acids, ROS concentration, and activity of fatty acid degrading enzymes, and controls the occurrence of IB injury through membrane oxidative degradation.

Contrasting responses of fine root biomass and traits to large‐scale nitrogen and phosphorus addition in tropical forests in the Guiana shield

Fine roots mediate plant nutrient acquisition and growth. Depending on soil nutrient availability, plants can regulate fine root biomass and morphological traits to optimise nutrient acquisition. Little is known, however, about the importance of these parameters influencing forest functioning. In this study, we measured root responses to nutrient additions to gain a mechanistic understanding of plant adaptations to nutrient limitation in two tropical forests in French Guiana, differing twofold in their soil nutrient statuses. We analysed the responses of root biomass, mean root diameter (RD), specific root length (SRL), specific root area (SRA), root tissue density (RTD) and carbon (C), nitrogen (N) and phosphorus (P) concentrations in roots down to 15 cm soil depth after three years of N and P additions. At the lower‐fertility site Paracou, no changes in root biomass or morphological traits were detected with either N or P addition, although P concentrations in roots increased with P addition. In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition, with no changes in morphological traits. In contrast, N addition shifted root traits from acquisitive to more conservative by increasing RTD. A significant interaction between N and P in Nouragues pointed to stronger responses to P addition in the absence of N. Our results suggest that the magnitude and direction of root biomass and trait expression were regulated by soil fertility, corroborated by the response to N or P additions. At low fertility sites, we found lower plasticity in root trait expression compared to more fertile conditions, where N and P additions caused stronger and antagonistic responses. Identifying the exact role of mechanisms affecting root nutrient uptake in Amazon forests growing in different soils will be crucial to foresee if and how rapid global changes can affect their carbon allocation.

Subsoiling tillage increased core microbiome associated with nitrogen fixation in the fallow season under rainfed maize monoculture

Subsoiling tillage (ST) is a promising agronomy practice to improve soil physicochemical properties, soil microbial diversity during the crop growing season, and ultimately crop yield, but little is known about whether and how the ST practice will impact soil physicochemical properties and microbial communities in fallow season and their impacts on crop growth in next season. Here, a four-year continuous field experiment was conducted to compare the impacts of three tillage treatments, i.e., the ST, the no-tillage (NT), and the rotary tillage (RT), on soil physicochemical properties and microbial communities in maize fallow season. The results showed that compared with the RT treatment, the ST treatment improved maize yield by 2.3%, 4.2%, 11.4%, and 9.7% from 2018 to 2021, respectively, while there was no significant yield loss between the NT and RT. The ST treatment improved root biomass and soil available nitrogen by 25.1% and 34.0%, respectively, but scarcely impacted soil bulk density and water-filled pore space in comparison with the RT treatment in the maize fallow season in 2021. In addition, changes in root biomass further altered soil bacterial core microbiomes. Compared with the RT treatment, the ST treatment increased the relative abundance of core microbiomes related to nitrogen fixation and denitrification by 169.5% and 62.0%, respectively, but reduced the relative abundance of core microbiomes related to nitrification by 39.0%. The potential functional profile of core microbiomes predicted by the FAPROTAX database also showed that the ST treatment significantly improved nitrogen fixation and ureolysis by 115.9% and 346.9%, respectively, while decreased nitrification by 57.1% in comparison with the RT treatment. The results of the structural equation model showed that ST-induced changes in the function of nitrogen fixation improved soil available nitrogen content in the maize fallow season, which could supply nutrients for maize growth in the next growing season. Additionally, although the NT treatment improved microbial diversities in comparison with the RT and ST treatments, it reduced the relative abundance of microbiomes related to nitrogen cycling in the maize fallow season. These results indicate that the subsoiling tillage could increase the abundance of core microbiomes related to nitrogen fixation and mineralization, which increase soil available nitrogen content in the fallow season of maize cropping in the northeast of China.

Differential sensitivity of above- and belowground plant biomass to drought and defoliation in temperate grasslands

Multi-year droughts combined with other stressors such as defoliation are likely to have substantial ecological impacts. However, grasslands vary significantly in their response to drought and defoliation, and interpretations rarely address the importance of roots despite evidence showing roots are likely to respond differently to drought and defoliation than shoots. Here, we conducted a three-year manipulative experiment, combining a reduction in rainfall treatment (drought, 45% of ambient) with each of a time-of-defoliation (early vs. late) and an intensity-of-defoliation (none, light, heavy) treatment at seven temperate grassland sites to test three a priori hypotheses: 1) defoliation early relative to late in the season would exacerbate drought impacts on aboveground net primary productivity (ANPP) and root biomass; 2) ANPP and root biomass would progressively decrease with increasing intensity of defoliation early in the growing season under drought; 3) drought and defoliation effects on ANPP and root biomass would vary along a gradient of long-term mean annual precipitation of study sites. Across all seven sites, the combined effects of drought and defoliation led to greater changes in root biomass than ANPP. Under drought conditions specifically, defoliation early in the growing season reduced root biomass, but not ANPP, compared to defoliation late in the growing season. The decline in root biomass under drought was more substantial when the intensity of early-season defoliation increased from none to heavy. Furthermore, variation in the timing and intensity of defoliation altered root biomass more in mesic than arid grasslands, while their effects on ANPP remained unchanged across the seven sites. These results indicate that root systems may be more responsive than ANPP to simultaneous drought and defoliation, and could lead to long-term changes in plant productivity.

Mass-based trophic transfer of polystyrene nanoplastics in the lettuce-snail food chain

To investigate the potential transfer of nanoplastics (NPs) from water to plants and subsequently to a higher trophic level, we established a food chain and evaluated the trophic transfer of polystyrene (PS) NPs based on mass concentrations by pyrolysis gas chromatography–mass spectrometry. Lettuce plants were cultivated in Hoagland solution with varying concentrations of PS-NPs (0.1, 1, 10, 100 and 1000 mg/L) for a period of 60 d and then a total of 7 g lettuce shoot was fed to snails for 27 d. Shoot biomass exposed at 1000 mg/L PS-NPs was reduced by 36.1 %. No significant change in root biomass was observed, however, root volume was reduced by 25.6 % at 100 mg/L. Moreover, PS-NPs were detected in both lettuce roots and shoots across all concentrations. Additionally, PS-NPs were transferred to snails and primarily found in feces (>75 %). Only 28 ng/g of PS-NPs were detected in the soft tissue of snails indirectly exposed at 1000 mg/L. Although PS-NPs were bio-diluted when transferred to species at higher trophic levels, they significantly inhibited the growth of snails, indicating that their potential risk to high trophic levels cannot be ignored. This study provides key information on trophic transfer and patterns of PS-NPs in food chains and helps to evaluate risk of NPs in terrestrial ecosystem.

Agricultural soil aggregation is affected by the crop root biomass rather than morphological characteristics

AbstractBackgroundIn areas prone to water erosion, crop selection strategies should be based on assessment of their effects on soil structural properties.AimsThe present study compared the effects of the cultivation of forage maize (Zea mays L.) and forage oat (Avena sativa L.) and their cultivars on soil aggregation relative to potato (Solanum tuberosum L.) or wheat (Triticum aestivum L.) at a hydrothermally limited site on the Loess Plateau, China.MethodsThe water‐stable aggregate (WSA) distribution in soil was measured under three cultivars in each of maize, oat, wheat, and potato (a total of 12 cultivars from four crops) in their flowering stage of three cropping seasons, when root biomass was largest.ResultsIn each year, the water‐stable macroaggregates (>0.25 mm) content and mean weight diameter (MWD) of WSAs in the top 20 cm of soil did not differ between tested cultivars of every crop but increased under maize and oat, compared with those under wheat or potato. The increased soil aggregation under maize and oat, compared with wheat or potato, was consistent with the pattern of change in root biomass but was not consistent with the changes in root length density, root surface area, or root mean diameter across the crops. The water‐stable macroaggregates content and MWD of soil was positively correlated with root biomass across cultivars and crop species within each cropping season.ConclusionsWe suggest that increased root biomass under maize and oat relative to potato or wheat resulted in increased soil aggregation in maize and oat cultivated soils. It is demonstrated that, in areas prone to soil water erosion, planting high‐biomass‐yielding crops such as maize and oat is more beneficial for increasing soil aggregation and stability, compared with low‐biomass‐yielding crops such as wheat or potato.

Responses of Tillering Stipa breviflora Traits to a Long-Term Grazing Gradient

Abstract The Stipa breviflora desert steppe is an important component of the Eurasian steppe, and its ecosystem functions are directly affected by changes in the individual functional traits of S. breviflora . Based on 14 years of data from the grazing experiment in S. breviflora desert steppe, we investigated changes in the individual tillering traits of S. breviflora in response to four levels (none, light, moderate, heavy) of long-term grazing. The results showed that: ( i ) long-term grazing resulted in a greater decrease in species richness and increased biomass contribution of S. breviflora in the communities; ( ii ) long-term grazing resulted in significant differences in aboveground/belowground plant tillering functional traits and their relationships under different grazing intensities; ( iii ) the leaf biomass of S. breviflora tillering individuals was strongly dependent on leaf number, while the change in root biomass was strongly dependent on the total root length, specific root length, root furcation number, and root crossing number. The response of S. breviflora biomass to grazing intensity and its relation to tillering individual traits revealed that long-term grazing leads to vast tillering in S. breviflora tussock and significant changes in S. breviflora tillering traits, which will have a profound influence on the function of the desert grassland ecosystem.

Drought Impacts on Tree Root Traits Are Linked to Their Decomposability and Net Carbon Release

Root trait plasticity can facilitate plant adjustment to water shortages, but the impact of altered traits on belowground carbon (C) cycling is mostly unknown. While drought and nutrient availability can alter root morphological and chemical traits that may affect root decomposition, direct assessments of drought mediated changes on decomposability are not available. We exposed four tree species contrasting in drought stress tolerance and root traits to three dry-down and recovery periods (over 5 months after 11 months of growth in well-watered conditions) under high and low nutrient conditions. We then assessed early stage root decomposability in relation to their morphology and chemistry as well as implications for CO2 release when accounting for effects on root biomass. While each species showed a unique set of responses, drought generally reduced root diameter and increased nitrogen concentration. We found limited evidence that morphological responses to drought were counteracted by high nutrient supply. Results indicated that the degree of association between morphological and nutrient root trait responses to drought and decomposability varied with different species. However, across these contrasting woody species, drought-induced increases in nitrogen and phosphorus concentrations were associated with drought-induced increases in early stage root decomposability. When accounting for changes in root biomass, estimated overall C loss through root decomposition increased with drought stress. Our experimental results demonstrate that changes in tree root traits with drought can enhance C loss via root decomposition, and with other factors being equal, drought may potentially contribute to a positive feedback to climate change. Our findings contribute empirical evidence to help disentangle the multiple factors involved in root contribution to C balances at the ecosystem level.

Non-additive effects of nitrogen and phosphorus fertilization on microbial biomass and residue distribution in a subtropical plantation

High nitrogen (N) and phosphorus (P) availability has significant influence on microbial-driven soil carbon (C) sequestration. Microbial residues are a significant contributor of soil stable C pool, their distribution among aggregate fractions determines long-term soil C stability. However, very little is known about the interactive effects of N and P fertilization on soil microbes, especially their residues, at aggregate scale in plantation ecosystems. Since 2012, a field-manipulated experiment with N (200 kg N ha−1 year−1) and/or P fertilization (50 kg P ha−1 year−1) has been conducted to examine their interactive effects on microbial community and residues in bulk soil and three soil aggregate fractions: large macroaggregates (>2 mm, LMA), small macroaggregates (0.25–2 mm, SMA), and microaggregates (<0.25 mm, MA) in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. Results showed that N and P fertilization, either individually or in combination, decreased microbial biomass of bulk soils to a similar extent (by up to 37.0%). This reduction was due to the decreased bacterial biomass in SMA and MA and fungi in LMA. By contrast, adding N and P fertilizer together (NP) significantly stimulated fungal residues in SMA and further redistributed microbial residues from LMA to SMA, although single fertilization had no effects on microbial residues or their distribution. Changes in root biomass moderated the direct effects of fertilization on aggregate-associated microbial groups and the indirect effects of NP fertilization on microbial residue distribution. Together, our results provide new insights into the microbial mechanisms through which multiple fertilization control soil C persistence in subtropical plantation. These findings highlight that separating bulk soil into distinct aggregate fractions and considering the interactive effect of N and P fertilization are needed to predict the soil C dynamics under fertilization.

Comparing conventional aerification practices with the core recycler

AbstractConventional aerification practices on putting greens involve soil core removal followed by sand topdressing, whereas the core recycler reutilizes sand from cores to replenish the soil. Recycling cores may reduce topdressing inputs, sustain plant and microbial activity, and increase fertilizer use efficiency. Research was conducted on a ‘Mini Verde’ ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt‐Davy] putting green established on a sand‐based profile meeting US Golf Association (USGA) specifications at the University of Georgia's golf course during summer in 2017. Treatments were arranged in an incomplete split‐block design; the main block was aerification method (conventional or core recycler) and the subplots were fertilizer treatments. The putting green was halved, with one side aerified to 7.6 cm with a hollow‐tine aerifier. Topdressing sand was applied at a rate of 237 m3 ha–1. The second half was aerified to the same specifications (cores not removed), topdressed at 118 m3 ha–1 (50% of the conventional rate), and passed over with the core recycler. We hypothesized that the aerification method and N fertility would influence organic matter (OM) content, carbon efflux, root biomass, turf color (TC), and normalized difference vegetation index (NDVI). The core recycler produced a greater OM percentage and change in root biomass than conventional aerification, which may be associated with higher TC and NDVI ratings in response to the core recycler treatment. However, OM retention may increase hydrophobic soil conditions and decrease putting green firmness, so rotating the core recycler with alternative techniques is warranted.

Effects of waterlogging and salinity increase on CO2 efflux in soil from coastal marshes

Coastal marshes play a notable role in sequestering carbon in plants and soil; however, coastal ecosystems are vulnerable to global change in terms of sea-level rise and saltwater intrusion. The effects of independent and interactive hydrological treatments of waterlogging and elevated salinity on soil CO2 effluxes in Spartina alterniflora marshes were investigated based on a mesocosm approach. This study highlighted the importance of respective soil respirations during inundation (nondrainage, Rs.ND) and reaeration (drainage, Rs.D) in the marshes soils. We found that waterlogging treatments heavily suppressed Rs.ND but increased the Rs.D, regardless of salinity levels. Light salinity enhanced soil respiration, whereas high salinity inhibited soil CO2 efflux, regardless of the water table level. Waterlogging strengthened the negative effects of salinity on Rs.ND and offset the negative effects on Rs.D. The variations in soil respiration under the hydrological treatments can be mainly attributed to changes in root biomass; indigenous soil microbial biomass; and activities of sucrase, cellulase and dehydrogenase, as well as ionic concentrations and oxidation-reduction potential. The temperature sensitivity (Q10 value) of soil respiration (only for Rs.D) after drainage showed a notable decline under the conditions of waterlogging and high salinity. The effect degree of coupled hydrological treatments on soil respiration and Q10 values was similar to a single waterlogging factor before drainage and more strongly than a single factor after drainage. We suggest that the soil CO2 efflux under water flooding and reaeration, inundation duration, and salinity levels need to be considered to understand the impacts of future hydrological changes on coastal marshes.

Biological Contribution of Ornamental Plants for Improving Slope Stability along Urban and Suburban Areas

Plants can reduce erosion during heavy raining periods and improve slope stability through their root morphology, development, biomass, and architecture. Heavy rains can increase erosion, becoming a danger for traffic and people who live around slopes. The control of slope stability is often required in urban and peri-urban environments, and for this reason ornamental species can be appropriately selected for a dual use, namely improving the aesthetical value of green areas along the urban and suburban roads and mitigating the erosion effects. The species used must have good tolerance to abiotic stresses, such as high and low temperature, drought, pollution and nutrient deficiency. Otherwise, their limited growth can reduce their beneficial effects. Ornamental plants that can be used for reducing the erosion of slopes must be in full growth during periods with a higher incidence of rains and must also be compatible with the temperature ranges in different seasons. These species can be also selected for their ability to avoid erosion and enhance the stability of slopes. In this review, the biological contribution of plants for improving slope stability has been reported and discussed with a special focus attention on the Mediterranean environment. Particular emphasis has been placed on root biomass changes and root growth parameters, considering their role as potential markers for selecting suitable plants to be used for enhancing slope stability. A brief description of planting on slopes and root growth has been also considered and discussed.

Root Secondary Metabolites in Populus tremuloides: Effects of Simulated Climate Warming, Defoliation, and Genotype.

Climate warming can influence interactions between plants and associated organisms by altering levels of plant secondary metabolites. In contrast to studies of elevated temperature on aboveground phytochemistry, the consequences of warming on root chemistry have received little attention. Herein, we investigated the effects of elevated temperature, defoliation, and genotype on root biomass and phenolic compounds in trembling aspen (Populus tremuloides). We grew saplings of three aspen genotypes under ambient or elevated temperatures (+4-6°C), and defoliated (by 75%) half of the trees in each treatment. After 4months, we harvested roots and determined their condensed tannin and salicinoid (phenolic glycoside) concentrations. Defoliation reduced root biomass, with a slightly larger impact under elevated, relative to ambient, temperature. Elevated temperature decreased condensed tannin concentrations by 21-43% across the various treatment combinations. Warming alone did not alter salicinoid concentrations but eliminated a small negative impact of defoliation on those compounds. Graphical vector analysis suggests that effects of warming and defoliation on condensed tannins and salicinoids were predominantly due to reduced biosynthesis of these metabolites in roots, rather than to changes in root biomass. In general, genotypes did not differ in their responses to temperature or temperature by defoliation interactions. Collectively, our results suggest that future climate warming will alter root phytochemistry, and that effects will vary among different classes of secondary metabolites and be influenced by concurrent ecological interactions such as herbivory. Temperature- and herbivory-mediated changes in root chemistry have the potential to influence belowground trophic interactions and soil nutrient dynamics.

Barley (Hordeum vulgare) seedling growth declines with increasing exposure to silver nanoparticles in biosolid-amended soils

Silver nanoparticles (AgNPs), a component of many consumer products, are considered an environmental risk due to the broad-spectrum toxicity of Ag+ to non-target organisms. Most AgNPs released from consumer products will end up as biosolids in wastewater treatment plants, which are often applied as a fertilizer to agriculture. Land application of biosolids may add AgNPs to the soil–plant system, with unknown consequences. This study investigated the growth of Hordeum vulgare seedlings, Ag bioconcentration and distribution in shoot and root tissues of barley exposed to biosolid-amended Delacour and Organization for Economic Co-operation and Development (OECD) soils spiked with AgNPs (up to 366 mg Ag kg−1 dry soil). In both soils, root and shoot growth declined linearly as the concentration of AgNPs increased. Barley had higher Ag bioconcentration values when grown in the OECD soil than in the Delacour soil. Silver bioavailability was greater in the OECD soil due to its physicochemical properties, such as low calcium concentration and acidic pH, relative to the Delacour soil. Barley seedlings exhibited morphological changes, including smaller shoots and shorter, thick roots after 14 d exposure to AgNPs. We conclude that plant structural responses, particularly changes in root biomass, could be an early diagnostic of seedling exposure to AgNPs in biosolid-amended soils.

Aridity stimulates responses of root production and turnover to warming but suppresses the responses to nitrogen addition in temperate grasslands of northern China

Global warming and nitrogen (N) deposition are known to affect root dynamics in grasslands. However, previous studies were based only on a single ecosystem type, so it is unclear how warming and N addition affect root traits (root biomass, root-shoot ratio, root production and turnover) along the aridity gradient. In this study, we conducted an experiment to determine the effects of warming and N addition on root traits in desert, typical, and meadow grasslands in northern China, where the aridity gradually decreases from west to east across the region. Warming increased root-shoot ratio in dry year due to decline in soil water, but had a downward trend in root production and turnover in all three grasslands. N addition decreased root-shoot ratio in humid year due to increase in soil N, whereas did not significantly affect root production in any grasslands and increased root turnover in desert and meadow grasslands rather than typical grassland. Warming combined with N addition had negatively additive effects on root turnover in typical and meadow grasslands rather than desert grassland. N addition-induced changes in root biomass and root-shoot ratio were negatively affected by aridity in dry year. Aridity positively affected responses of root production and turnover to warming but negatively affected those responses to N addition. However, root-shoot ratio, root production and turnover under warming combined with N addition were not affected by aridity. Our results suggest that warming suppresses root carbon (C) input but N addition may exacerbate it in temperate grasslands, and warming combined with N addition suppresses it only in wet grasslands. Aridity promotes root C input under warming but suppresses it under N addition. However, aridity may little affect soil C and nutrient dynamics under global warming combined with N deposition in temperate grasslands in the future.

Historical genetic responses of yield and root traits in winter wheat in the yellow-Huai-Hai River valley region of China due to modern breeding (1948–2012)

The Yellow and Huai Valleys Winter Wheat Zone (YHVWWZ) is the predominant wheat-producing region in China. This study aimed to identify genetic gains in root characteristics and grain yield of winter wheat (Triticum aestivum L.) cultivars to assist future breeding strategies. Field trials were conducted in the wetter-than-average 2014–2015 and drier-than-average 2015–2016 growing seasons. Yield and related traits were measured in 17 wheat cultivars released for irrigated conditions in the YHVWWZ from 1948 to 2012. Yields have increased in the 60 years of breeding and selection of cultivars in this region. No change in root biomass with year of release was evident in 2014–2015, but it increased significantly in 2015–2016. The density of shallow roots (0–1 m) increased significantly with year of release in both seasons, while the density of deeper roots (1–2 m) decreased significantly in 2014–2015 and increased significantly in 2015–2016. Aboveground biomass increased with year of release in 2014–2015 but did not change in 2015–2016, and total biomass (root plus shoot) increased with year of release in both seasons. Modern wheat cultivars are better adapted to different watering levels in irrigated areas than older cultivars, with more root biomass at shallow depth, higher plasticity of the root system with depth, and increased yields.

Drought-induced changes in root biomass largely result from altered root morphological traits: Evidence from a synthesis of global field trials.

Extreme drought is likely to become more frequent and intense as a result of global climate change, which may significantly impact plant root traits and responses (i.e., morphology, production, turnover, and biomass). However, a comprehensive understanding of how drought affects root traits and responses remains elusive. Here, we synthesized data from 128 published studies under field conditions to examine the responses of 17 variables associated with root traits to drought. Our results showed that drought significantly decreased root length and root length density by 38.29% and 11.12%, respectively, but increased root diameter by 3.49%. However, drought significantly increased root:shoot mass ratio and root cortical aerenchyma by 13.54% and 90.7%, respectively. Our results suggest that drought significantly modified root morphological traits and increased root mortality, and the drought-induced decrease in root biomass was less than shoot biomass, causing higher root:shoot mass ratio. The cascading effects of drought on root traits and responses may need to be incorporated into terrestrial biosphere models to improve prediction of the climate-biosphere feedback.

Modelling the effect of changing precipitation inputs on deep soil water utilization

AbstractForests in the Southeastern United States are predicted to experience future changes in seasonal patterns of precipitation inputs as well as more variable precipitation events. These climate change‐induced alterations could increase drought and lower soil water availability. Drought could alter rooting patterns and increase the importance of deep roots that access subsurface water resources. To address plant response to drought in both deep rooting and soil water utilization as well as soil drainage, we utilize a throughfall reduction experiment in a loblolly pine plantation of the Southeastern United States to calibrate and validate a hydrological model. The model was accurately calibrated against field measured soil moisture data under ambient rainfall and validated using 30% throughfall reduction data. Using this model, we then tested these scenarios: (a) evenly reduced precipitation; (b) less precipitation in summer, more in winter; (c) same total amount of precipitation with less frequent but heavier storms; and (d) shallower rooting depth under the above 3 scenarios. When less precipitation was received, drainage decreased proportionally much faster than evapotranspiration implying plants will acquire water first to the detriment of drainage. When precipitation was reduced by more than 30%, plants relied on stored soil water to satisfy evapotranspiration suggesting 30% may be a threshold that if sustained over the long term would deplete plant available soil water. Under the third scenario, evapotranspiration and drainage decreased, whereas surface run‐off increased. Changes in root biomass measured before and 4 years after the throughfall reduction experiment were not detected among treatments. Model simulations, however, indicated gains in evapotranspiration with deeper roots under evenly reduced precipitation and seasonal precipitation redistribution scenarios but not when precipitation frequency was adjusted. Deep soil and deep rooting can provide an important buffer capacity when precipitation alone cannot satisfy the evapotranspirational demand of forests. How this buffering capacity will persist in the face of changing precipitation inputs, however, will depend less on seasonal redistribution than on the magnitude of reductions and changes in rainfall frequency.

Secondary succession and root biomass changes in madagascar dry deciduous forest (Mikea forest)

Succession secondaire et changements de la biomasse racinaire en forêt décidue sèche à Madagascar (forêt Mikéa). La structure et la distribution de la biomasse racinaire ont été caractérisées le long d’une chronoséquence de forêt secondaire (jachères âgées de 2, 6, 12 et 30 ans) et deux écosystèmes de référence (une forêt mature et une savane boisée) afin de décrire le processus de régénération de la forêt dense sèche dans le sud-ouest de Madagascar. La distribution de la biomasse racinaire en fonction de la profondeur s’ajuste bien à une fonction puissance de type B = aDb (B : biomasse racinaire en mg. dm-3 et D : profondeur en cm). Les racines sont plus profondes dans les forêts matures et les jachères jeunes mais elles sont plus superficielles dans les vieilles jachères et la savane boisée où les sols sont plus compacts. La biomasse racinaire augmente avec l’âge de la jachère jusqu’à la douzième année et une diminution a été enregistrée dans la jachère de 30 ans. La biomasse racinaire était de 3,58 t. ha-1 dans la jachère de 2 ans, 4,96 t. ha-1 dans la jachère de 6 ans et 10,00 t. ha-1 dans la jachère de 12 ans. Les valeurs de la biomasse racinaire des jachères et de la savane boisée (7,00 t. ha-1) sont largement inférieures à celles de la forêt mature (18,5 t. ha-1). Ainsi, le coût écologique de la déforestation dans la zone d’étude correspond une perte de 16,9 t. ha-1 de biomasse racinaire après 30 ans d’abandon.